Economic evaluation of the precipitation of phosphate as struvite at pilotscale

A novel approach using ureolytic induced MAP formation, for the recovery of phosphate, has been economically evaluated. The ureolytic MAP crystallizationon has been tested on anaerobic effluent of a potato processing company in a pilot plant, with MgCl2.6H2O as magnesium source. The pilot plant showed a high phosphate removal efficiency of 82 ± 9 %, resulting in a final effluent concentration of 13 ± 7 mg/L PO4-P. XRD analyses confirmed the presence of struvite in the precipitate. During operation pH and the molar magnesium : ammonium : phosphate ratio are the most important operational parameters influencing MAP crystallization. Results show that for high phosphate concentrations in wastewater (e.g. 100 mg/L PO4-P) the ureolytic phosphate precipitation is a cost effective method (6.1 € kg-1 Premoved). Moreover, the technique is competitive with the chemical phosphate precipitation of struvite (6.2 € kg-1 Premoved)

Synthesis of Zeolitic-type Adsorbent Materials from Municipal Solid Waste Incinerator Bottom Ash and its Application in Heavy Metal Adsorption

Municipal solid waste incinerator (MSWI) bottom ash (BA) was converted to zeolitic-type adsorbent materials by hydrothermal conversion under strongly alkaline conditions. The conversion product was determined to be a mixture of sodium aluminum silicate hydrate (SASH) (Na2O·Al2O3·1.68SiO2·1.73H2O) and tobermorite (Ca5Si6O16(OH)2·4H2O). The BET specific surface area was 22.1 m2/g, which represented a significant gain compared to the BA (4.6 m2/g) due to the formation of micropores and mesopores. The converted BA demonstrated promising performance for application as a sorbent towards several heavy metals (oxyanions of As(V), and Cd2+, Co2+, Ni2+, Pb2+, and Zn2+). Its performance was found to be generally superior to that of a mainly-clinoptilolite natural zeolite, achieving greater sorption extents and better stabilizing capability of contaminated sediments. At a lower dosage rate (50 mg sorbent per gram sediment) to that of natural zeolite, converted BA achieved greater than 80% reduction of cationic heavy metal concentrations in sediment porewater. These results suggest a promising route for reutilization of MSWI-BA, which can greatly enhance the sustainability of waste incineration technology

Adsorption of Multi-heavy Metals Onto Water Treatment Residuals: Sorption Capacities and Applications

Inherently formed iron-based water treatment residuals (WTRs) were tested as alternative sorbents for multi-heavy metal removal from synthetic solutions, contaminated sediments, and surface waters. The WTRs were mainly composed of iron (hydr)oxides and had a high BET surface area (170.7 m2/g), due to the presence of micro- and mesopores. The sorption capacity of WTRs for As(V), Cd2+, Pb2+ and Zn2+ from synthetic solutions surpassed that of a commercially available goethite by 100-400% for single contaminant tests, and by 240% for total sorption in multi contaminant tests. The maximum sorption capacity of WTRs towards As(V), Pb2+ and Zn2+ was estimated by Langmuir equation fitting to range between 0.5 to 0.6 mmol/g, and their maximum sorption capacity for Cd was 0.19 mmol/g. WTRs performed significantly better than goethite for adsorption of cationic contaminants (Cd, Co, Ni, Pb, Zn) in the sediment tests, independent of the dosage or sediment sample. At the highest WTRs dosage (250 mg/g), concentrations of the cationic contaminants decreased by at least 80%, while approximately 40% removal was obtained with 50 mg/g dosage. Sorbent mixtures composed of WTRs with goethite, and with a clinoptilolite natural zeolite were used to reduce As leaching. The sorbent mixtures delivered the desired performance, with the natural zeolite performing better than the goethite as an amendment to WTRs. In addition, up to 90% removal of surface water contaminants was achieved with both fresh WTRs and the WTRs regenerated using 0.01 M EDTA

Strategic Selection of an Optimal Sorbent Mixture for In-Situ Remediation of Heavy Metal Contaminated Sediments: Framework and Case Study

