ACHIEVING 0.3 MG/L TOTAL PHOSPHORUS WITH THE CANNIBAL®SOLIDS REDUCTION PROCESS

The City of Clovis, CA recently advertised a Design/Build/Operate (DBO) project to construct a green-field 2.8 mgd water reclamation facility. The required effluent quality for this facility includes an 8 mg/L total nitrogen daily limit and the requirement to be able to achieve an effluent total phosphorus (TP) of 0.3 mg P/L or less. In response, the City selected a process offered by the CH2M HILL family of companies consisting of a membrane bioreactor (MBR) system coupled with a Siemens Cannibal® Solids Reduction Process.Conventional methods of phosphorus removal include the use of metal salts, such as alum or ferric chloride, to precipitate and remove soluble ortho-phosphate (OP), and biological phosphorus removal to removal phosphorus. Neither of these methods are directly applicable to the process proposed for the City of Clovis. Biological phosphorus removal is not practical as a result of low wastage rates, and metal salts are not practical since they would build up in the bioreactor over time and require wastage that would not otherwise be needed.An ASM 2d based model predicted significant PAO growth and resultant phosphorus release in the interchange tank. This was later qualitatively confirmed by testing of other Cannibal facilities by Siemens Water Technologies. Based on these model results and on the confirmations from Siemens, the Clovis ST/WRF was design as an MBR/Cannibal based system with a high degree of phosphorus removal.Essentially, the Cannibal process can be set up as a system that is similar to the original Pho-Strip system, where an elutriation tank is used to separate phosphorus rich liquid from the mixed liquor and the soluble phosphorus is then precipitated in an external system. In the case of this particular design, the interchange tank acts as the elutriation tank and it was possible to dispose of this phosphorus rich liquid into a nearby sewer for disposal. The end result is a process that is capable of routinely meeting a 0.3 mg/L effluent TP.