Long-term phosphate removal by the calcium-silicate material Polonite in wastewater filtration systems

Phosphorus removal from municipal wastewater using calcium/iron oxide composites: Adsorption efficiency and impact on plant growth

Phosphate minerals are crucial for the production of fertilizers, but limited availability does not meet the growing agricultural demand. At the same time, the discharge of phosphorus by municipal wastewater treatment plants leads to eutrophication. Removal and recovery of phosphorus from wastewater can both provide nutrients to agriculture and decrease eutrophication. This research aims to evaluate phosphorus removal from municipal wastewater in Latvia by mineral-based calcium/iron composites and examine spent oxides' phytotoxic effect on plant growth. Two CaFeOxides from Latvian earth pigments (iron oxide pigments) deposits were synthesized and characterised by X-ray powder diffraction, differential scanning calorimetry/thermogravimetry, scanning electron microscopy-energy dispersive X-ray analysis and specific surface area analysis. Adsorption properties of obtained oxides were evaluated with a standard phosphate solution, and real municipal wastewater. The phytotoxic effect of P-loaded composites was evaluated in a hydroponic system with common wheat (Triticum aestivum). The results indicated that calcium/iron oxide composites have higher P adsorption efficiency than the commercial Polonite material. The maximum sorption capacity of CaFeOxides was 63.29 and 83.33 mg P/g, and 53.19 mg/g for Polonite. Furthermore, the P-loaded CaFeOxides demonstrated no phytotoxic effect on the growth of Triticum aestivum, and at higher CaFeOxides concentrations, morphological and physiological parameters of wheat increased, showing great potential for reuse in agriculture.

Thin-layer capping with granular activated carbon and calcium-silicate to remediate organic and metal polluted harbor sediment - A mesocosm study

Sediments polluted with hydrophobic organic contaminants (HOCs) and metals can pose environmental risks, yet effective remediation remains a challenge. We investigated a new composite sorbent comprising granular activated carbon (GAC) and a calcium-silicate (Polonite®, PO) for thin-layer capping of polluted sediment, with the aim to sequester both HOCs and metals. Box cores were collected in polluted Oskarshamn harbor, Sweden, and the sediments were treated with GAC and/or Polonite in a 10-week mesocosm study to measure endpoints ranging from contaminant immobilization to ecological side effects on native fauna and biogeochemical processes. The GAC particle size was 300-500 μm to reduce negative effects on benthic fauna (by being non-ingestible) and of biogenic origin (coconut) to have a small carbon footprint compared with traditional fossil ACs. The calcium-silicate was a fine-grained industrial by-product used to target metals and as a carrier for GAC to improve the cap integrity. GAC decreased the uptake of dioxins (PCDD/Fs) in the bivalve Macoma balthica by 47 % and the in vitro bioavailability of PCB by 40 %. The composite cap of GAC + Polonite decreased sediment-to-water release of Pb < Cu < Ni < Zn < Cd by 42-98 % (lowest to highest decrease) and bioaccumulation of Cd < Zn < Cu in the worm Hediste diversicolor by 50-65 %. Additionally, in vitro bioavailability of Pb < Cu < Zn, measured using digestive fluid extraction, decreased by 43-83 %. GAC showed no adverse effects on benthic fauna while Polonite caused short-term adverse effects on fauna diversity and abundance, partly due to its cohesiveness, which, in turn, can improve the cap integrity in situ. Fauna later recovered and bioturbated the cap. Both sorbents influenced biogeochemical processes; GAC sorbed ammonium, Polonite decreased respiration, and both sorbents reduced denitrification. In conclusion, the side effects were relatively mild, and the cap decreased the release and bioavailability of both HOCs and metals effectively, thus offering a promising sustainable and cost-effective solution to remediating polluted sediments.

Assessment of the calcium-silicate Polonite as a sorbent for thin-layer capping of metal contaminated sediment

Sediments contaminated with hazardous metals pose risks to humans and wildlife, yet viable management options are scarce. In a series of laboratory experiments, we characterized Polonite® - an activated calcium-silicate - as a novel sorbent for thin-layer capping of metal-contaminated sediments. We tested a fine-grained by-product from the Polonite production as a cheap and sustainable sorbent. First, Polonite was reacted with solutions of Cu, Pb, and Zn, and the surface chemistry of the Polonite was examined using, e.g., scanning electron microscopy to investigate metal sorption mechanisms. Batch experiments were conducted by adding Polonite to industrially contaminated harbor sediment to determine sorption kinetics and isotherms. Importantly, we measured if the Polonite could reduce metal bioavailability to sediment fauna by performing digestive fluid extraction (DFE). Finally, a cap placement technique was studied by applying a Polonite slurry in sedimentation columns. The results showed rapid metal sorption to Polonite via several mechanisms, including hydroxide and carbonate precipitation, and complexation with metal oxides on the Polonite surface. Isotherm data revealed that the sediment uptake capacity (Kf) for Cu, Pb, and Zn increased by a factor of 25, 21, and 14, respectively, after addition of 5% Polonite. The bioavailability of Cu, Pb, and Zn was reduced by 70%, 65%, and 54%, respectively, after a 25% Polonite addition. In conclusion, we propose that sediment treatment with low doses of the Polonite by-product can be a cheap, sustainable, and effective remediation method compared to other more intrusive methods such as dredging or conventional isolation capping.

Ferrate as a coagulant prior to sand filters treating secondary wastewater effluent for reuse

Wastewater reuse is one of the crucial water resources in Egypt due to the ongoing need to increase water resources and close the supply-demand gap. In this study, a new coagulant has been investigated before sand filters as an advanced wastewater treatment method. The sand filter pilot was run at a hydraulic loading rate of 0.75 m/h and two different dosages of three coagulants (Alum, FeCl3, and Ferrate VI) were selected using the jar tests. The sand filter without coagulant removed 12% of BOD5 and 70% of turbidity. Applying in-line coagulation before the sand filter provided effluents with better quality, especially for turbidity, organics, and microorganisms. Ferrate provided the highest removal of turbidity (90%) and BOD5 (93%) at very low dosages and lower costs compared with other coagulants, however, it adversely impacted both conductivity and dissolved solids. A significant effect on reducing bacteria was obtained with 40.0 mg/L of alum. According to the study's findings, the ferrate coagulant enhanced the sand filter's performance producing effluents with high quality, enabling it to meet strict water reuse regulations as well as aquatic environmental and health preservations.

