Evaluating the potential of a novel anaerobic baffled reactor for anaerobic digestion of thin stillage: Effect of organic loading rate, hydraulic retention time and recycle ratio

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Highlights

The performance of a novel anaerobic baffled reactor was evaluated at various organic loading rate (OLR).

Increasing the recycle ratio (RR) reduced the average volatile fatty acid concentration.

Increasing the RR increased the COD removal contribution of latter compartments.

The rate of sludge wash out increased as a result of increasing RR or decreasing HRT.

Nutrient recycling from the effluent of the bioreactor was evaluated for struvite precipitation.

Abstract

Anaerobic digestion of thin stillage in a novel anaerobic baffled reactor (ABR) was evaluated with respect to the selected operating conditions including organic loading rate (OLR), hydraulic retention time (HRT) and recycle ratio (RR). The hybrid ABR achieved the chemical oxygen demand (COD) removal, sulfate removal and methane yield of 92.5-78.9%, 97-93% and 305-275 mL CH4 g−1 CODremoved, respectively at OLR of 3.5–6 kg COD m−3 d−1, HRT of 20-11.7d and RR of 15. However, the COD and sulfate removal and methane yield didn’t change significantly at the RR range of 10–20 and OLR of 3.5 kg COD m−3 d−1 (HRT of 20d). Results showed that, increasing RR from 10 to 20, increased the contribution of later compartments to COD removal from 9% to 16%. On the other hand, the composition of VFA changed in response to the change in OLR. The removal of nitrogen and phosphorus from thin stillage digestate was around 37% and 49% in the novel ABR, respectively due to struvite precipitation. Struvite precipitation from the effluent of novel ABR with the addition of magnesium led to further nitrogen and phosphorus removal of 44% and 81%, respectively, indicating the potential of digestate for nutrient recycling.

Keywords

Thin stillage

Anaerobic digestion

Recycle ratio

Hydraulic retention time

Hybrid anaerobic baffled reactor

© 2018 Elsevier Ltd. All rights reserved.

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