April 2012, Vol. 24, No.4

A big leap toward energy self-sufficiency

A WWTP in Bakersfield, Calif., builds a solar power system using federal and state funding

Seeta art.jpg Vamsi Seeta, Surendra Thakral, Louis Sun, and Zac Meyer

In California, renewable energy generation at wastewater treatment plants (WWTPs) is gaining momentum, largely fueled by generous federal and state grants and incentives. However, one particular source of renewable energy — solar projects — is not commonplace in the wastewater industry. The reasons are many, including high initial costs, lack of understanding of current regulations, a relatively complex interconnection process with utility companies, and limited knowledge of incentives.

With meticulous planning and early coordination with all stakeholders, the City of Bakersfield, Calif., was able to implement a successful solar photovoltaic project at one of its wastewater treatment plants in 2011 using a design–build delivery approach. Through the execution of the project, the city has made a big leap toward energy self-sufficiency at its WWTP and has set an example for other utilities to follow. Read full article (login required) 


A natural solution for industry-heavy wastewater

A Virginia wastewater treatment plant tests an algae-based nitrogen removal system to help meet nutrient limits at a reasonable cost

Grandstaff art.jpg Jeanie Grandstaff, Christopher Limcaco, and Thomas Kochaba
In its search for cost-effective biological nutrient removal (BNR), the Hopewell (Va.) Regional Wastewater Treatment Facility is conducting a pilot study of a treatment system that mimics nature, using air, sunlight, bacteria, and algae. The project has been operating consistently since June 2010. Although the test has encountered some difficulties, the algae-based system featuring a wheel-shaped apparatus has shown some promise. Read full article (login required) 


Operations Forum Features

Bigger savings from biogas

By optimizing its biogas use, a Virginia utility saves energy and money while increasing the reliability of its nutrient removal proce

Rohrbacher art.jpg Joe Rohrbacher, Bryan Lisk, Christopher Szoch, C. Michael Bullard, Jennifer Whitaker, Robert Wichser, and Thomas Frederick

During the design of modifications to provide additional nutrient removal at its 57,000-m3/d (15-mgd) Moores Creek Wastewater Treatment Plant, the Rivanna Water and Sewer Authority (RWSA; Charlottesville, Va.) realized that it would need to make additional improvements to its aeration and digestion facilities.

Seeking to maintain its nutrient removal capability, as well as the practice of beneficially using biogas generated onsite, RWSA began evaluating options for optimizing its digester heating process. The results of this evaluation have enabled RWSA to achieve significant energy savings, reduce greenhouse gas emissions, and improve treatment performance. Read full article (login required) 


The oxidation index: a tool for controlling the activated sludge process

Three versions of a relatively simple process parameter can be used to determine the treatment power needed for particular wasteloads

Schuyler_Art.jpg Ronald G. Schuyler, Joseph R. Tamburini, and Steven J. Tamburini

A common approach to controlling the activated sludge process involves adjusting the amount of biomass in the system according to season. As temperatures decline from summer to winter, operators usually try to raise mean cell residence time (MCRT), increasing biomass concentration to compensate for reduced bioactivity. The opposite is true from winter to summer. However, determining how much to increase or decrease MCRT is difficult. In part, the decision must be based on the wastewater treatment plant (WWTP) capacity — that is, the treatment power — required to adequately treat the influent wasteload.

This article evaluates the oxidation index (OXI), a relatively simple process control parameter that can be used as a basis for making such decisions. Furthermore, the authors relate this process to activated sludge settleability and compare three approaches for calculating a control parameter based on OXI. Read full article (login required) 


Measuring the quality of screenings

A simplified leaching method helps operators at a German wastewater treatment plant determine the effectiveness of their influent wash presses

Roediger art.jpg Markus Roediger and Wolfgang Branner

Screenings are odorous, attract pathogen vectors, and contain fecal matter and large amounts of water. Influent screens remove solids and some biochemical oxygen demand (BOD) and chemical oxygen demand (COD) but little nitrogen. A lower BOD-to-nitrogen ratio in wastewater can impair denitrification during secondary treatment, but if the screenings are well washed, nearly the entire amount of removed BOD is returned to the wastewater, which maintains the denitrification process.

A study team recently compared the performance of launder-type and conventional wash presses at German wastewater treatment plants. The team also developed a leaching method that is less complicated than the current German standard method. Read full article (login required) 


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