Phosphorus recovery from wastewater and bio-based waste: an overview

Advancements and feasibility of synergistic approaches in phosphorus recovery from wastewater: A critical review

This review explores the potential and challenges of synergetic approaches, such as coupling, hybrid, and sequential methods, to enhance phosphorus recovery while minimizing environmental impacts. It emphasizes phosphorus recovery's economic and ecological dimensions, stressing the imperative for ongoing research and development to bolster economic viability and scalability. This review also discusses factors for improvement and outlines the exploration of innovative technologies and comprehensive techno-economic assessments to bridge the gap between advancements and real-world implementation. Its highlights include global efforts for phosphorus recovery, the need for synergetic approaches, an understanding of the difference between efficiency and performance approaches, required innovation in the future, and the environmental and economic implications.

Phosphorus mining and bioavailability for plant acquisition: environmental sustainability perspectives

This review aims to examine microbial mechanisms for phosphorus (P) solubilization, assess the impacts of P mining and scarcity, and advocate for sustainable recycling strategies to enhance agricultural and environmental resilience. Phosphorus is an indispensable macronutrient for plant growth and agricultural productivity, yet its bioavailability in cultivation systems is often constrained. This scarcity has led to a heavy reliance on fertilizers derived from mined phosphate rock (PR), which is a finite resource usually contaminated with hazardous elements such as uranium, radium, and thorium. Plants absorb only about 10-20% of P from applied fertilizers, leading to significant inefficiencies and negative environmental consequences. Additionally, the uneven geographic distribution of PR reserves exacerbates global socioeconomic and geopolitical vulnerabilities. Healthy soils enriched with diverse microbial communities provide a sustainable avenue to address these growing challenges. Rhizospheric organisms, including phosphorus-solubilizing and phosphorus-mineralizing bacteria and arbuscular mycorrhizal fungi, are capable and pivotal in the sustainable conversion of inorganic and organic P into bioavailable forms, reducing reliance on synthetic fertilizers. The mechanisms used by these microbes often include releasing organic acids to lower soil pH and solubilize insoluble inorganic phosphorus compounds and the production of enzymes, such as phosphatases and phytases, to break down organic phosphorus compounds, including phytates, into bioavailable inorganic phosphate. Some microbes secrete chelating agents, such as siderophores, to bind metal ions and free phosphorus from insoluble complexes and use biofilms for P exchange. This review also advocates for the recycling second-generation P from organic waste as a sustainable and socially equitable alternative to conventional phosphate mining.

A critical review on phosphorus recovery from source-diverted blackwater

Source-diverted blackwater refers to toilet wastewater, sometimes including kitchen wastewater, which is rich in essential nutrients such as nitrogen (N) and phosphorus (P). Blackwater, especially concentrated blackwater collected from low-flush vacuum toilet systems, represents a valuable source for P recovery, addressing future P scarcity and mitigating environmental issues like eutrophication. While there has been growing interest in technologies for P recovery from blackwater, these technologies are still in the early stages of development. This study provides a comprehensive review of the mechanisms behind phosphate salt formation, the technologies for P recovery from blackwater-particularly through struvite and calcium phosphate precipitation-and the safety concerns associated with the use of recovered products. Despite advancements, most research is limited to lab-scale experiments, leaving significant gaps in optimizing P recovery technologies for broader application. Future research will be likely to focus on integrating bioenergy recovery with P recovery in anaerobic digestion (AD) systems, aiming to create a more sustainable and zero-waste approach. Addressing current challenges and scaling up from lab research to real-world applications will be crucial for making P recovery more efficient and economically viable.

Enhancing phosphorus recovery from poultry litter ash through microwave-assisted thermochemical treatment for improving its solubility

This study explores for the first time the P recovery from poultry litter ash (PLA) using microwave-assisted thermochemical treatment, aiming to improve its bioavailability for utilization as a fertilizer. PLA samples, originating from laying hens' manure incineration, were subjected to microwave treatment with the addition of sodium bicarbonate, and their physical-chemical characteristics were analyzed using X-ray fluorescence (XRF), X-ray diffraction (XRD), and scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS). The results indicate that the microwave treatment led to the formation of NaCaPO4 crystals, with a significant increase in P solubility post-treatment, which is crucial for plant uptake. Moreover, increasing the amorphous content of the ash led to a decrease in P solubility because sodium atoms tend to diffuse within the silica network. However, in this case, interesting glass materials with promising optical properties may be obtained. This study provides a novel approach to valorizing biowaste and contributes to sustainable phosphorus management practices.

