No abstract

No abstract

Carbon dioxide (CO) injection in anaerobic digestion has recently been proposed as an interesting possibility to boost methane (CH) recovery from sludge and organic waste by converting a greenhouse gas into a renewable resource. This research assessed the effects of exogenous CO injection on performance and process stability of single-phase continuous anaerobic digesters. Two pilot scale reactors treating sewage sludge were operated for 130days. One reactor was periodically injected with CO while the other acted as control. Two injection frequencies and injection devices were tested. The results indicated that CO enrichment allowed an increase in CH production of ca. 12%, with a CH production rate of 371±100L/(kgVS·d) and a CH concentration of ca. 60% when dissolved CO levels inside the test reactor were increased up to 1.9-fold. Results also indicated an improvement in process resilience to temporary overloads and no impacts on stability parameters.

Energy consumption of the water sector presents an increasing energy demand, contrary to GHG mitigation aims. As a result, research aimed at capturing emitted CO 2 and at developing treatment technologies with a low energy demand and increased renewable energy production has increased, leading to a surge in implementation of anaerobic digestion (AD). Valorisation of the biogenic CO 2 emitted with biogas AD (estimated at over 1 MtCO 2 per annum for the UK water and organic waste sectors), presents an opportunity to further reduce carbon footprint and support energy supply decarbonisation. This paper reviews bioconversion of CO 2 into CH 4 in ADs (without addition of H 2) as a means to valorise CO 2 emissions. The review has concluded this to be a promising solution to reduce carbon footprint and uplift renewable energy production. However, in order to increase readiness for implementation (1) the mechanisms of CO 2 utilisation need to be elucidated, including the sources of additional H 2 needed, (2) studies need to report more thoroughly the conditions of CO 2 injection and (3) trials where ADs are integrated with gas to liquid mass transfer technologies need to be performed.

The increasing concentration of carbon dioxide (CO2) in the atmosphere and the stringent greenhouse gases (GHG) reduction targets, require the development of CO2 sequestration technologies applicable for the waste and wastewater sector. This study addressed the reduction of CO2 emissions and enhancement of biogas production associated with CO2 enrichment of anaerobic digesters (ADs). The benefits of CO2 enrichment were examined by injecting CO2 at 0, 0.3, 0.6 and 0.9 M fractions into batch ADs treating food waste or sewage sludge. Daily specific methane (CH4) production increased 11-16% for food waste and 96-138% for sewage sludge over the first 24h. Potential CO2 reductions of 8-34% for sewage sludge and 3-11% for food waste were estimated. The capacity of ADs to utilise additional CO2 was demonstrated, which could provide a potential solution for onsite sequestration of CO2 streams while enhancing renewable energy production.