Snail Shells as Circular Biofilm Carriers for the Continuous Treatment of Real Cooperative Dairy Effluent: Performance and Biofilm Age Effect

The rapid growth of Morocco’s dairy sector has led to the discharge of high-strength effluents, particularly from cleaning and cooling operations. In the face of water scarcity and limited access to conventional infrastructure, this study proposes a novel, plastic-free treatment strategy using snail shells as circular biofilm carriers in a moving bed biofilm reactor (MBBR). Real effluent was collected directly from a cooperative dairy outlet and treated under continuous flow conditions. The system was inoculated with Aspergillus niger, a filamentous fungus known for its biofilm-forming ability. Snail shells achieved higher pollutant removal rates than industrial Kaldnes K3 carriers: 92.9% COD, 84.75% BOD₅, 88.7% TKN and 82.9% total phosphorus within 72 hours of biofilm maturation. Their porous and hydrophilic surface supported faster colonization (16 h start-up) and improved biofilm stability. This is the first study to evaluate the effect of biofilm age and shell surface characteristics in the continuous treatment of real dairy wastewater using natural carriers. In addition to reducing reliance on synthetic polymers, this low-cost approach promotes biodegradability, circular resource use, and enhanced ecological performance. These findings support the replacement of plastic media with nature-based alternatives in decentralized wastewater treatment systems.