Limited Oxygen Activated Sludge Cooperated With Fenton-Anaerobic Filter-Biological Aerated Filter For Treating Landfill Leachate

Landfill leachate in Hangzhou Tianziling landfill contains complicated organic component, high nitrogen, so the wastewater is high toxic and hard to biodegrade. According to the characteristic of the landfill leachate, limited oxygen activated sludge cooperated with the two stage Fenton -anaerobic filter (AF)- biological aerated filter(BAF) processes were applied.The theoretical principle of limited oxygen activated sludge is short-cut nitrification and denitrification. The DO value of the bioreactor is the main control method to achieve short-cut nitrification and denitrification reaction. The DO values of 1#, 2#, 3#, 4# bioreactor were about 0.1 mg/L, 1 mg/L, 0.5 mg/L, 0.1 mg/L respectively basing on the pilot plant study. The measure made the four bioreactors into the anaerobic/ facultative/ facultative/ anaerobic bioreactor. In order to strengthen the treating capacity and anti impact load, the effluent and sludge of bioreactor were backflowed to dilute pollutant concentration and increase mixed liquor suspended solid(MLSS). It helped to form high efficient organic, ammonia nitrogen and total nitrogen treatment process. Therefore, the average COD, ammonia nitrogen and total nitrogen removal rate reached 90%,99.8% and 90% separately. The C/N ratio was one of very important influencing factors in short-cut nitrification and denitrification. And it was significant restricting factor of nitrate nitrogen and nitrite nitrogen transforming into nitrogen. It was able to achieve favorable result in the condition of C/N ratio≥4.Because the effluent of limited oxygen activated sludge still contained a portion of total nitrogen and refractory organic, the two stage Fenton-AF-BAF advanced treatment process was applied. Fenton oxidative reaction was capable of removing refractory organic and colour in wastewater effectively. The experimental result showed that the optimal operational condition of Fenton oxidative reaction treating effluent of limited oxygen activated sludge was: H₂O₂/COD= 1.5, n(Fe²⁺) / n(H₂O₂)= 1, the initial pH of wastewater= 4, the retention time= 2 h. In the condition, the COD declined from 740 mg/L to 240 mg/L and the COD removal rate was 68%. In the light of the varieties of the reaction condition and COD removal rate, n(Fe²⁺) / n(H₂O₂) ratio and the initial pH of wastewater were the most significant factor of treatment effect. H₂O₂/COD ratio took the second place. And the retention time was the least important factor.And then increase C/N ratio to 3-5 through adding carbon source methanol. Through nitrification- denitrification reaction, AF- BAF process could remove total nitrogen and organic in wastewater. And it made the effluent meet the the requirement of national landfill leachate discharge standard (GB-16889-2008).