Characterizing a Newly Designed Steel-Wool-Based Household Filter for Safe Drinking Water Provision: Hydraulic Conductivity and Efficiency for Pathogen Removal

Abstract

This study characterizes the decrease of the hydraulic conductivity (permeability loss) of a metallic iron-based household water filter (Fe0 filter) for a duration of 12 months. A commercial steel wool (SW) is used as Fe0 source. The Fe0 unit containing 300 g of SW was sandwiched between two conventional biological sand filters (BSFs). The working solution was slightly turbid natural well water polluted with pathogens (total coliform = 1950 UFC mL−1) and contaminated with nitrate ([NO3−] = 24.0 mg L−1). The system was monitored twice per month for pH value, removal of nitrate, coliforms, and turbidity, the iron concentration, as well as the permeability loss. Results revealed a quantitative removal of coliform (>99%), nitrate (>99%) and turbidity (>96%). The whole column effluent depicted drinking water quality. The permeability loss after one year of operation was about 40%, and the filter was still producing 200 L of drinking water per day at a flow velocity of 12.5 L h−1. A progressive increase of the effluent pH value was also recorded from about 5.0 (influent) to 8.4 at the end of the experiment. The effluent iron concentration was constantly lower than 0.2 mg L−1, which is within the drinking-water quality standards. This study presents an affordable design that can be one-to-one translated into the real world to accelerate the achievement of the UN Sustainable Development Goals for safe drinking water.

Steel Wool for Water Treatment: Intrinsic Reactivity and Defluoridation Efficiency

“…This corresponds to a reactivity ratio of about 1/6. However, the k EDTA values were determined in experiments lasting for just three days and correspond at best to the initial kinetics of iron corrosion which is well-known to be nonlinear [43,73]. The results of long-term leaching presented herein (Section 3.1.3) have documented waves (even) in this initial corrosion rate.…”

“…It should be added that Fe 0 corrosion in an O 2 scavenging process implying that oxidation of Fe 0 contributes to produce anoxic conditions [81]. The extent to which O 2 scavenging is achieved implies that some removal processes (e.g., denitrification) are just indirectly mediated [43]. In other words, the thermodynamic of the Fe 0 /H 2 O system implies that Fe 0 can be universally used for: (i) H 2 generation, (ii) O 2 consumption, and (iii) generation of FeCPs (iron hydroxides and oxides).…”

“…For example, while testing Fe 0 SW for household water treatment, Bradley et al [42] realized that there was a Fe 0 complete depletion of grade 0000 (extra fine-d = 25 µm) after six months (170 days). Tepong-Tsindé et al [43] tested grade 0 (fine-d = 50 µm) for 12 months and have not achieved any material depletion. The four Fe 0 SW (Table 1) tested in column leaching experiments herein were depleted to 57.5% to 66.2% after 53 leaching even.…”

“…In general, testing SW for water treatment became common place, even though available results are to be regarded as independent reports [35]. From 1995 on, SW was tested for the removal of various contaminants including arsenic [36,37], chromium [38,39], nitrate [40,41], pathogens [42,43], and selenium [44]. However, SW is just used as a class of reactive material mostly without any reactivity characterization [35].…”

Metallic Iron for Environmental Remediation: Starting an Overdue Progress in Knowledge

“…The lack of systematic investigations has also affected the selection of Fe 0 materials used for pathogen removal [141][142][143][144][145][146]. Using various Fe 0 materials and very different experimental conditions, discrepant results have been reported [141,146]. Lu et al [142] can be regarded as a perfect reflection of the state-of-the-art knowledge.…”