19 20The production and discharge of large volumes of wastewater during coal mining activities are one of 21 the major environmental issues in Australia. Therefore, it is crucial to develop and optimise effective 22 treatment processes for the safe disposal of coal mining wastewater (CMWW). In this study, we 23 investigated the performance of a recently developed polytitanium tetrachloride (PTC) coagulant and 24 compared with the performance of titanium tetrachloride (TiCl 4 ) and the commonly used ferric 25 chloride (FeCl 3 ) coagulant for the treatment of CMWW from one of the coal mining sites in Australia. 26The use of Ti-based coagulants is particularly attractive for the CMWW treatment due to the 27 advantage of being able to recycle the sludge to produce functional titanium dioxide (TiO 2 ) 28 photocatalyst; unlike the flocs formed using conventional coagulants, which need to be disposed in 29 landfill sites. The results showed that both PTC and TiCl 4 performed better than FeCl 3 in terms of 30 turbidity, UV 254 and inorganic compounds (e.g. aluminium, copper or zinc) removal, however, PTC 31 performed poorly in terms of dissolved organic carbon removal (i.e. less than 10%). While charge 32 neutralisation and bridging adsorption were the main coagulation mechanisms identified for TiCl 4 33 treatment ; sweep coagulation and bridging adsorption seemed to play a more important role for both 34 PTC and FeCl 3 treatments. The flocs formed by PTC coagulation achieved the largest floc size of 35 around 900 µm with the highest floc growth rate. Both Ti-based coagulants (i.e., PTC and TiCl 4 ) 36 2 showed higher strength factor than FeCl 3 , while TiCl 4 coagulant yielded the flocs with the highest 37 recovery factor. This study indicates that Ti-based coagulants are effective and promising coagulants 38 for the treatment of CMWW. 39

Seasonal green algae blooms in freshwaters have raised attention on the need to develop novel effective treatment processes for the removal of algae in water. In the present study, the performance of newly developed polytitanium tetrachloride (PTC) coagulant for the removal of freshwater microalga Chlorella vulgaris has been investigated and compared with titanium tetrachloride (TiCl 4) coagulant and the conventional ferric chloride (FeCl 3) coagulant. The main benefit of using titaniumbased coagulants is that the sludge produced after flocculation may be recycled into a valuable product: titanium dioxide photocatalyst. Both titanium-based coagulants achieved good flocculation over a broader pH range and coagulant dose compared to conventional FeCl 3 coagulant. All three coagulants achieved comparable performance in terms of turbidity removal (i.e. turbidity removal efficiency > 97%); although TiCl 4 performed slightly better at the lower tested dose (i.e. < 9 mg/L). Zeta potential measurements indicated that charge neutralisation may not be the sole mechanism involved in the coagulation of algae for all three coagulants. Analysis of the dynamic floc size variation during floc breakage showed no regrowth after floc breakage for the three coagulants. The flocs formed by both Ti-based coagulants were larger than those formed by FeCl 3 and also grew at a faster rate. This study indicates that Ti-based coagulants are effective and promising coagulants for algae removal in water.