Carbon dioxide and methane emissions during composting and vermicomposting of sewage sludge under the effect of different proportions additive of straw pellets

Sewage sludge poses a serious threat to the environment as the world struggles to keep up with its rapid generation. Biological waste treatment technologies such as composting and vermicomposting are widely regarded as clean and sustainable methods to manage sewage sludge. The aim of this study was to evaluate the carbon dioxide and methane emissions during composting and vermicomposting of sewage sludge under the effect of different proportions of additive straw pellets. Composting and vermicomposting with Eisenia Andrei treatments were conducted over a 60 days lasting period, taking sewage sludge as the processing object and using pelletized wheat straw as the additional substrate. Four treatments were set up (T1) 100% sewage sludge, (T2) 75% sewage sludge + 25% pelletized wheat straw,(T3) 50% sewage sludge + 50% pelletized wheat straw, (T4) 25% sewage sludge + 75% pelletized wheat straw. The percentage is presented as the weight ratio of both substrates for all treatments. All the treatments were transferred to fermenter barrels for composting and also, the same treatments used in composting were transferred to worm-bins for vermicomposting. Methane and carbon dioxide concentration in the gas phase released from treatments were daily measured. The results indicated that both composting and vermicomposting produce a significant (p≤0.001) amount of methane and carbon dioxide emissions from all treatments. The results showed that vermicomposting significantly reduced methane emissions by 38%, 34%, and 18% for treatments contains 25%, 50%, and 75% straw pellets respectively compared to composting. The same proportions of pelletized wheat straw used in composting increased carbon dioxide emissions during vermicomposting by 75%, 64%, and 89%. In conclusion, vermicomposting is effective at reducing greenhouse gas emissions from composting. Therefore, from this finding, vermicomposting could represent an option for reducing gas emissions particularly the emission of methane which is radiatively stronger than carbon dioxide.

Acknowledgment: Financial support for this work was provided by the Ministry of Agriculture of the Czech Republic under the NAZV project number QK1910095.