Evaluating Sustainable Development Pathways for Protein- and Peptide-Based Bioadsorbents for Phosphorus Recovery from Wastewater.

Recovering phosphate (P) from point sources such as wastewater effluent is a priority in order to alleviate the impacts of eutrophication and implement a circular economy for an increasingly limited resource. Bioadsorbents featuring P-binding proteins and peptides offer exquisite P specificity and sensitivity for achieving ultralow P concentrations, i.e., <100 µg P L-1, a discharge limit that has been implemented in at least one treatment facility in nine U.S. states. To prioritize research objectives for P recovery in wastewater treatment, we compared the financial and environmental sustainability of protein/peptide bioadsorbents to those of LayneRT anion exchange resin. The baseline scenario (reflecting lab-demonstrated performance at a full-scale implementation) had costs that were 3 orders of magnitude higher than those for typical wastewater treatment. However, scenarios exploring bioadsorbent improvements, including increasing the P-binding capacity per unit volume by using smaller P-selective peptides and nanoparticle base materials and implementing reuse, dramatically decreased median impacts to $1.06 m-3 and 0.001 kg CO2 equiv m-3; these values are in line with current wastewater treatment impacts and lower than the median LayneRT impacts of $4.04 m-3 and 0.19 kg CO2 equiv m-3. While the financial viability of capturing low P concentrations is a challenge, incorporating the externalities of environmental impacts may provide a feasible path forward to motivate ultralow P capture.

Effects of Regional Climate and BMP Type on Stormwater Nutrient Concentrations in BMPs: A Meta-Analysis.

Nutrient treatment performance of stormwater best management practices (BMPs) is highly variable. Improved nutrient management with BMPs requires a better understanding of factors that influence stormwater BMP treatment processes. We conducted a meta-analysis of vegetated BMPs in the International Stormwater BMP Database and compared influent and effluent nitrogen and phosphorus concentrations to quantify the BMP effect on nutrient management across climates. BMP effect on nutrient concentration change was compared between vegetated BMPs in wet and dry climates. We examined paired dissolved inorganic nitrogen (DIN), total nitrogen (TN), dissolved inorganic phosphorus (DIP), total phosphorus (TP), and combinations of these analytes as dissolved inorganic ratios and N:P ratios. Meta-analysis with subgroup analysis was used to determine differences between wet and dry climates and among vegetated BMP types. We found that across both wet and dry climates, BMPs leach DIP and TP, increase the fraction of dissolved inorganic P (DIP:TP), and decrease dissolved N:P ratios. Dry-climate BMPs leach DIP and TP more consistently and at a higher magnitude than wet-climate BMPs, and bioretention leaches more DIP than grass strips and swales. These findings generally align with biogeochemical cycling, differences in influent chemistry, and BMP design types and goals.

Adsorption of recalcitrant phosphorus compounds using the phosphate-selective binding-protein PstS.

Currently available wastewater phosphorus (P) treatment technologies target removal of reactive forms of P. Selective adsorption of more recalcitrant soluble non-reactive phosphorus (sNRP) can improve P removal and recovery. A phosphate-selective phosphate-binding protein (PBP), PstS, was immobilized onto NHS-activated beads to assess the ability of this novel bioadsorbent to remove (adsorb) and subsequently recover (desorb) a range of sNRP compounds. Four sNRP compounds representative of wastewater sNRP were selected for use in this study: phytic acid (PA), sodium triphosphate (TrP), beta-glycerol phosphate (BGP), and sodium hexametaphosphate (HMP). Using PBP, adsorption of all sNRP compounds was thermodynamically favorable. The PBP had nearly equivalent binding affinity for PA compared to PBP's typical target, orthophosphate, although it had less affinity for the other sNRP compounds. Adsorption followed pseudo-second order reaction kinetics, with 95% of maximum adsorption occurring within 4 min. This was substantially faster sNRP adsorption compared to other adsorbents in the literature. Adsorption was modeled using the Langmuir isotherm, reflecting that one phosphate molecule attached to one PBP binding site. Notably, this selective 1:1 attachment resulted in higher total P removal for sNRP molecules with high P content. The binding site lost activity with increasing pH, and as such, highest desorption was achieved at pH 12, making the system amenable to sNRP removal as well as controlled recovery.

Electro-oxidation to convert dissolved organic nitrogen and soluble non-reactive phosphorus to more readily removable and recoverable forms.

