Water, reuse

The trend in the use of deep bed filters in water treatment is to eliminate conventional flocculators and sedimentation tanks, and to employ the filter as a flocculation reactor for direct filtration of low turbidity waters. The constraints of batch operation can be removed by using one of the available continuous filters which provide continuous backwashing of a portion of the medium. Such systems include moving bed filters, radial flow filters, or traveling backwash filters. Further development of continuous deep bed filters is likely. Besides clarification of Hquids, which is the most frequent use, deep bed filters can also be used to concentrate soflds into a much smaller volume of backwash, or even to wash the soflds by using a different Hquid for the backwash. Deep bed filtration has a much more limited use in the chemical industry than cake filtration (see Water, Industrial water treatment Water, Municipal WATERTREATiffiNT Water Water, pollution and Water, reuse). 

Water reuse is usually a question of the tradeoff between the costs of raw water and the costs associated with treatment for reuse and for discharge. If biological treatment is to be employed, several factors must be considered. These are an increase in concentration of organics, both degradable and nondegradable. This may have a negative effect in terms of final effluent toxicity. An increase in temperature or total dissolved soHds may adversely affect the performance of the biological process. 

Over the past decade, water pollution control has progressed from an art to a science. Increased emphasis has been placed on the removal of secondary pollutants, such as nutrients and refractory organics, and on water reuse for industrial and agricultural purposes. This in turn has generated both fundamental and appHed research, which has improved both the design and operation of wastewater treatment faciUties. 

Paradoxically, even rapid lowering of demand may cause rapid cost escalation this was the case in New Jersey during a 1981 drought when conservation caused substantial shrinking of demand and private water companies had to double their water prices. The continued increase of demand and reduction of supply portend real and relendess water-cost increases in every part of the United States in the future. One possible way to assure at least adequate suppHes, and possibly to moderate these cost increases, is through water reuse. 

Beginning in 1976 it began organising international congresses in desalination and water reuse. The proceedings of its conferences have been pubUshed (30). It also pubhshes a trade magasine (31). 

A notable example of controlled water reuse was utilization of secondary sewage effluent from the Back River Wastewater Treatment Plant in Baltimore by the Sparrows Point Works of Bethlehem Steel (6). The Sparrows Point plant was suppHed primarily by weUs located near the brackish waters of Baltimore harbor. Increased draft on the weUs had led to saltwater intmsion. Water with chloride concentration as high as 10 mg/L is unsuitable for many steelmaking operations. Rollers, for example, are pitted by such waters. However, treated effluent from the Back River Plant can be used for some operations, such as coke quenching, and >4 x 10 m /d (10 gal/d) are piped 13 km to Sparrows Point. This arrangement has proved economical to both parties for >40 yr. 

Counter-current rinsing and rinse-water reuse are useful tips for reducing usage. Counter-current contact systems are more efficient in promoting heat and mass exchanges, which are important to gas absorption, extraction, and many types of chemical reactions. 

Much lip service is paid to water re-use, which, on the whole, is more fashionable than practicable. Better opportunities arise from simple economy in water consumption at each point of use. Water reuse after effluent treatment is not often practicable. It appears, if at all, most favorable in the re-use of slightly contaminated water for some low-grade purpose such as washing down. 

Today, in an era of water reuse and higher costs for premium-quality water, condensate line corrosion may be an inevitable and serious drawback when using naturally high-alkalinity water as a MU supply source. Some form of dealkalization pretreatment process generally is provided to high MU demand boiler plants but unfortunately not so often to smaller facilities. 

Laronge, Thomas M. Water Reuse via Condensate Polishing. Industrial Water Treatment, Tall Oaks Publishing, Inc., USA, September/October 1996. 

Keywords Integrated water management, Public technology. Regulations, Water reuse applications... 

In many Mediterranean countries, water reuse regulations to be applied have long been uncertain. Several countries have not yet set up their own water reuse regulations. This raises doubts about the credibility of water reuse criteria and thus about the treatment technologies to be used and the reliability and appropriateness of those aheady implemented. The result is that in several countries, a number of planned water reuse projects are getting postponed. 

Therefore, sound pohcies should be reluctant to invest in agricultural water reuse schemes. Other options, such as urban or industrial uses as well as indirect potable reuse are much more likely to be economically justified. 

Fig. 1 Water reuse schemes identified within the Aquarec European programme [12]...

Fig. 2 Examples of treatment trains including disinfection through intensive or extensive processes for water reuse in agriculture and other applications implemented in different countries [16]...

Intensive methods are preferred for big size water reuse schemes, not only for their reduced footprint but also because high technology systems, when implemented by skilled staffs, are assumed to allow higher microbial performance predictability. Moreover, designers and engineers are confident in techniques that allow... 

Administrative representatives are often shy about developing water reuse projects. Evaluations of the risks related to water reuse have been twisted so as to be employed in political arguments during election campaigns, which may explain the reluctance of politicians. Examples of failure and success of indirect potable reuse projects in the United States are provided by [13]. Such experiences point out the importance of public education as regards the human interaction with the water cycle and the management of water resources. The population should be aware that... 

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