Reducing Biosolids with Cannibals

"CH2M Hill" Case Study in Oregon Demonstrates the Benefits of Using Cannibal Solids Reduction Technology to Reduce Biosolids

Oak Lodge Sanitary District provides wastewater collection and treatment and surface water management services to32,000 area residents in unincorporated Clackamas County, Oregon. In 2012, OLSD implemented the Cannibal® Solids Reduction process to significantly reduce biosolids, as part of a larger $44 million upgrade at its 10.5 MGD Oak Lodge Water Reclamation Facility.

Implementing this technology is beneficial to OLSD—significantly reducingoperational costs for hauling biosolids offsite—savings that can be passed on to the District's customers.

Cannibal® Solids Reduction technology has been incorporated in relatively few U.S. water reclamation facilities to date. The Cannibal process consists of three basic elements:

• A mixed liquor recycle rotating screen (physical component of the process)
• Conventional activated sludge secondary process
• Interchange Bioreactors (biological component of the process)

Key elements of the Cannibal process are utilized to accomplish reduction of hauled biosolids:

• Mixed Liquor Screen: a 250-micron drum screen continuously screens a portion of the mixed liquor, resulting in sludge yield reduction due to trash removal
• Activated Sludge System : additional organic degradation is provided through an extended aeration system with an SRT of 10-15 days
• Interchange Bioreactors: facultative microbes are cultivated, with a much slower growth rate. The cycling between different biological environments (Aerobic, Anaerobic, and Anoxic) breaks cells down and open, increasing food availability and accessibility.

CH2M HILL worked with OLSD to systemically and successfully implement the process at its WRF. Several of the lessons learned in the start-up and activation of the process can be utilized and applied to other process startups, including:

• Collaborative approach to tracking and managing system performance —information developed and data produced as part of the startup effort was clearly documented and shared
• Extensive training -Operations and Maintenance staff were engaged throughout design and construction phases; technical and process trainings were developed to ensure smooth implementation and start-up
• Strict attention to sampling accuracy -staff consistently reviewed sampling protocols and procedures to verify the system's performance

After fully implementing the Cannibal process, the system was tested from July 1, 2013 to December 31, 2013. During that time, the facility treated more than 800,000 pounds of BOD and wasted only 300,000 pounds of biological solids. The system was tested again from April 2014 to September 2014, after making several adjustments to the system, such as optimizing mixed liquor screen performance; modifying aeration basin configuration to introduce return sludge into an anaerobic environment; implementing simultaneous nitrification-denitrification; and modifying the interchange bioreactor aeration control strategy to optimize the anaerobic environment. Though the testing is not yet complete, results are similar to the initial test.

While OLSD is still working to optimize and reduce biosolids production at its WRF, the benefits of the Cannibal process are already apparent. The reduced yield of biosolids represents a significant operational cost savings related to reduced hauling costs. The impact of the mixed liquor screen is noticeable; in addition to reduced biosolids hauling, it offers the advantage of cleaner biosolids for land application.

Source: CH2MHill

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