Ali Tavallali, - Department of Civil and Environmental Engineering, Shiraz University, Shiraz, Iran
Ayoub Karimi-Jashni - Department of Civil and Environmental Engineering, Shiraz University, Shiraz, Iran

The wastewater used in this study enters the reactor after pretreatment via a septic tanksystem. The bioreactor used in this study had a useful volume of ۲۱۰۰ liters. Novel mediaconsisting of ۷۲ woolen strings and ۱۲ sheets of curtain-style media with total surface areasof ۲۹۱۸ and ۱۹۵۰۰ m۲ were used as biofilm formation surfaces. The system was first set todetermine chemical oxygen demand (COD) removal for retention times of ۱۰, ۸, ۶, and ۴hours; then, the optimal hydraulic retention time was determined. COD removal was ۹۵.۷%,۹۲.۹%, ۸۸.۸%, and ۶۵.۴% for ten, eight, six, and four-hour HRTs, respectively. Thehydraulic retention time of ۶ hours was selected as the optimal HRT time since it iseconomical to operate and maintain, and its efficiency in removing COD that can meet thestandard of the Iranian Department of Environment for groundwater recharge. These resultsindicate that the utilized media were reliable and could remove organic matters satisfactorilyto meet the standard. Compared to other conventional treatment methods like activatedsludge and MBR, which use more complicated installation and technology, maintenance andinstallation procedures were easier.

Septic tank, COD removal, fixed-bed, biofilm, bioreactor