Toxicological risk of urban effluents discharged into the North-Western Coast in Lake Tanganyika (Democratic Republic of Congo) and their treatment by pressure-driven membrane filtration by Vercus LUMAMI KAPEPULA

Water scarcity is one of the problems caused by global industrialization. In developing countries, population increase, rural exodus and environmental degradation are major threats to humanity. Inadequate wastewater treatment is a major concern, as it contributes greatly to the destruction of water resources when discharged into the environment. In the Democratic Republic of Congo, sanitation is not sufficiently developed. The remarkable lack of qualified human resources for the analysis and monitoring of environmental quality, technical and/or financial means does not allow for the implementation of coherent programs adapted to the realities and challenges facing the country. Much of the work carried out by researchers in the Democratic Republic of Congo is limited to the evaluation and quantification of pollution, concluding that population should not consume fish or water from polluted sites. However, there is an expression commonly used in low-income countries, which says "a hungry stomach has no ears". With this in mind, this study focuses on the application of emerging technology based on reverse osmosis and nanofiltration to treat urban effluent discharged into the north-western coast of Lake Tanganyika (Democratic Republic of Congo).

Two main global objectives were considered in this study, namely: i) the determination of pollution and toxicological risk of pollutants on the northwestern slope of Lake Tanganyika, and ii) the development of a treatment method of domestic and industrial wastewater by commercial membranes, including the preparation of a low-cost membrane to remove pollutants.

The determination of pollution was based on chemical analysis of organic and inorganic micropollutants, and the toxicity test by bio-testing was experimented in aquariums at the laboratory of the Hydrobiology Research Center in Uvira. The results show that the wastewater is polluted by highly toxic inorganic and organic compounds. The sources of pollution came from the reference hospital of Uvira, the penitential center of Uvira, the households, the artisanal food-processing industries, the degradation of non-recycled household waste and the physical alteration of the sedimentary rocks of the Precambrian period that form the substrates.
The real waters sampled in Uvira were filtered on 200 μm filter paper to retain large particles that can affect membrane fouling and clogging. These real waters had not undergone any other chemical pre-treatment. After the physical pretreatment, they were filtered on commercial reverse osmosis membranes of polyamide type and NF90, NF270 to remove inorganic micropollutants.

The synthetic waters were prepared in the laboratory with the specific ions under study at known concentrations. Those waters were filtered through commercial reverse osmosis membranes, as well as nanofiltration membranes (NF90 and NF270) to remove metal ions. The experimentation of commercial membranes allowed to evaluate its performance. Next, a membrane containing chitosan and the metallic organic framework ZIF-8 (i.e., CS/ZIF-8 mixed matrix membrane) was prepared at the laboratory and characterized by XRD, SEM, FTIR, angle contact, and tested in the reverse osmotic unit using the synthetic waters at different concentrations.

The results obtained show that the retention of ions by the polyamide reverse osmosis membranes is excellent, although the permeate flux is low. The retention with nanofiltration membranes depends on the feed concentration and ionic interactions at the membrane surface. Regarding the self-made CS/ZIF-8 mixed matrix membrane, it shows better retention performance for Cr3+, Pb2+, Cd2+ and Ni2+ ions in a concentrated feed solution and high-water permeability at low operating pressure. In addition, industrial scaling-up of the CS/ZIF-8 membrane is more attractive, as the manufacturing cost is low and the permeate flux high. The economic feasibility analysis shows that the investment cost is high, but energy consumption is low.

Jury members:

• Prof. Luis Alconero Patricia (UCLouvain, Belgium), supervisor
• Prof. Musibono Eyul Dieudonné (Université de Kinshasa, RDC), supervisor
• Prof. Soares-Frazao Sandra (UCLouvain, Belgium), chairperson
• Prof. Raskin Jean-Pierre (UCLouvain, Belgium)
• Prof. Figoli Alberto (Insitute on membrane Technologie, Italy)
• Prof. Buleng Njoyim Estella (University of Dschang, Cameroun)
• Prof. Vanhove Maarten (Université Hasselt, Belgium)
• Prof. Mputu Kanyinda Jean-Noël (Université de Mons, Belgium)

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