Alternate: Enhancing Anaerobic Digestion of Sewage Sludge Through Strategic Bioaugmentation with Optimized Microbial Consortia

Abstract The transition to a circular economy, prompted by increasing population, urban growth, and economic advancements, underscores the need to recover resources from waste. Anaerobic digestion (AD) is a valuable method for stabilizing organic waste and producing renewable biogas rich in methane; however, it encounters obstacles such as operational instability, fatty acid buildup, ammonia inhibition, and suboptimal yields. This study explores the potential of the novel Ydro Process® bioaugmentation in sewage sludge AD. Results demonstrated that pre-hydrolysis of sludge occurred, indicated by a rise in volatile fatty acids (VFA) from 134 mg HAc/L in untreated TWAS to 997 mg HAc/L in bioaugmented sludge, alongside increased soluble chemical oxygen demand (SCOD) yields. Additionally, sludge viscosity dropped by 41% with the Ydro Process® bioaugmentation. Biogas output rose markedly, from 732 mL/day to 1338 mL/day in semi-continuous digestion, with methane yields improving from 116 mL/g TCODadded to 218 mL/g TCODadded. Microbial analysis further revealed a greater presence of hydrogenotrophic methanogens. Keywords: Bioaugmentation, Microbial Community, Resource Recovery, Anaerobic Digestion Introduction Rapid urbanization, industrial growth, and population expansion have increased municipal waste production to unprecedented levels, with global municipal solid waste exceeding 2 billion tons in 2020 [1]. North America alone produces over 85 billion cubic meters of wastewater biosolids annually [2]. Amidst a rising energy crisis, a shift toward resource recovery from municipal sewage sludge-particularly biogas and volatile fatty acids (VFAs)-has become essential. Anaerobic digestion (AD) is a sustainable option that stabilizes organic waste and generates renewable biogas through a sequence of microbial processes. However, effective biological breakdown of complex organics in sewage sludge often requires pre-treatment, including thermal, chemical, and biological methods, each with associated costs. Biological additives, such as bioaugmentation, enhance AD by boosting microbial diversity or enzyme activity, offering potential remediation against operational challenges like ammonia inhibition [3-4]. This study assesses the potential of Ydro Process® bioaugmentation-a microbial treatment developed by Hydrotech Environmental L.P. and Tradeworks Environmental Inc.-to enhance AD efficiency in thickened waste-activated sludge (TWAS). Ydro Process® combines targeted microorganisms, nutrients, bio-enhancers, and hydrolyzing enzymes tailored for challenging waste types such as those from meat processing and agriculture. The primary aim is to evaluate how Ydro Process® impacts energy recovery and biogas production in TWAS anaerobic digestion. Methodology Two continuously stirred tank reactors (CSTRs) were operated under mesophilic conditions (37 ± 1 °C) with a working volume of 1.5 L. The CSTRs, made of glass and equipped with spouts, airtight caps, and mechanical stirrers, were submerged in a water bath set to 45 °C to maintain the internal temperature at 37 ± 1°C, adjusted daily due to evaporation. Initially, both reactors used raw thickened waste-activated sludge (TWAS) as a control, followed by Ydro Process®-activated TWAS for bioaugmentation analysis. Each reactor was started with 1 L of seed and 0.5 L of TWAS, and both systems were maintained at pH 7 and fed daily with 100 mL to sustain a 15-day hydraulic retention time over 187 days. Biogas was collected in Tedlar gas sampling bags for daily measurement. For Ydro Process® activation, a freeze-dried mixture was matured with dechlorinated water for 12 hours, then mixed with digestate at a 10% ratio for 6 hours before feeding. Analytical methods included measuring solids, viscosity, and chemical oxygen demand following Standard Methods [5]. Samples were centrifuged, filtered, and analyzed spectrophotometrically. DNA extraction from centrifuged sludge was performed using a PowerSoil kit, and sequencing targeted 16S rRNA. Microbial diversity was analyzed through QIIME2, with Spearman's correlation and chord diagrams visualizing microbial taxa relationships in the TWAS samples. Results Following the introduction of Ydro Process®-activated TWAS, daily biogas production significantly rose to 1440 mL/day, later stabilizing at 1338 mL/day after a three-SRT acclimation period for microbial adaptation (Fig.1). Throughout, pH levels remained stable between 7 and 7.65. Biogas analysis showed methane contents of 55% for raw TWAS and 61% for the Ydro-activated system. Methane production demonstrated a 52% increase in average daily output, attributed to the bioaugmentation's specialized microbial blend that enhanced both methane volume and quality. A microbial analysis was conducted to correlate biogas production with the tailored microorganisms. The results revealed a significant increase in the abundance of various fermenters and hydrolytic bacteria in the bioaugmented digestate sample (Fig.3). Conclusion Ydro Process® bioaugmentation significantly improved the anaerobic digestion of TWAS, doubling daily methane production and increasing methane yield by 87% (from 116 to 218 mL/g COD added). It also enhanced sludge characteristics, with TCOD levels rising, SCOD increasing fourfold, and VFA concentrations reaching 4-7 times those of raw TWAS, all while maintaining stable pH. Bioaugmentation balanced the microbial community, boosting digestion efficiency by shifting populations toward hydrogenotrophic methanogens.