Increasing water scarcity necessitates safe reuse to narrow the gap between demand and supply of irrigation water. This study investigated the role of biofilm on two different particle sizes (0.5-1mm and 1-2 mm) of granular wood charcoal (GWC) in enhancing the effluent quality of primary wastewater treatment to develop a cost-effective wastewater treatment method. Granular wood charcoal (GWC) was characterized by surface area, pore volume, fourier transforminfrared (FTIR) and scanning electronmicroscopy (SEM) to demonstrate the physicochemical properties. Bench scale column experiments were conducted for the two different particle sizes column (1), 0.5 – 1mm, and column (2), 1-2 mm, with an average flow rate of 10 cm3/min and 6.54 h as average empty bed contact time (EBCT). GWC biofilm formation was confirmed by SEM examination in voids and channels and on surfaces of the GWC. The role of biofilm on the GWC has demonstrated consistently removal organic matter as chemical oxygen demand (COD). COD was monitored with time and extended to 96 day to examine the performance of the biofilter column. COD tended to decrease with time for both columns. Slight increase in the removal efficiency of COD with time in column1 (91.36 %) in comparison to that of column2 (87.69 %) was observed. Such in crease could be due to difference in surface area of the two particles size. Effluent can be characterized as slight to moderate degree of guideline restriction in irrigation reuse for salinity and sodicity for both columns. For safe irrigation reuse, addition disinfection step may be needed even with obtained results of Escherichia coli (E. coli) removal efficiency more than 99%. The results indicated that biofilter process can be an efficient option for upgrading the primary wastewater treatment method.