Bioavailability Of Dissolved Organic Nitrogen In Typical Origins

As a part of dissolved total nitrogen(DTN),Dissolved organic nitrogen(DON)plays an important role in biogeochemical nitrogen cycle.Studying on DON composition,content and biological effect is significant for understanding DON load to the natural water bodies such as lakes environmental effects and the influence mechanisms.Understanding DON bioavailability in effluents from the industrial and municipal wastewater treatment plants(WWTPs)is helpful for providing a guide role of regulating internal nitrogen input and revealing the water nutrient cycle and water eutrophication.The bioavailability of sediment DON study can also explain endogenous release effect in the aquatic biological mechanism and provide the scientific basis for revealing the environmental benefits of DON in water environment.In this paper,effluents from municipal and industrial WWTPs and sediment DON were studied,the effect of small molecular DON components to algal uptake was discussed.Some pretreatment methods were also conducted to extract and divide DON for algal and bacterial uptake experiments.This topic thesis was to provide theoretical support for water ecological system in different DON sources and the mechanisms of biological effects and environmental effects research.The main conclusions are as follows:(1)Selenastrum Capricornutum was able to utilize various amino acids for growth,the amino acids ultilized rates ranged from 99.0%to 100%.In the individual amino acids experiments,the rank order of the use of amino acid was:arginine>alanine>glutamic acid>aspartic acid>serine>glycine.In the mixed amino acids experiments,algal cell growth rate was significantly higher than that of individual amino acid group.Meanwhile,in low amino acid concentration condition(<120 ?mol/L),the maximum algal cell number was also increased with the increase of mixed amino acid concentration.DFAA ultilization rate reached 82.5%?99.6%in the first 2 days,algal cell could also ultilize amino acids for growth under aseptic condition.Selenastrum Capricornutum can also release other kinds of amino acids when using the individual amino acid,mainly as aspartic acid and glycine.(2)Anion exchange resin was used to recover DON from effluents of industrial wastewater,and the recovery rate ranged from 62.15%to 110.66%,averaged for 93.93%.Industrial wastewater effluent DON can stimulate algal cell growth,and DON ultilization rates ranged from 39.50%to 61.21%.Three-dimensional fluorescence spectroscopy combined with parallel factor analysis method(EEM-PAFARAC)was used to assess fluorescent components change during algae growth.And three components were identified including two humic-like substances(C1 and C3)and one protein-like component(C2).During the incubation,C1 relative fluorescent intensity increased for 56.63%to 227.0%,C2 and C3 relative fluorescent intensity in most samples except for Xiandai electroplate sample increased for 16.26%to 81.17%,29.32%to 34.71%,respectively.(3)XAD-8 resin coupled with nanofiltration and anion exchange resin was used to divide the effluent DON into hydrophilic and hydrophobic components.DON components recovery rates ranged from 72.86%to 102.25%,averaged 87.56%.Hydrophilic DON was the major fraction,accounting for 66.24%-73.52%of effluent DON.During the algal incubation,the rank order of maximum algal biomass and DON ultilization amounts was:hydrophilic DON group>raw water DON group>hydrophobic DON group.Four components were identified by EEM-PAFARAC model in algal incubation,including two humic-like fluorescent substances(C1 and C3),and two protein-like fluorescent substances(C2 and C4).Because of the algal adsorption,all the relative fluorescent intensities of the four components decreased at the beginning of the algal growth(first two days);and some algal organic matter was released into the samples due to algal cell decomposition,resulting in the relative fluorescent intensity of all fluorescence components increase.(4)DON extracted in the lake sediments were separated into hydrophilic and hydrophobic forms by DAX-8 resin coupled with anion exchange resin.DON recovery rates ranged from 72.39%?105.06%,averaged 83.86%.DON biodegradable rate(BDON)by bacteria inoculation ranged from 13.15%to 91.47%,which were higher than DON bioavailable rate(ABDON)of the algal inoculation ranging from 7.49%to 75.11%.Hydrophilic DON components stimulate the bacterial and algal growth more.Using EEM-PARAFAC analysis,samples in both two experimental group contained three fluorescence components.Bacterial incubation group were divided into two humus-like substances(C1 and C2),and one protein-like component(C3);while algal incubation were divided into two protein-like components(C2 and C3),and two humic-like composition(C1).