PERFORMANCE EVALUATION AND MICROBIAL COMMUNITY DYNAMICS OF VERMIFILTRATION

Abstract

The present study was designed to determine the effect of earthworms and microbial community dynamics on the removal of pathogens and organic matter degradation during wastewater and solid waste treatment by vermifiltration. The study was divided in different phases. The results of a lab scale study showed that vermifiltration resulted in an effluent with biochemical oxygen demand (BOD) < 20 mg/L, chemical oxygen demand (COD) < 100 mg/L, total suspended solids (TSS) < 30 mg/L, and pathogens < 103 MPN/100 mL, signifying high treatment efficacy. The decay rate constant (k) for indicator organisms and pathogens was observed to be within the range of 5.99–7.96 md −1 and the population of total heterotrophic bacteria, total fungi and actinomycetes were reduced remarkably by 2–3 log, respectively. The suitability of different filter media (riverbed gravel, mud balls, wooden coal and glass balls) was explored during vermifiltration and results indicated that naturally occurring riverbed material and mud balls were found to be better suited for the treatment with higher pathogen removal efficacy. The higher BOD, COD, and pathogen removal efficiency, higher microbial diversity in the filter bed, increase in earthworm’s number and biomass, and no abrasions on the body walls of earthworms concluded that river bed material is a promising filter media. Overall, the observed trend of VFs in terms of treatment efficacy was observed to be riverbed material ≥ mud balls > glass balls > wooden coal. The study further investigated the microbial community dynamics and antibacterial & enzymatic properties of microorganisms in a vermifiltration system. It included the isolation and identification of diverse microbial community from a vermifilter (VF) with earthworms and its comparison with a conventional geofilter (GF) without earthworms. The burrowing activity of earthworms promoted the aeration conditions in VF which led to the predominance of the aerobic microorganisms, accounting for complex microbial community diversity. In vitro antimicrobial assay also showed that the present microflora had strong inhibitory efficiency against pathogens S. aureus, E. coli, P. aeruginosa and K. aerogenes. The release of antimicrobial substances by earthworms and associated microflora was found to be responsible for the removal of pathogens. The enzymatic activity of microorganisms is responsible for the biodegradation and stabilization of organic matter. The kinetics evaluation showed the predominance of first order removal model during vermifiltration. The study on the effect of seasonal temperature on the treatment efficiency and pathogen removal efficacy from wastewater was also performed. The results showed a significant effect on BOD & COD reduction, indicator organisms & pathogen removal, iii earthworm population, bacterial and actinomycetes population with a variation in ambient temperature, but had no effect on TSS removal and fungi population. The study showed that higher BOD and COD removal was accomplished during the spring and autumn period when the mean temperature was 25-27°C. This temperature range is optimum for the earthworm species Eisenia fetida for its activity, growth and reproduction and any variation in temperature from the optimum range led to decrease in treatment efficiency and earthworm population. The pathogen removal efficacy of VF increases with the increase in temperature, as shown by linear regression analysis, which implied that temperature had a significant contribution to the pathogen removal efficiency of VF. Pearson coefficient of correlation (r) derived an important relationship between the seasonal temperature and treatment efficiency, pathogen removal efficacy and microbial population during vermifiltration. The last phase of the study brings an insight to the performance evaluation of a pilot scale VF during the combined treatment of domestic wastewater and organic fraction of municipal solid waste (OFMSW). The study showed that VF resulted in an effluent with BOD < 20 mg/L, COD < 100 mg/L ammonia NH4 +-N ≤ 1 mg/L, nitrate NO- 3-N > 10 mg/L, and coliforms < 103 MPN/100 mL and mature vermicompost with high nutrient value (C: N ratio < 20) signifying high treatment and pathogen removal efficacy. A total of 41 bacterial colonyforming units (CFUs) were isolated, out of which 12 strains were selected, that exhibited higher antimicrobial activity against tested pathogenic bacteria and fungi. The comparative sequence analysis of 16S rRNA genes showed two phylogenetically different clusters of the characterized bacterial strains. Six strains were affiliated with Firmicutes (Family Bacillaceae and Enterococcaceae), and six with γ-Proteobacteria (Family Enterobacteriaceae). The identified strains contribute to enhance the disinfection efficiency during wastewater treatment