ABSTRACT
Energy recovery while treating low organic loads has been investigated using longitudinal tubular microbial fuel cell (MFC) reactors. Duplicate reactors, each consisting of two modules, were operated with influent sucrose organic loading rates (OLRs) between 0.04 and 0.42 g COD/l/d. Most soluble COD (sCOD) removal occurred in the first modules with predominantly VFAs reaching the second modules. Coulombic efficiency (CE) in the second modules ranged from 9% to 92% which was 3-4 times higher than the first modules. The maximum energy production was 1.75 W h/g COD in the second modules at OLR 0.24 g/l/d, up to 10 times higher than the first modules, attributable to non-fermentable substrate. A simple plug flow model of the reactors, including a generic non-electrogenic reaction competing for acetate, was developed. This modular tubular design can reproducibly distribute bioprocesses between successive modules and could be scalable, acting as a polishing stage while reducing energy requirements in wastewater treatment.
Subject(s)
Bioelectric Energy Sources/microbiology , Conservation of Energy Resources/methods , Organic Chemicals/chemistry , Sucrose/chemistry , Waste Disposal, Fluid/methods , Water Purification/methods , Biodegradation, Environmental , Bioreactors/microbiology , Computer Simulation , Electricity , Kinetics , Models, Chemical , Oxygen/isolation & purification , SolubilityABSTRACT
The global flour industry produces 96 million ton/year of wheatfeed, which is mainly used for animal feed. This co-product is high in carbohydrates and potentially a significant substrate for biohydrogen production. A 10 l bioreactor, inoculated with sewage sludge, was operated on wheatfeed (10 g l(-1)) at pH 5.5 and 35 degrees C in batch and semi-continuous mode (15 h hydraulic retention time (HRT)). Wheatfeed hydrolysate was also investigated in continuous mode (15 h HRT). NaOH-H2O2 treatment of 25 g l(-1) wheatfeed resulted in hydrolysate containing on average 8.1 g l(-1) total sugar. Hydrogen yields of 64 and 56 m3 H(2) per ton dry weight were produced from wheatfeed in batch and 56 m3 H2 per ton dry weight of wheatfeed in semi-continuous mode. Hydrogen yields from hydrolysate were only 22 and 31 m3 H2 per ton dry weight, (or 0.9 mol H2 per mol hexose degraded, assuming all sugar is hexose). Fermentation of unhydrolysed wheatfeed is therefore recommended. It is calculated that approximately 264 m3/ton of CH4 can be produced from a subsequent anaerobic digestion stage. The biohydrogen produced (diesel equivalents) from the 1.2 million ton/year of wheatfeed in the UK would be more than twice that required for transportation by the UK flour industry.