Treatment efficiency of package plants for on-site wastewater treatment in cold climates

Package plants (PP) are implemented around the world to provide on-site sanitation in areas not connected to a sewage network. The efficiency of PP has not been comprehensively studied at full scale, and the limited number of available studies have shown that their performance varies greatly. Their performance under cold climate conditions and the occurrence of micropollutants in PP effluents have not been sufficiently explored. PP are exposed to environmental factors such as low temperature, especially in cold regions with low winter temperatures and deep frost penetration, that can adversely influence the biochemical processes. The aim of this study was to investigate the treatment efficiency and possible effects of cold temperatures on PP performance, with focus on traditional contaminants (organics, solids, nutrients and indicator bacteria) and an additional assessment of micropollutants on two PP. Eleven PP hosting different treatment processes were monitored. Removal of biological oxygen demand (BOD) was high in all plants (>91%). Six out of the 11 PP provided good phosphorus removal (>71%). Small degrees of nitrification were observed in almost all the facilities, despite the low temperatures, while denitrification was only observed in two plants which achieved the highest nitrification rates (>51%) and had sludge recirculation. No strong correlation between wastewater temperature and BOD, nutrients and indicator bacteria concentration in the effluents was found. The high data variability and the effects of other process parameters as well as snow-melt water infiltration are suggested as possible reasons for the lack of correlation. However, weak negative relations between effluent concentrations and wastewater temperatures were detected in specific plants, indicating that temperature does have effects. When managed adequately, package plants can provide high BOD and phosphorus removal, but nitrogen and bacteria removal remain challenging, especially at low temperatures. Pharmaceutical compounds were detected in the effluents at concentrations within or above ranges reported for large treatment plants while phthalate ester concentrations were below commonly reported effluent concentrations.

The opoka-rock in N and P of poultry manure management according to circular economy

European Green Deal (EGD) and the Circular Economy Action Plan (CE) promote recycling of materials in line with circular economy principles and enhance the value of material flows. Recently, new technologies have been introduced to produce value-added products from agricultural residues and food processing side streams. However integrated approach is necessary for organic waste utilization as environmentally safe product according to the bio-economy rules. The so-called opoka-rock is characterized as a transitional rock between carbonate (app. 71%) and those of a silica character (app. 26%). This study identifies research gaps on how circular bioeconomy can be achieved through application of opoka for improvement of sustainable nitrogen and phosphorous management of poultry manure as safe fertilizer according to CE. Initially, it was found that opoka was able to effectively absorb the N and P ions from water solution and then gradual release to environment. Thermal treatment (900 °C) increased rapidly sorption capacity of opoka to 100% in the case of phosphorous, value of pH and content of Ca²⁺ions in eluates. Moreover, the volume ratio of opoka to poultry manure in experimental mixtures was optimized to determine of nitrogen and phosphorus release into the solution. The substrate was characterized by good desorption properties - the tests confirmed gradually release of N and P ions to solution with the maximum concentration obtained after 32 h equal almost 71% of initial value in mixtures in the case of phosphorous and almost 40% in the case of nitrogen. The novelty of such approach gives opportunity use opoka-rock not only as a single sorbent but also for improvement of poultry manure as mineral-organic fertilizers in the context of CE. This also allow to control for ions N, P release and maintain suitable pH value of soil environment.

Removal of Phosphorus from Hypolimnetic Lake Water by Reactive Filter Material in a Recirculating System—Laboratory Trial

A toolbox of methods must be available for the remediation of lakes and water bodies suffering from eutrophication. One method suggested is hypolimnetic withdrawal based on a closed-circuit system. Prior to the start of a pilot-scale test at Lake Hönsan, Sweden, a laboratory trial with containers filled with water and bottom sediment from this lake was performed. A peristaltic pump distributed equal bottom water volume to four columns, two filled with glass beads and two with the filter material Polonite, and then back to the surface of the containers. The reactive filter medium (RFM) removed phosphate (PO4-P) efficiently (98.6%), despite the relatively low influent concentration (390 µg L−1). The control column filled with glass beads, removed 2.9% of the PO4-P. The anoxic sediment, containing 2.47 mg P g−1, released PO4-P, which was indicated by the increased concentration in near-bottom water. The redirected water after RFM filtration had high pH (x¯=11.1); however, an equalization took place in the water mass to a lower but still increased pH value (x¯=8.7) compared to the control (x¯=7.02). This article reports the pros and cons of a full-scale system using the proposed method.

AlgalTextile - a new biohybrid material for wastewater treatment

Efficient nutrient extraction from wastewater and reuse as bio-fertilizer is an important task for reducing anthropogenic load toward circular economy. Inspired by microbial mats and biofilms, we developed a new material AlgalTextile (AT) that effectively absorbs nutrients from a medium. AT consists of three fully organic components: microalgae, alginate and textile. AT sequestered up to 99% of phosphorus (P-PO4) and 76% of total bound nitrogen from a medium. The uptake rate of phosphorus and nitrogen by AT was highest among all methods using photosynthetic microorganisms, but lower than EBPR and physicochemical methods for phosphorus removal, and anammox and denitrifying bacteria for nitrogen removal. Advantages of AT are its easy production, possibility of seasonal use and utilization as fertilizer. AT as biofertilizer for cress resulted in 35% greater length compared to the control. This outlines a promising technique for seasonal wastewater treatment, improving soil fertility and treatment of polluted surface runoff.

Copper and Zinc Removal Efficiency of Two Reactive Filter Media Treating Motorway Runoff—Model for Service Life Estimation

The predominant techniques used for road runoff treatment are sedimentation and filtration. In filtration systems, the ability of the media to adsorb the contaminants is a finite process. Consequently, construction, operation and maintenance managers of such systems should know in advance the service life, i.e., when the used medium should be replaced, and associated costs of operation and maintenance. A batch experiment followed by a packed bed reactor (PBR) experiment addressed the kinetics of the studied media argon oxygen decarburization slag (AOD) and Polonite, followed by the development of a 1D-model to describe the change of concentration of Cu and Zn within time. The batch test results showed that Cu and Zn adsorption followed the Freundlich isotherms for AOD and Polonite. Those results coupled with the linear driving force model and the developed model resulted in good agreement between the PBR results and the simulation. The model was capable to predict (i), the service life at the hydraulic load of 0.18 m/h for AOD (Cu: 395 d; Zn: 479 d) and Polonite (Cu: 445 d; Zn: 910 d), to show (ii) the profile concentration in the PBR within time and the gradient of the concentration along the height of the reactor.

