Dual upflow reactive filtration by a slowly moving sand bed with continuously renewed, hydrous ferric oxide‐coated sand is used for removing polluting substances and for meeting the ultralow 0.05 mg/l total phosphorus discharge permit limits at a 1.2 million liters per day (0.32 million gallons per day) water resource recovery facility in Plummer, Idaho, in the United States. A life cycle assessment (LCA) of this reactive filtration installation was carried out to assess the environmental hotspots in the system and analyze alternative system configurations with a focus on CO₂ equivalent (CO₂e) global warming potential, freshwater and marine eutrophication, and mineral resource scarcity. “What if” scenarios with alternative inputs for the energy, metal salts, and air compressor optimization show trade‐offs between the impact categories. Key results that show a comparative reduction of global warming potential include the use of Fe versus Al metal salts, the use of renewable energy, and the energy efficiency benefit of optimizing process inputs, such as compressor air pressure, to match operational demand. The LCA shows a 2 × 10⁻² kg CO₂e footprint per cubic meter of water, with 47% from housing concrete, and an overall freshwater eutrophication impact reduced by 99% versus no treatment. The use of renewable hydropower energy at this site isolates construction concrete as a target for lowering the CO₂e footprint.Practitioner Points: The main LCA eco‐impact hotspots in this dual reactive filtration tertiary treatment are construction concrete and the ferric sulfate used. Iron salts show smaller impact in global warming, freshwater eutrophication, and mineral resource scarcity than “what if scenario” aluminum salts. The energy mix for this site is predominantly hydropower; other energy mix “what if” scenarios show larger impacts. Operational energy efficiency and thermodynamic analysis show that fine tuning the air compressor helps reduce carbon footprint and energy use. LCA shows a favorable 2 x 10‐2 kg CO2e/m3 water impact with 99% reduction of freshwater eutrophication potential versus no treatment.

Biochar (BC) use in water treatment is a promising approach that can simultaneously help address societal needs of clean water, food security, and climate change mitigation. However, novel BC water treatment technology approaches require operational testing in field pilot‐scale scenarios to advance their technology readiness assessment. Therefore, the objective of this study is to evaluate the system performance of BC integrated into hydrous ferric oxide reactive filtration (Fe‐BC‐RF) with and without catalytic ozonation (CatOx) process in laboratory and field pilot‐scale scenarios. For this investigation, Fe‐BC‐RF and Fe‐CatOx‐BC‐RF pilot‐scale trials were conducted on synthetic lake water variants and at three municipal water resource recovery facilities (WRRFs) at process flows of 0.05 and 0.6 L/s, respectively. Three native and two iron‐modified BCs were used in these studies. The commercially available reactive filtration process (Fe‐RF without BC) had 96%–98% total phosphorus (TP) removal from 0.075‐ and 0.22‐mg/L TP, as orthophosphate process influent in these trials. With BC integration, phosphorus removal yielded 94%–98% with the same process‐influent conditions. In WRRF field pilot‐scale studies, the Fe‐CatOx‐BC‐RF process removed 84%–99% of influent total phosphorus concentrations that varied from 0.12 to 8.1 mg/L. Nutrient analysis on BC showed that the recovered BC used in the pilot‐scale studies had an increase in TP from its native concentration, with the Fe‐amended BC showing better P recovery at 110% than its unmodified state, which was 16%. Lastly, the field WRRF Fe‐CatOx‐BC‐RF process studies showed successful destructive removals at >90% for more than 20 detected micropollutants, thus addressing a critical human health and environmental water quality concern. The research demonstrated that integration of BC into Fe‐CatOx‐RF for micropollutant removal, disinfection, and nutrient recovery is an encouraging tertiary water treatment technology that can address sustainable phosphorus recycling needs and the potential for carbon‐negative operation.Practitioner Points: A pilot‐scale hydrous ferric oxide reactive sand filtration process integrating biochar injection typically yields >90% total phosphorus removal to ultralow levels. Biochar, modified with iron, recovers phosphorus from wastewater, creating a P/N nutrient upcycled soil amendment. Addition of ozone to the process stream enables biochar‐iron‐ozone catalytic oxidation demonstrating typically excellent (>90%) micropollutant destructive removals for the compounds tested. A companion paper to this work explores life cycle assessment (LCA) and techno‐economic analysis (TEA) to explore biochar water treatment integrated reactive filtration impacts, costs, and readiness. Biochar use can aid in long‐term carbon sequestration by reducing the carbon footprint of advanced water treatment in a dose‐dependent manner, including enabling an overall carbon‐negative process.

