Process trains for WWTPs

Microbial Fuel Cells. By Bruce E. Logan Copyright 2008 John Wiley Sons, Inc. 

Wastewater leaving the TF enters a secondary clarifier to remove biofilm solids produced in the system. Treatment by the TF is usually not as effective as an AS process as the BOD5 may only be 45 mg/L. 

After the wastewater leaves the biological treatment process, it is usually chlorinated in treatment plants in the US to kill bacteria, and then dechlorinated to protect the aquatic 

The sludge that is produced from the clarifiers goes into a treatment train typically consisting of an anaerobic digester (AD) having a HRT of 15 to 20 days or more. The liquid effluent from the AD is recycled back to the head of the plant. The gas produced, containing primarily methane and carbon dioxide, can be used for electricity production in gas turbines with the waste heat used to heat the ADs. In some plants the gas is used to heat the digester directly with the excess methane burned (flared). The solids from this process are filter pressed to remove more water, and composted. These treated and stabilized solids, called biosolids, are now suitable for safe land application and often times can be used as a source of fertilizer. 

From this summary of a WWTP process train we can see that an MFC would replace the AS or TF treatment system. The MFC is a biological treatment process, and thus its function will be to remove BOD in the same manner as accomplished by the AS aeration tank or the TF. There are four main advantages of using an MFC instead of one of these conventional bioreactors  

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