What are the anaerobic biological treatment methods for wastewater? What is the principle of anaerobic treatment?

Anaerobic digestion has the following advantages: no stirring and oxygen supply, less power consumption; It can produce a large amount of methane-containing biogas, which is a good energy material and can be used for power generation and household gas. It can feed water with high concentration and maintain high sludge concentration, so its solvent organic load reaches the national standard and still needs further treatment; Long initial startup time; High temperature requirements; Sensitive to the effects of poison; After being destroyed, the recovery period is longer. The anaerobic biological treatment process of sewage can be divided into anaerobic activated sludge process and anaerobic biofilm process according to the coagulation form of microorganisms. Anaerobic activated sludge process includes common digester, anaerobic contact digester, upflow anaerobic sludge bed (UASB), anaerobic granular sludge expanded bed (EGSB) and so on. Anaerobic biofilm process includes anaerobic biofilter, anaerobic fluidized bed and anaerobic biological turntable.

Generally speaking, there are many complex organic substances in wastewater, which are degraded by anaerobic decomposition in four stages:

(1) Hydrolysis stage: Because of its large molecular volume, high molecular organic matter can not directly pass through the cell wall of anaerobic bacteria, and needs to be decomposed into small molecules by extracellular enzymes in vitro. Typical organics in wastewater, such as cellulose, are decomposed into cellobiose and glucose by cellulase, maltose and glucose by starch, and short peptides and amino acids by protein. After decomposition, these small molecules can enter the cell body through the cell wall for further decomposition. The answer comes from environmental protection.

(2) Acidification stage: the above-mentioned small molecular organic substances enter cells and are transformed into simpler compounds, which are distributed outside the cells. The main products in this stage are volatile fatty acids (VFA), and some products are also produced, such as alcohols, lactic acid, carbon dioxide, hydrogen, ammonia and hydrogen sulfide.

(3) Acetic acid generation stage: At this stage, the products of the previous step are further transformed into acetic acid, carbonic acid, hydrogen and new cellular substances.

(4) Methane production stage: At this stage, acetic acid, hydrogen, carbonic acid, formic acid and methanol are all converted into methane, carbon dioxide and new cellular substances. This stage is also the most important stage of the whole anaerobic process and the rate-limiting stage of the whole anaerobic reaction process.