WASTE-TO-ENERGY: Water and Waste Meet in the Incinerator

Paul L. Hauck

How can the power from a waste-to-energy (WTE) plant help create drinking water for communities? Paul Hauck from Tampa, Fla.-based Kisinger Campo and Associates, and Dr. Joan Rose of the University of South Florida, St. Petersburg, Fla., recently proposed a plan to the city of Tampa, Fla., for harnessing the energy from the city's WTE plant to sterilize potable water.

The Tampa Bay area is similar to many of the world's urban areas that need additional water. Adding to this water crunch in the future will be the requirements of the Safe Drinking Water Act. This act will force costlier and more energy intensive treatments to provide alternative water resources, such as reverse osmosis, membrane polishing, and ozone and ultraviolet light disinfection.

Among the proposals currently being considered in coastal areas are desalination and wastewater reclamation.

Hauck and Rose's idea is to use steam from a WTE plant to boil reclaimed water to destroy problematic microorganisms. This distillation leaves behind undesirable suspended solids, reclaims the water and produces an ultra-pure water quality.

Several attributes make the distillation process a good candidate for reuse applications. High-quality water is produced, and the treatment is reliable and robust. Post-treatment activities, such as blending and disinfecting for distribution, are not likely to produce byproducts or other undesirable effects.

The presence of volatile organic compounds (VOCs) in drinking water-supply sources present a special problem for many municipalities. Many VOCs are mobile, persistent and toxic. Distillation can bleed off VOCs at different stages, depending on their boiling temperature.

At a pilot project in Lake Alfred, Fla., Rose studied the effects of evaporation technology contaminant removal for production of high-quality potable water. The plant was challenged with two microorganisms and latex particles in seeded trials.

During the experiments, no viruses, bacteria or fluorescent beads were detected in the condensate (product water). Temperature, as well as the evaporative process, does not allow the carryover of suspended solids and thus reduces bacteria and viruses.

However, the team's proposal also takes the idea one step further: The most efficient, cost effective way to develop sustainable, clean water may come from integrating utility treatment plants onto a single site - a municipal utility complex with the WTE plant as the anchor tenant.

A modern WTE plant capable of combusting 1,000 tons per day can produce 30 megawatts of electrical power. However, a considerable amount of waste heat is released into the environment through the chimney and cooling tower. WTE plants only use 15 percent of their electrical output to operate their own equipment, leaving 85 percent for municipal utility complex use.

In this scenario, low-pressure steam and waste heat can be used synergistically in other processes. The net effect will be improved thermal efficiency for the complex. The costs of treating solid waste, wastewater and potable water will be lower in the municipal utility complex than in separate plants with power purchased from the grid.

By using a WTE plant's energy within the municipal utility complex, municipalities can realize substantial cost savings.

For example, an integrated utility complex requires fewer resources - energy, tools, equipment, property, operation and maintenance staff - and optimizes the solid waste, wastewater and potable water treatment processes. In addition, a regional complex for treating urban and industrial waste streams can encourage recycling and manufacturing plants to use the locally recovered materials.

In the end, integration of such facilities may prove to be beneficial, cost-effective and environmentally friendly. For those communities with a WTE facility, the leap simply may be one small step.

And, with today's pressure to streamline government and reduce costs, governments may have no choice but to move beyond conventional practices to do more with less.