1. What is biochemical treatment of wastewater?

2. How do microorganisms decompose and remove organic pollutants in wastewater?

Due to the presence of carbohydrates, fats, and proteins in wastewater, these lifeless organic substances serve as food for microorganisms. A portion is degraded and synthesized into cellular substances (anabolism products), while another portion is degraded and oxidized into water and carbon dioxide (catabolism products). During this process, organic pollutants in the wastewater are degraded and removed by microorganisms.

In addition to nutrients, microorganisms require suitable environmental factors such as temperature, pH, dissolved oxygen, and osmotic pressure for survival. Abnormal environmental conditions can affect microbial life activities, even causing mutations or death.

In wastewater biological treatment, the optimal temperature range for microorganisms is generally 16-30℃, with a maximum temperature of 37-43℃. Microorganisms will cease growth when the temperature falls below 10℃. Within the suitable temperature range, for every 10℃ increase in temperature, the metabolic rate of microorganisms increases accordingly, and the COD removal rate also increases by about 10%; conversely, for every 10℃ decrease in temperature, the COD removal rate decreases by 10%. Therefore, the biochemical removal rate of COD in winter is significantly lower than in other seasons.

Microbial life activities and material metabolism are closely related to pH. Most microorganisms adapt to a pH range of 4.5-9, while the optimal pH range is 6.5-7.5. When the pH is below 6.5, fungi begin to compete with bacteria. When the pH reaches 4.5, fungi will completely dominate the bioreactor, resulting in serious impairment of sludge settling. When the pH exceeds 9, the metabolic rate of microorganisms will be hindered. Different microorganisms have different requirements for the suitable pH range. In aerobic biological treatment, the pH can vary between 6.5-8.5; in anaerobic biological treatment, microorganisms have stricter pH requirements, with the pH ranging from 6.7-7.4.

Oxygen dissolved in water is called dissolved oxygen. Aquatic organisms and aerobic microorganisms rely on dissolved oxygen for survival. Different microorganisms have different requirements for dissolved oxygen. Aerobic microorganisms require sufficient dissolved oxygen; generally, dissolved oxygen should be maintained at 3mg/L, and should not be lower than 2mg/L. Facultative anaerobic microorganisms require dissolved oxygen in the range of 0.2-2.0mg/L; while anaerobic microorganisms require dissolved oxygen below 0.2mg/L.

Biochemical treatment can be divided into two categories according to the oxygen requirements of microbial growth: aerobic biochemical treatment and anoxic biochemical treatment. Anoxic biochemical treatment can be further divided into facultative anaerobic biochemical treatment and anaerobic biochemical treatment. In aerobic biochemical treatment, aerobic microorganisms must grow and reproduce in the presence of a large amount of oxygen to reduce organic matter in wastewater; while in facultative anaerobic biochemical treatment, facultative anaerobic microorganisms only require a small amount of oxygen to grow and reproduce and degrade organic matter in wastewater. If there is too much oxygen in the water, facultative anaerobic microorganisms will not grow well, thus affecting their efficiency in treating organic matter. Facultative anaerobic microorganisms can adapt to wastewater with higher COD concentrations, with influent COD concentrations up to 2000mg/L or more, and a COD removal rate generally ranging from 50-80%; while aerobic microorganisms can only adapt to wastewater with lower COD concentrations, with influent COD concentrations generally controlled below 1000-1500mg/L, and a COD removal rate generally ranging from 50-80%. The duration of facultative anaerobic biochemical treatment and aerobic biochemical treatment is not long, generally 12-24 hours. People utilize the differences and advantages between facultative anaerobic biochemical treatment and aerobic biochemical treatment, combining facultative anaerobic biochemical treatment and aerobic biochemical treatment. Wastewater with higher COD concentrations undergoes facultative anaerobic biochemical treatment first, and then the effluent from the facultative anaerobic tank is used as the influent for the aerobic tank. This combined treatment can reduce the volume of the bioreactor, saving both environmental investment and daily operating costs. The principle and function of anaerobic biochemical treatment are the same as those of facultative anaerobic biochemical treatment. The difference between anaerobic biochemical treatment and facultative anaerobic biochemical treatment is that anaerobic microorganisms do not require any oxygen during their reproduction, growth, and degradation of organic matter, and anaerobic microorganisms can adapt to wastewater with even higher COD concentrations (4000-10000mg/L). The disadvantage of anaerobic biochemical treatment is that the biochemical treatment time is long, and the wastewater residence time in the anaerobic bioreactor generally needs to be more than 40 hours. 8. What are the applications of biological treatment in wastewater treatment engineering? The most widely and practically used technologies for biological treatment in wastewater treatment engineering fall into two categories: activated sludge process and biofilm process. The activated sludge process is an aerobic wastewater treatment method using the biochemical metabolism of suspended microbial populations. During growth and reproduction, microorganisms can form flocs with a large surface area, which can flocculate and adsorb a large amount of suspended colloidal or dissolved pollutants in wastewater, and absorb these substances into the cells. With the participation of oxygen, these substances are completely oxidized to release energy, CO

8. 生物处理在废水处理工程上有哪些应用？