Impact of effluent organic matter on perfluoroalkyl acid removal from wastewater effluent by granular activated carbon and alternative adsorbents.

Occurrence of perfluoroalkyl acids (PFAAs) in wastewater effluent coupled with increasingly stringent regulations has increased the need for more effective sorption-based PFAA treatment approaches. This study investigated the impact of ozone (O3)- biologically active filtration (BAF) as integral components of non-reverse osmosis (RO)-based potable reuse treatment trains and as a potential pretreatment option to improve adsorptive PFAA removal from wastewater effluent by nonselective (e.g., granular activated carbon (GAC) and selective (e.g., anionic exchange resins (AER) and surface-modified clay (SMC)) adsorbents. For nonselective GAC, O3 and BAF resulted in similar PFAA removal improvements, while BAF alone performed better than O3 for AER and SMC. O3-BAF in tandem resulted in the highest PFAA removal performance improvement among pretreatments investigated for selective and nonselective adsorbents. Side by side evaluation of the dissolved organic carbon (DOC) breakthrough curves and size exclusion chromatography (SEC) for each pretreatment scenario suggested that despite the higher affinity of selective adsorbents towards PFAAs, the competition between PFAA and effluent organic matter (EfOM) (molecular weights (MWs): 100-1000 Da) negatively impacts the performance of these adsorbents. The SEC results also demonstrated that transformation of hydrophobic EfOM to more hydrophilic molecules during O3 and biotransformation of EfOM during BAF were the dominant mechanisms responsible for alleviating the competition between PFAA and EfOM, resulting in PFAA removal improvement.

PFAS adsorbent selection: The role of adsorbent use rate, water quality, and cost.

Per- and polyfluoroalkyl substance (PFAS) contamination in aqueous matrices has intensified the search for PFAS adsorbents with elevated capacity, selectivity, and cost effectiveness. A novel surface modified organoclay (SMC) adsorbent was evaluated for PFAS removal performance in parallel with granular activated carbon (GAC) and ion exchange resin (IX) for the treatment of five distinct PFAS impaired waters including groundwater, landfill leachate, membrane concentrate and wastewater effluent. Rapid small scale column tests (RSSCTs) and breakthrough modeling were coupled to provide insight on adsorbent performance and cost for multiple PFAS and water types. IX exhibited the best performance with respect to adsorbent use rates in treatment of all tested waters. IX was nearly four times more effective than GAC and two times more effective than SMC in the treatment of PFOA from water types excluding groundwater. Employed modeling strengthened the comparison of adsorbent performance and water quality to infer adsorption feasibility. Further, evaluation of adsorption was extended beyond PFAS breakthrough with the inclusion of unit adsorbent cost as a decision metric influencing adsorbent selection. An analysis of levelized media cost indicated treatment of landfill leachate and membrane concentrate was at least three times more expensive than groundwaters or wastewaters evaluated.

Impact of ozone-biologically active filtration on the breakthrough of Perfluoroalkyl acids during granular activated carbon treatment of municipal wastewater effluent.

The presence of perfluoroalkyl acids (PFAAs) in municipal wastewater has highlighted the need to develop PFAA treatment approaches for wastewater effluent and potable reuse applications. Ozone (O3) and biologically active filtration (BAF) were investigated as standalone and combined pretreatment processes to improve the performance of granular activated carbon (GAC) for PFAA removal from wastewater effluent. As individual processes, ozonation at all three investigated doses (0.35, 0.75, 1.0 mg O3/mg DOC) and BAF at both tested empty bed contact times (EBCT; 15 and 20 min) led to significant improvement in PFAA removal by subsequent GAC treatment. With respect to standalone ozonation, the specific O3 dose of 0.75 mg O3/mg DOC was proven to be the optimum operating condition as further increase of the specific ozone dose to 1.0 mg O3/mg DOC did not provide considerable additional improvement. Extending the EBCT during standalone BAF from 15 to 20 minutes significantly improved the efficacy of GAC for the removal of tested PFAAs. Pretreatment with O3-BAF (0.75 mg O3/mg DOC; 20 min EBCT) in tandem outperformed both standalone ozonation and BAF for the removal of PFAA by GAC. Characterization of effluent organic matter (EfOM) by size exclusion chromatography (SEC) and Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR-MS) before and after pretreatments suggest that among multiple co-occurring phenomena, the shift towards smaller and more polar EfOM may have predominantly alleviated pore constriction/blockage without having adverse impact on direct site competition. This observation is supported by SEC and FT-ICR-MS results indicating reduced EfOM molecular size through O3 and BAF pretreatment as well as transition to more hydrophilic byproducts.

