Red mud-based inorganic polymer spheres: Innovative and environmentally friendly anaerobic digestion enhancers

Red mud-based inorganic polymer spheres were used as alternative pH regulators and process enhancers in sequencing batch anaerobic reactors treating cheese whey. This byproduct tends to quickly acidify under anaerobic conditions, and the common route to control pH and ensure suitable conditions for methane production involves the use of commercial alkaline raw materials. The spheres were synthesized using significant amounts of hazardous and toxic waste, red mud (50 wt% of solid components), whose recycling is challenging. The inorganic polymeric spheres, when compared to virgin alkaline raw materials, improved organic matter removal by 44%, prevented VFA accumulation (acidification degree less than 20%), maintained pH values in a range (6.5-7.2) to ensure maximum methanogenic activity by archaea microorganisms, and boosted the methane volume by ~90%. These promising results demonstrate the feasibility and performance advantages of using these innovative spheres instead of virgin raw materials, which is an important tool towards sustainable development.