Addition of Different Biochars as Catalysts during the Mesophilic Anaerobic Digestion of Mixed Wastewater Sludge

Marco Chiappero,Francesca Cillerai,Ondřej Mašek,Silvia Fiore,Franco Berruti

doi:10.3390/catal11091094

Marco Chiappero, Francesca Cillerai + Show 3 more

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https://doi.org/10.3390/catal11091094

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Abstract

Biochar (BC) recently gained attention as an additive for anaerobic digestion (AD). This work aims at a critical analysis of the effect of six BCs, with different physical and chemical properties, on the AD of mixed wastewater sludge at 37 °C, comparing their influence on methane production and AD kinetics. AD batch tests were performed at the laboratory scale operating 48 reactors (0.25 L working volume) for 28 days with the addition of 10 g L−1 of BC. Most reactors supplemented with BCs exhibited higher (up to 22%) methane yields than the control reactors (0.15 Nm3 kgVS−1). The modified Gompertz model provided maximum methane production rate values, and in all reactors the lag-phase was equal to zero days, indicating a good adaptation of the inoculum to the substrate. The potential correlations between BCs’ properties and AD performance were assessed using principal component analysis (PCA). The PCA results showed a reasonable correlation between methane production and the BCs’ O–C and H–C molar ratios, and volatile matter, and between biogas production and BCs’ pore volume, specific surface area, and fixed and total carbon. In conclusion, the physic-chemical properties of BC (specifically, hydrophobicity and morphology) showed a key role in improving the AD of mixed wastewater sludge.

Highlights

Wastewater treatment plants (WWTPs) generate large amounts of sludge, whose management can account for up to the 30% of the capital costs and 50% of the total operating costs of a WWTP [1], and up to 40% of the total greenhouse gas emissions [2]
Cellulose, hemicellulose, and lignin are reduced to carbon in BCs, whereas mineral constituents tend to accumulate in ashes
This work investigated the impacts of six BCs with different physic-chemical properties on methane production and kinetics during the Anerobic digestion (AD) of mixed sludge (MS)

Summary

Introduction

Wastewater treatment plants (WWTPs) generate large amounts of sludge, whose management can account for up to the 30% of the capital costs and 50% of the total operating costs of a WWTP [1], and up to 40% of the total greenhouse gas emissions [2]. Wastewater sludge is considered a resource for the recovery of materials [3,4] and energy [5]. Anerobic digestion (AD) is an established technology used for the stabilization of wastewater sludge and its energy recovery in the form of biogas. To increase the methane yields from the AD of sludge, which can affect its economic feasibility, many solutions have been proposed, e.g., physical, chemical, and biological pre-treatments [9,10] or co-digestion with other substrates [11,12]. The implementation of these solutions requires additional capital investments and retrofitting of existing facilities [13]

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