| Hang-Jia-Hu plain is well known for the reputation of ’the land of fish and rice, the mansion of silk and satin’. In recent years, with the accelerating urbanization as well as the development of modern large-scale and intensive agriculture, the pollution of natural water, includng drinking source water, has become an important problem attracting more attention. Since1990s, the aerobic biofilm pre-treatment unit has been used as added to the traditional process of coagulation-sedimentation-disinfection in the waterworks in Hang-Jia-Hu plain. This modified process can obviously improve the water quality and reduce the subsequent processing load. However, there are still some problems need to be resolved, such as the slow growth rate of functional microbial community, the poor removal efficiencies of total nitrogen and trace toxic organics as well as the adverse effect of seasonal variation. Based on the investigation of typical pollution characteristics of drinking source water in Hang-Jia-Hu plain, the fast start up methods of biofilm reactor under low temperature, the enhancing removal of organics, nitrogen and endocrine-disrupting pesticides (EDPs) via biofilm pretreatment were studied. A new biofilm pretreatment process with plant biomass addition for multi-pollutants simultaneously removal was developed. The main contents are presented as follows:1) To ascertain the pollution characteristics of source water, the organic matter, nitrogen and phosphorus pollution characteristics of typical source water in Hang-Jia-Hu plain river network were systematical investigated. The levels, spatial and temporal distribution as well as the risk assessment of EDPs were studied based on SPE-GC/MS. Results showed that the major pollutants of source water in river network of Hang-Jia-Hu plain were organics and nitrogen compounds and the eutrophication is serious. The concentration ranges of CODMn and TN were7.44-17.52mg·L-1and1.62～8.35mg-L·1, respectively, exceeding the limit of class III in surface water quality standards (GB3838-2002). The major pollutants of source water from Canal Rivers were CODMm, NH4+-N and TN, while TN (mainly NO3--N) in Tiaoxi stream catchment was the main pollutant, but TN and TP pollution was significant in reservoirs. Temporal distribution characteristics demonstrated that the levels of organics and nitrogen obviously changed with seasonal variation, and nitrogen levels were much higher in winter-spring than that in other seasons, but an opposite situation was observed in the variation of organics.Simultaneous detection methods using SPE-GC/MS technology were developed for the detecting of7categories and21kinds of typical EDPs (four organochlorines, four organophosphoruss, six pyrethroidss, two amides, two anilines, two carbamates and one triazine). These results showed that EDPs were often detected in source water with a total concentration of37.9～2948.9ng L-1. The main EDPs were dicofol, cypermethrin. chlorpyrifos, fenvalerate and2,4-D. Cluster analysis obtained the differences order of EDPs pollution of different drainage> seasonal variation> different tributaries in the same drainage. The levels of EDPs pollution in Tiaoxi stream were much lower than those of Canal Rivers; EDPs levels in summer and fall were higher than those in winter and spring, which was consistent with the seasonal variation of organics. Risk assessment results showed that EDPs levels were in an acceptable range, which could not directly impair human’s health but could cause high ecological risk. The enhanced biofilm pretreatment process should be developed for the removal of multi-pollutants in source water.2) As to the problems of start-up of biofilm reactor under low temperature and low nutrients levels, a method for fast start up of biofilm pretreatment process was developed. Optimizing carriers, inoculation methods and influent loads, modified biofilm pretreatment reactors with different carriers and under different operating conditions were studied for the operation in winter-spring season. After two months-operation, the average removal efficiencies of NH4+-N and CODMn were84.4%-94.2%and69.7%-76.6%, respectively. The removal efficiencies of NH4+-N and CODMn with elastic filler were much higher than those with AquaMats(?). The analysis of bacterial community structure showed that the bacterial community structure of biofilms adhered to the elastic filler was stable within two weeks, which was fast than that on the AquaMats(?). The dominant bacteria of biofilm adhered to elastic filler were Pseudomonas, Sphaerotilus and Janthinobacterium. Janthinobacterium was aerobic bacteria in charge of degrading organics, which