Anaerobic biological treatment is the process of forming the nutritional and environmental conditions required by anaerobic microorganisms under anaerobic conditions, using such microorganisms to decompose organic substances in wastewater and generate methane and carbon dioxide.
The anaerobic degradation process of polymer organic matter can be divided into four stages: a hydrolysis stage, a fermentation (or acidification) stage, an acetic acid-producing stage, and a methanogenic stage.
(1) Hydrolysis stage Hydrolysis can be defined as the process in which a complex non-soluble polymer is converted into a simple soluble monomer or dimer.
(2) Fermentation (or acidification) stage fermentation can be defined as the biodegradation process of organic compounds as both electron acceptors and electron donors. In this process, soluble organic matter is converted into end products mainly composed of volatile fatty acids. This process is also called acidification.
(3) Acetic acid production stage Under the action of hydrogen-producing acetic acid bacteria, the products of the previous stage are further converted into acetic acid, hydrogen, carbonic acid, and new cellular material.
(4) Methane phase At this stage, acetic acid, hydrogen, carbonic acid, formic acid and methanol are converted into methane, carbon dioxide and new cellular material.
The reaction in the acidification tank is part of an anaerobic reaction.
Anaerobic tank is a reaction tank without dissolved oxygen or nitrate. An anoxic cell is a reaction cell without dissolved oxygen but with nitrate.
Acidification tank --- hydrolysis, acidification, acetic acid production, limiting methanation, and a decrease in pH. The process is simple, easy to control and operate, and can remove some COD. Objective to improve biodegradability;
Anaerobic tank --- Hydrolysis, acidification, acetic acid production, and methanation proceed simultaneously. Need to adjust pH, not easy to operate and control, remove most of the COD. The purpose is to remove COD.
Hypoxia tank --- there is a hydrolysis reaction, the pH value increases during the denitrification process. In the denitrification process, it mainly plays the role of denitrification to remove nitrate nitrogen, while removing some BOD. It also has the effect of improving the biodegradability by hydrolysis reaction.
There is no need for aeration device inside the hydrolysis acidification tank, the residence time is controlled, and the hydrolysis and acidification stages do not occur. The COD removal rate in the first two stages is not very high, because his purpose is to change Into small molecules organic matter, the general removal rate is about 20%, the COD removal rate in the gas production stage is generally about 40%, but this is the hydrogen sulfide gas generated to be deodorized, and the residence time to reach the gas production stage is longer than The first two stages are long, that is, an anaerobic state is required. An aeration device should be set in the anoxic tank to control the dissolved oxygen at 0.3-0.8mg / l, and facultative microorganisms and biofilms are used to degrade organic matter in the wastewater. The aerator in the oxidation tank should be selected carefully when contacting the aerator. The amount of oxygen must be ensured to facilitate the shedding and regeneration of the biofilm. Generally, the micro-hole aerator is not used as the aerator at the bottom of the pool.
The aerobic pond is a structure that maintains the dissolved oxygen content in the water at about 4 mg / l through aeration and other measures, which is suitable for the growth and reproduction of aerobic microorganisms, so as to treat the pollutants in the water.
The anaerobic tank does not do aeration, and the concentration of pollutants is high, because dissolved oxygen is consumed in the decomposition so that there is almost no dissolved oxygen in the water body, which is suitable for anaerobic microorganisms to treat the structures in the water;
Anoxic ponds are structures with insufficient or no aeration but low levels of pollutants, which are suitable for aerobic and facultative microorganisms.
Different oxygen environments have different microbiomes. Microbes also change their behavior when the environment changes, so as to achieve the purpose of removing different pollutants.
The role of the aerobic tank is to allow the activated sludge to perform aerobic respiration, and further decompose organic matter into inorganic matter. Removes pollutants. The good operation is to control the oxygen content and other optimal conditions of the microorganisms, so that the microorganisms can perform aerobic respiration with the greatest benefits.
Anaerobic treatment is the use of anaerobic bacteria to remove organic matter in wastewater, which usually takes a long time. The anaerobic process can be divided into a hydrolysis stage, an acidification stage and a methanation stage.
The products of hydrolysis and acidification are mainly small molecule organic matter, which significantly improves the soluble organic matter in the wastewater, and only the soluble small molecule matter can be directly entered into the cells by the microorganisms. The insoluble macromolecular matter must first pass the extracellular enzyme The decomposition can enter the microorganisms and metabolize. For example, natural glues (mainly starches) are first converted into polysaccharides and then hydrolyzed to monosaccharides. Cellulose is hydrolyzed into cellobiose and glucose by cellulase. Hemicellulose is hydrolyzed into oligosaccharides and monosaccharides by polyxylase and the like.
The hydrolysis process is slow and affected by many factors at the same time. It is the rate-limiting stage of anaerobic degradation. At the acidification stage, the small-molecule compounds formed in the first stage above are converted into simpler compounds in the cells of fermenting bacteria, ie, acidifying bacteria, and secreted outside the bacteria, mainly including volatile organic acids (VFA), milk alcohol, alcohol And the like, and then further converted into acetic acid, hydrogen, carbonic acid and the like. The acidification process is completed by a large number of fermenting bacteria and acetogenic bacteria, most of which are strictly anaerobic bacteria, which can decompose sugar, amino acids and organic acids.