Features
3 Present situation and problem of small-scale membrane Johkasous
TUYOSHI YAHASHI

Japan Education Center of Environmental Sanitation 
Department of Research & Development


1. Structure and features of small-scale membrane Johkasous
To date, the three types of small-scale membrane Johkasous approved by the Minister of Land, Infrastructure and Transportation (Table) are the KM, FM, and MB. The KM and FM types were granted in 1999, while the MB type was only approved in 2005. In a countrywide scale, approximately 500 KM and FM Johkasous have already been installed. TMG is the gappei-shori device or combined treatment of flush toilet wastewater and grey water, which can be incorporated in the installed tandoku-shori Johkasou or treatment of flush toilet wastewater


Table1 Putline of small-scale membrane Johkasous


1.1 Small-scale membrane Johkasous (Fig. 1)
The KM and FM types are the membranes for the removal of biological oxygen demand (BOD) and nitrogen (BOD less than 5mg/L,T-N less than 10mg/L), which are combined with the denitrification tank (flow equalization chamber) and nitrification tank. In this technique, nitrified water recirculation type-activated sludge process is employed. The membrane modules are soaked in the nitrification tank and the surplus sludge is stored in the tank for adjusting MLSS. The effective capacity of this method is 2.6 ? 4.0m3 (NUD from 5 to 10).


Fig.1 Flowsheet of small-scale membrane Johkasous and outline of membrane module

Fig.1 Flowsheet of small-scale membrane Johkasous and outline of membrane module

On the other hand, the MB type is applied for the elimination of BOD only (BOD less than 5mg/L). This method does not adopt the circulation system. The membrane modules are soaked in the membrane separation tank and the resulting surplus sludge is transported from the membrane separation tank into the solid-liquid separation tank. Some of the surplus sludge is stored in the membrane separation tank. The effective capacity of this technique is 2.2 ? 4.6m3 (NUD from 5 to 10).
In the case of a flat sheet membrane element, the membrane module is constructed of two flat sheet membranes (made of polyolefin, 0.4μm in pore diameter) attached on the frame with the nozzle at the top. Permeable water is filtered toward the inner side from the outside of the two flat sheet membranes and is discharged from the nozzle. The ten elements (effective membrane area approx. 8.0m2) in the membrane case and the diffuser on the bottom are installed. Filtration is performed continuously by a suction pump. The float switch mounted in the denitrification tank controls the operation and cessation of the pump. Since the pressure-normalized flux is kept constant by activating the constant flow valve, suction pressure rises with a membrane blockade.
On the other hand, as regards a tubular membrane element, the membrane is cylindrical with a diameter of approximately 11mm. The membrane module is composed of about 625 tubular membrane elements (effective membrane area approximately 10.9m2). In the membrane module, the guidance tube connects the net for the diffuser and the sludge dispersion is attached. After the permeable water is filtered toward the outside from the inner side of each tubular membrane, it is transported to the disinfection tank by the air-lift pump. For filtration, gravity is applied by the difference in water head between the membrane separation tank and the output of filtrate. Since the volume of filtrate water is changed by the water level of the membrane separation tank, the membrane blockage is judged by the relationship between the water level of the membrane separation tank and the volume of filtrate water.

1.2 Gappei-shori device of the installed tandoku-shori Johkasou
The TMG type is the method for the operation of the installed tandoku-shori Johkasou as a sedimentation tank (a pump chamber) with the addition of an aeration tank (membrane separation device) and a disinfection tank (Fig.2). If the number of users for designing (NUD) is six persons or more, a sludge storage tank needs to be added as well. Since the auxiliary equipment can be positioned in an area away from the installed tandoku-shori Johkasou, the site area can be used efficiently. Usually, both flush toilet wastewater and grey water flow into the installed tandoku-shori Johkasou. However, an additional flow equalization chamber can be also fitted in granting the installed tandoku-shori Johkasou cannot be utilized. The membrane modules used are similar to the flat sheet membrane employed on the KM and FM types. The effective capacity without the presence of a flow equalization chamber is 0.8 ? 1.5m3 (NUD 5 to 10).



Flg.2 Flow sheet of TMG type

Flg.2 Flow sheet of TMG type

2. Problem of small-scale membrane Johkasous
A small-scale membrane Johkasou is the equipment expected to promote advanced sewage treatment of grey water. However, it has not been widespread yet. The following reasons are being considered: 1) There are many equipments, such as various controls and membrane modules, in addition to the high-maintenance cost. 2) The maintenance cost, such as replacement of membranes and use of electricity, is high. 3) The maintenance techniques required are different from the conventional small-scale Johkasous. 4) Many cases do not demand advanced sewage treatment.
Regarding the cost problem, cost reduction in the utilization of the membrane area and the development of a membrane for long-term use are needed. In addition, lesser responsibilities for the installation personnel are important as follows: demonstration of exchange frequency and cost of membranes; establishment of delivery system of membranes; handling of membranes on lease.
Furthermore, an appropriate person with sufficient knowledge and information on the techniques different from the conventional small-scale Johkasous is necessary to ensure smooth operation.


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