| Lacking water resources and water eutrophication are major problems to environmental protection in the world. As the issue of eutrophication is becoming more severely, the standard of wastewater discharge according to the regulatory requireents is controlled strictly even more. Nitrogen and phosphorus removal technology with the advantages of economic and energy efficient has been one of the hot subjects in the field of water treatment. Aiming at the subsistent problems of traditional process, such as high energy consumption, carbon source competition and sludge age competition, denitrifying phosphorus removal technology was proposed in the base of original wastewater treatment process of nitrogen and phosphorus removal. A continuous-flow, two-sludge, short-cut nitrification and denitrification phosphorus removal combined, Anaerobic-Anoxic/Nitrification (A2N) system was established. The influencing factors and long-term stable system operation were investigated. Physiological and biochemical characteristics of denitrifying phosphorus removal bacteria and molecular biology were studied.N-SBR steadily providing electron acceptor for denitrifying phosphorus removal reaction is the key factor for A2N process. N-SBR system was firstly started up by gradually increasing the influent substrate concentrations of ammonia nitrogen. The effects of temperature, pH, solid retention time (SRT) and dissolved oxygen (DO) on the operation of short-cut nitrification system were monitored. The result showed that the optimal temperature ranges for short-cut nitrification were at 11～14℃ and 30-33℃ rather than at 15～20℃, while no positive correlation between nitrite accumulation and temperature was observed. In addition, nitrite accumulation could be improved by extending the micro-aerobic aeration time. The concentration of free ammonia (FA) altered with pH change. When the concentration of FA was below 10 mg.L-1, nitrite accumulation was proportional to pH. In the process of short-cut nitrification, the curve of pH showed a rapid increase after a sudden decline, and then a shape drop-off once again. With a SRT of 8 days, maximum accumulation of nitrite bacteria was occurred because the SRT was longer than generation period of nitrite bacteria but shorter than generation period of nitrate bacteria. The low DO concentration was beneficial to growth of ammonia oxidizing bacteria (AOB) that the optimal short-cut nitrification occurred with DO concentration of 0.5～1.2 mg.L-1. The optimum operating conditions for short-cut nitrification were that the temperature was at the range of 25～27℃, pH was 7.2～7.5, SRT was 8d, DO was about 0.5～1.2 mg.L-1. The nitrite accumulating efficiency was 90.62%. The concentration of effluent nitrite was 62.06 mg.L-1. The maximum accumulating rate of nitrite was 8.36mg.g-1VSS.h-1.The A2-SBR system of denitrifying phosphorus removal was sucessfully started up by gradually acclimating polyphosphate accumulating organisms (PAOs) to accommodate and utilize NO2- as electron acceptor. Influencing factors such as pH, SRT and temperature were inquired. The results revealed that anaerobic phosphate release rate and anoxic phosphorus uptake rate were positively correlative to pH as pH was at the range of 6.5-8. When pH was above 8, phosphate precipitation occurred resulted in a decline of phosphorus removal efficiency. The phosphorus removal efficiency of A2-SBR system was unstable with no sludge discharge where the removal efficiency of phosphorus became poor 26 days later. When SRT was no more than 24 days, more external carbon source was absorbed and transformed to poly-β-hydroxybutyric acid (PHB) by denitrifying phosphorus removing bacteria (DPB) along with the extension of SRT as a result of a better phosphorus removal effect and lower COD in efflux. High temperature could boost metabolism of microbes, thus the release efficiency and uptake efficiency of phosphorus was improved by raising temperature in reactor. However, when the temperature exceeded 32℃, the sludge concentration increasing led to a reduction in denitrifying phosphorus removal efficiency as no sufficient external carbon source. Nitrite dosage and its dosing method was the key of stable operation of the system. In comparison with intensive adding nitrite, inhibitory of DPB could be avoid from reaching the threshold inhibitory concentration of nitrite in manner of continuous dropping. The ideal concentration of nitrite was determined as 26 mg.L-1. The average removal efficiency of phosphorus was 88.04% and the effluent concentration of phosphorus was 1.05 mg.L-1 under the optimum operating conditions of pH 8, SRT 24 days, temperature 24℃, and nitrite adding concentration 26 mg.L-1.Based on synthetic wastewater, the system of two-sludge (A2N SBR) was run continuously for 30 days. The result indicated thatthe average concentration of COD, TN and TP in effluent were 26.72 mg.L-1,5.8 mg.L-1 and 2.1 mg.L-1 respectively. COD removal was almost completed in N-SBR typical cycle of 60 min. The concentration and accumulation efficiency of nitrite were 74.4 mg.L"1 and 94.8% in the end of short-cut nitrification. The amount of the anaerobic release phosphorus was 10.53 mg.L-1. In A2-SBR system, the concentration and removal rate of TP in effluent were 1.14 mg.L-and 88.8%, the The effluent concentration of NO2--N was 0.53 mg/L in the end of anoxic stage.The mechanism of denitrifying phosphorus removal is very similar to that of the traditional aerobic phosphorus removal. but the only difference is the electron acceptor. In denitrifying phosphorus removal process, the amount of phosphorus uptake alternates with the amount of ATP generated by consuming NADH2 per unit. Changes of substrate concentration could reflect the DPAO metabolic process. Under anaerobic conditions,74.07 mg.L-1 COD and 78.61 mg.L-1 glycogen were converted into 150.88 mg.L-1 PHB accompanied with phosphorus release. Under anoxic conditions, denitrifying phosphorus removal occured while PHB was as electron donor and 19.55mg/L N02--N was as electron acceptor. The effluent concentration of phosphorus was 1.08 mg.L-1 and the removal efficiency of phosphorus was 84.79%.By isolating and screening in A2-SBR,13 strains of bacteria with denitrifying phosphorus removal trait were obtained. Physiological and biochemical characteristics of the bacteria were then studied. PCR and 16S rDNA were carried out in order to acquire genetic information. According to the results, NC1-1, NG1 and NG2 were Gordonia alkanivorans, PC was Sphingomonas sp, PD1 was Paracoccus marcusii, PD2 was Sphingomonas sp, PE was Dietzia sp, PG was Brevundimonas sp, NC1-2 and NC1-3 were Stenotrophomonas sp, NF were Pseudomonas stutzeri.The suuject established tow-sludge system, which could denitrify and removal phosphorous and operate stablely. It provided the new directions and ideas for biological nitrogen and phosphorus removal. Four strains of denitrifying phosphorus removing bacteria riched phosphorus removing bacteria. The researchs are important both in application and theory. |
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