Sediment Remediation with New Composite Sorbent Amendments to Sequester Phosphorus, Organic Contaminants, and Metals

This study tested two sediment amendments with active sorbents: injection of aluminum (Al) into sediments and thin-layer capping with Polonite (calcium-silicate), with and without the addition of activated carbon (AC), for their simultaneous sequestration of sediment phosphorus (P), hydrophobic organic contaminants (HOCs), and metals. Sediment cores were collected from a eutrophic and polluted brackish water bay in Sweden and incubated in the laboratory to measure sediment-to-water contaminant release and effects on biogeochemical processes. We used diffusive gradients in thin-film passive samplers for metals and semi-permeable membrane devices for the HOC polychlorinated biphenyls and polycyclic aromatic hydrocarbons. Al injection into anoxic sediments completely stopped the release of P and reduced the release of cadmium (Cd, -97%) and zinc (Zn, -95%) but increased the sediment fluxes of PAH (+49%), compared to the untreated sediment. Polonite mixed with AC reduced the release of P (-70%), Cd (-67%), and Zn (-89%) but increased methane (CH₄) release. Adding AC to the Al or Polonite reduced the release of HOCs by 40% in both treatments. These results not only demonstrate the potential of innovative remediation techniques using composite sorbent amendments but also highlight the need to assess possible ecological side effects on, for example, sedimentary microbial processes.

Primacy of ecological engineering tools for combating eutrophication: An ecohydrological assessment pathway

Eutrophication of freshwater bodies causes loss of earth's biological resources and aggravates climate change, thus assuming major environmental concern. Both endogenous and exogenous nutrient enrichment are responsible for eutrophication. Numerous monitoring and management studies conducted worldwide have resulted high-level technological innovations. These studies cumulatively uphold the significance of ecohydrological and ecological engineering approaches. However, holistic and insightful reviews with feasible recommendations of such huge academic outputs are rather scanty. Therefore, our main objective was to introduce a new perspective of eutrophication as an ecohydrological component; to discover all possibilities of monitoring and restoration of eutrophic water bodies. Furthermore, the present study critically analyzes various methods of treatment of eutrophication (physical, biological, chemical, and eco-engineering). Comprehensive volume of literature has been surveyed using search engines like Scopus, Google Scholar, PubMed, ScienceDirect etc. Meaningful keywords were used to obtain reliable information on methods of ecohydrological assessment in relation to eutrophication of freshwater bodies. According to our survey, ecohydrological research is diversified into conceptual knowledge (37.2%), assessment (32.6%), climate change (9.3%), algae/cyanotoxins (7%), engineering and restoration (7%), modelling (4.6%) and biodiversity (2.3%), in the instant decade (2010-2020). We have identified a clear trend of transition of restoration methods from traditional towards modern techniques over time. Moreover, this review recognizes a pool of biophysicochemical and ecological engineering techniques, which are very effective in regard to time, cost, and labor and have immense scopes of modification for improved results. This work focuses on the importance of ecohydrology and eco-engineering tools for restoration of eutrophic water bodies for the first time. We have highlighted how these approaches have emerged as one of the best suitable and sustainable water resource conservation routes in the present era.

Treatment of Hypolimnion Water on Mineral Aggregates as the Second Step of the Hypolimnetic Withdrawal Method Used for Lake Restoration

The study aimed to assess the usefulness of mineral aggregates in orthophosphate (OP) removal from hypolimnetic water withdrawn from eutrophic lakes. Two low-cost and easily available reactive materials were tested: lightweight expanded clay aggregate (LECA) and crushed limestone (LS). Their performance regarding OP removal and the effect on the pH, Ca2+, Mg2+, N-NO3 and N-NH4 concentrations of treated water were investigated in a column experiment with four-filter beds made of LECA and amended with LS (additions of 0, 25, 50 and 75% of the bed volume). The highest OP removal (>50%) was achieved in LECA beds with high (75% by volume) amendments of LS. Neither LECA nor LS distinctly affected the pH (maximum pH increase, from 7.1 or 7.2 to 7.6, occurred in the case of the LECA bed). In real-life conditions, it is not feasible to install a full-scale bed made of these mineral aggregates on the outflow from a lake due to the large required size of such a bed. At the operation time set for 30 d, the size of a bed would need to reach between 6113.2 and 12,226.4 m3. The proposed bed should be just one of the elements of an integrated treatment system. Constructions consisting of sorption beds ought to be coupled with adequately designed zones of aquatic vegetation. Three conceptional solutions were proposed for in situ treatment of the withdrawn water, differing in arrangement and construction of the potential sorption bed. Application of such solutions should be regarded as a substantial improvement of Olszewski’s method, as it can mitigate the pollution of downstream ecosystems.

Reactive Materials in the Removal of Phosphorus Compounds from Wastewater-A Review

Modern technologies designed to treat wastewater containing phosphorus compounds are based on the processes of adsorption and precipitation. In addition, more environmentally friendly and cheaper materials are being sought to ensure greater conformity with overarching assumptions of green chemistry and sustainable development. Against that background, this paper offers a review and analysis of available information on the considered reactive materials that have the capacity to remove phosphorus from wastewater. These materials are categorised as natural (with a sub-division in line with the dominant sorption groups of Al/Fe or Ca/Mg), waste, or man-made. Notably, most studies on sorbents have been carried out in laboratory systems via experimentation under static conditions. Among the natural materials, opoka has the highest sorption capacity of 181.20 g P/kg, while red mud (in the waste material category) is most efficient at binding phosphorus with a level of 345.02 g P/kg. Finally, among the group of commercial materials, Rockfos® has the highest sorption capacity of 256.40 g P/kg. In addition, this paper recognises the effect of composition, pH, and physical properties on a reactive material's capacity to absorb phosphorus, as well as the possibility for further potential use in the production of fertilisers.

Chemical Clogging and Evolution of Head Losses in Steel Slag Filters Used for Phosphorus Removal

The objective of this study was to propose a conceptual model of clogging in alkaline granular filters. Two slag columns were operated for 600 days and monitored using piezometers and tracer tested at regular intervals. The type of influent (organic or inorganic) affected the loss of effective porosity in the filters. Well organized and loose crystal structures were observed by scanning electron microscopy in columns with inorganic and organic influents, respectively. It was postulated that the formation of crystals in unorganized structures results in confined voids that are not accessible for water flow, thus accelerating porosity loss. The effect of the combination of chemical clogging and biofilm on the porosity loss is higher than the effect of these two factors separately. The Kozeny-Carman equation for hydraulic conductivity could not efficiently predict the evolution of head losses in the column fed with an inorganic influent. The crystal structure and connectivity in the presence of homogeneous or heterogeneous precipitation are concepts that could improve predictions of hydraulic conductivity. The results of this study highlighted the importance of the inlet zone on the development of pressure head in alkaline granular filters. Future research on clogging should focus on precipitation mechanisms in the inlet zone and on the design of the feeding system.

