Exploiting Electrochemistry in Water Treatment – from Membranes to Coagulation
In water treatment processes, electrochemistry is a convenient and efficient means of water purification. It finds applications from the formation of coagulants to the fabrication of new membrane materials. Electrochemistry carries great potential for improved processes and applications. However, in view of its complexity compared to other available methods, it is an under-utilized approach.In this dissertation, we first studied the important pre-treatment step - coagulation and flocculation. Model contaminated water based on wastewater produced by oil & gas refineries, as well as groundwater, were treated using both chemical and electrocoagulation. It was found that although chemical coagulation works well in low doses of an iron coagulant, electrocoagulation was eventually able to achieve higher removal rates than chemical coagulation could. The production of coagulants by means of oxidizing a sacrificial anode is a cheaper way of producing coagulants since the transport and storage of chemical coagulants includes the weight of counterions and hydrated components. In the second study about electrocoagulation, morphological and compositional changes of a sacrificial aluminium electrode was looked at using various modern characterization tools as electrocoagulation proceed. Surprisingly, although fouling occurred at the cathode, the most energy intensive step in electrocoagulation is the dissolution of aluminium owing to thickening of the aluminium oxide film. iii The fabrication of new membrane materials was also explored using two electrochemical methods: electropolymerization and electrically-mediated atom transfer radical polymerization. Electropolymerization was successfully employed to form a dense salt-rejecting barrier using aromatic moieties similar to state-of-the-art polyamide membranes. Although its permselectivity is not as high as conventional polyamide RO membranes, electropolymerization offers an alternative fabrication technique that enables the use of environmentally benign solvents (ie. water) as the polymerization medium. Poly(acrylic acid) brushes grafted from an electrically conducting ultrafiltration membrane was shown to respond to the application of positive voltages by expanding and collapsing. Pore gating was achieved as a result, commanding the passage of 11 kDa particles on the flip of a switch. The response time was rather quick (within 10 minutes) and was attributed to the migration of hydrated counter ions as different voltages are applied to the membrane.