Municipal wastes management and disposal have always been one of the most important environmental issues facing the world today as a global problem. Landfill wastes produce a leachate containing a high amounts of organic materials, ammonia, nitrogenous materials, heavy metals, organic chlorine, inorganic salts, and pathogens. Application of combined processes for treatment of municipal landfill leachate can be considered as a potential and cost-effective solution. Thus, two-stage anaerobic and continuous completely stirred tank reactors with the hydraulic retention time of 5 and 15 days and effective volume of 10 and 30 L respectively, aerobic settling reactor and aerated and settling tank (hydraulic retention time of 0.12, 7 and 0.12 days, and with effective volume of 2, 14, and 2 L) and chemical reactor with 12 L volume were developed in lab-scale. In this combined system, treatment of fresh landfill leachate from Mashhad landfilling site was investigated in three stages over a period of 5 months; two-stage anaerobic, aerobic digestion, and chemical-coagulation. The portable treatment system has the capability for precisely controlling the operational parameters of anaerobic digestion process including the complete air sealing, temperature, mechanical stirrer, stirring system (stirring speed and time), biogas measurement system, substrate level monitoring, temperature supporting system, and biaxial pumping and aeration system. To assess the system performance, continuous experiments were performed with the fixed rate of 2 L/day and under six organic loading rates in the mesophilic conditions. After the reactor start-up, the organic loading rate was increased from 0.07 kgCOD/m3.day to 2.65 kgCOD/m3.day. The results of experiments showed that the acceptable organic loading rate is 2.05kgCOD/m3.day in which chemical oxygen demand removal efficiency of the two-stage, aerobic, chemical reactors, and total treatment system were obtained 93, 37, 50 and 93%, respectively. Biochemical Oxygen Demand removal efficiency of the entire system was 98.11%. However, in two-stage anaerobic reactor, ammonia nitrogen and alkalinity were increased by 31.28 and 15.18%, respectively. While these parameters were decreased in the aerobic (at 50.30 and 57.23%) and chemical (at 88.55 and 88%) reactors. The optimal level of turbidity was increased in the anaerobic reactors (18.7%) but it was decreased in the aerobic (72.1%) and chemical reactors (98.9%). Under some stable conditions, the methane percentage of the first and second anaerobic reactors were 76.4 and 81.3%. Combined biological-chemical process can be used as the effective process for degradation and removal of the organic pollutants. |
