49

Development and Implementation of Technologies for
Recycling Phosphorus in Secondary Resources in Japan
Hisao OHTAKE and Kenji OKANO
Department of Biotechnology, Osaka University,
2-1, Yamada-oka Suita-shi, Osaka, 565-0871, Japan*e-mail: hohtake@bio.eng.osaka-u.ac.jp

Abstract
The recovery of phosphorus (P) from secondary resources is critical to closing the anthropogenic P loop.
The recovered P should be recycled effectively for agricultural and industrial purposes without jeopardizing
human health and the environment. Although various technologies are potentially applicable to P recovery
and recycling, their implementation remains hindered by socioeconomic factors such as insufficient policy
support, an immature market for recovered P and a lack of public awareness. Recently, Japan has experienced
good practices in recycling P in secondary resources despite these hindrances. Japan’s experience may provide a clue on how to develop and implement technologies for P recovery and recycling, even if the legal,social and economic structures are not fully developed for the security of future P supplies.
Key words: phosphorus recycling, phosphorus recovery, sustainable use of phosphorus

1. Introduction
Since Japan has no economically viable phosphate(Pi) rock reserves, it is almost entirely dependent on imported phosphorus (P). According to a P flow analysis by
Matsubae et al. (2011), total P imports into Japan are
estimated to be approximately 630 kilotons of P per year
(ktP/y) (Fig. 1). Of this, approximately 160 ktP/y isassociated with the importation of food and animal feedfrom abroad. In addition, approximately 140 ktP/y isrelated to the importation of mineral resources such asiron ore and coal for the iron and steel industry. Taken
together, they account for about 48% of the total P imports into Japan. Since P goes almost entirely to foodwaste, animal manure, sewage sludge and steel-making
slag, P recovery from these secondary resources has apotential for recycling a total of 330 ktP/y within Japan.
On the other hand, approximately 300 ktP/y is used as
mineral fertilizer and animal feed additives in Japan’s
agricultural sector. The current use of P in the agriculturalFig. 1 P flow in Japan (2005). Source: Matsubae et al. (2011).
Global Environmental Research
19/2015: 49-65
printed in Japan©2015 AIRIES

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H. OHTAKE and K. OKANO

sector, however, is by no means sufficiently efficient,since it is common for farmers to apply P in excess tomake it more available to crops and livestock. Consequently, the Ministry of Agriculture, Forest and Fisheries
of Japan (MAFF) has adopted a package of measures toreduce P use in the agricultural sector by 20–30% foreconomic and environmental reasons. If the P loss in the
agricultural sector is reduced by improving P management practices as expected, P recycling from the abovementioned secondary resources could supply the majority of P demand from the agricultural sector of Japan.
P recovery from secondary resources is critical toclosing the anthropogenic P loop (Cordell et al., 2011).
Although various technologies are potentially applicable
to P recovery and recycling, their implementation remains hindered by socioeconomic factors such as insufficient policy support, an immature market for recovered
P and a lack of public awareness. Recently, Japan has
experienced good practices in P recycling despite thesehindrances. Japan’s experience may provide a clue on
how to develop and implement technologies for P recovery and recycling, even if the legal, social and economic
structures are not fully developed for the security of thisessential element.
In this paper, we provide an overview of the current
state of development and implementation of technologies
for P recovery and recycling in Japan. The locations offull-scale operating plants for recovering and recycling P
from secondary resources in Japan are shown in Fig. 2.

●

MatsueLake Kasumigaura

Tottori
Lake Shinji

KHB●

Senboku●● Gifu●●

NPA, JOM
JSA●

Tokyo Bay

Fukuoka●
Hakata Bay

Kobe SC●

Seto Inland Sea
●
●

MBR

Kobayashi Hitz

Fig. 2 Locations of full-scale plants operating for P recovery
and recycling in Japan. Only full-scale operating plants
in the public sector are shown in this figure.

2. P Recycling in the Public Sector
Municipal wastewater is a major secondary P resource. P is removed from municipal wastewater inwastewater treatment plants (WWTPs), aiming to control
eutrophication in natural bodies of water. The P removed
from wastewater ultimately ends up in sewage sludge at
WWTPs. Obviously, the direct application of sewage
sludge to agricultural land is the simplest option forrecycling P from municipal wastewater. The nutrient-richorganic solids may be considered a low-grade fertilizer orsoil amendment to improve the chemical and physicalproperties of soil. A number of factors, however, aremaking land application of sewage sludge increasingly
difficult (Laturnus et al., 2007). Sewage sludge contains
a variety of organic contaminants, heavy metals andpathogens, which may place human health at risk.
Long-distance transportation of sewage sludge fromurban areas to arable land where it may be applied isanother problem. In Japan, both land filling and land
application of sewage sludge are prohibited for practical
purposes, because of land scarcity, environmental protection and potential health risks. P needs to be recoveredfrom sewage sludge and used for the manufacture of
fertilizers that are safer to store, handle and apply.
Various technologies have already been developed forremoving P from wastewater (Morse et al., 1998). Not all
the P removal technologies, however, can be applied to P
recovery for recycling, because the quality of the recovered product is critical to P recycling. For instance,
chemical precipitation with Al3+ or Fe3+, which is acommonly used technology for P removal, is unsuitablefor P recycling. These cations form insoluble P precipitates that are unavailable to plants when applied to agricultural land as fertilizer. In addition, Al3+ and Fe3+ often
hamper Pi recovery from secondary resources such as
sewage sludge and its incinerated ash (Kalmykova &Karlfeldt Fedje, 2013). Biological P removal (Bio-P) is
more amenable to P recycling, because P is bioaccumulated by sludge microorganisms in the form ofpolyphosphate (polyP), which can be readily recovered
as soluble Pi (Kato et al., 1993, Kuroda et al., 2001,
Hirota et al., 2010). For example, polyP can be released
from Bio-P sludge by heating at 70oC for about one hour
(Kuroda et al., 2002). Pi is readily obtained by thedegradation of polyP. On the basis of this evidence, a
simple process (named the Heatphos process) has beendeveloped to recover Pi from Bio-P sludge by heating it at
70oC (Kuroda et al., 2002).
2.1 P recovery from incinerated sludge ash
Pi is thermally stable and does not volatilize during sludge incineration at 800–900oC (Donatello &Cheeseman, 2013). Pi can be concentrated in the incinerated sludge ash as whitlockite-type, tricalcium phosphates (Ca3(PO4)2). In particular, ashes from a monoincinerator, which is fed solely with sewage sludge, havea high P content, typically ranging between 4 and 8 wt%(10–20 wt% P2O5). The direct application, however, ofDevelopment and Implementation of Technologies for Recycling Phosphorus in Secondary Resources in Japan51

incinerated sludge ash to farmland as Pi fertilizer is notpossible because it contains toxic heavy metals. In addition, the P accumulated in incinerated sludge ash exhibits
low bioavailability when applied as Pi fertilizer. The P in
incinerated sludge ash needs to be transformed to a morebiologically available form for recycling.
Chemical Pi leaching is a technology option for recycling P in incinerated sludge ash (Kalmykova & Karlfeldt
Fedje, 2013). Full-scale plants for recovering P fromincinerated sludge ash have been implemented at
WWTPs in Gifu and Tottori cities (Figs. 3 and 4). At the
WWTPs of both cities, Pi is released from incinerated
sludge ash by alkaline (NaOH) leaching technology at
20–50oC and pH above 11 for 6 h. Alkaline leaching
technology was adopted because acid leaching inevitably
dissolves heavy metals, thereby contaminating therecovered product. In addition, the relatively low level ofCa (typically less than 10 wt% CaO) in the incinerated
sludge ash makes alkaline leaching sufficiently efficient.
After Pi is extracted with NaOH, it is precipitated with
Ca(OH)2 from the leach solution without removing heavy
metals. The NaOH solution is returned to the Pi leaching
reactor for recycling. The recovered product, which is
calcium hydroxyapatite (HAP), is dewatered, dried andgranulated into pellets to obtain Pi fertilizer. The Pi fertilizer, whose efficacy has been demonstrated in farmland,is sold to farmers through fertilizer companies. The solid
residues that are left after Pi recovery are subjected to
weak-acid cleaning with a dilute H2SO4 solution for
5–30 min at 50–70oC to remove heavy metals. Afterdrying, they are used as construction materials or soil
amendments for street trees.
Gifu is a medium-size city with a population of about
410,000 (Fig. 2). This city owns four WWTPs (North,South, Central and Northwest), which generate a total of
29,000 t/y of dewatered sludge. Two WWTPs (North andSouth) have a mono-incinerator fed solely with dewatered sludge. No biogas production plants have been
installed at the Gifu WWTPs, mainly because of land

