| The sanitary landfill disposal is the most common strategy for municipal refuse treatment. Landfill leachate, the secondary pollutants produced by landfill, has high concentration of pollutants and is difficult to deal with. The water quality and quantity of landfill leachate varied with the time of landfill. The longer time the landfill lasts, the higher concentration of ammonia nitrogen and lower concentration of organics the landfill leachate will have. The carbon and nitrogen ratio will be seriously disordered in aged landfill leachate, which will be quite hard for biological disposal. Municipal Refuse Landfill Pollution Control Standards proposed a more stringent emission standards on the effluent of landfill leachate, which made especially challenge for the treatment of aged landfill leachate.Biofilter reactors were used to treat landfill leachate because of the carrier in the reactor can intercept and adsorb pollutants and the microbial adhered on the carrier could treat the pollutants, which make the leachate purified. That is an economical and environmentally friendly strategy. For aged landfill leachate treatment, due to the disorders of the radio of carbon to nitrogen caused by high levels of ammonia nitrogen, biological nitrogen removal is hard to take place, which eventually made it difficult to meet emission standards for effluent. In this paper, biofilter reactors were built to study the pollutants removal efficiency of landfill leachate. About ten years aged refuse collected from Shanghai Laogang Landfill was packed as carrier. The biofilter was operated at different temperature (15℃and 30℃) and hydraulic loading. The quality of effluent and pollutants removal rate under different conditions in the reactor were studied to propose a more efficient method of de-nitrogen treating mature landfill leachate.The main conclusions were drawn as followings:(1) At a low temperature of 15℃, the hydraulic loading raises from 8.5L/(m3·d) to 17L/(m3·d), the removal efficiency of ammonia nitrogen and BOD were not affected, COD decreased, however, total nitrogen removal rate raises from 36.7%to 64.2%. Therefore, improving the loading at low temperatures was conducive to denitrification efficiency.(2) At a low temperature of 15℃, maintaining recirculation ratio of 100%, increasing the amount of water, the hydraulic loading raises from17L/(m3-d) to 34L/(m3·d), BOD removal rate is not affected, ammonia nitrogen removal rate returns to normal after fluctuating for a period of time, the total nitrogen removal rate raises from 39.1% to 52.5%; When remaining the same amount of water, improving the recirculation ratio to 200%, BOD removal rate keep constant, ammonia nitrogen and COD removal rate decreases, total nitrogen removal rate raises to 66.5% from 52.5%. The total nitrogen removal rate increases fourteen percentage on the basis of previous stage with a 100% recirculation ratio. Recirculation at low temperatures can be used as a relatively simple way to improve nitrogen removal efficiency.(3) At a low temperature of 15℃, external carbon source will reduce the effluent COD and BOD in a short term, the removal rate of total nitrogen from 55.8% rise to 83.7%,but when the carbon source runs out, all will return to the previous level.(4) At 30℃, raising the hydraulic loading from 17L/(m3·d) up to 34L (m3·d), will reduce the ammonia nitrogen, BOD and COD removal rate, but the total nitrogen removal rate increased from patients to 73.1%. Therefore, at 30℃, improve the hydraulic loading can improve the denitrification efficiency.(5)When the loading condition stayed at 17L/(m3·d), the temperature had little effect on ammonia nitrogen removal, which stayed above 99% no matter before or after the increase of temperature. But after temperature increasing, the removal of ammonia nitrogen increased from 64.7% to 70.1%, as well as the removal of COD increasing from 75.4% to 81.5%.(6)The ammonia nitrogen removal stayed above 98% at the condition that the recirculation ratio was 200% and the loading was 51L/(m3·d),as well as the BOD removal above 96% and COD and TN removal essentially the same. The total nitrogen removal rate was not followed the increase of temperature. Threrefore, increasing the loading and recirculation and adding carbon source were potential control strategy to increase the TN removal of the aged refuse bioreactor.To sum up, at a low temperature of 15℃, de-nitrogen in aged refuse bioreactor could be improved by appropriate increasing the hydraulic loading and recirculation and carbon source adding. At a high temperature of 30℃, the aged refuse bioreactor could run at the higher loading, and appropriate improving recirculation can also improve nitrogen removal efficiency. Since the lack of carbon source, the heavy hydraulic loading and recirculation ratio will reduce the nitrogen removal efficiency. |
PDF Full Text Request