Conventional wastewater treatment processes cannot effectively remove dissolved organic nitrogen (DON) and soluble non-reactive phosphorus (sNRP), which can pose regulatory compliance challenges for total nitrogen and total phosphorus discharges. Moreover, DON and sNRP are not easily recoverable for beneficial reuse as part of the waste to resource paradigm. Conversion of DON and sNRP to more readily removable dissolved inorganic nitrogen (DIN) and soluble reactive phosphorus (sRP), respectively, will help meet stringent nutrient limits and facilitate nutrient recovery. In this study, electro-oxidation (EO) was evaluated for conversion of four DON compounds to DIN and five sNRP compounds to sRP. EO was more efficient and provided higher extents of conversion of the recalcitrant nutrient fractions compared to a more traditional advanced oxidation process, UV/H2O2. Direct electron transfer was likely the dominant oxidation mechanism for EO-based DON and sNRP conversion, with DON being more recalcitrant. Among the DON compounds tested, greater availability of primary amine (C-N bonds) yielded greater conversion compared to compounds with fewer primary amine or those with secondary amine (C-N-C bond). Among the sNRP compounds tested, those with P-O-C bonds (organic sNRP) converted more readily than those with P-O-P bonds (inorganic sNRP), presumably because cleavage of the latter bond requires greater energy. Using 30 min of EO treatment, the highest DON and sNRP compound conversion was 11.7 ± 0.09% for urea and 31.1 ± 0.75% for beta-glycerol phosphate. A similar extent of EO-based conversion of DON (6.41 ± 1.5%) and sNRP (32.7 ± 3.3%) was observed in real wastewater.

Editorial: Let's talk about P(ee).

PRACTITIONER POINTS: Phosphorus recycling and reuse are imperative, and the water industry has an important role to play in this effort. Technologies capable of removing phosphorus to ultra-low levels and subsequent recovery for phosphorus reuse are needed. Inorganic ion exchange resins and organic bioadsorbents are promising for phosphorus removal and recovery as part of the waste-to-resource paradigm.

Conversion of soluble recalcitrant phosphorus to recoverable orthophosphate form using UV/H2O2.

Soluble non-reactive phosphorus (sNRP), such as inorganic polyphosphates and organic P, is not effectively removed by conventional physicochemical processes. This can impede water resource reclamation facilities' ability to meet stringent total P regulations. This study investigated a UV/H2O2 advanced oxidation process (AOP) for converting sNRP to the more readily removable/recoverable soluble reactive P (sRP), or orthophosphate, form. Synthetic water spiked with four sNRP compounds (beta-glycerol phosphate, phytic acid, triphosphate, and hexa-meta phosphate) at varying H2O2 concentration, UV fluence, pH, and temperature was initially tested. These compounds represent simple, complex, organic, and inorganic forms of sNRP potentially found in wastewater. The efficiency of sNRP to sRP conversion depended on whether the sNRP compound was organic or inorganic and the complexity of its chemical structure. Using 1 mM H2O2 and 0.43 J/cm2 (pH 7.5, 22 °C), conversion of the simple organic beta-glycerol phosphate to sRP was 38.1 ± 2.9%, which significantly exceeded the conversion of the other sNRP compounds. Although conversion was achieved, the electrical energy per order (EEO) was very high at 5.2 × 103 ± 5.2 × 102 kWh/m3. Actual municipal wastewater secondary effluent, with sNRP accounting for 15% of total P, was also treated using UV/H2O2. No wastewater sNRP to sRP conversion was observed, ostensibly due to interference from wastewater constituents. Wastewater utilities that have difficulty meeting stringent P levels might be able to target simple organic sNRP compounds, though alternative processes beyond UV/H2O2 need to be explored to overcome interference from wastewater constituents and target more complex organic and inorganic sNRP compounds.

Cell surface-expression of the phosphate-binding protein PstS: System development, characterization, and evaluation for phosphorus removal and recovery.

Simultaneous overabundance and scarcity of inorganic phosphate (Pi) is a critical issue driving the development of innovative water/wastewater treatment technologies that not only facilitate Pi removal to prevent eutrophication, but also recover Pi for agricultural reuse. Here, a cell-surface expressed high-affinity phosphate binding protein (PstS) system was developed, and its Pi capture and release potential was evaluated. E. coli was genetically modified to express PstS on its outer membrane using the ice nucleation protein (INP) as an anchoring motif. Verification of protein expression and localization were performed utilizing SDS-polyacrylamide gel electrophoresis (SDS-PAGE), western blot, and outer membrane separation analyses. Cell surface characterization was investigated through acid-base titration, X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR). These tests provided information on the macromolecular structure and composition of the bacteria surface as well as the proton-exchange properties of the surface functional groups (i.e., pKa values). Phosphate desorption and adsorption batch experiments were conducted to evaluate the effects of temperature, pH, and ionic strength on phosphate capture and release. The PstS surface-displayed cells demonstrated greater potential to release and capture phosphate compared to non-modified cells. Higher temperatures up to 40°C, basic pH conditions (pH = 10.5), and higher ionic strength up to 1.0 mol/L KCl promoted 20%-50% higher phosphate release.

Managing Diffuse Phosphorus at the Source versus at the Sink.

