Author : Mehrez Harmassi
Publisher :
ISBN 13 :
Total Pages : 249 pages
Book Rating : 4.:/5 (112 download)
Book Synopsis Valorization of Phosphate from Industrial and Domestic Effluents as By-products for Fertilizers Production by : Mehrez Harmassi
Download or read book Valorization of Phosphate from Industrial and Domestic Effluents as By-products for Fertilizers Production written by Mehrez Harmassi and published by . This book was released on 2016 with total page 249 pages. Available in PDF, EPUB and Kindle. Book excerpt: Phosphorus in wastewater is mainly present as inorganic phosphate forms and is commonly removed through chemical co-precipitation using Al(III) and Fe(III) salts. However, precipitation is expensive and generates a waste to be disposed. If the recovery of phosphorus is the target objective the solution could be based on the integration of specific chemical processes or physico-chemical treatment process to recover phosphorous as pure mineral phases or supported onto low-cost inorganic sorbents. Recovery of phosphate from diluted streams has been evaluated by integration of a pre-concentration step using P-selective sorbents to provide concentrated effluents of phosphate (e.g. from 0.1 to 2 g P-PO43-/L) typically at alkaline pH values due to the use of alkaline solutions in the regeneration step (e.g 1% NaOH). In this study, phosphorus recovery as hydroxyapatite (Hap) from alkaline phosphate concentrates (0.25 to 1 g P-PO43-/L) using calcium chloride solutions in batch reactors was evaluated. When pH was kept constant in alkaline values (from 8 to 11.5), Hap precipitation efficiency was improved. At pH 11.5, higher phosphorus precipitation rate was registered but lower degree of crystallinity was observed. The increase of the total initial phosphate concentration lead to the formation of Hap powders with higher degree of crystallinity and crystal diameter, but also lower mean particle size. Afterwards, the detrimental effects of the presence of magnesium (II) in synthetic brines on hydroxyapatite precipitation were also evaluated. Two synthetic brines with Mg/Ca molar ratios of 2.2 and 3.3 were continuously fed to reach a Ca/P molar ratio of ̃1.67 to promote Hap formation. For both brines, inhibition of Hap precipitation and formation of the amorphous mineral phases of Ca-, Mg- and Ca/Mg-phosphates were observed at pH >9.5. Mg(II) severely inhibited phosphate precipitation, allowing the formation of amorphous calcium phosphate from meta-stable clusters due to Mg(II) incorporation into Ca-phosphate. In the experiments at pH 8, the formation of stable nanometre-sized pre-nucleation clusters promoted nucleation inhibition, even in supersaturated solutions. On the other hand, phosphate P(V) recovery by using low-cost reactive inorganic materials with improved efficiency in terms of equilibrium and kinetics has been also evaluated. The integration of powder inorganic adsorbents fly ashes and zeolitic materials for selective removal of phosphate provided phosphorus (P) containing by-products with fertilizing properties. Fly ash samples from two different coal power stations and with different CaO(s) content (Los Barrios (FA-LB)) and (Teruel (FA-TE)) were evaluated on phosphate removal from aqueous solutions. P(V) recovery, in the expected pH conditions (6 to 9) of wastewater treatment plant (WWTP) secondary effluents, proceeds as combination of the dissolution of CaO(s) and formation of brushite (CaHPO4(s)) onto the fly ash particles avoiding the formation of more insoluble Ca-phosphates as hydroxyapatite with a limited fertilizing properties. Removal kinetics data were well described as diffusion-based process and the CaO(s) dissolution was discarded as the rate-controlling step. A powder zeolitic material synthetized from fly ash (NaP1-NA) and its calcium modified form (CaP1-NA) were also studied as sorbent materials for the recovery phosphate from treated waste water effluents. The sorption capacity of both zeolites on the expected pH for waste water effluents (pH from 7 to 9) was slightly dependent on pH. The stability of the loaded phosphate zeolites samples as fertilizer was evaluated by extraction experiments. Finally, the performance of Ca-activated powder zeolite (CaP1) on removing P(V) was evaluated by integrating the sorption step and the solid phase recovery by using an hybrid sorption-ultrafiltration system using a hollow fibre module.
