Different from current nutrient recovery technologies of recovering one or two nutrient components (PO 4 3or NH 4 + ) from wastewater, this study aimed to fractionate various nutrient anions and cations simultaneously, including PO 4 3-, SO 4 2-, NH 4 + , K + , Mg 2+ and Ca 2+ , into several streams. The recovered streams could be further paired together to produce high-value products. A novel electrodialysis process was developed by integrating monovalent selective anion and cation exchange membranes into an electrodialysis stack. Results revealed that nutrient recovery was achieved effectively by fractionating PO 4 3and SO 4 2into the anionic product stream, whereas bivalent cations (Mg 2+ and Ca 2+ ) were extracted in the cationic product stream and the monovalent cations (K + and NH 4 + ) were concentrated in the brine stream. For the permeation capabilities of anions, SO 4 2and Clpossessed the higher preference, whereas PO 4 3permeated the membrane more difficult. As to the cations, the permeation sequence was: NH 4 + ≈K + >Ca 2+ >Mg 2+ ≈Na + . Enhancing voltage values not only promoted ion migration rates, but also led to the increase of energy consumption. Although elevating initial phosphate concentration in the anionic product streams from 60 mg/L to 470 mg/L did not influence phosphate fractionation significantly, the current efficiency decreased from 3.55% to 0.65% and a remarkable increased of energy consumption from 29.42 kWh/kg NaH 2 PO 4 to 160.13 kWh/kg NaH 2 PO 4 was observed. Further experiments were conducted for phosphorus recovery by pairing two recovered product streams, which revealed that phosphate precipitation could be achieved by using inherent Ca 2+ and Mg 2+ in the wastewater

Wastewater of potato processors contains high amounts of phosphorus and its recovery as calcium phosphate (CP) is investigated. In contrast to struvite, CP can be cotreated with phosphorous ore in phosphoric acid production, as far as it does not contain too much magnesium phosphate. The precipitation of CP was studied from the effluent of an upstream anaerobic sludge blanket reactor (UASB) after lab scale nitrification or lab scale nitrification and denitrification by batch experiments and continuous experiments. Nitrification excludes the possibility of struvite precipitation but did not result in complete removal of dissolved inorganic carbon (DIC). Only a narrow window at neutral pH is available for magnesium-free calcium phosphate precipitation. The additional denitrification caused a pH increase, which resulted in an unwanted magnesium phosphate precipitation and an increase in DIC, causing an increase of calcium carbonate contamination. The saturation index (SI) of CP can be enhanced by increasing the molar Ca/P ratio in the effluent, but this enhances also the contamination with calcium carbonate. Calcium chloride added in a tenfold molar excess relative to the phosphate-P concentration (a total molar Ca/P ratio of about 13) to nitrified effluent resulted in a phosphate recovery as CP of 83 %, but in all conditions, it was difficult to obtain carbonate-free CP.

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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 [Ca]/[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.

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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 (EPSs) 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.

After treatment of the wastewater from the potato processing industry in an upflow anaerobic sludge blanket reactor (UASB) the effluent is rich in phosphate and dissolved inorganic carbon (IC). Increasing the pH of the UASB effluent with NaOH to precipitate phosphate as calcium phosphate leads to contamination with magnesium phosphate. Increasing the pH with Ca(OH)2 had a positive effect on phosphate precipitation, but after increasing the pH with Na2CO3 no precipitate was formed. After prior nitrification of the UASB effluent to remove IC, less NaOH was needed to increase the pH and the ions precipitated in a ratio that agreed with calcium phosphate formation. When the pH of the nitrified effluent was increased with Na2CO3 neither calcium nor phosphate precipitated. This inhibitory effect of IC on phosphate precipitation as calcium phosphate could not be derived from the saturation indexes calculated by the geochemical modelling program PHREEQC.