Microalgae disintegration in raw water as pre-treatment using sonic wave

Abstract

Microalgae bloom significantly affects the quality and quantity of water produced at the Semberong Barat Drinking Water Treatment Plant (SBDWTP) at Semberong Barat Dam (SBD) Kluang, Johor, Malaysia. The water source is severely polluted by microalgae bloom due to the use of large quantities of fertilisers by farmers. Consequently, this has increased the presence of nutrients such as nitrate, phosphate, and potassium from the release of fertilisers to the lake nearby, resulting in the rapid growth of microalgae and aquatic plants. Therefore, reducing the microalgae count in raw water is crucial to ensure minimal impact on subsequent water treatment processes. Concurrently, the presence of excessive residual soluble aluminium coagulants in the treated water are also caused microalgal interference that can severely affect the water purification process. Hence, this study was undertaken to investigate the best coagulant that can enhance the reduction of microalgae for the water treatment processes at SBDWTP coupled with sonic treatment. The selected coagulants used include Polyaluminium Chloride (PAC) Type 1, 2, and 3 which differed from each other in terms of density of aluminium, basicity and concentration of sulphate ions. Different types of microalgae were identified in the raw water. These microalgae were treated using ultrasonic wave coupled with the coagulants. The coagulants work to enhance the efficiency of water treatment at SBDWTP. Identification study showed the presence of genera Spirulina, Oscillatoria, Microcystis, Asterionella, Navicula, Peridinium, Ceratium, Coelastrum, Planktosphaeria, Actinastrum, Chlorella, Ankistrodesmus, Scenedesmus, Pediastrum, Staurastrum, Golenkinia, Rhodomonas and Euglena in the microalgal bloom. Results showed that the use of sonic wave coupled with PAC successfully reduced the microalgae count by 79%, with PAC Type 3 as the best coagulant. The correlation coefficient (R2) between the raw water intake and the residual aluminium was 0.9986. Meanwhile, the R2 between the raw water intake and the dam level was 0.9984, and between raw water intake and the turbidity value was 0.9979. The turbidity of the raw water was probably due to the presence of high residual aluminium. The findings of this study showed that the coupling of the pre-treatment using ultrasonic wave with coagulant agent (PAC) enhanced the treatment of microalgal bloom, and improved the production of drinking water, making the production to be above the current level of 54 million litres/day (MLD).