The Cost of Waste

Treating wastewater is expensive. Yet, 70% of the cost to run a wastewater treatment plant is in two elements: electricity to power the aeration blowers and residual sludge treatment. An emerging technology promises to eliminate those costs.The treatment method, Microbial Fuel Cells (MFCs), developed by a number of companies including Emefcy, an Artemis Top 50 Company, reduces energy consumption to zero, produces green electricity to be fed into the grid and reduces excess sludge by 80%.

The Old Way

Conventional wastewater treatment relies on aerobic bacteria to munch organic contamination, resulting in a 50% reduction in dry weight. The remaining 50%, sludge, settles to the bottom of sedimentation  basins  and following a series of treatment processes is removed to landfills or disposed of as fertilizer.Aerobic bacteria require oxygen, so compressors blow air into the aeration basins. As the bacteria break the organic waste into smaller and smaller molecular chains, electrons are discharged. The dissolved oxygen molecules in the water capture the electrons, creating oxidization.In the mean time, the oxygen energizes the bacteria, which undergo mitosis, multiplying like microscopic rabbits. All of which end up as sludge on the bottom of the treatment basin, destined for landfills. Half of every dry tonne of incoming organic waste becomes sludge. But sludge is not dry: it’s 20% solids and 80% water, meaning every dry tonne of incoming organic waste turns into 2.5 tonnes of sludge that must be thickened, dewatered, digested and dried through an expensive process and then exported.

A New Way

Microbial Fuel Cells rely on a different sort of bacteria: electrogenic. As their name denotes, electrogenic bacteria generate electricity. Kept in an anaerobic chamber and fed raw wastewater, the bacteria attempt to ferry electrons through a conductive cable to the oxygen rich chamber on the other side.  The flow of electrons through this cable, from the wastewater section to the air section generates electric current.

Shuttled up the wire, the green electric current is fed into the energy grid where it’s used to run microwaves and the latest episode of Glee.In the mean time, the bacteria remain in the anaerobic chamber. They don’t need compressors (saving electricity), because they don’t need the oxygen. And since most of their energy is stolen by the cable, the rate of mitosis is limited. Only 10% of each dry tonne of incoming waste ends up as sludge. It’s an 80% reduction in sludge production.For each kilogram of incoming organic contamination, microbial fuel cells net 1 kilowatt-hour of electricity. 2/3 of that is savings from efficiency (MFCs don’t require air compressors) and 1/3 is energy produced during the treatment process.

Application Example – Intraindustry Collaboration

The effluent from MFCs isn’t bad, but it isn’t great either. Enter Membrane Bio Reactors (MBRs). MBRs have lauded themselves as the next big thing in wastewater treatment, namely because they produce pristine effluent. Yet, they consume energy like a flock of Hummers. On their own they’re even less efficient than traditional wastewater treatment.However, coupled with MFCs, they become efficient. First, MFCs send MBRs 90% less waste to filter from the water, reducing the energy intensive workload. Second, MFCs produce enough electricity to compensate for the MBRs’ demands. Combined, MFCs and MBRs are far more efficient than traditional treatment methods, and the effluent they create together is purer than drinking water.