Features

November 2013, Vol. 25, No.11

Spreading the wealth  

California utility sells surplus renewable energy generated at its water resource recovery facility 

Feature 3 Hake art John M. Hake

Resource recovery programs at water resource recovery facilities (WRRFs) are greatly increasing biogas production and electricity generation for those facilities accepting high-strength organic wastes — such as fats, oils, grease, or food waste — in their digesters. In some cases, the increased generation may exceed the demand required to serve onsite load, resulting in surplus power that may be sold to buyers for a “green premium.” The East Bay Municipal Utility District (EBMUD) in Oakland, Calif., has a WRRF that is a net renewable energy generator with surplus power that is available for sale. In 2012, it negotiated a power purchase agreement with a publicly owned utility. The sale of this green power includes renewable-energy certificates (RECs) that are bundled with the underlying energy, significantly increasing the revenue received by an agency for surplus-energy sales.   

Understanding institutional and contractual arrangements for the sale of surplus renewable energy from EBMUD’s WRRF and how this sale comports with current state regulations and markets is essential. Other options also are available to WRRFs for sale of surplus green power. EBMUD’s power sale serves as a case study of all these options, including renewable-generator certifications, registrations, agreements, and coordination with various regulatory authorities in California. Read full article (login required) 

 

Membrane bioreactors are not energy hogs    

 

Comparing energy consumption between membrane bioreactors and conventional activated sludge for municipal wastewater treatment 

Feature 4 Cote art P. Côté, T. Young, S. Smoot, and J. Peeters

Membrane bioreactor (MBR) technology has developed rapidly in the past decade for such applications as water reuse and discharge to sensitive surface waters. However, questions and misconceptions remain about the true cost of operating an MBR plant. Read full article (login required)  

 

 

Operations Forum Features

 During the deluge  

Understanding data from ultrasonic level meters 

Feature 1 guis art William B. Guis and John H. Grace

When it rains, it pours into many places, including wastewater systems. Older systems in the East and Midwest may include combined sewer areas where stormwater runoff is captured intentionally. However, areas with separate sanitary sewers also feel the effects of heavy rain. 

One of the most important types of information for operators is the level of wastewater at various points in the collection and conveyance piping and structures. Several types of devices provide real-time level measurements in collection and conveyance systems, but the pulsed ultrasonic level meter probably is the most common. These are time-tested and reliable devices, but their behavior when the system is stressed heavily and the meters are underwater should be understood. Read full article (login required) 

 

Creative innovations in sewer flow monitoring 

 The Department of Watershed Management division in Atlanta invents a ‘sewer boat’ to monitor flows and bypass obstacles 

 

Feature 2 Woodall art Patrick L. Woodall and Christopher J. Parrish
The City of Atlanta’s Department of Watershed Management (DWM) Flow Monitoring Division’s mission statement is to collect the best possible data, save ratepayers money, and promote workplace safety. To help do so, DWM maintains more than 250 monitoring stations that include sewer flow-monitoring sites. Obtaining accurate and consistent data directly from these meters with minimal editing gives the overall best results. 
To help alleviate the inherent hazards of these working conditions and to improve the quality of data, a simpler, safer solution was needed. The DWM flow-monitoring team devised an idea of inverting and floating a sensor on top of the water. Read full article (login required)  

 

A smooth blend 

A FOG–solids mix boosts digester gas production with operational benefits at a regional facility 

Feature 5 Norgaard art Kevin Norgaard, Steve Swanback, and Dan Frost

 The Fresno/Clovis Regional Wastewater Reclamation Facility (RWRF) serves the City of Fresno, Calif., and the surrounding metropolitan area in the agriculturally rich Central Valley. It is the fourth largest municipal water resource recovery facility in Northern California, with a treatment capacity of 330,000 m3/d (88 mgd), and sits in a prime location to receive and treat a variety of agricultural waste streams. The RWRF is a conventional activated sludge treatment facility with 13 mesophilic digesters of various sizes spread over a 68.0-ha (168-ac) site. 

In 2009, the City of Fresno recognized the need for large-scale fats, oils, and grease (FOG) receiving stations in the region. The RWRF FOG receiving station has been fully operational since June 2011 receiving up to 57,000 L/d (15,000 gal/d) of FOG. 

After 2 years of operation, the city vetted the design, made minor improvements as necessary, created simple standard operating procedures (SOPs), and gathered meaningful operational data for gas generation and energy production. This has been accomplished without an increase in operations and maintenance staff. Read full article (login required)