Non-biological methods for phosphorus and nitrogen removal from wastewater: A gap analysis of reinvented-toilet technologies with respect to ISO 30500

The aims of the Reinvent the Toilet Challenge (RTTC) include creation of an off-the-grid sanitation system with operating costs of less than US$0.05 per user per day. Because of the small scale at which many reinvented toilets (RT) are intended to operate, non-biological treatment has been generally favored. The RTTC has already instigated notable technological advances in non-sewered sanitation systems (NSSS). However, increasingly stringent liquid effluent standards for N and P could limit the deployment of current RT in real-world scenarios, despite the urgent need for these systems. The newly adopted ISO 30500 standards for water reuse in NSSS dictate minimal use of chemical/biological additives, while at the same time requiring a 70% and 80% reduction in total nitrogen and phosphorus, respectively. This document provides a brief overview of the mature and emerging technologies for N and P (specifically ammonia/ammonium and orthophosphate) removal from wastewater. At present, the dearth of nutrient removal methods proven to be effective at small scales is a significant barrier to meeting ISO 30500 standards. Closing the gap between RTs and ISO 30500 will require significant investments in basic R&D of emerging technologies for non-biological N and P remediation and/or increased reliance on biological processes. Adaptation of existing nutrient-removal technologies to small-scale NSSS is a viable option that merits additional investigation.

An Efficacy Assessment of Phosphate Removal from Drainage Waters by Modified Reactive Material

Phosphates may pose a threat to the aquatic ecosystem when there is a connection or a path between the soil and the aquatic ecosystem. Runoff and drainage ditches connect arable land with the waters of the receiver. Phosphates in the runoff and the ditches contribute to the negative phenomenon of surface water eutrophication. In order to prevent it, certain reactive materials are used which are capable of the selective removal of compounds by way of sorption or precipitation. Zeolites can be distinguished among the many reactive materials. Within the present analysis, the modification of a reactive material containing zeolites was carried out using calcium hydroxide solutions of different concentrations. A certain concentration of calcium hydroxide was created for use in further studies. In order to characterise the new material, an analysis was done of the chemical and mineral composition, as well as the porous texture and morphology. The efficacy of phosphate removal for its typical concentrations in drainage waters in Poland was confirmed by way of an experiment. Using a modified reactive material as an element of landscape structures may reduce the negative impact of phosphates on the quality of surface water.

Filter Media-Packed Bed Reactor Fortification with Biochar to Enhance Wastewater Quality

Contamination of water sources by inappropriately disposed poorly treated wastewater from countryside establishments is a worldwide challenge. This study tested the effectiveness of retrofitting sand (Sa)- and gas–concrete (GC)-packed reactors with biochar (C) in removing turbidity, dissolved organic carbon (DOC), phosphate (PO43−), and total phosphorus (Ptot) from wastewater. The down-flow reactors were each intermittently loaded with 0.063 L/d for 399 days. In general, all reactors achieved <3 NTU (Nephelometric Turbidity Units) effluent turbidity (99% efficiency). GC reactors dominated in inlet PO43− (6.1 mg/L) and DOC (25.3 mg/L) reduction, trapping >95% and >60%, respectively. Compared to Sa (PO43−: 35%, DOC: 52%), the fortified sand (SaC) filter attenuated more PO43− (>42%) and DOC (>58%). Student t-tests revealed that C significantly improved the Sa PO43− (p = 0.022) and DOC (p = 0.034) removal efficacy. From regression analysis, 53%, 81%, and 85% PO43− sorption variation in Sa, C, and SaC, respectively, were explained by variation in their effluent pH measures. Similarly, a strong linear correlation occurred between PO43− sorption efficiency and pH of fortified (r > 0.7) and reference (r = 0.6) GC filters thus suggesting chemisorption mechanisms. Therefore, whereby only sand may be available for treating septic tank effluents, fortifying it with biochar may be a possible measure to improve its efficacy.

Leachability and plant-availability of phosphorus in post-sorption wastewater filters fortified with biochar

Sand and gravel are widely applied for filtering pre- or primary-treated wastewater in small-scale wastewater treatment (SWT) systems. However, ecological materials continue to attract increasing interest in use as retrofits for achieving better performance in removing dissolved contaminants and recovering nutrients from wastewater. In this study, we assessed the plant availability and leachability of phosphorus (P) from sand (Sa) and gas concrete (GC) media previously fortified with biochar (BC) and used for phosphorus (P) removal in laboratory-scale packed bed reactors and field-scale constructed filter beds. Batch and leaching experiments were conducted, with distilled water and ammonium lactate (AL) solutions (1:20 solid-liquid (w/v) ratio) applied as extractants. In the findings, reference (Sa) and fortified (Sa-BC) sand filters leached 11.2 and 20.5 mg P kg^-1 respectively, to percolating water while the P seemed less likely to leach from GC systems. Extraction with AL showed that P retained in GC was plant-available and that GC could release up to 90 mg kg^-1 of the bound mass. These findings highlight the need to evaluate risks of nutrient leaching from filter media for SWT systems especially where groundwater and surface water are final recipients of such effluents. For greater sustainability of use of the media, the weakly bound P in media such as Sa and BC and strongly bound in media such as GC types of materials may be recovered by recycling the spent material to agriculture. However, this may require re-design of the treatment system especially with respect to particle size to make recycling technically feasible.

Performance of an On-Site Wastewater Treatment System Using Reactive Filter Media and a Sequencing Batch Constructed Wetland

Many on-site wastewater treatment systems, such as soil treatment systems, are not sustainable in terms of purification efficiency, nutrient recycling potential, and economics. In this case study, a sequencing batch constructed wetland (SBCW) was designed and added after a package treatment plant (PTP) using reactive filter media for phosphorus (P) removal and recycling. The treatment performance of the entire system in the start-up phase and its possible applicability in rural areas were investigated. Raw and treated effluents were sampled during a period of 25 weeks and analyzed for nitrogen, phosphorus, BOD7, and bacteria. Field measurements were made of wastewater flow, electrical conductivity, oxygen, and temperature. The entire system removed total-P and total inorganic nitrogen (TIN) by 83% and 22%, respectively. High salt concentration and very low wastewater temperature were possible reasons for these unexpectedly low P and TIN removal efficiencies. In contrast, removal rates of bacteria (Escherichia coli, enterococci) and organic matter (as BOD) were high, due to filtration in the alkaline medium Polonite® (Ecofiltration Nordic AB, Stockholm, Sweden) and the fine sand used as SBCW substrate. High pH in effluent from the PTP was efficiently reduced to below pH 9 in the SBCW, meeting recommendations by environmental authorities in Sweden. We concluded that treating cold on-site wastewater can impair treatment performance and that technical measures are needed to improve SBCW performance.

