The dosing of coagulants such as iron is essential in many drinking water and wastewater treatment processes. However, this linear process, where coagulant is only dosed once before disposal, is coming under increasing pressure due to variability in markets and supply chains and tightening environmental regulations. Innovations are therefore required to protect this process, to prevent disruption of the production of potable water and clean effluent into the future.

A novel method is proposed to separate iron from sludge using a biological method, with the intention of its local re-use as coagulant. This method would use iron reducing bacteria (IRB), which are known to be present in wastewater sludge, to reduce iron from insoluble Fe(III) to soluble Fe(II). A review of literature has allowed rules to be developed to identify the key opportunities of biological coagulant recovery:

1)    Fe(III) species present should be reducible by IRB
2)    Ageing of Fe(III) species should be minimised
3)    Sludge conditions should be suitable for IRB to reduce iron

Following these rules should allow IRB to release iron from target sludges, allowing for its local re-use as coagulant. This would introduce circularity to the previously linear coagulation process, thereby increasing its resilience and sustainability.