Development of volcanic-ash-derived new flocculation agent
Tetsujii Ozaki 2;Astec, Inc. (NBH technical advisor Ltd.)Ai Kuchibune ;Former Astec, Inc.
Tatsuo Morimoto; Astec, Inc.
Shinichiro Wada; Kyushu University agriculture research academy plant resource science
sectionThe flocculation method is one of the main process of the water treatment. Flocculation
agent is used in the coagulation process. In general, flocculation agent is artificiallymanufactured, and the discharged sludge in the water processing plant contains in relatively
considerable quantity of aluminum that is the component of the flocculation agent. Therefore,
recycling of the sludge is difficult, and it is mainly disposed as industrial waste. For thesimilar reasons, it is difficult to use this flocculation agent in the treatment of environmental
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turbidity of dam lakes.volcanic-ash-derived new flocculation agent is developed . This
agent contains the natural mineral without an artificial material, and has the equal cohesion
to conventional flocculation agent. The turbid water treatment by this new flocculation agent
such as at water treatments and dam lakes is highly expected in situ.

Condensation method and flocculation agent
Purification of water means to remove turbid and contaminants from water; and the main
method is the condensation method. First, to make the target material a solid, then second,
to separate it from water is the condensation method.

For this separation, thesedimentation method is entirely used. Turbidity is categorized as comparatively bigmaterials such as sand or clay mineral such as small colloidal particles (about 1nm（10−9ｍ）〜１µｍ(10−6ｍ）). The contaminant adheres to colloidal particle or is soluble in water. In

case of dissolution, as a preprocessing, the contaminant is changed into a solid material(colloidal particle) by the oxidation or is adsorbed by puting the adsorptive material (colloidalparticle) in the contaminant.
The influence of gravity voluntarily settles out greatly to a big material such as sand.
However, the colloidal particle doesn't settle out easily because it greatly undertakes aninfluence Brownian motion (*1). compared with gravity. It is this colloidal particle that
becoming the object of the cohesion method.

Van der Waals attraction (*2) always works as power to attract against each otherbetween colloid particles. If the particle attracts against each other mutually according to this1power, it flocculates. If the particle grows, the influence of gravity strengthens and it
subsides. Then, why does not the colloidal particle flocculate? It is because the surface ofthe colloidal particle usually is electrically-charged of the plus or the minus; therefore, due tothe particles next to each other are like charges, they mutually repulse. Since this repulsion
surpasses Van der Waals’ forces, the colloidal particle keep floating without agglutinate.

2)

Therefore, in the process of condensation method, to reduce the repulsion power by thischarge, flocculation agent is poured in. The component of the flocculation agent iselectrolyte that becomes an ion in water. The charge of the colloidal particle is neutralizes by
this ion. If it makes neutralized, the influence of the Van der Waals force grows, and thecolloidal particle agglutinate and subside.

There are an inorganic flocculation agent and an organic polymer coagulant. PAC(polyaluminum chloride) and the sulfuric acid band (sulphonated aluminum) are well known
in the in organic flocculant. Polyacrylamide is well known in the organic polymer coagulant.
Both an inorganic flocculant and an organic polymer coagulant can make neutralize thecolloidal particle. Especially an organic polymer coagulant has cross-linking action in which
the colloidal partial are linked by polymer; therefore, the agglutinate force is very high.
Both of these flocculant are chemical compounds. The reactivity is well and they candemonstrate the effect to any types of turbid water. However, the unreacted elements may
remain in the treated water in case of using it voluminously. Moreover, because sediment
after the process includes aluminum and the high polymer, it is detrimental to recycle.
Flocculation agent that is made from natural mineral was developed in order to make up thisdisadvantage. However, most of these natural minerals are made from alkali earth metal bywhich the pH in the treated water is raised, and the cohesive force is low. Moreover, thesediment is likely to be alkalify that remains the difficulty of recycling. Therefore, pulverized
powder of volcanic ash and the pumice-weathering stone is developed as a flocculation.
However, because the cohesive force of this type of flocculation agent is also low, several
thousands of ppm is necessary for the process and this amount is not practicable.

New flocculation agent and the cohesion mechanism
To solve the above-mentioned problem, a volcanic-ash-derived flocculation agent isdeveloped. The volcanic ash is distributed Tohoku, Kanto, San-in, and the Kyushu region
and it is from a lower part with low organic substance. The main clay mineral of the volcanic
ash is aqueous aluminum silicate.
The procedure for manufacturing flocculation agent from the volcanic ash are :2put

volcanic ash through a sieve and control its sizeand disperse the mineral particle

add water to size-controlled volcanic ash

According to circumstances, add pH adjuster to thecompound liquid .

The most important point in the process ofandis to disperse the mineral particles

without destroying them but with keeping them close to unit particle. The difference between
our flocculation agent and the natural mineral flocculation agent is in this excellent
dispersibility.

Resulting properties of the flocculation agent are shown in Table 1, and theelements are shown in Figure 1, and photograph is shown in Photograph 1.
There are two cohesion mechanism by the developed flocculation agent:

neutralization ofsurface charge of the colloidal particle that is the component of turbidity.

the physicalincorporate of the colloidal particles by the self-cohesion of flocculation agent.
A large amount of colloidal particles that are the causes of turbidity consist of the clay
mineral, and their surface hold negative charge with pH 3 or more, and they repulse anddisperse each others in water.

