Industrial Discharges of Metals in Kigali, Rwanda, and the Impact on Drinking Water Quality

Rwanda is a landlocked country located in Africa's Central-East Great Lakes region. It has a population of 7.5 million which occupies 26,338 km'. Its population density (285/km') is one of the highest in the world and has prompted fear of a rapid degradation of the ecosystem. There are no central sewer systems in Rwanda. The use of pit latrines and septic tanks is common in urban and rural areas. People still defecate in the fields (World Bank, 1989). Less than half of the urban population is served by a central water supply. The majority of people get their water untreated from rivers that have been polluted by chemicals and human excreta. In and around the capital city of Kigali, there is a concentration of people, farms, and industries which discharge wastewater into the Nyabarongo River and its tributaries. The Nyabarongo River, a tributary of the Nile, empties into the Akagera River which flows into Lake Victoria. Nyabarongo River water is used for drinking water, cooking, bathing, and agriculture in the Kigali area. There has been very little monitoring of the water quality of the Nyabarongo River and of industrial outfalls located on tributaries of the Nyabarongo River. As a first step in understanding the water quality of the Nyabarongo River, wastewater samples were collected in 1993 from industrial outfalls located on tributaries of the Nyabarongo River. Most of the facilities sampled had no wastewater treatment. The impact of these discharges on the water quality of the Nyabarongo River was evaluated.

Centrifugal separation of molten steel and glass mixtures

A lot of mixed vitrified waste exists at DOE sites, which contain valuable metal having great potential for being reused in industry. Of these useful metals, steel constitutes more than 45% of the volume. Using the differential centrifugal separation technology, steel is separated by using remote melting of the mixed waste. The high costs involved are directly proportional to the time involved in separation of the steel from the mixed waste. This is determined by using similitude principles. Having obtained a solidified steel ingot by melting, it is essential to determine the decontaminated portions of the ingot that can be released to industry. Two parameters representing measures of separation are proposed—the Centrifugal Fluid Separation Number and the Thermal Separation Number. Regression correlations are determined to express the estimated time of separation. Experimental analysis of solidified ingots has shown that when the Thermal Separation Number is less than 1700 the steel contains little or no trace of glass. This result can be used to recycle steel back to industry. ^