Technical Research And Mathematics Model On The Nutrient Removal Process By Sludge Adsorption

Municipal sewage with low carbon source increases the contradictions between denitrification and phosphorus release. In most municipal sewage treatment plants, effluent qualities could not reach the present criterions, because the carbon source is too little to meet the demanding of conventional biological treatment processes. How to achieve an effective treatment efficiency becomes a great problem in the treatment of municipal wastewater with low carbon source.In this paper, a nutrient removal process by sludge adsorption was employed for the treatment of municipal wastewater with low C/N ratio. The whole flow included sludge adsorption stage, anaerobic phosphorus release stage, as well as multiple aerobic nitrification and anoxic denitrification stage. Influent and returned sludge were pumped into sludge adsorption tank, in which influent CODCr was adsorped by activated sludge. After sedimentation, the adsorption sludge flowed into anaerobic zone for phosphorus release, and the adsorption supernatant was distributed to multiple aerobic and anoxic zones,. By doing so, the sludge concentration in the whole system could be increased, which was preferable for the proliferation of phosphate accumulating organisms (PAOs) and nitrifiers. Supernatant was distributed into anoxic zones to supply carbon source for denitrifiers. By the operation mode of multiple aerobic and anoxic reactions, NO3-N and NO2-N produced by nitrification were consumed in anoxic zones in time, avoiding its inhibitation on nitrification and aerobic phoshorus accumulation.Based on the mechanisms of sludge adsorption and phosphorus release, both the model on sludge adsorption and the model on phosphorus release were put forward and analyzed by experimental studies and data fitting. With the two models, sludge adsorption time and phosphorus release time were determined. The technical research on the experimental nutrient removal process by sludge adsorption was carried out in the conditions determined by experiments. With microbiological analysis, the sludge characteristics and floras were analyzed. The chief achievements are as follows.(1) Put forward the sludge adsorption model as S t= S 0' e-kT, in which, S0 ' was initial CODCr concentration, and k was the adsorption rate constant, which was related to sludge concentration, organics variety, and so on.From the model, the sludge adsorption effect was influenced by sludge concentration and adsorption time, with the sludge concentration as the chief factor. By fitting analysis, the sludge adsorption model could well describe the sludge adsorption process.(2) Put forward a new phosphorus release model as in which, Pm was maximum TP concentration in PAOs that could be released, P0 was initial TP concentration, and K was the phosphorus release rate constant. From the model, phosphorus release effect was influenced by sludge concentration, as well as release time and organics variety. High sludge concentration and long release time were beneficial for phosphorus release. By fitting analysis, the phoshorus release model could well describe the phosphorus release process. The phosphorus release rate constant was related to PAOs characteristics, sludge concentration, organics variety and TP concentration in PAOs that could be released. In the experimental conditions, the value of K was between 0.01~0.02 L/(mg·min).(3) Put forward a new activate sludge process for nutrient removal, which was the nutrient removal process by sludge adsorption. According to the sludge adsorption model and the phosphorus release model, the design parameters for the nutrient removal processs by sludge adsorption were determined, with the adsorption time 22 min, and anaerobic phosphorus release time 50 min. The sludge concentration was high to 10 g/L, so the phosphorus release time was greatly decreased.From the experimental results, the operation parameters were set as multiple aerobic/anoxic orders 5, adsorption time 22 min, returned sludge ratio 0.8, sludge age 20 d, and DO concentraion 2.5~3.0 mg/L in aerobic zones.(4) The results during the stable operation showed that with the nutrient removal process by sludge adsorption conditions, the removal rates of NH3-N, TN, and TP were 91.7%, 89.1%, and 87.2%, respectively. Effluent qualities (except TP meeting ClassⅠ-B criteria) could meet the"ClassⅠ-A criteria specified in Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant"(GB18918-2002).(5) In the whole experimental process system, carbon source was rationally utilized. There exsited significant NH3-N and CODCr concentration changes in the anoxic tanks, indicateing the occurrences of denitrification and ammonia oxidation. The phosphorus release amount of PAOs was high even in relatively short time.In the same operation conditions, the nutrient removal effect of the nutrient removal process by sludge adsorption was superior to that of traditional A~2/O process. On the premise of the effluent qualities (except TP meeting ClassⅠ-B criteria) meeting the"ClassⅠ-A criteria specified in Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant"after treatment by the nutrient removal process by sludge adsorption, the influent C/N ratio was 3 at least.(6) From the analysis and comparison on floras with other two treatment systems, there were less nitromonas and denitrifiers, but more nitrosomonas in the nutrient removal system by sludge adsorption.