.ENERGY EFFICIENCY OF COMPOSTING SEWAGE SLUDGE WITH THE ADDITION OF MAIZE STRAW

Composting is a natural biochemical process that effectively neutralizes most biological waste from households, sewage treatment plants, fruit and vegetable processing plants. and agriculture. Composted matter is transformed into humus, which is a useful fertilizer for agricultural crops. The main parameters which determine the effectiveness of composting are temperature, humidity, pH and aeration. Composting is also influenced by the natural parameters of the substrate: the C/N ratio, volume and nutrient content. Not all of types of biological waste are suitable for direct composting on account of their chemical composition or structure. Due to its physico-chemical properties, sewage sludge cannot be effectively composted without the addition of other substrates. Various types of additives are used to improve the C/N ratio and the structure of the substrate, and to maximize the efficiency of the composting process. The aim of this study. was to optimize the composting process by maximizing the utilization of sewage sludge and the amount of generated heat. The feasibility of composting sewage sludge as a low-temperature heat source without affecting the quality of the obtained humus was also investigated. The laboratory composting system used in this study consisted of 3 insulated composting reactors with a volume of 165 L each (0.5 mx0.5 mx0.66 m= 0.165 m(3)), equipped with a mechanical aeration system, flow controllers, temperature sensors, a portable gas analyzer (CH4, O-2, CO2, H2S, NH3) and condensate and leachate collectors. This closed-vessel system was designed and developed to simulate windrow composting under laboratory conditions. The system has separate condensate and leachate collectors which can be used to monitor water flow during composting. The collected data can also be monitored and.accessed via an online data tracking system. The analyzed substrate was sewage sludge combined with maize straw in three proportions. The composition of each substrate was determined based on the results of a previous study, which aimed to improve the C/N ratio, porosity and aeration of the composted material. The quality of the composting process can be more reliably evaluated based on the amount of heat released from substrate dry matter and the degree of decomposition of the composted product. The results of this study indicate that the C:N ratio is not the only critical parameter of sewage sludge intended for composting. Moisture content and optimal aeration of composted material are also important considerations.