Advanced Water Management Centre, The University of Queensland, St Lucia, QLD 4072, Australia.
Advanced Water Management Centre, The University of Queensland, St Lucia, QLD 4072, Australia; Department of Chemistry and Bioengineering, Tampere University of Technology, P.O. Box 541, 33101 Tampere, Finland.
Water Res. 2017 Nov 1;124:210-218. doi: 10.1016/j.watres.2017.07.043. Epub 2017 Jul 20.
Electro-concentration enables treatment and nutrient recovery from source-separated urine, and is a potential technology for on-site treatment using a 3 compartment configuration that has anode, cathode and middle concentrate compartments. There is a particular focus on driving concentration towards the precipitation threshold in the concentrate compartment to generate solid ammonium salts, including ammonium bicarbonate. To evaluate controlling mechanisms and the feasibility of achieving high concentrations, a dynamic mechanistic model was developed and validated using experiments with synthetic urine. It was identified that high concentrations are prevented by increased back diffusion (diffusion from the middle chamber to the anolyte and catholyte) due to large concentration gradients, and the preferential migration of protons or hydroxide ions due to a loss of buffering capacity in the anolyte and catholyte (due to pH extremes). Model-based sensitivity analysis also identified that electrolyte ion concentrations (including buffer capacity) were the main controlling mechanisms, rather than membrane or electrolyte current transfer capacity. To attain high concentrations, operation should be done using a) a high current density (however there is a maximum efficient current density); b) feed at short hydraulic retention time to ensure sufficient buffer capacity; and c) a feed high in ammonium and carbonate, not diluted, and not contaminated with other salts, such as pure ureolysed urine. Taking into account electron supply and bio-anodic buffer limitations, model testing shows at least double the aqueous concentrations observed in the experiments may be achieved by optimising simple process and operational parameters such as flow rate, current density and feed solution composition. Removal of total ammonium nitrogen (TAN) and total carbonate carbon (TCC) was between 43-57% and 39-53%, respectively. Balancing the sometimes conflicting process goals of high concentrations and removal percentage will need to be considered in further application. Future experimental work should be directed towards developing electrodes capable of higher current densities. In addition it would be desirable to use ion exchange membranes with higher resistance to water fluxes and which limit back diffusion. Future modelling work should describe osmotic and electro-osmotic water fluxes as a function of the concentration gradient across the membranes and ionic fluxes, respectively. More generalised wastewater physico-chemistry speciation models should identify best methods where relatively simple Davies activity corrections do not apply.
电浓缩使源分离尿液的处理和养分回收成为可能，是一种使用 3 隔室配置（包括阳极、阴极和中间浓缩隔室）进行现场处理的潜在技术。特别关注的是在浓缩隔室中将浓度推向沉淀阈值，以生成固体铵盐，包括碳酸氢铵。为了评估控制机制并实现高浓度的可行性，使用合成尿液进行了实验，开发并验证了一个动态的机制模型。结果表明，由于浓度梯度较大，反向扩散（从中室扩散到阳极电解液和阴极电解液）会阻止高浓度的形成，并且由于阳极电解液和阴极电解液的缓冲能力丧失（由于 pH 值极端），质子或氢氧根离子优先迁移。基于模型的敏感性分析还表明，电解质离子浓度（包括缓冲能力）是主要的控制机制，而不是膜或电解质电流传递能力。为了实现高浓度，操作应使用：a）高电流密度（然而，存在最大有效电流密度）；b）进料时水力停留时间短，以确保有足够的缓冲能力；c）进料中铵和碳酸盐浓度高，不稀释，且不被其他盐污染，例如纯尿酶解尿液。考虑到电子供应和生物阳极缓冲限制，模型测试表明，通过优化简单的工艺和操作参数（例如流速、电流密度和进料溶液组成），可以实现至少是实验中观察到的水相浓度的两倍。总铵氮（TAN）和总碳酸盐碳（TCC）的去除率分别为 43-57%和 39-53%。在进一步的应用中，需要考虑实现高浓度和去除率这两个有时相互冲突的过程目标。未来的实验工作应致力于开发能够承受更高电流密度的电极。此外，使用对水通量的阻力更高且限制反向扩散的离子交换膜将是理想的选择。未来的建模工作应描述渗透压和电渗流作为跨膜浓度梯度和离子通量的函数的水通量。更通用的废水物理化学形态模型应确定适用于相对简单的戴维斯活度校正不适用的最佳方法。
