WERF Odor Study Phase III: Effect of Alum Addition on Odorant Production from Anaerobically Digested Biosolids

Abstract

In recent years, extensive research has been performed to verify and identify offensive odor gases of their production mechanisms during biosolids cake storage prior to land application. It was identified that volatile organic sulfur compounds (VOSCs) including methanethiol (MT), dimethyl sulfide (DMS), and dimethyl disulfide (DMDS) contribute to the offensive odor. The formation of VOSCs was linked to microbial degradation of biomolecules, specifically residual proteins, thus mitigation measures were recommended to reduce the bioavailable portion of proteins in biosolids. In this research, alum (aluminum sulfate) was used as a potential binder to reduce accessibility of soluble proteins in biosolids, thus prevent them from biodegradation. Both laboratory trials and field trials were performed to verify the potential of alum on biosolids odor reduction. The laboratory trial results indicated that alum can effectively reduce biosolids odor, and up to 100% removal of total VOSCs (TVOSCs) was observed at high doses of alum. In a field trial, although not 100% removal, up to 55% peak TVOSCs reduction was observed. In addition, alum also reduced polymer demand required to achieve optimum polymer dose for dewatering which could offset alum costs.

Impacts of aluminum‐ and iron‐based coagulants on municipal sludge anaerobic digestibility, dewaterability, and odor emission

“…It should be noticed that when sulfate‐containing aluminum slats were added into the feed of anaerobic digesters, the VSCs level may be elevated as a result of the conversion of sulfate contained in aluminum‐based coagulants to H 2 S by sulfate reduction bacteria (Abbott & Eskicioglu, 2015; Akgul et al, 2017). Previous studies have shown that both aluminum and iron cations can reduce odor emission from dewatered biosolids (Table 4), that is, up to 100% VOSCs reduction with the aluminum cations dose at 4% (g Al 3+ g −1 dry) has been achieved in a laboratory trial (Chen, Adams, Erdal, Forbes, Hargreaves, Higgins, & Witherspoon, 2007), and 20%–55% total VOSCs reduction with the aluminum cations dosage at 2%–4% has been achieved in field trials (Chen, Adams, Erdal, Forbes, Hargreaves, Higgins, & Witherspoon, 2007; Gruchlik et al, 2013; Higgins, 2010). Similarly, iron addition at the doses of 2% and 4% (g Fe 3+ g −1 dry solids) resulted in 23% and 50% VOSC reduction in dewatered biosolids, respectively (Gruchlik et al, 2013).…”

“…For example, H 2 S and MT are the microbial degradation by‐products of sulfur‐containing amino acid such as methionine and cyctein (Higgins et al, 2006). Aluminum‐/iron‐based coagulants can bind the bioavailable proteins in dewatered biosolids, which in turn reduces the pool of odor precursors (Abbott & Eskicioglu, 2015; Chen, Adams, Erdal, Forbes, Hargreaves, Higgins, & Witherspoon, 2007; Novak & Park, 2010; Park & Novak, 2013). Additionally, iron can react with sulfide ions to form highly insoluble FeS precipitates.…”