Microbial fuel cell (MFC) technology shows promise as an alternative to conventional wastewater treatment systems due to renewable energy production and the potential to treat wastewater. The goal of this study was to solve challenges when applying MFC to winery wastewater treatment. A 100 mL air cathode MFC using carbonaceous material as the electrodes was designed and fabricated, inoculated with winery sludge and fed with synthetic winery wastewater.

The pH was found to be essential for the enrichment and maintenance of the MFC. An optimum pH of 6.5 maintained by phosphate buffer (PB) provided stable MFC performance for both power production and chemical oxygen demand (COD) removal. When the reactor was maintained at 1000 mg/L COD, the highest COD removal rate was reached within 4 hours (h) and overall removal reached ~80% within 60 h, the maximum output voltage was obtained within 0.5 h and lasted for 60±3 h. A COD:​PB ratio (COD(mg/L):​PB(mM)=100:​1) was suggested to counter pH fluctuations during MFC operation. With sufficient buffer, the COD removal rate and energy recovery efficiency were linearly related to SWW strength until the system limit was reached. Dog food was an effective alternative feed to maintain an active microbial population during the off season. An external resistance set close to the internal resistance maximized the treatment efficiency, whereas a higher external resistance increased energy recovery. Allowing time for a mature biofilm to form reduced the internal resistance of the reactor and provided better output power density.

A numerical model developed in this work predicted the output voltage from experiment but did not predict the COD removal rate well. The explanation was the existence of a complex mixed culture in the reactor consuming more COD and an increasing role of planktonic organisms at higher concentration. The model also revealed that the anode contributed ~2.5x higher to COD removal than the cathode, and that increasing the anode biofilm thickness resulted in a higher output power.