The main objective of this study is to investigate the potentiality of cellulase producing isolates, Bacillus licheniformis 1-1v and Bacillus sonorensis 7-1v, as microbial additives on composting of rice straw materials. Different pyramid shape piles were constructed, and each contained 80 kg of rice straw and 288 kg of cattle manure, with/without 5 kg of feldspar supplementation (0.75%, w/w). C/N ratio was adjusted to 35.8 before microbial inoculation. The piles were inoculated with either single strain or mixed cultures. The physical, chemical and biological parameters indicating the decomposition of organic material, maturation and quality of the compost product were investigated during the composting process. A rapid increase in compost temperature was obtained in inoculated piles. Moreover, piles containing mixed inoculants exhibited longer time at high temperatures >55 °C for 15 consecutive days compared to control treatments that lasted for only 5 consecutive days. The microbial inoculation had greatly reduced the composting time by 40–43% (from 89–96 days to 51–58 days). Additionally, it resulted in a higher decrease in the total organic carbon and carbon-to-nitrogen ratio, as well as increase in compost quality by an increase in total nitrogen, phosphorus, and potassium content. The analysis of moisture content, bulk density, pH value, electrical conductivity, phytotoxicity, and pathogenic bacterial content of the final compost products exhibited maturation and good quality of final product to be used without any limitations.
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