Implementation of an anaerobic selector step for the densification of activated sludge treating high-salinity petrochemical wastewater

Sludge bulking is a common challenge in industrial biological wastewater treatment. Leading to difficulties such as bad sludge settling and washout, which is a problem also encountered in the petrochemical industry. Anaerobic feeding strategies can be used to induce the growth of storage-capable organisms, such as glycogen-accumulating organisms (GAO), leading to denser sludge flocs and better settling. In this study, the implementation of an anaerobic feeding strategy was investigated for high-salinity petrochemical wastewater (±35 g salts·L−1), using a sequencing batch reactor. Influent, effluent and sludge characteristics were analyzed throughout the operational period, which can be divided into three stages: I (normal operation), II (increased influent volume) and III (longer anaerobic mixing). Good effluent quality was observed during all stages with effluent chemical oxygen demand (COD) < 100 mgO2·L−1 and removal efficiencies of 95%. After 140 days, the sludge volume index decreased below 100 mL·g−1 reaching the threshold of good settling sludge. Sludge morphology clearly improved, with dense sludge flocs and less filaments being present. A maximum anaerobic dissolved oxygen carbon (DOC) uptake was achieved on day 80 with 74% during stage III. 16S rRNA amplicon sequencing showed the presence of GAOs, with increasing relative read abundance over time from 1 to 3.5%. HIGHLIGHTS Dense and compact sludge flocs were achieved under high-saline conditions; Filamentous organisms were suppressed in the system, favoring the growth of glycogen-accumulating organisms; Settling characteristics of the sludge were improved to the point of the sludge being characterized as well-settling

Glycerol used for denitrification in full-scale wastewater treatment plants: nitrous oxide emissions, sludge acclimatization, and other insights

Glycerol is commonly employed for denitrification purposes in full-scale wastewater treatment. In non-acclimatized biomass, the glycerol is very inefficient resulting in a high C/N ratio and low-standard denitrification rates. The acclimatization is driven by the microbial enrichment of Saccharimonadales and Propionibacteriales as found in different sampled municipal sludges flanking the dominant presence of Burkholderiales. The selective strategy is based on a very efficient process in terms of C/N ratios and standard denitrification rates, but it leads to nitrite accumulation. As a result, severe and unexpected nitrous oxide emissions were found in full-scale with emission factors up to 2.5% kgN2O (kgKJNremoved)−1. Simultaneous dosage of isobutirate in a full-scale experiment could counter the nitrous oxide emissions. As nitrous oxide emissions were found proportional to the dosed glycerol-based COD, the authors suggest that, in case of acclimatization of biomass to glycerol, an emission factor based on the dosed COD should substitute the general nitrous oxide emission factors based on incoming or removed nitrogen to the plant. HIGHLIGHTS Acclimatization to glycerol leads to an increase in C/N ratios and standard denitrification rates.; We observed microbial enrichment of Saccharimonadales and Propionibacteriales and nitrite accumulation.; N2O emission factors reached up to 2.5% kgN2O/kgKJNremoved.; In case of acclimatization, the N2O emission factor is best expressed in function of the dosed glycerol COD.; Simultaneous isobutirate dosage countered the N2O emissions.