| Dissolved organic nitrogen (DON) is not only the significant component of thedissolved nitrogen pool, but also a relatively important portion of dissolved organicmatter (DOM) in most natural waters. The wastewater treatment plant (WWTP) isone of the main sources of nitrogen in surface water in the world. The effluent DONcan be used as a nutrient by creatures and can stimulate algae growth, leading toeutrophication of water bodies. The effluent DON from the WWTP has become themain source of DON in river basin, posing a serious threat to water qualitydownstream. Therefore, how to control the effluent DON of the WWTP effectivelyhas become a new hot point in the field of wastewater treatment at present. Becauseof the highly complexity of organic nitrogen, current acknowledgement of the DONis quite lacking, and the accuracy of DON measurement has always been the keyfactor which has effect on investigating its nature deeply. In recent years, someresearches on the source, transformation and influence mechanism of DON in theWWTP have been carried out, but it is lacking in the transformation, influencemechanism and control measures of DON in different treatment processes. It isweak internationally, and it is rarely seen in reports about DON transformation indifferent processes of WWTP and characteristics and biological availability ofeffuent DON in our country. In this paper, a nanofiltration (NF) pretreatmentmethod was presented to determine the concentration of DON accurately, and thedistribution and transformation of DON in both landscape water and wastewaterfrom different treatment processes in WWTP are analyzed. At the same time,combining with ultrafiltration technology, the composition and chemicalcharacteristics of DON are investigated. Moreover, the distribution and conversionof dissolved free amino acids (DFAAs) and combined amino acids (DCAAs) arealso analyzed. The main conclusions are as follows:(1) The standard deviation of DON measurement could be reduced using nanofiltration (NF) pretreatment method. Compared with dialysis pretreatmentmethod, the NF pretreatment could save time and cost less which is more suitablefor DON determination in the laboratory. Through the comparison of two kinds ofnanofiltration membrane (NF90, NF270), we found that NF270has higher DINpermeability and DON retention than NF90, so NF270was selected for samplepretreatment to determine the concentration of DON.(2) There was seasonal variation in the concentrations of DON in landscapewater from the Olympic Forest Park, and there was significant difference betweenthe north and south part in different months. Moreover, the molecular weightdistribution of dissolved organic matter (DOM) was studied by ultrafiltrationmethod. The results indicated that the DOM in the landscape water of OlympicForest Park was mainly composed of low molecular weight organic matter. DON inlandscape water from the Forest Park is the potential nutrition of algae, and it isremarkable in the process of eutrophication control.(3) DON concentration in the WWTP with different water quality and differenttreatment processes is different in different months and the removal rate of DON fordifferent treatment processes is also different. DON concentrations in AWWTPranged from0.62to1.28mg/L in different months, and DON concentrations inBWWTP ranged from0.74to1.81mg/L in different months.(4) Molecular weight (MW) fraction of <5KDa was72.4%,85.0%and72.4%for influent, anaerobic, and effluent of the AWWTP in June2012, respectively. Theresults showed that most of wastewater-derived DON was composed of smallmolecules. The MBR process could effectively remove high MW organics, but therewas no elimination of the <1KDa fraction. The <5KDa fraction was71.8%,86.5%and71.8%for influent, anaerobic, and effluent of the BWWTP in March2012,respectively. The results showed that DON in water samples from differenttreatment processes was also composed of small molecules.(5) The composition of wastewater is complex. RP-HPLC method could not beused for DFAA analysis because of high concentration of ammonia and volatileamines in wastewater samples. These compounds form fluorescent products withsome amino acids during OPA derivitizations, making detection and quantification of these amino acids impossible. So they needed to be removed with necessarypretreatment methods. The pH-adjusted wastewater sample was then purged with N2gas. The method could eliminate the interference to make the chromatographicpeaks clearer and to quantify the amino acids in wastewaters, which could be usedas a relatively ideal pretreatment method for wastewater DFAA analysis.(6) Dissolved combined amino acids (DCAA) dominated the dissolved aminoacids in different treatment processes of WWTP, and dissolved combined aminoacids (DFAA) accounted for less than1%of DON and DCAA accounted for about1.0%-6.4%of DON. |
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