| Currently, eutrophication, one of many great environmental problems, has aroused global concern. How to control eutrophication of water bodies and restore its function has become a hottopic. Immobilized microorganism technology as a promising biological technology, with its unique advantages, has been applicated and investigated around the world. In this study, activated sludge and a certain percentage of denitrifying sludge (cultured in laboratory) are mixed with polyvinyl alcohol (a certain amount of additives were added) by embedding, letting it become spherical with 3-4 mm diameter. Finally, evaluate its entire and short-cut nitrification and denitrification ability, respectively. The main results are as follows:(1) In selected medium and anaerobic culture conditions, using activated sludge in CASS pool as seed sludge, after about seven-day acclimatization, its denitrification rate within 2 hours could reach to about 10.08mgNO3--N/gMLSSh. The color of mature denitrifing sludge is brown and it have flocculent and delicated appearance.(2) Investigated a method of embedding that mainly used polyvinyl alcohol (PVA) as embedding medium. Using the removal of TN and COD as indicator, by 4 factors and 3 levels of orthogonal experiments, we studied the best conditions for embedding. The results showed that the best condition was PVA concentration at 10%, activated sludge and the sludge denitrification in the mass ratio of 2:1, crosslinker concentration (CaCl2) at 2.5%, crosslinking time at 24h. Under these conditions, the mechanical strength and mass transfer performance of embedded particles were all the best.(3) According to single factor experiments, when the influent ammonia concentration was 55mg/L, COD was 285mg/L, fill rate of the reactor was 7-8%, dissolved oxygen control was 4mg/L, pH value controlled at between 7.5-8.0, the temperature controlled at around 28℃, both the full and short nitrification and denitrification performance were the best. Under these conditions, the removal rate of ammonia nitrogen and COD removal could both up to more than 95%, meanwhile the TN removal rate could reach to 87%.(4) At temperature of 31±1℃, embedded particles fill rate is 7%-8%, influent ammonia nitrogen was 55mg/L, COD is 280mg/L, pH value of 8.0, DO concentration of about 4.0, HRT is 10h cases, the water nitrification rate, COD and TN removal rates were 95%,95% and 85%, and place a stable nitrification and denitrification. Influent COD concentration from 150mg/L increased to 750mg/L, TN removal efficiency increased from 73.66% to 96.79%. In the case of excessive aeration run 7 cycles, the partial nitrification with full conversion to the trend. Maintain the pH value of 8.0, the temperature dropped from 30℃to 25℃, denitrification decreased, but did not change shortcut nitrification and denitrification. Temperature of 25℃, when the pH value gradually decreased from 8.0 to 7.5, the full nitrification occurred.(5) In the whole reaction period, the TN removal of shortcut nitrification and denitrification was always higher than that of full about 5-33%, shortcut nitrification denitrification rate was more rapid. The ammonia degradation rate of full and partial nitrification and denitrification were 3.77mg/Lh and 4.37mg/Lh, respectively. |
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