4 Application of multi-soil-layering method in wastewater treatment
Tsugiyuki Masunaga, Kuniaki Sato *
Toshiyuki Wakatsuki **
Faculty of Life and Environmental Science,
Shimane University *
Faculty of Agriculture, Kinki University**

1. Multi-soil-layering method

Soil has been mainly employed in the treatment of household wastes for years. It is commonly used in the individual treatment of home drainage, in advanced treatment of substances containing nitrogen and phosphorus, and in treatment of wastes from different kinds of facilities lacking specific drainage for wastes. With its characteristic physical, chemical, and biological properties, soil possesses highly effective auto-cleaning functions, such as filtration, absorption, and decomposition. In addition, it is a valuable resource which exists in almost all parts of the earth. However, the aforementioned properties and functions depend on the type of soil. The primary limitation in the application of soil in treatment of wastewater is its permeability to water.

Compared with conventional land treatment process, the multi-soil-layering method can treat high loads of waste, its cleaning function is self-regulated, and its use in the advanced treatment of wastes is maintained.

(1) The structure shown in Fig.1 illustrates a water-permeable layer filled with uniform size of soil grains, which contribute to the high permeability to water. The soil mixture layer with high auto-cleaning function is piled in multiple layers, just like laying bricks. This arrangement of the soil layer improves water permeability. (enhancement of high-speed treatment function)

Fig.1 Structure of Multi-Soil-Layering system

Fig.1 Structure of Multi-Soil-Layering system

(2) The innate auto-cleaning function of the soil is augmented by the addition of substances, such as activated carbon, charcoal, metal iron, and sawdust. The purification function of the equipment is also strengthened by using zeolite, pumice stone, and charcoal as part of the water-permeable layer. (enhancement of advanced treatment capability)
(3) With or without the introduction of aeration, anaerobic and aerobic conditions in the equipment are controlled. (control of treatment function)
The continuous development in the research of this method has been greatly supported not only by the authors, public institutions of both local and national governments, but also in collaboration with many private enterprises and overseas organizations.

2. Characteristics of sewage purification by equipment using multi-soil-layering method
Table 1 presents the three factors affecting the cleaning function of multilayering method.
They are the quality of targeted sewage, amount of load to the equipments, and purification ability.

Table1Quality of sewage as treatment object in the past by multi soil layering method, amount of load to the equipment, and purification ability of the method
Table1Quality of sewage as treatment object in the past by multi soil layering method, amount of load to the equipment, and purification ability of the method

Treatment by biological oxygen demand (BOD). Although the BOD in raw water and absolute load to the equipments vary, most of the equipments and conditions demonstrated a removal rate between 80 and 90%. Also, the change in BOD purification ability by different soil types and mixtures is small. BOD removal shows a tendency to decrease when water load is beyond 2000 l/m3 a day. However, when water load is below 2000 l/m3 a day, the removal level between a low BOD with high speed treatment and a high BOD with low speed treatment has no difference. The suspended solids (SS) and COD show similar purification characteristics.
Nitrogen treatment. The removal ratio of T-N from low concentration to high concentration ranges from 40 - 70 %. As regards the removal of ammonia nitrogen, no difficulty in any of the equipments and treatment conditions occur. Concerning home and toilet drainage treatment, in which T-N load is approximately 3 - 20 g/m3a day, T-N concentration in the treated water is lowered as water load is increased from 500 to 2000 l/m3 a day. That is, in the case of similar T-N load (concentration X the product of water load), the treatment of sewage with low T-N concentration using high-speed treatment can result in more productive removal ability. The organic matters in sewage, ratio of nitrogen (COD/T-N etc.), and redox status inside the equipments are involved in the dynamic state of nitrogen inside the equipment, hence, T-N removal is affected. In sewage containing less biodegradable organic matters, the nitrogen ratio for nitrogen removal, redox status inside the equipment can be controlled by supplementing appropriate organic materials and metal iron. The nitrogen removal ability can be enhanced, as well.
Phosphorus treatment. The average removal rate changes between 44-88% depending on the conditions of equipment or sewage load. The presence of high T-P concentration in wastewater results in the tendency to achieve high purification efficiency. The purification ability of phosphorus improves considerably by adding approximately 5-10% metal iron according to soil weight. The removal rate can be increased up to 90% in high-speed treatment. The added metal iron is oxidized to divalent iron in a soil layer, or chelated and solubilized. Subsequently, it flows into the aerobic water-permeable layer. It is then oxidized and forms a coat of rust made of insoluble iron hydroxide on the surfaces of the materials like zeolite and pumice stone. Consequently, adsorption of phosphorus can be performed efficiently.
Aeration maintains BOD, nitrogen, and phosphorus treatments inside the equipments through decomposition of organic matters, nitrification, and oxidation of iron. However, excessive aeration can result in nitrogen efflux and reduction of T-N removal ability. Therefore, it is necessary to examine suitable aeration conditions of the water quality of targeted sewage.

