Thursday, May 31, 2018

WSSC to Eliminate Class B Biosolids

WSSC announced this month that their Commissioners have approved the first phase of a $250 million project that will transformation of WSSC current Class B Biosolids into Class A (pathogen-free) Biosolids material, recovering energy and reducing disposal costs along the way. The first phase is a $44 million contract that will allow WSSC to begin design and site preparation of the Piscataway Bio-Energy Project which will be located at the Piscataway Water Resource Recovery Facility (formerly the Piscataway waste water treatment plant) in Prince George’s County.

The Water Resource Recovery treatment process uses screens to remove large solids from wastewater, and performs some rudimentary treatment to remove crude solids of human waste and skim off grease, oil and fat. Wastewater sits in settling tanks where most of the heavy solids fall to the bottom of the tank, where they become thick slurry known as primary sludge.

The sludge is separated from the wastewater during the primary treatment is further screened and allowed to gravity thicken in a tank. Then the sludge is mixed with the solids collected from the secondary and denitrification units. The combined solids are pumped to tanks where they are heated to destroy pathogens and further reduce the volume of solids. With treatment sludge is transformed (at least in name) to Biosolids. Currently, WSSC treats their sewage Biosolids to only Class B at their 5 Water Resource Recovery Facilities (formerly waste water treatment plants). The problem, however, is how to dispose of the never ending supply of Biosolids.

To ensure that Biosolids applied to the land as fertilizer do not threaten public health, the EPA created the 40 CFR Part 503 Rule in 1989 that is still in effect today. It categorizes Biosolids as Class A or B, depending on the level of fecal coliform and salmonella bacteria in the material and restricts the use based on classification. The presence of other emerging contaminants in the Biosolids is not tracked. The land application of Class B Biosolids has been a growing area of concern. Research at the University of Virginia found that organic chemicals persist in the Class B Biosolids and can be introduced into the food chain. The new Biosolids treatment system will reduce the overall amount of Biosolids and improve their safety by producing only Class A Biosolids-free of pathogens.

WSSC says that this facility is the largest and most technically advanced project ever constructed by WSSC in its 100-year history.

“The Piscataway Bio-Energy Project will save our customers more than $3 million per year and underscores our commitment to green energy,” said WSSC General Manager and CEO Carla A. Reid. “Through cutting-edge technology, we will be able to recover vital resources from the wastewater treatment process and reduce our greenhouse gas emissions.”

In the future, the Biosolids (sludge) will be screened and dewatered at each plant then hauled from the four treatment plants to the Piscataway plant. The new plant will have thermal hydrolysis trains, digesters, dewatering equipment and a combined heat and power plant at a cost now estimated to be $250 million. The new digester system will use thermal hydrolysis (heating to over 160 degrees under high pressure) followed by anaerobic digesters. The system will produce methane gas which will be captured and used to run turbines to produce power that will meet Piscataway’s electric demand and the digestion process is projected to destroy nearly one half of the total Biosolids and produce Class A Biosolids reducing the chemical treatment costs and the transportation costs to get rid of the Biosolids. This is projected to save WSSC $3 million a year. Even with all these savings the project has a payback of over 83 years, so this was not about savings, but rather better sewage treatment, tighter EPA regulation for disposal of Class B Biosolids and meeting the Chesapeake Bay TMDL. Class A Biosolids are safer and easier to use in agriculture.

As an added benefit, the process to create the Class A Biosolids will generate renewable fuel to help run the plant. This new process produces methane gas, which will be captured to provide the Piscataway facility with a reliable power source that is completely off the grid. The new process will reduce WSSC’s greenhouse gas emissions by 15%.

The $44 million contract for the first phase of the project was awarded to PC Construction Company. The first Phase of work includes design and demolition of existing on-site facilities and relocation of existing utilities. Phase Two is expected to be awarded fall 2019. The entire project should be complete and operational in spring 2024.

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