Abstract
Groundwater (GW) is one of the main potable water sources worldwide. However, the presence of undesirable compounds and particularly manganese (Mn) and iron (Fe) (mainly co-existing in GWs) are considered as objectionable components of potable water for both health and aesthetic issues. As such, individual dwellings supplied by domestic wells are especially threatened by these issues. Current domestic treatment technologies are complicated to operate and even dangerous if improperly maintained (e.g., catalytic filtration) or consume salts and produce spent brine which pollutes the environment (i.e., ion exchange resins). Therefore, it is of prime importance to design a simple and compact, yet robust, system for Mn and Fe control of the domestic GW sources, which can reliably guarantee the desired Mn limit in the finished water (g/L). In the course of this study, we demonstrated, for the first time, that a hybrid hollow fiber nanofiltration (HFNF)–calcite contactor process is a promising alternative for treating domestic GWs with elevated levels of Mn, Fe, natural organic matter (NOM) and hardness. The efficacy of the HFNF membranes in terms of removal of Mn, Fe, NOM and fouling was compared with commercially available NF270 and NF90 membranes. The results revealed that HFNF (100–200 Da) and NF90 maintained considerably high rejection of Mn, Fe and NOM due to their dominant sieving effect. In contrary, the rejections of the above-mentioned components were decreased in the presence of high hardness for the looser HFNF (200–300 Da) and NF270 membranes. No membrane fouling was detected and the permeate flux was stable when the hard GW was filtered with the HFNF membranes, regardless of their molecular weight cut-off and transmembrane pressure, while the permeability of the NF270 and NF90 membranes steadily decline during the filtration. Integrating a calcite contactor, as a post filtration step, to the HFNF process yielded further Mn, Fe and NOM removals from the HFNF permeate and adjustment of its hardness level. The best performance was achieved when a blend of Calcite–CorosexTM () was used as a post-treatment to the tight HFNF (100–200 Da).
Highlights
Groundwater (GW) comprises a significant amount of all unfrozen fresh water and provides approximately half of the world’s drinking water supply
Increasing the driving force by exerting a higher TMP led to a higher permeate flux which translates into high productivity
One can note that filtration of the hard GW with the flat sheet membranes (i.e., NF 270 and NF90) and loose hollow fiber nanofiltration (HFNF) (200–300 Da) resulted in higher permeate specific volumes; the permeate flux of the NF270 and NF90 membranes declined significantly throughout the filtration experiments, regardless of the applied TMP (p = 0.03)
Summary
Groundwater (GW) comprises a significant amount of all unfrozen fresh water and provides approximately half of the world’s drinking water supply. Membranes 2019, 9, 90 and staining of laundry and plumbing fixture [1,2]) were the primary motivation for the Mn and Fe removal from the potable water sources, the findings of recent epidemiological studies addressed chronic neurological effects of elevated Mn level on school-age children [3,4,5]. The United States Environmental Protection Agency added Mn to the fourth Candidate Contaminant Candidate List [7]
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