Aquatic sediments contaminated with heavy metals originating from mining and metallurgical activities of aquatic sediments poses significant risk to the environment and human health due to the fact that these sediments not only act as a sink for heavy metals, but can also constitute a secondary source of heavy metal contamination. A variety of sorbent materials has demonstrated the potential to immobilize heavy metals. However, the complexity of multi-element contamination makes choosing the appropriate sorbent mixture and application dosage highly challenging. In this paper, a strategic framework is designed to systematically address the development of an in-situ sediment remediation solution through Assessment, Feasibility and Performance studies. The decision making tools and the experimental procedures needed to identify the optimum sorbent mixtures are detailed. Particular emphasis is given to the utilization and combination of commercially available, and waste-derived sorbents to enhance the sustainability of the solution. A specific case study for a contaminated sediment site in Northern Belgium with high levels of As, Cd, Pb and Zn originating from metallurgical activities is presented. The proposed framework is utilized to achieve the required remediation targets and to meet the imposed regulations on material application in natural environments

Effects of Bioleaching on the Chemical, Mineralogical and Morphological Properties of Natural and Waste-Derived Alkaline Materials

Bioleaching is a potential route for the valorisation of low value natural and waste alkaline materials. It may serve as a pre-treatment stage to mineral carbonation and sorbent synthesis processes by increasing the surface area and altering the mineralogy of the solid material and by generating an alkaline rich (Ca and Mg) aqueous stream. It may also aid the extraction of high value metals from these materials (e.g. Ni), transforming them into valuable ore reserves. The bioleaching potential of several bacteria (Bacillus circulans, Bacillus licheniformis, Bacillus mucilaginosus, Sporosarcina ureae) and fungi (Aspergillus niger, Humicola grisea, Penicillium chrysogenum) towards the alteration of chemical, mineralogical and morphological properties of pure alkaline materials (wollastonite and olivine) and alkaline waste residues (AOD and BOF steel slags, and MSWI boiler fly ash) at natural pH (neutral to basic) was assessed. Bioleaching was conducted using one-step and two-step methodologies. Increased solubilisation of alkaline earth metals and nickel were verified. Alteration in basicity was accompanied by alteration of mineralogy. AOD slag experienced solubilisation-precipitation mechanism, as evidenced by the decline of primary phases (such as dicalcium-silicate, bredigite and periclase) and the augmentation of secondary phases (e.g. merwinite and calcite). Nickel-bearing minerals of olivine (clinochlore, lizardite, nimite and willemseite) significantly diminished in quantity after bioleaching. Altered mineralogy resulted in morphological changes of the solid materials and, in particular, in increased specific surface areas. The bioleaching effect can be attributed to the production of organic acids (principally gluconic acid) and exopolysaccharides (EPS) by the microorganisms. The similarities between fungal and bacterial mediated bioleaching suggest that biogenic substances contribute mostly to its effects, as opposed to bioaccumulation or other direct action of living cells

Batch tests to examine the role of Inorganic Carbon in the recovery of phosphate as calcium phosphate

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Phophorus reclamation by end-of-pipe recovery as calcium phosphate from effluent of wastewater treatment plants of agroindustry

Phosphorus is essential for live and must be recovered from all possible secondary resources. One of these secondary resourcesmaybetheeffluentofawastewatertreatmentplantinwhichnoobviousmeasuresaretaken to remove or recover the phosphorus. Effluent water of the wastewater treatment facility of a potato processor was spiked with 40–50 mg phosphate-P.L−1 to simulate such a water that can be subjected to an end-of-pipe recovery of phosphate. Simulations with PHREEQC were calculated and batch experiments were performed. Continuously stirred tank reactors (CSTR) were fed with P-spiked effluent. Increasing the Ca/P ratio promoted calcium phosphate precipitation but increased also the calcium carbonate contamination. With calcium added in fourfold excess relative to endogenous phosphate-P concentration, 90 % removal can be obtained. For the recovery of phosphorus from this purified effluent the same Ca/P ratio is necessary than in the case where phosphorus is recovered from nitrified UASB effluent. The recovery is stimulated by aeration, which however should not be continuous and by the addition of 5 g L−1 hydroxyapatite and reaches up to 95 %. In contrast to what was expected based upon the batch experiments, but in agreement with the simulations, the precipitates contained up to 6 m% magnesium phosphate, which probably can further be reduced by using shorter hydraulic retention times in the reactor.status: Published onlin

