Reactivity of Fe-amended biochar for phosphorus removal and recycling from wastewater

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Iron–ozone catalytic oxidation (CatOx) shows promise in addressing challenging wastewater pollutants. This study investigates a CatOx reactive filtration (Fe‐CatOx‐RF) approach with two 0.4 L/s field pilot studies and an 18‐month, 18 L/s full‐scale municipal wastewater deployment. We apply ozone to leverage common sand filtration and iron metal salts used in water treatment into a next‐generation technology. The process combines micropollutant and pathogen destructive removal with high‐efficiency phosphorus removal and recycling as a soil amendment, clean water recovery, and the potential for carbon‐negative operation with integrated biochar water treatment. A key process innovation is converting a continuously renewed iron oxide coated, moving bed sand filter into a “sacrificial iron” d‐orbital catalyst bed after adding O3 to the process stream. Results for the Fe‐CatOx‐RF pilot studies show >95% removal efficiencies for almost all >5 × LoQ detected micropollutants, with removal rates slightly increasing with biochar addition. Phosphorus removal for the pilot site with the most P‐impacted discharge was >98% with serial reactive filters. The long‐term, full‐scale Fe‐CatOx‐RF optimization trials showed single reactive filter 90% TP removal and high‐efficiency micropollutant removals for most of the compounds detected, but slightly less than the pilot site studies. TP removal decreased to a mean of 86% during the 18 L/s, 12‐month continuous operation stability trial, and micropollutant removals remained similar to the optimization trial for many detected compounds but less efficient overall. A >4.4 log reduction of fecal coliforms and E. coli in a field pilot sub‐study suggests the ability of this CatOx approach to address infectious disease concerns. Life cycle assessment modeling suggests that integrating biochar water treatment into the Fe‐CatOx‐RF process for P recovery as a soil amendment makes the overall process carbon‐negative at −1.21 kg CO2e/m3. Results indicate positive Fe‐CatOx‐RF process performance and technology readiness in full‐scale extended testing. Further work exploring operational variables is essential to establish site‐specific water quality limitations and responsive engineering approaches for process optimization. Practitioners Points Adding ozone to WRRF secondary influent flows into tertiary ferric/ferrous salt dosed sand filtration amplifies a mature reactive filtration technology into a catalytic oxidation process for micropollutant removal and disinfection. Expensive catalysts are not used. Iron oxide compounds used to remove phosphorus and other pollutants act as sacrificial catalysts with ozone, and these rejected iron compounds can be returned upstream to aid in secondary process TP removal. Biochar addition to the CatOx process improves CO2e sustainability and phosphorus removal/recovery for long‐term soil and water health. Short duration field pilot scale and 18‐month full‐scale operation at three WRRFs with good results demonstrate technology readiness.

Section: Resultsmentioning

confidence: 99%

Iron–ozone catalytic oxidation reactive filtration of municipal wastewater at field pilot and full‐scale with high‐efficiency pollutant removal and potential negative CO₂e with biochar

Baker

McCarthy²,

Taslakyan

et al. 2023

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“…The addition of biochar provides another means to treat wastewater since reactive filtration with metal salts may not remove micropollutant contamination to sufficiently low levels (Baker et al, 2023). Alternately, Fe-modified biochar addition can present an engineered reactive substrate targeted to P adsorption (Strawn et al, 2023). The influent water then enters the reactive sand filter 1 where an airlift assembly continuously moves sand particles to a washbox.…”

Section: Reactive Filtration Process With Biocharmentioning

confidence: 99%

“…Recycling and reusing P to address water pollution, eutrophication of aquatic ecosystems, and soil fertility can supplement limited global reserves of phosphate rock (Carpenter, 2008;Cordell et al, 2009;Yanhui Dai et al, 2023;Glibert, 2020;Lim et al, 2022;Reijnders, 2014;Schindler et al, 2016;Jianlong Wang, Chu, et al, 2020). Adsorption of P moieties onto native and chemically modified biochar is an increasingly studied approach for the removal and recovery of P from wastewaters (Strawn et al, 2023). Biochar from forestry and agricultural green waste is a promising resource for carbon sequestration because it can lock carbon in soils for years, magnifying its ability to be engineered to adsorb P for use as a soil amendment (Lehmann & Joseph, 2015;Möller & Strawn, 2019;Weber & Quicker, 2018).…”

Section: Introductionmentioning

confidence: 99%

Biochar integrated reactive filtration of wastewater for P removal and recovery, micropollutant catalytic oxidation, and negative CO₂e: Process operation and mechanism

Yu,

Baker,

Crump

et al. 2023

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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.

