Saline adaptation of granules in mesophilic UASB reactors

We exposed mesophilic up-flow anaerobic sludge blanket (UASB) reactors to high concentrations of NaCl to elucidate the saline adaptation capacity of their granular sludge. We operated 10 lab-scale UASB reactors at 37 °C and added NaCl to the influent either abruptly or gradually. With abrupt addition, NaCl concentrations were increased from 0 g L⁻¹ to 20, 30, 35, 40, 45, or 50 g L⁻¹. With gradual addition, the NaCl concentrations were gradually increased from 0 to 64 g L⁻¹ or 0 to 40 g L⁻¹. We successfully saline-adapted the granules up to 32 g NaCl L⁻¹, while maintaining high reactor performance, suggesting that 32 g NaCl L⁻¹ is a practical level for system operation. In the UASB reactors gradually exposed to 32 g L⁻¹ NaCl, methane production decreased by only 13%. We also learned that combining abrupt and gradual salinity increases could shorten the adaptation period. Thus we were able to shorten the adaptation period to only 30 days by increasing the salinity abruptly to 20 g L⁻¹, followed by gradual adaptation to 30 g NaCl L⁻¹.