Demonstration of Dehydration and Dryer Technology for Biosolid Reuse asFertiliser and Fuel in Small or Medium Scale STP
T.Yamoto*, T.Ota*, H.Yamashita*, M.Matsuhashi*, Y.Horii*, M.Itakura** National Institute for Land and Infrastructure Management, Asahi 1, Tsukuba, Ibaraki 305-0804, Japan,
yamoto-t922w@mlit.go.jp
Abstract: This study aims to evaluate the performance of two innovative technologies as energy saving
biosolids reusable technology for both fertilizer and fuel use. The result of comparing innovative technology
with conventional technology indicated that both of innovative technologies can reduce Life Cycle Cost (LCC)or the maintenance cost. In addition, it was suggested that the energy efficiency of both innovative technologies
was obviously higher than that of conventional one. Furthermore, we conducted evaluation of the quality of thedried sludge by analysing its ingredient in order to confirm the compliance with the standard in the Fertilizer
Regulation Act for fertilizer use and with the standard of JIS Z7312 BSF-15 for fuel use. As a result, bothinnovative technologies fulfilled these two standards for fertilizer and fuel.
Keywords: Biosolids reuse, Utilization of sewage sludge, Life cycle cost (LCC)

Introduction
Sewage sludge, has been disposed of in landfill as a waste, but now is expected to bevarious biomass resources such as biogas, sludge fuel, fertilizer, and so on. In Japan, theenergy potential of sewage sludge is equal to the electricity consumption of approximately 1.1
million households. From the viewpoint of resources, sewage sludge contains phosphorus
equal to 10% of its import from abroad. In 2015, biomass utilization rate in Japan was as low
as about 26%. Thus, MLIT (Ministry of Land, Infrastructure, Transport and Tourism)
considers sewage sludge as a resources made in Japan in its Productivity Revolution Projectand aims to improve utilization rate to 40% by 2020 through thorough utilization. On theother hand, it is difficult for the small or medium scale sewage treatment plant (STP) tointroduce the high-cost facilities because of their severe financial status. NILIM (NationalInstitute for Land and Infrastructure Management) is implementing B-DASH project in orderto promote spreading of innovative technologies with guidelines. We conducteddemonstrative study of two innovative technologies. One is ‘Demonstration of sewage sludge
conversion to fertilizer and fuel with dehydration and drying system’ (Dehydration andDrying Technology). Another is ‘Demonstration of high efficiency heat pump dryer for
sewage sludge based on self-heat recuperation’ (Self-heat Dryer Technology).
Outline of full scale demonstration technology
1. Dehydration and Drying Technology
Schematic flow and appearance of Dehydration and Drying Technology is shown in Figure
1 and Figure 3. Dehydrated sludge of fine particulate and low adhesion is generated by insidedouble coagulation type centrifugal dehydrator and then dried by circulating flash dryer. This
combination enables moisture content of dried sludge to be controlled from 10% to 50%,
suitable for various utilization.
2. Self-heat Dryer Technology
Schematic flow and appearance of Self-heat Dryer Technology is shown in Figure 2 andFigure 4. This technology incorporates a heat pump system which enables highly efficientheat collection by recovering the latent heat of the exhaust gas.

Demonstration methods
1. Evaluation of cost saving effectWe evaluated the benefit of innovative technology through estimating the initial cost,maintenance cost and LCC in case of installing innovative technology in small or medium
scale sewage treatment plant by using cost functions1).
2. Estimation of the energy efficiency
We estimated the energy efficiency of both innovative technologies. The conventional
technology with many introduction cases and of the same type of heating was selected forcomparison with each innovative technology. The conventional technology of hot air rotating
dryer is selected for comparison with Dehydration and Drying Technology. The conventional
technology of indirect heating dryer is selected for comparison with Self-heat Dryer
Technology. Calculation conditions of energy balance are shown in Table 1. Calculation
formula of energy efficiency is shown in Table 2.
3. Evaluation of quality as fertilizer and fuel use
We measured the amount of assurance component and harmful component in dried sludge
and confirmed that it satisfies the standard value in the Fertilizer Regulation Act for fertilizer
use. We also measured total calorific value and moisture content of dried sludge to confirm
that it satisfies the standard value of JIS Z7312 BSF-15 for fuel use.
Results and Discussions
1. Evaluation of cost saving effectResult of LCC comparison between Dehydration and Drying Technology and conventional
one is shown in Figure 5. LCC of the innovative technology decreased by about 24% than thatof the conventional dehydration and dryer system. Comparison result of maintenance cost
between Self-heat Dryer Technology and conventional one is shown in Figure 6. The
reducing ratio of LCC is about 42%. Result of maintenance cost comparison between Selfheat Dryer Technology and conventional one is shown in Figure 6. Maintenance cost of theinnovative technology decreased by about 62% than that of the conventional dryer.
2. Estimation of the energy efficiency
Estimation result of energy efficiency is shown in Table 3. It is indicated that the energy
efficiency of both innovative technologies are obviously higher than that of conventional one.
Especially in case of Self-heat Dryer Technology, because input heat energy is lower thanrequired heat energy for evaporation of water, the energy efficiency exceeded 100%.
3. Evaluation of quality as fertilizer and fuel use
The result of ingredient analysis of dried sludge as the fertilizer use and the fuel use isshown in Table 4. The quality of the sludge satisfied the standard value of Fertilizer
Regulation Act for fertilizer use and JIS Z7312 BSF-15 for fuel use.
Conclusions
From the above result, both of innovative technologies were successfully proved to low costand energy saving dehydration and dryer system for fertilizer and fuel use. Future work isverifying stability to seasonal variation.
References
1) The manual of basic plan for Biosolids application in Japanese, Japan Sewage Works Association, 2004

Figure 1 Schematic flow of dehydration and drying process(Dehydration and Drying Technology)

Figure 2 Schematic flow of drier process(Self-heat Dryer Technology)

Figure 3 Appearance of full-scale demonstration plant(Dehydration and Drying Technology)

Figure 4 Appearance of full-scale demonstration plant(Self-heat Dryer Technology)

Figure 5 Comparison of Life Cycle Cost (LCC)(Dehydration and Drying Technology)

Figure 6 Comparison of maintenance cost
(Self-heat Dryer Technology)

Table 1 Calculation conditions of energy balance

Table 2 Calculation formula of energy efficiency

Table 3 The result of estimation of energy efficiency

Table 4 The result of ingredient analysis of dried sludge as the fertilizer use and the fuel use
Contents

Fertilizer

Fuel

NitrogenPhosphoric acid
Potassium oxide
Assurance components
CopperZinc
Calcium oxide
Cadmium
Mercury
Arsenic or the compoundHarmful components
NickelChromeLead
Total calorific value
Moisure content

Unit%
%
%
mg/kg
mg/kg
%
mg/kg
mg/kg
mg/kg
mg/kg
mg/kg
mg/kg
MJ/kg
%

Dehydration andDrying Technology(digested sludge)
6.2
4.3
0.2
560
520
1.8
<10.5
4.2
2227
<117.311

Self-heat Dryer
Technology(dewatered sludge)
5.6
2.40.1120
310
1.0
<1
0.2
1.6
14
16
17
19.8
10.7

Tolerance<5<2<50<300<500<100>15<20