scarcity. The Central and Northwest WWTPs transport
dewatered sludge by road to the North WWTP, where it isincinerated in the mono-incinerator. Since the incinerated
sludge ash of the South WWTP is also transported byroad to the North WWTP, a total of 700–1,000 t/y of ash
piles up at the North WWTP. Until 2008, incinerated
sludge ash was used for the manufacture of construction
bricks at the North WWTP. The price spike of Pi rock in
2008, however, spurred the initiation of P recovery fromincinerated sludge ash at the North WWTP, as it had a
P content comparable to that of high-grade Pi rock
(25–29 wt% P2O5).
After a two-year feasibility study, called the LOTUS(Lead to Outstanding Technology for Utilization of
Sludge) project, which was supported by the Ministry ofLand, Infrastructure, Transport and Tourism (MLITT), a
full-scale P recovery plant started operation in April 2010
(Fig. 3). Since then, this plant has been recovering P in
the form of HAP, thereby generating Pi fertilizer at approximately 300 t/y. The heavy metal contents, including
As, Cd, Hg, Ni, Cr and Pb, have never exceeded theirstandards in the commercial Pi fertilizer. Although astable supply of HAP is somewhat difficult to guarantee,
farmers favor the use of Pi fertilizer as long as the quality
is stable (Wemyss, 2012). The P recovery operation has
brought some economic benefits to the Gifu WWTPs,
since it reduces the total operating cost compared withthe manufacture of construction bricks. The manufactureof bricks requires quite high fuel costs for firing at hightemperatures (800 –1,300oC). Compared with ash disposal as industrial waste, however, the cost of P recovery
is still high owing to the cost of the chemicals (NaOH and
Ca(OH)2). Further cost reduction will be required tomake P recovery from incinerated sludge ash economically viable.
Tottori City has ten WWTPs, most of which are relatively small (capacity of 1,000– 3,000 m3 of wastewater
per day). Among them, only the Akisato WWTP, which
has the largest capacity, of 72,400 m3/d, has a mono-

Fig. 3 Full-scale plant for recovering P from sludge incineration
ash in Gifu City. Photograph courtesy of K. Goto (Gifu
City Office).

Fig. 4 Full-scale plant for recovering P from sludge incineration
ash in Tottori City (inset, recovered product, calcium
hydroxyapatite (HAP)). Photograph courtesy of M.
Hashimoto (University of Tokyo).

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H. OHTAKE and K. OKANO

incinerator that handles 40 t/d of dewatered sludge. Other
WWTPs transport their dewatered sludge by road to the
Akisato WWTP, where it is incinerated in the monoincinerator. The Akisato P recovery plant started operation in April, 2013 (Fig. 4). When the Akisato WWTP
needed to renovate its sludge treatment facilities, including an anaerobic thermophilic sludge digestion plant,
Tottori City decided to recover P from the incinerated
sludge ash. This was because approximately 50% of therenovation expenses could be covered by a government
subsidy if it embarked on P recycling from sewage sludge.
The struvite precipitation problem in the thermophilicsludge digestion plant was another reason for converting
the operation of the Akisato WWTP to facilitate P recovery. On the other hand, there was no need to remove
Pi for eutrophication control, because the effluent concentration of total P (T-P) was below the regional effluent
standard of 16 mgP/L.
The P recovery technology at the Akisato WWTP isessentially the same as that employed by the Gifu WWTP.
In full operation, it is expected to recover approximately
150 t/y of HAP from 500 t/y of incinerated sludge ashwith 25–30 wt% P2O5. Solid residues after P extraction
are accepted by a cement company, because their low P
content makes them suitable for cement production.
Stable channels for the distribution and sale of therecovered HAP (citric acid-soluble P (C-P) >15 wt%)
have been established within the local area. In this respect, the Japanese Agriculture Association (JA Zen-noh)provides help in manufacturing a marketable fertilizer
from the recovered product. As described above, theexperiences of Gifu and Tottori cities have demonstrated
the significant potential of incinerated sludge ash as asecondary P resource for the manufacture of Pi fertilizer.
The expanded use of this technology, however, requires
reduced operating costs, which strongly depend on theamount of chemicals needed for Pi extraction andprecipitation.
2.2 Struvite recovery from sludge digestion liquor
Anaerobic sludge digestion is a well-established process for stabilizing sewage sludge and reducing its
volume through biogas (methane) production. If ananaerobic sludge digestion process is available, P can bereleased from P-rich sludge biomass into the liquid phaseof the digester. Struvite formation, however, has oftencaused difficult scaling problems in pumps, pipes anddewatering facilities of WWTP sludge lines (Marti et al.,2010). The blockage of pipes by struvite precipitatescauses significant operational problems, leading to anincrease in maintenance costs at WWTPs. Conversely, if
struvite precipitation is minimized in the digester,
struvite can be recovered from the Pi-rich stream in thedownstream process of the digester (Jaffer et al., 2002).
Fukuoka and Matsue cities (Fig. 2) needed to remove
Pi from wastewater for the control of eutrophication in
Hakata Bay and Lake Shinjiko, respectively. They employed a Bio-P process, the sludge from which was subjected to anaerobic digestion followed by solid-liquid

separation for dewatering. Although the Bio-P process
could remove approximately 90% of Pi from the wastewater, difficulties soon occurred owing to struvite
precipitation in the downstream processes. Struvite precipitates were particularly visible in the anaerobic sludge
digesters and ancillary facilities. To solve this problem,
both cities decided to implement struvite recovery fromanaerobic sludge digestion liquor at the North, South andWasui WWTPs in Fukuoka city and the Lake Shinji-East
WWTP in Matsue city. Their processes are technologically identical but have different struvite-recovery
capacities. Briefly, struvite particles are formed in a
fluidized-bed tower reactor (Fig. 5). They are circulated
in the tower reactor by air bubbles until being withdrawn
via the corn-shaped bottom part of the reactor.
Full-scale plants for struvite recovery in Fukuoka
started operation in 1997. They currently recover a totalof 100– 140 t/y of struvite for recycling. The recovered
struvite is sold to fertilizer companies as a chemicalfertilizer. Struvite precipitation, however, still poses
difficult problems in sludge manipulation. Because of
unwanted struvite wall growth, frequent washing of thereactor with citric and acetic acids is required. In addition,
the pipes of the downstream lines need to be replaced byplastic tubes, which are easily removable at onset ofclogging. Owing to these operational difficulties, only
one-third of the anaerobic sludge digestion liquor is processed by the struvite recovery plants in Fukuoka. As aresult, struvite recovery in itself has failed to bring economic benefits to the Fukuoka WWTPs. About half ofthe operating cost comes from chemicals. As a whole,
only 2% of influent P is recovered as struvite at the
Fukuoka WWTPs.
The Lake Shinji-East WWTP has long suffered fromhigh levels of P in the anaerobic sludge digestion liquor,
which is rejected by a solid-liquid separator. The high Pi
concentration (more than 1,000 mg/L) increases theconcentration of chemicals for Pi removal, inevitably
increasing the operating cost. The aims of struvite recovery at the WWTP are threefold: (i) to lower the Pi
concentration in the sludge return stream, (ii) to reduce

Fig. 5 Full-scale plant for recovering struvite from anaerobic
sludge digestion liquor in Matsue City.

Development and Implementation of Technologies for Recycling Phosphorus in Secondary Resources in Japanchemical costs for Pi removal, and (iii) to recycle P as achemical fertilizer (Ueno & Fujii, 2001). The Matsue
struvite recovery plant started operation in 1998 (Fig. 5).
There are three fluidized-bed reactors with capacities of500, 150, and 500 m3/d of anaerobic sludge digestion
liquor. MgCl2 is added to the reactor at Mg/P molar ratios
of 0.7–0.9. The pH is controlled in the range of 8.5–9.0
using NaOH solution. Since suspended solids (SS) in therejected liquor can adsorb struvite and inhibit its crystal
growth, special attention is paid to making the concentration of influent SS lower than 200 mg/L.
Struvite particles, which grow in a granular shape(0.5–1.0 mm in diameter), are withdrawn from the bottom of the reactor at a retention time of 10 days. Approximately 100–150 t/y of struvite (10–15 t/y as P) isrecovered by the Matsue plant. This accounts for about
20% of the P in the inflow to the Lake Shinji-East WWTP.
The remaining 80% of the P ends up in the sludge cakefrom the solid-liquid separator. The recovered struvite issold to a fertilizer company as a slow-release Pi fertilizer.
The fertilizer company manufactures commercial fertilizers adapted to specific local requirements by blending
the recovered product with appropriate inorganic andorganic components. The cost of transportation iscovered by the fertilizer company. Struvite recovery at
Matsue city is currently unprofitable mainly owing to thecost of chemicals.
2.3 P recovery from blackwaterBlackwater is a type of wastewater containing humanfeces and urine. In local areas without sewage treatment
facilities, human feces and urine are separately collected
and transported by truck to a blackwater treatment plant.
The blackwater treatment plant at Senboku City has acapacity of approximately 60 m3 of blackwater per day(Fig. 6). Blackwater is collected and transported by roadfrom households and decentralized septic tanks in thelocal area. Senboku City needed to renovate an old blackwater treatment plant to deal with complaints of foulodors from local residents. The new plant was completed
in 2009, equipped for nitrogen (N) and P removal andmainstream sludge treatment processes. N and P removal
was needed to secure an agreement with local residents
on the construction of the new plant. N is removed fromundiluted blackwater using a jet aeration system. Since
approximately 50% of dissolved organics are converted
to acetic acid in the reactor, it is not necessary to add
methanol as a carbon source for denitrification. As aresult, the concentration of BOD: Biological Oxygen
Demand is decreased by nearly 100% in the liquid phaseconcomitantly with N removal.
Pi is precipitated with CaCl2 from the liquid rejectedby a membrane-type solid-liquid separator after N removal. On average, the liquid contains approximately
45 mg/L P. The reactor for Pi precipitation is a continuously stirred tank, to which a CaCl2 solution is fed in acontinuous mode. HAP crystals are allowed to grow to an
average diameter of 370 μm in the reactor during aretention time of two hours. Approximately 72% of the P

