Search

This work aims to evaluate the effect of new contaminant diclofenac (DCF) in sewage on the performance of Enhanced Biological Phosphorus Removal (EBPR) and its mechanism. The results showed that low-level DCF had no significant effect on EBPR. However, when the concentration of DCF was 2.0 mg/L, the removal efficiencies of chemical oxygen demand (COD), NH 4 -N and soluble orthophosphate (SOP) decreased significantly to 71.2 ± 4.2%, 78.6 ± 2.9%, and 64.3 ± 4.2%, respectively. Mechanisms revealed that DCF promoted the ratio of protein to polysaccharide in activated sludge extracellular polymers and inhibited anaerobic phosphorus release and oxic phosphorus uptake. Intracellular polymer analysis showed that when the DCF content was 2.0 mg/L, the maximum content of polyhydroxyalkanoates (PHA) was only 2.5 ± 0.4 mmol-C/g VSS, which was significantly lower than that in the blank. Analysis of key enzyme activities indicated that the presence of DCF reduced the activities of exopolyphosphatase and polyphosphate kinase.+ -N and soluble orthophosphate (SOP) decreased significantly to 71.2 ± 4.2%, 78.6 ± 2.9%, and 64.3 ± 4.2%, respectively. Mechanisms revealed that DCF promoted the ratio of protein to polysaccharide in activated sludge extracellular polymers and inhibited anaerobic phosphorus release and oxic phosphorus uptake. Intracellular polymer analysis showed that when the DCF content was 2.0 mg/L, the maximum content of polyhydroxyalkanoates (PHA) was only 2.5 ± 0.4 mmol-C/g VSS, which was significantly lower than that in the blank. Analysis of key enzyme activities indicated that the presence of DCF reduced the activities of exopolyphosphatase and polyphosphate kinase., Competing Interests: Declaration of competing interest Statement All authors have read and understood the requirements of the Journal. We declare that there are no conflicts of interest. Jianwei Zhao, Mingxue Xin, Jing Zhang, Yingjie Sun, Siyi Luo, Huawei Wang, Yanan Wang, Xuejun Bi. E-mail：zhaojianwei@hnu.edu.cn； Zhaojianwei1213@yahoo.com.mailto:Zhaojianwei1213@yahoo.com, (Copyright © 2019 Elsevier Ltd. All rights reserved.)

The separation of urine at source for phosphorus (P) recovery is attractive taking into account the high P concentration and small volume. However, the treatment of urine is still challenging due to its unpleasant odor and hygiene problems. Because the above problems could be solved by acidification to keep the pH of urine below 4, we propose a novel strategy to recover P from acidified urine using tailored hydrous zirconia-coated magnetite nanoparticles (Fe 3 O 4 @ZrO 2 ). This strategy involves the selective adsorption of phosphate by easily separable and reusable Fe 3 O 4 @ZrO 2 , the desorption of adsorbed phosphate, and the precipitation of desorbed phosphate as calcium phosphate fertilizer. The results indicated that at pH 4, the P in synthetic urine was selectively adsorbed and could be exhausted using Fe 3 O 4 @ZrO 2 . Nearly all (>97.5%) of the sequestered P on the Fe 3 O 4 @ZrO 2 nanoparticles was stripped using ≥1 M NaOH solution and ~100% of the stripped P was then successfully transformed into calcium phosphate, upon adding CaCl 2 at pH >12 and a Ca/P molar ratio of 3. The liquid/solid (Fe 3 O 4 @ZrO 2 particles) mixture could be conveniently separated for reuse using an external magnetic field. The reusability of the Fe 3 O 4 @ZrO 2 nanoparticles in the extraction of P from synthetic urine was confirmed using five cycles of the adsorption-desorption process and their performance validated using real urine samples. The mechanism of phosphate adsorption was investigated using XPS, FTIR and zeta potential measurements, showing that phosphate was chemically adsorbed on the surface through direct coordination to zirconium atom via ligand exchange., (Copyright © 2019 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Due to the shortage of phosphorus resources and the limitations of existing phosphorus recovery methods, phosphorus recovery in the form of vivianite has attracted considerable attention with its natural ubiquity, easy accessibility and foreseeable economic value. This review systematically summarizes the chemistry of vivianite, including the characteristics, formation process and influencing factors of the material. Additionally, the potential of phosphorus recovery as vivianite from wastewater has also been comprehensively examined from the prospects of economic value and engineering feasibility. In general, this method is theoretically and practically feasible, and brings some extra benefits in WWTPs. However, the insufficient understanding on vivianite recovery in wastewater/sludge decelerate the development and exploration of such advanced approach. Further researches and cross-field supports would facilitate the improvement of this technique in the future., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Phosphate rock in Guiyang (Southwest of China) is used for the phosphate production, and hence generating a by-product phosphogypsum (PG). From 2007, part of the PG was used as main raw material for cemented backfill. The main objective of this paper is to investigate the geochemical evolution of metals before and after the PG inclusion into the backfill matrix. A sequential extraction procedure was selected to determine the chemical speciation of metals in phosphate rock, PG, binder and field backfill samples. Dynamics of metals going from phosphate rock and PG to backfill have been evaluated. The results showed that almost all the metals in the PG and binder had been effectively transferred to the backfill. Furthermore, compared to metals taken out along with phosphate rock exploitation, PG-based cemented backfill might bring some metals back but with only little metals in mobile fraction. Additionally, in order to determine the long-term behavior of metals in PG-based cemented backfill, the field samples which were backfilled from 2007 to 2016 were collected and analyzed. The results showed that total amounts of metals in backfill were all within similar range, indicating that the cemented PG backfill could be an effective method to solidify/stabilize metals in PG. Nevertheless, Due to the high water-soluble fractions detected, the concentrations of As, Mn and Zn should be continuously monitored., (Copyright © 2017. Published by Elsevier Ltd.)

Biochar is the solid product of biomass pyrolysis that can be used for carbon sequestration, soil amendment, and pollution remediation. The use of biochar as an adsorbent for the removal of water contaminants has elicited increasing interest due to the multifunctional properties of this material. The application of biochar in the adsorption of inorganic nutrients from eutrophic water has not been reviewed. This review focuses on recent research on the use of biochar for the adsorption of inorganic nitrogen (ammonium and nitrate) and phosphorus (phosphate) from water, especially for the main influence factors and mechanisms for nitrogen and phosphorus adsorption on biochar.

In this study, a granular material (GM) developed from building waste was used for phosphate removal from phosphorus-containing wastewater. Batch experiments were executed to investigate the phosphate removal capacity of this material. The mechanism of removal proved to be a chemical precipitation process. The characteristics of the material and resulting precipitates, the kinetics of the precipitation and Ca 2+ liberation processes, and the effects of dosage and pH were investigated. The phosphate precipitation and Ca 2+ liberation processes were both well described by a pseudo-second-order kinetic model. A maximum precipitation capacity of 0.51 ± 0.06 mg g -1 and a liberation capacity of 6.79 ± 0.77 mg g -1 were measured under the experimental conditions. The processes reached equilibrium in 60 min. The initial solution pH strongly affected phosphate removal under extreme conditions (pH <4 and pH >10). The precipitates comprised hydroxyapatite and brushite. This novel GM can be considered a promising material for phosphate removal from wastewater.

