Valorization of fecal sludge stabilization via vermicomposting in microcosm enriched substrates using organic soils for vermicompost production

High generation of fecal sludge without proper treatment is a major sanitation problem. A key step in curbing this problem is producing value-added resources such as vermicompost from fecal sludge through substrate enrichment. Substrate enrichment is a vermicomposting technique that involves augmenting vermibed substrates with organic rich materials to provide additional nutrients, as well as underlying layers needed for microcosm development to produce desirable vermicompost. The aim of this study was to investigate effects of substrate enrichment with organic soils (black soil, red laterite soil and sandy soil) combined with coconut coir as bulking material, on the fecal sludge vermicomposting process and quality of the end-product. The purpose of the study was to promote the development of highly nutritive vermicompost from fecal sludge using substrate enrichment as a low-cost innovative vermicomposting technique. The enriched substrates were prepared with 160g of coconut coir, 120g of fecal matter (65–70% dry matter) and 80g of organic soil. The treatments were labelled T(1), T(2) and T(3) representing systems containing black soil, red laterite soil and sandy soil respectively. The control treatment (T(4)) contained no soil. Triplicate treatments were setup and about 20 3-week old clitellated earthworms of the species Eisenia. fetida with live weights ranging from 255 to 275mg, released into each system for vermicomposting over a period of 12 weeks. Physicochemical parameters such as pH, Organic Carbon (C(org)), Total Nitrogen (N(tot)), Available Phosphorus (P(avail)), Exchangeable Calcium (Ca(exch)), Iron (Fe), Lead (Pb) and Aluminium (Al) were determined for both the fecal sludge and the vermicompost. The vermicompost in the setup with black soil (T(1)) showed the highest C(org) mineralization and N(tot), P(avail) and Ca(exch) enhancement followed by T(2), T(3) and T(4). Treatment T(1) also resulted in the lowest concentration of Fe, Pb and Al in the vermicompost. Concentrations of these heavy metals were found to be higher in the other treatments in increasing order of T(2), T(3) and T(4). Less than 16% earthworm mortality was recorded in all treatments except T(4), in which the mortality was about 38% (38.33 ± 13.74). The enriched substrates were therefore found to provide a more suitable microclimate for earthworm development and produced vermicompost with high nutrient content. However, a more comprehensive study on metal accumulation in the earthworm tissues as a potential metal contaminant is needed to establish a strong hypothesis in the safe use of earthworms for this vermicomposting technique.