Department of Chemical, Metallurgy and Materials Engineering, Staatsartillirie Rd, Pretoria West 0183, Tshwane, University of Technology, Pretoria, South Africa.
Council for Scientific and Industrial Research (CSIR), Built Environment (BE), Hydraulic Infrastructure Engineering (HIE), P.O Box 395, Pretoria, 0001, South Africa; Department of Environmental Sciences, School of Agriculture and Environmental Sciences, University of South Africa (UNISA), P. O. Box 392, Florida, 1710, South Africa.
J Environ Manage. 2019 Nov 15;250:109493. doi: 10.1016/j.jenvman.2019.109493. Epub 2019 Sep 12.
Phosphate and nitrate enrichment largely impair aquatic ecosystem functions and services, thus comprising an emerging problem of environmental concern. The problem pertains to developing countries where their discharge to surface water is on the rise due to a rapid growth in population. Herein, these pollutants (phosphate and ammonia) were removed from real municipal wastewater using a simple, fast, and cost-effective process. Raw cryptocrystalline magnesite, a mineral abundant in South Africa, was simply milled and calcined (mechano-thermo processing) in order to produce the activated magnesite (feed). The feed was then used in batch processing for pollutants adsorption and precipitation from real wastewater. The process was optimised by varying the treatment or contact time, feed dosage, concentration, pH, and temperature. The feed and product mineral (produced sludge) were characterised using X-ray Diffraction (XRD), field emission scanning electron microscopy (FESEM) compatible with energy dispersive spectroscopy (EDS), and Fourier Transform Infrared Spectrometer (FTIR). It was identified that the optimal conditions differed for each pollutant, highlighting the importance of tailoring the process to fit the local wastewater characteristics and as part of a treatment train system. Specifically, maximum P removal was achieved after 5 min of mixing, using 1 g L of feed, 123 mg L initial phosphate concentration, pH 8 - 10, and was not affected by temperature variations; whereas, for ammonia removal, optimal conditions were 180 min, 16 g L feed dosage, 80 mg L initial concentration, pH 10 and temperature > 45 °C. The optimal conditions for the removal of both pollutants from real wastewater were 30 min, 6 g L dosage, and ambient temperature and pH. Furthermore, Mg and Ca concentration was found to influence the process. Reduction in total dissolved solids (TDS) and electrical conductivity (EC) suggest an attenuation of chemical species. Characterisation revealed that the product mineral obtained under the optimal conditions for pollutants removal is rich in quartz, periclase, brucite, calcite, magnesite, and struvite. This was further supported by the FTIR results, which indicated the presence of Mg-O, PO, N-H and OH stretches. In addition, the EDS verified the presence of Mg, Ca and P in product mineral. Results are suggestive of the high efficiency of the mechano-thermo activated magnesite treatment process for phosphate and ammonia removal and struvite crystallization. Thus, this technology could valorise municipal wastewater effluents and open new horizons for the effective and sustainable management of wastewater effluents, since struvite can replace the mined phosphate fertilizers, which are rapidly depleting, in the agriculture industry.
磷酸盐和硝酸盐的富集会极大地破坏水生生态系统的功能和服务，因此成为一个新的环境问题。这个问题涉及到发展中国家，由于人口的快速增长，这些国家的污水排放量正在上升。在此，使用一种简单、快速且具有成本效益的工艺，从实际市政废水中去除这些污染物（磷酸盐和氨）。原始的隐晶菱镁矿是一种在南非丰富的矿物，只需简单地研磨和煅烧（机械热加工）即可生产出活性菱镁矿（饲料）。然后，在批处理中，利用饲料从实际废水中吸附和沉淀污染物。通过改变处理或接触时间、饲料用量、浓度、pH 值和温度来优化该过程。利用 X 射线衍射（XRD）、场发射扫描电子显微镜（FESEM）与能量色散光谱（EDS）相结合、傅里叶变换红外光谱仪（FTIR）对饲料和产品矿物（产生的污泥）进行了表征。结果表明，每种污染物的最佳条件都不同，这突出了根据当地废水特性定制该工艺的重要性，这也是处理系统的一部分。具体来说，在混合 5 分钟后，当使用 1g/L 的饲料、123mg/L 的初始磷酸盐浓度、pH 值 8-10 且不受温度变化影响时，磷酸盐的去除率达到最大值；而对于氨氮的去除，最佳条件为 180 分钟、16g/L 的饲料用量、80mg/L 的初始浓度、pH 值 10 和温度>45°C。从实际废水中去除这两种污染物的最佳条件是 30 分钟、6g/L 的剂量以及环境温度和 pH 值。此外，Mg 和 Ca 浓度被发现会影响该过程。总溶解固体（TDS）和电导率（EC）的降低表明化学物质的衰减。特性表明，在去除污染物的最佳条件下获得的产品矿物富含石英、方镁石、水镁石、方解石、菱镁矿和鸟粪石。这进一步得到了 FTIR 结果的支持，FTIR 结果表明存在 Mg-O、PO、N-H 和 OH 伸缩。此外，EDS 验证了产品矿物中存在 Mg、Ca 和 P。结果表明，机械热激活菱镁矿处理工艺对磷酸盐和氨氮的去除以及鸟粪石结晶具有很高的效率。因此，该技术可以使城市废水处理厂的废水得到有效利用，并为废水处理的有效和可持续管理开辟新的前景，因为鸟粪石可以替代快速消耗的开采磷酸盐肥料，在农业领域。
