Background and purpose: Pulp and paper industries produce large quantities of effluent that release various pollutants daily. Among various methods for treating such effluents, anaerobic biosorption process is of interest because of lower need to mechanical energy, boigasses production, high organic loading rate (OLR), low sludge production, and resistant system. OLR is one of the most important effective hydrodynamic parameters. In this study, the effect of OLR was investigated on anaerobic biosorption reactor in treating pulp and paper effluent.

Materials and methods: A 1.96L effective volume cannon pilot was used and wastewater was injected by pumping to the bed of the reactor. Temperature and pH were maintained about 30±2°C and 6.8-7.2, respectively. The effect of OLR on efficiency of system was studied in 1-12 kgCOD/m³.d. All experiments were performed under steady state conditions using procedures outlined in Standard Methods.

Results: In OLR 7kgCOD/m³.d and upflow velocity of 0.56m/h the system was able to reduce over 80% of COD concentration after 33-39h. No significant increase was observed in efficiency of the system at more OLRs, so it was selected as optimum loading rate. System efficiency was found to have a direct relation with decrease of upflow velocity and increase of HRT. The gas generation rate was 0.32 m³/kg COD removed.

Conclusion: According to this study, anaerobic biosorption system satisfactorily treated pulp and paper mill effluent and could perform this close to wastewater discharge standards established by national guidelines.