Remoção de matéria orgânica em tanque séptico com biomassa aderida

Abstract

In Brazil about 50,3% of the population is served by a sewage collection network, of which only 42,7% is treated. A 12% share of the country’s total population uses septic tank to treat sewage generated in their homes. Despite their advantages, septic tanks present moderate removal of organic matter, spinning around 50%. In this sense, it is necessary to improve this system in order to improve its efficiency. The increase of microbial biomass concentration in the system by the insertion of support material is a method frequently used for this purpose, as this allows the microorganisms to remain for longer in the system, increasing their time of contact with the sewage and, consequently, increasing the efficiency of organic matter degradation. The PET bottle has been studied as a septic tank support material. The use of this material in individual sewage treatment systems is related to the development of a technique that is sustainable and accessible to communities without access to the collection network. In this sense, the objective of this research was the introduction of support material in a septic tank in a bench scale, which was operated in four stages: Step 1 (without support material), Step 2 (50% occupation), Transition (without support material) and Step 3 (10% occupation). The support material used were sands PET bottle strips, with 1,5 cm wide and 15,5 cm long. The monitoring parameters, evaluated in the influent and effluent sewage were: pH, total alkalinity, volatile fatty acids (VFA), total and filtered COD and solid series. The concentration of microorganisms adhered to the support material in Stages 2 and 3 was monitored by means of the concentration of proteins (PT), polysaccharides (PST) and adhered total volatile solids (STVA). The results of the monitoring of pH, alkalinity and VFA indicated stability of the system in all stages of operation, and the presence of support material did not interfere in these results. The insertion of support material contributed to increase the efficiency of the system, and the highest removal rates of DQOT and DQOF were in Step 3 (77.9% and 74.4%) and the lowest in Step 1 (49.7% % and 40.5%). In relation to solids, Step 2 presented the best removal efficiencies of total solids (42.1%) and total suspended solids (82.3%), and Step 3, total dissolved solids (33,2%) and volatile (87,4%). The analyzes of PT, PST and STVA indicated the highest concentration of microbial biomass on support material in Step 2, a fact that did not reflect the better efficiency of organic matter removal. It was concluded that the insertion of strips of PET bottle as a support material in septic tank showed an improvement in the organic matter removal efficiency, and the occupancy percentage of 10% presented the best results.