In recent years, due to serious water shortages, overpopulation and need to consume more water, the use of wastewater treatment plant effluent has been attracted many attentions. In most cases, effluent from the treatment plant has not met the criteria for re-use. In these cases it is necessary to choose an easy and inexpensive method, to improve the effluent quality parameters and the use of renewable water resources. When the pollution load is not high, biofilm reactors are commonly used. In this study the use of porous concrete as a bed biofilm growth, in reducing pollution load of wastewater was investigated. Experimental design was a randomized complete block. In order to evaluate the ability of porous concrete, a mix design was selected according to regulations ACI211.3R. To increase the specific surface area of concrete for biofilm growth, fine sand (10% of course sand by weight) was added to mix design in three stages. A rectangular channel (with cross sectional 20×30 cm 2 ) and 8 meter in length was constructed, lined with ceramic and filled with porous concrete cubes. The beginning and end of the channel, two stilling basin was built. Stilling basin walls were sealed with cement mortar. Wastewater was transferred from treatment plant to channel using a siphon tube. Then the concrete blocks were made, putted on the channel and biofilm processing operations performed on the pores of porous concrete cubes. After processing, based on the calculated porosity of concrete blocks, constant flow rate of wastewater was passed through the channel. The flow rate was considered for each mix design based on the hydraulic conductivity, that was for the first to fourth mixed design 5, 6, 7 and 8 liters per minute, respectively. After 24 hours, when the flow was stable, samples were taken at the inlet and outlet of stilling basin and BOD, COD, TSS and total coliform were measured. Results show that percentages of removal increases with adding fine particles. The average removal rates of BOD, COD, TSS and total coliform for the first mix designs were 25.1, 33.67, 45.42 and 37.05, respectively. Similarly, the average removal rates of BOD, COD, TSS and total coliform for the fourth mix were 36.48, 40.5, 57.3 and 81.69, respectively. Finally, it is concluded porous concrete can be used as a bed biofilm and in considering the results of the analysis of variance table; third mixes the best mix design for the project to be assessed.