53

A

B

C

Fig. 6 P recovery plant at the blackwater treatment plant in
Senboku City. (A) Continuous reactor to recover P fromthe liquid fraction of blackwater; (B) Flexible container
bag that can serve as a separation filter to collect recovered
P products; (C) Recovered P product as calcium hydroxyapatite (HAP). Photograph courtesy of H. Sasaki (Hitachi
Zosen Corp.).

can be removed, thereby reducing the effluent T-P
concentration to below 20 mg/L. HAP particles arewithdrawn from the reactor and transferred into a flexible
container bag that can serve as a separation filter. The
recovered product contains approximately 30 wt% citrate-soluble P2O5 (C-P2O5) on a dry weight basis. It is
shipped out in wet form containing about 30–40% water.
The production rate of HAP is approximately 50 kg per
day (about 10–15 t/y). Approximately 20% of the P isrecovered as HAP, whereas the remaining 80% ends up in
dewatered sludge, which is incinerated and landfilled.
The HAP obtained is sold to a fertilizer company, which
manufactures a more versatile fertilizer using HAP as araw material in the local area. The Senboku blackwater
treatment plant started operation in April 2009. Currently,
the P recovery cost is less than one tenth of the total operating cost. Its chemical costs, however, are higher thanthe cost of using polyferric chloride for Pi precipitation.
About 60% of the construction costs were covered by agovernment subsidy from the Ministry of Environment(MOE), with the remaining 40% covered by local government bonds. The government subsidy offers a financial incentive for promoting resource recycling in thewaste management sector. Up to now, five cities otherthan Senboku have been recovering HAP from blackwater using processes similar to that described above.

3. P Recycling in the Private Sector
3.1 Phosphoric acid production using incinerated
sludge ash
In Japan, only two companies manufacture indus-

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H. OHTAKE and K. OKANO

trial-grade phosphoric acid. Nippon Phosphoric Acid Co.
(NPA) is the principal supplier of phosphoric acid,mainly for agricultural purposes. This company produces
approximately 90 kt/y of phosphoric acid (P2O5) and14.3 kt/y of diammonium Pi ((NH4)2HPO4) for the
manufacture of fertilizers. NPA employs the wet acidprocess in which sulfuric acid is used to extract Pi fromimported Pi rock. In the wet acid process, gypsum(CaSO4) is generated as a byproduct, the market for
which is an indispensable prerequisite for the phosphateindustry in Japan. NPA uses Pi rocks imported from
Morocco, China and Jordan. Phosphoric acid is madefrom a mixture of Pi rocks to reduce cadmium andradioactive contamination, the levels of which are
relatively high in Morocco Pi rock.
In 2009, NPA began a feasibility study for the use ofincinerated sludge ash for the manufacture of phosphoricacid. This was triggered by the Pi rock price surge in 2008.
NPA intended to diversify P resources, thereby minimizing the risk associated with the instability of the Pi rock
supply. NPA saw the possibility of using incinerated
sludge ash as a substitute for Pi rock, because sufficientamounts of Pi-rich incinerated sludge ash were available
at WWTPs. Additionally, MLITT encouraged NPA to use
incinerated sludge ash as a secondary P resource for
agricultural purposes. Incinerated sludge ash samples,with P2O5 levels in the range of 24–35 wt%, were collected from different WWTPs and examined for theirsuitability for the wet acid process. The collected ash
samples contained less As, Cd and Hg than Pi rock did.
Their Pb and Zn levels, however, were significantly
higher than those of Pi rock. Accordingly, NPA needed toblend incinerated sludge ash with imported Pi rock toguarantee the quality of the phosphoric acid as well as the

byproduct gypsum.
Currently, incinerated sludge ash is transported over
400 km to the phosphoric acid manufacturing plant froma WWTP using an 8-ton powder-conveying motor truck.
NPA chose this WWTP because it is equipped with a
Bio-P process to remove Pi without using ferric- or
aluminum-based flocculants. The transportation cost iscovered by the WWTP. Incinerated sludge ash is blended
with roller-milled Pi rock and fed to a noncompartmentalized reactor (Fig. 7). The mixture is then dissolvedin concentrated sulphuric acid to generate phosphogypsum slurry. The phospho-gypsum slurry is continuously filtered to separate the phosphoric acid from thegypsum. The gypsum is used as a raw material for the
manufacture of building boards and cement. At present,
NPA uses a total of 1,000 t/y of incinerated sludge ash forthe manufacture of phosphoric acid. In full operation, themanufacturing plant has the capacity to accept 5,000 t/yof incinerated sludge ash.
The blend ratio of incinerated sludge ash withroller-milled Pi rock is currently less than 2.5% (<97.5%
Pi rock). This is needed to guarantee the quality of boththe phosphoric acid and the gypsum. Increasing the blend
ratio changes the structure of gypsum from rhombic to
the needle-type form. This structural change makes it
difficult to use gypsum for the production of building
boards. It is also necessary to meet restricted levels of
toxic heavy metals such as Cd, Pb and Hg in gypsum.
These requirements are currently satisfied by choosing
incinerated sludge ash with less heavy metal content andcontrolling the blend ratio between the ash and powdered
Pi rock. As long as the blend ratio is lower than 2.5%,
there is no need to remove or detoxify heavy metals.
NPA acquired a business license from the government
A maximum of 5%
(w/w)

Ash

Mixing ash with rock P

Storage

Sulfuric acid
Phosphoric acid& gypsum

FilterReactorPhosphoric acid

Fig. 7 Wet acid process for the manufacture of phosphoric acid using incinerated sludge ash as a
substitute for Pi rock. Photograph courtesy of T. Mochiyama (Nippon Phosphoric Acid Co.).

Development and Implementation of Technologies for Recycling Phosphorus in Secondary Resources in Japanto purchase incinerated sludge ash from WWTPs.
Importantly, it was not necessary for it to modify its existing facilities to accept incinerated sludge ash as a raw
material. NPA could reduce its raw material costs, depending on the amount of incinerated sludge ash used. At
the same time, the WWTPs could cut waste disposal
expenses by valorizing incinerated sludge ash. To increase the blend ratio of ash with Pi rock, it will be criticalto reduce the Pb and Zn levels in incinerated sludge ash.
Currently, Japan’s phosphate industry imports a total of
334 kt/y of Pi rock. If 7.5 kt/y of incinerated sludge ash isused as a substitute for Pi rock, NPA can save a tankerload of Pi rock.
3.2 P recovery from industrial wastewater
Approximately 15% of the global P demand is consumed in the manufacturing industry (Cordell et al.,2009). For example, high-grade phosphoric acid is used
as an iron-coating material in the automotive industry,etching agents for liquid crystal glass substrates, andfeedstock for food additives, chemical catalysts andflame retardants. P is also one of the crucial raw materials
for the manufacture of rechargeable batteries.
Recently, the manufacturing industry has begun toconsider P recycling as an economically beneficial option
in waste management. This is because P recycling canpotentially reduce waste disposal costs by turning P-richwaste into a resource. Japan Synthetic Alcohol Co., Ltd.
(JSA) is a principal supplier of chemically synthesizedethanol for industrial purposes. This company canpotentially produce ethanol (95 v/v%) by a direct
ethylene hydration process, in which high-grade Pi isused as a chemical catalyst. In addition, JSA can potentially generate 99 v/v% ethanol by dehydration ofhydrous ethanol. In the process used by JSA, fresh
ethylene gas is fed into a tower reactor, where Pi isimpregnated in silica beads, and converted to ethanol as it
passes through the reactor. Wastewater from the towerreactor contains high levels of Pi, which leaches from thepacked silica beads.
JSA needed to remove Pi from the wastewater to meetthe strict regulation of total P emissions to Tokyo Bay(less than 18.2 kgP/d). This company adopted a P recovery process for wastewater in 1998. The process employs
a commonly used technology involving Pi precipitation
with Ca(OH)2 at a high pH. To avoid unwanted CaCO3
formation, decarbonation is carried out by lowering thepH with H2SO4 before adding Ca(OH)2. The formed
HAP is partially recycled to increase its pellet size before
dewatering and drying. Approximately 75% of the P isrecovered as HAP from the wastewater. The HAP pellets,
which contain 30 wt% P2O5 and 10% water, are sold to a
fertilizer company at a low price. Unexpectedly, about
25% of the P in the wastewater failed to be precipitatedwith Ca(OH)2. This is probably due to the presence of
reduced Pi, which is generated during the ethylene
hydration reaction.
Because the wastewater is basically a Pi solution, therecovered product is excellent for the manufacture of55

