Is removal and destruction of perfluoroalkyl and polyfluoroalkyl substances from wastewater effluent affordable?

Several jurisdictions are currently evaluating regulatory standards for perfluoroalkyl and polyfluoroalkyl substances (PFAS) in municipal water resource recovery facility (WRRF) effluent. Effective and responsible implementation of PFAS effluent limits should consider the costs and capabilities of currently available technologies, because the costs of meeting WRRF PFAS limits could disproportionally fall to ratepayers. Cost curves were developed for currently available PFAS separation and destruction options, assuming effluent treatment targets near current analytical detection limits. Removing and destroying PFAS from municipal WRRF effluent is estimated to increase costs per household by a factor of between 2 and 210, using Minnesota-specific data as an example. Estimated costs per household would increase more for residents of smaller communities, averaging 33% of median household income (MHHI) in communities smaller than 1000 people. This exceeds the U.S. Environmental Protection Agency (EPA)-developed affordability index of 2% of MHHI by a factor of 16. Estimated costs per household to remove and destroy PFAS varied among locations, primarily based on WRRF and community size, median income, rural versus urban, and type of wastewater treatment processes currently used. PRACTITIONER POINTS: Required tertiary treatment before WRRF effluent PFAS separation, using currently available technologies, is a significant portion (~40-80%) of estimated costs. Adding PFAS separation, destruction, and pre-treatment would make Minnesota wastewater rates unaffordable (defined by EPA affordability guidance) without external funding. The estimated cost per household is higher for smaller communities and would require substantial external funding to maintain rate affordability. Design and operating uncertainties remain for full-scale WRRF retrofits to consistently remove and destroy effluent PFAS with limited full-scale applications.

Impacts of ammonia loading and biofilm age on the prevalence of nitrogen-cycling microorganisms in a full-scale submerged attached-growth reactor.

This study reports the impacts of seasonal ammonia load changes and biofilm age on the quantity of biomass and on the prevalence of ammonia- and nitrite-metabolizing organisms within a submerged attached-growth reactor (SAGR™) following lagoon treatment. Ammonia (NH3 ) loadings (0.12-3.17 kg/d) in the primary SAGR were measured over 223 days from May to December in 2017. Adjustment of the wastewater flow path on September 1 successfully increased NH3 loading to the primary SAGR, which subsequently caused reactor biomass to increase. The NH3 removal rate in October (0.5 kg/d) was greater than rates in June and July (0.3 and 0.2 kg/d) despite a water temperature decrease from >24 to 15.6°C. This elevated removal rate in October, and the sustained removal rate in December (0.4 kg/d, 5.3°C) were associated with a measured increase in microbial biomass. The relative abundance of the anammox organism C. Brocadia was 5 times greater in the mature biofilm after 686 days of growth, and the genus Pseudomonas increased sevenfold. The presence of Pseudomonas, which contains denitrifying species, and anammox suggests a high potential for removal of total nitrogen in SAGRs. PRACTITIONER POINTS: Pseudomonas prevalence and the presence of anammox suggest a high potential for total nitrogen removal in mature SAGR biofilms. The abundance of the anammox microorganism C. Brocadia was greater after 686 days of biofilm growth compared with 33 days. Simple operational changes can increase biomass in the SAGR to maintain, or even increase, NH3 transformation rates during cold weather.