The utilization of alum sludge as constructed wetlands’ media to reduce nutrient in communal wastewater treatment plant effluent

Communal wastewater treatment plants (WWTPs) typically used Anaerobic Baffled Reactors (ABRs) due to their low operational costs and ease of maintenance. However, studies indicated that nutrients such as ammonia and phosphate in ABR effluents often failed to meet quality standards. This issue became increasingly urgent as untreated nutrients significantly contributed to environmental degradation, including eutrophication in water bodies, which posed a severe threat to aquatic ecosystems and public health. The pressing need to explore efficient nutrient removal techniques highlighted the importance of investigating innovative approaches such as constructed wetlands using alum sludge. On the other hand, drinking water treatment processes usually required the addition of aluminum sulfate for coagulation, which generated sludge containing aluminum. This alum sludge was often disposed of without proper treatment, leading to environmental degradation. For the first time, this research connected two separate fields-wastewater treatment and alum sludge management-revealing an interdisciplinary approach that transformed alum sludge into a sustainable material for nutrient removal. This innovation addressed dual environmental challenges: mitigating nutrient pollution and repurposing waste materials. Research suggested that dried alum sludge from drinking water treatment plants had the potential to be used as media in constructed wetlands to reduce nutrient levels. A comprehensive literature review was conducted to explore methods of dewatering alum sludge before its use as constructed wetland media, various designs of constructed wetlands using alum sludge and the mechanisms of nutrient removal. This work unveiled promising business opportunities, particularly for industries focusing on sustainable waste reuse technologies and eco-friendly infrastructure development. Prospective directions for further research included optimizing the longevity and efficiency of alum sludge as constructed wetlands media under different wastewater conditions. Future challenges included addressing potential aluminum leaching, maintaining media performance over time and exploring scalability for industrial applications. The results indicated that alum sludge was typically air-dried and then oven-dried before being used as an alternative media in constructed wetlands. Key mechanisms for nutrient removal in constructed wetlands with alum sludge included adsorption through ligand exchange, nitrification-denitrification, microbial activity and plant uptake. Single-stage constructed wetland designs demonstrated higher removal efficiency compared to multi-stage designs, suggesting pathways for cost-effective implementation in decentralized wastewater treatment systems.