Features
1 Domestic wastewater treatment facility(Small-scale Gappei-shori johkasou)
Takao Nakahashi
Nikko-company

Introduction
In the last ten years, the johkasou has gradually changed from a conventional anaerobic filter contact aeration machine (hereinafter called “structural standard type”) to a new, more compact machine, called the small-scale gappei-shori johkasou. This compact johkasou is 70% of the volume of the standard type, and is feasible for small installation spaces. In this paper, the structure of the compact type johkasou, the availability of representative johkasous in the market, johkasou performance, and trends in shipping are described.

1. Structure of the compact type johkasou
The structure of the johkasou is set by structural criteria (Ministerial Notification No. 1292, The Ministry of Construction) 1) . Regarding the disposal process, the anaerobic filter contact aeration process was mainly used for installed johkasous. The new, compact type johkasou is approximately 70% of the total volume of the structural standard type and has a treatment performance of BOD concentrations of 20mg/L or less. The structure examples of the structural standard type and the compact type johkasou (products of our company) are shown in Fig. 1.

Fig. 1 Structure of the structural standard type and the compact type johkasou
Fig. 1 Structure of the structural standard type and the compact type johkasou

Regarding the structure of the structural standard type, primary treatment equipment is composed of the anaerobic filter tank (1st room) with 40% of media filled and the anaerobic filter tank (2nd room) with 60% of media filled. Secondary treatment equipment is composed of the contact aeration tank and the sedimentation tank with 55% of luffa spongelike contact media filled. Structurally, the influent sludge is treated and discharged by a push-out process.
The compact type johkasou also has primary treatment equipment composed of the anaerobic filter tank (1st room) and the anaerobic filter tank (2nd room). The flow equalization chamber is added at the upper portion of the primary treatment equipment. Even when sludge inflows rapidly, the sludge is temporarily stored in the tank and a certain amount of sludge can be transferred into the next tank. In the biofilm filtration tank in the secondary treatment equipment, 60% of the small cylindrical media (Φ16×15mm) with large specific surface area is filled. It allows a volume load of 0.7kg/m3 or less per day against inflowing BOD and high-load operation. In addition, SS (suspended solids) in sludge adsorbed and filtrated in the biofilm filtration tank are automatically washed back twice a day using a programmable timer and sent back to the anaerobic filter tank (1st room) to prevent blockage. In the next tank, called the storage tank, 3 times the average inflow per day circulates; the storage tank also has a capacity for 3 hour retention time. Thus, the compact type johkasou has the same performance as the structural standard type at only 70% of the size.

2. Examples of the compact type johkasou for domestic use sold in the market
Examples of the compact type johkasou for domestic use available are shown in Table 1

Table1 Examples of the compact type johkasous for domestic use2)

Table1 Examples of the compact type johkasous for domestic use2)


.Primary treatment equipment is composed of the anaerobic filter chamber, the pump chamber and the aeration sludge storage chamber. By raising the retention amount of microorganisms and enlarging the surface area of media, such as the moving bed biofilm tank using spongy media and the biofilm filtration tank using small cylindrical media, a highly efficient disposal process is employed in the main part of the secondary treatment equipment. The compact type johkasou is only 70%-80% the size of the structural standard type. The blowing unit of the compact type johkasou has two air outlets for backwashing and for diffusion using a programmable timer and is employed in large numbers.

3. Performance of the compact type johkasou
By using sludge pumped from the flow equalization tank in the johkasous installed in a residential estate for 365 NUD (Number of Users for Design) as raw water, the performance of the compact johkasou NSR-5 type was examined. The inlet time was 14 hours from 7:00 to 21:00. The peak flow of 350L/hour from 8:00 to 9:00 and from 19:00 to 20:00 was released. 58L/h was released for the other hours. The total water dosage was 1.4m3/day which indicates 1m3/day more than designed. In the biofilm filtration tank during the test, the lowest water temperature was 13 degrees Celsius in December, and the highest was 20.1 degrees Celsius in October. The minimum value of BOD concentrations in raw water was 150mg/L and the maximal value was 230mg/L. The average value was 182mg/L, which ensured BOD concentrations almost as designed. The minimum value of BOD concentrations in the treated water was 7.9mg/L, and the maximal value was 14mg/L. The average value was 10mg/L, which indicated the satisfied result.

4. Situation of widespread use
According to the shipping statistics of the JSA (Johkasou System Association), the total volume of shipments of the factory production jouhkasou for domestic use made from plastic, shown in Fig. 2, has been decreasing since 1997, similar to the decrease of the Tandoku-shori johkasou. Single type johkasous have not been shipped since 2001 due to the revision of the Johkasou Law. On the other hand, the shipment of the Gappei-shori johkasou increased year by year, until 2001, when it peaked. Thus, the structural standard type was the most popular model until approximately 1998. However, after the first compact type johkasou came on to the market at the end of 1997, it increased its shipment ratio steadily. As shown in Fig. 3, in 2005 the compact type johkasou reached near 90% of the total installation number.

Fig. 2 Volume of shipments of the compact johkasou for domestic use
Fig. 2 Volume of shipments of the compact johkasou for domestic use

Fig. 3 Rate of shipments of the compact type johkasou
Fig. 3 Rate of shipments of the compact type johkasou

 


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Technological trends with the small-scale domestic johkasou(johkasou :On-site waste water treatment system)
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