article · Clean Technologies
Access to safe drinking water requires efficient methods to eliminate harmful contaminants such as heavy metals. This investigation evaluates commercial reverse osmosis and nanofiltration membranes for clearing metal ions from synthetic solutions and natural surface water taken from Lake Tanganyika near Uvira in the Democratic Republic of Congo. Reverse osmosis membranes demonstrated superior rejection, eliminating over 98% of chromium, lead, cadmium, arsenic, nickel, and antimony ions across both synthetic mixtures and genuine surface water. Nanofiltration membranes achieved strong removal rates for chromium, nickel, and cadmium, but performed less effectively on lead, arsenic, and antimony. However, nanofiltration provided considerably higher water flux rates than reverse osmosis. Both membrane types achieved treated water concentrations that satisfy World Health Organization drinking water standards when treating natural water with low initial metal concentrations.
Industrial activities and human settlements can contaminate freshwater reserves with toxic heavy metals. Demonstrating that commercially available filtration membranes can purify natural water from Lake Tanganyika to World Health Organization drinking standards shows a viable technical path for protecting public health. This evidence helps water treatment engineers and municipal planners select appropriate filtration technologies tailored to specific metal contaminants and required throughput.
Because this study tested off-the-shelf commercial reverse osmosis and nanofiltration membranes on real surface water, the technology is applied and tested rather than early stage. Municipal water utilities, industrial water treatment providers, and local operators could deploy these systems directly to treat contaminated surface waters. While reverse osmosis offers higher removal rates, nanofiltration provides significantly faster throughput, presenting trade-offs for commercial system designers depending on which heavy metals dominate local water sources.
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This study evaluates the performance of commercial reverse osmosis (RO) and nanofiltration (NF) membranes for the removal of metal ions from synthetic water and surface water carried from the north-west of Lake Tanganyika in the city of Uvira, in the east of the Democratic Republic of Congo. Metal ion analyses were performed by the standardized ICP-MS and ICP-OES methods. The RO membrane showed higher metal ion rejection in high-concentration solutions (synthetic samples) prepared in the laboratory as well as in low-concentration samples from real raw water collected near Lake Tanganyika. Rejection levels were higher than 98% for Cr3+, Pb2+, Cd2+, As3+, Ni2+, and Sb+3 ions in the synthetic solutions, and 99.2, 98.8, 98.6, 99.2, 98.4, and 98.8%, respectively, in the real samples. The concentrations of metals in the permeate varied depending on the feed concentration and were 0.15 to 1.02 mg/L, 0.33 to 22 mg/L, and 0.11 to 22 mg/L in RO, NF90, and NF270 membranes, respectively. Regarding the NF membranes, the rejection of Cr, Ni, and Cd ions was interesting: 98.2, 97.8, and 92.3%, respectively. However, it was lower for Pb, As, and Sb ions: 76.9, 52.5 and 64.1%, respectively. The flux of NF was 329 to 375 L/m2.h, much higher than for RO membranes, which had a flux of 98 to 132 L/m2.h. The studied membranes are thus a feasible solution to remove the studied metals from real water sources at low concentrations since they meet the standards of the World Health Organization on specific values assigned to chemicals from industrial sources and human habitation areas where these ions are present in drinking water.
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DOI: 10.3390/cleantechnol4040080
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