Effects of Earthworms and Effective Microorganisms on the Composting of Sewage Sludge with Cassava Dregs in the Tropics.

The present study revealed the role of earthworm (EW)-effective microorganisms (EM) in converting sewage sludge and cassava dregs into a valuable product. Sewage sludge was toxic to earthworm, therefore it was mixed with cassava dregs in the proportions 80:20 on dry weight basis. Treatments included mixed substrate inoculated vs. not inoculated with EM and treated with or without earthworms. The pH, total organic carbon, total nitrogen and C: N ratio decreased from the initial in the range of 17.43-18.46%, 25.48-33.82%, 19.60-25.37% and 6.68-14.05% respectively. But the electrical conductivity and available phosphorus increased from the initial in the range of 113.47-158.16% and 42.42-57.58% respectively. In addition, they interactively increased total phosphorus from 19.84-63.01% and potassium from 16.41-50.78%, and decreased the PAH content of substrate from 21.17-32.14% with increase in earthworms from 51.71-57.69 respectively. Earthworms and EM could be used together as an efficient method for co-composting SS plus CD in the tropics. This could be expected to result in, stabilization of waste, increase in the nutrients and reduction of pollutant content. Implication Statement The first reports of interaction of earthworms and effective microorganisms in the treatment of sewage sludge and cassava dregs in the tropics. Co-composting was an efficient technology for treating sewage sludge and cassava dregs at the same time, in the tropics. The survival rate of the earthworms both > 95%, the highest number of cocoons (640.33) and hatchlings (4694.33) both in EW+EM (Earthworms added and EM inoculated) treatment. Earthworms and EM (Only EM inoculated) interactively increased total phosphorus and potassium content, and decreased the PAH content of substrate with increase in earthworms.