A core tertiary wastewater reactive filtration technology, where continuously renewed hydrous ferric oxide coated sand is created in an upflow continuous backwash filter, has been adopted in about 100 water resource recovery facilities in several countries. Primarily focused on ultralow phosphorus discharge requirements to address nutrient pollution impacts and harmful algae blooms, the technology has also demonstrated the capacity to address high-efficiency removals of Hg, As, Zn, N, and other pollutants of concern, in addition to water quality needs met by common sand filtration, including total suspended solids. Recent work has demonstrated the capability of an additive iron–ozone catalytic oxidation process to the core reactive filtration technology platform to address micropollutants such as pharmaceuticals. Most recently, direct injection of frangible biochar into the reactive sand filter bed as a consumable reagent demonstrates a novel biochar water treatment technology in a platform that yields dose-dependent carbon negativity. In this work, the reactive filtration technology performance is reviewed from field pilot-scale to full-scale installation scenarios for nutrient removal and recovery applications. We also review the potential of the technology for nutrient recovery with the addition of biochar and micropollutant destructive removal with catalytic oxidation. Research exploration of this reactive filtration technology includes life cycle assessment (LCA) and techno-economic assessment to evaluate the environmental and economic impacts of this advanced water treatment technology. A recent LCA study of a pilot-scale field research and full-scale municipal system with over 2200 inventory elements shows a dose-dependent carbon negativity when biochar is injected into the process stream of reactive filtration. In this study, LCA demonstrates that reactive filtration has the potential as a negative emissions technology with −1.21 kg CO₂e/m³, where the negative contribution from the dosed biochar is −1.53 kg CO₂e/m³. In this biochar water treatment configuration, the system not only effectively removes pollutants from wastewater but also contributes to carbon sequestration and nutrient recovery for agriculture, making it a potentially valuable approach for sustainable water treatment.

The use of biochar in water resource and recovery facilities (WRRF) shows promise for recovery of phosphorus (P) to use as a biochar-based fertilizer (BBF) that can replace conventional fertilizers, promote carbon sequestration, and improve soil quality. In this study, biochar was recovered after being dosed into secondary-treated discharge from a municipal WRRF. The value of the recovered biochar as a BBF was tested in a lettuce (Lactuca sativa) growth trial. The BBF was compared to an inorganic fertilizer, raw biochar, and controls that had either only nitrogen (N) fertilizer or no amendment. The ability of the treatments to support plant growth was determined by measuring plant height, biomass, leaf tissue total N and P concentration, and plant quality. Plant quality for the Fe-modified biochar used in the WRRF was 9.05 (±0.44) on a 10-point scale compared to 9.61 (±0.46) for the inorganic fertilizer treatment and 2.22 (±0.82) for the untreated control. Plant tissue P concentrations were 6.28 (±0.83), 9.88 (±0.90), 15.46 (±2.54), and 6.36 (±1.91) g plant⁻¹ for the raw biochar, Fe-modified biochar used in the WRRF, inorganic fertilizer, and no amendment treatments, respectively. Soil P availability and P uptake amount in the leaves indicated that the BBF released P more slowly than the inorganic P fertilizer; however, it was sufficiently available for uptake to support plant growth to maturity. Results from these experiments show that Fe-modified biochar used in WRRF can supply adequate P to plants. The slow release will reduce P leaching into surface waters.

Wave minimal surfaces (WMSs) are mathematically defined structures that are commonly observed in nature. Their unique properties have allowed researchers to harness their potential for engineering applications. Since WMSs can be represented by mathematical equations, the geometry can be parametrized and studied using computational fluid dynamics (CFD) for particle separation. Low energy particle separation in water treatment can yield low-carbon footprint technology approaches such as biochar water treatment where removal and recovery of adsorbed N and P on biochar can address water pollution, climate change and food security. The objective of this work was to demonstrate the capability of WMS as a crossflow filtration system to remove particulates in water. For this purpose we used CFD to optimize WMS geometry and studied the performance of the 3D-Printed (3DP) optimized WMS using experimental fluid dynamics (EFD) in a water tunnel. CFD studies quantified planar vorticity, fluid filtrate flux, and particle behavior of WMS. For inflow velocities of 0.2–0.4 m/s, CFD results showed that a reverse wave filter design with convex shape leading-edge, angle of incidence of 90^o, and maximum width of n = 1.0 captured 15–25% of upstream velocity at the filter port. CFD analysis showed more than 95% separation efficiency at velocities and pressures of 0.2–0.32 m/s and 5–35 kPa, respectively. Particle Image Velocimetry (PIV) was used for EFD fluid flow measurements with an optimized wave minimal surface (OMWS). Comparison of OMWS CFD and PIV velocity fields showed good agreement with a root-mean-square error of less than 10%. Particle size analysis showed that the 3DP OMWS could filter particle sizes ranging from 1–30 μm with at least 50% particle count reduction in the filtrate. Thus, we successfully demonstrated a novel framework for analyzing a crossflow water filtration system from conceptual design to initial benchtop experiments using iterative CFD, 3DP, and EFD.