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What are the influencing factors of anaerobic biological treatment？

The principle of anaerobic treatment of wastewater
The methanogenesis reaction is the control stage of the anaerobic digestion process. Therefore, in general, when discussing the influencing factors of anaerobic biological treatment, the main factors affecting methanogens are discussed; the main influencing factors are: temperature, pH value, oxidation Reduction potential, nutrients, F/M ratio, toxic substances, etc.

1. Temperature:

The effect of temperature on Anaerobic Microorganisms is particularly significant; anaerobic bacteria can be divided into thermophilic bacteria (or high temperature bacteria) and mesophilic bacteria (mesophilic bacteria); correspondingly, anaerobic digestion is divided into: high temperature digestion (about 55°C) and mesophilic digestion (about 35°C); the reaction rate of calcification is about 1.5~1.9 times that of mesophilic digestion, and the gas production rate is also higher, but the methane content in the gas is lower; when treating wastewater containing pathogenic bacteria and parasite eggs or High temperature digestion can achieve better hygienic effect, and the dewatering performance of sludge after digestion is also better; with the development, research and application of new anaerobic reactors, the effect of temperature on anaerobic digestion is no longer very important ( The biomass in the new reactor is large), so it can be carried out at normal temperature (20~25°C) to save energy and operating costs.

2. pH and alkalinity:

pH value is the most important influencing factor in the process of anaerobic digestion; important reason: methanogens are very sensitive to changes in pH value, and it is generally believed that the optimal pH value range is 6.8~7.2, and when <6.5 or >8.2 , the methanogens will be severely inhibited, which will further lead to the deterioration of the entire anaerobic digestion process; the pH value in the anaerobic system is affected by many factors: the pH value of the influent water, the influent water quality (organic matter concentration, organic matter species, etc.) , biochemical reaction, acid-base balance, dissolution balance between gas, solid and liquid phase, etc.; anaerobic system is a pH buffer system, mainly controlled by carbonate system;
The increase of fatty acid content (accumulation) in the system will consume −HCO3 and lower the pH; but the action of methanogens can not only consume fatty acids, but also produce −HCO3, which will raise the pH of the system. Alkalinity was once considered to be a crucial factor in anaerobic digestion, but in fact its main function is to ensure that the anaerobic system has a certain buffer capacity and maintain a suitable pH value; once the anaerobic system is acidified, It will take a long time to recover.

3. Redox potential:

Strict anaerobic environment is the basic condition for methanogenic bacteria to carry out normal physiological activities; non-methanogenic bacteria can grow and operate normally in the environment with redox potential of +100~-100mv; the optimal redox potential of methanogenic bacteria is - 150~-400mv, in the initial stage of culturing methanogens, the redox potential should not be higher than -330mv;

4. Nutritional requirements:

The requirements of Anaerobic Microorganisms for nutrients such as N and P are slightly lower than that of aerobic microorganisms, and they require COD: N: P = 200: 5: 1; most anaerobic bacteria do not have the function of synthesizing some necessary vitamins or amino acids. Therefore, it is sometimes necessary to add: ① K, Na, Ca and other metal salts; ② trace elements Ni, Co, Mo, Fe, etc.; ③ organic trace substances: yeast extract, biotin, vitamins, etc.

5. F/M ratio:

The organic load of anaerobic biological treatment is higher than that of aerobic biological treatment, generally up to 5~10kgCOD/m3.d, even up to 50~80kgCOD/m3.d; no oxygen transfer limitation; higher biomass can be accumulated . The reaction rate of the acid production stage is much higher than that of the methane production stage, so the organic load must be selected very carefully; the premise of high organic volumetric load is high biomass, and correspondingly low sludge load; high organic volumetric load can be Shorten HRT and reduce reactor volume.

6. Toxic substances:

——Common inhibitory substances are: sulfide, ammonia nitrogen, heavy metal, cyanide and some organic compounds;
①Sulfide and sulfate: sulfate and other sulfur oxides are easily reduced to sulfide during anaerobic digestion; when the soluble sulfide reaches a certain concentration, the anaerobic digestion process is mainly methane production Inhibition effect; adding some metals such as Fe can remove S2-, or stripping H2S from the system can alleviate the inhibition effect of sulfide.
②Ammonia nitrogen: Ammonia nitrogen is a buffer for anaerobic digestion; however, if the concentration is too high, it will have a toxic effect on the anaerobic digestion process; the inhibitory concentration is 50-200 mg/l, but after domestication, the adaptability will be enhanced.
③Heavy metals: - The enzyme system of anaerobic bacteria is destroyed.
④Cyanide:
⑤Toxic organic substances

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