Purification of Roof-Harvested Rainwater Using Progressive Freeze Concentration

Abstract

Rainwater can serve as a safe and sustainable source of drinking water. One common way to harvest rainwater is through runoff from the roofs of buildings. Depending on the cleanliness and material of the roofs, this roof-harvested rainwater can have very different water quality like colour, turbidity, pH and total dissolved solids (TDS) compared to the rainwater. Roof-harvested rainwater TDS was not correlated with antecedent dry days (ADD) and weakly negatively correlated with rainfall amount. This paper demonstrated the use of progressive freeze concentration (PFC) to purify rainwater through reduction of colour, turbidity and TDS. In lieu of a specialised PFC equipment, falling-film ice making equipment was used to purify rainwater. Falling-film equipment was chosen for PFC as supercooling that could adversely affect separation efficiency was not observed. Two parameters, circulation time and initial rainwater quality were investigated for their effects on yield and quality of purified rainwater quality (colour, turbidity and TDS). Preliminary results showed the reduction of colour to within drinking water standard and TDS by more than 93 %. Higher circulation time was shown to decrease yield but improve effective partition coefficient (K). Initial rainwater quality has negligible effect on yield and removal efficiency. In conclusion, PFC is a potential method to purify roof-harvested rainwater into drinking water.