Features

September 2013, Vol. 25, No.9

Greensboro experience  

Addition of a second fluid-bed sewage sludge incinerator at T.Z. Osborne Water Reclamation Facility and its compliance with the new MACT emission requirements 

Feature 1 art Don Howard, Ky Dangtran, and Levent Takmaz

In 2007, the City of Greensboro, N.C., began a project to add a second fluid-bed wastewater residual incinerator at its T.Z. Osborne Water Reclamation Facility. The project would provide the capacity to handle an additional 59 dry Mg/d (65 dry ton/d) of primary solids — the existing fluid-bed incinerator can handle 54 dry Mg/d (60 dry ton/d) — and to replace the existing fluid bed during scheduled maintenance. 

Upon initial startup and performance testing in September 2011, the new unit satisfied the existing air quality emission requirements. However, the U.S. Environmental Protection Agency (EPA) finalized its new maximum available control technology (MACT) emission requirements for sewage sludge fluid-bed incinerators in March 2011. EPA’s new emission limits were very strict, compared to previous emission limits. 

These new limits required retesting the emissions from the incinerator to ensure that they were in compliance and making process changes — both within the incinerator and downstream — to meet the new limits. Read full article (login required)    

 

Offsetting an environmental burden  

Partners pursue the first certified methodology for carbon credits given to a wetland municipal effluent assimilation system in Louisiana 

Feature 2 art Sarah K. Mack, Robert R. Lane, and John W. Day

Wetland restoration is critical to combating wetland loss. It also is an effective climate change mitigation strategy, because it enhances carbon sequestration and avoids carbon releases that would occur in the absence of restoration activities. 

“Restoration of Degraded Deltaic Wetlands of the Mississippi Delta,” certified by the American Carbon Registry (ACR; Arlington, Va.), is the name of the first carbon-offset methodology that is specifically focused on U.S. wetlands. It also is the first wetlandoffset methodology in the world that is applicable on a large scale to broadly address wetland restoration through numerous eligible techniques, including hydrological management, reforestation, and afforestation. 

An environmental consulting firm applied the wetland methodology to the Luling Oxidation Pond Wetland Assimilation System — wetlands near Luling, La. — to conduct the first pilot project in the U.S. to determine the true costs, benefits, and barriers to implementation. It is also the first offset project in the U.S. that demonstrates the ability to create public–private partnerships that leverage carbon finance. Read full article (login required) 

 

Sonic boost  

High-strength organic wastes yield greater hydrogen and methanewith ultrasonication 

feature 4 art Elsayed Elbeshbishy, Hisham Hafez, Ahmed Eldyasti, and George Nakhla

Anaerobic digestion (AD) is a proven technology for the treatment of various organic wastes and production of methane. However, the rate-limiting step in AD is hydrolysis, or solubilization, where the cell wall is broken down, allowing organic matter inside the cell to be available for biological degradation. The AD process may therefore be improved if hydrolysis can be enhanced. Pretreatment often is required to release lignocellulosic material and thus accelerate the degradation process via waste solubilization.   

Ultrasonication increasingly is used as a pretreatment method for AD due to its ability to enhance solubilization. The use of ultrasonication in solids pretreatment not only enhances hydrolysis but also improves the operational reliability of anaerobic digesters, decreases odor generation, and enhances solids dewatering. Read full article (login required) 

 

Operations Forum Features

You’ve got grit-slurry problems. Now what? 

Design strategies for successful grit-slurry pumping systems serving large combined sewer systems 

feature 3 art Mike Gerbitz

The purpose of preliminary treatment systems is to remove debris and grit from influent and protect downstream processes from these damaging materials. While screening devices remove debris, grit-removal processes remove smaller grit particles. Grit particles that accumulate and concentrate at the bottom of a grit-removal system are commonly referred to as “grit slurry.” 

Ironically, a process that is intended to prevent or reduce downstream maintenance often is plagued with maintenance issues. Frequent problems include plugged grit-slurry collection sumps, plugged grit-slurry piping, failed grit-slurry pumps, and plugged grit-slurry concentrators. 

Adherence to sound design and operating strategies can avoid or minimize the occurrence and severity of problems frequently encountered by grit-slurry extraction, pumping, and processing systems. Read full article (login required)