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A wide range of materials known for their adsorption properties have the potential for being used for the removal of trace substances from drinking and wastewaters. These include physically and chemically activated carbons, surface modified carbons, non-porous resins with ion exchange capacities, inorganic microporous solids like zeolites and clays, and mixed organic-inorganic materials like bone chars. The adsorption capacity exhibited by each material relates primarily to its textural and chemical properties. Other factors, however, such as apparent density, regeneration potential and cost, need to be taken into consideration when selecting one adsorbent over another. A comparative investigation of 18 solids and their capacity to remove organics and metals from natural waters and solutions reconstituted to simulate the conditions in natural waters is presented. The experiments were carried out using batch and small-scale column adsorption tests. In general, zeolites and ion exchange resins exhibited limited capacities to remove organic matter from solution but were highly effective with metallic species like manganese and aluminium. Activated carbons adsorbed organic matter very efficiently, with results showing a correlation between adsorption capacity and surface area (up to 1791 m 2 g −1 ). Metal removal was highly variable and was enhanced in activated carbons subjected to acid washing. Owing to its mixed organic/inorganic nature, and despite its poorly developed micropore structure, bone char exhibited a strong adsorption capacity for both organic and metal species. The high apparent density of this material (0.763 g cm −3 ) meant that its performance was greatly improved when tests were conducted on the basis of volume, matching and surpassing the performance of the best carbons. The possibility of using mixtures of complementary adsorbents for the removal of organic and inorganic species from solution was also successfully evaluated in this work.

With the adoption of European Community Directives regarding bathing water quality and the potential extension of bathing waters standards to all recreational waters, the disinfection of wastewater effluents has become an option of increasing interest. Ozone is a very powerful oxidant, capable of fast and effective disinfection. Due to its oxidizing potential, its application to final municipal effluents could have a beneficial effect on the effluent quality, although some concerns exist over the formation of potentially harmful by-products such as organic halides. This paper describes a preliminary laboratory-based study designed to investigate the changes in the physico-chemical properties of a secondary municipal effluent after ozonation, as well as the effect of ozone on the concentration of organic halides and effluent toxicity. The treatability and the performance of the system for different methods of ozone application also is evaluated. The effluent was treated with ozone generated from air and from oxygen. Using oxygen as a feed gas, three different ozone concentrations in the gas were examined, namely 1.5% w/w, 4.5% w/w and 13.5% w/w.The results showed that ozone affected the physico-chemical properties of the effluent by reducing the COD, BOD 5 and color concentrations, and by increasing the dissolved oxygen concentration of the effluent. In the ozone dose range likely to be applied for disinfection, the amount of halogenated organic species increased. This increase, however, was not associated with changes in toxicity. At higher ozone doses, the organic halide concentration was found to decrease, whereas toxicity, although undetectable with the use of standard protocols, was found to increase. For a constant ozonation rate, the treatment performance was similar for 133 Downloaded by [Laurentian University] at 04:49 09 December 2014 T 134 P. Paraskeva et al.all ozonation conditions. However, an increased ozone concentration in the feed gas increased the mass transfer rate of ozone to the liquid, resulting in a faster effluent treatment.

Thermal regeneration is increasingly being used for the recovery of field-spent granular activated carbons (GAC) generated by the water treatment industry. Despite its commercial success, conventional methods using oxidising conditions (usually steam) are known to damage the porosity of the regenerated carbons, thus reducing their adsorption capacity and economic value. This paper presents a comparative investigation into the benefits of using inert conditions for the regeneration of field-spent GAC. For the purpose of this work, a sample of spent carbon was regenerated in nitrogen and in steam to different degrees of burn off. The resulting samples were analysed for their porosity and surface area characteristics using nitrogen gas adsorption, and for their aqueous adsorption capacities using phenol and methylene blue. Experimental results showed that steam was sightly more effective than nitrogen at regenerating the total micropore volume and BET surface area of the carbons. However, these benefits were largely counteracted by greater losses in the carbon yield and damage to the narrow microporosity. Carbons regenerated in nitrogen exhibited greater adsorption capacities for the adsorption of small molecular size compounds (phenol) from solution, while carbons regenerated in steam adsorbed larger molecular size compounds (methylene blue) more effectively. However, when product yields were taken into consideration, inert regeneration was found to produce significantly better results than steam regeneration. An optimum process temperature was determined to be 950 degrees C.

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