Combined Bio-treatment Processes For Severely Polluted Urban Stream In South China

Urban river are often heavily polluted, a situation that is not confined to a particular geographic region of the world, but common to all areas subject to urbanization. It is the potentially cost-effective and environmentally acceptable remediation technology that has been particularly emphasized as a significant approach so as to realize healthy and sustainable river ecosystem. Taking a typical polluted urban stream in Shenzhen (China) as the target stream, the aim of this study is to discuss the pollutants removal by combined bio-trentment technology.The results would provide a basis for reasonable, highly effective, economical remediation technology for the bioremediation scheme of the polluted urban stream. Results of pollution survey indicated that Buji stream suffered from serious organic and nitrogen pollution. The mean value of COD, BOD, TN and NH4+-N were 211±50.2 mg/L, 117±21.3 mg/L, 29.8±8.86 mg/L and 24.4±8.3 mg/L respectively. The investigation of ecological structure and functions of nitrogen-related bacteria showed that fast growth rate and high activity of ammonifying bacteria and denitrifying bacteria made them predominant in Buji stream. The MPN of ammonifying bacteria and denitrifying bacteria reached about 1012 MPN/ml and 106 MPN/ml respectively in Buji stream. In contrast, the MPN of nitrifying bacteria in water and sediment were about 102 MPN/ml and 104 MPN/g respectively. The imbalance distribution of various nitrogen-related bacteria resulted in ammonia nitrogen accumulation and serious nitrogen pollution in Buji stream.Full-scale enhanced hybrid biofilm-activated sludge process (EHYBFAS) with short hydraulic retention time (HRT=3.5h) was a novel and promising for wastewater treatment. Results indicated that EHYBFAS were capable of achieving efficient organic removals. The average removals of BOD and COD achieved 86.0±3.6% and 83.7±4.6% at organic loading rates of 0.33~0.93 kg BOD/(m3·d) and 0.93~2.53 kg COD/(m3·d), respectively.The removal of TN and NH4+-N were 25.7±7.2% and 22.2±12.7% when the influent volume loading was 0.15~0.32 kg TN/(m3·d) and 0.11-0.22 kg NH4+-N/(m3·d), respectively. In EHYBFAS system, nitrogen-related bacteria were rich but the proportion of nitrifying bacteria was very low (0.21~0.3% in mixed liquor, 0.12~0.6% in fibrous carriers), which could weaken nitration and finally resulted in low removal rate of TN and NH4+-N. AOB community was investigated by PCR-DGGE. Results demonstrated the natural successions of AOB were completed successfully. The prominent bands were excised from DGGE gels and sequenced. Nine 16s rDNA sequences were obtained and the Genbank accession no. was from GU073369 to GU073378. Sequence analyses revealed five 16s rDNA sequences belonged to Nitrosomonas lineage and the similarity ranged from 98 to 99%. A fully coupled biofilm-activated sludge model is proposed and the simulation results indicate that the numerical simulation values of the coupled model were more consistent with real values.The combined bio-treatment technology of in-situ and en-situ was a practical and feasible method for stream regulation. In this study, a pilot-scale biological contact oxidation ditch (BCOD) was bioaugmented by inoculating enriched nitrifying bacteria for treatment of nitrogen-rich stream water. Results showed that the augmented BCOD obtained the effluent concentration of 13.4±3.5 mg/L of TN and 7.3±2.6 mg/L of NH4+-N, respectively. The removals of TN and NH4+-N reached 50.3% and 60.1%. The microbial biomass increased greatly in biofilm carriers especially after bioaugmentation and nitrifying bacteria accounted for about 1.31% of the nitrogen-related bacteria. Concomitant increases in the diversity of the bacterial community were also observed which had optimized the community structure of nitrogen-related bacteria and enhanced denitrification capacity.The introduction of aquatic plants into BCOD for treatment of polluted stream water not only improved treatment effect but also could overcome the defects of phytoremediation measures such as high operating conditions, long processing time and large occupation area. Results showed that the effluent TN and NH4+-N concentration were 15.5±1.84 mg/L and 6.6±0.56 mg/L and the removals of TN and NH4+-N reached 56.9% and 72.5% respectively. In addition, microbial biomass increased greatly due to aquatic plant especially the nitrifying bacteria which accounted for about 0.39% of the nitrogen-related bacteria from the initial 0.12%. The results had optimized the community structure of nitrogen-related bacteria and enhanced denitrification capacity.