April 2007, Vol. 19, No.4

A Model Decision

An understanding of fluid dynamics combined with innovative modeling helped a utility determine how best to expand digester capacity

amodeldecision.jpg James J. Marx, Shahriar Eftekharzadeh, Robert B. Stallings, Dorian Harrison, and James L. Burror Jr.
When Isaac Newton first developed his ideas regarding fluid dynamics, he likely did not have wastewater solids in mind. Nonetheless, Newton’s findings in this area greatly affected subsequent rheological studies, and his concepts continue to have implications for modern wastewater treatment

practices. For example, a major wastewater utility that serves a population of 3 million people recently had to consider Newton’s findings as it evaluated options for enhancing the digesters at one of its treatment facilities.

The Orange County Sanitation District (Fountain Valley, Calif.) recently embarked on a capital improvement project designed to meet the dual demands of expected future population growth and increased environmental pressures on its wastewater treatment infrastructure. A key facet of the project was the development of a long-range biosolids management plan, which proposed to expand the anaerobic digestion capabilties at the district’s Wastewater Treatment Plant No. 1. Read full article (login required) 


Clarifying CFD Modeling’s Benefits 

Using computational fluid dynamic modeling, engineers can improve clarifier capacity greatly to accommodate peak wet weather flows

Clarifying CFD.jpg Rion Merlo, Denny Parker, and Eric Wahlberg
Peak wet weather flow (PWWF) can present a substantial challenge for wastewater treatment plants, potentially causing such problems as collection system overflows, hydraulic failures within a plant, process failures in any number of process units, or a combination of these events.

A municipal wastewater treatment plant’s critical design condition usually is met under PWWF conditions.

The capacity of an activated sludge process often depends on the performance of a secondary clarifier. Failure of a secondary clarifier can cause elevated effluent suspended solids (ESS) concentrations that may lead to permit violations. For plants required to perform nutrient removal, elevated ESS levels may result in violation regardless of how other aspects of the biological process perform. However, if an activated sludge process can be optimized to handle PWWFs, the expense associated with constructing additional secondary clarifiers can be avoided. Read full article (login required) 


Succeeding at Simulation

As wastewater process simulators become increasingly powerful, users of these tools must understand their potential as well as their pitfalls

succeedingatsimulation.jpg Andrew Shaw, Heather M. Phillips, Baneeta Sabherwal, and Christine deBarbadillo
The use of mathematical models to design and optimize wastewater treatment processes has advanced greatly during the last 15 years. The increased power of PCs and development of more user-friendly software have resulted in widespread use of process models by professionals

throughout the industry. Simulation software that was developed originally and used predominantly by researchers on mainframe computers until the early 1990s is now available for consultants and operators to use on their own PCs.

With increased ease of use and widespread application of modeling software comes the recognition that expert guidance is needed to ensure that these models are constructed and used correctly. Although it is a simple matter to construct and run a model with modern software, knowing which parameters should be adjusted in the model and how the model’s results should be interpreted and applied requires experience and know-how that all budding process-modelers must learn. Read full article (login required) 


Operations Forum Features

Mountain Fresh

Air-ionization technology shows promise in reducing odors at U.S. treatment facilities

mountainfresh.jpg Dennis Tulenko and William Black
Polarized air-ionization technology produces positively and negatively charged oxygen molecules, or ions, without creating ozone. Developed in Switzerland, the technology has been used successfully at commercial manufacturing buildings, wastewater treatment facilities, and “sick buildings” in Europe
for more than 20 years. Ionized air oxidizes most air contaminants, including hydrogen sulfide, ammonia, volatile organic compounds, and other toxic gases. Besides controlling odors and providing a safe work environment, air ionization has been shown to prevent the corrosion of electronics and equipment. Read full article (login required) 


The Scale of Smell

Making sense of hydrogen sulfide limits

thescaleofsmell.jpg Dana C. Buske, Matthew L. Riegert, and Michael T. Lannan
Hydrogen sulfide is a hard odor to miss. Noticeable at small concentrations (1 to 10 ppbv), it smells putrid (like rotten eggs or a swamp) and is commonly emitted from manufacturing and waste management facilities. That’s why it’s often used as a surrogate in odor regulations.

Many people believe that odors — especially from a wastewater treatment plant, landfill, or industrial facility — signal a health concern. This misperception can become problematic for an odorous site and its neighbors, because the odor-detection limits for sulfur compounds typically are much lower than their health-related limits. Read full article (login required) 


Done in One

Conversion to a single-stage activated sludge process reduces wet weather overflows

doneinone.jpg David Nailor, Paul Pitt, and Andre van Niekerk
The Western Virginia Water Authority (Roanoke, Va.) operates a 42-mgd (159,000-m3/d) activated sludge plant that treats wastewater from Roanoke and adjoining municipalities. The plant has consistently met relatively stringent permit limits under normal, but in the past few years, peak wet weather

flows have exceeded 140 mgd (529,900 m3/d), forcing the plant to depend on flow equalization. But bven with equalization sometimes the plant would experience overflows.

The plant looked to a single-stage stage activated sludge process to improve treatment plant reliability and peak flow capacity, while reducing reliance on flow equalization during wet weather events and minimizing equalization basin overflows. Read full article (login required)