Co-composting of meat packing wastewater sludge and organic fraction of municipal solid waste

The use of organic manures as amendments to improve soil organic matter level and long term soil fertility and productivity is gaining importance. The disposal of the great quantity of organic wastes produced by the municipal, agricultural and agroindustrial activities, is causing energetic, economic and environmental problems. Sludge composting and using them in agriculture should be a priority for their disposal. Sludge should be treated not as a waste but as a valuable non-farm sources of organic matter to soil. The composting process is a useful method of producing a stabilized material that can be used as a source of nutrients and soil conditioner in fields. The objective of this study was estimation of optimal dose of sewage sludge in composting mixture to obtain of mature and stable compost. The mixture was prepared from sewage sludge (10-40%), organic fraction of MSW(30%), grass (20-50%), sawdust as a bulking agents. Maximum temperature in the bioreactor reached 68.9°C between 1st and 3rd day of composting, and the mean temperature during this period fluctuated from 36 to 46°C. Later, the temperature gradually decreased and after 30 days of composting it approached ambient air temperature which means the end of process. There was significant impact of the high temperature on the rate of the process and of the extent of the hygienisation. The results show that all initial samples are infected with helminth eggs but there is a large variation in the degree of infection for the different sludge samples (102 to 256 eggs kg-1 d.m.). The inactivation of the helminth eggs in the compost can be accomplished, if the temperature inside of the reactor is sufficient as in the case M III and M IV. The final compost M III and M IV was well sanitized as a result of the high temperature achieved due to higher grass addition in those mixtures. Composts M I and M II can not be used in agriculture because of bad microbiological characteristic, however MII can be used for recultivation after hygienisation. The composted material assumed the appearance and structure similar to the so-called horticultural soil. As an exothermic process, composting caused very high loss of water in composted material. All the composts were granular, dark grey in color without foul odor and attained an ambient temperature after 30 days of composting, indicating the stable nature of composts. Additional researches are required in order to optimize the better organic and nitrogen compounds degradation during co-composting process.