Survey on the current leachate treatments of public municipal solid waste landfills and the potential impact of per- and polyfluorinatedalkyl substances in the Eastern and Northwestern United States.

Leachate from landfills can be a significant challenge to manage and treat due to conventional contaminants. The addition of emerging contaminants such as per- and polyfluorinatedalkyl substances (PFASs) makes treatment even more complex. PFASs enter landfills through consumer waste and have been detected in landfill leachates at varying concentrations. The design and decision-making on leachate treatment require essential information since it depends on local factors, e.g. climate, proximity to wastewater treatment plants, and waste type. This study conducted a survey on actively operated public municipal solid waste (MSW) landfills in the Eastern and Northwestern regions of the US to understand the current leachate treatment practices and views from public MSW landfill managers on PFAS treatment. The survey aims to explore the possible adaptations from the industry to the pending regulatory guidelines for the potential PFASs treatment. Results show the majority of the landfills are currently using off-site disposal (72% of the responses), followed by complete onsite treatment (18% of the responses) and pre-treatment onsite and off-site disposal methods (10% of the responses). The factors that guided the selection of treatment methods included climate, economics, and future regulations. Evaporation and recirculation were the most prevalent onsite treatment technologies for public landfills, which reduced the leachate quantity for treatment. The public landfills expressed awareness of the potential impact of PFASs on the changes in leachate treatment. The current state-level regulation, potential federal PFAS regulation, and treatment costs are raising awareness of the onsite treatment for PFASs. The results of this study will benefit the improvement of PFAS awareness and provide critical information that will directly affect the leachate treatment process for PFASs.Implications: This study presents a survey on the current leachate treatment process in the public municipal solid waste landfills in the eastern and northwestern U.S. and their potential process improvement on the impact of PFASs. This study is relevant to the topic of the JA&WMA because the research falls directly within the scope of this journal, and it documents the leachate treatment of landfills, and the results of this study will immediately contribute to our understanding of the waste treatment, benefiting the improvement of PFASs awareness, and providing critical information that will directly affect the leachate treatment process.

Priority control factors for heavy metal groundwater contamination in peninsula regions based on source-oriented health risk assessment.

Peninsula regions in China face serious environmental issues, such as heavy metal (HM) groundwater contamination. However, attempts to investigate the pollution sources and health risks of HM contamination in such regions require considerable resources and costs. Moreover, the priority control factors for groundwater HMs remain unclear. In this study, absolute principal component score/multiple linear regression (APCS/MLR) was used to quantify the groundwater pollution sources of typical peninsular areas in China, and a health risk assessment (HRA) was performed to assess the health risks caused by different sources. The results showed that the concentrations of Mn and Fe were higher than those of other HMs, and HM pollution was high in shallow groundwater. The dominant source of HMs in groundwater was agricultural activities (31.12 %), followed by natural sources (26.33 %), industrial activities (22.47 %), and atmospheric deposition (20.09 %). The non-carcinogenic risks to residents were acceptable, whereas the carcinogenic risks were high. Agricultural sources, atmospheric deposition sources, and Cr and As were identified as the priority control factors for HM groundwater contamination. This study has implications for improving the control of groundwater HM contamination in peninsula regions and ensuring sustainable groundwater development.

Tracking denitrification in green stormwater infrastructure with dual nitrate stable isotopes.

Strategies to mitigate watershed nitrogen export are critical in managing water resources. Green infrastructure (GI) has shown the ability to remove nitrogen from stormwater, but the removal mechanism is unclear. Denitrification removes nitrate from water permanently, making it the most desirable removal mechanism. The year-round field performance of a roadside infiltration GI practice (bioretention) in Northern Virginia was monitored to investigate the transport of nitrogen and the occurrence and contribution of denitrification. Stormwater runoff volumes, nitrogen concentrations, and nitrate isotope ratios (δ15N-NO3- and δ18O-NO3-) were measured at the inlet and outlet of the bioretention during 24 storm events over 14 months. Nitrate concentration reductions (inlet vs. outlet) displayed seasonal trends, with higher reductions happening during warmer events and lower reductions or increases occurring during colder events. Cumulative bioretention nitrate and total dissolved nitrogen load reductions were 73% and 70%, respectively. Two out of 24 monitored events displayed denitrification isotope trends, indicating that although bioretention has denitrification potential, it is infrequent and other nitrogen removal mechanisms (i.e. infiltration and plant uptake) are primarily responsible for nitrogen surface effluent reductions. Only approximately 1.4% of the total reduced nitrate surface effluent load over the monitoring period was attributable to denitrification. Denitrification occurred during two of the largest monitored events, suggesting increased hydraulic retention time (HRT) promotes denitrification. Future GI designs should consider increasing HRT to encourage the important ecosystem service denitrification provides.

Green stormwater infrastructure redirects deicing salt from surface water to groundwater.

Winter deicing salt application has led to water quality impairment as stormwater carries salt ions (Na+ and Cl-) through watersheds. Green infrastructure (GI) is a promising urban stormwater management practice, but its efficacy in managing salt is unknown. GI is not yet designed to remove salt, but may have potential to mitigate its loading to surface waters. Two roadside infiltration-based GI practices in Northern Virginia (bioretention and bioswale) were monitored year-round over 28 precipitation events to investigate the transport of salt through modern stormwater infrastructure. Stormwater runoff volumes and concentrations of salt ions entering and exiting each GI were monitored to determine reductions of salt ions. Both the bioretention and bioswale significantly reduced effluent surface loads of Cl- and Na+ (76% to 82%), displaying ability to temporarily retain and infiltrate salts and delay their release to surface waters. Changes in bioretention soil chemistry revealed a small percentage of Na+ was stored long-term by ion exchange, but no long-term Cl- storage was observed. Limited soil storage along with groundwater observations suggest the majority of salt removed from stormwater by the bioretention infiltrates into groundwater. Infiltration GI can buffer surface waters from salt, but are also an avenue for groundwater salt loading.

Graphene oxide/polydimethylsiloxane composite sponge for removing Pb(ii) from water.

An efficient adsorbent to remove Pb(ii) from water was prepared by treating polydimethylsiloxane (PDMS) sponge with polyvinyl alcohol and then coating the sponge with graphene oxide (GO). The GO-PDMS sponge was highly hydrophilic, easily handled during and after use, and easily recycled. The kinetics and isotherms of Pb(ii) sorption onto the GO-PDMS sponge were investigated by performing batch sorption tests. The kinetics of Pb(ii) sorption onto the GO-PDMS sponge indicated that sorption equilibrium occurred rapidly (within 60 min) and that the sorption data could be described using a pseudo-second-order model. Maximum Pb(ii) sorption onto the GO-PDMS sponge occurred at pH > 5. Increasing GO loading on the PDMS sponge increased the amount of Pb(ii) that could be sorbed. The isotherm for Pb(ii) sorption onto the GO-PDMS sponge was non-linear and was well described by the Langmuir isotherm model, indicating that Pb(ii) sorption onto the GO-PDMS sponge was homogeneous and occurred through sorption of a monolayer of Pb(ii). The GO-PDMS sponge, used as a filter, removed Pb(ii) efficiently from water. The Pb(ii) removal efficiencies were more than 50% and the maximum was 85%.