Optimization for the removal of orthophosphate from aqueous solution by chemical precipitation using ferrous chloride

Abstract

The precipitation reaction between the orthophosphate and Fe2+ ions was studied to describe the optimum condition for the removal of orthophosphate from the aqueous solution. The effects of pH, Fe:P molar ratio, and alkalinity were evaluated for the initial orthophosphate concentrations in the range from 1.55 to 31.00 mg/L - PO4(3-) -P. The optimum pH was found to be 8.0 in all orthophosphate concentration ranges. When the stoichiometric moles of Fe2+ were added, the removal efficiencies were significantly less than the theoretical values. It is likely that the precipitation of Fe(OH)2(s) is partially formed. For the initial orthophosphate concentration of 3.10 mg/L PO4(3-) -P or greater, the removal efficiencies with the Fe:P molar ratio of 3.0:1.0 approached to the theoretical values, yielding greater than 98.5%. If the molar ratio of Fe:P was great enough, the precipitation reaction was completed within 1 h. As the alkalinity increases, the experimental removal efficiencies were significantly greater than the theoretical values. This is because the formation of vivianite is favoured over FeCO3(s). Finally, it was demonstrated that the orthophosphate (1.40-6.80 mg/L PO4(3-) -P) in the secondary effluents from wastewater treatment plants was effectively removed by dosing sufficient amount of Fe2+ ions.

Effects of iron salt addition on biosolids reduction by oxic-settling-anoxic (OSA) process

“…The average molar Fe/P ratio in the influent tank was only 1.27 and 0.85 at the period when FeCl 2 concentration was 15 and 30 mg l -1 , respectively (Table 3). An et al (2014) investigated the formation of vivianite in synthetic wastewater with FeCl 2 dosing and found that the Fe/P molar ratio should be more than 3 to enable significant vivianite formation. The authors attributed this to the partial formation of ferrous hydroxides, which hindered the formation of vivianite.…”

“…The role of iron in the flocculation (Higgins and Novak, 1997) and floc destruction under anaerobic conditions (Novak et al, 2003) has been reported, but its impact on OSA performance has not been systematically studied. Iron salts are commonly added to wastewater in full-scale plants for phosphorous removal by chemical process (Paul et al, 2001;An et al, 2014). When Fe(II) salt is added to an aerobic reactor, iron is spontaneously oxidised to Fe(III) given the availability of oxygen in the system (i.e., 2Fe 2+ + 2H + + ½O 2 2Fe 3+ + 2H 2 O, E°c ell = +2.0 V).…”

Cellulose citrate: a convenient and reusable bio-adsorbent for effective removal of methylene blue dye from artificially contaminated water

“… 20,21 In spite of everything, methylene blue is surely one of the most used dye in textile industries and, for this reason, the developing of new strategies for the efficient removal from water effluents is still ongoing and of great interest. 22–27 The common methods for the removal of organic dyes include: chemical oxidation or reduction, 28 precipitation, 29 ion exchange, 30 electrolysis, 31 photo-catalytic processes, 32,33 membrane filtration, 34 ozonation, 35 degradation, 36 bio-sorption 37 and adsorption. 38,39 In particular, adsorption is one of the most used techniques because it relies on a simple mechanism, does not produce handling problems, and the process can be reversible.…”

Exploring the effects of ZVI addition on resource recovery in the anaerobic digestion process

“…However, during the ZVI corrosion process Fe 2+ is released and strongly influences the physicochemical properties of the system [11]. Fe 2+ can reduce the biogenic sulfide due to pyrite precipitation (FeS 2 ), but can also interact with other anions, notably bicarbonate and phosphate, to form siderite (FeCO 3 ) and vivianite (Fe 3 (PO 4 ) 2 •8H 2 O) [12]. Vivianite precipitation entraps the soluble P released upon AD.…”