Acceleration of decomposition phase of agroindustrial and urban sludges composting process aiming the organic compost use in agriculture

Abstract

Most sludge generated in Brazilian are not in accordance to parameters established by the Brazilian agricultural legislation, since these wastes present contaminants such as pathogens and heavy metals, nutritional unbalances and low stability of organic material. Composting is considered an excellent alternative for pos-treatment of these wastes, considering technical, economic and environmental aspects. However, the composting of large waste volume requires vast areas, especially in the decomposition stage, which lasts around 60 days, besides this process can present high operating costs due to needs of machines and operators for revolving of composting piles and, too, representing risks to workers health. The project aim is use the waste recycling machine 5ECOS for accelerate the composting process of organic sludges with vegetal materials, performing the decomposition stage on this "anaerobic reactor" that present structural rod for the automatic revolving, temperature automatic control, and a microbial mass present at the equipment base. This machine has been commercialized for accelerate composting (24 hours) of food wastes from industrial restaurants and waste from hortifruti sector, producing an organic material with water contents around of 5-15%, and physical aspect similar organic compost. Germination test results, physic-chemical, and chemical characterization showed that the agricultural use is not possible. Studies performed by equip of this project resulted in hypothesis of that the unbalances in C/N ratio and the water content excess could have caused the fermentative process of organic mass. Low values of pH and composts phytotoxicity showed that the actual machine temperature programming caused a reduction in aerobic decomposition time, which was rapidly ended due to the temperatures higher than 60ºC for final product sterilization. Organic matter and carbon low contents, high C/N ratio, and low CTC/C reflected the composts low stability, which were not humified. Tests were performed with mixture of sludge with tree pruning, balancing the C/N ratio and water content of this mixture, and after 48ºC there was increasing in mass temperature, without costs with electrical energy, similar a phase of field composting process that occur during 10-15 days. Improvements in material characteristics were observed, indicating that the acceleration composting acceleration is possible, in other words, performing the decomposition phase completely inside the machine. This project proposes to confront three composting process scenarios: (i) inside of waste recycling machine 5ECOS; (ii) in field composting piles; (iii) in laboratory by respirometry test, evaluating three sludges types (sewage, agroindustrial, and from swine waste treatment) and two bulking agent (tree pruning and sugarcane bagasse/wood shavings), totaling 36 treatments. During the several process phases, the wastes and composts will be monitored as to temperature, water content, organic matter, C, N-total, N-NO3-, N-NH4+, other plants and heavy metals, as well as thermotolerant coliforms, Salmonella spp, helminth eggs and protozoan cysts. The daily data will be used as database for the project second phase, for software construction that automates the dates collecting for process conduction, as well as, for collecting and automatic analysis of parameters required for composting conduction as: water content, C, N, humification index, by sensor means to be installed on machine and determinations to be done by photonic techniques. The process monitoring in this three scenarios will make it possible to promote changes in machine and in the process, for more fast execution of composting, with low operation costs and with compost characterization in accordance to parameter established by Brazilian legislation about registration and commercialization, thus, using wastes that are disposed in landfill and reducing costs with chemical fertilizers use. (AU)