Optimising wastewater anaerobic digestion through small-scale screening studies

Both now, and in the future, a warming climate and a clearer understanding of our ecological impact will require us to take a closer look at how we generate electricity and treat our waste. Anaerobic digestion as part of the treatment of wastewater, is an area of research where both of these concerns overlap. During anaerobic digestion, organic material is degraded into biogas, a methane rich product that can be burnt to generate heat and electricity, and a nutrient rich digestate that can be used as organic fertilizer. Not only can anaerobic digestion help to produce green energy and recycle nutrients, but also reduces the tonnage of organic material that would otherwise be sent to landfill or incineration. A better understanding and optimization of such a valuable process is essential.
Traditionally experimental anaerobic digestion is done under conditions that do not accurately reflect real world processes. These can include either singularly or in combination: batch rather than continuous feeding, the use of synthetic feedstock material, shorter experimental run times due to increased labour and <1L digesters. A fleet of 60 semi-continuous anaerobic digestors was built and trialled to better simulate process scale anaerobic digestion of sewages sludges at lab-scale. The digesters were able to run continuously and fed real world feedstocks collected from a local wastewater treatment plant hourly for months at a time.
Biologically triplicate digesters showed high consistency in producing biogas andreducing the organic load of the digestate in initial trials, and stability under varying real-world feedstocks. The digesters also showed stability while trialling the integration of a new industrial waste stream into anaerobic digestion, as well as the scalability of the data up to full scale integration.
Finally, reduction of hydraulic retention time and increase of feeding rates had no impact on biogas yields or reduction of organic solids. The digesters were run for 94 days with a retention time of 8.9 days with no measurable instability or reduction in biogas yields compared to digesters with a 14 day retention time.
These data show how the use of System 60 is able to assist in the derisking and making of commercially relevant decisions at smaller scale than pilot scale, by more accurate simulation of a full scale anaerobic digestion plant.