Environmentally relevant level of perfluorooctanoic acid affect the formation of aerobic granular sludge

Unraveling the impact of perfluorooctanoic acid on sulfur-based autotrophic denitrification process

PFOA has garnered heightened scrutiny for its impact on denitrification, especially given its frequent detection in secondary effluent discharged from wastewater treatment plants. However, it is still unclear what potential risk PFOA release poses to a typical advanced treatment process, especially the sulfur-based autotrophic denitrification (SAD) process. In this study, different PFOA concentration were tested to explore their impact on denitrification kinetics and microbial dynamic responses of the SAD process. The results showed that an increase PFOA concentration from 0 to 1000 μg/L resulted in a decrease in nitrate removal rate from 9.52 to 7.73 mg-N/L·h. At the same time, it increased nitrite accumulation and N2O emission by 6.11 and 2.03 times, respectively. The inhibitory effect of PFOA on nitrate and nitrite reductase activity in the SAD process was linked to the observed fluctuations in nitrate and nitrite levels. It is noteworthy that nitrite reductase was more vulnerable to the influence of PFOA than nitrate reductase. Furthermore, PFOA showed a significant impact on gene expression and microbial community. Metabolic function prediction revealed a notable decrease in nitrogen metabolism and an increase in sulfur metabolism under PFOA exposure. This study highlights that PFOA has a considerable inhibitory effect on SAD performance.

Critical review on salt tolerance improvement and salt accumulation inhibition strategies of osmotic membrane bioreactors

The osmotic membrane bioreactor (OMBR) is a novel wastewater treatment and resource recovery technology combining forward osmosis (FO) and membrane bioreactor. It has attracted attention for its low energy consumption and high contaminant removal performance. However, in the long-term operation, OMBR faces the problem of salt accumulation due to high salt rejection and reverse salt flux, which affects microbial activity and contaminants removal efficiency. This review analyzed the feasibility of screening salt-tolerant microorganisms and determining salinity thresholds to improve the salt tolerance of OMBR. Combined with recent research, the inhibition strategies for salt accumulation were reviewed, including the draw solution, FO membrane, operating conditions and coupling with other systems. It is hoped to provide a theoretical basis and practical guidance for the further development of OMBR. Finally, future research directions were prospected. This review provides new insights for achieving stable operation of OMBR and promotes its wide application.

When aerobic granular sludge faces emerging contaminants: A review

The evolution of emerging contaminants (ECs) has caused greater requirements and challenges to the current biological wastewater treatment technology. As one of the most promising biological treatment technologies, the aerobic granular sludge (AGS) process also faces the challenge of ECs. This study summarizes the recent progress and characteristics of several representative ECs (persistent organic pollutants, endocrine disrupting chemicals, antibiotics, and microplastics) in AGS systems that have garnered widespread attention. Additionally, the biodegradation and adsorption mechanisms of ECs were discussed, and the interactions between various ECs and AGS was elucidated. The importance of extracellular polymeric substances for the stabilization of AGS and the removal of ECs is also discussed. Knowledge gaps and future research directions that may enable the practical application of AGS are highlighted. Overall, AGS processes show great application potential and this review provides guidance for the future implementation of AGS technology as well as elucidating the mechanism of its interaction with ECs.

Impact of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) on secondary sludge microorganisms: removal, potential toxicity, and their implications on existing wastewater treatment regulations in Canada

Perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) are two of the most commonly researched per- and polyfluoroalkyl substances (PFAS). Globally, many long-chain PFAS compounds including PFOS and PFOA are highly regulated and, in some countries, PFAS use in commercial products is strictly prohibited. Despite the legal regulation of these 'forever chemicals' under the Canadian Environmental Protection Act, PFOA and PFOS compounds are still found in high concentrations in discharges from wastewater treatment plants, both from liquid and sludge streams. Yet, their potential impact on wastewater treatment effectiveness remains poorly understood. The findings of this research show that: (1) PFOS and PFOA might be hindering the overall outcome treatment performance - calling into question the efficacy of Canada's existing wastewater treatment regulatory standard (Wastewater Systems Effluent Regulations, SOR/2012-139), and (2) specific microorganisms from the Thiobacillus and Pseudomonas genera seem capable of adsorbing PFOS and PFOA onto their cell wall and even degrading the chemicals, but it is unclear as to what extent degradation occurs. The results also raise questions whether existing wastewater regulations should be expanded to include the detection and monitoring of PFAS, as well as the establishment of a regulatory wastewater treatment plant discharge standard for PFAS that is protective of human and ecological health.

