Influence of earthworms on the nitrogen transfer of sewage sludge in the vermifilter process.

A 6-year laboratory study was conducted to explore the performance of the vermifilter (VF) on reducing sewage sludge. Sewage sludge was found to be reduced significantly in the VF and exhibited a better performance of sludge reduction as compared with the conventional biofilter (BF), which could be traced through the nitrogen-rich organic matter. The nitrogen stable isotope technology was applied to study the matter flow of sewage sludge in the VF process and the influence of earthworms Eisenia fetida on sewage sludge reduction. Results showed that (1) the protein material could be consumed more than the polysaccharide and lipid materials, respectively, in the VF; (2) the presence of earthworms could enhance the consumption capacity of the VF on the protein-rich material of the sewage sludge; (3) earthworms played a leading role on the nitrogen lifting of the sewage sludge, leading to the performance difference of the effluent sludge or biofilm sludge between the VF and BF; (4) in the VF, nitrogen-isotope accumulation in either biofilms or earthworms happened more significantly in the lower layer than in the upper one, while nitrogen transfer of sewage sludge happened more significantly in the upper layer than in the lower one; (5) earthworms improved the feeding environment of organisms (microorganisms in biofilms, moth fly larvae, Limacidaes, and Lymnaeidaes); (6) biofilms, Limacidaes, and moth fly larvae performed better than leeches, Lymnaeidaes, and moth fly adults at nitrogen transfer of sewage sludge.