Specifications include, but are not limited to: The City of Meridian is requesting bids for the cleaning of Digester 5 at the City's Water Resource Recovery Facility (WRRF) located at 3401 N Ten Mile Rd. 1. The City of Meridian intends to have a contractor drain, clean, and dewater solids from an existing anaerobic digester at the municipal WRRF. Digester criteria include: 1) Diameter – 70 feet 2) Side Water Depth – 26 feet 3) Volume – approximately 800,000 gallons 4) Estimated Solids Concentration – 3% 5) Estimated Solids Content – 200,150 pounds 6) Fixed Cover Digester 2. There are two available drain connections on the digester. One drain is located on the rectangular access hatch approximately 12 feet above the bottom of the digester cone floor. The access hatch connection consists of a 6-inch flanged isolation valve. The 6-inch drain connection could be used to drain the liquid level down to the access hatch so that the hatch could be removed and the remainder of the digester could be drained through an existing 6-inch line constructed within the digester, by a suction pump, vactor truck, or other appropriate means. 3. The second potential drain connection is located on the 8-inch digester discharge piping which runs from the bottom of each digester cone into the digester building. A portion of the piping would need to be removed inside the building by the contractor and a new connection made to allow draining of the digester contents. The 8-inch drain connection could potentially be used to drain the majority of the liquid contained within the digester. 4. The two drain locations are included within the attached Figures. 5. The goal is to drain as much liquid sludge out of the digester as possible using one or both of the drain connections. The major concern is the potential for grit, rags, hair and other solid waste plugging these lines during digester dewatering efforts. There is a crust approximately 2-3 feet thick located towards the top of the digester that may be difficult to break up and remove. Additionally, there is a substantial amount of sand, grit, rags and other solid waste accumulated along the bottom of the digester that could impact the ability to pump liquid solids out of the digester. If the liquid level can be drawn down far enough to remove the access hatch, at that point mechanical or manual methods can be used to remove the remaining material. Manual removal of hair, rags, grit and other solid waste accumulated within the digester is likely. Non-potable water is available for use by the contractor to assist with fluidizing material within the digester for removal. 6. As the digester is being drained, the digester contents will be pumped to a dewatering system. The contractor will be responsible for furnishing and operating the pumping system, including electrical power if necessary. The City may supply welded 6-inch HDPE pipe which can be used by the contractor for conveying contents from the digester to the dewatering system. The contractor will furnish and operate the polymer system necessary for dewatering and supplying the polymer chemical. The contractor is responsible for furnishing and operating the dewatering equipment, including electrical power if necessary. 7. Liquid resulting from the contractor’s dewatering process must be diverted back into the treatment facility drain system or into a storage tank. The contractor is responsible for diverting the liquid into the drain or storage tank. The location of discharge must be approved by City staff. Performance Requirements: 1. To allow disposal at the landfill, liquid and all materials pumped or removed from the digester must be dewatered to pass a paint filter test. The dewatering method will be up to the contractor. It is the contractor’s responsibility to dewater the digester contents without aid of other bulky materials so they are suitable for landfill disposal and capture solids to not cause operational issues at the WRRF. 2. The contractor will be responsible for conducting polymer jar testing prior to dewatering activities to determine the type and amount of polymer necessary to adequately dewater the solids using their proposed dewatering method. 3. The dewatering approach involves setting up dewatering equipment within or around the northeast sludge drying bed. This is the only drying bed available. As the solids are being dewatered, liquid resulting from dewatering will be sent into the plant drain or into one of the centrate holding tanks. 4. The contractor will be responsible for operating the dewatering equipment and adhering to the performance criteria (i.e. maximum allowable centrate TSS). 5. Dewatered solids produced by the contractor will be transported by the contractor to a designated pile, separate from the standard plant operations pile, for paint filter testing. Upon passing the required test, the City will combine the separated pile with the existing biosolids storage pad. The City will be responsible for loading the dewatered solids from the storage pad into transport trucks for removal and disposal. 6. The maximum allowable total suspended solids (TSS) in the liquid return is 500 mg/L. The City will conduct random sampling and laboratory testing to ensure the TSS limit is met. If the TSS limit is exceeded, the contractor must shut down and make the necessary adjustments to adhere to the TSS limit. 7. The dewatered solids must pass a paint filter test. The City will conduct random sampling and laboratory testing to ensure the dewatered solids pass the paint filter test. If the solids do not pass the paint filter test, the contractor must shut down and make the necessary adjustments to adhere to the dewatering requirements. 8. The contractor will clean and remove the struvite from the interior of the digester by means of power tools and hand scraping. Both methods must meet the workmanship finish product standards of SSPC – SP No. 11. Any other methods of removal must be approved by the City. 9. Removed solids produced by the contractor will be transported by the contractor to a designated pile, separate from the standard plant operations pile. The City will be responsible for loading the solids from the storage pad into transport trucks for disposal. 10. The contractor will maintain a clean working environment. Any sludge, biosolids, polymer, dewatering liquid or other material that is spilled during the contractor’s maintenance activities will be promptly cleaned. In the case of a larger spill of sewer sludge or dewatering liquid caused by contractor negligence, the contractor may be held liable for all costs associated with the cleanup, regulatory reporting, and fines imposed by any regulatory agency. The contractor must immediately notify proper City staff if a spill or overflow (SSO) occurs.
