Chemically Enhanced Primary Sludge as an Anaerobic Co-Digestion Additive for Biogas Production from Food Waste

Abstract

In order to overcome process instability and buffer deficiency in the anaerobic digestion of mono food waste (FW), chemically enhanced primary sludge (CEPS) was selected as a co-substrate for FW treatment. In this study, batch tests were conducted to study the effects of CEPS/FW ratios on anaerobic co-digestion (coAD) performances. Both soluble chemical oxygen demand (SCOD) and protease activity were decreased, with the CEPS/FW mass ratio increasing from 0:5 to 5:0. However, it was also found that the accumulation of volatile fatty acids (VFAs) was eliminated by increasing the CEPS/FW ratio, and that corresponding VFAs concentrations decreased from 13,872.97 to 1789.98 mg chemical oxygen demand per L (mg COD/L). In addition, the maximum value of cumulative biogas yield (446.39 mL per g volatile solids removal (mL/g VSs removal )) was observed at a CEPS/FW ratio of 4:1, and that the tendency of coenzyme F420 activity was similar to biogas production. The mechanism analysis indicated that Fe-based CEPS relived the VFAs accumulation caused by FW, and Fe(III) induced by Fe-based CEPS enhanced the activity of F420. Therefore, the addition of Fe-based CEPS provided an alternative method for FW treatment.Chemically enhanced primary sedimentation (CEPS) is produced during the chemically enhanced primary treatment process of wastewater treatment plants (WWTPs) using an Fe/Al-based coagulant addition that contains a large amount of polymeric sludge rich in Fe/Al. As described by Lin [14], ferric chloride (FeCl 3 ) (10-12 mg Fe/L of dosage) was used to enhance the primary wastewater treatment of the Stonecutters Island Sewage Treatment Works in Hong Kong, and a large number of Fe-based CEPS sludge was produced. Fe is an essential trace metal for anaerobic microorganisms that participates in the synthesis of some important metalloenzymes in methanogenesis [15]. It has been demonstrated that addition of ferric chloride could disinhibit excessive volatile fatty acids [16] and enhance biogas production by enriching Coprothermobacter for protein fermentation and Methanosarcina for methanogenesis from the perspective of microorganisms [17]. It has been proposed that the introduction of FeCl 3 might contribute to a reduction of VFAs content and protect methanogenesis from the accumulation of volatile acids. Thus, the effects of Fe-based CEPS on VFAs reduction and methanogenesis during the coAD of FW need to be studied deeply.This study intends to explore coAD performance of FW and Fe-based CEPS from the perspective of organic matter degradation, while simultaneously investigating the relationship between biogas production and Fe-based CEPS content under mesophilic digestion. Different mixing ratios of the CEPS and FW were conducted to study the typical substances involved in the coAD process, including organic substrate solubilization, VFAs variation, and biogas production. Meanwhile, representative enzyme activities associated with AD were monitored to analyze process stability of biogas production. Materials and Methods Substrat...

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“…The pH of fermentation solution was fixed to 7.2 with sodium bicarbonate solution at the start-up period in the ABD reactor, and slightly increased to 7.41 after a short decrease on the second day. The pH decrease was caused by the acidification of food waste in the acidogenesis step, but it turned to a self-adapted range when the acidogenesis and methanogenesis reached a balanced state [6,33]. The same phenomenon was obtained in the control reactor, wherein the pH increased from 7.2 to 7.28 ( Figure 3).…”

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