The impact of perfluorooctanoic acid shock on hydrogen-driven nitrate and arsenate removal

Perfluorooctanoic acid (PFOA) is a type of toxic per- and poly-fluoroalkyl substance (PFAS) commonly found in groundwater due to its use in firefighting and industrial applications. The main purpose of this study was to investigate the influence of PFOA shock on the biological performance of a hydrogen-driven bioreactor for nitrate and arsenate removal. Four hydrogen-driven removal reactors (HdBRs) used for the simultaneous removal of nitrate and arsenal were operated with concentrations of either 0, 1, 5, and 10 mg/L of PFOA to induce shock on the systems and examine the corresponding bacterial response. Our results showed that PFOA shock inhibited and decreased the maximum hydrogen-driven arsenate removal rate. Principal Component Analysis (PCA) confirmed that this performance decrease occurred due to a bacterial strike triggered by PFOA shock. PFOA toxicity also led to protein secretion and sludge density decreases. Bacterial analyses showed shifts in the community population due to PFOA shock. The dominant bacteria phylum Proteobacteria became more abundant, from 41.24% originally to 48.29% after exposure to 10 mg/L of PFOA. Other phyla, such as Euryarchaeota and Bacteroidetes, were more tolerant to PFOA shock. Although some of the predominant species within the sludge of each HdBR exhibited a decline, other species with similar functions persisted and assumed the functional responsibilities previously held by the dominant species.

Retention and recycling of granules in continuous flow-through system to accomplish denitrification and perchlorate reduction

This study employed a completely anoxic reactor and a gravity-settling design for continuously separating from flocculated biomass and hydraulically recycling granules back to the main reactor. The average chemical oxygen demand (COD) removal in the reactor was 98 %. Average nitrate (NO₃^--N) and perchlorate (ClO₄^-) removal efficiencies of 99 % and 74 ± 19 % were observed, respectively. Preferential utilization of NO₃^- over ClO₄^- led to COD limiting conditions, which resulted in ClO₄^- in the effluent. The average granule diameter in continuous flow-through bubble-column (CFB) anoxic granular sludge (AxGS) bioreactor was 6325 ± 2434 µm, and the average SVI₃₀/SVI₁ was > 90% throughout its operation. 16s rDNA amplicon sequencing revealed Proteobacteria (68.53% - 88.57%) and Dechloromonas (10.46% - 54.77%) to be the most abundant phylum and genus present in reactor sludge representing the denitrifying and ClO₄^- reducing microbial community. This work represents a pioneering development of CFB-AxGS bioreactor.

Effect and mechanism of perfluorooctanoic acid (PFOA) on anaerobic digestion sludge dewaterability

Perfluorooctanoic acid (PFOA) as nonbiodegradable organic pollutant, its presence and risks in wastewater treatment system has aroused wide concern. This study investigated the effect and underlying mechanism of PFOA on anaerobic digestion sludge (ADS) dewaterability. Long-term exposure experiments were set up to investigate the effect with various concentration of PFOA dosed. Experimental results suggested that the existence of high concentration PFOA (over 1000 μg/L) could deteriorate ADS dewaterability. The long-term exposure to 100,000 μg/L PFOA of ADS increased specific resistance filtration (SRF) by 81.57%. It was found that PFOA promoted the release of extracellular polymeric substances (EPS), which was strongly associated with sludge dewaterability. The fluorescence analysis revealed that the high PFOA concentration could significantly improve the percentage of protein-like substances and soluble microbial by-product-like content, and then further deteriorated the dewaterability. The FTIR results showed that long-term exposure of PFOA caused loose protein structure in sludge EPS, which led to loose sludge floc structure. The loose sludge floc structure aggravated the deterioration of sludge dewaterability. The solids-water distribution coefficient (K_d) decreased with the increase of initial PFOA concentration. Moreover, PFOA significantly affected microbial community structure. Metabolic function prediction results showed significant decrease of fermentation function exposed to PFOA. This study revealed that the PFOA with high concentration could deteriorated sludge dewaterability, which should be highly concerned.