Composto orgânico de lodo de reator UASB e casca de café: qualidade e oportunidades para produção e uso agrícola em Minas Gerais

Abstract

Sewage sludge is a solid byproduct generated during the treatment of sanitary sewage which has great potential for agricultural use due to its high organic matter and nutrients content. However, their use must be made in a sanitary safe way by the definition of doses that do not cause chemical imbalances in the soil and groundwater pollution and by hygienization due to the presence of pathogenic microorganisms. This research evaluates the sanitation of sludge from an upflow anaerobic sludge blanket (UASB) reactor though the composting technique, and the coffee husk was used as the structuring material. The microbiological and chemical quality of the organic material was evaluated at the end of the composting process by monitoring the microbiological indicators established in CONAMA Resolution 375/2006 and organic fertilizers quality benchmarks. The contents of macronutrients nitrogen, phosphorus and potassium in the organic compound were compared to the fertilization needs of the coffee plant. In addition, the research identified the coffee plantation areas located around the STP composed by UASB reactors and the compatibility of these areas as suppliers of coffee husks and receiver of the fertilizer. The results showed that the composting technique was efficient for the production of a sanitary safe compost, once there was not identified the presence of viable helminth eggs, salmonella and coliphages (as indicators of the presence of enteric virus) in the organic compost and the concentration of fecal coliforms was less than 10³ MPN/gTS in all samples analysed. Regarding the analysis of the macronutrients present in the compost, the results revealed that the organic compost have the potassium as a reference element to determine the application rate of the fertilizer in the soil (if the agricultural use was made in the coffee plantations). Furthermore, it was verified that the content of nitrogen and phosphorus in the compost could supply 42% and 56%, respectively, of the nutrients demanded by coffee plantation. Finally, according to the estimation of the areas of coffee plantations in the vicinity of the STPs, to the production of coffee husks in these areas and to the appropriate proportion among the raw materials for the composting process, were verified that 38% of the STPs could compost the entire volume of UASB sludge generated in their units, which represents 17% of all UASB sludge produced in Minas Gerais. According to the quality of the organic compost produced and the application rate recommended, it was verified that the totality of the fertilizer that can be produced in the state could be used to fertilize the coffee plantations located in the vicinity of Minas Gerais STPs.