Homogeneous nucleation of hydroxyapatite (HAP) crystallization in high levels of supersaturation solution has a negative effect on phosphorus recovery efficiency because of the poor settleability of the generated HAP microcrystalline. In this study, a new high-performance approach for phosphorus recovery from anaerobic supernatant using three series-coupled air-agitated crystallization reactors was developed and characterized. During 30-day operation, the proposed process showed a high recovery efficiency (∼95.82%) and low microcrystalline ratio (∼3.11%). Particle size analysis showed that the microcrystalline size was successively increased (from 5.81 to 26.32 μm) with the sequence of series-coupled reactors, confirming the conjectural mechanism that a multistage-induced crystallization system provided an appropriate condition for the growth, aggregation, and precipitation of crystallized products. Furthermore, the new process showed a broad spectrum of handling ability for different concentrations of phosphorus-containing solution in the range of 5-350 mg L -1 , and the obtained results of phosphorus conversion ratio and recovery efficiency were more than 92% and 80%, respectively. Overall, these results showed that the new process exhibited an excellent ability of efficient phosphorus recovery as well as wide application scope, and might be used as an effective approach for phosphorus removal and recovery from wastewater., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

The patients with end-stage of renal disease (ESRD) need to take oral phosphate binder. Traditional phosphate binders may leave the disadvantage of aluminum intoxication or cardiac calcification. Herein, Mg-Fe-Cl hydrotalcite-like nanoplatelet (HTln) is for the first time characterized as potential oral phosphate binder, with respect to its phosphorus uptake capacity in cow milk and cellular cytotoxicity. A novel method was developed for synthesizing the Mg-Fe-Cl HTln powder in different Mg(2+): Fe(3+) ratios where the optimization was 2.8:1. Addition of 0.5 g Mg-Fe-Cl HTln in cow milk could reduce its phosphorus content by 40% in 30 min and by 65% in 90 min. In low pH environment, the Mg-Fe-Cl HTln could exhibit relatively high performance for uptaking phosphorus. During a 90 min reaction of the HTln in milk, no phosphorus restoration occurred. In-vitro cytotoxicity assay of Mg-Fe-Cl HTln revealed no potential cellular cytotoxicity. The cells that were cultured in the HTln extract-containing media were even more viable than cells that were cultured in extract-free media (blank control). The Mg-Fe-Cl HTln extract led to hundred ppm of Mg ion and some ppm of Fe ion in the media, should be a positive effect on the good cell viability.

Phosphorus is one of the elements that have a significant impact on such environmental problems as eutrophication or algal bloom. Phosphorus compounds in water can be hydrolyzed to orthophosphate that is the only form of phosphorus that algae can assimilate. In this study, phosphorus removal in terms of orthophosphate and total phosphorus from wastewater was studied using alum or ferric ions as coagulants. It was observed that alum shows higher phosphorus removal efficiency than ferric ions in the same mole ratio concentrations. The proportion of orthophosphate among total phosphorus did not change significantly during coagulation process when the coagulant concentration is low. However, the proportion becomes gradually decreased as the coagulant concentration increases. Not only the electrolyte concentration difference in solution, but the characteristics of orthophosphate and polyphosphate such as reactivity and ionic size might also cause the differences in the removal rate. Orthophosphate that has greater reactivity than other phosphorus species would be involved in chemical reactions dominantly when large amounts of coagulants are applied. However, the effect of reactivity was diminished due to the large ionic size of polyphosphate and low concentration of electrolyte in low coagulant concentration during the coagulation process., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

This study investigated the role of extracellular polymeric substances (EPSs) in enhanced performance of phosphorus (P) release from waste activated sludge (WAS) by adding rhamnolipid (RL). Results showed that compared to WAS without pretreatment, the released PO4(3-)-P increased with RL addition from 0 to 0.2 g/gTSS (total suspended solid), and increased by 208% under the optimal condition (0.1 g RL/g TSS and 72-h fermentation time). The cumulative PO4(3-)-P was better fitted with pseudo-first-order kinetic model. Moreover, the contents of metal ions increased in liquid but decreased in EPSs linearly with RL addition increasing, and WAS solubilizations were positively correlated with the released metal ions. The enhanced total dissolved P mainly came from cells and others (69.39%, 2.27-fold higher than that from EPSs), and PO4(3-)-P was the main species in both liquid and loosely bound EPSs, but organic P should be non-negligible in tightly bound EPSs., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Membrane adsorption hybrid system (MAHS) was evaluated for the removal of phosphate from a high rate membrane bioreactor (HR-MBR) effluent. The HR-MBR was operated at permeate flux of 30L/m(2)h. The results indicated that the HR-MBR could eliminate 93.1±1.5% of DOC while removing less than 53% phosphate (PO4-P). Due to low phosphate removal by HR-MBR, a post-treatment of strong base anion exchange resin (Dowex(∗)21K-XLT), and zirconium (IV) hydroxide were used as adsorbent in MAHS for further removal of phosphate from HR-MBR effluent. It was found that the MAHS enabled to eliminate more than 85% of PO4-P from HR-MBR effluent. Hence, HR-MBR followed by MAHS lead to simultaneous removal of organics and phosphate in a reliable manner. The experiments were conducted only for a short period to investigate the efficiency of these resins/adsorbents on the removal of phosphorus and high rate MBR for organic removal., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Humic substances (HS) are a major fraction of dissolved organic matters in wastewater. The effect of HS on phosphorus removal by struvite precipitation was investigated using synthetic wastewater under different initial pH values, Mg/P molar ratios and HS concentrations. The composition, morphology and thermal properties of harvested precipitates were analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM) and thermo-gravimetric analysis (TGA), respectively. It showed that inhibition effect of HS reached its maximum value of 48.9% at pH 8.0, and decreased to below 10% at pH>9.0. The increase of Mg/P ratio enhanced phosphorus removal efficiency, and thus reduced the influence of HS on struvite precipitation. At pH 9.0, the inhibitory effect of initial HS concentration matched the modified Monod model with half maximum inhibition concentration of 356mgL(-1), and 29% HS was removed in conjunction with struvite crystallisation. XRD analysis revealed that the crystal form of struvite precipitates was changed in the presence of HS. The morphology of harvested struvite was transformed from prismatic to pyramid owing to the coprecipitation of HS on crystal surface. TGA results revealed that the presence of HS could compromise struvite purity., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