Enhancement of the Plant-Accessible Phosphate Fraction in Sewage Sludge Ashes by Na+ or K+ Addition Prior to Combustion

With the aim of transforming sewage sludge into a P-fertiliser material in a single combustion step, the chemical processes underlying sewage sludge combustion were analysed using powder X-ray diffraction (P-XRD), infrared spectroscopy (IR), thermogravimetric (TGA) as well as elemental analyses (EA). In addition to the combustion of sewage sludge on its own ("mono-combustion"), additions of different additives prior to the combustion step were also carried out. Based on the very positive effects of the additives sodium and potassium carbonate on the obtained ashes concerning their phosphate solubilities in neutral ammonium citrate (NAC) solution, sewage sludge combustions after additions of Na2CO3 or K2CO3 were investigated in detail. We found that these additions altered the main phosphate-containing product found in the ashes from whitlockite (Ca9(Mg,Fe)(PO3OH)(PO4)6), a hardly plant-accessible species, to other phosphate containing compounds such as buchwaldite (CaNaPO4), which is known for a long time as a very good P-source for plants. Consecutive greenhouse experiments with maize (Zea mays L.) as test plant confirmed the results of the chemical analyses and demonstrated that Na- or K-ashes obtained from a "co-combustion" of sewage sludge mixed with alkali carbonates exhibit relative P-fertilising efficiencies of up to ~80 % in comparison to commercial superphosphate, making these materials promising surrogate phosphate mineral sources for agricultural production.

Wastewater sample storage for physicochemical and microbiological analysis

Wastewater-based epidemiology (WBE) is a crucial tool for health and environmental monitoring, providing real-time data on public health indicators by analysis of sewage samples. Ensuring the integrity of these samples from collection to analysis is paramount. This study investigates the effects of different cold-storage conditions on the integrity of wastewater samples, focusing on both microbiological markers (such as extractable nucleic acids, SARS-CoV-2, and crAssphage) and physicochemical parameters (including ammonium, orthophosphate, pH, conductivity, and turbidity). Composite samples from the combined raw wastewater influent from five wastewater treatment works in South Wales, UK, were stored at 4°C, -20°C, and -80°C, and subjected to up to six freeze-thaw cycles over one year. The study found significant effects of storage temperature on the preservation of certain WBE markers, with the best yield most frequently seen in samples stored at -80°C. However, the majority of WBE markers showed no significant difference between storage at -80°C or at 4°C, demonstrating that it may not always be necessary to archive wastewater samples at ultra-low temperatures, thus reducing CO2 emissions and laboratory energy costs. These findings underscore the importance of optimized storage conditions to maintain sample integrity, while ensuring accurate and reliable WBE data for public health and environmental monitoring.

Perspectives on innovative non-fertilizer applications of sewage sludge for mitigating environmental and health hazards

As waste production increases and resources become limited, sewage sludge presents a valuable resource with potential beyond traditional land use and incineration. This review emphasizes exploring innovative non-fertilizer applications of sewage sludges and advocates for viewing wastewater treatment plants as sources of valuable feedstock and carbon sequestration. Innovative uses include integrating sewage sludge into construction materials such as asphalt pavements, geopolymer, cementitious composites, and masonry blocks. These methods not only immobilize heavy metals and mitigate environmental hazards but also support carbon sequestration, contrasting with incineration and land application methods that release carbon into the atmosphere. The review also addresses emerging technologies like bio-adhesives, bio-binders for asphalt, hydrogels, bioplastics, and corrosion inhibitors. It highlights the recovery of valuable materials from sewage sludge, including phosphorus, oils, metals, cellulose, and polyhydroxyalkanoates as well as enzyme production. By focusing on these non-fertilizer applications, this review presents a compelling case for re-envisioning wastewater treatment plants as sources of valuable feedstock and carbon sequestration, supporting global efforts to manage waste effectively and enhance sustainability.

