Improving Post-Anaerobic Digestion of Full-Scale Anaerobic Digestate Using Free Ammonia Treatment

Publication Type:
Journal Article
ACS Sustainable Chemistry and Engineering, 2019, 7 (7), pp. 7171 - 7176
Issue Date:
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© 2019 American Chemical Society. Post-anaerobic digestion of full-scale anaerobic digestate (AD) is used in enhancing sludge reduction in some sewage treatment plants (STPs). However, the AD degradation is usually inhibited due to its slow hydrolysis rate and low degradability. This study presents an innovative pretreatment method by using free ammonia (FA, i.e., NH 3 ) to improve post-anaerobic digestion full-scale AD degradation. The FA treatment at over 360 mg NH 3 -N/L for 24 h has improved AD degradation with the highest solubilization (0.1 mg chemical oxygen demand (COD)/mg volatile solids (VS), at 850 mg NH 3 -N/L), being 5.3 times that without pretreatment (0.019 mg COD/mg VS). After 8 days of post-anaerobic digestion, non-pretreated AD has degraded 8.5%, while the FA pretreated AD at 360-850 mg NH 3 -N/L has degraded 9.9-10.9%, representing a relative increase of 14-22%. The mathematical model captured the tested data well with R 2 > 0.994 in all cases, and the model revealed that AD degradation improvement was attributed to an increase in AD degradation percentage. Economic analysis shows that the FA pretreatment method could be economically favorable in enhancing full-scale AD post-anaerobic digestion.
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