Modelling Phosphorus Sorption Kinetics and the Longevity of Reactive Filter Materials Used for On-Site Wastewater Treatment

Use of reactive filter media (RFM) is an emerging technology in small-scale wastewater treatment to improve phosphorus (P) removal and filter material longevity for making this technology sustainable. In this study, long-term sorption kinetics and the spatial dynamics of sorbed P distribution were simulated in replaceable P-filter bags filled with 700 L of reactive material and used in real on-site treatment systems. The input data for model calibration were obtained in laboratory trials with Filtralite P®, Polonite® and Top16. The P concentration breakthrough threshold value was set at an effluent/influent (C/C0) ratio of 1 and simulations were performed with P concentrations varying from 1 to 25 mg L−1. The simulation results showed that influent P concentration was important for the breakthrough and longevity, and that Polonite performed best, followed by Top16 and Filtralite P. A 100-day break in simulated intermittent flow allowed the materials to recover, which for Polonite involved slight retardation of P saturation. The simulated spatial distribution of P accumulated in the filter bags showed large differences between the filter materials. The modelling insights from this study can be applied in design and operation of on-site treatment systems using reactive filter materials.

Non-biological methods for phosphorus and nitrogen removal from wastewater: A gap analysis of reinvented-toilet technologies with respect to ISO 30500

The aims of the Reinvent the Toilet Challenge (RTTC) include creation of an off-the-grid sanitation system with operating costs of less than US$0.05 per user per day. Because of the small scale at which many reinvented toilets (RT) are intended to operate, non-biological treatment has been generally favored. The RTTC has already instigated notable technological advances in non-sewered sanitation systems (NSSS). However, increasingly stringent effluent standards for N and P could limit the deployment of current RT in real-world scenarios, despite the urgent need for these systems. The newly adopted ISO 30500 standards for water reuse in NSSS dictate minimal use of chemical/biological additives, while at the same time requiring a 70% and 80% reduction in total nitrogen and phosphorus, respectively. This document provides a brief overview of the mature and emerging technologies for N and P removal from wastewater. At present, the dearth of nutrient removal methods proven to be effective at small scales is a significant barrier to meeting ISO 30500 standards. Closing the gap between RTs and ISO 30500 will require significant investments in basic R&D of emerging technologies for non-biological N and P remediation and/or increased reliance on biological processes. Adaptation of existing nutrient-removal technologies to small-scale NSSS is a viable option that merits additional investigation.

Calcined Eggshell as a P Reactive Media Filter-Batch Tests and Column Sorption Experiment

The goal of the study was to assess the sorption properties of calcined eggshells (CEs) as a P reactive media filter. The CEs were calcined in a temperature of 900 °C. A double stage test was performed: batch studies (kinetic and equilibrium) and small-scale column experiment. The estimation of optimal mass ratio of CEs for perspective usage was the additional benefit of column experiment. The short kinetic tests showed that 5 min of contact time with solution of initial concentration of 6.020 mgP-PO₄ L^-1 is enough to reduce the P-PO₄ in 100%. The equilibrium studies were conducted with P-PO₄ solution of 6.020 to 977.7 mg L^-1 with contact time of 30 min. The obtained data was compensated by non-linear regression using the Marquardt algorithm in the Statgraphics Centurion XVI. The eggshell calcined characterized by high sorption capacity (S _max = 72.87 mg g^-1) obtained from the Langmuir isotherm model with a good fit (96.77%). To choose the appropriate ratio of a sand filter to eggshells amendment, four small columns were constructed and fed with P-PO₄ solution (C _in ≈ 5 mg L^-1). The percentage mass (m/m) of CEs in the columns was 0.0 (the reference one); 1.0; 2.5; and 5.0. The unit sorption obtained during 95 days of column experiment was 10.668, 4.277, and 2.286 mg P-PO₄ g^-1 for 1.0, 2.5, and 5.0%, respectively. For practical implementation, the most recommended addition seems to be 1% of CEs. It corresponds, e.g., to the mass of 49 kg CEs for septic tank system.

Immobilization of powdery calcium silicate hydrate via PVA covalent cross-linking process for phosphorus removal

Calcium silicate hydrate (CSH) is a popular material used for phosphorus removal in recent years. In this work, a novel immobilized material, polyvinyl alcohol-CSH (PVA-CSH), was prepared using a 1:10 weight ratio of CSH powder to 8% PVA solution and then used for phosphorus removal. Samples were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The adsorption mechanism and practical application properties of phosphorus wastewater were studied by sequential batch and continuous flow experiment. The results showed PVA-CSH possessed a porous network structure and an average pore diameter of 24.94 ± 0.11 nm. Furthermore, the CSH functional groups were unaffected by PVA immobilization. Compared with CSH, PVA-CSH did not easily lose CSH after being immobilized by PVA, and the duration of efficient phosphorus removal stage was approximately 20 h longer than that of CSH. In addition, the effluent turbidity of PVA-CSH was 0.11 ± 0.03 NTU during the continuous operation period, which was significantly lower than CSH. In summary, this research study demonstrated the significant potential of PVA-CSH for practical phosphorus removal.

Removal of pharmaceuticals, perfluoroalkyl substances and other micropollutants from wastewater using lignite, Xylit, sand, granular activated carbon (GAC) and GAC+Polonite® in column tests - Role of physicochemical properties

This study evaluated the performance of five different sorbents (granular activated carbon (GAC), GAC + Polonite^® (GAC + P), Xylit, lignite and sand) for a set of 83 micropollutants (MPs) (pharmaceuticals, perfluoroalkyl substances (PFASs), personal care products, artificial sweeteners, parabens, pesticide, stimulants), together representing a wide range of physicochemical properties. Treatment with GAC and GAC + P provided the highest removal efficiencies, with average values above 97%. Removal rates were generally lower for Xylit (on average 74%) and lignite (on average 68%), although they proved to be highly efficient for a few individual MPs. The average removal efficiency for sand was only 47%. It was observed that the MPs behaved differently depending on their physicochemical properties. The physicochemical properties of PFASs (i.e. molecular weight, topological molecular surface area, log octanol water partition coefficient (K_ow) and distribution coefficient between octanol and water (log D)) were positively correlated to observed removal efficiency for the sorbents Xylit, lignite and sand (p < 0.05), indicating a strong influence of perfluorocarbon chain length and associated hydrophobic characteristics. In contrast, for the other MPs the ratio between apolar and polar surface area (SA/SP) was positively correlated with the removal efficiency, indicating that hydrophobic adsorption may be a key feature of their sorption mechanisms. GAC showed to be the most promising filter medium to improve the removal of MPs in on-site sewage treatment facilities. However, more studies are needed to evaluate the removal of MPs in field trials.

