Wood ash amendment to biogas reactors as an alternative to landfilling? A preliminary study on changes in process chemistry and biology

Abstract

Wood ash addition to biogas plants represents an alternative to commonly used landfilling by improving the reactor performance, raising the pH and alleviating potential limits of trace elements. This study is the first on the effects of wood ash on reactor conditions and microbial communities in cattle slurry-based biogas reactors. General process parameters [temperature, pH, electrical conductivity, ammonia, volatile fatty acids, carbon/nitrogen (C/N), total solids (TS), volatile solids, and gas quantity and quality] were monitored along with molecular analyses of methanogens by polymerase chain reaction- denaturing gradient gel electrophoresis and modern microarrays (archaea and bacteria). A prompt pH rise was observed, as was an increase in C/N ratio and volatile fatty acids. Biogas production was inhibited, but recovered to even higher production rates and methane concentration after single amendment. High sulphur levels in the wood ash generated hydrogen sulphide and potentially hampered methanogenesis. Methanosarcina was the most dominant methanogen in all reactors; however, diversity was higher in ash-amended reactors. Bacterial groups like Firmicutes, Proteobacteria and Acidobacteria were favoured, which could improve the hydrolytic efficiency of the reactors. We recommend constant monitoring of the chemical composition of the used wood ash and suggest that ash amendment is adequate if added to the substrate at a rate low enough to allow adaptation of the microbiota (e.g. 0.25 g g(-1) TS). It could further help to enrich digestate with important nutrients, for example phosphorus, calcium and magnesium, but further experiments are required for the evaluation of wood ash concentrations that are tolerable for anaerobic digestion.

Comparative assessment of single-stage and two-stage anaerobic digestion for biogas production from high moisture municipal solid waste

“…High moisture MSW with IFA addition for pH adjustment could improve the self-buffering capacity to meet the demands of microbial growth ( Zhang et al, 2016 ). The results were confirmed by Podmirseg et al (2013) , who found that the loading of 0.5 g ash g − 1 TS could enhance biogas production as well as improve the hydrolysis rate. The IFA addition of 0.5–1%w/v into high moisture MSW could improve hydrogen yield (2–6 times) and methane yield (0.2–0.5 times) for the two-stage AD process.…”

Designing full-scale biodigestion plants for the treatment of vinasse in sugarcane biorefineries: How phase separation and alkalinization impact biogas and electricity production costs?

“…Nevertheless, further studies on alternative alkalizing strategies for vinasse should still be considered, in an effort to improve both economic and environmental performances of the biodigestion plants. Additional strate-gies could include the use of ashes from incinerators (Banks and Lo, 2003;Podmirseg et al, 2013) and the optimization of dosing alternative chemicals (e.g. urea, limestone and caustic potash-KOH).…”

A case study for a cost-benefit-based, stepwise optimization of thermo-chemical WAS pre-treatment for anaerobic digestion

“…Furthermore, the utilisation requisites of waste aluminate are not yet clarified and if the waste product is used, it has a variable composition. Ash is less effective with regard to NaOH, although it has been found to act beneficial to methane concentrations and hydrolytic efficiency in cattle slurry-based biogas plants [29]. However, the here required amounts to reach the desired alkalinity of 0.04 M were rather high and would result in 400 t to be sieved and amended annually.…”