Moreover, the surface of algae that occur in lake andreservoir are also electrically charged by the carboxyl group. On the other hand, ourflocculation agent includes plentiful of clay minerals that surface is plus charged. Beside,
more plus charges are added to agent in the process of manufacturing. Therefore, when ourflocculation agent is poured in water, dispersed minus charges in clay minerals and algae
are neutralized and are cohered.

On the other hand, our flocculation agent coheres voluntarily in water because it has
self-cohesive property (*3). To be paid attention is that it physically incorporates the floating
colloidal particle when cohering, and then it forms the fluck. The formed fluck settle out. Thisaction occurs in any condition of the colloidal particle charges, and it is a similar physicalagglutinative action even it is different from the action of cross-linkage process of theorganic polymer coagulant. Moreover, due to this self-cohesive property of the flocculation
agent, the unreacted agent doesn't remain in the treated water in case of excessive amountof flocculation agent is poured in. This is confirmed its safety oftreat water in a fish acutetoxicity testing by killifish.
Figure 2 shows pattern diagrams of the cohesion mechanism of above-mentioned ourflocculation agent. The relationship between the additive amount and the turbidity of ourflocculation agent to china clay (clay mineral) murky waters is shown in Figure 3, and Figure
4 shows an outcome of an experiment. The experiment indicate the result that the sameamount of our flocculation agent and the pulverized volcanic ash are poured in the low
density simulated murky waters made by the red clay of Okinawa Prefecture. These figuresclarify that our flocculation agent has great cohesive force. Photograph 2 shows the3

cohesion situation when our flocculation agent is added to the red clay murky waters.

Application cases to the dam lake turbid water
Turbidity in a river or a reservoir happens after heavy rain, and it continues for a longperiod. In many cases, negatively charged clay mineral causes these types of turbidity. Theimpurity becomes a problem visually or, in case of stocking turbidity with the downstream, it
becomes an environmental preservative issue.

Althoughagglutinating and subsiding

turbidity is the most appropriate treatment; as previously stated, there is a problem in using
existing flocculation agent. So that usage of the flocculation agent is low.

Here is the verification test using our flocculation agent. The murky water of this test was thedam lake where turbidity did not disappear for a long term of period, and the cause ofimpurity was the mica minerals with the minus charge. In this verification test several
experimental tanks were set up in the vicinity of the intake of the reservoir, and 10 ㎥ ofimpure lake water were pumped up into each tank. Each of the follows: our flocculation
agent, natural mineral flocculation agent, PAC, and natural mineral flocculation agent+PAC,
was mixed with each water tank, and the water quality afterwards was observed. For thecomparison, the water tank with raw water entered was prepared (control plot). Figure 5
shows the result. The turbidity of the murky water mixed with our flocculation has decreased
the turbidity rapidly. On the other hand, the both electric conductance and the pH indicate
almost the same numerical value as the raw water. What this test proved is that ourflocculation agent can keep excellent cohesive force without changing the water quality.
Regarding the cohered treat water (supernatant water), the followed items are analyzed: 5items concerning the environmental standards on the maintenance of living conditions(lakes and marshes), 26 items concerning environmental standards on the protection ofhuman health, and 6 items concerning fisheries water quality criterion. As a result of theanalysis, beside the slight increase in pH and BOD, any of declining water quality orincrease of the noxious substance were not been confirmed.
Table 3 shows the analysis result of elution volume and contained amount of cohesion
sediment. The analysis items of elution volume include 26 items of environmental standards
that is similar to the treat water, and copper and aluminum. As a result, it was not detected in26 items in the precipitation of our flocculation agent as well as others, and lead wasdetected slightly as well as raw water. However, aluminum was detected from all
precipitation comparatively in a high density.

The density of both our flocculation agent andnatural mineral flocculation agent was as same as that of raw water; however, the density offlocculation agent using the natural mineral flocculation agent and PAC together showed
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several times higher density than that of the raw water. As a result of the analysis of thecontained amount, each item of the sediment by our flocculation agent was almost equal tothe precipitation of the raw water. On the other hand, precipitation that used the naturalmineral flocculation aget with PAC indicated a high value with the ignition loss, the moistureweight percentage, and aluminum.

It was confirmed that our flocculation agent had an effective cohesive force for theimpurity of the dam lake, and that it did not aggravate the treated water or no changes wasseen on precipitation.
Our flocculation agent demonstrates the cohesive force for not only murky water, but also
blue-green algae of lakes. Moreover, the volcanic ash that is the raw material of ourflocculation agent is confirmed that the adsorption ability of heavy metals is high. Thesesuggest that our flocculation agent has a various performance. By our flocculation agent, thedispersibility of the naturally exist clay mineral was improved, and it is again emphasizedthat environmental load in manufacturing and use of our flocculation agent is extremely low.
Note)
*1 An irregular movement of the colloidal particle. It happens because solvent molecules (water) that are surrounding
particles, collides from unpredictable directions with irregular speed.
*2 Universally worked gravity besides the intermolecular chemical linkage*3 The character to cohere by sensitively reacting to even little electrolyte concentration in water. It coheres even in waterwith little suspended solid (colloidal particle), even in natural water or membrane filtered water with few suspended
substances.

Reference1) Ai Kuchibune, Tatsuo Morimoto, and Wada Shinichiro (2006); Development of efficient flocculation agent made fromclay mineral

The 16th environmental geology association symposium2) Yasuhisa Adachi ・Shingo Iwata (2003); Colloidal phenomenon of soil

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