Co-composting of coir pith and cow manure: initial C/N ratio vs physico-chemical changes

Background: As objective of this study was focused on efficacy of composting of a recalcitrant organic waste material, co-composting of coir pith with cow manure and rice bran was endeavored to evaluate influence of initial C/N ratios, i.e., 30, 25, and 20, on physico-chemical changes, e.g., temperature, pH, organic matter (OM) degradation, and total nitrogen (TN) losses. Results: Results showed that OM and TN losses were significantly affected by C/N ratio (p < 0.05), whereas C/N ratio played insignificant role on temperature and pH evolution within the pile (p > 0.05) during composting process. OM and TN losses were highest within the first 2 weeks of thermophilic phase. Through the composting process, pile with 25 C/N ratio showed the highest biodegradation rate constant of organic matter (k = 0.309 day−1) and the highest TN losses (41.9%), while pile with C/N ratio of 30 showed the lowest N loss (−7.3%). However, for all three compost piles, maturity, as indicated by the pile temperature converging to the ambient temperature, was attained within 1 month post-composting. Conclusion: Results suggested that simple pile turning yielded effective co-composting of coir pith under comparatively low C/N ratio. Considering the composting performance and the amount of coir pith to be utilized, the initial C/N ratio of 30 was considered suitable for coir pith composting.