Quality index assessment for compost derived from municipal solid waste using novel bacterial consortia

Abstract

Composting is one of the integral components of the global circular bio-economy platform. Traditional composting requires a prolonged time, and the inoculation of efficient bacterial consortia is a novel technique to enhance the composting rate. Further, assessing compost quality is crucial because the application of immature compost can cause phyto-toxicity, damage the natural ecological balance and disrupt soil structure. The present study focused on the quality assessment of compost produced by five novel microbial consortia (C1–C5) using indexing methods; Clean Index (CI), Fertilizing Index (FI), Germination Index (GI) and Vigor Index (VI). The experiment was conducted using an organic fraction of Municipal Solid Waste (MSW); composed bins made out of concrete were filled with 90 kg of MSW and 2% of v/w each broth consortia were separately inoculated. The experiment was conducted in an open environment, and all the treatments were triplicated. A control treatment with three replicates was used without the addition of any broth consortia. The bins were closely monitored over 30 days for the composting parameters including the pH, conductivity, bulk density and the compost analysis was done following the standard methods. The FI was determined based on the characterization results of the final compost and the CI was determined based on the analyzed heavy metals Cd, Zn, Cr, Pb and Cu analysis carried out using the ICP-OES technique following the acid digestion. The GI and VI were determined using healthy and mature green gram (Vigna radiate) seeds and data were statistically analyzed using Tukey’s test. The FI and CI were calculated using a weighting scale of heavy metals based on their toxicity and the GI and VI were calculated based on the seed germination and their radical lengths. Based on the results, the FI, CI, GI and VI values were significantly different (p < 0.05) and ranged from 3.0–4.5 and 4.0–5.0, 72.4–110.2 % and 364.8–551.0 respectively. Further, the greatest FI, CI, GI and VI values were recorded in the C5 compost, which inoculated the consortium which comprises Bacillus haynesii (PP391133), Bacillus amyloliquefaciens (PP391056) and Bacillus safensis (PP391033) strains. Consequently, the compost produced by the C5 consortium was categorized into the compost quality “A” category indicating its high quality and fertilizing potential. In contrast, the control compost belonged to the compost quality “D” category indicating the lowest quality. Thus, the results evidenced the potential applicability of the C5 consortium to produce good quality compost as a sustainable waste management approach.