Charcoal Ash as an Alternative pH Buffer in Single-Chamber Microbial Fuel Cells: Effects on Open Circuit Voltage and Substrate pH Dynamics

Abstract

The escalating cost of commercial pH buffer reagents remains a critical impediment to the large-scale commercialization of microbial fuel cell (MFC) technology. This study evaluates charcoal cooking ash as a low-cost, locally available alternative pH buffer in single-chamber MFCs fed with domestic sewage substrate. Two identical single-chamber MFCs were operated at 35 °C for seven days using carbon rod anodes and aluminium rod cathodes. Ash was added incrementally in 2 g doses at 10-minute intervals, and open circuit voltage (OCV) was continuously monitored. In the ash-supplemented cell, OCV increased progressively from 722 mV (Day 1) to a peak of 986 mV (Day 5), stabilising at 909 mV at Day 7. Substrate pH rose monotonically from 7.82 (0 g ash) to a maximum of 11.63 (180 g), before stabilising at pH 10.98 at the buffering saturation point of 324 g. In contrast, the unsupplemented control exhibited a sustained voltage decline from 737 mV to 543 mV over the same period. These results demonstrate that charcoal ash exerts a dual buffering and ion-conductivity-enhancing function, sustaining favourable cathodic conditions and extending the operational lifetime of the cell. The findings propose charcoal ash as a viable, zero-cost buffer substitute with competitive electrochemical performance relative to conventional commercial buffers, warranting further investigation for decentralised wastewater treatment applications.