Application of biological purification in water pollution control -—by x academic number: X Abstract: Water pollution control includes internal environmental control and external environmental control. The former is the treatment of pollution sources, which is difficult and costly. The latter uses ecological self-purification ability to control water pollution. Biological purification is an important means to control the external environment. There are species and genera of organisms that can participate in purification everywhere on the earth. They absorb, accumulate, decompose and transform pollutants through unique metabolic activities, reduce the concentration and toxicity of pollutants, and finally meet the emission standards. Its high efficiency and simplicity make biological purification more and more important. Abstract: At present, nearly half of the seven major water systems in China are seriously polluted, and the water quality of 86% urban river sections generally exceeds the standard. Water pollution not only aggravates the shortage of water resources, but also seriously threatens people's physical and mental health. According to preliminary investigation, 700 million people in China drink water with excessive Escherichia coli and 654.38+0.9 billion people drink water with excessive harmful substances. Among them, about 35 million people drink water with excessive nitrate, more than 63 million people drink high fluorine water, 2 million people drink high arsenic water, and more than 38 million people drink brackish water. The endemic area of schistosomiasis is about 654.38+0. 1 10,000 people. Quite a few cities have serious water pollution, which threatens the quality of drinking water. At present, the harm of drinking water quality has seriously affected people's life and health. Looking at these shocking figures, people can't help but feel fear. However, when people are immersed in the superior material life and gradually forget these things, this year's Harbin water cut-off incident once again sounded the alarm for us! All kinds of realities make people wonder, what is the root cause of these pollution? The answer is-pollution and waste. With the development of economy, the amount of wastewater increases rapidly. However, most of the wastewater is directly or indirectly discharged into the water without treatment, which seriously pollutes the water resources. And people's waste of water resources makes the available water resources even scarcer. Faced with various crises, people began to pay attention to the protection of water resources and the treatment of water pollution. Water pollution control includes internal environmental control and external environmental control. The former is the treatment of pollution sources, which is difficult and costly. The latter is to use the purification ability of the natural environment to control water pollution. Biological purification is an important means to control the external environment. Because there are biological species that can participate in purification activities everywhere on the earth, they absorb, accumulate, decompose and transform pollutants through their own unique metabolic activities, reduce the concentration of pollutants, make toxic substances non-toxic, and finally reach the water discharge standard. Therefore, people attach importance to the biological purification of sewage. The commonly used methods are: (1) sedimentation for purifying domestic sewage. On the premise that pollutants do not destroy the self-purification ability of water, simple grids are adopted to improve the self-purification ability of water through the activities and movements of filter-feeding and sink-feeding animals in the water, promote the precipitation of suspended solids in the water and bury them in the sediment to purify sewage. (2) Aquaculture is used for domestic sewage and industrial wastewater containing organic pollutants. Biodegradation of pollutants by aquatic organisms is an effective measure to prevent eutrophication of water bodies. 1. Autotrophic aquatic plants such as stocking aquatic vascular plants (referred to as aquatic plants) have good tolerance to water pollution. They can not only improve water quality by absorbing CO2 and releasing O2 in the environment through photosynthesis, but also eliminate many pollution elements. At present, it has been found that many of them have strong purification ability for organic pollutants, phenolic pesticides and heavy metals. The removal rate of BOD in domestic sewage by Zizania latifolia and Sagittarius can reach above 80%; Typha latifolia, POTAMOGETON POTAMOGETON and Eichhornia crassipes can remove 95% organic pollutants from petroleum wastewater. When the DDT of Polygonum plants in water is 0.3ppb, the concentration in vivo can reach 