Bioconversion of organic wastes: treatment sludges, animal manures, and agricultural wastes

This study aimed to investigate the compostability of treatment sludge and to determine the effects of adding different animal manures (cattle, pig, horse, and chicken) and agricultural waste (sunflower stalks) on the composting process. Five different compost reactors (M1, M2, M3, M4, and M5) were operated. Sunflower stalks were added to all reactors as a bulking agent at the rate of 20%. Treatment sludge (80%) and bulking agent were added to the M1 reactor, where animal manure was not added, while 40% treatment sludge and 40% animal manure were added to the other reactors. In the reactors where animal manure was added, cattle (M2), pig (M3), horse (M4), and chicken (M5) manure were used, respectively. The temperature, pH, electrical conductivity, organic matter (OM), carbon to nitrogen ratio (C/N), total Kjeldahl nitrogen, and total phosphorus were monitored during the 21-day process. The highest OM loss (64.8%) occurred in the M2 reactor, and the maximum temperature (62.7 degrees C) was achieved. The high temperatures reached in the reactor increased microbial activity, resulting in rapid decomposition of OM and elimination of pathogens. With a maximum reduction in the C/N ratio (40%), carbon and nitrogen balance was achieved, thus obtaining a more stable and higher quality compost for plants in this reactor. In the M1 reactor, where only treatment sludge was composted, lower microbiological activity occurred compared to the other mixtures due to the lack of substrate. It can be said that composting treatment sludge together with animal manures will provide higher quality end products.