The present work determines the effect of phosphorus content on phosphate uptake rate in a mixed culture of Chlorophyceae in which the genus Scenedesmus dominates. Phosphate uptake rate was determined in eighteen laboratory batch experiments, with samples taken from a progressively more P-starved culture in which a minimum P content of 0.11% (w/w) was achieved. The results obtained showed that the higher the internal biomass P content, the lower the phosphate removal rate. The highest specific phosphate removal rate was 6.5mgPO4-PgTSS(-1)h(-1). Microalgae with a P content around 1% (w/w) attained 10% of this highest removal rate, whereas those with a P content of 0.6% (w/w) presented 50% of the maximum removal rate. Different kinetic expressions were used to reproduce the experimental data. Best simulation results for the phosphate uptake process were obtained combining Steele equation and Hill function to represent the effect of light and intracellular phosphorus content, respectively., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Phosphorus (P) recovery was carried out through struvite precipitation from urines. Human urine, however, contains not only high nutrients for plants, such as P and nitrogen, but also pharmaceuticals and hormones. In this work, effects of magnesium (Mg) dose (in terms of Mg:P ratio) on P recovery efficiency and pharmaceutical amounts contained in struvite were investigated. Batch-scale experiments of synthetic and human urines revealed that struvite precipitation formed more X-shaped crystals with an increased molar ratio of Mg:P, while the amount of pharmaceuticals (tetracycline, demeclocycline, and oxytetracycline) in struvite decreased with an increased molar ratio of Mg:P. The lowest pharmaceutical amounts in struvite were found at the Mg:P ratio of 2:1 from both samples. Moreover, the maximum P recovery efficiency, quantity and purity of struvite were found in the range of 1.21 to 2:1. It indicated that the molar ratio of Mg:P has a significant impact on struvite precipitation in terms of pharmaceutical amounts in struvite; morphology, quantity and purity of struvite; and P recovery.

The adsorption phenomena and specific reaction processes of phosphate onto wasted low grade iron ore with high phosphorus (WLGIOWHP) were studied in this work. Zeta potential and Fourier transform infrared spectroscopy (FTIR) analyses were used to elucidate the interaction mechanism between WLGIOWHP and aqueous solution. The results implied that the main adsorption mechanism was the replacement of surface hydroxyl groups by phosphate via the formation of inner-sphere complex. The adsorption process was characterized by chemical adsorption onto WLGIOWHP. The non-electrostatic model (NEM) was used to simulate the surface adsorption of phosphate onto WLGIOWHP. The total surface site density and protonation constants for NEM (N(T)=1.6×10(-4) mol/g, K(a1)=2.2×10(-4), K(a2)=6.82×10(-9)) were obtained by non-linear data fitting of acid-base titrations. In addition, the NEM was used to establish the surface adsorption complexation modeling of phosphate onto WLGIOWHP. The model successfully predicted the adsorption of phosphate onto WLGIOWHP from municipal wastewater., (Copyright © 2014 Elsevier Inc. All rights reserved.)

At physiological maturity, nutrients in crop residues can be released to the soil where they are incorporated into different labile and non-labile pools while the remainder is retained within the residue itself. The chemical speciation of phosphorus (P) in crop residues is an important determinant of the fate of this P. In this study, we used chemical fractionation and (31)P nuclear magnetic resonance (NMR) spectroscopy, first separately and then together, to evaluate the P speciation of mature oat (Avena sativa) residue. Two water extracts (one employing shaking and the other sonication) and two acid extracts (0.2N perchloric acid and 10% trichloroacetic acid) of these residues contained similar concentrations of orthophosphate (molybdate-reactive P determined by colorimetry) as NaOH-EDTA extracts of whole plant material subsequently analysed by solution (31)P NMR spectroscopy. However, solution (31)P NMR analysis of the extracts and residues isolated during the water/acid extractions indicated that this similarity resulted from a fortuitous coincidence as the orthophosphate concentration in the water/acid extracts was increased by the hydrolysis of pyrophosphate and organic P forms while at the same time there was incomplete extraction of orthophosphate. Confirmation of this was the absence of pyrophosphate in both water and acid fractions (it was detected in the whole plant material) and the finding that speciation of organic P in the fractions differed from that in the whole plant material. Evidence for incomplete extraction of orthophosphate was the finding that most of the residual P in the crop residues following water/acid extractions was detected as orthophosphate using (31)P NMR. Two methods for isolating and quantifying phospholipid P were also tested, based on solubility in ethanol:ether and ethanol:ether:chloroform. While these methods were selective and appeared to extract only phospholipid P, they did not extract all phospholipid P, as some was detected by NMR in the crop residue after extraction. These results highlight the need for careful interpretation of results from chemical fractionation, as separation can be compromised by incomplete recovery and side reactions. This study also highlights the benefits of employing a technique that can simultaneously detect multiple P species (solution (31)P NMR) in combination with chemical fractionation., (Copyright © 2014 Elsevier B.V. All rights reserved.)

The organics and nutrients in industrial and domestic wastewater are increasingly being regarded as a valuable resource for energy and nutrient recovery. Emerging concepts to redesign wastewater treatment as resource recovery systems include the use of different bacteria and algae to partition carbon and nutrients to the particulate phase through assimilation or bio-accumulation. This study evaluates the use of purple phototrophic bacteria (PPB) (also known as purple non-sulphur bacteria or PNSB) for such a biological concentration process through a series of batch tests. The key objectives are to (a) demonstrate consistent selection and enrichment of PPB using infrared light in a non-sterile medium, and (b) achieve effective partitioning of soluble organics, ammonium and phosphate into the PPB culture. PPB were successfully enriched from pre-settled domestic wastewater within 2-3 days and identified as members of the order Rhodobacterales. Under anaerobic conditions with infrared irradiation the enrichment culture was able to simultaneously remove COD (63 ± 5%), NH4-N (99.6%-0.12 ± 0.03 mgN L(-1)) and PO4-P (88%-0.8 ± 0.6 mgP L(-1)) from primary settled domestic wastewater in 24 h. In this experiment, acetate was added as an additional carbon source to demonstrate the maximal nitrogen and phosphorous elimination potential. Almost all the COD removed was assimilated into biomass rather than oxidised to CO2, with the total COD actually increasing during the batch experiments due to phototrophic synthesis. NH4-N and PO4-P were also assimilated by the biomass rather than removed through destructive oxidation or accumulation. The process offers the opportunity to concentrate organics and macronutrients from wastewater in one solids stream that can be anaerobically digested to generate energy and recover nutrients from the concentrated digestate. Technical challenges include the design of a continuous reactor system, as well as efficient delivery of electrons, either through light or chemical sources., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

In the view of limited phosphorous resources and tightened discharge regulations, the recovery of phosphate and nitrate from wastewater is of great interest. Here, the integration of microalgae into wastewater treatment processes is a promising approach. A prototype-scale Twin-Layer photobioreactor immobilizing the green alga Halochlorella rubescens on vertical sheet-like surfaces was constructed and operated using primary and secondary municipal wastewater. The process was not impaired by suspended solids, bacteria or loss of algal biomass by leaching. The average areal microalgal growth was 6.3 gm(-2) d(-1). After treatment, P and N concentrations in the effluents could efficiently be reduced by 70-99%, depending on element and type of wastewater. Mean effluent values of ⩽ 1.0mg L(-1)P and 1.3 mg L(-1)N met the legal discharge limits of the European Water Framework Directive and show a potential to comply with upcoming, more stringent legislation., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

