Each year, Americans consume over 6.3 billion gallons of beer. As a result, over 50 billion gallons of brewery wastewater is created annually. Wastewater pre-treatment is an important investment for craft breweries as the biological oxygen demand (BOD) and the total suspended solids (TSS) from the waste stream leaving the brewery have to be significantly reduced before it enters the municipal system. Therefore, the treatment of brewery wastewater is an enormous and expensive part of the environmentally conscious brewing business.

Brewery wastewater is characterized with high amounts of sugar, starch, and proteins, which makes it perfect candidate for Microbial Fuel Cell (MFC) application. MFCs have been proven as a promising technology for sustainable wastewater treatment and also as a way for direct recovery of electric energy [1].

In this study, two 10 liter MFCs were used to treat brewery waste collected from Stone Brewery, Escondido, CA. The MFCs had tubular design with a nanofiltration membrane separator, submerged oxygen reducing cathode and carbon cloth anode (Fig. 1). The two reactors were connected in series and operated under continuous flow. The objective of the study was to evaluate the long-term treatment capacity of the MFCs and optimize the operational parameters for maximum volumetric treatment rates and energy recovery.

Three main parameters were used to evaluate the MFCs performance. These were chemical oxygen demand (COD) removal, the magnitude of the generated current density and the columbic efficiency (CE) of the COD transformation into electricity.  The MFCs had an anode volume of 10L and anode surface area of 65 m².  The first MFC in the series (MFC #1) was first had an inflow of diluted buffered brewery wastewater effluent.  MFC #2 was operated with the outflow of MFC #1.  The MFCs was continuously running for 250 days when various flow rates of 1ml/min, 2ml/min, 3ml/min and 5ml/min were explored during the study.

Over the period of 250 days and loading rates between 1ml/min to 5 ml/min, MFC #1 demonstrated an average COD removal rate of 51.6 ± 19.4%, current density of 2.77 ± 0.99 A/m³ and CE of 8 ± 7%. MFC #2 had an average COD removal of 50.9 ± 20.5%, current density of 2.0 ± 0.6 A/m³ and CE of 14 ± 11% (Fig. 2).  Thus the whole system showed an average COD removal of 74.7 ± 19.2%, COD treatment rate of 0.56 ± 0.37 kg-COD/anode-m³-day, CE of 9 ± 6%, and current density of 2.4± 0.6 A/m³. 

This study demonstrated that MFCs could be useful devices for long-term continuous treatment of brewery wastewater. The system tested is modular, scalable and constructed from cost-effective materials. Future work will include additional large-scale pilot testing and further design and operational optimization to accomplish higher volumetric treatment rates.

References:

[1] Liu H, Ramnarayanan R, Logan BE. Production of electricity during wastewater treatment using a single chamber microbial fuel cell. Environ Sci Technol 2004;28:2281–5.