Biological treatment of saline wastewater using a salt-tolerant microorganism

Abstract

Biological aerobic treatment of saline wastewater provides the material of this study. A salt-tolerant microorganism (Staphylococcus xylosus) was isolated from a vegetable pickled plant containing about 7.2% salt. Selection, identification and characterization of the microorganism were carried out. The isolated microorganism was used as inoculum for biodegradation. An activated sludge reactor operated in a fed-batch mode was used for the treatment of synthetic saline wastewater using three different microbial cultures namely: activated sludge (100%), a mixture of Staphylococcus supplement by activated sludge (1:1) and pure S. xylosus (100%) at different salt concentrations ranging from 0.5 to 3% NaCl. The results obtained showed that at low NaCl concentration (1%), the removal efficiency of chemical oxygen demand (COD) using different microbial cultures were almost the same (80–90%). However, increasing the NaCl concentration to 2% and using Staphylococcus-supplemented mixture by activated sludge and S. xylosus alone improved the treatment performance as indicated by COD removal rates which reached 91% and 93.4%, respectively, while the system performance started to deteriorate when activated bacterial culture was used alone (74%). Furthermore, the increase in NaCl concentration up to 3% and with the inclusion of Staphylococcus-supplemented mixture by activated sludge increased the COD removal to 93%, while the use of S. xylosus alone further improved the COD removal rate up to 94%. Also, the use of S. xylosus alone proved to be capable for biological treatment of a real case study of a vegetable pickled wastewater containing 7.2% salinity; the removal efficiency of COD reached 88% at this very high concentration of NaCl.