Updated: July 2002

1. Equipment outline

UASB's official name is Upflow Anaerobic Sludge Blanket or Bed. UASB is the equipment from which 80-90% of BOD is removed with the methane-fermentation bacteria which carried out the self-granulation. A methane-fermentation bacteria become granular to be referred to as granular sludge (diameter of 1-2mm). In it, the hydrolysis bacteria, the acid-formation bacteria, the methane generation bacteria, etc. are intermingled. Granular sludge is in the lower part of equipment, and waste water flows in from a lower part, and carries out an overflow from the upper part. In our company, 2-stage system was developed newly. This is the system which sends the treated water of the 1st step of UASB to the 2nd step of UASB, as shown in the following flow chart. Conventional acid-formation tank + UASB and conventional fixed-bed + UASB are evolved further.

2-stage methane fermentation processing system flow diagram (ex. discharge to sewage)

2. Feature

Describe the general feature below. Since the proliferation rate of a cell is slow, there are few amounts of generating of an excess sludge (about 1/10 excess sludge of a standard activated sludge process). In 2-stage system, it decreases further. Even when the decomposition nature of waste water is bad, in 2-stage system, two steps of systems can be utilized effectively and it can correspond flexibly. In the conventional 2-phase system, a big tank is needed and management of control of temperature and pH etc. becomes complicated. In 2-stage system, the margin is taken to the 2nd step of design in BOD volumetric loading. Therefore, flexible correspondence can be performed even when load becomes high in the future. There was a case which installs aerobic equipment in the latter part of UASB conventionally, or dilutes a treated water. Aerobic equipment may be unnecessary, reduction of running cost can be performed, and it excels in 2-stage system at maintenance.

3. Performance

2-stage system can attain the high rate of BOD removal as compared with the former. In sewer discharge, it is acceptable to the raw water concentration of 12000 mg/l in BOD 600 mg/l regulation area. Furthermore, it is acceptable to 6000 mg/l in 300 mg/l area.

4. Adaptation Field and Processing Subject

(1) Food waste water treatment
Since a food stuff industry has many production items, the processing method suitable for each is searched for. Generally pressure air flotation equipment is required of the waste water with many oils. Moreover, for the quality of a starch, or waste water with much suspended solid, an acid-formation tank is needed.
(2) Stock raising feces-and-urine processing
The concern about residents' environmental preservation is increasing by an expansion of a stock raising scale, contiguity in a residence, etc. In stock raising feces and urine, the suspended solid concentration in raw water was quantity. As a pretreatment, although solid-liquid separation is needed, a good compost can be made by the method which does not use a flocculating agent.
(3) White-distilled-liquor waste fluid processing
White-distilled-liquor waste fluid also has the high suspended solid concentration in raw water. As a pretreatment, although solid-liquid separation is needed, since a flocculating agent is not used, good feedization can be carried out.

5. In addition

When high-concentration sulfuric acid ion is contained in waste water, sulfuric acid ion changes to a hydrogen sulfide, and it prevents bio-process. In our company by using stripping technology, the stable processing is possible even if a certain amount of high-concentration sulfuric acid ion is contained.