Anaerobic Co-Digestion of Tannery and Slaughterhouse Wastewater for Solids Reduction and Resource Recovery: Effect of Sulfate Concentration and Inoculum to Substrate Ratio

Abstract

Anaerobic digestion is considered unsuitable for the bioremediation of tannery effluent due to process inhibition, mainly due to high concentrations of sulfur species, and the accumulation of H2S and/or NH3. This study using the standardized biochemical methane potential protocol showed that efficient processing is possible with slaughterhouse wastewater, provided sufficient functional biomass is present at the start of the process and the SO42− concentration is below inhibition threshold. Methanogenic activity (K = 13.4–17.5 and µm = 0.15–0.27) and CH4 yields were high when reactors were operated ISR ≥ 3 and/or lower SO42− ≤ 710 mg/L while high SO42− ≥ 1960 mg/L and ISR < 3.0 caused almost complete inhibition regardless of corresponding ISR and SO42−. The theoretical optimum operating conditions (922 mg/L SO42−, ISR = 3.72) are expected to generate 361 mL biogas/gVS, 235 mL CH4/gVS with reduction efficiencies of 27.5% VS, 27.4% TS, 75.1% TOC, 75.6% SO42−, and 41.1% COD. This implies that tannery sludge will be reduced by about 27% (dry mass) and SO42− by 76%, with a fraction of it recovered as S0. The models displayed a perfect fit to the cumulative CH4 yields with high precision in the order Logistic > Cone > modified Gompertz > first order.

Characteristics of Biogas Production from Organic Wastes Mixed at Optimal Ratios in an Anaerobic Co-Digestion Reactor

“…The results of the theoretical methane yield based on the elemental composition according to each OLR indicated that the theoretical methane yield increased owing to the increasing carbon content as the OLR increased [34]. A previous study improved the methane yield by adding carbon to the AD reactor [35]. The researchers reported that methane yield was improved as the carbon addition increased within an optimal OLR range [35].…”

“…A previous study improved the methane yield by adding carbon to the AD reactor [35]. The researchers reported that methane yield was improved as the carbon addition increased within an optimal OLR range [35]. It was concluded that food waste can produce more methane than other substrates because of its high carbon content.…”

“…The results of this study show that co-digestion can be operated fluidly by adjusting the mixing ratios of sewage sludge, food waste, and livestock manure. Moreover, a lower pH and alkalinity in food waste can be supplemented by livestock manure with a higher pH and alkalinity [38], and lower carbon content and biodegradability can be supported by food waste with higher carbon content and biodegradability [35,39]. These mutual supplementations can help to balance the reaction rates of each step by solving representative problems in the AD reactor, such as a low pH, lack of alkalinity, and the presence of toxic substances [35].…”

“…Moreover, a lower pH and alkalinity in food waste can be supplemented by livestock manure with a higher pH and alkalinity [38], and lower carbon content and biodegradability can be supported by food waste with higher carbon content and biodegradability [35,39]. These mutual supplementations can help to balance the reaction rates of each step by solving representative problems in the AD reactor, such as a low pH, lack of alkalinity, and the presence of toxic substances [35]. Therefore, co-digestion may be a realizable strategy for the improvement of biogas production and achievement of process stability when various substrates are mixed at optimal ratios [38,40].…”

Biological Desulfurization of Tannery Effluent Using Hybrid Linear Flow Channel Reactors

“…The characteristics of the TWW are given in Table 1. All analytical procedures were performed as previously described [18].…”