Water Research Centre, School of Civil and Environmental Engineering, University of New South Wales, Sydney, 2052, Australia.
Water Research Centre, School of Civil and Environmental Engineering, University of New South Wales, Sydney, 2052, Australia.
Water Res. 2017 Nov 1;124:341-352. doi: 10.1016/j.watres.2017.07.076. Epub 2017 Jul 31.
Iron salts are routinely dosed in wastewater treatment as a means of achieving effluent phosphorous concentration goals. The iron oxides that result from addition of iron salts partake in various reactions, including reductive dissolution and phosphate adsorption. The reactivity of these oxides is controlled by the conditions of formation and the processes, such as aggregation, that lead to a reduction in accessible surface sites following formation. The presence of organic compounds is expected to significantly impact these processes in a number of ways. In this study, amorphous ferric oxide (AFO) reactivity and aging was investigated following the addition of ferric iron (Fe(III)) to three solution systems: two synthetic buffered systems, either containing no organic or containing alginate, and a supernatant system containing soluble microbial products (SMPs) sourced from a membrane bioreactor (MBR). Reactivity of the Fe(III) phases in these systems at various times (1-60 min) following Fe(III) addition was quantified by determining the rate constants for ascorbate-mediated reductive dissolution over short (5 min) and long (60 min) dissolution periods and for a range (0.5-10 mM) of ascorbate concentrations. AFO particle size was monitored using dynamic light scattering during the aging and dissolution periods. In the presence of alginate, AFO particles appeared to be stabilized against aggregation. However, aging in the alginate system was remarkably similar to the inorganic system where aging is associated with aggregation. An aging mechanism involving restructuring within the alginate-AFO assemblage was proposed. In the presence of SMPs, a greater diversity of Fe(III) phases was evident with both a small labile pool of organically complexed Fe(III) and a polydisperse population of stabilized AFO particles present. The prevalence of low molecular weight organic molecules facilitated stabilization of the Fe(III) oxyhydroxides formed but subsequent aging observed in the alginate system did not occur. The reactivity of the Fe(III) in the supernatant system was maintained with little loss in reactivity over at least 24 h. The capacity of SMPs to maintain high reactivity of AFO has important implications in a reactor where Fe(III) phases encounter alternating redox conditions due to sludge recirculation, creating a cycle of reductive dissolution, oxidation and precipitation.
铁盐通常作为实现废水处理中磷浓度目标的手段而投加到废水中。添加铁盐后生成的铁氧化物会参与各种反应，包括还原溶解和磷酸盐吸附。这些氧化物的反应活性受形成条件和导致形成后可及表面位点减少的聚合等过程控制。预计有机化合物的存在将以多种方式显著影响这些过程。在这项研究中，在向三个溶液体系中添加三价铁 (Fe(III)) 后，研究了无定形氧化铁 (AFO) 的反应性和老化：两个含有或不含有藻酸盐的合成缓冲体系，以及一个含有来自膜生物反应器 (MBR) 的可溶性微生物产物 (SMP) 的上清液体系。通过确定短（5 分钟）和长（60 分钟）溶解时间内抗坏血酸介导的还原溶解的速率常数，以及一系列（0.5-10mM）抗坏血酸浓度下，来量化这些体系中添加 Fe(III) 后不同时间（1-60 分钟）Fe(III) 相的反应性。在老化和溶解期间，使用动态光散射监测 AFO 颗粒的粒径。在藻酸盐存在的情况下，AFO 颗粒似乎可以防止聚集稳定。然而，藻酸盐体系中的老化与无机体系非常相似，老化与聚集有关。提出了一种涉及藻酸盐-AFO 组合内重构的老化机制。在 SMPs 的存在下，存在更多种类的 Fe(III) 相，其中既有小的有机络合 Fe(III) 易变池，又有稳定的 AFO 颗粒的多分散体。低分子量有机分子的存在促进了形成的 Fe(III) 氢氧化物的稳定，但在藻酸盐体系中观察到的后续老化并没有发生。上清液体系中的 Fe(III) 反应性保持不变，至少在 24 小时内几乎没有反应性损失。SMP 保持 AFO 高反应性的能力在铁 (III) 相由于污泥回流而遇到交替氧化还原条件的反应器中具有重要意义，这会产生还原溶解、氧化和沉淀的循环。