fertilizer. JSA can reduce its sludge disposal costs byselling the recovered product to a fertilizer company. At
the same time, the fertilizer company also benefits fromthis deal, since P is available at a low price. The usedsilica beads need to be replaced with new ones once ayear. Currently, the used silica beads are disposed of as
industrial waste, thereby wasting approximately 38 t/y ofP2O5 without recycling. JSA is looking into the possibility of selling the used silica beads as a raw material forthe manufacture of Si and P fertilizer.
KYOWA HAKKO BIO CO., LTD. (KHB) is one of
the major Japanese companies in the fermentation industry. This company manufactures nucleic acids and aminoacids as feedstocks for foods, seasonings and pharmaceutical agents. The company applies a fermentation
process using Pi as an essential raw material, thereby
generating Pi-rich wastewater at about 60 kgP/d. The Pi
concentration in the wastewater is as high as 1,000 mg/L.
KHB has a treatment plant that can handle 60,000 m3/d ofwastewater. KHB began to recover Pi from the wastewater to meet legal standards for total P emissions to the
Seto Inland Sea in 2006. Importantly, the company
considers P recycling a zero-emissions target. P isremoved from the wastewater by precipitation with
Ca(OH)2 (P removal > 90%) (Fig. 8). The recovered
product is HAP (typically 29 wt% P2O5 and 59 wt% CaO).
After drying, the HAP is sold to a fertilizer company,

A

B

Fig. 8 P recovery from fermentation wastewater at KYOWA
HAKKO BIO CO., LTD. (A) Pi precipitation tank;(B) Recovered P product (HAP). Photograph courtesy of
H. Hidaka (KYOWA HAKKO BIO., CO., LTD.).

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H. OHTAKE and K. OKANO

which covers the transportation expenses. At present,
approximately 60–90 t/y of P is recycled from fermentation wastewater at KHB.
P recovery at KHB has decreased P emissions by approximately 4 t/y, thereby contributing to the preservation of water quality in the Seto Inland Sea. Since P
recycling is part of the company’s commitment tocorporate social responsibility (CSR), it is not importantwhether KHB benefits economically from P recycling.
The recovery product from the fermentation wastewater
has no harmful substances and is suitable for the manufacture of fertilizer. Although P is essential for the growthof microorganisms in fermentation processes, Pi recycling in the fermentation process appears difficult because of quality control reliability.
J-Oil Mills, Inc. (JOM) is a principal supplier ofvegetable oil in Japan. Edible oil is purified from crude
oils extracted from grains and fruits including soybeans,grapes, peanuts and walnuts. Crude vegetable oil contains various phosphatides such as phosphatidyl choline,
phosphatidyl inositol, phosphatidyl ethanolamine, andphosphatidic acid. They need to be removed in the earlyrefining stage, because they are responsible for refining
losses due to emulsion formation (Van Nieuwenhuyzen& Tomas, 2008). The elimination of phosphatides fromcrude vegetable oil (called degumming) is a key step invegetable oil refining. High-grade Pi is used to remove
nonhydratable phosphatides by the liberation of phosphatides from Ca and Mg salts.
In acid degumming processes, Pi is added as an 85%
solution to crude oil at a concentration in the range of
0.05–0.15 v/v%. Since Pi is added excessively to crudeoils, wastewater from the acid degumming process contains high levels of Pi. JOM recovers Pi from the wastewater by chemical precipitation with Ca(OH)2. Since thewastewater contains essentially no harmful substances,the quality of the recovered product (HAP) is suitable forthe manufacture of fertilizer. JOM sells the recovered
HAP as a byproduct Pi fertilizer (approximately 260 t/y).
JOM needed to remove P to meet stringent effluent
standards on P. Pi precipitation with Al3+ and Fe3+, however, increased the amount of waste sludge and therefore
its disposal costs. JOM could reduce waste disposal costsby selling HAP to a fertilizer company. At the same time,
the P supply at a low price brought economic benefits tothe fertilizer company.
In the manufacture of liquid crystal glass substrates,
Pi is commonly used as an aluminum etching agent.
Wastewater from aluminum chemical etching processes
contains Pi at concentrations as high as 5,000 mg/L.
Although the Pi-rich wastewater can be chemicallytreated with FeCl3 or Ca(OH)2, this generates large
amounts of precipitates, which must be disposed of as
industrial wastes. Waste reduction (ideally, zero emissions) is critical to the manufacturing industry for environmental and economic reasons. Kurita Water Industries Ltd. (KWI) has developed a system for recovering P
from the spent etching solution of a liquid crystal substrate manufacturing process. The wastewater contains Pi,

acetic acid, nitric acid and aluminum (pH 2.0). Afterremoving SS by filtration, aluminum is removed from thewastewater using an H-type cation exchange column.
Then, Pi is separated from the acetic and nitric acids using
a two-step reverse osmosis membrane system at 0.7–2
and 4 MPa, respectively. Since Pi is blocked by thereverse osmosis membrane, it can be concentrated to
4–7%, which is 40–60 times higher than that of the spentetching solution.
This technology uses essentially no chemicals to recover Pi from the spent etching solution. Pi can be further
condensed to 50% or higher by reduced-pressure distillation. The resulting Pi solution contains no impurities
such as heavy metals. This process has been installed inthree liquid crystal manufacturing plants (two in Japanand one in Taiwan). About 2.7 m3 of 50% Pi solution canbe generated from 800 m3/d of spent etching solution
with 3,000 mg Pi/L. More than 1,000 t/y (about 3 t/d) of P
has been recovered, leading to a reduction of 120 t/d ofwaste product (60% water). The recovered P can be used
as a raw material for the manufacture of P-containing
chemicals.
3.3 P recycling from other secondary resources
Animal manure has often been considered a waste
product and disposed of by applying it to land within alimited distance from where it is produced (Bateman
et al., 2011). Animal manure, however, is a major
secondary P resource with a potential to reduce relianceon mineral Pi fertilizers. P is added to the diet of pigs andpoultry to prevent health problems, weak bones and impaired fertility. Since much of the P ingested by animals
is excreted in their feces, animal manure can be a valuable source of plant nutrients and organic matter if it isadequately managed and applied.
Use of animal manure is currently hindered by its
bulky nature, the risk of transmitting pathogens, contamination by heavy metals, its undesirable odors and thegeographical separation of livestock farming from crop
production. Many farms do not have enough land on
which they can use the manure produced as organic
fertilizer. Since the concentration of P in animal manure
is not high, transporting it, especially over long distances,
costs more than the P is worth. Additionally, if animal
manure is applied as organic fertilizer over long periods,
Pi overaccumulation in soil can lead to transference of Pi
to surrounding water bodies, causing eutrophication(Bateman et al., 2011).
The incineration of animal manure to minimize thelogistical difficulties of handling surplus manure and to
recover energy is practiced in regions with high animal
densities (Ro et al., 2009). Although the incineration ofanimal manure has been proposed as a solution to manure
disposal problems, it has remained economically infeasible due to the high cost of ash disposal. Miyazaki
Biomass Recycle Co. (MBR) implemented a power plantto generate electricity by incinerating broiler chicken
manure in 2005 (Fig. 9). Broiler chicken manure, with awater content of typically 43 wt%, can produce about

Development and Implementation of Technologies for Recycling Phosphorus in Secondary Resources in Japan

Fig. 9 Power plant for generating electricity by incinerating
broiler chicken manure. Photograph courtesy of K. Yano
(Miyazaki Biomass Recycle Co.).

1,900 kcal/kg when incinerated. MBR intended to reduce
excess animal manure, thereby solving problems such as
nutrient over-accumulation, offensive odors and nitratecontamination of ground water. Additionally, it needed torespond to enhanced regulations on animal manure disposal by the government in 1999.
The MBR power plant has an incineration capacity of
132,000 t/y of broiler chicken manure, thereby generating electricity of 11,350 kW. Of this, about 20% is consumed locally, while the remaining 80% is sold to a local
power company. About 500 t/d of broiler chicken manure(more than 50% water) is transported by road from400 poultry houses in the Miyazaki area to the MBR
plant. Approximately 45% is transported less than 40 km,
while the remaining 55% is transported more than 40 km
to the power plant. The collected manure is incinerated ina self-sustaining combustion furnace at 7.43 MPa and
468oC. After incineration, approximately 13,000 t/y ofash (about 10% of the original weight) is transported byroad to a fertilizer company. Subsequently, the ash disposal problem is solved by recycling incineration ash as
PK fertilizer (20 wt% P2O5 and 15 wt% K on average).
P recovery from incinerated chicken manure ash has
also been investigated using an acid leaching-alkali
precipitation method at a pilot scale (Kaikake et al.,2009). Approximately 92% P could be recovered, demonstrating the potential of incinerated chicken manure
ash as a secondary P resource. Approximately 6.6 mt/y ofmanure is generated from broiler chicken houses in Japan.
If all of the manure were incinerated, it is estimated that a
total of 61 kt/y of P could end up in the incineration ash.
This is comparable to 8% of the total P imports into
Japan.
Monoammonium Pi (NH4H2PO4) has been used as adry chemical, fire-extinguishing agent, since it shows
good flame suppression properties. Spent fire-extinguishing agents are potentially usable as NP fertilizer.
However, since fire-extinguishing agents need to bebuoyed over water for extinguishing fires, they are coatedwith silicon to make them water-repellent. Because ofthis, they cannot be used directly as fertilizers for plants.

