CASCADING ALUM SLUDGE FROM DRINKING WATER PLANTS

The challenge

Alum sludge is a byproduct at many drinking water utilities using surface water as a raw water source. According to our estimates, worldwide over 5 million tonnes of sludge are landfilled or sent to waste disposal sites annually. Only a minor portion is used beneficially, e.g. in the cement industry or in construction materials. Numerous attempts have been made while pursuing recovery of aluminum salts, however not successfully applied at full scale yet. The question was raised whether the reuse potential can be increased by cascading the alum sludge from drinking water plants. 

Solution and impact

Aluminum based coagulants are used both in potable water production and in wastewater treatment, however for different purposes. In potable water the main objective is to remove suspended solids in the pretreatment stage. In wastewater water treatment phosphate removal is key. Obviously, purity requirements are much more important in potable water treatment rather than in wastewater processes. We developed a concept based on (1) using aluminum based coagulant in potable water production, (2) an acid treatment of the remaining alum sludge, next (3) using this material in a nearby wastewater plant e.g. for phosphate removal, while replacing the use of fresh aluminum based coagulant. This results in a higher circularity level.  

Status

Allied Waters elaborated on the concept, mainly as part of a project in cooperation with the UK water industry and Isle Utilities (Opportunities for recovering valuable resources from water treatment sludges). Based on a more detailed review of costs and benefits we conclude that this way of ‘cascading’ alum sludge provides a potential cost saver.  

Learn more here.