Work

Assessing the aerobic/anoxic enrichment efficiency at different C/N ratios: polyhydroxyalkanoate production from waste activated sludge

Year: 2024

Type: article

Abstract: • Waste activated sludge was used as feedstock to produce polyhydroxyalkanoates (PHA). • The aerobic/anoxic enrichment strategy was adopted to produce PHA from fermentation. • Carbon and ammonia removal was always higher than 80 % despite the C/N shift. • Low C/N ratio enhanced nitrite production, nitrification and denitrification. • Low C/N ratio worsened overall nitrous oxide emission and PHA production by 45 %. Polyhydroxyalkanoates (PHA) can be produced using fermentation products of an excess sewage sludge fermentation process. An efficient method to enrich a PHA-producing community is an aerobic-feast/anoxic-famine enrichment strategy. The effect of different carbon to nitrogen (C/N) feed ratios of 1, 2 and 3.5 g COD/g N on the process performance was studied. The study was executed on a pilot plant scale using fermented waste activated sludge as the organic carbon source. The system's performance was monitored in terms of removing contaminants, producing PHA, and reducing N 2 O emissions. The results indicated that a lower C/N ratio results in lower PHA production, with PHA content in the sludge of 20, 24 and 36 % w/w for C/N ratios of 1, 2 and 3.5 g COD/g N, respectively. At the lowest C/N ratio, the highest nitrite accumulation rate (77 %), nitrification efficiency (89 %) and denitrification efficiency (89 %) were observed, but the N 2 O production was also the highest (0.77 mg N 2 O-N/L). The long-term comprehensive monitoring carried out in this study revealed high carbon and ammonia removal efficiencies (never below 80 %) despite the C/N shifts and high COD and ammonia concentrations. At the same time, the system showed relatively low PHA production and high environmental impact in terms of high gaseous N 2 O emission. These findings question the sustainability of the aerobic-feast/anoxic-famine enrichment strategy for PHA production in full-scale plants.

Source: Water Research

DOI: 10.1016/j.watres.2024.122687

Authors: Antonio Mineo, Mark M.C. van Loosdrecht, Giorgio Mannina

Institutions: University of Palermo, Delft University of Technology

Language: English

Topic: Wastewater Treatment and Nitrogen Removal

Subfield: Pollution

Field: Environmental Science

Domain: Physical Sciences

SDGs: Responsible consumption and production, Clean water and sanitation, Climate action

Open Access status: hybrid

Estimated APC paid: $4,520