Study On Ozonation-BAF Process And Total Nitrogen Removal Treatment Of Mature Landfill Leachate

Mature landfill leachate has the features of complicated organic composition, high nitrogen content, biological toxity and poor biodegradability. It is very difficult to dispose. The major problems are high chemical oxygen demand (COD) and high total nitrogen (TN) concentrations. Hence the mature landfill leachate of Jiangmen solid waste treatment company in Guangdong province was studied to seek for an efficient advanced treatment. The study included two segments, the combining processes of ozonation and biological aerated filter (BAF) to treat the refractory organic substances and the two-stage BAF to remove total nitrogen.The combining processes of ozonation and BAF were used as the advanced treatment after biological treatment and coagulation treatment. The factors which influence the treating efficiency on mature landfill leachate by ozonation and BAF processes were studied. The results indicated that the lower pH the better treating effect with ozonation, the optimal terms were as follows:the dosage of ozone was 144mg/L, the reaction time was about 16h, the hydraulic retention time (HRT) of the up-flow BAF was 4h. The biodegradability of the landfill leachate was improved by ozonation, and the BOD5/COD increased from less than 0.1 to about 0.3. After the combining processes of ozonation and BAF, the maximum COD efficiency could reach 65% and COD of the effluent was less than 100mg/L. Kinetics of the ozonation reaction was analyzed and it showed that the degradation of the organic substances and time didn't have a simple linear relationship. There were three phases of the reaction, the rate tended to slow down. Considering the operation, management, safety and sencondary pollution issues, ozonation had the advantages in replacement of Fenton oxidation in advanced treatment of mature landfill leachate.After routine treatment, nitrogen concentration of the landfill leachate was still high in the form of nitrate nitrogen. Two-stage BAF aerated in the middle were used as the further treatment to remove nitrogen in the landfill leachate after advanced oxidation process. The startup and domestication process of the reactors were studied. It could be concluded that carbon sources promoted the growth of denitrifier, there were arobic/anoxia areas inside the reactors, nitrification and denitrification might happen simultaneously and nitrogen removal efficiency could be more than 60% when domestication was finished. The factors which influence the nitrogen removal efficiency on mature landfill leachate by this process were studied and discussed. The results indicated that the optimal conditions were as follows:water temperature was 25-30℃, methanol as carbon source with C/N was 4, DO was 4.5mg/L and HRT of the BAF was 7h. After a period of steady operation, COD of the effluent was 60mg/L in average, and TN was 17mg/L in average.The quality of the effluent after advanced oxidation to treat the refractory organic substances and two-stage BAF process to remove nitrogen could finally meet the the requirement of national landfill leachate discharge standard (GB-16889-2008).