Salinity Effect on Textile Dyeing Wastewater Treatability in an Up-flow Anaerobic Sludge Blanket Reactor

In this study, the performance of an up-flow anaerobic sludge blanket (UASB) reactor in treating synthetic textile dyeing wastewater containing azo dye Reactive Red ۱۹۵ was evaluated under three salinity levels of ۵, ۲۰, and ۳۵ g/L NaCl over three operational phases (۷۲ days). All experiments were conducted at a hydraulic retention time of ۲۴ h and an operating temperature of ۳۲±۲ °C. Results showed that at ۵ g/L NaCl, the removal efficiencies of total chemical oxygen demand (CODt) and soluble chemical oxygen demand (CODs) were ۸۹.۳۹±۰.۰۰% and ۹۱.۸۹±۰.۶۵%, respectively, while color removal reached ۷۵.۴±۲.۲۸%, and biogas production rate was ۶.۳±۰.۳ L/d. Increasing salinity to ۲۰ g/L caused a decline in the MLVSS/MLSS ratio to ۰.۵۶, with CODt removal dropping to ۸۰.۴۹±۰.۳۲%. However, under these conditions, CODs removal efficiency remained unaffected (۹۴.۰±۰.۶۵%) and color removal efficiency and biogas production rate increased to ۸۴.۹۲±۰.۵۰% and ۷.۳±۰.۱ L/d, respectively. At the highest salinity of ۳۵ g/L, the MLVSS/MLSS ratio as well as CODt removal efficiency decreased further to ۰.۵۰ and ۵۷.۴۴±۰.۴۰%, respectively, whereas CODs removal efficiency remained relatively constant (۹۱.۵۱±۰.۴%). Biogas production rate dropped to ۵.۹±۰.۱ L/d, but color removal continued to rise, reaching ۸۷.۰۳±۱.۴۵%. These findings indicate that elevated salinity primarily inhibits methanogenic activity and leads to increased CODt due to cell lysis, while CODs remains largely unaffected. Moreover, cell lysis enhances biomass surface exposure, thereby promoting the physical removal of dye even under high salinity stress.

Keywords:

Anaerobic Wastewater Treatment , Textile Dyeing Wastewater , Up-flow Anaerobic Sludge Blanket Reactor , Salinity , Biogas