Pilot-scale field demonstration of a hybrid nanofiltration and UV-sulfite treatment train for groundwater contaminated by per- and polyfluoroalkyl substances (PFASs).

Previous laboratory scale studies indicate nanofiltration (NF) and UV-sulfite photochemical treatments as promising technologies for the removal and destruction, respectively, of per- and polyfluoroalkyl substances (PFASs) from contaminated water. This study reports on a field demonstration of a pilot-scale hybrid NF and UV-sulfite treatment train for the remediation of 12 PFASs detected in groundwater impacted by aqueous film-forming foam (AFFF) at a U.S. Department of Defense installation. For most of the detected PFASs, NF rejection was consistently ≥ 95% over a 30-day field trial when operating at 90% total permeate recovery. Rejection of short-chain perfluorosulfonic acids (PFSAs) by NF decreased when recoveries increased from 90 to 97%; tests with a reverse osmosis (RO) membrane showed ≥ 99% rejection of all PFASs regardless of increasing recovery. UV treatment of the NF reject following 90% permeate recovery resulted in variable destruction of individual PFASs, with rates also being dependent on pH and the identity and concentration of UV photosensitizer. Rates of perfluorocarboxylic acid (PFCA) degradation were greater than those measured for PFSAs and perfluoroalkyl acid (PFAA) precursors and were independent of perfluoroalkyl chain length. In contrast, rates of PFSA degradation increased with increasing chain length. Consistent levels of PFAS degradation by UV-sulfite were observed during a 30-day demonstration experiment in NF reject water amended with 10 mM sulfite and adjusted to pH 11.2. Collectively, > 75% of the detected PFAS mass in the NF reject was destroyed after 4 h of UV treatment, increasing to > 90% after 8 h of treatment. An analysis of electrical energy inputs for the hybrid NF/UV-sulfite treatment train showed energy per order magnitude (EE/O) requirements ranging from ≤ 13.1 kWh/m3 for PFCAs and 14.1 kWh/m3 for PFOS to values > 100 kWh/m3 for more recalcitrant short-chain PFSA analogues. The UV reactor and water-cooling system were the major contributors to overall energy requirements and represent the greatest opportunities for improving efficiency of the technology.

Simultaneous ozone and granular activated carbon for advanced treatment of micropollutants in municipal wastewater effluent.

The main objective of this study was to compare the efficacy of ozone (O3) and O3 with granular activated carbon (GAC) (O3/GAC) at pilot-scale for the enhanced removal of micropollutants (MPs) from wastewater effluent. The results revealed enhanced removal of tris (2-carboxylethyl) phosphine (TCEP), sucralose, and meprobamate during the O3/GAC treatment experiments compared to the sum of their removal during isolated ozonation and GAC adsorption experiments. The long-term O3/GAC experiment showed the promotive effect of GAC substantially decreased after 20 h of O3 exposure. This decreased performance correlates with changes to GAC surface properties caused by O3. After 6 h of operation, O3 initially led to an increase in Brunauer-Emmett-Teller (BET) surface area on the GAC improving the elimination level of investigated MPs (except N-nitrosomorpholine (NMOR)). However, after 20 h of exposure, O3 ultimately caused structural damages to the GAC surface, decreased the BET surface area in the final stages of the experiment, and a 4-fold increase in O1s:C1s ratio on the GAC surface was observed due to an increase in surface acidic functional groups caused by O3 treatment.

Removal of per- and polyfluoroalkyl substances using super-fine powder activated carbon and ceramic membrane filtration.

Contamination of drinking water sources with per- and polyfluoroalkyl substances (PFASs) is a major challenge for environmental engineers. While granular activated carbon (GAC) is an effective adsorbent-based treatment technology for long-chained PFASs, GAC is less effective for removal of short-chained compounds, necessitating a more complete treatment strategy. Super-fine powder activated carbon (SPAC; particle diameter <1 um) is potentially a superior adsorbent to GAC due to high specific surface area and faster adsorption kinetics. This study served to evaluate SPAC coupled with ceramic microfiltration (CMF) for PFAS removal in a continuous flow system. Comparison of PFAS mass loading rates onto SPAC and GAC to 10% breakthrough of PFASs using contaminated groundwater indicates that SPAC has nearly double the adsorption potential of GAC. Limitations reaching breakthrough for the SPAC system led to additional higher mass loading experiments where PFAS adsorption onto SPAC reached 2990 µg/g (for quantifiable PFASs), 480x greater than GAC and is thought to be a function of adsorbent size, pore content and PFAS chain length. Additional analysis of system performance through the application of liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QToF-MS) revealed the presence of additional PFASs in influent samples that were removed by the SPAC/CMF system.