July 2012, Vol. 24, No.7

Clarifying wet weather enhancements

Assessment of initial secondary clarifier modifications in Cincinnati provides valuable feedback to help maximize wet weather treatment capacity

feature 3 Lu art.jpg Ting Lu, Donald Linn, Andrew Shaw, Scott Reed, Julian Turnbull, and John Esler

The Mill Creek Wastewater Treatment Plant is the largest of seven major wastewater treatment plants owned and operated by the Metropolitan Sewer District of Greater Cincinnati (MSD) to collect and treat combined sewer flows. Mill Creek treats an annual average flow of 530,000 m3/d (140 mgd).

As part of a systemwide effort to reduce combined sewer overflows, MSD is upgrading Mill Creek’s secondary treatment processes to provide reliable treatment of up to 908,000 m3/d (240 mgd) of sustained wet weather flows. With the upgrades one-third complete, MSD and the upgrade’s designers paused to measure how well the new designs were operating. They used a combination of field testing and computational fluid dynamic (CFD) modeling to assess the new operation and find some additional measures to fine-tune the project. Read full article login required


Getting out the gas

Vacuum mixed liquor degassing system improves settling and process performance

feature 4 vacuum art.jpg Matthew Maciejewski, Andrzej Golcz, Grzegorz Budzisz, and Jan A. Oleszkiewicz

The City of Częstochowa Wastewater Treatment Plant in Poland could adequately manage biological nutrient removal during average flow conditions — about 44 ML/d (11.6 mgd) — and warm weather conditions. But, during cold weather, denitrification rates dropped and the plant experienced bulking and solids carry-over from its secondary clarifiers.

To reduce solids carry-over, the overflow launders in the secondary clarifiers were converted to submerged slotted pipes. This, however, did not prevent frozen foam from accumulating during winter and often required the use of heavy machinery to break the frozen scum on the surface.

While the addition of two large clarifiers helped to some extent, the plant continued to operate at relatively low mixed liquor suspended solids (MLSS) concentrations — 2200 to 3500 mg/L.

Operating the plant was difficult. The risk of discharging effluent that would not meet regulatory requirements was high. To reduce the bulking problems and increase treatment efficiency, the plant installed a patented mixed liquor vacuum degassing system (MLVDS). This process removes gas bubbles from the mixed liquor and reduces the concentration of dissolved gases. Read full article login required


Operations Forum Features

When green really isn’t the greenest

When implementing its odor control project, a WWTP weighs the pros and cons of using a ‘green’ bark medium

Feature 1 Collett art.jpg Aaron N. Collett, Timothy Mills, and Philip Wolstenholme

The Eugene–Springfield (Ore.) Regional Water Pollution Control Facility is a state-of-the-art facility that serves the greater Eugene–Springfield area. The wastewater treatment plant (WWTP) and associated collection system clean an average of 114,000 m3/d (30 mgd). The Metropolitan Wastewater Management Commission (MWMC), which operates, maintains, and administers the plant, has a good-neighbor policy that extends to strategic efforts that affect the WWTP’s direct neighbors, such as homes, schools, businesses, and parks, and the community as a whole. Controlling odors associated with wastewater treatment processes is acknowledged as an important component of that policy.

In 2004, MWMC developed a new facilities plan and began a capital improvement program that included an odorous-air treatment expansion project.  The initial challenges for the odor-control project included problems with the existing bark-media biofilters, which are commonly used to treat wastewater odors. These biofilters appear to be a “green” technology, as they are not only made of an organic medium, they also may be recycled for landscape use. Despite these apparent advantages and the media’s low initial cost, bark chips present challenges when designing an effective biofilter for long-term use. Read full article login required


Enhancing iron

To reduce odors in its collection system, a California utility tests an innovative approach that uses magnesium hydroxide to boost performance of ferrous chloride

feature 2 Reed art.jpg Brian K. Reed and Carla D. Dillon

Faced with significant cost increases and short-term supply limitations associated with the chemicals it uses to control odors in its extensive collection system, the Orange County (Calif.) Sanitation District (OCSD) has sought to diversify and optimize its approaches to odor control. In particular, OCSD routinely evaluates products and technologies to help it reduce costs, improve treatment, and work toward a more sustainable approach to odor control.

For example, OCSD is working to reduce its use of iron in odor control because of the material’s volatile price. To this end, OCSD conducted a field trial of a novel treatment approach that combined the use of ferrous chloride with magnesium hydroxide. By integrating the compounds synergistically, OCSD was able to use iron more efficiently and improve cost performance. Read full article login required


Performance under pressure

Practical perspectives on pumping and energy

Feature 5 Pascke art.jpg Ned W. Paschke

Almost all wastewater collection and treatment systems need pumps to some degree. Pumps require energy, sometimes a lot, to do their work. But by understanding pumps and pumping systems, these energy needs can be minimized. To find potential energy savings requires examining the key components, issues, and constraints faced within a wastewater pumping operation. Read full article login required

This article also includes an open-access Online Extra on total pumping head. Click here to download.


© 2012 Water Environment Federation. All rights reserved.