Energy balances for WWTPs

Power used for wastewater treatment. The power required at different WWTPs varies widely, but general trends can be developed based on the type of treatment process. TFs are reported to use 430 kW per mVs, with AS using 2.4 to 5.9 times as much power (1020-2550 kW per m /s) (Table 9.1). These estimates for AS are a little higher than Shizas and Bagley (2004) reported for the North Toronto Wastewater Treatment (NT) plant of 680 kW per m /s (30 kW/mgd). The wastewater at this plant contained 431 mg-COD/L and 1930 mg-TS/L, and contained in the influent a total of 2616 kW. Thus, the energy content of the wastewater was 9.3 times that required to treat the wastewater (283 kW). A membrane bioreactor (MBR) system requires 8520 kW per m /s for treatment, and thus could not be self-sustaining based on the energy content of the wastewater. 

Another advantage of the MFC process versus an aerobic treatment process, such as AS, is a reduced production of solids from the bioreactor. The subject of cell yields from MFCs is addressed in Chapter 7. As noted there, estimated cell yields from an MFC process with acetate are thought to be on the order of Yxjs = 0.16g-COD-cell/g-COD. This 

As mentioned above, a solids contact process will likely be needed to further remove BOD from the MFC effluent. This process could be expected to improve the settling characteristics of the MFC biofilms. It is unknown at this point how well the SC reactor system would function. It is also possible that the solids from the primary clarifier could be used to augment the MFC solids or improve their settling characteristics, but primary clarifier solids can vary substantially in character and such a process has yet to be examined. 

It is clear that many questions remain on implementation of the MFC into a wastewater treatment system process train. However, there is ample environmental engineering experience to provide the needed judgment on how best to assess the performance of a new MFC system in a wastewater treatment system. All that is required now is the incentive and funding to begin such testing and analysis of these systems. 

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