An algae-based membrane bioreactor (A-MBR) was evaluated for high-density algae cultivation and phosphorus (P) removal. The A-MBR was seeded with Chlorella emersonii and operated at a hydraulic retention time of 1day with minimal biomass wastage for about 150days. The algae concentration increased from initially 385mg/L (or 315mg biomass COD/L) to a final of 4840mg/L (or 1664mg COD/L), yielding an average solids (algae biomass+minerals) production rate of 32.5gm(-3)d(-1) or 6.2gm(-2)d(-1). The A-MBR was able to remove 66±9% of the total P from the water while the algal biomass had an average of 7.5±0.2% extracellular P and 0.4% of intracellular P. The results suggest that algae-induced phosphate precipitation by algae is key to P removal and high-density algae cultivation produces P-rich algal biomass with excellent settling properties., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Excessive phosphorus in aquatic systems causes algal bloom resulting in eutrophication. To treat wastewater including effluent of wastewater treatment plant containing various amounts of phosphorus, a series of continuous experiments on removal of phosphorus from water were performed by using an electrochemical method. The spherical type of zero valent iron (ZVI) and silica sand were packed at appropriate volume ratio of 1:2 in a cylindrical column. An electric potential was applied externally, which can be changed as per the operational requirement. The results indicate that optimum hydraulic retention time of 36 min was required to meet the effluent standards with our laboratory-scale experimental setup. Lower amounts of phosphorus were removed by precipitation due to contact with iron, and additional electric potential was not required. In order to remove high amounts of phosphorus (around 150 mg/L as phosphate), external electric potential of 600 V was applied to the reactor. As the precipitation of phosphate mainly occurs at neutral pH, it is likely that FeHPO4 will be the main phosphorus-containing compound. Through the results of the large-scale experiments, the ZVI packed reactor can be used as a filter for removal of phosphorus of less than 10 mg/L as phosphate concentration.

This study investigated the feasibility of using soybean milk by-products (okara) as a sustainable biosorbent for phosphate removal in water and wastewater. The results show that raw okara could hardly decontaminate phosphate from aqueous solutions. Hence, in this work, okara was modified by being cationized using FeCl3 0.25 M (namely iron loaded okara, ILO) to enhance the phosphorus adsorption capacity. The phosphate sorption onto ILO was well achieved under the conditions of pH 3, initial phosphorous concentration of 25 mg/L, biosorbent dose of 20 mg/L and contact time of 7 h. Based on Langmuir model, the maximum adsorption capacity of phosphate by ILO was 4.785 mg/g. The effects of interfering anions were in the order of CO3(2-)>SO4(2-)>NO3(-). It was also observed that Fe(III) was detached during operation. This problem can hinder the sustainable usability of ILO. Thus, further research would be necessary for improving the modification method., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

The mechanisms of carbon and nutrient removal in an open algal-bacterial biofilm reactor and an open bacterial biofilm reactor were comparatively evaluated during the treatment of centrates and domestic wastewater. Comparable carbon removals (>80%) were recorded in both bioreactors, despite the algal-bacterial biofilm supported twice higher nutrient removals than the bacterial biofilm. The main carbon and nitrogen removal mechanisms in the algal-bacterial photobioreactor were assimilation into algal biomass and stripping, while stripping accounted for most carbon and nitrogen removal in the bacterial biofilm. Phosphorus was removed by assimilation into algal-bacterial biomass while no effective phosphorous removal was observed in the bacterial biofilm. Carbon, nitrogen and phosphorus removals of 91 ± 3%, 70 ± 8% and 85 ± 9%, respectively, were recorded in the algal-bacterial bioreactor at 10d of hydraulic retention time when treating domestic wastewater. However, the high water footprint recorded (0.5-6.7 Lm(-2)d(-1)) could eventually compromise the environmental sustainability of this microalgae-based technology., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

The purpose of this study was to develop an efficient and, possibly, a practically operated methodology to recover phosphorus (P) from P-saturated dewatered aluminium sludge cakes (DASC) after the DASC have been beneficially reused as constructed wetlands substrate for P-rich wastewater treatment. A three-step procedure of 1) P extraction by H2SO4, 2) decolorization of extraction leachate via H2O2 oxidation, and 3) AlPO4 precipitation by pH adjustment, has been explored. The optimal conditions to form the precipitates of AlPO4 were determined, with 97% of P and 99% of Al being recovered. The obtained compounds were identified by XRD, FTIR and SEM analyses. Although the purity, structure, characteristics and production control of the compounds are worthy of further investigation, this study provides a showcase of a 'closed loop' regarding the beneficial reuse of a 'waste' and the recovery of useful elements after the reuse.

Biologically and chemically mediated adsorption and precipitation processes offer a range of approaches for removing phosphorus (P) from agricultural, domestic and industrial effluents. Technologies implemented at full-scale include filtration by adsorbent media, such as steel slag, and recovery of phosphorus as struvite, which has been successfully commercialised as a fertiliser. Other promising technologies under investigation include P removal by polymers and nanomaterials as well as struvite formation by bacteria. There is a need to focus future research on improving the efficiency of P removal by adsorption and precipitation. This can be achieved by techniques such as regenerating filters, polymers and nanomaterials for renewed P removal. Research is also needed to optimise the fertiliser potential of struvite precipitates., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

This paper explores the use of a novel microalgae membrane photoreactor (mMR) to polish the effluent from an aerobic membrane bioreactor (MBR) fed with domestic wastewater. Four microalgae species Chlorella (Chlorella sp.), Chlorella vulgaris (C. vulgaris), Scenedesmus quadricauda (S. quadricauda) and Scenedesmus dimorphus (S. dimorphus) were isolated from the environment and tested in batch reactors fed with permeate from the aerobic MBR to evaluate the nutrient removal rates for each species. All four microalgae species were able to completely remove NH4 in the reactor within 3 days. The removal rates of NO3, NO2 and PO4 were between 43-54%, 83-95% and 70-92%, respectively after 3 days in the batch reactor. Subsequently, an MBR-mMR system was operated for 23 days. The mMR was able to remove on average 50% of NH4, 75% of NO2, 35% of NO3 and 60% of PO4 consistently from the MBR effluent under the conditions tested., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Air-cathode single chamber microbial fuel cells (MFCs) were operated with swine wastewater. The maximum power density, the maximum current density, the average value of COD-removal efficiency, and the coulombic efficiency were 1-2.3 W/m(2), 6.0-7.0 A/m(2), 76-91%, and 37-47%, respectively. During operation, 70-82% of the phosphorus was removed from the influent, and some precipitations were observed on the surface of the liquid side of the cathodes. The amount of phosphorus contained in these precipitates was estimated to be equivalent 4.6-27% of the influent. The main component of these precipitates was revealed by X-ray diffraction analysis to be struvite. Furthermore, our results indicate that phosphorus in suspended solid form was first dissolved, and then precipitated on the cathode. By scanning electron microscope observation, the morphology of the precipitates was irregularly shaped, including crystals with hexagonal cross-section surfaces, and was different from the familiar needle-like ones. These results indicate that simultaneous recovery of electrical power and phosphorus from wastewater by microbial fuel cell is possible., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Phosphorus (P) is an element vital for all living organisms, yet the world's reserves of phosphate rock are becoming depleted. This study investigated an effective P recovery method from sludge ash via struvite precipitation. Results showed that more than 95% of the total P content was extracted from sludge ash by applying 0.5 mol/L HCl at a liquid/solid ratio of 50 mL/g. Although heavy metal leaching also occurred during P extraction, cation exchange resin efficiently removed the heavy metals from the P-rich solution. Orthogonal tests showed that the optimal parameters for P precipitation as struvite would be a Mg:N:P molar ratio of 1.6:1.6:1 at pH 10.0. X-ray diffraction analysis validated the formation of struvite. Further investigations revealed that the harvested precipitate had a high struvite content (97%), high P bioavailability (94%), and low heavy metal content, which could be considered a high quality fertilizer.

