A constant composition technique for quantifying the effect of As(V) on struvite crystallization under various operational conditions

Abstract

Struvite crystallization was one of the most promising techniques for nutrient recovery from nutrient-rich wastewater. However, As(V) derived from the wastewater has been proved to adversely affect struvite crystallization. Constant composition technique was employed to quantify the effect of As(V) on struvite crystallization in the presence of As(V) under various operational conditions such as supersaturation, pH and ionic strength. Subsequently, the interaction mechanisms between As(V) and struvite crystals were further elucidated by means of XPS and FTIR. Interestingly, the roles of adsorption and coprecipitation in the interaction under various operational conditions were primarily evaluated. At a supersaturation of 0.4, pH 8.5 and 0.1 mol/L NaCl, the crystal growth rate of struvite was substantially reduced from (14.2 ± 0.3) × 10−6 to (7.6 ± 0.1) × 10−6 mol/min with As(V) concentration increasing from 0 to 10 mg/L. Nevertheless, As(V) scarcely changed the surface diffusion growth mechanism of struvite. Moreover, the adsorption and coprecipitation of As(V) accounted for its interaction with struvite. Thereinto, the adsorption mechanism was triggered by the bidentate inner-sphere surface complexes and the electrostatic interaction between As(V) and struvite. Furthermore, the influence of supersaturation and ionic strength on the inhibitory effect was found to be highly dependent of the adsorption of As(V), whereas the coprecipitation of As(V) is mainly responsible for the impact of pH. The finding herein provided a novel approach to elucidate the inhibitory mechanisms of heavy metals on struvite crystallization, which facilitated to obtain pure struvite crystals from the wastewater contaminated by heavy metals.