Performance and adsorption mechanism of a magnetic calcium silicate hydrate composite for phosphate removal and recovery

A novel magnetic calcium silicate hydrate composite (Fe₃O₄@CSH) was proposed for phosphorus (P) removal and recovery from a synthetic phosphate solution, facilitated by a magnetic separation technique. The Fe₃O₄@CSH material was characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), powder Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), zeta-potential and magnetic curves. The chemical composition and structure of Fe₃O₄@CSH and the successful surface loading of hydroxyl functional groups were confirmed. Phosphate adsorption kinetics, isotherm, and thermodynamic experiments showed that adsorption reaches equilibrium at 24 h, with a maximum adsorption capacity of 55.84 mg P/g under optimized experimental conditions. Adsorption kinetics fitted well to the pseudo second-order model, and equilibrium data fit the Freundlich isotherm model. Thermodynamic analysis provided a positive value for ΔH° (129.84 KJ/mol) and confirmed that phosphate adsorption on these materials is endothermic. The P-laden Fe₃O₄@CSH materials could be rapidly separated from aqueous solution by a magnetic separation technique within 1 min. A removal rate of more than 60% was still obtained after eight adsorption/desorption cycles, demonstrating the excellent reusability of the particles. The results demonstrated that the Fe₃O₄@CSH materials had high P-adsorption efficiency and were reusable.

Impact of on-site, small and large scale wastewater treatment facilities on levels and fate of pharmaceuticals, personal care products, artificial sweeteners, pesticides, and perfluoroalkyl substances in recipient waters

One of the main risks associated with effluents from both wastewater treatment plants (WWTPs) and on-site sewage treatment facilities (OSSFs) is the release of micropollutants (MPs) in receiving water bodies. However, the impact of MPs present in the effluents of OSSFs in the aquatic environment has not been studied so far. The current study evaluates the impact of the effluents of OSSFs and small-to-large scale WWTPs on natural waters. The discharge of 74 MPs was assessed including pharmaceuticals, personal care products, pesticides, artificial sweeteners and perfluoroalkyl substances (PFASs). The sampling was carried out within a Swedish catchment and included three sites that are exclusively affected by OSSFs and other sites that are mainly affected by WWTPs or a mixture of sources (7 sites, 28 samples). Results show that although OSSFs serve a much smaller total number of people, the MPs emitted from OSSFs reached the aquatic environment in significant quantities (concentrations of >150ngL^-1 of ∑MPs). The composition profiles for sites affected by WWTPs were similar and were dominated by sucralose (27% of the ∑MPs), caffeine (27% of the ∑MPs), lamotrigine (10% of the ∑MPs), desvenlafaxine (5% of the ∑MPs), and diclofenac (4% of the ∑MPs). In contrast, the sites affected by OSSFs showed high variability, exhibiting a different profile from those affected by WWTPs and also from each other, demonstrating that OSSFs are not homogeneous sources of MPs. Some specific compounds, such as diethyltoluamide (DEET) and caffeine, were proportionally much more important at sites affected by OSSFs than at sites affected by WWTPs (representing a much higher percentage of the ∑MPs in the OSSFs). In contrast, PFASs did not show high concentration variation among the different sampling sites and the composition profiles were relatively similar, indicating that these substances follow different routes of entry into the aquatic environment.

Phosphorus removal from UASB reactor effluent by reactive media filtration

The phosphorus (P) and BOD7 removal performance of an upflow packed bed reactor (PBR) filled with two reactive filter media was studied over 50 weeks. The lower one-fifth of the reactor was filled with calcium-silicate-hydrate (Sorbulite®) and the upper four-fifth with calcium-silicate (Polonite®). A laboratory-scale upflow anaerobic sludge bed reactor (UASB) delivered wastewater to the PBR. A model was developed to describe the gradient in P concentration change in the reactor, based on reaction kinetics. The reaction terms were assumed to follow the Langmuir isotherm, based on the results obtained in a batch test. First, a comparison was made between experimental and simulated results. The capability of the model to forecast P removal capacity was then tested for three hypothetical cases: (i) reactor filled with Sorbulite and Polonite, (ii) reactor filled with only Sorbulite, and (iii) reactor filled with only Polonite. Finally, a sensitivity analysis was performed for the main parameters in the model. The average removal of P and BOD7 from the UASB effluent was 98% and 90%, respectively. The starting pH of the dual-medium effluent was 12.2 and decreased gradually over time to 11.1. The simulation both overestimated and underestimated mean measured P removal but was within the range of maximum and minimum measured values. The hypothetical cases revealed that most P was removed by Polonite due to calcium phosphate precipitation. The removal capacity of the two filter materials and their layer height in the reactor were the most sensitive parameters in the simulation.

Evaluation of thermally-modified calcium-rich attapulgite as a low-cost substrate for rapid phosphorus removal in constructed wetlands

The cost-effective and geographically available substrates are vital for the design of constructed wetlands (CWs), especially the saturated subsurface flow CWs, which are deemed as an efficient way to remove the inlet-lake phosphorus concentrations. In this study, phosphorus removal of thermally-treated calcium-rich attapulgite (TCAP) with varied particle sizes (0.2-0.5 mm, 0.5-1 mm and 1-2 mm) was assessed using batch and long-term column experiments to evaluate its feasibility as a CWs substrate. The phosphorus-bound mechanism in TCAP was identified in various initial phosphorus concentrations. Batch studies indicated that more than 95% of P can be rapidly (<1 h) removed by TCAP from solution with a concentration of 20 mg P/L, and P sorption can be well fitted by a pseudo-second-order equation. The maximum P sorption capacity of TCAP was in the range of 4.46-5.99 mg P/g, and the availability of Ca²⁺ concentration might limit the P removal capacity of TCAP at high phosphorus concentrations. Both the P removal rate and capacities decreased with the increase of TCAP particle sizes. Column P removal experiments indicated that hydraulic retention time (HRT) exerts great influence on P removal performance and longer HRTs favor the dissolution of CaO in TCAP, consequently increasing the P removal rate. In a 150-day P removal experiment, TCAP removed an average of 93.1%-95.4% of the influent P with a HRT of eight hours. Both the batch and chemical extraction of the P fraction of TCAP showed that the P removed by TCAP was mainly through formation of Ca phosphate precipitation. However, the species of Ca-P precipitation formed might be varied in different phosphorus concentrations. All results indicated that TCAP can be a suitable substrate when used in CWs, and field experiments should be carried out to test its real P removal performance in the future.

Screening and prioritization of micropollutants in wastewaters from on-site sewage treatment facilities

A comprehensive screening of micropollutants was performed in wastewaters from on-site sewage treatment facilities (OSSFs) and urban wastewater treatment plants (WWTPs) in Sweden. A suspect screening approach, using high resolution mass spectrometry, was developed and used in combination with target analysis. With this strategy, a total number of 79 micropollutants were successfully identified, which belong to the groups of per- and polyfluoroalkyl substances (PFASs), pesticides, phosphorus-containing flame retardants (PFRs) and pharmaceuticals and personal care products (PPCPs). Results from this screening indicate that concentrations of micropollutants are similar in influents and effluents of OSSFs and WWTPs, respectively. Removal efficiencies of micropollutants were assessed in the OSSFs and compared with those observed in WWTPs. In general, removal of PFASs and PFRs was higher in package treatment OSSFs, which are based on biological treatments, while removal of PPCPs was more efficient in soil bed OSSFs. A novel comprehensive prioritization strategy was then developed to identify OSSF specific chemicals of environmental relevance. The strategy was based on the compound concentrations in the wastewater, removal efficiency, frequency of detection in OSSFs and on in silico based data for toxicity, persistency and bioaccumulation potential.

