Water reclamation implementation and management practices at municipal wastewater treatment plants throughout the world are reviewed and some implementation and operational issues are defined. The information is based on a conventional literature survey, on an in depth survey study of European, Israeli and Australian medium and large-scale water reclamation utilities and on the findings of a dedicated international workshop.
The review identified over 3,300 water reclamation projects and designed the map of the main process technologies and their fields of product water application. The main conclusion of the enquiry is that the technological risks no longer represent a major concern for the development of water reclamation projects, rather issues such as the financing, failure management and social acceptance have become more critical.
Municipal and industrial wastewater treatment plants produce large amounts of sludge, mostly mechanically dewatered to approx. 25% DS and containing organic and mineral components. This sludge needs to be evacuated. Possible reductions of the amount of sludge produced are, hence, important. This paper describes the experimental results of peroxidation of thickened sludge (6% DS content). It can be concluded that peroxidation is efficient in reducing the residual sludge amounts. The optimum conditions correspond with adding 0.037 g H 2 O 2 /100 mL sludge at pH 5 3 and in the presence of Fe 21 ions (1 mg Fe 21 /100 mL sludge). Under these conditions, the rate of mechanical dewatering is significantly improved, and the amount of DS to be dewatered is reduced to approx. 80% of the initial untreated amount. Peroxidation preferentially releases ODS into the water phase. The slightly increased BOD/COD ratio converts this water phase into a more biodegradable and accessible carbon source for nitrification/denitrification. Heavy metals are also released in the water phase, and can be subsequently precipitated, thus reducing the residual heavy metal concentration in the residual DS.
A packed granular activated carbon (GAC) biobed, inoculated with the ethane-degrading strain Mycobacterium E3, was used to study ethene removal from a synthetic waste gas. Ethene, for which the dimensionless partition coefficient for an air-water system at 20 degrees C is about 7.6, was used as a model compound for poorly water soluble gaseous pollutants. In a first mode or operation, the GAC biobed was sprinkled intermittently and the waste gas influent was continuously pre-humidified, establishing relatively moist conditions (water content >40% to 45%). A volumetric ethene removal rate of 0.382 kg COD x m(-3) x d(-1) (0.112 kg ethene x m(-3) x d(-1)) was obtained for an influent concentration of 125 ppm, a superficial waste gas velocity of 3.6E-3 m x s(-1) and a pseudo residence time of 45 s. However, in the second mode of operation, omitting the pre-humidification of the waste gas influent and establishing a "dry" biobed (water content <40% to 45%), and thus obtaining better mass transfer to the biofilm, the ethene removal could be doubled for otherwise comparable operating parameters. Furthermore, under decreased wetting and for the given experimental conditions (influent concentration 125 to 816 ppm, waste gas superficial velocity 3.0E-3 m x s(-1), pseudo waste gas residence time 43 s), the ethene removal was not limited by mass transfer of ethene through the water layer covering the biofilm.
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