First, sewage treatment is generally divided into production sewage treatment and domestic sewage treatment. Production sewage includes industrial sewage, agricultural sewage and medical sewage, while domestic sewage is the sewage produced in daily life, which refers to the complex mixture of inorganic and organic substances in various forms, including: ① floating and suspended solid particles; ② Colloidal and gelatinous diffusers; ③ Pure solution.
Now let's introduce the treatment methods of domestic sewage:
1. Chloride ion ① inspect the concentration of hydrochloride in wastewater by testing chloride ion; ② The content of chloride ion is too high, which directly affects the determination of COD.
2. SS (suspended solids) the test method of SS strictly complies with the standard test method for wastewater quality analysis. The sum of all residues in water is called total solids (TS), which includes dissolved substances (DS) and suspended solids (SS). After the water sample is filtered, the solid obtained by evaporating the filtrate is dissolved solid (DS), and the filter residue is suspended solid (FS) after dehydration and drying. When the solid is burned at 600 ℃, the amount volatilized is volatile solid (VS), and the burning residue is solid substance (FS). The soluble solids of the community sewage treatment equipment represent the salt content, the suspended solids represent the amount of insoluble solid substances in the water, and the volatile solids represent the organic component of solids. SS is the most important index to evaluate the treatment effect of coagulation reaction. The main function of coagulation reaction is to remove suspended solids and colloidal substances from wastewater.
3. Composition of activated sludge: activated sludge is the main active substance in the activated sludge system. The appearance of activated sludge for normal treatment of urban domestic sewage is yellowish brown flocculent particles with particle size of 0.02~0.2mm, unit surface area of 2 ~ 10m2/l, relative density of 1.002 ~ 1.006 and moisture content of more than 99%. Living organisms with strong vitality inhabit the activated sludge. These biological groups are mainly bacteria and protozoa, but also fungi and metazoans dominated by rotifers. The solid content of activated sludge accounts for less than 1% and consists of four parts:
1. Active biological population (MA);
2. Microbial self oxidation residue (me);
3. Inert substances (MI) carried by raw sewage that cannot be degraded by microorganisms;
4. Inorganic substances (MII) carried by raw sewage and attached to activated sludge. Under the metabolic action of microorganisms, the organic matter in sewage is degraded and removed. At the same time, the proliferation of activated sludge microorganisms and the subsequent growth of activated sludge are produced. The key to controlling sludge growth is the ratio f/m of organic substrate (f) and microbial biomass (m), that is, the organic load of activated sludge.
Rural sewage mainly consists of domestic sewage and agricultural sewage. The composition of domestic sewage is relatively fixed, mainly containing carbohydrates, proteins, amino acids, fats and other organic substances, which are more suitable for the growth of bacteria and become a place for the survival and reproduction of bacteria and viruses; However, domestic sewage generally does not contain toxicity and has certain fertilizer effect, which can be used to irrigate farmland. The components of agricultural wastewater are diverse. In different seasons, different places and villages and towns with different development goals, their wastewater needs different treatment methods. In sewage treatment, in order to reduce the sewage discharge and its complexity, the toilet flushing water (black water) and other domestic water (grey water) should be separated in combination with the construction of biogas digesters that the country is vigorously promoting. Grey water is treated by natural purification system, and black water and human and animal feces are treated by anaerobic biogas digester, which can not only reduce sewage discharge, complexity and treatment cost, but also have important significance for developing clean new energy in rural areas, protecting human settlements and promoting the sustainable development of rural economy and society.