Composition of carbohydrate, protein and lipid derived from microalgae using thermally pretreated solid waste

Microalgae are widely recognized for their capacity to generate value-added products in a variety of sectors, including the pharmaceutical and food industries, bioenergy industries and wastewater industries. The quality of a microalga is significantly influenced by its proliferation. Along with growth, the biochemical profile may also vary based on the nutrient that is supplemented. The majority of the supplemented nutrients utilized are not in a functional state, as they are typically extracted in liquid form or pretreated prior to use. Parallel to numerous commonly applied pretreatment processes, including chemical, mechanical and biological, thermal pretreatment appears to receive less attention. Hence it is crucial to comprehend the potential for thermal pretreatment as well as its mechanism in militating the solid waste to release additional nutrients in order to enhance the biochemical profile of microalgae. The current review takes a closer look at the impact of various thermal pretreatments on solid waste on influencing microalgal performance in terms of their overall biochemical profiles such as carbohydrates, proteins and lipids. This approach is likely to enhance the circular economy by utilizing waste products and effectively closing the loop on waste. © 2024 Society of Chemical Industry.

Supramolecular Binding of Phosphonate Dianions by Nanojars and Nanojar Clamshells

Despite the widespread use of phosphonates (RPO32-) in various agricultural, industrial, and household applications and the ensuing eutrophication of polluted water bodies, the capture of phosphonate ions by molecular receptors has been scarcely studied. Herein, we describe a novel approach to phosphonate binding using chemically and thermally robust supramolecular coordination assemblies of the formula [RPO3⊂{cis-CuII(μ-OH)(μ-pz)}n]2- (Cun; n = 27-31; pz = pyrazolate ion, C3H3N2-; R = aliphatic or aromatic group). The neutral receptors, termed nanojars, strongly bind phosphonate anions by a multitude of hydrogen bonds within their highly hydrophilic cavities. These nanojars can be synthesized either directly from their constituents or by depolymerization of [trans-CuII(μ-OH)(μ-pz)]∞ induced by phosphonate anions. Electrospray-ionization mass spectrometry, UV-vis and variable-temperature, paramagnetic 1H and 31P NMR spectroscopy, single-crystal X-ray diffraction, along with chemical stability studies toward NH3 and Ba2+ ions, and thermal stability studies in solution are employed to explore the binding of various phosphonate ions by nanojars. Crystallographic studies of 12 different nanojars offer unprecedented structural characterization of host-guest complexes with doubly charged RPO32- ions and reveal a new motif in nanojar chemistry, nanojar clamshells, which consist of phosphonate anion-bridged pairs of nanojars and double the phosphonate-binding capacity of nanojars.

Phosphorus Availability and Balance with Long-Term Sewage Sludge and Nitrogen Fertilization in Chernozem Soil under Maize Monoculture

A continuous long-term field experiment with maize monoculture was conducted to evaluate the P availability and balance, DM yield, P uptake, and P sorption parameters in chernozem soil after 27 years. A total of 2 doses of nitrogen (120 and 240 kg ha-1) were applied as mineral nitrogen (N120 and N240) and sewage sludge (SS120 and SS240) and compared with unfertilized control (Con). The aboveground biomass (DM) yields significantly increased in the order of Con < SS120 < SS240 < N120 < N240 treatments and the maximum P uptake was recorded for both N240 and SS240 (25.1 kg P ha-1) according to the nutrient application gradient. The N120 and N240 treatments positively influenced the DM yield but negatively influenced the P balance (-648 and -678 kg P ha-1 27 years-1), gradually bringing a risk of P deficiency in the soil. On the other hand, applications of SS120 and SS240 positively influenced the P availability and pseudototal (PAR) content in the soil, which resulted in a buildup of legacy P or an increase in P saturation greater than the environmental threshold value. Aluminum was found to be a major controlling sorption factor for P in our chernozem soil.

Enhanced removing of phosphate ions from agricultural drainage wastewater by using microwave-assisted synthesized attapulgite (Fullers earth) @carboxymethylcellulose nanocomposite

Contamination of various water resources with phosphate pollutant owing to the excessive use of phosphate fertilizers was labeled by dangerous consequences. Most of the water remediation methods are not efficient for phosphate recovery and always generate secondary wastes. Therefore, the current study is aimed to prepare a novel ecofriendly and sustainable APT500@CMC nanocomposite via simple covalent binding of thermally treated attapulgite clay at 500 °C (APT500) with carboxymethyl cellulose (CMC) using microwave irradiation process. The assembled nanocomposite was confirmed by diverse techniques. The optimum conditions for efficient 10, 25 and 50 mg/L PO43- removal were detected at pH 3, time 30 min, temperature 25 °C and mass 200 mg. The kinetic and isotherms were fitted both to a combination of pseudo 1st - 2nd orders and Langmuir model, while thermodynamic parameters verified PO43- removal via spontaneous and exothermic reaction behavior. The mode of interaction and binding of PO43- ions onto the surface of APT500@CMC were suggested via ion-pair interaction process. Excellent PO43- recovery (98.8 %) from real agricultural drainage wastewater was established. The explored APT500@CMC afforded good stability for five regeneration cycles. Therefore, the collected results confirm the validity of APT500@CMC for excellent removal of PO43- from real agricultural drainage wastewater.