57

Although fire-extinguishing agents must be replacedwith new ones at regular periods, they have been considered as industrial wastes and landfilled without recycling.
Kanesada Kosan Co. recycles spent extinguishing
agents as NP fertilizer (28 wt% P2O5 and 16 wt% N) after
a physicochemical treatment. The patented treatment
technique can remove silicon coatings from fire-extinguishing agents, thereby improving P availability forplant growth. Since the steel container of a fire extinguisher is also recyclable, this company has developed awin-win business model with the manufacturer throughrecycling. The manufacturer no longer needs to pay fordisposal of spent fire-extinguishing agents. Currently, it
is estimated that approximately 10,000 t/y of old fireextinguishing agents are disposed of as industrial waste
in Japan. This company plans to recycle about 1,000 t/yof spent fire-extinguishing agents as NP fertilizer.

4. Technologies Being Developed
4.1 Solid adsorbents for P recovery
Although Pi can be recovered from wastewater bychemical precipitation, the recovered product inevitably
contains a considerable amount of organic and inorganic
impurities. In addition, after chemical precipitation, it isdifficult to remove the low concentration of Pi remaining
in the secondary treatment effluent of a WWTP. Asahi
Kasei Chemicals Corporation (AKC) has developed ahigh-speed P adsorbent made of ion-exchangeable
ceramic beads (Midorikawa et al., 2008). The ceramicbeads, which have an average diameter of 0.55 mm and
85% porosity, exhibit a high specificity for Pi (Fig. 10).
The high porosity allows fast Pi diffusion and smooth Pi
adsorption on the ceramic beads. In addition, the ceramics are very stable across a wide pH range from 2 to 14.
Their Pi adsorption capacity is maintained even after
being used more than 100 times.
Large-scale demonstration experiments have been
conducted by the Ibaraki Prefectural Government
and Japan Sewage Works Agency to examine the performance of these beads for removing Pi from thesecondary treatment effluent at the Kasumigaura WWTP
(89,000 m3/d). The Kasumigaura WWTP employs aconventional activated sludge process and discharges thesecondary treatment effluent to Lake Kasumigaura. To
control eutrophication in Lake Kasumigaura, it is desirable to remove P from the secondary treatment effluent,which contains 1–3 mg P/L. The AKC system consists of(i) Pi removal from the secondary treatment effluent byadsorption, (ii) Pi desorption from the adsorbent with
NaOH solution, and (iii) Pi recovery from the alkaline
solution by precipitation with Ca(OH)2. The AKC system
has been approved by MLITT as an innovative technology for P recovery at WWTPs.
In the demonstration experiments, Pi removability
was examined using three packed column tower reactors
at a space velocity (SV) of 20 h-1. While two tower reactors were removing Pi from the secondary treatment
effluent, Pi was detached in the remaining column using a

58

H. OHTAKE and K. OKANO

A

B
Exterior Surface

Cross section

Internal Structure

FibrilCavities

Fig. 10 High-speed P adsorbent made of ion-exchangeable ceramic beads. (A) Ceramic beads packed in acolumn (bar, 0.5 mm); (B) Scanning electron microscopy image of the ceramic beads (bar, 2 μm).
Photograph courtesy of I. Midorikawa (Asahi Kasei Chemicals Corp.)

5% NaOH solution at SV = 3 h-1. Pi was detached when
the amount of Pi adsorbed reached 2 g P/L-adsorbent. To
prevent the packed column tower reactors from clogging,
SS was removed from the secondary treatment effluent
by sand filtration. The demonstration plant had a capacity
to treat an average of 500 m3/d of secondary treatment
effluent (max., 600 m3/d). The P recovery process wasoperated using a fully automated control system.
Approximately 97% of the P was removed from thesecondary treatment effluent, reducing the T-P concentration of the treated water to less than 0.05 mg/L. After
detachment, the Pi was recovered by adding Ca(OH)2 at a
Ca/P molar ratio in the range of 2.0–2.5. The recovered
product contained approximately 16% of its dry weightas P. The levels of heavy metals such as As, Cd, Cr, Cu,
Hg, Pb and Zn were negligible, compared with those inimported Pi rock. Importantly, there was no significant
carbonate inhibition of P recovery. The adsorbent can be
repeatedly used for P removal after being washed with
7.5% NaOH. The NaOH solution can also be recycled for
Pi detachment from packed ceramic beads.
This process has several advantages over Pi recovery
by chemical precipitation: (i) it requires smaller quanti-

ties of chemicals for P recovery than does chemical
precipitation; (ii) because of the high Pi selectivity, therecovered product has a lower impurity content than Pi
precipitated with Ca2+; (iii) it produces no significant
amount of waste sludge, and (iv) the high speed of
P removal makes the reactor compact. It is estimatedthat the implementation of this technology at theKasumigaura WWTP may enable the recovery of approximately 250 t/y of HAP from the secondary treatment effluent, thereby reducing the P load to Lake
Kasumigaura.
Another solid adsorbent for P recovery is preparedfrom concrete sludge, which is an alkaline industrial
byproduct consisting of hydrated cement aggregates andwater (Iizuka et al., 2012). Concrete sludge is commonly
available at construction sites where more concretematerials are generated than required. Until recently,
concrete sludge has been used as a landfill material after
solid-liquid separation followed by neutralization with astrong acid (Tsunashima et al., 2012). This is costly, however, and a wasteful consumption of resources. Nippon
Concrete Industries Co., Ltd. (NCI) has developed an
inexpensive solid adsorbent, named PAdeCS (Phospho-Development and Implementation of Technologies for Recycling Phosphorus in Secondary Resources in Japan

rus Adsorbent derived from Concrete Sludge), for recovering Pi from wastewater (Iizuka et al., 2012). The
development of an inexpensive adsorbent is one of the
key issues for economic incentives to encourage theimplementation of P recovery. The aims for developing
PAdeCS were twofold: economical recycling of concretesludge and an inexpensive supply of adsorbents for P
recovery.
To produce PAdeCS, concrete sludge is mixed withwater at room temperature and atmospheric pressure.
After solid-liquid separation, the solids are dewatered,dried and pulverized. Since the liquid phase is strongly
alkaline and rich in calcium, it can be used as an aqueous
solution for CO2 absorption. The resulting precipitates
can be recovered as marketable CaCO3 with a purity ofmore than 95 wt%. Various sizes of PAdeCS particles canbe prepared, depending on their application. PAdeCS can
rapidly remove Pi from aqueous solutions, simultaneously acting as the calcium source, alkali substance andseed material. Pi is removed in the form of lowcrystallinity HAP on PAdeCS particles. NCI suggeststhat P recovered by PAdeCS can be used as a substitutefor Pi rock. Since PAdeCS can be supplied in large
quantities, it is also possible to use it as a pH neutralizer
for acidic drainage water from abandoned mine sites andhot springs.
4.2 Direct struvite recovery from digested sludge
Direct removal of struvite from digested sludge iseffective not only for preventing scaling problems but
also for improving sludge dewaterability. Improvementof sludge dewaterability leads to a significant reduction
in sludge disposal costs, since it reduces the volume ofsludge that needs to be transported and incinerated. Morestruvite can be recovered directly from digested sludge
than from liquor rejected by a solid/liquid separator. In
addition, since struvite is naturally formed in digested
sludge, it is not necessary to supply crystal seeds for
struvite growth.
Swing Corporation (SC) has been operating a fullscale demonstration plant to recover struvite directlyfrom digested sludge at the Higashi-Nada WWTP
(capacity of 70,000 m3/d) in Kobe City since 2012
(Fig. 11). This project has been supported by MLITT as a
B-DASH (Breakthrough by Dynamic Approach in
Sewage High technology) project. The Higashi-Nada
WWTP has three anaerobic sludge digesters (each 6 mhigh and 3 m in diameter). Digested sludge, which contains Pi at concentrations as high as 600 mgP/L, is fed tothe continuously stirred reactor at a retention time of 6 h.
Mg(OH)2 is supplied to the reactor as a source ofmagnesium. Digested sludge in the reactor is mechanically mixed to enhance the contact between solid andliquid, because it has a relatively high viscosity. The
mechanical mixing also causes decarbonization andcollision of struvite crystals, thereby controlling theirsizes in the reactor. After struvite crystals grow in thereactor, they are continuously withdrawn from the reactor
and collected by centrifugation. By this process, the59Fig. 11 Full-scale plant for recovering struvite directly fromdigested sludge (Higashi-Nada WWTP at Kobe).
Photograph courtesy of N. Ishigami (Swing Corp.).

