The Formation Mechanism Of Black-odor Water In Nanning

With the rapid development of economy,the environmental problems are becoming more and more serious,and river pollution is the most serious problem.By the end of 2016,about 1,880 urban rivers with black-odor water were found.64%of the rivers are located in the coastal areas of southern China.Therefore,it is urgent to solve the problem of black-odor rivers.At present,the research on black-odor water at home and abroad focuses on the main influencing factor and the evaluation methods of black-odor water,but the research on the formation mechanism of black-odor water is obviously insufficient.In this paper,the literature is used to artificially simulate black odor water,focusing on the mechanism of total organic carbon(TOC),sulfur,nitrogen and iron on dissolved oxygen(DO)and oxidation reduction potential(ORP)during the formation of black odor in water.And the evolution of black and odor,has been studied,and makes a preliminary analysis of the black-odor bacteria by simulated black-odor water.The main conclusions are as follows:(1)The presence of TOC in water leads to the consumption of DO.With the decrease of ORP value,when DO content is less than 1 mg/L and ORP value is reduced to-200 mv,the water body exhibits strong reduction ability,which can be regarded as one of the signals that water body will form black and odor.However,pure TOC pollution will not produce black-odor water,and the formation of black-odor water follows a complex biochemical process.(2)The formation of black and odor in water is a process accompanied by black and odor,in which microorganisms play a crucial driving role.Under the taxonomy of phylum,the dominant microbial flora mainly consisted of Proteobacteria(38.7%-49.4%),Firmicutes(2.8%-19.3%),Bacteroidetes(6.9%-18.5%)and Actinobacteria(4.7%-10.3%).Under the classification of the class,the dominant microflora consisted mainly of Betaproteobacteria(5.2%-15.6%),Flavobacteria(1.2%-13.4%),Deltaproteobacteria(2.4%-12.7%),Gammaproteobacteria(5.7%-11.9%),Alphaproteobacteria(1.8%-10.2%),Clostridia(2.1%-10.1%).Sobs,Shannon and sinpsoneven indices were selected to analyze the composition and diversity of microorganisms in the lower layer of the black-odor river compared with that in the upper layer.It was proved that sediment as a hotbed of microorganisms contributed greatly to the black and odor of the water.(3)Sulfur-containing substances play an important role in the formation of black-odor river.Under the condition of anaerobic strong reduction,sulfiur-containing substances participate in biochemical reaction to produce black odor-causing substances.Inorganic sulfur(IS)is more likely to participate in the reaction to produce H2S gas,while organic sulfur(OS)is more likely to produce volatile organic sulfide(VOSCs)such as methyl mercaptan(MTL).The flora that assimilates IS to produce MTL and the flora that assimilates IS to produce methyl sulfide(DMS)are probably one kind of flora.SO42-converts into OS during the formation of black-odor water,and then promotes the formation of volatile organic sulfides,accelerates the formation of black-odor river.When the water is in anaerobic state,the formation of S2-will be accelerated,resulting in more metal sulfide precipitation.Therefore,blocking SO42-conversion pathway is one of the effective ways to solve the problem of black-odor water.(4)In the process of formation of black-odor water,inorganic nitrogen(IN)can promote the consumption of DO,accelerate the production of suitable environment for the formation of black-odor water,and produce NH3,which aggravates the foul odor in water.The microorganisms involved in the transformation of organic nitrogen are mainly anaerobic or less oxygen-consuming microorganisms.When the content of IN is too high,it can inhibit some microorganisms involved in the black-odor behavior.Under anaerobic conditions,NO3-N is more easily converted into NH4+-N than denitrification to produce N2.Nitrogen cycle in water will accumulate to NH4+-N after being destroyed due to environmental changes.Therefore,the formation of NH4+-N can also be used as one of the indicators for the formation of black-odor water.(5)The iron cycle will be destroyed during the formation of the black-odor water,which accumulates a large amount of Fe2+,and then produces black Fe2S,which makes the water body appear black.