Recent developments in metallic-nanoparticles-loaded biochars synthesis and use for phosphorus recovery from aqueous solutions. A critical review

Phosphorus (P) represents a major pollutant of water resources and at the same time a vital element for human and plants. P recovery from wastewaters and its reuse is a necessity in order to compensate the current important depletion of P natural reserves. The use of biochars for P recovery from wastewaters and their subsequent valorization in agriculture, instead of synthetic industrial fertilizers, promotes circular economy and sustainability concepts. However, P retention by pristine biochars is usually low and a modification step is always required to improve their P recovery efficiency. The pre- or post-treatment of biochars with metal salts seems to be one of the most efficient approaches. This review aims to summarize and discuss the most recent developments (from 2020- up to now) in: i) the role of the feedstock nature, the metal salt type, the pyrolysis conditions, and the experimental adsorption parameters on metallic-nanoparticles-loaded biochars properties and effectiveness in recovering P from aqueous solutions, as well as the dominant involved mechanisms, ii) the effect of the eluent solutions nature on the regeneration ability of P-loaded biochars, and iii) the practical challenges facing the upscaling of P-loaded biochars production and valorization in agriculture. This review shows that the synthesized biochars through slow pyrolysis at relatively high temperatures (up to 700-800 °C) of mixed biomasses with Ca- Mg-rich materials or impregnated biomasses with specific metals in order to from layered double hydroxides (LDHs) biochars composites exhibit interesting structural, textural and surface chemistry properties allowing high P recovery efficiency. Depending on the pyrolysis's and adsorption's experimental conditions, these modified biochars may recover P through combined mechanisms including mainly electrostatic attraction, ligand exchange, surface complexation, hydrogen bonding, and precipitation. Moreover, the P-loaded biochars can be used directly in agriculture or efficiently regenerated with alkaline solutions. Finally, this review emphasizes the challenges concerning the production and use of P-loaded biochars in a context of circular economy. They concern the optimization of P recovery process from wastewater in real-time scenarios, the reduction of energy-related biochars production costs and the intensification of communication/dissemination campaigns to all the concerned actors (i.e., farmers, consumers, stakeholders, and policymakers) on the benefits of P-loaded biochars reuse. We believe that this review is beneficial for new breakthroughs on the synthesis and green application of metallic-nanoparticles-loaded biochars.

Production of Nano Hydroxyapatite and Mg-Whitlockite from Biowaste-Derived products via Continuous Flow Hydrothermal Synthesis: A Step towards Circular Economy

Biowastes from agriculture, sewage, household wastes, and industries comprise promising resources to produce biomaterials while reducing adverse environmental effects. This study focused on utilising waste-derived materials (i.e., eggshells as a calcium source, struvite as a phosphate source, and CH₃COOH as dissolution media) to produce value-added products (i.e., calcium phosphates (CaPs) derived from biomaterials) using a continuous flow hydrothermal synthesis route. The prepared materials were characterised via XRD, FEG-SEM, EDX, FTIR, and TEM analysis. Magnesium whitlockite (Mg-WH) and hydroxyapatite (HA) were produced by single-phase or biphasic CaPs by reacting struvite with either calcium nitrate tetrahydrate or an eggshell solution at 200 °C and 350 °C. Rhombohedral-shaped Mg-WH (23-720 nm) along with tube (50-290 nm diameter, 20-71 nm thickness) and/or ellipsoidal morphologies of HA (273-522 nm width) were observed at 350 °C using HNO₃ or CH₃COOH to prepare the eggshell and struvite solutions, and NH₄OH was used as the pH buffer. The Ca/P (atomic%) ratios obtained ranged between 1.3 and 1.7, indicating the formation of Mg-WH and HA. This study showed that eggshells and struvite usage, along with CH₃COOH, are promising resources as potential sustainable precursors and dissolution media, respectively, to produce CaPs with varying morphologies.