Abstract
Significant growth of the human population is expected in the future. Hence, the pressure on the already scarce natural water resources is continuously increasing. This work is an overview of membrane and filtration methods for the removal of pollutants such as bacteria, viruses and heavy metals from surface water. Microfiltration/Ultrafiltration (MF/UF) can be highly effective in eliminating bacteria and/or act as pre-treatment before Nanofiltration/Reverse Osmosis (NF/RO) to reduce the possibility of fouling. However, MF/UF membranes are produced through relatively intensive procedures. Moreover, they can be modified with chemical additives to improve their performance. Therefore, MF/UF applicability in less developed countries can be limited. NF shows high removal capability of certain contaminants (e.g. pharmaceutically active compounds and ionic compounds). RO is necessary for desalination purposes in areas where sea water is used for drinking/sanitation. Nevertheless, NF/RO systems require pre-treatment of the influent, increased electrical supply and high level of technical expertise. Thus, they are often a highly costly addition for countries under development. Slow Sand Filtration (SSF) is a simple and easy-to-operate process for the retention of solids, microorganisms and heavy metals; land use is a limiting factor, though. Rapid Sand Filtration (RSF) is an alternative responding to the need for optimized land use. However, it requires prior and post treatment stages to prevent fouling. Especially after coating with metal-based additives, sand filtration can constitute an efficient and sustainable treatment option for developing countries. Granular activated carbon (GAC) adsorbs organic compounds that were not filtered in previous treatment stages. It can be used in conjunction with other methods (e.g. MF and SSF) to face pollution that results from potentially outdated water network (especially in less developed areas) and, hence, produce water of acceptable drinking quality. Future research can focus on the potential of GAC production from alternative sources (e.g. municipal waste). Given the high production/operation/maintenance cost of the NF/RO systems, more cost-effective but equally effective alternatives can be implemented: e.g. (electro)coagulation/flocculation followed by MF/UF, SSF before/after MF/UF, MF/UF before GAC.
Highlights
John Hoslett a, Theoni Maria Massara a, Simos Malamis b, Darem Ahmad a, Inge van den Boogaert a, Evina Katsou a, Balsam Ahmad c, Heba Ghazal d, Stefaan Simons a, Luiz Wrobel a, Hussam Jouhara a,⁎
Whilst the more complex Activated Carbons (ACs) used in developed nations can remove heavy metals and other contaminants [e.g. see Table 4: (Kårelid et al, 2017; Katsigiannis et al, 2015)], ACs implemented in less developed areas can be used in conjunction with other methods (e.g. MF and Slow Sand Filtration (SSF)) to face pollution that results from the outdated water network [e.g. see Table 4: (Guo et al, 2017)] and, produce water that is of acceptable drinking quality
Materials produced in the lab are often difficult to fabricate in developing nations as they require expertise and technology that is not available there (Sustainable DG Fund, 2015; World Health Organization (WHO), 2017b) This paper shows that SSFs and biochar are two potentially accessible technologies that can push towards the direction of Goal 6
Summary
Another problem in surface waters is eutrophication. When an excess of nutrients enters a water body, an algal bloom occurs inducing increased consumption of the dissolved oxygen (DO) in the water. Heavy metals and metalloids are commonly removed from wastewater and surface water using granular activated carbon (GAC). This can require process optimization to achieve higher/complete removal (Sounthararajah et al, 2015). According to more recent advances, The WHO issues guidelines in contaminant parameters that must be met for a water source to be considered safe and drinkable It sets guidelines for the performance of specific parts of a water treatment system. For the purposes of producing an insightful and acceptable in length review, the focus from will be on filtration (MF/UF, NF/ RO, sand filtration) and GAC that target specific pollutants such as heavy metals and metalloids (e.g. Cd, Pb, As, copper (Cu)), and indicator parameters (e.g. total organic carbon (TOC), E. coli, oil emulsions, etc.). This work aims at presenting an overview of the MF/UF, NF/RO, sand filtration and GAC systems in terms of efficiency, applicability in developing countries, and cost aspects, always by extracting information from the most up-to-date studies
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