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Ammonia recovery from wastewater using a Microbial Electrolysis Cell (MEC)

Flavigny, Raphael (2011) Ammonia recovery from wastewater using a Microbial Electrolysis Cell (MEC). Honours thesis, Murdoch University.

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Wastewater contains ammonium that requires removal to prevent environmental degradation. The most common way of removing ammonium is by using nitrification and denitrification (i.e.: activated sludge), which requires energy (457 J/mmolNH4+ removed). Microbial Electrolysis Cell (MEC) is proposed, as a new process, to recover ammonium in the form of ammonia gas, from mild concentrated ammonium wastewater stream (50 mM). Such process has the advantage of removing organics and producing a current that enables the migration of ammonium against its concentration gradient to the cathode. The MEC also produces a high pH (>9.5) in the cathode, which favours ammonia gas production. It is demonstrated that the ammonium can accumulate against a maximum concentration gradient of 1 M ammonium in the catholyte. The ammonium migration from the anode to the cathode is caused by the electron flow (i.e.: current) due to bacteria biodegrading organics and donating electrons to the anode. The presence of current enables ammonium migration against its concentration, in a ratio of 0.47mmolNH4+/mmole-.The ammonium is accumulated in the cathode, and forms ammonia due to the high pH and dissociation constant (pKa = 9.2).

The energy requirements for this novel process are similar to traditional activated sludge, and about five times less than electrodialysis. However these two processes are treating urban and high ammonium concentrated (up to 500 mM) wastewater, while the MEC proposed in this project treats wastewater with 50 mM ammonium concentration. The MEC is not proposed as a replacement for current technology but as an alternative to remove ammonium and organics from specific industrial wastewaters.

Ammonia gas is used in large quantities to produce fertilisers. The MEC process recovers ammonia at half the cost of conventional technology. However there are limitations to the application of the system on a large scale, mainly because of the required membrane surface area.

Publication Type: Thesis (Honours)
Murdoch Affiliation: School of Environmental Science
Supervisor: Ho, Goen and Cord-Ruwisch, Ralf
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