A review on alum sludge reuse with special reference to agricultural applications and future challenges

• Economical and sustainable disposal of alum sludge is a major social and environmental concern.
• Commercially viable options on large scale disposal of alum sludge were not well studied.
• Land application offers a great potential; however, there are serious limitations to be addressed.
• Soil acidification, Al toxicity and P deficiency were the main concerns in agricultural use.
• Strategies to address the present and future challenges of Alum sludge use were identified.

Alum salts are commonly used in the water industry to promote coagulation in the production of clean drinking water, which results in the generation and accumulation of ‘waste’ by-product ‘alum sludge’ in large volumes. Effective and efficient management of alum sludge in an economically and environmentally sustainable manner remains a significant social and environmental concern with ever increasing demand for potable water as a result of rapidly escalating world population and urban expansion. Various intensive practices have been employed to reuse the alum sludge in an attempt to figure out how to fill the gap between successful drinking water treatment process and environmentally friendly alum sludge management for over the years. This paper primarily aimed at comprehensive review of the existing literature on alum sludge characteristics, its environmental concerns and their potential utilization, especially in agricultural and horticultural sectors leading to update our recent state of knowledge and formulate a compendium of present and past developments. Different types of alum sludge utilizations in various fields were recognized and examined. The strengths, weaknesses, opportunities and potential risks of alum sludge reuse options with particular reference to agriculture were highlighted and knowledge gaps were identified. Research priorities and future challenges that will support in the development of effective alum sludge management practices in agriculture with multi-prong strategies were discussed.