Economic wastewater treatment

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. 

Tighter control of water use can reduce the volume of wastewater requiring treatment, and result in cost savings - it can sometimes reduce volumes and increase concentrations to the point of providing economic material recovery in place of costly wastewater treatment. 

Hafez A, Khedr M, Gadallah H (2007) Wastewater treatment and water reuse of food processing industries. Part II Techno-economic study of a membrane separation technique. Desalination 214 261-272... 

Many of the waste streams from U.S. process industries are water containing small quantities of metal ions that the law requires be removed before the wastewater is disposed of There is an economic incentive to recoup at least some of the cost of wastewater treatment by recovering and selling the metal content instead of merely disposing of the metals as sludge. Because the waste streams are dilute in desired materials, research is needed to devise efficient extraction and separation processes. 

In developing countries, additional advantages of using CWs can be obtained. They may provide economic benefits and could encourage small communities to maintain natural wastewater treatment systems. The production of plant biomass can provide economic returns to communities through production of biogas, animal feed, compost, and fiber for paper according to the type of pollutant.46... 

Economic and Social Commission for Western Asia Wastewater Treatment Technologies A General Review, United Nations, New York, 2003. 

In Section 27.2, the principles of a DAF unit and the entire improved activated sludge wastewater treatment system are disclosed in detail. The economic use of secondary flotation in the improved system requires only a relatively inexpensive high-rate DAF cell that is commercially available. The consulting engineers should understand such principles for the selection of an appropriate DAF unit and for the optimization of the entire improved wastewater treatment system. 

For waste treatment rather than fermentation for product formation, again few examples of process economics exist in the literature. Those that do, favor fluidization. Badot et al. (1994) described an industrial prototype fluidized bed reactor that competed favorably on an economical basis with activated sludge processes for treating carbon pollution and was estimated to be economically comparable to fixed bed processes for denitrification. Schneeberg (1994) described the successful and economically-sound implementation of fluidization as an upgrade to an existing wastewater treatment plant. The restricted space available for extension of the wastewater plant made fluidization particularly advantageous in this case. 

Identification and selection of the complete wastewater treatment system that is optimal in economical, technical and environmental respects. 

In the aforementioned closed loop water system the polluted process water is purified completely in one wastewater treatment scenario. Only one type of process water is produced for reuse. In practise several types of process water are needed, and also several types of polluted wastewater streams are produced. This is schematically shown in Figure 2. In that case it can be advantageous in technical, economic and environmental respects to include several closed loop water systems within one production line. 

A further improvement in the sustainability of an industrial production process may be achieved by closing the water loops for a number of adjacent industrial production processes. This may be achieved in a so-called eco-industrial area where the primary aim is to arrange industrial production processes in such a way that water, wastes, materials, and energy can be exchanged between the various production processes in an environmentally sustainable and cost effective manner. A shared process water production plant and wastewater treatment plant is then a crucial step. It will, however, be clear that such an approach requires a thorough and detailed study which incorporates not only technical and economical aspects but also legal, organisational and infrastructural aspects as well. 

The successful design of an industrial wastewater treatment system is a complex decision and often integrated into site and process specific considerations. The quantity of wastewater can be established from an overall water balance. The quality is determined from the process design. The wastewater treatment unit operations will vary as a function of discharge requirements, reuse considerations, and economic reviews. 

The vendor claims that Mixflo is an economical option for capacity expansion and emission control at wastewater treatment plants. According to the vendor, upgrading air-based activated sludge treatment systems with Mixflo can reduce energy costs by greater than one third (D22912J,... 

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