Experimental Study On Treatment To The Condensed Liquid Of Landfill Leachate Rejected By Membrane Of Different Landfill Age

Nowadays,the most effective way to treat landfill leachate is the membrane unit followed by biological system,however,lager amount of liquid is rejected by membrane to form condensed liquid.Condensed liquid of leachate rejected by membrane(CLLRM for short thereinafter) is characterized by it's high concentration of biorefractory organic matters,the difficulty of treatment has limited the application of combined process of biological system and membrane unit in the leachate treatment process.Recently,the mainly used ways to treat CLLRM are recirculation and vaporization,however,the pollutants could be accumulated in the recycling process,the performance of membrane unit can be declined,and the landfill site could be brought forward to the old age phase;To the vaporization,the application is difficult to be extended for it's costliness equipments and high consumption of energy.Therefore,it is high time to investigate the effective and economical method to treat CLLRM.The characteristic of CLLRM was varied with landfill age,the concentration of organic matters in Mature sample outclass Younger sample,so different process of treatment would be employed to the CLLRM of different landfill age.To Mature sample of CLLRM,both flocculation and micro-electrolysis(adding H₂O₂) were employed seriesly to form the combined process in the experiment,single process of flocculation,single process of micro-electrolysis and combined process were studied.It was indicated that poor effect was appeared by single process of flocculation or single process of micro-electrolysis.Prominent effect was achieved by combined process,which was the effective way to treat Mature sample of CLLRM.The optimal operating conditions were obtained as follows:pH value was regulated to 4,during the flocculation period,flocculant(PAC) dosage(according to Al₂O₃) was 525 mg/L;during micro-electrolysis period,the ratio of iron to carbon was fixed to 3,aeration intensity was 200 L air/(L water·h),when reaction time achieved 30 min,adding H₂O₂(30%)to the water,the dosage was 0.5 ml/L.After 3 hours of reaction,the water quality of effluent were as follows:chroma was 720 times,UV₂₅₄ was 11.2 cm^-1 and COD was 1350 mg/L,the removal rate achieved 90.8%,81.1%and 79.2%respectively,the value of BOD₅/COD was enhanced to 0.31 from 0.03,which implied that the biodegradability for the organic matters was improved evidently,it was benefic to the biotreatmentment.To Younger sample of CLLRM,single process of flocculation was employed in the experiment,the optimal operating conditions were obtained as follows:pH value not to be regulated,flocculant dosage(according to Al₂O₃) was 360 mg/L,mixed round at the speed of 180 rpm for 1 min and then at the speed of 60 rpm for 8 min.The quality of effluent could met the requirement of the emission standard:Standard for Pollution Control on the Landfill Site of Municipal Solid Waste(GB16889-2008),the Younger sample was permitted to be discharged when treated by single process of flocculation.The flocculation mechanism of Mature sample of CLLRM was as follows:under the condition of weak acidity,the reaction of Al-humic coprecipitation occurred.The flocculation mechanism of Younger sample of CLLRM was as follows:under the condition of weak alkali,aluminium hydroxide formed,and sweep flocculation occurred,the organic matter was catched or adsorbed through van der Waals force.The dissolution of iron was accelerated when H₂O₂ was added to the micro-electrolysis system,The effect of micro-electrolysis had also been intensified due to employ H₂O₂.Through the analysis of UV Spectra,it was indicated that the absorption peak of Mature sample of CLLRM had a tendency of blue shift and the value of absorption fell down evidently by single micro-electrolysis or combined process,the unsaturated chemical-groups and chromophoric groups could be destroyed,the conjugate system could be weaken,and the biodegradability of the wastewater was improved evidently.The combined process of flocculation and enchanced micro-electrolysis(adding H₂O₂),and the single process of flocculation had presented good experimental effect to the Mature and Younger sample of CLLRM respectively,there exists theoretical and realistical value,it will play a positive role in the treatment of CLLRM.