30.3ppm, and the enrichment coefficient is 654.38+ million. Eichhornia crassipes can accumulate 5468ppm in lead water containing 3ppm, which is 1823 times of lead concentration in water. In the water containing 6ppm cadmium, the stems and leaves can absorb 700ppm cadmium, and the content of roots is 10 ~ 16 times that of stems and leaves. Eichhornia crassipes can get 75gAg from abandoned mine water every four days. Many aquatic plants grow fast and can absorb a lot of N, P and K nutrients. Eichhornia crassipes can absorb N 1989kg, P 322kg and k 3188 kg; Per hectare per year; Stocking 60% Chlorella, Chlorella and Scenedesmus on the water surface can reduce the content of nitrogen, phosphorus, iron and sodium by 55% in only 1 day, and make the pollution concentration almost zero in 9 days, which can completely turn domestic sewage into drinking water. Planting reed, water chestnut and cattail can purify toxic substances in industrial wastewater. For example, cyanogen combines with serine in reed to form alanine, which is then converted into asparagine and aspartic acid, thus losing the toxicity of cyanogen; Arsenic, mercury and cadmium are stored in aquatic plants, thus reducing the concentration of toxic substances in wastewater. 2. Aquaculture is used to purify domestic sewage. Some people keep fish and shellfish in 1/5 sewage pond, but they can still survive normally, and the weight gain rate is higher than that of pure water. Using sewage to cultivate some herbivorous fish can not only use nutrients, but also use cyanobacteria in ponds as bait to eliminate eutrophication of water bodies. Because the animals cultured by this method often have peculiar smell or accumulate substances harmful to health, which affects the edible value, there are few applications and reports on purifying sewage by aquatic animals at present. (3) Biological stabilization pond method is a traditional method used to treat domestic sewage and petrochemical, coking, papermaking and pharmaceutical wastewater at home and abroad. 1. Aerobic pond is a typical algae growth system, which uses the absorption, decomposition and oxidation of aquatic plants, algae and microorganisms in natural ponds, depressions and puddles to purify sewage. Depending on the relationship between algae and bacteria, not only sewage can be recycled and purified in the pond. Removing toxic substances through physical, chemical and biochemical actions in the pond; Organic pollutants are degraded by microorganisms; Due to the coagulation and precipitation caused by physical factors in the pond, suspended solids are removed; Pathogens die because they don't adapt to the environment; Due to the proliferation and absorption of algae, nitrogen and phosphorus are partially removed. It has been proved that a 30-mu shallow algae pond can treat 20 thousand domestic sewage, and the BOD removal rate can reach 80% ~ 95%. 2. Under anaerobic conditions, anaerobic tanks degrade organic pollutants through anaerobic bacteria and facultative bacteria, which generally consists of two steps. One is hydrolysis, in which insoluble macromolecular organic pollutants are degraded into water-soluble low molecular weight amino acids, monosaccharides and organic acids by extracellular enzymes of Bacillus, Proteus and Streptococcus; Secondly, organic acids are degraded into CO2 and CH4 by methanobacteria and methanogens, thus purifying sewage. This method can increase the depth of the pond to 4 meters. Because the removal rate of BOD is only 50% ~ 70%, it is often used for the pretreatment of industrial wastewater. (4) Activated sludge process is suitable for large sewage treatment plants and industrial and mining wastewater treatment. This method forms biological flocs (activated sludge) from wastewater containing a lot of organic pollutants under the action of aerobic bacteria. Using the adsorption of pollutants by activated sludge and the decomposition and oxidation of toxic substances by microorganisms, algae, protozoa and oligochaetes on flocs, the wastewater stays in the aeration tank for 4 ~ 10 h, so that the sludge can fully contact with the wastewater to complete the purification process. Composition of activated sludge: 1. The composition of sludge flocs is complex, which varies with the nature of wastewater to be treated, but most flocs are formed by bacterial micelles. 2. The biota around which sludge organisms live mainly include amoeba, flagellates, poda and ciliates, especially Cladosporium and Belladonna. This method has good purification effect and is developing towards perfection at present. (5) Biofilm method is used to purify wastewater from food industry and fermentation industry. Biofilter is commonly used in practice, which uses the adsorption of filter materials (granite, anthracite, etc.). ) or the rotary table retains bacteria, algae and micro-animals in sewage to form a biofilm with a thickness of 2 ~ 3 mm, in which protozoa swallows bacteria to update the membrane continuously, worms swallows organic residues, and animal movements loosen the sticky biofilm, forming an ecological equilibrium niche with a thickness of 0. 