Water Purification and Management

Oily wastewaters are generated in many industrial processes, such as petroleum refining, petrochemical, food, leather and metal finishing. Fats, oils and greases (FOG’s) present in these wastewaters have to be removed before the water can be reused in a closed-loop process or discharged into the sewer system or to surface waters. These oily waters are mainly in the form of oil-in-water (O/W) emulsions that pose a great problem in facilities attempting to stay in compliance with discharge limits. Emulsion breaking and oil removal require a basic understanding of the physical properties and chemical composition of O/W emulsions. Several properties playing a key role in the stability of an O/W emulsion should be measured for the selection of the appropriate separation process. Only those of industrial relevance will be discussed here, specifically, surface and interfacial tension, contact angle (wetting), zeta potential and droplet size distribution. Treatment of oily wastewaters is performed by a variety of methods and the degree of oil removal depends mainly on the concentration and physical nature of the oil present and its droplet size. The purpose of this work is to study oil/water system characteristics and properties, and techniques for removing oil and grease from industrial wastewaters in analogy with sewage treatment processes. These techniques include gravity and centrifugal separations, chemical treatment, flotation, filtration, membrane processes, evaporation, activated carbon adsorption, biological treatment, and integrated or hybrid processes. Operating parameters, equipment design, treatment costs, range of operation, and the possibility of O/W emulsion reformulation before treatment will also be covered.

This chapter is focused on the main physicochemical methods used in the treatment of waste– and ground-waters. The bases, selection rules, and the main guidelines for the design of distillation-evaporation, adsorption-ion exchange, air stripping, chemical precipitation and chemical reduction/oxidation processes are briefly summarized in the present work. In order to systemize this study, these physico–chemical processes were classified according to their controlling mechanism: phase equilibrium (adsorption), chemical equilibrium (precipitation), kinetics (reduction and oxidation processes), or mass transfer (desorption, distillation). The selection of the most appropriate physicochemical treatment for a given water treatment problem –in terms of matrix properties, degree of depuration and economics – has been afforded in this work through several industrial examples. The main calculations needed for each treatment, (equilibrium, stoichiometry, pumping and mixing requirements) are also summarized. Although most of these operations are well–known within the field of the Chemical Engineering, their application to water treatment presents additional difficulties, such as the complexity of the matrix, the higher conversion levels usually needed, or the difficulty for parameter estimation. Therefore, the use of approximate rules (rules of thumb) is usually needed for preliminary design of physicochemical operations. Finally, a reference to updated available information on this issue in Europe (BREF documents) and United States (EPA resources), is provided in order to advise the reader into the selection of a physic-chemical treatment for a given water treatment problem.

We summarize a review of the various techniques used for removal metals from industrial effluents. From the classical methods to innovative of them, we describe the processes showing both their advantages and inconvenient. On the other hand, we talk about some hybrid processes which are tested at laboratory scale and which would be an alternative for some treatments. It has been shown that the choice of the metals removal technique is highly dependent of the nature of the stream.

Until recently, membranes in bioreactors were essentially regarded as micro/ultra porous barriers to promote high cell concentrations for process intensification and to avoid contamination of the treated water with the biocatalyst. This chapter will discuss in particular the use of membrane bioreactors for treatment of water supplies contaminated with micro14 polluting ions. The contamination of drinking water sources with inorganic compounds is a matter of concern, because of their harmful effect on human health. Some of these compounds are highly soluble in water and dissociate completely, resulting in ions that are chemically stable under normal water conditions. Examples of polluting ions include nitrate, nitrite, perchlorate, bromate, arsenate and ionic mercury, for which the proposed guideline values for drinking water quality are quite low (in the range of µg/L to a few mg/L) owing to their carcinogenic effects or other risk factors to public health.

Many water streams, both wastewater effluents and drinking8 water sources, contain pollutants that cannot be removed or destroyed by conventional physical or biological treatment processes. In such cases it is necessary to seek alternatives. One approach is to destroy the pollutant by application of a strong oxidizing agent. Chlorine is one candidate reagent, but it can produce undesirable reaction products, and residual chlorine can be toxic to aquatic life. Ozone is also used, but it is expensive, and its low solubility in water limits process efficiency. Another category of oxidation processes has been developed in recent years based on the oxidizing strength of hydroxyl radicals. Other processes that involve electrochemical treatment or ultraviolet radiation have received attention. This chapter describes some of these processes, particularly those using peroxide and catalyzed by iron ions in the so-called Fenton reaction (Fenton 1894). Modifications and enhancements of the Fenton process include combinations with UV radiation, semiconductor catalysts, and electrolysis. It has been found that such combinations are necessary and appropriate in order to achieve satisfactory water purification.

According to Cleaner Production (CP) strategy, industrial companies have a number of options for exploring improvements of the water resource management and reducing pollution generation, e.g. input substitution, product/production process modification, optimization of technological processes, improvement of process control, technology substitution. The value of simple good-housekeeping measures should not be underestimated too. This chapter deals with water saving, reuse and recycling in Lithuanian industrial companies by Cleaner Production strategy, which is achieved by applying know-how, by improving technology and/or by changing attitudes. Cleaner Production strategy included the following prevention methods: good housekeeping, input substitution, better process control, equipment modification, technology change, product modification and on-site recovery/reuse. In Lithuania, CP strategy was introduced in 1993. Since then 12 Cleaner Production programmes have been implemented in different economic sectors (three CP programmes were integrated with implementation of environmental management systems). To facilitate implementation of CP innovations that require investments, a special revolving facility to finance CP investments was created in the Nordic Finance Corporation (NEFCO) in 1998. The main objective of the facility is to provide soft loans for the implementation of high-priority CP investments with rapid payback that yield environmental and economical benefits. The results of innovations on water saving and reuse by applying CP methods from 69 companies, representing 12 branches of industry is presented.

In most wastewater treatment processes large quantities of soids and sludge (refuse) are produced that must be disposed of. Such refuse is a complex mixture of substances, both physically and chemically. The properties of solid waste streams generated during the treatment of municipal and industrial wastewaters are summarized, and alternatives for their treatment and final disposal are reviewed. The main alternatives currently used for the management of these wastes, such as conditioning, thickening (sedimentation and flotation), and dewatering (evaporation and centrifugation) are described along with relevant process-performance parameters.