June 2007, Vol. 19, No.6

Sizing Denitrification Filters

Extensive modeling enabled designers to develop cost-effective denitrification processes for two very different treatment plants

Sizing Denitrification Filters.jpg John Bratby, Peter Schuler, Mark Richards, Jose Jimenez, and Kirk Petrik

Although different in many respects, the Littleton–Englewood (Colo.) Wastewater Treatment Plant (WWTP) and the Orange Water and Sewer Authority (OWASA) Mason Farm WWTP (Chapel Hill, N.C.) both must adopt denitrification filters to meet increasingly stringent limits on nutrients in

their effluent. For each facility, Brown and Caldwell (Walnut Creek, Calif.) conducted extensive analyses to size the denitrification facilities, requiring the development of kinetic denitrification equations that then were incorporated into process models developed for the two plants.

The denitrification facilities for both WWTPs were sized based on accurate predictions of secondary effluent nutrient loads. This approach enables the correct total number of filters to be used to treat partial or full flows and to accommodate blending. The approach also predicts a plant’s effluent quality after blending under all flow conditions, including peak flows. This approach is particularly important when effluent must comply with daily maximum limits.  Read full article (login required)   


Testing the Watershed

North Carolina’s NPDES Discharge Coalition Program enables basinwide monitoring and analysis

Testing the Watershed.jpg Jennie R. Atkins, Carol Hollenkamp, and Jay Sauber

In North Carolina, coalitions of wastewater dischargers are working with the state Division of Water Quality (DWQ) to create and manage coalition-led watershed monitoring programs that operate in conjunction with DWQ’s ambient chemistry and biological programs.

Why join a monitoring coalition instead of going it alone? Through the North Carolina program, permit holders benefit from easy access to more comprehensive data, greater involvement in watershed management, and exemption from instream monitoring requirements.  Read full article (login required)  


Hard Lessons, Simple Truths 

Restoring large water systems requires the willingness to learn from experience — and time

hardlessons.jpg Paul L. Freedman, Victor J. Bierman Jr., and Joseph V. DePinto

In the second half of the 20th century, water pollution grew from a local issue limited to heavily used areas of streams and rivers to a wider-ranging issue affecting large rivers, lakes, and estuaries. Since the 1970s, the United States has made outstanding advancements in restoring water quality in localized areas. However, progress with large systems has been mixed — despite the millions of dollars spent studying these systems and the hundreds of millions of dollars spent trying to restore them. We have made considerable improvements, but with each gain, old problems persist and new ones arise.

This article explores some simple truths learned from this long and difficult history. Hopefully, these lessons will help us make better decisions in the future as we work to protect and restore large water systems.  Read full article (login required)  


Taking the Long View

The journey toward sustainable water resources management begins by determining the most important water issues and indicators

Taking the Long View.jpg Ethan T. Smith and Harry X. Zhang

As water quality professionals work toward sustainable management of water resources, we are constrained by institutional arrangements designed for past conditions. While our institutions have served us well, they are limited to physical, chemical, engineering, and other traditional water concerns. For the future, we must take a holistic view of wetlands, watersheds, and habitats — simultaneously considering water quality and availability; freshwater and

coastal waters; surface water and groundwater; water and land use; and physical, chemical, and ecological characteristics. Furthermore, we must consider this great variety of water resources in relation to other environmental and natural resources, as well as our national economy and culture.

In an effort to address these issues, the Sustainable Water Resources Roundtable (SWRR) was created in 2001. This subgroup of the U.S. Advisory Committee on Water Information was formed to promote information exchange among representatives of government, industry, and environmental, professional, public interest, and academic groups. The roundtable is intended to provide an open venue for examining water resource interrelationships and their future implications.

To date, SWRR has focused on defining the most important water issues and determining indicators for tracking these issues over time.  Read full article (login required)  


Operations Forum Features

Biological Limitations

Chemical processes may be better at achieving strict effluent phosphorus limits

biologicallimitaions.jpg Thomas E. Wilson and John McGettigan

biological is better when it comes to nutrient removal. Biological nutrient removal processes are proven to meet moderately low total nitrogen and total phosphorus standards without chemicals or excessive sludge. But rising energy costs and stricter nutrient limits on the U.S. East Coast have prompted treatment professionals to re-evaluate biological nutrient removal and ask themselves some tough questions.

Why choose energy-intensive biological processes?
How valid is the “extra sludge” argument?
Is all that reactor tankage really necessary?
Is chemical nutrient removal really more expensive than BNR? 
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Let It Snow 

A membrane bioreactor helps keep the slopes skier-friendly

letitsnow.jpg Marie-Laure Pellegrin, Lawrence Riegert, and Steve Brewer

Designing an effective wastewater treatment plant for the day-use Stevens Pass Ski Area was challenging. Influent flows and loading potentially increase eight-hundredfold on the day skiing season begins. The plant also has to operate at low water temperatures, as well as meet strict discharge limits associated with a pristine mountain environment. Add to those conditions, a small indoor footprint and extreme winter
weather that prevents supplied deliveries once the snow is falling.

To meet these requirements, the Stevens Pass (Wa.) Sewer District project team decided to convert the existing plant into a membrane bioreactor. Read full article (login required)   


Water Tables Turn 

U.S. Follows Europe’s Lead in Nutrient Removal

Water Tables Turn.jpg Miguel Gutierrez

Today’s conventional wastewater treatment works have evolved into complex systems that require a high level of operating and maintenance skill to sustain increasingly tighter nutrient limits. The Chesapeake Bay Watershed initiative, for example, will require wastewater treatment plants (WWTPs) to limit total nitrogen to 3 mg/L and total phosphorus to 0.3 mg/L
by 2010. By comparison, in Europe, several consent decrees limit effluent to 2 mg/L total nitrogen and 0.15 mg/L total phosphorus levels. Regardless of location, publicly owned and private operating companies are constantly challenged to reduce capital and operating costs.

To help overcome some of these issues, several U.S. and European plants are using continuous backwash filtration (CBF) techniques as attached growth processes for the biological conversion of nitrogen and polishing units for phosphorus removal.  Read full article (login required)