Judicious phosphorus (P) management is a global grand challenge and critical to achieving and maintaining water quality objectives while maintaining food production. The management of point sources has been successful in lowering P inputs to aquatic environments, but more difficult is reducing P discharges associated with diffuse sources, such as nonpoint runoff from agriculture and urban landscapes, as well as P accumulated in soils and sediments. Strategies for effective diffuse-P management are imperative. Many options are currently available, and the most cost-effective and practical choice depends on the local situation. This critical review describes how the metrics of P quantity in kg ha-1 yr-1 and P form can influence decision-making and implementation of diffuse-P management strategies. Quantifying the total available pool of P, and its form, in a system is necessary to inform effective decision-making. The review draws upon a number of " current practice" case studies that span agriculture, cities, and aquatic sectors. These diverse examples from around the world highlight different diffuse-P management approaches, delivered at the source in the catchment watershed or at the aquatic sink. They underscore workable options for achieving water quality improvement and wider P sustainability. The diffuse-P management options discussed in this critical review are transferable to other jurisdictions at the global scale. We demonstrate that P quantity is typically highest and most concentrated at the source, particularly at farm scale. The most cost-effective and practically implementable diffuse-P management options are, therefore, to reduce P use, conserve P, and mitigate P loss at the source. Sequestering and removing P from aquatic sinks involves increasing cost, but is sometimes the most effective choice. Recovery of diffuse-P, while expensive, offers opportunity for the circular economy.

Biological Phosphorus Recovery: Review of Current Progress and Future Needs.

This review summarizes the main species of polyphosphate accumulating organisms (PAOs) and algae, illustrates their pathways and key enzymes, discusses biological phosphorous (P) recovery from dilute waters, and identifies research avenues to encourage adoption and implementation. Phylogenic analysis indicates that the Proteobacteria phylum plays an important role in enhanced biological phosphorus removal (EBPR). The use of meta-transcriptome analysis and single cell-based techniques to help overcome the challenges associated with non-PAO competition was discussed. For algae capable of luxury phosphorus uptake, fundamental research is needed to illustrate the phosphorus regulation process and key proteins involved. Emerging technologies and processes have great potential to further advance phosphorus recovery, including combined PAO/algae reactors, bioelectrochemical systems, and biosorption by phosphorus binding proteins. As the paradigm shifts toward holistic resource recovery, research is needed to explore P+ recovery with other resources (e.g., metals from sludge), using a combination of biological and chemical approaches.

High-affinity phosphate-binding protein (PBP) for phosphorous recovery: proof of concept using recombinant Escherichia coli.

Phosphorus (P) is a critical, non-renewable nutrient; yet excess discharges can lead to eutrophication and deterioration of water quality. Thus, P removal from water must be coupled with P recovery to achieve sustainable P management. P-specific proteins provide a novel, promising approach to recover P from water. Bacterial phosphate-binding proteins (PBPs) are able to effectively remove phosphate, achieving extremely low levels in water (i.e. 0.015 mg-P L-1). A prerequisite of using PBP for P recovery, however, is not only removal, but also controlled P release, which has not yet been reported. Phosphate release using recombinant PBP-expressing Escherichia coli was explored in this study. Escherichia coli was genetically modified to overexpress PBP in the periplasmic space. The impacts of ionic strength, temperature and pH on phosphate release were assessed. PBP-expressed E. coli demonstrated consistently superior ability to adsorb more phosphate from liquid and release more phosphate under controlled conditions relative to negative controls (unexpressed PBP E. coli and E. coli K12). Lower pH (3.8), higher temperature (35ºC) and higher ionic strength (100 mM KCl) facilitated increased phosphate release, providing a maximum of 2.1% P recovery within 3 h. This study provides proof of concept of the feasibility of using PBP to recover P.

Total Value of Phosphorus Recovery.

Phosphorus (P) is a critical, geographically concentrated, nonrenewable resource necessary to support global food production. In excess (e.g., due to runoff or wastewater discharges), P is also a primary cause of eutrophication. To reconcile the simultaneous shortage and overabundance of P, lost P flows must be recovered and reused, alongside improvements in P-use efficiency. While this motivation is increasingly being recognized, little P recovery is practiced today, as recovered P generally cannot compete with the relatively low cost of mined P. Therefore, P is often captured to prevent its release into the environment without beneficial recovery and reuse. However, additional incentives for P recovery emerge when accounting for the total value of P recovery. This article provides a comprehensive overview of the range of benefits of recovering P from waste streams, i.e., the total value of recovering P. This approach accounts for P products, as well as other assets that are associated with P and can be recovered in parallel, such as energy, nitrogen, metals and minerals, and water. Additionally, P recovery provides valuable services to society and the environment by protecting and improving environmental quality, enhancing efficiency of waste treatment facilities, and improving food security and social equity. The needs to make P recovery a reality are also discussed, including business models, bottlenecks, and policy and education strategies.