Abstract
Dry digestion is a suitable technology for treating organic wastes with varying composition such as the organic fraction of municipal solids waste. Yet, there is a need for further research to overcome some of the disadvantages associated with the high total solids content of the process. Optimisation of inoculum to substrate ratio, feedstock composition and size, liquid recirculation, bed compaction and use of bulking agents are some of the parameters that need further investigation in batch dry anaerobic digestion, to limit localised inhibition effects and avoid process instability. In addition, further attention on the relation between feedstock composition, organic loading rate and mixing regimes is required for continuous dry anaerobic digestion systems. This paper highlights all the areas where knowledge is scarce and value can be added to increase dry anaerobic digestion performance and expansion.
Highlights
According to the European Commission, 58 million tonnes of municipal solid waste were disposed to landfill in Europe in 2017 (Eurostat, 2018), of which 46% is considered to be organic (Kaza and Bhada-Tata, 2018)
The results showed higher operating pH as the alkalinity addition increased, with pH values of 6.5, 7.2 and 7.3 for each reactor, with lower total ammonia nitrogen (TAN) and volatile fatty acids (VFA) at the highest alkalinity and a production of 28% more methane; showing the positive effect of the alkalinity in the system
These results show the important relationship between alkalinity, pH and operational parameters when operating dry anaerobic digestion (AD) systems
Summary
According to the European Commission, 58 million tonnes of municipal solid waste were disposed to landfill in Europe in 2017 (Eurostat, 2018), of which 46% is considered to be organic (Kaza and Bhada-Tata, 2018). Notwithstanding the main advantages, dry ADs have some disadvantages, which include long degradation times and a potential accumulation of toxic and inhibitory compounds (e.g. volatile fatty acids, ammonia and heavy metals) due to the high TS content (Ajay et al, 2011) This can often lead to lower methane production per kilogram of VS and the need for higher inoculation ratios (Ajay et al, 2011; Chen et al, 2008). The paper aims to emphasize any gaps in knowledge that need to be addressed to enable a greater implementation of high solids digestion
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