Enhancement of The Start-up of an Up-flow Anaerobic Sludge Blanket Reactor Using Electrochemically Enriched Biofilms

Abstract

With rising issue of wastewater discharge and resulting pollution, anaerobic wastewater treatment has emerged as a prominent technology to overcome these issues. A myriad of anaerobic treatment techniques has demonstrated appreciable results in treating high strength wastewaters, with high-rate digesters being the popular option. The up-flow anaerobic sludge blanket reactor (UASB) is a high-rate anaerobic digester capable of achieving high COD removal rates under high organic and hydraulic loadings. A critical feature of the start-up of an UASB reactor is the acclimation of the inoculated biomass through a process known as granulation. Granulation is characterized by the agglomeration of specific types of bacterial and methanogenic archaea known to possess electroactive properties which allow cell to cell attachment through a mechanism known as direct interspecies electron transfer (DIET). Recently, several species known to be DIET participants, labeled as electroactive microbes, have been selectively enriched in microbial electrolysis cells known as bio-electrochemical reactors (BER) through applying constant electrode potentials favoring their proliferation through catalytic metabolism of reactor substrates. In this framework, the following thesis aimed to enhance the granulation and performance of an UASB reactor fed with high strength wastewater through supplementation with electroactive species enriched using BERs. An anodic BER (ABER) was poised at +400 mV vs Ag/AgCl to enrich electroactive bacterial species at the working electrode whereas a cathodic BER (CBER) was poised at -700 mV vs Ag/AgCl to enrich electrotrophic methanogens. After 5 feeding phases, the biofilms were extracted from the working electrodes of both BERs, in addition to the counter electrodes. An UASB reactor, operated at a HRT of 48 hours and OLR of 1 g-COD/L.d, was operated in two phases: Phase 1 being the control run and Phase 2 supplemented with the BER enriched biomass. Electrochemical analyses were performed on the BERs which showed the development of electrode respiring microbial communities based on cyclic voltammograms and chronoamperometric scans. Better COD and VSS removal rates were achieved in UASB Phase 2 as compared to Phase 1. Phase 2 COD removal of 85% was achieved in 20 days, whereas the same COD removal was achieved in 62 days for Phase 1. Settleability tests performed on the developed sludge in the UASB bed showed a highly granular sludge (SVI = 8.5 mL/gTSS) in Phase 2 compared to flocculant sludge (SVI = 33 mL/gTSS) in Phase 1 after 20 days of operation. The findings of this study prove that electrochemically enriched biofilms can be utilized in anaerobic digesters through direct supplementation of biofilms, rather than hybrid system integration, and can exhibit improved reactor performance.