Drinking Water Problems: Radionuclides

This is an introduction to water treatment systems and technology. It is not a design manual or an exhaustive treatise. It is intended for engineers who are not regularly involved in water treatment projects, but who are interested in learning some of the basics involved. Criteria to be followed in determining the necessity for and the extent of treatment are discussed here, as are procedures applicable to the planning of water treatment projects.

This paper aims at analyzing the drinking water issue in the Mediterranean region, highlighting the principal problems and the appropriate technologies applicable in the different countries. The countries of this area are characterized by a huge variety from social, cultural, economic and environmental point of view. In particular, water distribution is inhomogeneous between the North, East, and South; even the type of water sources and the related quantity and quality problems differ country by country. Potable water comes from brackish and seawater, surface water, groundwater and water reservoirs with each source face different issues. The main problem of brackish and seawater for example is the high salinity and the contamination by disinfection byproducts, in addition to the microbiological and chemical contamination due to human activities that characterize also other surface water sources. Groundwater is also affected by human activity and it is not exempted from salinity because of the water intrusion. Moreover, water reservoirs are often contaminated by seasonal algal blooms. Technologies applied for drinking water treatment vary country by country. The paper presents the main treatment processes associated with the main water pollutants, according to the Mediterranean region. Case studies of drinking water treatment plants are also analyzed, presenting alternative technologies appropriate for specific contexts, among others. The characteristics of each specific context should be carefully analyzed in order to develop the most appropriate technologies; high-end technologies for drinking water treatment may not be applied equally to all countries or communities of the Mediterranean region.

Introduction: Desalination using seawater reverse osmosis (SWRO) technology is an important option available to water-scarce coastal regions. Worldwide sea water desalination is a very effective and economical way of producing potable water for drinking and industries. Reverse osmosis plants to convert sea water to potable drinking water and for other usages have been prevalent throughout the world for more than 4 decades. Design and operation of seawater reverse osmosis plants strongly depend on the raw seawater quality to be treated. The performance of desalination reverse osmosis (RO) systems relies upon the production of high quality pre treated water, and the selection of the best pre treatment technology depends on the raw seawater quality and its variations. Number of full-scale experiences has shown that pre treatment is the key for this application of reverse osmosis technology. It is why during these last years, an import effort has been done to identify and to characterise the diverse organic and mineral components present in the seawater in a view to optimise the seawater pre-treatment and to develop advanced analytical methods for feed water characterization, appropriate fouling indicators and prediction tools. This Chapter describes firstly a comprehensive approach to characterize raw seawater samples through analytical tools which allow the knowledge of the characterization of seawater from many aspects: (a) inorganic content, (b) natural organic matter, (c) enumeration of micro-organisms and phytoplankton. Secondly, this Chapter describes the effect of each of these parameters on the fouling of the reverse osmosis membrane. Finally, this chapter describes the different possible pre treatments available to reduce or remove the elements or substances up-stream reverse osmosis stage.

All over the world the presence of arsenic in water sources for human consumption has been raising great concern in terms of public health since many epidemiologic studies confirm the potential carcinogenic effect of arsenic. Because arsenic removal is the most frequent option for safe drinking water, the development of more efficient and sustainable technologies is extremely important. Membrane separation processes are suitable for water treatment because they can provide an absolute barrier for bacteria and viruses, besides removing turbidity and colour. Their application is a promising technology in arsenic removal since it does not require the addition of chemical reagents nor the preliminary oxidation of arsenite required in conventional treatment options. However, since membrane technologies such as reverse osmosis can be a very expensive and unsustainable treatment option for small water supply systems, it becomes crucial that alternative methods are developed. This work presents a few conclusions based on a laboratorial study performed to evaluate the efficiency of arsenic removal using ultrafiltration, microfiltration and solar oxidation processes under different experimental conditions for relevant parameters. The results showed removal efficiencies higher than 90%. Key-words: safe drinking water, arsenic removal, membranes, public health.

In efforts to make package plants more compact, affordable and easier to operate and maintain, it has been noted that the design and performance of some of these plants containing conventional treatment processes is sometimes compromised if technical expertise in this regard is lacking. Generally, there are several risks associated with poorly designed treatment systems, including loss of production, poor safety and compromised equipment and process unit efficiency with associated higher operating and maintenance costs. These risks have more severe consequences in the case of desalination (including water reclamation and water re-use) package plants. The objective of this project is to develop a set of guidelines to assist municipalities, water treatment practitioners, designers and package plant manufacturers in the specification and design of appropriate unit processes and operating parameters to fit the influent water quality, operating environment and other special treatment requirements.