A novel anaerobic/aerobic/anoxic (AOA) process is proposed to realize denitrifying phosphorous removal in this study, and the characteristic of the AOA process is transferring part of the anaerobic mixed liquor to the post-anoxic zone for providing the carbon source needed for denitrification. The AOA process was operated for 3 months, and the average removal efficiencies of NH4+-N, TN and PO4(3-)-P were 93.0±3.1%, 70.3±2.9% and 87.3±11.8%, respectively. A mass balance analysis indicated that 0.49±0.02 g VSS(-1) d(-1) of PO4(3-)-P and 0.23±0.04 g VSS(-1) d(-1) of NO3--N were simultaneously removed in the anoxic zone, and it is speculated that denitrifying phosphorous removal occurred in the AOA process. Furthermore, 0.24±0.06 g VSS(-1) d(-1) of TN was removed in the aerobic zone via simultaneous nitrification and denitrification (SND). The results demonstrate that the multi-zone structure of the AOA process favors the enhancement of denitrifying phosphorous removal and SND for municipal wastewater treatment., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

A pilot-scale modified step feed process was proposed to enhance organics and nutrient (N and P) removal performance from municipal wastewater. It combined University of Cape Town (UCT) and step feed process. Effects of inflow distribution ratios and nutrients ratios were investigated. The highest removal efficiencies of 89% for chemical oxygen demanding (COD), 88% for total nitrogen (TN) and 93% for phosphorus were obtained, respectively, at the inflow distribution ratio of 40:30:30%. The phosphorus removal exhibited an upward trend with the increasing of influent COD/P and TN/P, and the nitrogen removal had a positive correlation with influent COD/TN. In addition, aerobic simultaneous nitrification and denitrification and anoxic denitrifying phosphorus uptake made a distinct contribution to enhance nutrient removal. The proposed system was demonstrated to be an attractive enhanced biological nutrient removal process for wastewater treatment plants due to relatively high nutrient removal, robust sludge settleability and energy savings., (2010 Elsevier Ltd. All rights reserved.)

Phosphorus removal from agricultural wastewater streams is an important aspect of managing surface water quality, due to the contribution of phosphorus to eutrophication. Removal of phosphorus through struvite precipitation allows for its recovery as a potential fertilizer, and by determining the best conditions for struvite precipitation the removal process can be optimized. The effects of pH, Mg:P ratio, and time on struvite precipitation from anaerobically digested swine manure effluent were investigated. Effluent with Mg:P ratios from 1.0:1 to 1.6:1 were adjusted to pH values between 7.5 and 9.5 and left to equilibrate for 24 h. Results indicate that phosphorus removal increased with increasing pH and Mg:P ratio; the maximum phosphorus removal achieved was 80% at pH 9.0 and a Mg:P ratio of 1.6:1. The purest struvite precipitate was found at pH 7.5, with calcium carbonate and struvite precipitating at higher pH values. A continuously stirred batch of centrate was adjusted to pH 8.4 to determine the struvite formation rate constant. The rate constant was found to be 1.55 h(-1), with 17% phosphorus removal during the first 20 min. The results indicate that struvite precipitation could be a viable method of phosphorus removal from anaerobically digested swine manure.

Constructed wetland systems have gained attention as attractive solutions for wastewater treatment. Wetlands are not efficient to treat wastewater with high concentrations of phosphorus (P). In order to remove high soluble P loads by wetland, sorbent beds can be added prior to the discharge of wastewater into wetlands. Sorption by sorbent materials is identified as a method for trapping excess P in wastewaters. In the present investigation, shale has been identified as a sorbent material for removal of phosphate (PO(4)-P) due to the cost effectiveness, stability and possibility of regeneration. The study focuses on the removal of PO(4)-P from wastewater using shale and the feasibility of using the P-sorbed material as slow-release fertilizer. Phosphorus sorption experiments were conducted by using shale (2 mm and 2-4.7 mm). Results indicate that Shale I (particle size = 2 mm) showed the highest sorption of PO(4)-P (500 +/- 44 mg kg(-1)). Breakthrough point was reached within 10 h in columns with flow rates of 2 and 3 ml min(-1). Lower flow rate of 1 ml min(-1) showed an average residence time of about 2 h while columns with a higher flow rate of 3 ml min(-1) showed a residence time of about 40 minutes. Variation in flow rate did not influence the desorption process. Since very low concentrations of PO(4)-P are released, Shale saturated with PO(4)-P may be used as a slow nutrient release source of P or as a soil amendment. The sorbent can also be regenerated by removing the sorbed PO(4)-P by using 0.1 N HCl.

Phosphorous removal & denitrifying phosphate uptake of the granular sludge was investigated in this study. Inoculated with flocculation sludge, the granulation of the biological phosphorous removal sludge was realized in a sequencing batch reactor (SBR) fed with sodium acetate by means of hydraulic selection under an anaerobic/oxic alternating operation (referred to as an A/O). Then the biological phosphorous removal granular sludge was induced into the denitrifying phosphate uptake granular sludge under an anaerobic/anoxic/oxic alternating operation (referred to as an A/A/O). The properties of the two kinds of granular sludge were studied. The biological phosphorus removal granular sludge was completed on the 82nd day. The biological phosphorus removal granule sludge showed some characteristics, e.g. pallideflavens in color, 0.5-1.5 mm in diameter, 20-30 m/h in settling velocity, 94% in water content, 1.043 9 in specific gravity, and below 50 mL/g in SVI. The max. specific release phosphorus rate (SRPR), the max. specific uptake phosphorus rate (SUPR) and the phosphorus content of the MLSS (TP/SS) was 67.7 mg/(g x h), 43.2 mg/(g x h) and 6.5% respectively on the 437th day. On the 448th day the operation of the reactor was changed into A/A/O. The max. SRPR, the max. anoxic SUPR and the TP/SS of the denitrifying phosphate uptake granular sludge was 30 mg/(g x h), 27.9 mg/(g x h) and 6.3% respectively on the 653rd day. The two kinds of granular sludge had potential to carry out phosphorus removal.