Removal and recovery of phosphate from water by calcium-silicate composites-novel adsorbents made from waste glass and shells

The removal and recovery of phosphate from water by calcium-silicate composite (CSC) and alkali-treated calcium-silicate composite (ASC) was investigated. ASC had a higher specific surface area and total pore volume, and exhibited better performance of phosphate adsorption than CSC. In the batch mode adsorption studies, the isotherm adsorption experiments data fitted well the Langmuir isotherm model and the maximum adsorption capacities were 120 and 73.0 mg/g for ASC and for CSC, respectively. For the kinetic study, the experimental data fitted very well the pseudo-second-order kinetic model. The uptake of phosphate could be performed well over a wide pH range, from 3.0 to 13.0 for ASC and from 4.0 to 13.0 for CSC. The adsorption of phosphate by ASC was very selective even with 10 times higher concentration of other coexistent anions. For the adsorption of low phosphate concentration (10 mg/L), ASC could efficiently remove phosphate at the dosage of 0.8 g/L, while CSC was even difficult to remove phosphate at the dosage of 4.0 g/L. Phosphate fractionation results and FTIR spectra showed that phosphate-Ca complex was formed through phosphate adsorption process. The adsorbed phosphate could be successfully desorbed by 2% citric acid solution, indicating that the adsorbent after adsorbed phosphate could be reusable as fertilizer in the agricultural field.

Phosphorus removal from wastewater by field-scale fortified filter beds during a one-year study

Due to low availability of alternative technologies, rural communities are unable to comply with national wastewater discharge limits. This study tested the effectiveness of filter bed fortification with biochar on phosphorus removal. Water-tight down-flow beds of sand and gas concrete, constructed alongside a reference sand bed (all 0.8 m deep and 0.75 m(2) surface area), were topped with a 0.2 m biochar layer. Pre-treated domestic wastewater with mean concentrations of 6.4 mg/L [Formula: see text] and 142.6 NTU, was infiltrated at 4 cm/d hydraulic loading rate. Ultimately, the biochar-sand was relatively outstanding in turbidity reduction, achieving <5 NTU. The biochar-gas concrete exhibited superior performance in [Formula: see text] removal, trapping 32.3 g (40.2%), compared with 20.5 g (25.6%) and 15.5 g (19.3%) by biochar-sand and reference bed respectively. However, statistical analysis revealed a weak correlation between pH and biochar-gas concrete removal efficiency (r(2 )= 0.2). The relationship was stronger for biochar-sand [Formula: see text] (r(2 )= 0.5) than reference (r(2 )= 0.4) bed. Paired samples t-tests showed that incorporating biochar into the sand bed significantly (p = .04) improved its [Formula: see text] removal efficiency. In conclusion, sand bed fortification with biochar could be an important measure for improving P removal and wastewater clarification efficiency.

Immobilization of lead by phosphate amended Polonite

Polonite is an alkaline material that is used to remove nutrients from domestic wastewater and it has been evaluated as a fertilizer. Stabilization of Pb by Polonite and Polonite amended with orthophosphate, PO4, (Polonite-P) was studied. Octacalcium phosphate (Ca8H2(PO4)6·5H2O) was a primary species of PO4 formed on the surface of Polonite-P. Lead was found to be associated with pozzolanic reaction products in Pb treated Polonite and Pb treated Polonite-P samples. Formation of Pb oxides, as precipitates or surface complexes, were substantial constituents of Pb treated Polonite. Dissolution of Ca8H2(PO4)6·5H2O followed by formation of Pb4O(PO4)2 was a probable mechanism of Pb removal by Polonite-P. Polonite-P could be a suitable replacement for current PO4 sources as a Pb stabilization agent. Finally, LDI-TOF was an effective technique for evaluating forms of Pb on Polonite and Polonite-P.

The use of reactive material for limiting P-leaching from green roof substrate

The aim of the study is to assess the influence of drainage layer made of reactive material Polonite(®) on the water retention and P-PO(4) concentration in runoff. A column experiment was performed for extensive substrate underlined by 2 cm of Polonite(®) layer (SP) and the same substrate without supporting layer as a reference (S). The leakage phosphorus concentration ranged from 0.001 to 0.082 mg P-PO(4)·L(-1), with average value 0.025 P-PO(4)·L(-1) of S experiment and 0.000-0.004 P-PO(4)·L(-1) and 0.001 P-PO(4)·L(-1) of SP experiment, respectively. The 2 cm layer of Polonite(®) was efficient in reducing P outflow from green roof substrate by 96%. The average effluent volumes from S and SP experiments amounted 61.1 mL (5.8-543.3 mL) and 46.4 mL (3.3-473.3 mL) with the average irrigation rate of 175.5 mL (6.3-758.0 mL). The substrate retention ability of S and SP experiments was 65% and 74%, respectively. Provided with reactive materials, green roof layers implemented in urban areas for rain water retention and delaying runoff also work for protection of water quality.

Effect of temperature on the performance of laboratory-scale phosphorus-removing filter beds in on-site wastewater treatment

P-sorbing filter beds appear to be viable options for treating wastewater to reduce P discharges and recover this non-renewable resource. However, greater knowledge of filters' responses to temperature variations is required to assess their likely performance in full-scale applications and facilitate the transfer of laboratory results to the field. Thus, in the present study two filter materials (Top16 and Polonite) were characterized physicochemically and effects of temperature on their performance were investigated under controlled laboratory conditions. Using a 2(2) factorial design and secondary wastewater eight filter columns were tested at temperatures of 4.3°C and 16.5°C. Temperature significantly (α=0.05) and strongly affected the P binding capacity of both materials, as it was 1.2- and 1.5-fold higher at 16.5°C than at 4.3°C for Top16 and Polonite, respectively. This is probably due to the enhanced precipitation of calcium phosphates at higher temperature. Observed reductions in total organic carbon content in the wastewater were also positively correlated with temperature, while the pH and reduction of dissolved organic carbon remained unaffected. The physicochemical analyses indicated that several calcium phases dissolved from the filter materials, primarily gypsum and bassanite from Top16 and Portlandite from Polonite. No clear evidence of any crystalline calcium phosphates was observed in the used materials. The results clearly show that temperature strongly influences the retention of P in filters and its effects should be carefully considered before using candidate filters in full-scale applications.

