Alleviating the membrane fouling potential of the denitrification filter effluent by regulating the COD/N ratio and carbon source in the process of wastewater reclamation

The process of denitrification filter (DNF) followed by ultrafiltration (UF) has been widely applied for wastewater reclamation in China. The performance of DNF could have significant influences on subsequent UF membrane fouling. In this study, different chemical oxygen demand to nitrogen (COD/N) ratios and carbon sources in DNF were investigated under pilot scale, with the secondary effluent of a wastewater reclamation plant as DNF influent, to explore the impacts of DNF operation on UF membrane fouling. DNF effluent with the increased COD/N ratios from 2.9 to 6.8 rendered more aggravated membrane fouling performance, suggesting that increase of carbon source dosage could significantly increase the fouling potential of DNF effluent. In terms of four commonly-used carbon sources, the fouling potential was higher in the order of glucose > methanol > ethanol > sodium acetate-fed DNF effluent. According to the resin fractionation and fluorescence spectroscopy analysis, water samples with higher membrane fouling potential contained a larger proportion of hydrophobic components. Extended Derjaguin Landau Verwey Overbeek (XDLVO) analysis revealed fouling mechanism that hydrophobic acids (HOA) and hydrophobic neutrals (HON) exhibited both notably attractive interaction with virgin membranes and a strong tendency to aggregate on the already fouled membranes. Compared with the other fractions, HOA and HON presented significantly stronger interaction energy, demonstrating that HOA and HON dominated the membrane fouling process. Therefore, the contents of HOA and HON fractions in DNF effluent could be effectively regulated by optimizing external carbon addition, thus alleviating the subsequent UF fouling. The DNF-UF process should be considered and optimized as an integrated system rather than independent units, and appropriate external carbon addition should be regulated to achieve an optimal process from the perspective of the whole wastewater reclamation plant.

Automated summary

This study investigated the impact of denitrification filter (DNF) operation on ultrafiltration (UF) membrane fouling during wastewater reclamation. It was found that increasing the carbon source dosage in DNF led to aggravated membrane fouling. Glucose was identified as the most fouling-prone carbon source. Water samples with higher fouling potential contained more hydrophobic components. Hydrophobic acids and hydrophobic neutrals dominated the membrane fouling process and exhibited strong interaction with the membranes. Optimizing external carbon addition could effectively regulate the levels of these fractions, thereby reducing UF fouling.