Study On The Advanced Treatment Of Landfill Leachatea

Landfill, as the primary means of municipal solid waste disposal today, produces a large amount of landfill leachate during its process. The landfill leachate contains a variety of organic, inorganic and heavy metal contents, which are high in concentration and often influenced by the age and type of solid wastes of a landfill site. Therefore, it has been generally known as a high-strength wastewater that is most difficult to deal with. And with the launch of the new Standard for Pollution Control on the Landfill Site of Municipal Solid Waste, finding an economic and effective way to treat landfill leachate properly becomes an urgent and challenging task to the local governments.This study was carried out to investigate the feasibility of two kinds of combined technology in treating leachate from Laogang Refuse Landfill in Shanghai so as to meet the newly launched discharge limit of landfill leachate (COD<100 mg/L).The two technologies are "biological pretreatment+pH regulation+iron-carbon micro-electrolysis+Fenton reagent" and "pH regulation with aeration+acid catalyzed reaction with aeration+Fenton reagent". After the optimization of technological parameters, the results showed that the leachate treated by either of the technologies could get its COD removed to less than 100 mg/L, meeting the newly launched discharge limit of landfill leachate. And a pilot-scale test using "pH regulation with aeration+acid catalyzed reaction with aeration+Fenton reagent" technology will be carried out on Laogang landfill site because of its low cost on construction and treatment as well as its high technical reliability.In the first technology, the anaerobic biological filtration process followed by aerobic biological contract oxidization technology was applied as pretreatment for leachate from Shanghai Laogang landfill. A macromolecular hydrophilic material was used as the filter, and the effluent from the anaerobic biological filter was recycled to the aerobic biological contract oxidization pond. When the recycling ratio was 200%, the HRT for anaerobic biological filter was 5 d and that for the aerobic biological contract oxidization pond was 18 h, the COD, TP, NH4+-N and TN of the effluent could be reduced by 25%,32%,45% and 46%, respectively. Besides, the biological treatment could make the subsequent pH regulation process much easier, saving calcium oxide by 5.4 g/L. After the pH value of leachate was adjusted to 12 using calcium oxide, the humic substances, heavy metals and phosphate radical could be effectively removed.On the foundation of biological treatment and pH regulation, the joint oxidation technology of iron-carbon micro-electrolysis and Fenton reagent was introduced to remove the remained pollutant in leachate, and the major parameters were evaluated with the traditional one-factor-at-a-time method in this study. The experimental results showed that when the initial pH was 4, the Ferric-Carbon quality rate was 1:1, the solid-liquid quality rate was 1:4, the reaction time was 2 h and the system was aerated constantly, the total removal rates of COD, TP, NH4+-N and TN could be further raised to 78%,97%,55% and 54%. As for the following Fenton process, results showed that the optimum operation conditions were pH of 2, H2O2/Fe of 5:1 (molar ratio), H2O2 dosage of 0.9 g/L and the reaction time of 2 h with Fenton reagent added at a time. Under the above conditions, the COD of leachate was reduced to 90 mg/L meeting the discharge demand of landfill leachate. And the total removal rates of COD, TP, NH4+-N and TN was 94%,99%,58% and 55%, respectively.In the second technology, the leachate was adjusted to pH=12 using calcium oxide and aerated for 2 h at first. After precipitation, an acid catalyzed reaction was carried out with pH=2 and aeration time of 2 h. Then the leachate was further treated with Fenton reagent to improve the water quality of the final effluent to meet the standard for safe discharge. When the pH was 2, the molar ratio of H2O2 to Fe2+ was 5:1, the H2O2 dosage was 2.4 g/L, the reaction time was 2 h, and Fenton reagent was added at a time, the COD of leachate could be reduced to 92 mg/L with the total removal rate of COD being 93%.