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Industrial Organic Sewage

The process water, discharged by food industry, feed mill,paper mill,etc., containing high content of COD and BOD5, featured with good biodegradability, is a great resource for biogas production.
The purpose of sewage treatment determines the choice of specific process. General speaking, there are three kinds of situations:
1.Purifying sewage is the only purpose, to remove organic matter as more as possible, to make water discharging environmental friendly. In this case, we adopt separation, air flotation, A2/O (Anaerobic-Anoxic-Oxic) technologies, etc.
2.Only for the purpose of biogas production. The loss of organic matter should be minimized in the front end of filtration. Improvement of BOD5/CODt ratio is necessary to raise the loading capacity of reactor. Biological technology is anaerobic digestion.
3.Combination of biogas and purification.
Herewith we only explain the technological process for biogas production.
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1.Primary treatment

Removal of big-size suspended solids and harmful substance, regulation of pH value and temperature, improvement of biodegradability and C/N element ratio would be implemented in this step.
Mechanical grilles, Spiral centrifugal and extrusion press are suitable for filtration. If composition is okay, the separated solids could be fed to animal, but exclusive of sands and the like. So we always advise clients not to mix the process water with the washing water in the works.
For the waste water with high content of insoluble COD(eg.lignin) when its BOD5/CODt ratio is lower than 0.5, it’s better for hydrolysis to mainly occurs in this step, to decompose insoluble COD into soluble COD, to degrade macromolecules into micromolecules.

2.Anaerobic digestion

The proper anaerobic reactor is UASB(Up-flow Anaerobic Sludge Blanket) when total solids content lower than 5%. Waste water enters reactor through bottom-located distribution system. There is a sludge blanket at the bottom position, most of organic substances are fermented here when biogas is formed. Resulting from stirring of flow and gas bubble,a sludge suspension layer is formed above blanket.
A three-phase separator is fixed at upper position in reactor. Via it,the separation of gas,fermented liquid and solids attached on gas bubbles would be achieved. Gas is stored in gas holder on top or pressed out through gas pipe, liquid flows out of reactor and sludge solids slide down into sludge blanket.
The loading capacity of UASB reactor could reach 3 ~ 12mgCOD/m³.d, HRT(Hydraulic Retention Time) is 5~10 days, suitable for biological treatment of high concentration organic waste water. COD removal could reach 85 ~ 90%.
EGSB (Expanded Granular Sludge Blanket) is the third generation of anaerobic reactors developed on the basis of UASB. Unlike the UASB, EGSB has a dedicated sewage recovery unit. The expansion of granular sludge blanket improves the contact between organic matter and microorganisms.
IC (Internal Circulation) has good performance of anti-load shocking. It has a large height-diameter ratio,seemingly two UASB in series. The incoming waste water could be diluted automatically through internal circulation. In this regard,the stability of concentration of waste water in the first reaction chamber is guaranteed. Due to high up-flow speed,suspended solids do not accumulate in reactor and sludge can maintain high activity.