was more than other species adhered to elastic filler and assuring the high removal efficiency of organics. The dominant bacteria of biofilm adhered to AquaMats(?) carrier contained the dominant bacteria of Pseudomonas, Sphaerotilus, Janthinobacterium, and Corvnebacterium aurimucosum. However, the aerobic bacteria Janthinobacterium is less than that adhered to elastic filler, which may be related to the microporous structure of AquaMats(?) carrier.The lag period of ammonia oxidation could be effectively shortened using the elastic filler combined the method of discharging sediment and gradually increasing influent velocity, and the removal efficiency of NH4+-N reached above50%a week early. The analysis of bacterial community structure found that this method could reduce the heterotrophic bacterial diversity but facilitate the rapid enrichment of ammonia oxidizing bacteria, which is help to obtain a higher NH4+-N removal performance in advance. The ammonia oxidation autotrophic bacteria were stable in biofilm within two weeks. Sequencing analysis results showed that the dominant ammonia oxidizing bacteria in mature biofilm were Nitrosomonas and Nitrosospira. Therefore, using elastic filler as the carrier with the biofilm culturing methods of discharging sediment and gradually increasing influent velocity could effectively shorten the lag phase of ammonia oxidation, accelerate the startup of biofilm pre-treatment unit, and obtain high removal performances of ammonia nitrogen and organics.3) As to the serious pollution of organics and nitrogen and distinct regional differences of river network source water in Hang-Jia-Hu plain, the biofilm pretreatment processes for nitrogen and carbon removal in various water qualities were studied based on heterotrophic denitrification technology. For the treatment of raw water with a high C/N and improve the utilization of carbon source in biological systems, the effects of step-feeding process on the performance of biofilm pretreatment system for carbon and nitrogen removal and on the microbial community structure were examined. This result showed that the average TN removal effiency increased obviously from29.5±2.2%to35±2.7%by step-feeding process. The average effective utilization rate of carbon source increased from0.211to0.199(mg mg-1). Microbial community structure analysis indicated that the bacteria diversity of biofilm in the middle or back reactor increased. The functional bacteria of Hyphomicrobium and Pseudomonas, which were responsible for nitrogen and organics removal, enriched in rector. It was revealed that step-feeding process could strengthen biofilm pretreatment process, enhancing the utilization efficiency of carbon source and enrichment of denitrifying bacteria.For the treatment of raw water with serious nitrogen pollution and low C/N ratio, the biofilm pretreatment process by optimizing C/N ratio and HRT and adding external carbon source was studied. Results showed that the denitrification efficiencies were positively correlated to the C/N ratio. The effluent NO3--N concentrations were below1.0mg L-1when C/N ratios were more than3.7. The disinfection by-products forecast model based on TOC and UV254forecasted that the production of THMs increased with the increase of influent C/N ratios. For better controlling of effluent organics and nitrogen, the optimized C/N ratio of2.2was chosen. At the HRT of18h, the highest effective utilization rates of carbon source and removal efficiency of nitrogen source were obtained. And the low effluent concentration of NO3--N (0.88±0.03mg L-1) and TOC (2.86±0.67mg L-1) were obtained. The analysis of microbial community showed that the bacterial diversity increased with the increase of C/N ratio.4) The pollution of EDPs was notable in river network of Hang-Jia-Hu plain, but the study of biofilm pretreatment process for removing EDPs was lack. To resolve these problems, the influence of substrates (ammonia nitrogen, nitrate nitrogen and organics) and dissolved oxygen on the removal of trace EDPs in the biofilm pretreatment system was conducted. The correlation between the removal of nitrogen and the removal of trace EDPs was explored. The levels of cypermethrin and chlorpyrifos, the representative of EDPs, were trace (approximately1μg L-1).The study of the influence of various substrates on the removal of EDPs was conducted. These results showed that aerobic conditions improve the removal of ammonia nitrogen (complete nitrification but nearly no denitrification). The increased ammonia nitrogen oxidation could not significantly enhance the removal of trace cypermethrin and chlorpyrifos. However, the removal efficiency of cypermethrin