Principle and application of sludge digestion?

The excess sludge contains a lot of organic matter and pathogenic bacteria. If discharged directly into nature, organic matter will stink under the action of microorganisms, causing serious harm to the environment, and pathogens will directly or indirectly contact the human body and cause harm. Therefore, sludge usually needs to be stabilized before dehydration. The common method of sludge stabilization is digestion, including aerobic digestion and anaerobic digestion.

1. Aerobic digestion of sludge

(1) Sludge aerobic digestion is actually a continuation of activated sludge process. In the process of digestion, organic sludge can be transformed into gas products such as carbon dioxide, ammonia and hydrogen by oxidation.

⑵ aerobic digestion classification

Aerobic digestion can be divided into ordinary aerobic digestion and autothermal high-temperature aerobic digestion.

⑶ Aerobic digester

Structurally, it generally includes aerobic digestion chamber, mud-water separation chamber, digested sludge discharge pipe and aeration system. Aerobic digestion is flexible and can be operated intermittently or continuously.

⑷ Advantages and disadvantages of aerobic digestion

Advantages: high degradation degree of biodegradable organic matter in sludge; The concentration of BOD in the clear liquid is low, the amount of digested sludge is small, odorless, stable, easy to dehydrate and convenient to handle; Digested sludge has high fertilizer content and is easily absorbed by plants; The operation and management of aerobic digester is convenient and simple, and the capital cost of structures is low. Therefore, it is especially suitable for sludge treatment in small and medium-sized sewage treatment plants.

Disadvantages: high energy consumption and high operating cost; Unable to recycle biogas; Because aerobic digestion is not heated, the decomposition degree of sludge organic matter fluctuates greatly with temperature; When digested sludge is concentrated by gravity, the SS concentration of supernatant is high.

2. Sludge anaerobic digestion

Anaerobic digestion refers to the decomposition of biodegradable organic matter in sludge into carbon dioxide and methane gas by facultative bacteria and obligate anaerobic bacteria under anaerobic conditions, thus stabilizing sludge.

(1) principle

The process of anaerobic digestion of sludge is extremely complicated, which can be summarized into three stages: in the first stage, carbohydrates, protein and fats are hydrolyzed and fermented into monosaccharides, amino acids, fatty acids, glycerol, carbon dioxide and hydrogen under the action of hydrolytic fermentation bacteria. In the second stage, the products of the first stage are transformed into hydrogen, carbon dioxide and acetic acid under the action of hydrogen-producing and acid-producing bacteria, and the microorganisms involved are hydrogen-producing and acid-producing bacteria and homoacetobacter. In the third stage, through the action of two groups of different methanogenic bacteria, one group converts hydrogen and carbon dioxide into methane, and the other group decarboxylates acetic acid to generate methane. The microorganisms involved are methanogenic bacteria, which belong to absolute anaerobic bacteria, and the main metabolite is methane.

⑵ Anaerobic digestion classification

Anaerobic digestion methods include traditional digestion, high-speed digestion and anaerobic contact method. The disadvantages of the traditional digester are: obvious stratification phenomenon, which makes the bacteria and nutrients unable to fully contact, so the load is small, the gas production is low, and the operation is difficult. The high-speed digester overcomes the shortcomings of traditional digestion methods and improves the load and gas production. The anaerobic contact method is based on continuously stirring the anaerobic digestion tank, adding sedimentation tanks to collect sludge, and returning anaerobic sludge to the digestion tank, which increases the concentration of anaerobic sludge in the reactor and significantly improves the treatment efficiency and load.

⑶ Influencing factors of anaerobic digestion

① Temperature factor

The adaptability of methanogens to temperature can be divided into two categories: mesophilic methanogens (the optimum temperature is 33 ~ 35℃) and thermophilic methanogens (the optimum temperature is 50 ~ 55℃), but the reaction speed between the two regions is reduced. The allowable temperature range of mesophilic or thermophilic anaerobic digestion is 65438 0.5 ~ 2.0℃, and when there is a change of 3℃, the digestion process will be inhibited.

② Load

The volume of anaerobic digester depends on the loading rate of anaerobic digestion. There are two expressions of load rate: volume load and organic load. Organic matter loading rate refers to the ratio of daily dry sludge volume to pond volume, which can better reflect the relative relationship between organic matter and microbial biomass.

③ Stir and mix.

Anaerobic digestion is a contact reaction between endogenous and exogenous enzymes of bacteria and substrates, which must be fully mixed. The general methods of stirring are: mechanical stirring, sludge pumping and biogas stirring.

④ C/N ratio

Too high C/N ratio, insufficient intracellular nitrogen, low buffering capacity of digestive juice, and easy reduction of pH value. If the C/N ratio is too low, the pH value may increase, thus inhibiting the digestion process.

⑤ Toxic substances

In the process of digestion, the main substances that inhibit digestion are heavy metal ions, S-2, ammonia and organic acids. When it reaches a certain concentration, digestion will be inhibited.

⑥ Buffering effect of pH, pH and digestive juice.

(4) Structure of digester

For more information about project/service/procurement bidding, and to improve the winning rate, please click on the bottom of official website Customer Service for free consultation:/#/? source=bdzd