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Marlay-Taylor Water Reclamation Facility Sludge Handling
(Latest update: May 25, 2006)
April 22, 2006
Purpose
The Marlay-Taylor WRF recently completed an upgrade to the sludge processing portion of the facility. This upgrade included a new raw and activated sludge thickening system to accommodate facility flow increases to 6 million gallons per day, improvements to the mixing and methane gas systems of the sludge digesters, and improvements to the stabilized sludge dewatering operation. After the start-up of the sludge thickening system, odors of an unforeseen magnitude were realized from this process. Disruption of the normal sludge digestion system also caused odors, which became present and noticeable in the neighborhood adjacent to the facility. The following actions are steps that have been taken by this Commission to minimize and contain odors from the Marlay-Taylor facility.
Sludge Digesters
We are experiencing biological difficulties with the start-up of primary digester #1. Sludge feed to the digester is limited while staff re-circulates and heats the digester as much as possible. Staff is transferring stable sludge from primary digester #2 on a daily basis to speed the biological stability of primary digester #1. Caustic soda is being used to control the pH of the digester, and to minimize foaming. This digester was inspected by Mr. Mumford of Mumford, Bjorkman, and Associates, a reputable tank inspection firm. The report on the tank inspection is pending.
Primary digester #2 is operating well. Recent foaming issues have been attributed to turbulence in the suction piping of the new chopper recirculation pump. We are currently using the existing recirculation pump without any issues. Design engineers will be charged with resolving the turbulence issue.
The secondary digester is in service. All primary sludge is transferred to the secondary digester. The thicker sludge is withdrawn from the secondary digester and is processed by the sludge presses. This sludge is more stable than the sludge processed from the primary digesters.
Once the sludge digestion process is back in full operation, the raw sludge will be pumped directly to the digesters, thereby eliminating the indirect exposure of the odorous raw sludge to the atmosphere. The sludge digestion process will produce an odor-free, stabilized sludge that meets state and federal standards for land application, and methane gas in sufficient quantity to provide heat for the facility, and eventually, a source for electrical generation.
Sludge Thickening
The decreased ability to feed sludge to primary digester #1, as well as the seasonal need to reduce the sludge inventory in the activated sludge reactors, has forced staff to take action to prevent issues with effluent quality. Staff began processing all raw and waste sludge through the thickening system on Thursday, April 20, 2006. This was necessary as a temporary measure to reduce the sludge volume and prevent hydraulic overloading of primary digester #2. Once primary digester #1 is operating properly, the raw and if necessary, activated sludge can be once again pumped directly to the primary digesters. Staff has taken measures to minimize odors from this system, including ensuring the optimal performance of the soil odor box, keeping the sludge tanks at minimal levels, and cycling the sludge tank blowers.
Conclusion
St. Mary’s County Metropolitan Commission staff continues to work diligently to address and correct issues with the sludge digestion and thickening systems that contribute to the odors experienced due to the recent upgrade of the Marlay-Taylor Water Reclamation Facility. This Commission strives to continue to provide an excellent environmental service through this facility, as well as continue being a good neighbor to the surrounding community.
May 4, 2006 Update
Sludge Digesters
We are seeing some progress in the biological start-up of primary digester #1. Sludge feed to the digester is still limited while staff continues to recirculate and to heat the digester as much as possible. Staff continues to transfer stable sludge from primary digester #2 on a daily basis. We have begun using biological enzymes to speed the biological stability of this digester. Caustic soda is no longer being used, as the pH of the digester has stabilized. We are awaiting a report on the structural inspection of this digester.
Primary digester #2 is operating well. Sampling analyses confirms that this digester is biologically healthy. We have experienced some minor foaming of this digester, which is believed to be caused by turbulence, which is being addressed by design engineers.
The secondary digester continues to operate well. The stabilized sludge that is processed by the dewatering units is frequently removed and landfilled by contractors.
We are experiencing an issue with the methane gas accumulation line from the sludge digestion system. The accumulation line has one or more “low spots” that allow condensation to pond, thereby preventing the flow of methane gas. This results in the inability to use the methane in either the building boilers or the waste burner. During calm wind conditions, the vented methane may be a source of odors. This is an outstanding issue that the design engineer has been tasked with.
Sludge Thickening
Staff is continuing to process raw and stabilized sludge through the sludge thickening system. The soil odor box is being well maintained and the sludge tank blowers are being cycled to allow minimal mixing. Staff is monitoring and logging odors, weather, and wind conditions.
Odors
As a result of the April 22, 2006 mailing and website update, staff has received some feedback from the neighbors of the facility. While most of the feedback is positive, we received two responses that occasional odors have been experienced. These odors were reported to have occurred the weekend of April 29-30, 2006, and the morning of May 3, 2006, and have been described as “occasional whiffs” and “lingering”. As a result of these responses, staff has responded by changing blower cycles and altering the sludge thickening strategies. We ask our neighbors to contact us immediately if they experience odors from the facility, so that staff may respond to pinpoint and mitigate the odors.
May 12, 2006 Update
Sludge Digesters
The start-up of primary digester #1 is continuing to progress well. Daily sample analyses indicate that the measures taken are improving the biological stability of this digester. The temperature of the digester is continuing to slowly rise. Primary digester #2 is operating well. Staff recently installed a timer to control the recirculation pump for this digester. This measure has appeared to be effective in reducing the foam in the digester. As the biological health and stability of these digesters improve, staff is able to slowly and gradually increase the amount of thickened raw sludge to the primary digesters.
Sludge Thickening
Staff continues to process all raw and activated sludge through the sludge thickening system. The thickening system continues to operate well.
Odors
Staff continues to monitor odors in and around the facility. Biological improvement of the primary digesters, as well as operational changes at the facility such as blower timer settings and minor adjustments to the soil odor box have all contributed to the improvement of odors at the facility. Staff has received no odor calls in the past week from neighbors of the facility. Follow-up calls to previous callers revealed one noticeable odor on May 9, 2006 at approximately 2:00 pm. Investigation found this odor resulted during the unloading of a portable toilet truck at the facility’s septage receiving station.
May 25, 2006 Update
Sludge Digesters
Sludge Thickening
The sludge thickening system continues to operate well. Staff has been able to reduce the sludge inventory in the treatment units, resulting in a decreased amount of sludge to be thickened. Staff is slowly increasing the sludge feed to the digesters, which will decrease the sludge levels in the thickening tanks.
Odors
One call was received from a neighboring business on May 22, 2006
to advise that an odor was noticeable adjacent to the facility. Staff responded
immediately and was unable to detect an odor. Staff noted that the sludge
processing system was not in use at the time of the odor call. Further
investigation revealed a leaking air seal on one of the thickening tank lids,
which was repaired. |