Microorganism Immobilization Technology Apply To Simulated Ammonia Nitrogen Wastewater Treatment For Synthetic Ammonia Industry

The preparation of immobilized microorganism gel beads by embedding method had been studied in this paper. Three aspects had been mainly investigated:the acclimation and affecting factors of ammonia oxidizing bacteria, the optimization of immobilization condition of ammonia oxidizing bacteria and the affecting factors and properties of immobilized microoganism gel beads.The activated sludge was acclimated by gradually increasing the ammonia concentration. After25days sludge acclimation, SBR is startup successfully; the ammonia removal rate of simulated wastewater has been over90%, and it has a stable accumulation of nitrite. The color of activated sludge change from grey black to khaki and the sedimentation performance of activated sludge do well. In a run cycle, ammonia removal rate reach91.72%, the average ammonia oxidation rate is21.9mg/(L-h). Quantity of ammonia oxidizing bacteria in the sludge has been significantly increased from1.2×l07cfu/(gMLSS) to3.91×108cfu/(gMLSS). After acclimation, the number of ammonia oxidizing bacteria is32.6times the number before. The optimum conditions for partial nitrification had been found:T=30℃, pH=8.5, DO=0.5mg/L, alkalinity is1786mgCaCO3/L, in this condition the dosing quantity of NaHCO3is3000mg/L, that is HCO3-/NH4+-N=7.26, the maximum influent ammonia concentration is400mg/L。L9(34) orthogonal experiments were carried out to find out the optimal immobilization condition:PVA%=6.0%(w/v), SA%=0.50%(w/v), A12(SO4)3%=0.3%(w/v), concentrated sludge and polyvinyl alcohol mass ratio is1.5:5. Through the comparison of properties on gel beads adding four kinds of inorganic materials, SiO2and CaCO3have been chosen to improve the properties of the immobilized microorganism gel beads. Single factor experiments were carried out to find out the optimal immobilization condition, the results showed that:PVA%=6.0%(w/v), SA%=0.50%(w/v), SiO2%=0.5%(w/v), CaCO3%=0.1%(w/v), the concentrated sludge and polyvinyl alcohol mass ratio is1.5:5, the crosslinking agent is saturated boric acid solution with0.3%A12(SO4)3(w/v), the crosslinking time is24h and washed with distilled water three times after the completion of crosslinking, dried at room temperature until the moisture content of gel beads is about82.2%, stored for use at4℃.The effect of temperature, pH and DO on immobilized ammonia oxidizing bacteria had been studied, and compared with free bacteria in the conditions. It also studied dosing quantity, the minimum activation cycle and srorage condition. The optimum conditions for immobilized ammonia oxidizing bacteria were:T=30℃, pH=8.5, DO=4mg/L. Compared with free bacteria, immobilized ammonia oxidizing bacteria are capable of high temperature resistance, acid and alkali resistance. When the initial ammonia concentration is300mg/L, the optimum dosing quantity of immobilized microorganism gel beads is15%, the minimum activation cycle is4cycle, and the optimal srorage condition is immersion with simulated wastewater at4℃.In addition, this paper also measured on the performance of the immobilized microorganism gel beads, the true wet density is1.0568g/cm3, slightly larger than the density of water, apparent wet density is0.5488g/cm3, the average size of gel beads is5.55mm, the color is khaki. SEM observation showed that:gel beads befor acclimated have a dense surface, bacterias rarely attach to the above, and bacterias uniformly attach to the network of the gel beads. After23days acclimation, the bacterias in immobilized microorganism gel beads from surface to inner appear distribution of succession phenomenon, more bacterias on the surface of the gel beads, the inner near the surface region have a small amount of bacterias, the central part of the gel beads hardly find bacterias.