USE OF TREATED MUNICIPAL WASTEWATER AT POWER GENERATION FACILITIES

 

Reclaim water (treated municipal wastewater) is being used more frequently as a source of cooling system makeup at electric generating facilities. Early examples of plants utilizing reclaim water typically occurred in water-short areas. Lately however, even proposed power facilities in locations where freshwater supplies are plentiful are considering the use of reclaim water due to state and/or municipal reluctance to use such a valuable resource for evaporative cooling systems.

Although the safe use of reclaim water as cooling tower makeup has been demonstrated for the last forty years, some states are imposing stringent standards on the use of reclaim water for this and other purposes. Very often, these standards provide for strict limits on turbidity and microorganism counts and require additional treatment of secondary municipal effluent prior to its delivery to users. Additional treatment equipment can be added at the municipal, publically-owned treatment works (POTW) or at the power facility. AQUAGENICS assists clients in negotiating with municipalities in determining what additional treatment equipment is required, the capital and operating costs of the equipment and its optimum location.

One of the most significant issues confronting a potential user of reclaim water for cooling tower makeup is whether to discharge the plant wastewater to a receiving stream or back to the headworks of the POTW. Discharging to a receiving stream requires an NPDES (or SPDES) permit; discharging to a POTW requires an industrial user discharge permit from the municipality (or county) that owns the POTW. Generally, it is easier and more expeditious to obtain the local permit. However, other factors must be considered. Recycling back to the headworks establishes a condition whereby the combined flow entering and exiting the POTW will have higher concentrations of dissolved solids. The power plant owner and the municipality must consider how water quality is affected in this respect, its effects on power plant operations, the potential interferences within the POTW and the impacts on the receiving stream. As the ratio of water evaporated in the cooling towers to the total wastewater flow through the POTW increases, this concentration effect becomes more pronounced. In addition, sewer connection fees can be quite substantial when discharging back to local sewer systems. AQUAGENICS assists clients in determining the ultimate quality of reclaim water as well as the optimum point of discharge and in obtaining the necessary discharge permits.

Very often, we are asked to assist our clients in negotiating water supply agreements with the reclaim water providers. Our experience has been beneficial in helping them obtain favorable terms.

Local circumstances sometimes dictate that the power facility utilize reclaim water as the influent to their makeup demineralizer system that produces high purity water for steam cycle makeup. AQUAGENICS has worked on several of these types of plants and knows which treatment processes work and which don't.

In water-short areas, power plant water management programs are developed to minimize the use of water, potentially resulting in a zero liquid discharge (ZLD) design. When power plants designed as ZLD (or plants where cooling systems employ sidestream softening to achieve high cycles of concentration) use reclaim water as their source of makeup, unique issues must be considered in the design of the treatment equipment.

AQUAGENICS has provided extensive services on a dozen power facilities that use reclaim water as plant makeup. In addition, we have provided consulting services on over a dozen more of such facilities. Acting as Owner's Engineers we have provided the following types of services:

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