Effect of organic load on phosphorus and bacteria removal from wastewater using alkaline filter materials

The organic matter released from septic tanks can disturb the subsequent step in on-site wastewater treatment such as the innovative filters for phosphorus removal. This study investigated the effect of organic load on phosphorus (P) and bacteria removal by reactive filter materials under real-life treatment conditions. Two long-term column experiments were conducted at very short hydraulic residence times (average ~5.5 h), using wastewater with high (mean ~120 mg L(-1)) and low (mean ~20 mg L(-1)) BOD7 values. Two alkaline filter materials, the calcium-silicate material Polonite and blast furnace slag (BFS), were tested for the removal capacity of total P, total organic carbon (TOC) and Enterococci. Both experiments showed that Polonite removed P significantly (p < 0.01) better than BFS. An increase in P removal efficiency of 29.3% was observed for the Polonite filter at the lower concentration of BOD7 (p < 0.05). Polonite was also better than BFS with regard to removal of TOC, but there were no significant differences between the two filter materials with regard to removal of Enterococci. The reduction in Enterococci was greater in the experiment using wastewater with high BOD7, an effect attributable to the higher concentration of bacteria in that wastewater. Overall, the results demonstrate the importance of extensive pre-treatment of wastewater to achieve good phosphorus removal in reactive bed filters and prolonged filter life.

Efficacy of reactive mineral-based sorbents for phosphate, bacteria, nitrogen and TOC removal--column experiment in recirculation batch mode

Two mineral-based materials (Polonite and Sorbulite) intended for filter wells in on-site wastewater treatment were compared in terms of removal of phosphate (PO4-P), total inorganic nitrogen (TIN), total organic carbon (TOC) and faecal indicator bacteria (Escherichia coli and Enterococci). Using an innovative, recirculating system, septic tank effluent was pumped at a hydraulic loading rate of 3000 L m(2) d(-1) into triplicate bench-scale columns of each material over a 90-day period. The results showed that Polonite performed better with respect to removal of PO4-P, retaining on average 80% compared with 75% in Sorbulite. This difference was attributed to higher CaO content in Polonite and its faster dissolution. Polonite also performed better in terms of removal of bacteria because of its higher pH value. The total average reduction in E. coli was 60% in Polonite and 45% in Sorbulite, while for Enterococci the corresponding value was 56% in Polonite and 34% in Sorbulite. Sorbulite removed TIN more effectively, with a removal rate of 23%, while Polonite removed 11% of TIN, as well as TOC. Organic matter (measured as TOC) was accumulated in the filter materials but was also released periodically. The results showed that Sorbulite could meet the demand in removing phosphate and nitrogen with reduced microbial release from the wastewater treatment process.

Batch investigations on P immobilization from wastewaters and sediment using natural calcium rich sepiolite as a reactive material

Phosphorus from wastewaters and sediment flux to surface water represents a major source of lake eutrophication. Active filtration and in situ capping (which refers to placement of a covering or cap over an in-situ deposit of contaminated sediment) are widely used as a means to immobilize phosphorus from wastewaters and sediment, to mitigate lake eutrophication. There is, however, a need to develop more efficient means of immobilizing phosphorus through the development of binding agents. In this study, natural calcium-rich sepiolite (NCSP) was calcined at a range of temperatures, to enhance its phosphorus removal capacity. Batch studies showed that the 900 °C calcinated NCSP (NCSP900) exhibited excellent sorption performance, attaining a phosphorus removal efficiency of 80.0%-99.9% in the range of 0.05 mg/L-800 mg/L phosphorus concentrations with a dosage of 20 g/L. The material displayed rapid sorption rate (maximum amount of 99.9% of phosphate removal with 5 min) and could lower the very high phosphate concentration (200 mg/L) to less than 0.1 mg/L after 4 h adsorption. It was also noted that factors such as pH, competing anions (except [Formula: see text] ) and humic acid, had no effect on phosphorus removal capacity. The sediment immobilization experiment indicated that NCSP900 had the capacity to transform reactive phosphorus into inert-phosphorus and significantly reduce the amount of algal-bioavailable phosphorus. The excellent phosphorus binding performance of NCSP900 was mainly due to the improvement of point of zero charge (pHPZC) as well as the transformation of the inert-calcium of NCSP to active free CaO during calcination. Phosphorus speciation indicated that phosphorus was mainly captured by relatively stable calcium-bound phosphorus (Ca-P) precipitation, which can account for 80.1% of the total phosphorus. This study showed that NCSP900 could be used as an efficient binding agent for the sequestration of phosphorus from wastewaters and sediment.

Synthesis and Enhanced Phosphate Recovery Property of Porous Calcium Silicate Hydrate Using Polyethyleneglycol as Pore-Generation Agent

The primary objective of this paper was to synthesize a porous calcium silicate hydrate (CSH) with enhanced phosphate recovery property using polyethyleneglycol (PEG) as pore-generation agent. The formation mechanism of porous CSH was proposed. PEG molecules were inserted into the void region of oxygen-silicon tetrahedron chains and the layers of CSH. A steric hindrance layer was generated to prevent the aggregation of solid particles. A porous structure was formed due to the residual space caused by the removal of PEG through incineration. This porous CSH exhibited highly enhanced solubility of Ca²⁺ and OH^- due to the decreased particle size, declined crystalline, and increased specific surface area (S_BET) and pore volume. Supersaturation was increased in the wastewater with the enhanced solubility, which was beneficial to the formation of hydroxyapatite (HAP) crystallization. Thus, phosphate can be recovered from wastewater by producing HAP using porous CSH as crystal seed. In addition, the regenerated phosphate-containing products (HAP) can be reused to achieve sustainable utilization of phosphate. The present research could provide an effective approach for the synthesis of porous CSH and the enhancement of phosphate recovery properties for environmental applications.

The effect of calcium on the treatment of fresh leachate in an expanded granular sludge bed bioreactor

This research investigated the calcium effect on the anaerobic treatment of fresh leachate in an expanded granular sludge bed (EGSB) bioreactor under mesophilic conditions. The observations show that the bioreactor, inoculated with anaerobic granular sludge, can be started up only in about 40 days for the treatment of calcium-containing fresh leachate with chemical oxygen demand (COD) removal efficiency above 90% and organic loading rate up to 72.84 kg COD/m(3) day. The calcium accumulation onto the granules was monotonically related to the calcium concentration, accounting for 17-18 wt.% of Ca in the suspended solid in the form of calcium carbonate, phosphates/phosphonates and carboxylates. The mineral formation significantly increased the granule settling velocity (by ∼ 50%) and the suspended solid concentration (by ∼ 100%). However, the effect of calcium precipitation on the specific methanogenic activity and the CH(4) production rate was complex, first positive during the start-up but later on negative.