The removal of dissolvable inorganic phosphate (H(2)PO(4)(-)) by sorbents prepared from hydrated lime (HL) and blast furnace slag (BFS) was fundamentally studied by an orthogonal experiment design. Based on statistic analysis, it is revealed that the weight ratio of BFS/HL is the most significant variable, and an optimized preparation condition is figured out. With the increase of HL content, the adsorption capacity increases, suggesting that the HL plays the important role in the removal process in the gross. However, in the lower HL content, it is interesting that the adsorption capacity of as-prepared sorbents exceed the sum of the capacities of the same ratio of BFS and HL. The further analysis indicate the excess capacities linearly depend on the specific surface area of sorbents, suggesting that the removal of H(2)PO(4)(-) is closely related with the microstructure of sorbents in the lower HL content, according to the characterization with SEM, XRD and pore analysis. Additionally, an adsorption model and kinetic are discussed in this paper.

The objective of this study was to investigate on the effect of mixing intensity (G) and mixing duration (t(d)) on struvite precipitation in the chemical mechanical polishing (CMP) wastewater generated from the semiconductor manufacturing process. Batch-scale experiments revealed that struvite crystallization was affected by both G and t(d). The mixing effect was to enhance the mass transfer of solute to the crystals in the process, resulting in the improvement of struvite crystallization and growth. By forming struvite, removal efficiencies of N and P increased logarithmic with the multiple values of G and t(d), i.e., Gt(d). Insufficient mixing energy with the Gt(d) value less than 10(5) caused an increase in the formation potential of unexpected precipitate unlike to pure struvite, causing a decrease in removal efficiencies of N and P in the process. At the Gt(d) value over 10(6), struvite precipitation was not restricted by fluoride, of which high level inherently contained in the CMP wastewater. The study results can be taken into consideration in the design and operation of the struvite precipitation process for both nutrient (N and P) removal and recovery.

The performance of biological phosphorus removal (BPR) in a sequencing batch reactor (SBR) with single-stage oxic process was investigated using simulated municipal wastewater. The experimental results showed that BPR could be achieved in a SBR without anaerobic phase, which was conventionally considered as a key phase for BPR. Phosphorus (P) concentration 0.22-1.79 mg L(-1) in effluent can be obtained after 4h aeration when P concentration in influent was about 15-20 mg L(-1), the dissolved oxygen (DO) was controlled at 3+/-0.2 mg L(-1) during aerobic phase and pH was maintained 7+/-0.1, which indicated the efficiencies of P removal were achieved 90% above. Experimental results also showed that P was mainly stored in the form of intracellular storage of polyphosphate (poly-P), and about 207.235 mg phosphates have been removed by the discharge of rich-phosphorus sludge for each SBR cycle. However, the energy storage poly-beta-hydroxyalkanoates (PHA) was almost kept constant at a low level (5-6 mg L(-1)) during the process. Those results showed that phosphate could be transformed to poly-P with single-stage oxic process without PHA accumulation, and BPR could be realized in net phosphate removal.

The denitrification and excessive P removal can be realized by denitrifying phosphate-accumulating organisms (DNPAOs) under low carbon condition. DNPAOs use poly-3-hydroxy- butyrate (PHB) as electron donor, and use nitrate and nitrite as electron acceptor during the denitrifying phosphate uptake. In this study the biological phosphorus removal granular sludge was induced into the denitrifying and phosphate uptake granular sludge under an anaerobic/anoxic/aerobic alternating operation (referred to as an A/A/O) in a sequencing batch reactor (SBR). When the system is stable, the P and N removal ratio is over 90% and 93% respectively; the release phosphorus is 25-33 mg/L at anaerobic stage; 1g NOx-N approximately takes up P 1.3 g at anoxic stage. In the typical cycle the anaerobic maximum specific release phosphorus rate (max. SRPR) is 18.39 mg/(g x h); the anoxic max. specific uptake phosphorus rate (SUPR) and the max. specific denitrification rate (SDNR) is 23.72 mg/(g x h) and 18.19 mg/(g x h) respectively; the aerobic max. SUPR is 17.15 mg/(g x h). The fraction of DNPAOs rises from 14.9% to 80.7%. Compared with the physical-chemical property of the biological phosphorus removal granular sludge, the settling velocity and the specific gravity of the denitrifying phosphate uptake granular sludge is elevated 0.16-0.7 times and 0.0031 respectively.

The influence of separate and mixed thickening of primary and secondary sludge on struvite recovery was studied. Phosphorus precipitation in the digester was reduced from 13.7 g of phosphorus per kg of treated sludge in the separate thickening experiment to 5.9 in the mixed thickening experiment. This lessening of the uncontrolled precipitation means a reduction of the operational problems and enhances the phosphorus availability for its later crystallization. High phosphorus precipitation and recovery efficiencies were achieved in both crystallization experiments. However, mixed thickening configuration showed a lower percentage of phosphorus precipitated as struvite due to the presence of high calcium concentrations. In spite of this low percentage, the global phosphorus mass balance showed that mixed thickening experiment produces a higher phosphorus recovery as struvite per kg of treated sludge (i.e., 3.6 gP/kg sludge vs. 2.5 gP/kg sludge in separate thickening).

In this study, the workability of a pilot-scale, fluidized reactor was examined to determine effectiveness in removing, and recovering, phosphorus as struvite, from centrate at Lulu Island Wastewater Treatment Plant (LIWWTP), Richmond, British Columbia. The crystallization process was run continuously over a period of 5 months in two runs (Run 1 for 4 months and Run 2 for a month). In addition to efficient recovery of phosphorus as struvite, the study also investigated factors that affect the growth of struvite. Chemical analyses were conducted on the harvested struvite to determine its purity. Results showed that the reactor was capable of removing over 90% of phosphate and 4% of ammonia-nitrogen, with greater than 85% of the phosphate removed being recovered as harvestable struvite crystals. It was possible to achieve over 90% P-removal at a pH of 7.5; this is contrary to the information found in literature, which recommends that a higher pH (8.2-9.0) is required. Factors that affected phosphate removal were the operating pH, the reactor supersaturation ratio (SSR), the N:P and Mg:P molar ratios. Analysis of the harvested product showed that the crystals were composed of nearly pure struvite (96% by weight), with small amounts of calcium and traces of other metals. High resolution SEM pictures were taken of the inside of the crystals to determine the influence of Mg:P molar ratio on the compactness of the crystals.

