The contractor shall remove material from the digester, screen, macerate, and then dewater it using a centrifuge and polymer to a continuous minimum of 24 percent solids. Polymer is to be supplied by the contractor. Digester material shall be screened (mesh on the screen shall be no larger than ½ inch) and then macerated to shred any material that passes through the screen. The contractor shall dewater the digester contents into a watertight container or dump truck supplied by the contractor. The Contractor is also responsible for selection of, and approvals into, appropriate disposal site(s), transport and disposal of the dewatered material and debris. After the disposal of the material the contractor will provide the WRBP a copy of the weight slips for each load and/or manifests to confirm compliant disposal. Dewatering of anaerobically digested sludge may result in high recycle loads to the headworks of the treatment plant which can rapidly impact the treatment process, severely degrade effluent quality, and cause the WRBP to violate its NPDES permit. The recycle is high in ammonia and BOD and, depending upon the capture rate of the dewatering equipment, recycle may also be high in suspended solids. The WRBP has experienced these problems in past contract dewatering projects or when large quantities of supernate are drawn from the digesters and recycled through the plant. The WRBP’s concerns with the quality of the contractor’s recycle flow are noted to make the contractor aware that the WRBP will be closely monitoring the capture rate of the dewatering process and that, on occasion, it may be necessary for us to request that the contractor take steps to reduce their recycle load to the treatment plant. These steps may include requirements such as operating the dewatering equipment to increase its capture rate or reducing the number of hours each day the contractor processes solids from the digester. Exercise of these steps shall not affect the contract cost or completion date.
