Cedar Rapids Water Pollution Control Facility Successful Recovery of a Solids Management System from a Catastrophic Flood

The City of Cedar Rapids was inundated by a catastrophic flood of the Cedar River in June of 2008. Damages included most of the solids processing facilities of the Cedar Rapids Water Pollution Control Facility (WPCF). The solids processing facility consists of primary sludge being concentrated by dissolved air flotation thickeners and dewatered with belt filter presses. Excess secondary sludge from liquid stream biological treatment is concentrated by gravity belt thickeners, conditioned with low pressure oxidation (LPO) thermal conditioning, and dewatered with centrifuges. The separate solids streams are combined and sent to a single multiple hearth incinerator, or back-up alkaline stabilization process. Incinerator emissions are controlled by combustion temperature and a wet scrubber system. Ash from the incinerator is pumped to an onsite lagoon for storage and ultimately disposed of at a beneficial use permitted location at a later time. The overall wet mass reduction is approximately 80 percent. After the flood, total wet sludge cake production more than doubled and had to be hauled to distant landfills (over 145 km (90 miles) away) or land applied as far as 121 km (75 miles) away. Raw secondary centrifuge cake processing restarted approximately three months after the flood. This material was land applied. FEMA involvement supported very limited emergency repairs to allow a damaged/unreliable incinerator to handle as much sludge as possible to minimize the excessive hauling and disposal costs. Emergency repairs allowed the incinerator to handle primary cake within nine months of the flood event. FEMA then obligated subsequent final repairs to restore as much of the pre-flood capacity as practical. By April 2012, final repairs were completed. Subsequently, several “engineering” stack tests were performed to evaluate whether additional capital emissions controls would be needed to comply with the MACT 129 rule. The test results demonstrated compliance within 75 percent of each MACT emission limit.