Attached growth wastewater treatment systems are considered to be effective in developing countries due to their low energy, operational and maintenance costs. Thus the present study mainly focused on the treatment of domestic wastewater by a pilot-scale trickling filter system (TFs) installed in the natural environment at a residential area of Quaid-i-Azam University, Islamabad, Pakistan, and it was operated under three different hydraulic retention times (HRT), i.e., 24, 48 and 72 hrs. Furthermore, pilot-scale TFs showed significant efficiency regarding the removal of physico-chemical and microbiological parameters under different HRTs, i.e., 70.9 and 23.5% reduction in COD and EC contents, respectively, at HRT of 48 hrs., while significant removal of TDS (34%), SO₄ (37%), PO₄ (81.8%) and TN (66.6%) were noticed during operation of the system after 72 hrs of HRT. Likewise, a maximum of 86.4%, 82.5% and 83% decrease in total bacterial count were observed at HRT of 24, 48 and 72 hrs, respectively. Finally, it was suggested that pilot-scale TFs have great potential to be transferred to field scale in the areas disconnected from a centralized treatment system for handling sewage of small communities in underdeveloped and developing countries.