New filtration materials covered with metallic oxides are good adsorbents for both cation and anion forms of pollutants. Sfax is one of the most important industrial towns in Tunisia. Its phosphate manufacture in particular is causing considerable amounts of water pollution. Therefore, there is a need to find out a new way of getting rid of this excessive phosphate from water. This work is aimed to examining the potential of three sorbent materials (synthetic iron oxide coated sand (SCS), naturally iron oxide coated sand (NCS) and iron oxide coated crushed brick (CB)) for removing phosphate ions from aqueous solutions. According to our literature survey CB was not used as adsorbent previously. Phosphate ions are used here as species model for the elimination of other similar pollutants (arsenates, antimonates). Optical microscope and scanning electron microscope (SEM) analyses were used to investigate the surface properties and morphology of the coated sorbents. Infra-red spectroscopy and X-ray diffraction techniques were also used to characterize the sorbent structures. Results showed that iron coated crushed brick possess more micro pores and a higher surface area owing to its clay nature. The comparative sorption of PO4(3-) from aqueous solutions by SCS, CB and NCS was investigated by batch experiments. The estimated optimum pH of phosphate ion retention for the considered sorbents was 5. The equilibrium data were analysed using the Langmuir and Freundlich isotherms. The sorption capacities of PO(4)3- at pH 5 were 1.5 mg/g for SCS, 1.8 mg/g for CB and 0.88 mg/g for NCS. The effect of temperature on sorption phenomenon was also investigated. The results indicated that adsorption is an endothermic process for phosphate ions removal. This study demonstrates that all the considered sorbents can be used as an alternative emerging technology for water treatment without any side effect or treatment process alteration.

9 kinds of substrate materials (gravel, aluminite stone, sands, soil, zeolite, ceramic granule, limestone, steel slag and vermiculite) were selected to examine the phosphorus adsorption and removal capacities from runoff by adsorption, captive test and dynamic adsorption experiments. The results showed that these substrate materials had higher removal efficiency for PO4(3-) than those of other phosphorus forms. The adsorption characteristics of the substrates could be described by both Freundlich and Langmuir adsorption isotherms. The equilibrium adsorption capacity of these substrates was in the following order: zeolite, soil and vermiculite > ceramic granule, steel slag and limestone > gravel, sands and aluminite stone. The dynamic adsorption capacity was zeolite, soil, limeramic granule, limestone > steel slag, gravel and sands > ceramic granule and vermiculite. In the meanwhile, the releasing phenomena of phosphorus also could be observed in the captive and dynamic test, particularly for vermiculite, ceramic granule and steel slag. In the dynamic adsorption experiment, the removal efficiency of P-pollutants was ranged from 30% to 87% for the substrate materials except vermiculite, ceramic granule and steel slag. The results suggest that zeolite, limestone and soil are appropriate substrates for removing P-pollutants from stormwater.

Objective: To investigate the feasibility of nitrogen and phosphorus recovery from swine waste biogas digester effluent and the effects of pH and NH4+: Mg2+: PO4(3-) molar ratio on its precipitation., Methods: Precipitation experiments with swine waste biogas digester effluent were conducted at pH 7.5, 8.0, 8.5, and 9.0 together with NH4+: Mg2+: PO4(3-) molar ratios 1: 0.2: 0.08, 1: 1: 1, and 1: 1.5: 1.5. Chemical and X-ray diffraction (XRD) analysis were done to determine the composition of the precipitate., Results: The highest removal and recovery of NH4+ and PO4(3-) were achieved at pH 9.0 in each experiment. The elevation of pH to 9.0 alone could decrease the initial PO4(3-) concentration from 42 mg L(-1) to 4.7 mg L(-1) and 89.2% PO4(3-) recovery was achieved. The pH-molar ratio combination 9.0-1: 1.5: 1.5 effected 76.5% NH4+ and 68.5% PO4(3-) recovery. The molar ratio of 1: 1: 1 together with pH elevation to 9.0 was determined to be the optimum combination for both NH4+ and PO4(3-) removal as it recovered over 70% and 97% of the initial NH4+ and PO4(3-), respectively., Conclusions: Nitrogen and phosphorus can be recovered from biogas digester effluent as struvite.

Aiming at the development of a phosphorus removal technology for waste water, phosphate (PO(4)(3-)) retention behavior of bituminous and lignitous coal ashes was investigated using a batch reactor. Ash samples, including fresh and weathered fly and bottom ashes, were studied for their sorption isotherms and reversibility. Fly ashes had a much higher phosphate retention capacity (4000-30,000mgP/kg) than bottom ashes (15-600mgP/kg). Lignitous coal ashes were more capable of retaining phosphate than bituminous coal ashes. The retention process was largely irreversible, and the irreversibility increased with the increase in the retention capacity. Weathering enlarged the retention capacity of the bituminous bottom ash, but substantially lowered that of the fly ash, likely due to the difference in the weather-induced changes between the fly and bottom ashes. Sorption isotherms of fly ashes were found to be adequately represented by the Langmuir model while those of bottom ashes fitted better to the Freundlich model. Concentrations of Ca(2+) and PO(4)(3-) in the aqueous phase were measured at the end of sorption and desorption experiments, and were compared with solubilities of three calcium phosphate minerals. The aqueous solutions were saturated or super-saturated with respect to tricalcium phosphate (Ca(3)(PO(4))(2)) and hydroxyapatite (Ca(5)(PO(4))(3)OH), and slightly under-saturated with respect to amorphous calcium phosphate. It is concluded that precipitation of calcium phosphate is the predominant mechanism for phosphate retention by coal ash under the conditions studied. There is a strong and positive correlation between alkalinity and phosphate sorption capacity. Consequently, acid neutralization capacity (ANC) can be used as an indicator of phosphate sorption capacity of coal ashes.

Phosphorus can be recovered from wastewater through crystallisation of struvite, MgNH(4)PO(4).6H(2)O. Approximately 1 kg of struvite can be crystallised from 100 m(3) of wastewater. Crystallisation is profitable compared to chemical and biological removal of phosphorus due to savings from the reduction in (i) chemicals used for precipitation and sludge disposal; and (ii) downtime for cleaning unwanted struvite formed during chemical and biological removal. The struvite produced annually from a wastewater treatment plant that processed 100 m3/d, would be sufficient to apply on 2.6 ha of arable land, as fertilizer. If struvite were to be recovered from wastewater treatment plants worldwide, 0.63 million tons of phosphorus (as P(2)O(5)) could be harvested annually, reducing phosphate rock mining by 1.6%. Therefore, this technology could provide opportunities to recover phosphorus sustainably from waste streams and preserve phosphorus reserves.

All the phosphate rock Japan needs must be presently imported from abroad because the country has no subterranean phosphorous resources. Therefore, there is a need to accelerate the development of and establish the technologies for phosphorous recovery from waste and wastewater. Swine wastewater has a high potential for phosphorous recovery in Japan. A reactor for removing and recovering phosphorous from swine wastewater was designed with dual functions, crystallization through aeration and separation of formed struvite by settling. However, a dehydration, composting and characterization process was first needed before using sediment sludge, including struvite, on farmland, since the struvite will settle along with huge amounts of other suspended solids (organic matter). For the recovery of pure struvite, an accumulation device was designed and its efficiency examined. The device has a struvite-accumulation face made of stainless steel wire mesh (1 mm in diameter, 1 cm(2) square) to reduce its total weight. During submergence in the aeration column of the demonstration reactor, struvite cross-bridged and accumulated on the face of the device. The struvite could be scraped off easily with only a light brushing, and was found to be approximately 95% pure. Because this device is a very simple structure, it is thought to be acceptable to swine farmers.

