1, the current situation of water pollution in china
china is short of water resources, and there are more than 400 cities lacking water in the whole country, of which more than 100 are seriously short of water. because of the large population, the per capita water resources occupy only 25% of the world's per capita, which is one of the world's poor water countries. because of the unbalanced distribution of water resources, there are more differences in space and time between the south and the north, the east and the west, and the summer and winter. however, under unfavorable conditions, industrial wastewater and agricultural wastewater are discharged arbitrarily without treatment, resulting in more serious water pollution. according to the 2010 national environmental quality data released by the ministry of environmental protection, china's surface water is seriously polluted, with seven major water systems (the yangtze river, yellow river, pearl river, songhua river, huaihe river, haihe river and so on). liaohe river is suffering from slight, moderate and severe pollution, and the eutrophication of lakes is prominent. in recent years, major water pollution incidents have occurred frequently, with a high incidence of 50%. water shortage is becoming more and more serious.
1.1 traditional sewage treatment technology
water pollution usually refers to the deterioration of water quality caused by man-made causes and the reduction of water use value. the main pollutants are solid wastes and chemicals (aerobic organic compounds, refractory organic compounds, heavy metals, plant nutrients, acids, alkalis and petroleum substances).
the commonly used sewage treatment technologies in china are:
(1) physical method is the separation technology of insoluble pollutants (gravity sedimentation, coagulation clarification, buoyancy floatation, centrifugal separation, magnetic separation, etc.).
(2) chemical method is the chemical transformation technology of pollutants (acid-base neutralization, chemical precipitation, oxidation-reduction, chemical and physical disinfection).
(3) physical and chemical separation technology of dissolved pollutants (adsorption, ion exchange, membrane separation, evaporation, freezing).
1.2 disadvantages of common methods
physical method covers a large area, high capital and operation costs, energy consumption, complex management, easy to appear sludge bulking phenomenon; equipment can not meet the requirements of high efficiency and low consumption, the effect of single use is not obvious. chemical methods are expensive in operation and consume a lot of chemical reagents, which are likely to cause two pollution. in most cases, the two must be combined.
2. microbial technology
how to make the municipal wastewater treatment process develop toward the sustainable direction of low energy consumption, high efficiency, less excess sludge, the most convenient operation and management, as well as the realization of phosphorus recovery and treatment water reuse, and the adopted technology must be based on low energy consumption and less resource consumption?
2.1 introduction of microorganism
microorganism is a kind of small single cell or individual structure of relatively simple multi-cell, even no cell structure of lower organisms, is invisible to the eye, hand can not touch, living micro-organisms, only with the help of optical microscopy and electron microscopy to see. microorganisms include bacteria, viruses, fungi and so on.
2.2 microbial technology and application
microbial technology is a single or comprehensive modern man-made technology system that monitors, evaluates, remedies and restores the polluted environment by using the metabolic reaction process of microorganisms and biosynthetic products (including enzymes). it includes not only all the characteristics of biotechnology, but also the prevention and control of environmental pollution and other engineering techniques. it has gradually developed into an effective means of solving increasingly serious environmental problems (especially water pollution) with both economic and environmental benefits.
according to the process of microbial degradation and the types of products, microbial treatment can be divided into aerobic treatment, anaerobic treatment and facultative treatment.
(1) aerobic microbial treatment, under the condition of sufficient oxygen, microorganisms decompose organic matter through aerobic respiration. aerobic microorganism treatment technology mainly includes:
(1) oxidation pond, with natural ponds and lakes as reference materials, imitates the principle that non-mobile water has its own purification function. a static sewage pond is constructed artificially. organic matters in the sewage are mainly degraded by bacteria in the pond, and the oxygen required by bacteria is used by the photosynthesis of algae and other photosynthetic microorganisms and the air above the water surface. provide. the method is simple and feasible, but it is only suitable for sewage treatment with light pollution and less quantity.
activated sludge process has the advantages of high treatment capacity and good effluent quality. the method is mainly composed of aeration tank, sedimentation tank, sludge reflux and excess sludge discharge system. wastewater and reflux activated sludge enter the aeration tank to form a mixture. the aeration tank is a biological reactor. it is filled with air by aeration equipment, and oxygen in the air dissolves into the mixture to produce aerobic metabolic reaction, and the mixture is stirred sufficiently to suspend. thus, the organic matter and oxygen in the wastewater can fully contact with the microorganisms. then the mixture enters the sedimentation tank, and the suspended solids in the mixture settle down in the sedimentation tank and separate from the water. the purified water flows out of the sedimentation tank. activated sludge not only has the ability to oxidize and decompose organic matter, but also has good coagulation and sedimentation performance, so that the activated sludge can be separated from the mixture to get clarified effluent.
(3) biofilm method is a kind of method to remove dissolved organic pollutants from wastewater by biofilm formed by microorganisms attached to the surface of solid carrier. biofilm process can also be divided into trickling filter (or biofilter), biological rotary table method, contact oxidation method and fluidized bed biofilm method.
(2) anaerobic microbial treatment, under anaerobic conditions, anaerobic bacteria through anaerobic respiration or fermentation decomposition of organic matter, organic matter is eventually converted to methane, carbon dioxide, water and a small amount of hydrogen sulfide and ammonia. anaerobic microorganism treatment processes are mainly as follows:
anaerobic digestion