1 ~ 0.2 mm on the outer layer of the membrane. When sewage flows through biofilm, organic pollutants are quickly absorbed and become metabolites of bacteria; Soluble pollutants are degraded and absorbed by microorganisms and converted into substances in the body for storage; Refractory pollutants are washed away by the filter and removed by biodegradation; Excessive aging biofilm is removed by preying on oligochaeta and insect larvae. In order to ensure the full contact between wastewater and mineralized biological filter media, wastewater needs to stay in the biological filter for 30 min, and the concentration of pollutants will be greatly reduced. (6) Treating domestic sewage and wastewater from wool spinning, chemical industry and pulping by biological contact oxidation. This method has the characteristics of both activated sludge process and biofilm process. The process adopted is as follows: 1. Bio-iron method uses the physical and chemical effects and biological effects of iron to treat coking wastewater; 2. Activated carbon biofilm method uses the adsorption of activated carbon to make microorganisms multiply on the surface of carbon, degrade pollutants and purify industrial wastewater containing chlorine compounds; 3. Treatment of nitrobenzene industrial wastewater by biological acidification, reduction and oxidation. (7) The land treatment system is used to treat domestic sewage and food industry wastewater. This method is a comprehensive process of materialization and biochemistry. Through the strong filtration, adsorption, oxidation and ion exchange of soil, the absorption and decomposition of microorganisms, and the barrier effect of soil structure and plant roots on pollutants, sewage can be completely purified. When sewage stays in paddy field for 3 ~ 8d, the removal rate of (BOD)5 can reach 80% ~ 95%, and the removal rates of P and N can reach 98% and 85% respectively. However, excessive oil and soap in sewage will block soil gaps and often bring "sewage disease" to irrigation fields, so it must be pretreated before application. (8) Immobilized cells are used to purify various industrial wastewater. Immobilized cells are directly prepared by microorganisms containing special catalytic enzymes in wastewater. This method must screen strains with special decomposition ability to form a balanced system and realize enhanced wastewater purification. Immobilized cells prepared by embedding pure microorganisms as adsorbents can effectively remove heavy metals, phenol and other aromatic toxic compounds in wastewater. Candida tropicalis was isolated from activated sludge, and the removal rate of phenol in coking wastewater reached 99%. This method has the highest purification effect, but it is difficult to select strains with high enzyme production and the cost is high, which affects the development. To sum up, biological purification has great vitality in water pollution control. According to the composition and treatment purpose of the treated sewage, it can play a great role to choose the appropriate treatment method or comprehensively treat the sewage. While hoping that these new methods will be applied, we should also realize that these treatment methods are only some remedial measures, and only a small amount of available water resources can no longer allow us to destroy them. Take the measures of prevention first and treatment second, adopt the strategic policy of combining prevention with treatment, eliminate pollution from the source, form the concept of water saving in everyone's consciousness, and take effective measures to treat polluted water bodies in practice. The source of life-water is limited, precious and non-renewable. In the face of painful lessons again and again, everyone should consciously establish water-saving consciousness, save every drop of water, and reduce and eliminate man-made water pollution. Water pollution is the pollution of civilization and the pollution of the times; The disappearance of water means the disappearance of the nation and the demise of mankind! For the rejuvenation of the nation, for the survival of mankind, for the continued existence of all life, cherish water resources, from now on, start from me! Reference book: Biological Bulletin 1993 Report Series No.7, Sustainable Development Strategy of Water Resources in China; Journal of Plant Resources and Environment edited by Qian and Zhang Guangdou of China Academy of Engineering; Institute of Botany, Chinese Academy of Sciences, Jiangsu Province.