Optimization of the configuration of the anion Selectrodialysis Stack for Fractionation of Phosphate from UASB effluent in Batch Mode on Lab Scale and Pilot Scale.

In anion selectrodialysis (aSED) multivalent anions are entrapped in the so called “product stream” between a standard anion exchange membrane (SA membrane) and a monovalent anion selective membrane (MVA membrane). This study was carried out on nitrified and ultra-filtrated effluent of an upflow anaerobic sludge blanket reactor (UASB) of a potato processor. The selectivity for phosphate of various membranes that could act as SA membranes was tested on lab scale. From the calculated selectivities and current efficiencies for phosphate transport two membranes, the Fujifilm Type 1 membrane and the PC-Acid 100 OT membrane from PCA are good candidates to replace the previously used PC-SA membrane from PCA. Lowering the pH had a negative effect on the mobility of the phosphate ions and it is proposed that the HPO42- is the ion that migrates through the SA membrane. Increasing the voltage resulted in a better phosphate mobility through the PC-Acid 100 OT membrane. Also, on pilot scale the PC-Acid 100 OT membrane performed much better than the PC-SA membrane: the current efficiency for phosphate transport was higher whereas the current efficiency for DIC transport was lower with the PC-Acid 100 OT membrane than with the PC-SA membrane. The PC ACID 100 OT is recommended as standard anion exchange membrane in pilot and full scale stacks for recovery of phosphate by aSED.status: Published onlin

Calcium phosphate precipitation in nitrified wastewater from the potato processing industry

Increasing environmental concerns and the awareness of the finite nature of natural resources make the valorization of waste materials to become a real challenge. The objective of the current research is to investigate the possibility of phosphate recovery as calcium phosphate salts from the wastewater from the potato-processing industry. Batch tests demonstrated that at high pH, struvite and calcium carbonate precipitations are competitive processes and that bicarbonate inhibits the precipitation of calcium phosphate salts. A biological nitrification of the wastewater removed the buffering capacity, the competitive formation of struvite and paved the way for phosphate precipitation as calcium phosphate salts as it also led to the simultaneous removal of (bi)carbonates. It is demonstrated that 75% of the phosphate precipitated as calcium phosphate at a [Ca2+]/[P] ratio of 2.5 at pH 8.5 and as such it provides a convenient alternative for the currently applied struvite processes in the agro-industrial industry.status: publishe

Phosphate recovery as hydroxyapatite from nitrified UASB effluent at neutral pH in a CSTR

The wastewater of the potato processing industry is typically rich in phosphorus. The effluent of a UASB of a potato processor was nitrified prior to phosphate recovery as hydroxyapatite. The nitrification of ammonium not only removes the ammonium which avoids competing struvite formation but also consumes the double equimolar amount of dissolved inorganic carbon. The latter reduces calcium bicarbonate inhibition and carbonate precipitation and makes the calcium available for calcium phosphate precipitation. After this biological pretreatment phosphate was precipitated as hydroxyapatite (Ca5(PO4)3OH) at neutral pH values (7.83) in a laboratory CSTR. This precipitation of hydroxyapatite consumed part of the inorganic carbon that remained after nitrification of the UASB effluent and the final yield was determined by the available Ca2+ ions. Both a higher pH (8.5–10.5) and a low [Ca2+]/[P] ratio initiate the coprecipitation of carbonates and magnesium phosphate. A conventional nitrification downstream the UASB facilitates phosphate recovery as a calcium phosphate salt. This calcium phosphate removal route is presented as an alternative to the currently applied struvite process.status: Published onlin