Using municipal solid waste as a carbon source for biogenic H2S production

Abstract

Hydrogen sulfide (H2S) is a precipitant used widely for metal recovery in metallurgical industries. A potentially low-cost method for producing H2S utilizes two waste products: municipal solid waste (MSW) and sulfate-rich wastewater. In this process, MSW serves as the electron donor and sulfaterich wastewater functions as an electron acceptor for sulfate-reducing bacteria (SRB) to produce H2S through the anaerobic respiration of SRB. The free liquid that is generated in a MSW landfill, referred to as leachate, has previously been tested as an electron donor for SRB. However, with high concentrations of recalcitrant organic carbon and biodegradable carbon typically scavenged by fermentative and methanogenic microorganisms, the use of leachate typically results in poor sulfate reduction rates. The liquor from the anaerobic fermentation of MSW (composed primarily of volatile fatty acids (VFAs)) could instead provide a more concentrated and readily available source of electron donors for SRB. Yet, the variability in the composition of organics within the liquor combined with the versatility of SRB and the presence of competitors for substrates results in poor predictions of sulfate reduction rates. Furthermore, the combined use of liquor from MSW fermentation (fermenter liquor) and sulfaterich wastewater would serve as an exemplar for using two locally available waste sources to produce a valuable resource of local demand. However, the high salinity of some sulfate wastewater streams, particularly in arid regions such as Australia, is found to make biological sulfate reduction less effective. Therefore, to explore the combined use of the two waste streams, the aim of this study was to examine the effectiveness of MSW fermenter liquor as an electron donor to be used with high salinity sulfate streams for biological H2S production. Studies have found that a limitation to using VFA mixtures as a feed to SRB cultures is that acetate is often not metabolized. As such, the capacity of different inocula to utilize all the fermentation products of MSW for sulfate reduction was investigated. The three inocula chosen for investigation were biofilm from a laboratory-scale reactor fed with sewage, sediment from a brackish mangrove, and sediment from a saline estuary. The salinities of the environments from which the inocula were sourced were maintained throughout the enrichment. The performance of each inoculum was evaluated for the extent that the chemical oxygen demand (COD) was utilized by SRB. The study found that the mangrove and estuarine inoculated reactors demonstrated higher sulfate removal efficiencies (80-88%) compared to the biofilm inoculated reactors (32-49%) as a result of the efficient use of COD. To explore VFA usage by sulfate-reducing cultures exposed to high salinity sulfate streams, the culture enriched from the estuarine sediment and hence grown under saline conditions of 20 g NaCl/L was subject to salinity increments of 7.5 g NaCl/L from 20 to 50 g NaCl/L. With a feed of ii synthetic fermenter liquor (VFA ...