Pilot-scale vermireactors for sewage sludge stabilization and metal remediation process: Comparison with small-scale vermireactors

Most of the previous studies on vermicomposting have been conducted as lab trials at small-scale (SS) using small quantity of waste mixtures. Efforts were made in this study to stabilize the sewage sludge amended with sugarcane trash using pilot-scale (PS) vermicomposting operation. Results of PS vermireactors were compared with SS trials in terms of quality of ready vermicompost and earthworm production rates. Results thus suggest a clear-cut difference between SS and PS in terms of waste mineralization rate and earthworm production. The waste mineralization rate in PS was significantly lower than SS (P < 0.05). Total N and available P were higher in end product from SS, while exchangeable cations (Ca2+ and K+) showed reverse behavior during the process of waste stabilization. There was significant difference between PS and SS for metal remediation rate in end materials. The growth and reproduction pattern of Eisenia fetida was completely different in PS as compared to lab trials, i.e. SS. Probably, the distinct earthworm stocking density and microclimate conditions in SS and PS were responsible for observed differences in results of waste mineralization rate and earthworm growth. This study suggests that SS laboratory trials may differ in PS field operations due to distinct behavior of earthworm in field conditions. It is concluded that SS laboratory trials should be tested in field at large-scale in order to measure the feasibility of technology for large-scale waste decomposition operations in open conditions.