Growth Of Microorganisms In Stored Rainwater And Their Effects On The Transformation Of Organic Components

With the development and the improvement of society and life style,the demand for water resources is increasing year by year.Rainwater has been widely used in the vast water shortage area because of its easy collection and utilization and the rainwater quality is good.However,the existing methods of rainwater use have many hidden dangers,such as paying attention to water quantity and ignoring water quality,emphasizing the use and despising the management.Three common water storage containers are used as the object of study,such as concrete,stainless steel and plastic.The characteristics of storage water quality,including routine physical and chemical indexes,heavy metal indexes and microbial indexes,were evaluated systematically.At the same time,combined with the characteristics of rainwater storage,the change characteristics of microbial community structure during repeated disinfection process and its influence on unit transfer and transformation in water were investigated.The main five conclusions are as follows:（1）Different water storage materials have great influence on rainwater quality.Among them,concrete has the greatest influence on water quality,plastic is second,and stainless steel has the least disturbance to the quality of rainwater.In detail,the transparency of rainwater increases slowly with the increase of the storage time in different containers.Due to the CO₂ dissolved,the pH and TDS of rainwater in plastic and stainless steel containers showed a downward trend,while the release of alkaline materials showed the reverse change.（2）In addition to the conventional indicators,the container material also has a certain impact on the content of heavy metals in rainwater.Among them,the concrete release of heavy metal elements of the most,stainless steel next,plastic material basically have no this problem.Concrete mainly causes the increase of Zn content in rainwater,although the increase is huge,it has no adverse effect on human health.Stainless steel containers will make the content of Ni in rainwater increase,and will exceed the standard value after 70 d.Therefore,it is not recommended to deposit rainwater in stainless steel containers for a long time.（3）The number of microorganisms shows the regularity of periodic proliferation and decline during the storage of rainwater.At the early stage of storage（within 6 d）,the bacteria did not reproduce in large numbers,and showed a downward trend under the action of adsorption and coprecipitation of turbidity substances.At this point,the total number of bacteria in all containers to meet the drinking standards.Then,with the proliferation of bacteria,rainwater is no longer suitable for drinking in concrete.As a result of the natural decline of microorganisms,the number of microorganisms in stainless steel containers and plastic containers has increased again at 23³9 and 34⁴5days.（4）Adding disinfectant to stored rainwater can effectively control the number of microorganisms,but the microbial species and quantity after two growth have changed greatly.This change is more pronounced with the increase in the number of disinfectants added.For example,Acidovorax,Rhizobium and Nitrobacter and other prokaryotes drastically reduced,and Heidegger’s genus antioxidant content of bacteria increased sheath strain.The types of eukaryotic microorganisms have declined markedly,but the numbers of dominant species such as flagellates have increased markedly and are not suitable for continued drinking.（5）Microbial metabolism and disinfection process have important effects on the content and composition of organic components in rainwater.Microbial proliferation makes water fractions from“non active”substances to the metabolically active microorganism transformation,at the same time as the metabolism of microbial degradation of non active organic components,the molecular size of organic matter and the degree of polymerization decreased continuously.However,after disinfection,the amino acids in the“inactive”organic components of the water are increasing due to the breakdown of the cell structure of the“active”organic component.In summary,the conventional physical and chemical indicators and microbiological indicators of heavy metals,in the rain,there are some changes exist in the process,if do not take corresponding control measures,concrete and plastic containers to exceed the standard problem of microbial,stainless steel container is prone to heavy metal exceed the standard problem.At the same time,because of the absence of hydraulic exchange in stored rainwater,repeated disinfection will lead to the evolution of microbial types and an increase in the amount of disinfection by-products.The above conclusions will provide theoretical and technical support for the storage and utilization of rainwater and the two purification and regulation of water quality in long-term storage,which has important theoretical and practical significance.