In Situ Self-adaptive BOD Sensor Based On Environmentally Domesticated Microbial Populations And Its Application

Biochemical oxygen demand（BOD）is an important water quality parameter.The standard 5-day incubation method is time-consuming.Rapid BOD measurement can reflect water quality changes in time,scientific guidance of wastewater treatment processes and early warning of sudden pollution events in the water ecosystem.Express BOD assessment is made possible by developing BOD biosensors.The bottleneck of rapid BOD method lies in the environment dependence of the biological reaction unit,resulting in poor biodegradation spectrum and uncontrollable microbial quantities.Here,taking the environmental microbial populations in water samples as the source,this work intend to construct a“gut-like”microfluidic coil bioreactor via on-site cultivation on the surface of the substrate of the reactor.The biofilm reactor established embraced a broad-spectrum biological reaction unit with dynamic balance of microbial population composition and high adaptability to water environment changes.The aim of this work is to develop a new way of on-line BOD monitoring method,achieving the scientific purposes of high efficient,stable,non-selective ability in biodegradation of environmental pollutants.The research of this thesis will overcome the technical difficulties in poor adaptation and uncontrollable quantity of microorganisms,and provide scientific basis for BOD automatic monitoring technology and industrial development of water quality.The main research contents and conclusions are as follows:（1）In order to solve the problem of low accuracy of measurement results due to the low biodegradation efficiency and selectivity of biological reaction units by the current rapid BOD method,in this work,the BOD bioreaction sensing system was reconfigured by arranging independent bioreactor and transducer units.With the environmental microbial populations in real sample as the source and the inner wall of the“gut-like”microfluidic coil bioreactor tube as the substrate,a self-adapted BOD sensor was conducted by the spontaneous adsorption and growth of the environmental microbial populations during the BOD determination process.The result of 16S r RNA gene sequencing showed that microbial populations on biological reaction unit were abundant.The BOD sensor displayed a wide linear range of 0～20.0 mg/L BOD.The test results of river water samples were highly accurate,with a maximum error of5.6%.The BOD sensor had a good long-term stability with a relative standard deviation of4.5%in the 180-day monitoring period.However,biodegradation selectivity was a pendent problem in this BOD sensor.The relative standard deviation of the six synthetic organic samples tested with all BOD₅concentrations of 10.0 mg/L was 32.5%,and the relative error of the test results was-33.5%and-14.3%for the pond water and sewage samples,respectivel.Obviously,the biodegradation selectivity is detrimental to an accurate BOD assessment of real samples with different organic composition.（2）The effect of the environmental matrix on the performance of BOD sensors was systematically investigated.The result showed that the initial microbial populations in the biofilm were replaced with the continuous supply of real samples.The working mode of the BOD bioreactor determined that the biofilm contacted with the real sample to fulfill the biodegradation.Consequently,the environmental microbial populations replaced the biofilm construction in each BOD detection process.The different compositions of organic matter in the water samples could selectively stimulate the metabolism and growth of dominant microbial populations.Once this stimulation or inhibition acts upon the microbial distribution of the biofilm,the bioactivity of the established biofilm varied correspondingly under the influence of the environmental matrix.Six synthetic organic samples were used to domesticate the microbial film,and the relative standard deviation of the test results decreased from 41.6%to 5.8%.The microbial populations in the biofilm dynamically self-renewed during the BOD test under continuous domestication by the real sample.The domestication by the real sample well addressed the tricky biodegradation selectivity problem to embrace the most representative biodegradation with the best adaptability to the environmental matrix in such a sample.（3）The biofilm constructed based on the strategy of environmental domestication institute exhibited excellent interference resistance as well as the best environmental adaptability.The relative error of test results was less than 15%with the p H range from 4.0 to9.2 and heavy metal ion interference from 1.0 to 10.0 mg/L.The aggregated abundant,adequate and adapted microbial populations in the BOD bioreactor rendered a total organic carbon（TOC）removal rate of 67.7%.Efficient biodegradation guaranteed the measurement accuracy of the BOD sensor.The test results showed excellent accuracy with relative error of less than 10%in 30 days of continuous monitoring of actual wastewater.The BOD sensor had a good stability during continuous application,and the relative standard deviation of the standard sample test results was only 3.7%.The BOD sensor based on environmentally domesticated microbial populations had shown good performance in practical applications,which is expected to development of BOD online monitoring instruments applied to the actual wastewater BOD long-term online monitoring.