Treatment of Leachate Obtained in Leiras de Compostagem de Remos de Alimentos (Composting of Food Remains) by Anaerobic Biodigestion Followed by Oxygenation: a Case Study in the Federal District

Objective: During the composting process of organic waste, the leachate from the degrading windrows requires treatment processes due to its significant load of polluting substances. Frequently, the approach adopted to treat leachate involves a combination of different processes. This study aimed to evaluate the performance of a biological treatment system, consisting of anaerobic digestion followed by oxygenation, applied to leachate from a composting company of organic waste obtained from residential and commercial kitchens located in the Federal District. The outlined hypothesis is that anaerobic treatment followed by oxygenation, with the material studied and under the experimental conditions, allows for the attainment of material with characteristics that permit its discharge into water bodies, according to CONAMA Resolution No. 430/2011, which complements and amends Resolution No. 357/2005. Method: The leachate was collected from the windrows through pipes and directed to a physical treatment system composed of a sand and grease trap. After that, it was pumped into two anaerobic reactors operating in sequence, with a total retention time of 15 days. The material was then directed to a waterproof masonry tank with natural and forced aeration. Samples were taken before and after the treatment of the leachate for the determination of electrical conductivity, temperature, pH, chemical and biochemical oxygen demands, total dissolved solids, total and volatile solids, total nitrogen, N-NH4+, N-NO3-, N-NO2-, total alkalinity, total phosphorus, thermotolerant coliforms, and Salmonella. Results and Discussion: The absence of Salmonella was observed in both the samples obtained before and after the treatment. Reductions in electrical conductivity (7.6%), temperature (16.2%), total alkalinity (23.0%), chemical oxygen demand (42.3%), biochemical oxygen demand (45.5%), total nitrogen (9.3%), N-NH4+ (18.4%), total phosphorus (30.1%), total solids (16.9%), total dissolved solids (14.0%), volatile solids (21.5%), and thermotolerant coliforms (99.9%) were observed after treatment. On the other hand, increases in pH (12.3%), N-NO3- (30.4%), and N-NO2- (14.4%) were noted. However, the material treated under the experimental conditions adopted did not meet the environmental discharge requirements established by Brazilian legislation (CONAMA Resolution 430/2011), especially for the parameters biochemical oxygen demand, total nitrogen, N-NH4+, total phosphorus, N-NO₃⁻, N-NO₂⁻, and thermotolerant coliforms. Research Implications: The volume of organic waste collected and treated by composting has been increasing in recent years in Brazil, especially due to legal requirements at state (district) and municipal levels. Since organic waste generally has high moisture content, a large volume of leachate from the windrows is produced and can become a significant source of environmental contamination. Biological treatments such as anaerobic digestion followed by aeration can be an important tool to prevent this contamination, but chemical and biochemical parameters, as well as conditions like retention time, need to be evaluated to verify the efficiency of treatment systems.