January 2010, Vol. 22, No.1

How Much Capacity Does It Really Have?

Researchers determine which secondary clarifier model is more useful

Feature 1 - Kelly Richard Kelly, Jose Jimenez, Adam Klein, and Rion Merlo

Staff at activated sludge treatment plants with sedimentation need to know exactly how much capacity their secondary clarifiers have. Knowing the secondary clarifiers’ capacity can help staff avoid solids loss and associated permit violations during peak-flow events. It also helps utility managers plan better for improvements needed due to population growth, capacity shortfalls, or more-stringent regulations for peak wet weather treatment.

Researchers compared two models commonly used to evaluate secondary clarifier treatment capacity: state point analysis (SPA) and 2Dc. They modeled secondary clarifiers at five municipal wastewater treatment plants to determine the advantages and disadvantages of both models. Read full article (login required)


The Model Says What?!? 

As with most tools, a model’s usefulness depends on who wields it

Feature 2 - Arora Madan Arora, Ali R. Ahmadi Motlagh, Rishina Dobhal, Lew Nelson, and Richard Bono

The wastewater treatment field has become more complex in recent years. Primary and secondary treatment often is not enough anymore; now, regulations require comprehensive solids management and advanced treatment. Meanwhile, U.S. citizens have become environmentally conscious, demanding that treatment plants not degrade the air they breathe or the waters they use. And worldwide water shortages are making water recycling a universal requirement.

So, today’s treatment plant designers need sophisticated tools. Several static and dynamic models have been developed to help engineers optimize a design with multiple water quality objectives. Computer models, in particular, can help process engineers optimize existing operations and develop cost-effective, user-friendly designs.

Models alone, however, are not the answer. In the hands of inexperienced engineers, models can lead to a design that, at best, may not be cost-effective but, at worst, could produce effluent that does not meet water quality objectives. Read full article (login required) 


Possible Paradigm Shift Ahead

Proposed water reuse scheme could eliminate Southern California farmers’ needs for both potable water and commercial fertilizer

Feature 3 - juby Graham J.G. Juby, G. Adam Zacheis, and Perry R. Louck

The avocado orchards, citrus orchards, and vineyards east and west of Temecula, Calif., use about 101,000 m3/d (30,000 ac-ft/yr, or 26.8 mgd) of potable water, but this practice is unsustainable in water-short Southern California. Recent regulatory changes may make potable water too expensive for many farmers in a few years, and they need another option.

In a similar vein, farmers spend considerable sums to provide the types of nutrients for their crops that treatment facilities spend considerable sums to remove from wastewater. If wastewater utilities could provide their nutrient-rich water to farmers instead, it would benefit both sectors. Also, water containing soluble nutrients could improve the plants’ nutrient uptake, thereby reducing nutrient runoff. Read full article (login required)


Operations Forum Features

Striking Contrast

Flume-based screenings transport improves headworks operations

Feature 4 - Mihm Mark S. Mihm, H. Lee Cronister, Richard Wagner, Mark Evers, Ewa Gorgi, and Nosa Irenumaagho

After its initial screenings-handling system failed, the 110-mgd (416,000-m3/d) Dallas Water Utilities Southside Wastewater Treatment Plant installed stopgap measures to continue operation of its bar screens. However, those measures led to additional unsavory work for operators, extreme odor problems, insect infestations, and higher landfill costs.

Then, in 2007, the plant began a renovation that included a number of important updates, including installing a flume water-transport system to collect and convey the screenings, as well as a pair of new washer–compactors to clean the screenings of organic content, recover biochemical oxygen demand (BOD) for the treatment process, and dewater the screenings to reduce odors, screenings volume, and moisture content.

Comparing the system before and after the renovation shows a striking contrast. The project has resulted in significant improvements in operations efficiency, labor cost savings, and appearance, as well as improvements in operator morale, health, and safety. Read full article (login required)


From Rags to Reliable

New headworks improves performance throughout the treatment plant 

Feature 5 - Casey Brian Casey, Bob Eimstad, Scott Thompson, Jim Wodrich, Greg Mooney, Tracy Cork, and Mike Guthrie

The largest city in central Oregon, Bend, has a population of about 78,000 and a wastewater reclamation facility with an average design flow of 11.8 mgd (44,660 m3/d). The facility’s headworks had long since surpassed its intended design life, and system reliability was faltering. One of the two existing screens had failed completely, and the other’s capacity was overwhelmed regularly, sending solids and floatables downstream. Facility staff members were spending significant time each week removing rags from primary clarifiers, secondary clarifiers, and the digester’s heat exchanger. Furthermore, the captured screenings contained so much moisture and organics that they had to be taken to the landfill weekly.

In short, Bend needed a new screening system. So, a few years ago, the plant began a project that would reduce maintenance requirements and trips to the landfill, as well as be safer than the existing headworks — considered a somewhat hazardous environment — and use “green” energy. Read full article (login required)


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