Anaerobic co-digestion of alkaline pre-treated grease trap waste: Laboratory-scale research to full-scale implementation

Anaerobic co-digestion (AcoD) of grease trap waste (GTW) and sewage sludge (SS) is an attractive management option for GTW valorisation and the transition to energy-neutral wastewater treatment plants (WWTPs). The main constraints that limit the direct use of GTW as a co-substrate in WWTP anaerobic digesters are the high content of non-disabled materials (floating plastics and fibres) and the low anaerobic biodegradability rates. This study assessed a single-step alkali and sieving pre-treatment of GTW at a low temperature (<25 degrees C) to improve the bioavailability of GTW and facilitate its use as a co-substrate. The experimental results showed that the alkaline pre-treatment of GTW at NaOH doses of 20-30 g(NaOH).kg(VS)(-1) allowed the recovery of approximately 55-62 % of organic matter (on a volatile solids basis) present in the GTW in the form of saponified fat and generated a small waste reject fraction. Full-scale anaerobic AcoD assays (SS and pre-treated GTW) did not show inhibitory or operational problems under the experimental conditions and tested concentrations. Finally, a preliminary economic assessment for a 160 000 population equivalent WWTP in a European scenario presented a payback period of 1.75 y. (C) 2021 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

Automated summary

The study shows that alkaline pre-treatment of grease trap waste can improve the bioavailability of organic matter and facilitate its use as a co-substrate. Full-scale anaerobic co-digestion assays of pre-treated grease trap waste and sewage sludge did not show inhibitory or operational problems under experimental conditions. An economic assessment for a 160,000 population equivalent WWTP in a European scenario showed a relatively short payback period.