3. Application of multi-soil-layering method
To date, the development of the method has been geared toward its application in the treatment of various types of sewage. Several experiments and verification tests have been conducted on house wastewater, wastewater from dining rooms and toilets, effluent from stock-raising farms, effluent containing chemical substances such as pesticides from golf links, nitrogenouse substances in groundwater, arsenic pollution, polluted river-water, advanced treatment of sewer water, etc. The water treatment equipment using multi-soil-layering method has been introduced into toilet, river water treatment facilities, etc. of public accommodations based on the results of this study. Fig. 2 shows the river-water treatment facility in Fukuoka Prefecture, which began its operation since 2005. The total area, including incidental facilities such as pretreatment, is approximately 2500m2 and the amount of water treatment a day is 7000m3. The practical application of the method is now being conducted in other countries using local materials. In association with Kasertsart University in Thailand, the treatment of effluents from dining rooms and toilets is performed. In cooperation with Andalas University in West Sumatra and Standardization of industry and training institute in Padang, Indonesia, treatment of industrial effluent from refined coconut oil, rubber refining, and tofu factories, etc. is carried out. In cooperation with University of Hawaii, treatment of effluent from stock-raising farm is conducted.

(Completed structure of multi-soil-layering method)
(Completed structure of multi-soil-layering method)
Fig.2 The Kumazoe River Purification Facility, Iizuka City, Fukuoka PrefectureKanatsu Engineering Construction Co. Ltd
(Construction of multi-soil-layering method)
Fig.2 The Kumazoe River Purification Facility, Iizuka City, Fukuoka PrefectureKanatsu Engineering Construction Co. Ltd.


 As regards the details of this method, please refer to the latest literary documents of the writer and his research group listed below.
・Sato, K., Masunaga, T., and Wakatsuki, T. Water movement characteristics in a multi-soil-layering system.Soil Sci. Plant Nutr., 2005; 51(1): 75-82.
・Sato, K., Masunaga, T., and Wakatsuki, T. Characterization of treatment processes and mechanisms of COD, phosphorous, and nitrogen removal in a multi-soil-layering system.Soil Sci. Plant Nutr., 2005; 51(2): 213-221.
・Masunaga, T., Sato, K., Zennami, T., Fujii, S. and Wakatsuki, T. Direct treatment of polluted river water by the multi-soil-layering method.J. of Water Env. Tech., 2003; 1(1) : 97-104.
・Boonsook P., Luanmanee S., Attanandana T., Kamidouzono A., Masunaga T. and Wakatsuki T. A comparative study of permeable layer materials and aeration regime on efficiency of multi-soil-layering system for domestic wastewater treatment in Thailand.Soil Sci. Plant Nutr., 2003; 49(6):873-882.
・Sato K., Masunaga T., Inada K., Tanaka T., Arai Y., Unno S. and Wakatsuki T.The development of high speed treatment of polluted river water by the multi-soil-layering method, Examination of various materials and structure.Jpn J. Soil Sci. Plant Nutr., 2005; 76(4):449-458.(in Japanese with English abstract)
・Unno S, Wakatsuki T, Masunaga T and Iyota K. Study on direct treatment of river by multi-soil-layering method and its characteristics of water purification. J. Jpn. Coc. Civil Eng., 2003; 726/II-62:121-129.(in Japanese with English summary)
・Masunaga T, Sato K and Wakatsuki T. Removal of Simazin, Fenitrothion, Napropamid and tetrachloroethylene by Multi-Soil-Layering Method. J. Jpn Soc. Water Env., 2002; 25:361-366. (in Japanese with English abstract)

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