“…Although RF with catalytic oxidation has a proven ability to remove more than 90% of total phosphorus to ultralow levels (>0.050 mg/L), addition of biochar in this process allows for nutrient recovery through adsorption on an engineered biochar surface as well as providing enhanced catalytic activity (Mohan et al, 2022;Möller & Strawn, 2019;Strawn et al, 2023;Yao et al, 2013;Yu et al, 2023). The application of phosphorus-upcycled biochar as a soil amendment has several environmental benefits further discussed in this paper.…”

Section: Introductionmentioning

confidence: 99%

“…This versatile system has demonstrated capability for very high oxidation potentials and contact times suitable for sterilization (Baker et al, 2023). Recent work with injection of biochar into the process stream with and without ozone demonstrates the removal and recovery of phosphorus in the postsecondary treatment municipal water producing a nutrient-upcycled biochar soil amendment capable of sequestering atmospheric carbon (Strawn et al, 2023;Yu et al, 2023).…”

Section: Introductionmentioning

confidence: 99%

Biochar‐integrated reactive filtration of wastewater for P removal and recovery, micropollutant catalytic oxidation, and negative CO₂e: Life cycle assessment and techno‐economic analysis

Taslakyan,

Baker,

Strawn

et al. 2023

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Life cycle assessment (LCA) and techno‐economic analysis (TEA) models are developed for a tertiary wastewater treatment system that employs a biochar‐integrated reactive filtration (RF) approach. This innovative system incorporates the utilization of biochar (BC) either in conjunction with or independently of iron‐ozone catalytic oxidation (CatOx)—resulting in two configurations: Fe‐CatOx‐BC‐RF and BC‐RF. The technology demonstrates 90%–99% total phosphorus removals, adsorption of phosphorus to biochar for recovery, and >90% destructive removal of observed micropollutants. In this work, we conduct an ISO‐compliant LCA of a 49.2 m3/day (9 gpm) field pilot‐scale Fe‐CatOx‐BC‐RF system and a 1130 m3/day (0.3 MGD) water resource recovery facility (WRRF)‐installed RF system, modeled with BC addition at the same rate of 0.45 g/L to quantify their environmental impacts. LCA results indicated that the Fe‐CatOx‐BC‐RF pilot system is a BC dose‐dependent carbon‐negative technology at −1.21 kg CO2e/m3, where biochar addition constitutes a −1.53 kg/m3 CO2e beneficial impact to the process. For the WRRF‐installed RF system, modeled with the same rate of BC addition, the overall process changed from 0.02 kg CO2e/m3 to a carbon negative −1.41 kg CO2e/m3, demonstrating potential as a biochar dose‐dependent negative emissions technology. Using the C100 100‐year carbon accounting approach rather than Cnet reduces these CO2e metrics for the process by about 25%. A stochastic TEA for the cost of water treatment using this combinatorial P removal/recovery, micropollutant destructive removal, and disinfection advanced technology shows that at scale, the mean cost for treating 1130 m3/day (0.3 MGD) WRRF secondary influent water with Fe‐CatOx‐BC‐RF using the C100 metric is US$0.18 ± US$0.01/m3 to achieve overall process carbon neutrality. Using the same BC dose in an estimation of a 3780 m3/day (1 MGD) Fe‐CatOx‐BC‐RF facility, the carbon neutral cost of treatment is reduced further to US$0.08 ± $0.01 with added BC accounting for US$0.03/m3. Overall, the results demonstrate the potential of carbon negativity to become a water treatment performance standard as important and attainable as pollutant and pathogen removal.Practitioner Points Life cycle assessment (LCA) of a pilot scale tertiary biochar water treatment process with or without catalytic ozonation at a WRRF shows a carbon negative global warming potential of −1.21‐kg CO2e/m3 while removing 90%–99% TP and >90% of detected micropollutants. Biochar‐integrated reactive filtration use can aid in long‐term carbon sequestration by reducing the carbon footprint of advanced water treatment in a dose‐dependent manner, allowing an overall carbon‐neutral or carbon‐negative process. A companion paper to this work (Yu et al., 2023) presents the details related to the process operation and mechanism and evaluates the pollutant removal performance of this Fe‐CatOx‐BC‐RF process in engineering laboratory pilot research and field WRRF pilot‐scale water resource recovery trials. Techno‐economic analysis (TEA) of this biochar catalytic oxidation reactive filtration process using Monte Carlo stochastic modeling shows a forecasted carbon‐neutral process cost with low P and micropollutant removal as US$0.11/m3 ± 0.01 for a 3780‐m3/day (1 MGD) scale installation with BC cost at US$0.03/m3 of that total. The results demonstrate the potential of carbon negativity to become a water treatmentperformance standard as important and attainable as pollutant and pathogen removal.