Abstract
Struvite precipitation from Wastewater involves an excess of ammonium to create a supersaturated initial solution. The remaining fraction can be a threat to the environment. This work combined struvite precipitation and ammonium sorption using natural zeolite to decrease the ammonium level in the effluent. Two approaches of estimation of feed sample doses were used. One consisted of gradient experiments for ammonium precipitation to the asymptotic level and was combined with clinoptilolite to lower the ammonium level in the effluent. This approach used doses of 0.05:1.51:0.61:1 of Ca:Mg:NH4+:PO43− mole ratios, respectively. In contrast, three level design with narrowed NH4+:PO43− range reached 0.25:1.51:0.8:1 for Ca:Mg:NH4+:PO43− mole ratios. The addition of zeolite decreased effluent ammonium concentration. In both ways, the P and N recoveries were higher than 94% and 72%, respectively. The complexity of the precipitation mixture decreased the ammonium sorption capacity (Qe) of clinoptilolite from Qe of 0.52 to 0.10 meq∙g−1 in single and complex solutions, respectively. Thermodynamically, the addition of 1.5 % of clinoptilolite changed the struvite precipitation spontaneity from ∆G of −5.87 to −5.42 kJ·mol−1 and from 9.66 to 9.56 kJ·mol−1 for gradient and three level experimental procedures, respectively. Thus, clinoptilolite demonstrated a positive effect on the struvite precipitation process and its environmental impact.
Highlights
Struvite is a phosphate salt formed by the association reaction of magnesium, ammonium and phosphate in aqueous alkaline conditions [1]
In order to evaluate the effect of other ions on ammonium sorption, the same equilibrium experiments were conducted on multi-components aqueous solution residue from struvite precipitation with the same range of ammonium concentration
The improved struvite precipitation process identified in this work highlights the use of smaller N:P and Ca:P mole ratios to avoid an excess of ammonium in the effluents and struvite inhibition, respectively
Summary
Struvite is a phosphate salt formed by the association reaction of magnesium, ammonium and phosphate in aqueous alkaline conditions [1]. Calcium phosphate was reported to be recovered from manure, while struvite is the recommended form for fertilizer use [8] The latter is more profitable due to its content of magnesium, nitrogen and P in the forms efficiently available to plants [9,10]. An unclosed loop for ammonium removal in subsequence of P recovery has negative impacts on the environment such as the increase of eutrophication and the non-conformity to standards of process life cycle [12,20,21] In this regard, the study combining struvite precipitation with ammonium removal is important for green process implementation. The research scope intends to contribute to the environmentally friendly process of P recovery through struvite precipitation
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