struvite concentration in the reactor remains nearly
constant.
The recovered struvite is washed with water to obtainhigh-purity products (5 wt% nitrogen, 27.3 wt% C-P2O5,
and 15 wt% MgO). This plant is expected to recover
approximately 360 kg/d of struvite from 239 m3/d ofdigested sludge with P recovery efficiencies of 30–40%.
This amounts to about 130 t/y of struvite, which isequivalent to one-tenth of the annual consumption of Pi
fertilizer in the Kobe area. Approximately 90% of the P
can be recovered from the liquid phase of the digester.
The struvite recovery plant will be put into full operation
at the Higashi-Nada WWTP in a year or less.
4.3 P recovery using amorphous calcium silicate
hydrates
Cost reduction is critical to the expanded use of P
recovery technologies. Amorphous calcium silicate
hydrates (A-CSHs) are a new cost-effective adsorbent forrecovering Pi from aqueous solutions. Taiheiyo Cement
Corporation (TCC) and Onoda Chemical Industry Co.,
Ltd. (OCI) have been developing a simple technology torecover P using A-CSHs as an inexpensive adsorbent(named Rintoru®). A-CSHs, which have a Ca/Si molar
ratio of 1.0 or greater, can be synthesized using unlimitedly available, inexpensive materials such as siliceous
shale and calcium hydroxide (Okano et al., 2013). Since
the reaction of Pi with A-CSHs occurs at pHs 7.0–9.0, it
is not necessary to adjust the solution to an alkaline pH.
The high settleability, filterability and dewaterability ofrecovered P are the advantages of A-CSHs over conventional CaCl2 and Ca(OH)2. Because of the high settleability, no chemical coagulant is required for Pi recovery
by A-CSHs. Moreover, unlike Ca(OH)2, no significant
carbonate inhibition occurs in Pi recovery using A-CSHs.
A-CSHs consist of inorganic silicate residues having
an average chain length of 3.5 in the form of liquid slurry.
The short-length silicate polymers are linked to eachother through ion bindings with Ca2+. A-CSHs releaseshort-length silicate polymers when they are dispersed in
an aqueous solution. This allows the divalent hydrogen
phosphate anion (HPO42-) to form ion bindings with Ca2+

60

H. OHTAKE and K. OKANO

in place of the silicate polymers. Conventional P recovery from wastewater is a multiple-step reaction processthat requires costly automatic process control. In thisrespect, A-CSHs have a potential to simplify P recovery
processes. A-CSHs can be added to a Pi-rich aqueous
solution in slurry form. After 10–20 minutes of mixing, P
adsorbed by A-CSHs is recovered by settling without
using any chemical coagulant. Importantly, the recovered
P can be directly used as a byproduct Pi fertilizer. TCC
plans to produce large amounts of inexpensive A-CSHs
using unlimitedly available materials for P recovery fromwastewater.
A mobile pilot plant for in situ P recovery experiments
has been developed by Mikuni Pharmaceutical Industry
Co., Ltd. (Fig. 12). Because of the simplicity of the P
recovery process using A-CSHs, the experimental
equipment can be loaded on a two-ton motor truck andtransported to a WWTP where P is recovered fromanaerobic sludge digestion liquor. In situ experiments
have demonstrated that approximately 70–80% of P
could be recovered from anaerobic sludge digestion
liquor at a WWTP. The levels of heavy metals such as As,
Cd, Cr, Cu. Hg, Pb and Zn were below their regulatory
standards. Since the mobile pilot plant is designed to beeasily transported and installed, it enables cost-effective
demonstration experiments at WWTPs. It is also possible
to obtain inexpensive Ca and silicates from acid digestionof concrete sludge and cement materials.
A-CSHs (originally named “CSH-lime”) have also
been examined for their ability to remove color andPi simultaneously from treated swine wastewater(Yamashita et al., 2012). Colored wastewater often contains nonbiodegradable and recalcitrant substances suchas melanoidin, humic substances and bile pigments. In
addition, the intense coloration of swine wastewater isproblematic because it makes local residents uncomfortable. A-CSHs can effectively remove P and color at
pH 10 or higher at a concentration of 2.0 w/v%. In addition, A-CSHs are effective for inactivating total heterotrophic and coliform bacteria in treated swine wastewater.
This is probably due to the increased pH after the addi-

Fig. 12 Mobile pilot-scale plant for the in situ examination anddemonstration of Pi recovery from wastewater.

tion of A-CSHs to swine wastewater. After P removal,
A-CSHs are recovered by filtration through a cloth filter.
The recovered product, which contains approximately
20 wt% C-P2O5, can be used as fertilizer. More recently,
A-CSHs have been examined by Mitsubishi Kakoki
Kaisha, Ltd. for their ability to remove Pi from blackwater.
4.4 P recovery from swine solids and wastewater
Intensive livestock production generates animal
manure in such large quantities that the supply of nutrients greatly surpasses the needs of crops. It is estimatedthat approximately 234 kt/y of P2O5 (101 kt/y of P) ends
up in animal manure in Japan. Carbonization is highlighted as one of the important technological options forrecovering P from swine manure (Ro et al., 2009).
Carbonization can promote the conversion of animal
manure into charcoal, thereby reducing the solid volume.
It is used as a pretreatment of raw biomass which is
not suitable for direct combustion because of the low
energy density and high moisture content (Liu &Balasubramanian, 2014). Since carbonization requires
relatively low technical resources, it is suitable forsmall-scale swine farms (Ro et al., 2009).
Hitachi Zosen Corporation (Hitz) has implemented apilot-scale plant for the carbonization of pig manure in
Kobayashi City (Fig. 13). The main aim of this project is
to reduce surplus compost, which is generated bylarge-scale hog farms much beyond the local demand.
Excess compost, as well as pig manure, leads to nutrient
overuse in farmland and illegal manure dumping into thenatural environment. The Hitz process was designed tocarbonize compost with a self-sustained heating system.
Importantly, the process can generate bio-char, which
adsorbs P in a condensed form from compost. Since
essentially no fuel is required for carbonizing compost, it
is an energy-effective, inexpensive process, comparedwith energy-intensive incineration. The Pi-rich bio-charis easily transported and sold as a valuable P source, since
it is readily soluble in citric acid.
Composts from swine farms contain approximately

Fig. 13 Pilot-scale plant for carbonization of pig manure in
Kobayashi City. Photograph courtesy of K. Ueda
(Hitachi Zosen Corp.).

Development and Implementation of Technologies for Recycling Phosphorus in Secondary Resources in Japan

6 wt% P and 35% water. Composts are collected fromlocal farms and anaerobically heated at 400oC using arotary kiln at a rotation speed of 0.2–2.0 min-1. Most
organic matter is converted to an energy-rich combustible gas and charcoal. The combustible gas is mixed with
air to burn in a secondary combustion chamber, whereby
the gas temperature reaches approximately 850oC. The
combustible gas is used to heat the rotary kiln indirectly.
Nearly all of the P present in pig manure can beaccumulated on the surface of the hydrothermally prepared bio-char. This is possible when pig manure isheated indirectly and evenly at a constant temperature of
400oC. P can be recovered in condensed form (20 wt%
P2O5) by mechanically collecting the P-rich surface fraction of the bio-char (P-rich bio-char). The remaining
fraction of bio-char contains less P (typically 12 wt%
P2O5). Approximately 120 kg of P-rich bio-char is produced from 1,000 kg of pig manure compost. These
P-rich materials can be effectively used as P fertilizer.
Bio-char can easily be transported and stored without thenuisances of odors and deterioration. Approximately
59 kt/y of P2O5 can be potentially recovered from pig
manure in Japan. This process is potentially applicable to
P recovery from poultry manure and also digested sludge
at WWTPs.
Feces, urine, and washing water from piggeries areusually separated into solid and liquid fractions by asolid-liquid separator. The solid fraction is composted,while the liquid fraction must be treated before being
discharged into the environment. A total of approximately 10 kt/y of P is lost by discharging swine wastewater in Japan. Since swine wastewater contains highlevels of Pi (100–600 mgP/L), NH4+, Ca, and Mg,
struvite is easily formed at alkaline pHs. If struvite formation is effectively controlled, Pi can be recovered as
struvite from swine wastewater.
The National Institute of Livestock and Grassland
Science (NILGS) has developed a reactor system to recover struvite from swine wastewater (Suzuki et al.,2007). Aeration is employed to decarbonize swine
wastewater, thereby increasing the pH to over 8.0 for
struvite formation. This is of practical importance forstruvite recovery, because alkaline addition is a costly
and laborious work for small-scale farms. Essentiallypure struvite can be recovered using an accumulator
submerged in the aeration column of the reactor.
Demonstration experiments were carried out using areactor of about 3.5 m height and 1.5 m diameter with acapacity of 4 m3/d. The retention time of swine wastewater in the aeration column of the reactor was 3.6 h.
While the swine wastewater contained P in a range from50 to 350 mg/L, the effluent P concentration was stably
maintained at approximately 30 mg/L. Struvite could
be easily recovered by scraping the surface of thesubmerged accumulation devise by light brushing. A
maximum of 170 g of struvite was recovered from 1 m3of swine wastewater without adding any chemicals. The
recovered product contained struvite at 95% of the dryweight and could be directly applied to farmland as61

