Chapter Eight: Treatment of Waters With Special Contaminants

1 Chapter Eight: TREATMENT OF WATERS WITH SPECIAL CONTAMINANTS

In recent times, there has been an emergence of water contaminants which in the past, were either of less concern or their health impacts not known. These special contaminants are bringing new dimension in the manners in which they are supposed to be dealt with. This chapter presents special water contaminants that have emerged to be of major health concern. Treatment techniques and methods for these special contaminants have also been presented.

1.1 NATURAL ORGANIC MATTER

Over the past 10–20 years, the amount of natural organic matter (NOM) has increased in raw water supplies in several areas. The presence of NOM causes many problems in drinking water treatment processes, including: (i) having a negative effect on water quality by colour, taste and odour, (ii) increased requirement of coagulant and disinfectant dose, (which in turn results into increased sludge and potential harmful disinfection by-product formation), (iii) increased biological growth in the water distribution system, and (iv) increased levels of complex heavy metals and adsorbed organic pollutants.

In Tanzania, this problem of organic matter in water is more pronounced at the Igombe dam, the source of water supply for Tabora Municipality. A study on water quality monitoring at the Dam conducted between October 2009 – November 2010, revealed that colour and turbidity of raw water is very high due its very high humic content and algal blooms. These substances are mainly the result of organic matter from the surrounding dry forest.

From the conclusions of the first report (February 2, 2010), it is now known that the current treatment of water in the area is not sufficient to guarantee a good water quality in the network, mainly due to the risk of bacterial re-growth and also due to acidic pH, causing pipe corrosion. Igombe Dam water is characterized by high concentrations of organic matter. The organic matter is mainly of natural origin, that is, natural organic matter (NOM). The collected water quality data confirms the high amount of natural organic matter (NOM) in the raw water of the Igombe Dam.

The high concentration of NOM in this water may cause different problems, including excessive chlorine demand, formation of disinfection by-products (DBPs), bad taste and odour problems and bacterial re-growth in the distribution system. The low concentration of the different nitrogen compounds (nitrate, ammonia) in the raw water of the Igombe Dam indicates moderate to little agricultural and human activities in the watershed, confirming that the source of the organic matter in the raw water is principally of natural origin.

Therefore, one of the principal objectives of the future water treatment plant at Igombe will involve the reduction of NOM (measured as DOC and UV254) through different treatment processes - principally coagulation/sedimentation and (biological) filtration.

1.2 ARSENIC

The occurrence of arsenic in groundwater is increasingly becoming a serious pollution problem to human health worldwide. The occurrence of such pollutants can either be geogenic or anthropogenic. Recently, elevated concentrations of arsenic (>10 μg/L) has been reported in the northern parts of Tanzania and are associated with gold mining activities within or near the Lake Victoria Basin (LVB). The geology of LVB is dominated by greenstone belts in the North-Western region up to Mpanda and Lupa Mineral fields in the Ubendian system of western Tanzania. These regions are characterized by small, medium and large scale mining, using various technologies. Several adverse human health effects are noticed among the communities living around the relevant mining areas. Based on the developed geostatistical model using past study results on total arsenic in 9 districts, a spatial trend (R² =0.19) in the east-west transect was also noticed. In addition, a spatial trend (R² =0.009) was observed along the north-south transect. The reported study results are a potential to watch in engaging in improved drinking water supplies targeting groundwater sources.

Thus, every water treatment must consider removing this pollutant. One way of completely removing this pollutant is to consider a number of different units and modules such as to include oxidation, coagulation, flocculation, and membrane techniques11.

1.3 RADIOACTIVE CONTAMINANTS

Radioactive contamination, also called radiological contamination, is the deposition or presence of radioactive substances on surfaces or within solids, liquids or gases, where their presence is unintended or undesirable. Such contamination presents a health hazard because of the radioactive decay of the contaminants, which produces such harmful effects as ionizing radiation (namely α, β, and γ rays) and free neutrons. The sources of radioactive pollution can be classified into two groups: natural and man-made. In Tanzania such radioactive materials have been reported in geographical areas of Chemba and Bahi.

Water sources with radioactive contamination should not be exploited by any water authority or project.