In an enhanced biological phosphorus reactor (EBPR), most poly-phosphate accumulating microorganisms (PAOs) exist as microbial aggregates, or flocs. Information contributing to a better understanding of the internal structure and function of flocs can lead to improvements in the modeling, design and operation of EBPR systems in wastewater treatment. A phosphate ion-selective microelectrode has been developed and was used to measure the phosphate profiles in flocs. The microelectrode uses cobalt as the sensing material and shows very good selectivity towards orthophosphate ions (H2PO4(-), HPO4(2-) and PO4(3-)). The potentiometric response showed a linear relationship with the logarithm of phosphate concentrations, with a slope of 31.5 mV per decade change of concentration. The solution pH did not show a significant effect on the microelectrode performance within the pH range of 7.5 to approximately 8.0. The effect of ionic strength was also investigated. Measurements using this microelectrode were made on activated sludge floc samples taken from a municipal wastewater treatment plant.

Regulations in many regions of the world require total phosphorus (TP) levels lower than 0.10 mgP/L (100 microgP/L) in effluents, resulting in the need to achieve very low ortho-phosphate (OP) concentrations. Chemical precipitation is a widely used technology for controlling effluent OP discharge, either on its own or supplementing biological methods. The various chemical and physico-chemical mechanisms that result in extremely low residual OP levels are complex and depend on pH. In practice, engineering calculations frequently use an empirical precipitation model. This model requires pH as input and predicts the lowest achievable OP residual of 35 microgP/L at a narrow optimum pH of 6.9-7.0, when an excess of ferric is added. The model has been combined with a biokinetic and weak acid/base chemistry based pH model, to allow accurate prediction of pH, OP residuals and chemical sludge production. Analysis of effluent data from the Blue Plains plant shows that residuals as low as 10 microgP/L OP can be achieved regularly, over a wider pH range. The precipitation model was recalibrated to match the newly available data. Subsequently it was compared with a new, mechanistic precipitation model based on solubility and dissociation constants for actual chemical compounds. The need for more accurate measurement of extremely low OP concentrations and considering the role of organics, adsorption and coagulation in chemical phosphorus removal is demonstrated.

In the present study, phosphorus removal was studied using as coagulant spent alum sludge from a water treatment plant of EYDAP (Athens Water Supply and Sewerage Company) and compared to alum (Al2(SO4)3.18H2O), iron chloride (FeCl3.7H2O), iron sulfate (Fe2(S04).10H2O) and calcium hydroxide (Ca(OH)2) at a constant pH (equal to 6). The comparison was based on their efficiency to remove phosphorus in synthetic wastewater consisting of 10 mg/L P as potassium dihydrogen phosphate and 50 mg/L N as ammonium chloride, The experiments were carried out using a jar-test apparatus and the measurements were performed according to the Standard Methods for the Examination of Water and Wastewater. Pure alum, iron chloride and iron sulfate were much more efficient in phosphorus removal than the spent alum sludge but in the case of calcium hydroxide, phosphorus removal was very low in pH = 6. Specifically, orthophosphate were totally removed by alum using 15 mg/L as Al, by alum sludge using 75 mg/L as Al and by FeCl3.7H2O or Fe2(SO4).10H2O using 30 mg/L of Fe while in the case of calcium hydroxide P removal was actually zero. pH measurements showed that the uptake of phosphates is associated to the release of OH ions in the solution and that the end of P uptake is accompanied by the stabilization of pH. Finally this spent alum sludge was tested on municipal wastewater and proved to be effective as apart from phosphorus it was shown to remove turbidity and COD.

Removal of phosphorus and nitrogen is required to prevent eutrophication problems in lakes and enclosed coastal seas. And recovery of phosphorus from wastewater has been attracting attention because of lack in phosphorus resources in the near future. In this study, reaction kinetics and design parameters of struvite production are experimentally investigated by using basic reaction type and a draft-tube type reactors. Struvite production rate, which is a very important parameter in reactor design and efficiency estimation, is formulated in an equation consisting of a rate constant (k2), and magnesium, phosphate and ammonium concentrations. The value of k2 is shown to be increased with struvite concentration and mixing intensity in the reactor. The developed equation is applied to the results obtained from the draft-tube type reactor experiments and verified for its applicability. High struvite concentration of 10-25% is maintained in the draft-tube reactor experiments. 92% removal and recovery efficiency with effluent phosphorus concentration of 17 mg/L is achieved under the conditions of 4 minutes reaction time, pH of 8.5 and Mg/P molar ratio of 1.1.

P-control technologies for municipal wastewater are essentially based on "destructive" methods, that lead to formation of concentrated solid-phases (sludge), usually disposed-off in controlled landfills. Ion exchange, as a "non-destructive" technology, allows for selective removal and simultaneous recovery of pollutants, which can be recycled to the same and/or related productive lines. In this context, the REM NUT process removes nutrient species (HPO4 = , NH4+, K+) present in biologically oxidised municipal effluents and recovers them in the form of struvites (MgNH4PO4; MgKPO4), premium quality slow release fertilisers. The main limitation to the extensive application of this ion exchange based process is the non-availability of selective exchangers for specific removal of nutrient species. This paper illustrates laboratory investigation and pilot scale development of a so-called "P-driven" modified REM NUT scheme based on a new phosphate-selective sorbent developed at Lehigh University, PA, USA.

Formation of struvite (MgNH4PO4 x 6H2O) at sewage treatment works can cause operational problems and decrease efficiency. Struvite has a commercial value and the controlled formation and recovery of it would be beneficial. A mass balance was conducted at full scale across the whole sewage treatment plant in order to identify a stream to conduct bench-scale struvite crystallisation studies. The most suitable stream was identified as the centrifuge liquors. The average flow of the liquor stream was 393 m3 d(-1) and the composition was as follows: 167 mg L(-1) phosphorus, 44 mg L(-1) magnesium, 615 mg L(-1) ammonium, 56 mg L(-1) calcium and 2580 mg L(-1) of alkalinity. The pH averaged at 7.6 and the stream had a predicted struvite precipitation potential of 140 mg L(-1). Struvite crystallisation occurred quickly during the trials, by raising the pH of the centrifuge liquors to 9.0 and dosing with magnesium. Up to 97% phosphorus removal as struvite was achieved. Struvite formation occurred when the molar ratio of magnesium:phosphorus was at least 1.05:1. Below this ratio phosphorus removals of 72% were observed, but not exclusively as struvite. Annual yields of struvite were calculated to be 42-100 tonnes a year, depending on the dose regime. Revenue from the sale of produced struvite could be between Pound Sterling8400 and Pound Sterling20,000 a year.