fertilizer. This is a simple, inexpensive process so it is
economically adaptable to small-scale pig farms.
4.5 Thermochemical conversion of incinerated
sludge ash to fertilizer
P leaching from incinerated sludge requires large
amounts of chemicals, thereby making it difficult to
reduce the cost below the economic value of the recovered product. If heavy metals need to be removed, additional costs are required to obtain safe recovered
products. An alternative for chemical Pi leaching fromsludge incineration ash is via thermochemical methods(Donatello & Cheeseman, 2013). Problematic heavy
metals can be removed from sludge incineration ash byheating at 900–1000oC in the presence of KCl or MgCl2.
P loss during the thermo-chemical treatment can be
minimized by granulating the sludge ash into pellets.
Thermochemically treated sludge ash can be used as an
NPK fertilizer after being supplemented with NH4NO3.
Since fertilizer is a relatively inexpensive commodity, thepotential of the thermochemical method as a P recycling
option will depend on finding ways to reduce the fuelcosts for calcination.
Taiheiyo Cement Corporation (TCC) has developed athermo-chemical treatment technology to convert incinerated sludge ash directly to mineral fertilizer (Fig. 14).
TCC has accepted sewage sludge and its incineration ash
from WWTPs as raw materials for the manufacture of
cement. Recently, however, the P contents of sewage
sludge and its incinerated ash have been significantly

A

B

Fig. 14 Pilot-scale kiln system for directly converting incinerated
sludge ash to fertilizer by calcination. (A) Rotary kiln for
demonstration experiments; (B) Calcined silicate Pi
fertilizer (left) and calcined mixed fertilizer (right).
Photograph courtesy of H. Takano (Taiheiyo Cement
Corp.).

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H. OHTAKE and K. OKANO

increased by enhanced P removal from wastewater. Since
P degrades the quality of cement, the amounts of sewage
sludge or its incinerated ash that are difficult to use forthe manufacture of cement have been increasing.
Demonstration experiments have been carried out using a rotary kiln (3.2 m long and 0.37 m in diameter).
CaCO3 is added as a calcium source (50 wt% CaO) to
incinerated sludge ash (typically 35 wt% P2O5).
Pelletized sludge ash is continuously fed to the rotarykiln at a rate of 30 kg dry wt/h and heated at 1,200–
1,350oC. This treatment can convert citrate-insoluble
AlPO4 to citrate-soluble Ca5(PO4)2SiO4, thereby increasing the C-P2O5/total P2O5 ratio from 44 to 98%. As aresult, the calcined product contains approximately
17.5 wt% C-P. The calcination treatment is also effectiveat improving the water solubility of SiO, which is criticalto wet-rice cultivation. Heavy metals such as Cd, Hg and
Pb are partially evaporated during calcination, thereby
lowering heavy metal contents below the regulationlevels. The calcined product is sieved to make mineral
fertilizer that can slowly release Pi for plant growth.
Together with P recovery from aqueous solution by
A-CSHs, TCC has developed a total system that canrecover approximately 90% of P in wastewater for recycling. This technology is potentially applicable to
low-grade Pi rock and incinerated sludge ash from a
blackwater treatment plant.
Sanki Engineering Co. has developed a melting system to convert incinerated sludge ash to fertilizer (named
EcoRin®) using an electric resistance furnace (SankiEngineering Co., 2005). P-rich incinerated sludge ash ismixed with additives such as MgO and CaO and fed intoa melting furnace, which is kept in a reducing atmosphereat approximately 1,400oC. In the melting furnace, P is
immobilized in molten slag, thereby separating it frommolten metals. The molten slag is withdrawn from themelting furnace, quenched in water and pulverized toobtain EcoRin®, which is easily handled as a fertilizer.
EcoRin® can be used as fused Pi fertilizer, which is richin P, Mg and Ca. Toxic heavy metals can be removed
from incinerated sludge ash as molten metals in themelting furnace. The efficacy of EcoRin® as Pi fertilizer
has been demonstrated by plant growth testing. EcoRin®
can be used as a slowly released P fertilizer containing
15–20 wt% C-P2O5.
4.6 P recovery from steel-making slag
In the steel-making process, P is present in raw
materials such as iron ore, coal and limestone at concentrations as low as 0.03 wt% P2O5 (Yamasue et al., 2013).
Since P has detrimental effects on the mechanicalproperties of steel, it needs to be removed into hot metal
pretreatment slag (dephosphorization slag). Dephosphorization slag contains approximately 2–10 wt% P2O5.
Since steel-making is a large industry in Japan, P emitted
into dephosphorization slag amounts to 100 kt/y, which isabout two times more than that of sewage sludge. Hence,
dephosphorization slag should be a quantitatively important secondary P resource, but it is currently landfilled

or used as cement and road construction materials(Matsubae-Yokoyama et al., 2009).
The main components of dephosphorization slag are
CaO, FeO, MnO, SiO2 and P2O5. Dephosphorization slag
generally contains a P-rich Ca3P2O8-Ca2SiO4 phase, a
Mn-rich FeO-MnO phase, and a FeO-CaO-SiO2 matrix
phase (Matsubae-Yokoyama et al., 2009). Since P-richparticles exhibit antimagnetic properties, it is possible toseparate P-rich particles after pulverizing dephosphorization slag using wet magnetic separation technology(Yokoyama et al., 2007). In laboratory experiments,
pulverized particles were suspended in water to avoid
coagulation during the magnetic separation. P-richparticles (< 30 μm) could be separated from pulverized
dephosphorization slag by applying a strong magnetic
field (0.30 tesla (T)). The recovered P-rich particles
contained approximately 31 wt% P2O5. This technology
is also applicable to the recovery of Mn-rich particles
from pulverized dephosphorization slag. P-free residues
could potentially be returned to steel-making processes,
enabling a reduction of the total input of new resources
such as FeO, CaO and SiO2. The composition andmorphology of dephosphorization slag must be controlled to improve the efficiency of P recovery by wet
magnetic separation technology.
Dephosphorization slag can be reduced in an ironbath furnace to extract Fe, Mn and P simultaneously(Dippenaar, 2005). P-enriched slag can be separated fromthe hot metal yield and used as P fertilizer. Modificationof slag composition would likely be effective at increasing the P content of the recovered product. Microwave
irradiation has also been investigated for recovering P
from steel-making slag at a bench scale (Morita et al.,2002). P is carbothermically reduced into its metallic
phase and then extracted from the metal by carbonate
flux treatment at 1,200oC. As a result, P is concentrated in
the fluxes at more than 9 wt%. Microwave processing is a
simple and efficient way of heating steel-making slag.
Recently, the iron and steel industry has paid considerable attention to P removal from dephosphorizationslag for economic and environmental reasons. The global
production of iron ore is approximately 2,000 mt/y.
Assuming that the P content of iron ore is 0.03 wt% on
average, it can be estimated that approximately 0.6 mt/yof P ends up in dephosphorization slag. This is equivalent
to one-fifth of the annual world demand for industrial
P (2.8 mt/y).
4.7 Elemental P regeneration from secondary
resources
The wet acid process for the manufacture of phosphoric acid requires highly beneficiated Pi ores as a raw
material and makes a rather impure grade of phosphoricacid. High-purity phosphoric acid, which is an essential
raw material in high-tech industries, is obtained mainly
by burning elemental P (P4) to phosphorus pentoxide(P4O10). Currently, production of elemental white P islimited to China, Vietnam, the USA and Kazakhstan(Schipper et al., 2004). In particular, China accounts forDevelopment and Implementation of Technologies for Recycling Phosphorus in Secondary Resources in Japan

