Environment and Ecology Research 10(1): 21-30, 2022 http://www.hrpub.org DOI: 10.13189/eer.2022.100103 Performance of Recovered Coagulant from Water Treatment Sludge by Acidification Process Nurakmal Hamzah * , Muhammad Arif Fahmi Roshisham, Md Faizal Zakaria, Muhamad Hasbullah Hassan Basri, Nor Azliza Akbar School of Civil Engineering, College of Engineering, Universiti Teknologi MARA, Cawangan Pulau Pinang, Kampus Permatang Pauh, 13500 Pulau Pinang, Malaysia Received May 21, 2021; Revised October 19, 2021; Accepted November 19, 2021 Cite This Paper in the following Citation Styles (a): [1] Nurakmal Hamzah, Muhammad Arif Fahmi Roshisham, Md Faizal Zakaria, Muhamad Hasbullah Hassan Basri, Nor Azliza Akbar , "Performance of Recovered Coagulant from Water Treatment Sludge by Acidification Process," Environment and Ecology Research, Vol. 10, No. 1, pp. 21 - 30, 2022. DOI: 10.13189/eer.2022.100103. (b): Nurakmal Hamzah, Muhammad Arif Fahmi Roshisham, Md Faizal Zakaria, Muhamad Hasbullah Hassan Basri, Nor Azliza Akbar (2022). Performance of Recovered Coagulant from Water Treatment Sludge by Acidification Process. Environment and Ecology Research, 10(1), 21 - 30. DOI: 10.13189/eer.2022.100103. Copyright©2022 by authors, all rights reserved. Authors agree that this article remains permanently open access under the terms of the Creative Commons Attribution License 4.0 International License Abstract Aluminium sulphate (Al 2 SO 4 ) 3 or commonly known as alum has been used as a coagulation-flocculation agent by water treatment industries around the world, including Malaysia. Regardless of its effectiveness in purifying the raw water, it produces a large volume of alum sludge. In Malaysia, alum sludge is categorized as scheduled waste where it requires to be transported only to approved landfills and the costs could be high. Hence, reusing and recycling the alum sludge may be beneficial for water treatment industries in reducing the disposal cost. In this study, acidification method using nitric acid at a molarity of 0.5M – 2.0M is employed to recover a maximum percentage of aluminium from alum sludge. The findings showed that the difference in molarity of nitric acid is proportional to the recovery rate of aluminium up to 99% of the recovery. The performance of recovered coagulant in removing turbidity from raw water was evaluated at variations of dosage (0.5 – 12 mg/l) and pH (2 – 13). At an optimum dosage of 2 mg/l, the recovered coagulant efficiently removes the turbidity of raw water at 93.32% and achieved 99.47% at pH 7. Consequently, the use of recovered coagulant can promote a sustainable environmental approach to converting waterworks residuals into usable resources, particularly in water/wastewater treatment industries. Keywords Recovered Coagulant, Recovered Aluminium, Alum Sludge, Acidification, Turbidity Removal 1. Introduction Drinking water treatment undergoes coagulation and flocculation process to enhance the ability of a water treatment process to eliminate all colloidal and suspended solids from raw water. In the coagulation-flocculation process, a chemical coagulant such as aluminium sulphate (Al 2 SO 4 ) 3 or alum is added in untreated water and hydrolysed to form a range of hydrolysis species, which will facilitate colloidal and suspended impurities to accumulate into larger flocs via charge neutralization and sweep-flocculation mechanisms [1]. For many years, alum has been used as a coagulation and flocculating agent by water treatment industries around the world including Malaysia for raw water purifications. This is because alum is the most basic aluminium-based coagulant and inexpensive product available in the water treatment industry. Despite its ability to purify raw water, it generates a significant amount of alum sludge. Consequently, alum sludge has been recognized as the most massive by-product generated and locally available by the water industries globally [2]. Due to the high volume of sludge production and its environmental drawbacks, the most persistent problem associated with alum sludge is finding the most cost-effective and efficient disposal method. As a