Effect of temperature on the performance of Rheofloc: conductivity removal from RO-reject

Abstract

South Africa is an arid country with an annual average rainfall less than half of the world’s average rainfall. The industrial sector uses 11% of this limited amount of water. Eskom is one of these users. Within the water treatment system at the Grootvlei power station, reverse osmosis (RO) is used. The retentate from the membranes is pumped into a sump. This water can be treated for further usage, which ensures that the plant abstracts less water from the environment. Rheofloc, an inorganic polymeric flocculant was used in this study in conjunction with lime treatment, to reduce the conductivity of the water. As the conductivity decreases, the number of ions in the water decreased. The jar test method consisted of the addition of the coagulant and flocculant during rapid mixing for 5 minutes at 240 rpm, thereafter the lime was added to increase the pH to 10.1 during slow mixing which occurred for 90 minutes at 80 rpm. This was done at 40°C and at 60°C to observe the effect that temperature has on the reduction of the conductivity in the water. Results showed that the reduction of conductivity levels was higher at 60°C. This is due to the increase of the rate of reaction with an increase in temperature. Thus the treatment of RO- reject is preferred at 60°C to achieve effective removal of ions with the potential of scale formation