Optimising mechanical separation of anaerobic digestate for total solids and nutrient removal
Date
2023-06-28
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Publisher
Elsevier
Abstract
Mechanical separation of anaerobic digestate has been identified as a method to reduce pollution risk to waterways by partitioning phosphorus in the solid fraction and reducing its application to land. Separators have adjustable parameters which affect separation efficiency, and hence the degree of phosphorous partitioning, but information on how these parameters affect separation performance is limited in the literature. Two well known technologies were investigated, decanter centrifuge and screw press, to determine the most efficient method of separation. Counterweight load and the use of an oscillator were adjusted for the screw press, while bowl speed, auger differential speed, feed rate and polymer addition were modified for the decanter centrifuge. Separation efficiency was determined for total solids, phosphorus, nitrogen, potassium, and carbon, and the total solids
content of resulting fractions was measured. The decanter centrifuge had higher separation efficiency for phosphorus in all cases, ranging from 51% to 71.5%, while the screw press had a phosphorus separation efficiency
ranging from 8.5% to 10.9% for digestate of ~5% solids (slurry/grass silage mix). Separation by decanter centrifuge partitioned up to 56% of nitrogen in the solid fraction leaving a reduced nitrogen content in the liquid fraction available for land spreading; this nitrogen would most likely need to be replaced by chemical fertiliser which would add to the cost of the system. The decanter centrifuge is better suited to cases where phosphorus recovery is the most important factor, while the screw press could be advantageous in cases where cost is a limiting factor.
Description
Publication history: Accepted - 16 June 2023; Published - 28 June 2023.
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Keywords
Anaerobic digestion, Mechanical separation, Screw press, Decanter centrifuge
Citation
Cathcart, A., Smyth, B.M., Lyons, G., Murray, S.T., Rooney, D. and Johnston, C.R. (2023) ‘Optimising mechanical separation of anaerobic digestate for total solids and nutrient removal’, Journal of Environmental Management. Elsevier BV. Available at: https://doi.org/10.1016/j.jenvman.2023.118449.