Identification of Foulants on Polyethersulfone Membranes Used to Remove Colloids and Dissolved Matter from Paper Mill Treated Effluent

Effect of antibiotics addition on nutrient removal stability and microbial community change of the solar-powered oxidation ditch-membrane bioreactor in treating building wastewater

The solar-powered oxidation ditch-membrane bioreactors (SOD-MBR) system was developed and operated with long solid retention times (SRTs) of 80 and 160 days. The aim was to investigate the effects of using a long SRT and antibiotics in building wastewater on the stability of nutrient removal, as well as membrane fouling. An increase in the SRT from 80 days to 160 days did not significantly affect the performance of the SOD-MBR system. Ciprofloxacin and Sulfamethoxazole removal efficiencies were 94.47 ± 1.54% and 87.54 ± 24.7%. However, the presence of antibiotics resulted in lower removal efficiencies for NH4+-nitrogen and phosphorus and stimulated the production of extracellular polymeric substances (EPS), particularly proteins in L-EPS and T-EPS of the foulant. FTIR and FEEM analysis revealed that the microbial sludge primarily consisted of proteins, carbohydrates, and lipids. Furthermore, the relative abundance analysis of microbial communities identified bacteria associated with nitrogen removal in the SOD-MBR system, including Anammox, AOB (ammonia oxidizing bacteria), DNB (denitrifying bacteria), and NOB (nitrite oxidizing bacteria), with a total of 25 genera. The majority of these bacteria were stimulated by the presence of antibiotics, resulting in higher relative abundance. Finally, the SOD-MBR system achieved energy savings of 97.38% by utilizing photovoltaic (PV) technology.

Assessment of the Potential of Using Nanofiltration Polymeric and Ceramic Membranes to Treat Refinery Spent Caustic Effluents

Spent caustic effluents are very challenging due to their very hazardous nature in terms of toxicity as well as their extreme pH (approximately 12–14). Spent caustic has presented a challenge for wastewater treatment in refineries, due to its composition rich in mercaptans, sulfides and other aromatic compounds. To address such problems, membrane filtration was studied using real effluents from Sines Refinery, in Portugal. The present study attempts to assess the potential for spent caustic treatment with nanofiltration (NF) polymeric and ceramic membranes, assessing membrane life expectancy. For that, membrane aging studies in static mode were performed with the polymeric membrane before attempting NF treatment (dynamic studies). A ceramic membrane was also tested for the first time with this type of effluents, though only in dynamic mode. Although the polymeric membrane performance was very good and in accordance with previous studies, its lifespan was very reduced after 6 weeks of contact with spent caustic, compromising its use in an industrial unit. Contrarily to expectations, the ceramic membrane tested was not chemically more resistant than the polymeric one upon direct contact with spent caustic (loss of retention capacity in less than 1 h in contact with the spent caustic). The results obtained suggest that a pH of 13.9 is very aggressive, even for ceramic membranes.