and chlorpyrifos increased from80.0±2.7%and68.4±0.8%to85.0±0.3%and75.1±3.9%, respectively. We speculated that the removal of trace EDPs was mainly conducted by heterotrophic bacteria rather than ammonia oxidation autotrophic bacteria under aerobic conditions. Under anoxic conditions the nitrate nitrogen concentration increased but the removal efficiencies of cypermethrin and chlorpyrifos were not significantly improved. The complete denitrification was observed when adding external carbon source. The removal efficiencies of cypermethrin and chlorpyrifos increased from65.0±1.3%and32.9±5.7%to77.9±1.6%and46.9±8.0%, respectively.Simultaneous enhancing removal of nitrogen and EDPs was realized, this may be related to the fact that adding external carbon source can obviously enhance the enrichment of functional bacteria for removal of nitrogen and EDPs, such as Methylovorus, Hyphomicrobium, Thauera, Paracoccus, etc. Comparing with the removal performance of various EDPs at different dissolved oxygen levels, the removal performance under aerobic conditions is significantly better than that under anoxic conditions (P<0.05). In order to simultaneously remove nitrogen and EDPs, the combined aerobic and anoxic processes with the method of increasing organics level were recommended in biofilm pretreatment systems.5) Based on the previous studies achievement, biofilm process for simultaneous nitrogen and EDPs removal by adding solid carbon resource was carried out. Reed was selected as a representative solid carbon resource, and the decomposition process showed that the nutrients release rates of reed were fast in the initial period then slow down. The main nutrients of reed were organics and nitrogen compounds (mainly ammonia), and the release rate of nitrogen was much lower than that of organics. The nutrients release rates of reed were easily affected by environmental factors, including dissolve oxygen and biomass.The nutrients of reed would release in biofilm pretreatment system. Using this characteristic, a fast start up method of biofilm reactors was obtained. Biofilm reactors were started up with sediment discharge method, adding20g and60g reed respectively to two aeration A/O/A (anoxic/aerobic/anoxic) processes. It was found that the removal efficiencies of NH4+-N were stable up to90%after operating for10days; the removal efficiency of TN was stable at67.0±3.7%when60g reed was added, but the reactor adding20g reed delayed one week to obtain a TN removal efficiency of65.4±5.5%. The effluent TOC concentrations in both reactors were stable at a lower level of approximately2.0mg L-1. After further operation for four months, TOC and NH4+-N removal efficiencies were not improved significantly, and the removal efficiencies of TN were decreased from65.0±3.4%to54.6±2.9%After3months operation. However, the performance of both reactors was still much better than that in biofilm reactor without adding reed. Separately operating the systems with elastic filler or reeds only, the removal efficiency of NH4+-N (82.9±1.5%) in the system with elastic filler only was higher than that in the system with reeds only (36.3±6.1%), While the removal efficiency of TN (40.3±7.3%) was lower than that (56.5±2.0%) in system adding reeds only. The combination of reed and elastic filler could be help to achieve a good performance of nitrogen and organics removal.For further improving the performance of reed added biofilm process, another120g reed was added to the reactors using different distribution modes (uniform distribution and nonuniform distribution). Results showed that TN removal efficiencies were stable up to75%within two months using nonuniform distribution mode to add reed; cypermethrin and chlorpyrifos removal efficiencies were significantly increased to80%and46.3%, respectively using uniform distribution mode and increased to79.7%and44,7%, respectively using nonuniform distribution mode (P<0.05). It was proved that simultaneous nitrogen and EDPs removal was enhanced via secondary addition of reed, and nonuniform distribution mode was an attractive choice. Long-term performance and operation stability analysis showed that the removal efficiencies of TOC (74%), NK4+-N (90.7%), TN (55.0%), cypermethrin (87.1%) and chlorpyrifos (51.1%) were all still stable at high levels after operation for four months when the reeds were secondary added, which satisfied the standards of drinking water quality (GB5749-2006). To avoid the adverse effect of the quickly release of nutrition in the initial phase when reed was added, appropriate reed addition amount of less than20g/d was recommended. |
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