Figure 7

Contour and response surface plots of pH under different conditions. (a) Contour plot of temperature and pH affecting pH. (b) Response surface plot of temperature and pH affecting pH. (c) Contour plot of temperature and COD/SO42− affecting pH. (d) Response surface plot of temperature and COD/SO42− affecting sulfur pH. (e) Contour plot of pH and COD/SO42− affecting pH. (f) Contour plot of pH and COD/SO42− influenced pH response surface plots.