Anaerobic Fermentation Techniques You May Want to Know

Anaerobic fermentation process is a productive and environmentally friendly biological treatment process, which has been widely used in livestock manure, wastewater, organic solid waste treatment and other fields. Anaerobic fermentation processes can be divided into the following categories from different perspectives: ambient temperature, moderate temperature and high temperature fermentation according to different fermentation temperatures; continuous and sequential batch fermentation according to feeding operation mode; wet and dry anaerobic fermentation according to the amount of solid content in fermentation materials; single-phase and two-phase anaerobic fermentation according to whether the reaction is carried out in the same reactor.

Ambient, moderate and high temperature fermentation

Temperature mainly affects the growth rate of microorganisms and the metabolic rate of microorganisms to the matrix by affecting the activity of some enzymes in anaerobic microbial cells, thus affecting the yield of sludge, the removal rate of organic matter, the treatment load that the reactor can reach, the flow direction of organic matter in biochemical reactions, the formation of some intermediates, the solubility of various substances in water, and the yield and composition of biogas in anaerobic biological treatment process.

Ambient fermentation is generally performed by digesting the material directly at natural temperature without external heating, and the fermentation temperature will fluctuate with the diurnal variation of seasonal climate. The fermentation process at room temperature is simple and inexpensive, but its disadvantage is that the treatment effect and gas production are unstable.

The temperature of medium temperature fermentation is between 30? and 40?. The medium temperature fermentation has less heat addition, the fermentation vessel has less heat dissipation, the reaction and performance are more stable, and the reliability is high. If the material has better pretreatment, the reaction speed and gas occurrence will be increased; the toxic inhibitory substance barrier effect is small, the recovery is fast after inhibition. There will be scum, foam, sediment deposition and other problems, and the treatment of scum, foam, sediment is a technical difficulty.

The temperature of high temperature fermentation is between 50? and 60?, which requires the outside world to continuously provide more heat. The metabolic rate, organic matter removal rate and killing of pathogenic bacteria in the high temperature anaerobic digestion process are higher than those in the medium temperature anaerobic digestion process. However, the high temperature fermentation is greatly affected by toxic inhibitors, which is difficult to return to normal after inhibition, with low reliability; the high temperature anaerobic gas production rate is slightly increased compared with the medium temperature anaerobic oxygen, increasing the amount of impurity gases, but the content of methane, the active ingredient in biogas, is not increased, limiting the application of high temperature anaerobic; the high temperature fermentor body and pipeline need materials with good high temperature corrosion resistance, complex operation and high technical content.

Continuous fermentation and sequential batch fermentation

Continuous fermentation is to add new materials to the fermenter and discharge biogas slurry continuously and quantitatively every day after the start of adding materials and after a period of stable fermentation. Sequential batch fermentation is a one-time fermentation with materials added, no new materials are added during the fermentation process. When the fermentation is completed, the residue is discharged and then new materials are added for fermentation again, generally the solid concentration of feed is between 15% and 40%.

The results show that the sequential batch reactor is more efficient than the fully mixed continuous reactor for the treatment of high lignin and cellulose materials if the kinetic rate is low and there is hydrolysis limitation. In addition, the degree of hydrolysis of the sequential batch fermentation is higher, the methane output is greater, and the investment in the continuous feed system is reduced by about 40%. Although the sequential batch feed processing system covers a larger area than the continuous feed processing system, it is suitable for popularization and application in developing countries because of its simple design, easy control, strong adaptability to thick impurities, and less investment.

Wet fermentation and dry fermentation

Wet fermentation is a biogas fermentation process using solid organic waste (fixed content of 10% ~ 15%) as raw material. Dry fermentation is a new biogas fermentation process with solid organic waste (fixed content of 20% ~ 30%) as raw material and no or almost no free flow. It is a new waste recycling method.

Wet fermentation system is similar to the anaerobic stabilization treatment technology of sludge in wastewater treatment, but many problems need to be considered in practical design, especially for urban domestic garbage, separation and removal of rough hard garbage, and pretreatment process of garbage into sufficient continuous slurry. In order to remove impurities and ensure the normal treatment of organic waste, it is necessary to use filtration, pulverization, screening and other complex treatment.

These pretreatment processes result in 15% to 25% loss of volatile solids. Slurry refuse cannot maintain uniform continuity because heavy matter settles and light matter forms a scum layer during digestion, resulting in the formation of two significantly different density substance layers in the reactor, and the accumulation of heavy matter at the bottom of the reactor may destroy the stirrer and must be removed by a specially designed hydraulic cyclone separator or pulverizer.

Single-phase fermentation and two-phase fermentation

The single-phase fermentation process is carried out in the same reactor with acidogenic and methanogenic bacteria. Two-phase fermentation process, which achieves the separation of biological phases, allows microorganisms to ferment under their respective optimal growth conditions.

The single-phase fermentation process will be affected by changes in impact load or environmental conditions, resulting in increased hydrogen partial pressure, which causes propionic acid accumulation. However, after biophase separation, the acidogenic phase can effectively remove a large amount of hydrogen and improve the treatment efficiency and operating stability of the entire two-phase anaerobic biological treatment system.

Compared with two-phase fermentation process, single-phase fermentation process has less investment and simple and convenient operation, so about 70% of the current fermentation process uses single-phase fermentation process. However, two-phase fermentation process has many advantages in the treatment of urban domestic garbage, for example, it can control the conditions of two different reactors alone, so that acidogenic bacteria and methanogenic bacteria can grow under their own most suitable environmental conditions; it can also control their organic load rate (OLR), hydraulic retention time (HRT) and other parameters alone, improve the number and activity of microorganisms, so as to reduce HRT and improve the treatment efficiency of the system.

Current research on two-phase fermentation processes mostly focuses on how to organically combine efficient anaerobic reactors and two-phase fermentation processes, and reactors for two-phase fermentation processes can use any kind of anaerobic bioreactors, such as anaerobic contact reactors, anaerobic biofilters, UASB, EGSB, UBI, ABR, or other anaerobic bioreactors, and the reactor forms used for the acidogenic and methanogenic phases can be the same or different

Collected by Profacgen, an insect cell protein production provider.