Hybrid Hollow Fiber Nanofiltration–Calcite Contactor: A Novel Point-of-Entry Treatment for Removal of Dissolved Mn, Fe, NOM and Hardness from Domestic Groundwater Supplies

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 ( 20 μ 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 and 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 ( 90 / 10 wt . % ) was used as a post-treatment to the tight HFNF (100–200 Da).

Progress in Research and Application of Nanofiltration (NF) Technology for Brackish Water Treatment

“…In addition, membrane fabrication should be “fitting for purpose” according to the specific brackish water quality and treatment requirements; The application of NF technology integrated with other emerging water treatment technologies is expected to further improve the performance of brackish water treatment. For instance, an integrated NF-calcite contactor process proposed by Haddad et al was proved to be a feasible method to effectively remove the undesirable compounds (particularly manganese (Mn), iron (Fe) and hardness) from groundwater [ 139 ]. Therefore, more novel hybrid brackish water treatment process combination with NF as core should be explored.…”

Susceptibility Prediction of Groundwater Hardness Using Ensemble Machine Learning Models

“…Hardness is considered as one of the essential quality factors of water [47]. Hardness assessment is particularly important to avoid costly blockage and breakdowns in pipelines, channels, water distribution systems, boilers, cooling towers, appliances, and any civil structures that may handle water [48,49]. Despite the importance of hardness susceptibility mapping, there is a research gap in the advancement of novel models [50].…”