approximately 70% of the world production. Japan
imports approximately 30 kt/y of white P. The manufacturing industry, however, has often struggled with thesoaring price of imported elemental P. Consequently, themanufacturing sector has paid considerable attention to
the sustainable supply of industrial-grade P, particularly
white P.
Pi can be reduced to elemental P using coke at atemperature of over 500oC (Schipper et al., 2004). With aboiling point of 280oC, elemental P is evaporated as tetrahedral P4 gas. AlPO4 and Ca3(PO4)2 can release P4 when
they are heated anaerobically at over 1,000 and 1,050 oC,
respectively. Consequently, Pi in incinerated sludge ash
can be reduced to white P at over 1,200oC as long as theiron content is sufficiently low. Iron forms ferrophosphorus with P, thereby disrupting the formation of P4 gas.
The reductive melting of incinerated sludge ash requires
the use of an electrical heating furnace with an enclosed
structure. P4 gas from the furnace can be recovered inliquid form using a cooling condenser at a temperature
higher than the melting point of white P (44oC). P4 canalso be oxidized to P2O5 and absorbed in water.
The usage of incinerated sludge ash as a secondary
feedstock in the production of white P has been investigated at a pilot-scale level by JFE Engineering Corporation. Incinerated sludge ash was mixed with powderedcoke (a reducing agent) at a wt/wt ratio of 10:1 andgranulated to produce hard pellets (9 × 6 mm2). Since
incinerated sludge ash is rich in silicates, it was notnecessary to supply pebbles (SiO2) for slag formation. A
furnace of 0.56 m height and 0.2 m diameter was heated
to 1,400oC by an external carbon heater (32 kw). Approximately 90% of the P in the incinerated sludge ash
vaporized in the furnace. Because of a mechanical seal
failure, however, only 16% of the P could be recovered as
elemental P from the incinerated sludge ash. The emitted
P4 gas was condensed in water at 60oC. The recovered P
had a purity of 99.75%. The impurity was mainly arsenate (As), which was present in the incinerated sludge
ash. On the basis of this result, it has been proposed torecover 0.5 kt/y of elemental P from 10 kt/y of incinerated sludge ash using an electric resistance furnace(30,000 kwh).
It is also possible to use a high-temperature kiln-based
process to generate P4 gas from P-rich incinerated sludge
ash as a substitute for high-grade Pi rock (Megy and Hard,
1982). Interestingly, it has been observed that a detectable amount of P is removed from steel-making slag to thegas phase as diphosphorus (P2) in a bench-scale experiment using an arc plasma furnace (Jiang et al., 2013).
This observation suggests the possibility of recovering
elemental P from steel-making slag, if the arc plasma
furnace is kept sealed.

5. The Phosphorus Recycling Promotion
Council of Japan
Despite increased attention toward sustainable P
issues, Japan was slow to formulate an effective national63

policy on P recycling. To turn the situation around, thePhosphorus Recycling Promotion Council of Japan(PRPCJ) was founded as a nationwide association amongindustry, academia, and government in 2008. The pricevolatility of Pi rock and elemental P in 2008 was anothertrigger for its establishment. Since then, the PRPCJ has
promoted P recycling in Japan by (i) taking action without delay, (ii) trying everything possible and (iii) bringing
economic benefits to industry. Collaborative approaches(i) and (ii) reflected a consensus that a long period of time
would be necessary to implement P recycling fully inJapanese society. Another consensus was that the manufacturing industry should play a visible role in the promotion of P recycling in Japan, because advocating industrial concern over sustainable P supply could effectively
call government attention toward P issues.
To fully realize P recycling in Japan, the PRPCJ
engages in a wide variety of activities with the support of
MAFF, the Ministry of Economy, Trade and Industry(METI), the Ministry of the Environment (MOE), and
MLITT. At present, this platform has more than
150 members, including 13 stakeholder associations and
62 private companies mainly in the manufacturing, agricultural and wastewater treatment sectors. Among them
are small- and medium-sized fertilizer companies. Their
participation is particularly important for P recycling,
because they are the principal end-users of recovered P
on the basis of local production for local consumption.
PRPCJ aims to (i) bring together a wide range of stakeholders, (ii) fill knowledge and information gaps between
different sectors, (iii) raise public awareness, (iv) develop
a strategy for implementing P recycling, (v) stimulate
research and technology development, (vi) promoteinternational collaboration, (vii) cooperate with local
governments and (viii) create market and business
opportunities for P recycling. Since the PRPCJ’s interestis oriented toward technology and business, it gives
emphasis to the development and implementation of
innovative technologies for P recovery and recycling.
The PRPCJ, however, has also paid strong attention tocooperative learning and problem solving at a global
scale, particularly for developing policy recommendations. The platform functions on a paid membership basis
and is open to public involvement.

6. Conclusions
Currently, approximately 48% of total P imports into
Japan are associated with food, animal feed and mineral
resources such as iron ore and coal (Matsubae-Yokoyama
et al., 2009). Pi rock accounts for only 15% of total P
imports from abroad. Hence, it seems understandable that
the Japanese people are unaware of how dependent Japanis on imported P. The sustainable supply of P is critical to
not only agricultural production but also industrial
manufacturing in this country. In a wide variety of
manufacturing processes, high-grade phosphoric acid isused as an essential raw material, such as an iron-coating
material in the automotive industry, etching agents for

64

H. OHTAKE and K. OKANOSECONDARY PHOSPHORUS RESOURCE

Human waste andsewage sludge

SECONDARYPRODUCT

USE ANDAPPLICATION

Crop residues andanimal manure

Metal surface
treatment agent

Car body
Steel plate

Intensively farmed
agricultural soil

Etching agent

Computer
Cellular phone
Liquid crystal TV

Food additive

Antioxidant
Flavor enhancer

Flame retardant

Home electronics
TextilePrinter

Electrolyte

Car Battery
PC battery

Intermediate
medicine

Antibiotics
Medicine

Chemicalproduct

Detergent
ShampooFertilizer andFeed additive

Crop production
Animal husbandryvegetable oil
refinery agent

Cooking oil
Salad oil

Waste and wastewaterfrom high-tech industry
Waste and wastewaterfrom chemical industry
Waste and wastewaterfrom food andfermentation industry

PHOSPHATE
REFINERYTECHNOLOGY
Phosphate (Pi)
Elemental P (P4)

Steel-making slag
(Dephosphorizing slag)
Garbage and kitchen
waste (Food waste)
Eutrophic water andbottom sedimentLow-grade rockphosphateFig. 15 Pi refinery technology.

liquid crystal glass substrates, and feedstock for foodadditives, chemical catalysts, and flame retardants.
Disruptions in the supply of high-grade phosphoric acidcould severely damage the manufacturing industry.
Although Japan has essentially no Pi rock reserves,
there are sufficient amounts of secondary P resources
such as food wastes, animal manure, sewage sludge andsteel-making slag. P recycling has been implemented atseveral WWTPs and blackwater treatment plants in Japan.
Given, however, that approximately 2,000 WWTPs and
1,000 blackwater treatment plants are operating in Japan,
their operation should be considered as the beginning of
the P sustainability movement. In the future, high-grade
phosphoric acid and, therefore, high-purity elemental P
will be required for food safety and quality control ofindustrial products. To realize P recycling fully, it will benecessary to develop Pi refinery technology, which enables the production of high-purity phosphoric acid andelemental P from a wide variety of secondary resources(Fig. 15).
P recycling is more difficult to implement than P
removal from wastewater, because channels need to becreated for the distribution and sale of recovered P products. It is, therefore, critically important to realize synergies with pollution control, energy/materials recovery
and reduction of surplus manure and compost. In addition,
the integration of technology innovation, corporate
strategies and public policies is critical to promoting P
recycling at a national level. The way toward realizing P
recycling may be to tailor national policies toward a P
recycling society, to raise public awareness, to accelerate
research and innovation, to promote international
cooperation and to create business opportunities.

Acknowledgements
This work was supported by a Grant-in-Aid for
Scientific Research from Japan’s Ministry of Education,
Culture, Sports, Science and Technology. We also thankMitsui & Co., Ltd. for their financial support for thiswork. Views expressed in this paper represent those of
the authors and should not be taken as representing theviews of any other members involved in P recycling inJapan.
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Hisao OHTAKE
Hisao OHTAKE is a professor of biochemicalengineering at the Department of Biotechnology,
Graduate School of Engineering, Osaka University. He graduated from the University ofTokyo (Department of Chemical Engineering,
Graduate School of Engineering) in 1973 and received his doctorate from Osaka University (Department of Fermentation Technology, Graduate School of Engineering) in
1978. He became an associate professor at the Institute of Applied
Microbiology, the University of Tokyo, in 1985. He worked as a visiting
associate professor with Prof. S. Silver at Washington University in St.
Louis and the University of Illinois in Chicago in 1985 –1987. He becamea professor in 1990 at the Department of Fermentation Technology,
Faculty of Engineering, Hiroshima University. In 2003, he moved to the
Department of Biotechnology, Graduate School of Engineering, Osaka
University. After retiring from Osaka University, he moved to Waseda
University in 2015. He is an emeritus professor of Osaka University and aguest professor in Waseda University. He has been serving as chairman of
the Phosphorus Recycling Promotion Council of Japan (PRPCJ) since
2008.

Kenji OKANO
Kenji OKANO is an assistant professor of biochemical engineering at the Department of Biotechnology, Graduate School of Engineering,Osaka University. He received his doctorate from
Kobe University (Department of Molecular
Science and Material Engineering, Graduate
School of Science and Technology) in 2009. Heworked as a researcher at Nippon Suisan Kaisha, Ltd. (HealthFundamental Research Group, Central Research Laboratory) in
2009–2011. In 2011, he became an assistant professor at the Department of
Biotechnology, Graduate School of Engineering, Osaka University. His
research interest is the efficient use of secondary phosphorus resources
with chemical and biological technologies.

(Received 19 September 2014, Accepted 13 January 2015)