Simultaneous biological removal of phenol, sulfide, and nitrate using expanded granular sludge bed reactor

Biological removal of sulfide, nitrate, and phenol at loading rates of 600 g S/(m(3) day), 900 g N/(m(3) day), and 450 g C/(m(3) day), respectively, from synthetic wastewaters was achieved in an expanded granular sludge bed (EGSB) reactor, whose rates are much higher than literature works and are considered feasible for handling high-strength petrochemical wastewaters without dilution. Effects of C/S ratio (2-2.5:1) on EGSB performance were noted insignificantly. The strains Bacillus sp., Thauera sp., and Pseudomonas sp. were the heterotrophic denitrifiers and the strains Thiobacillus sp., Azoarcus sp., and Sulfurovum sp. were the autotrophic denitrifiers in the EGSB granules. The EGSB reactor experienced biological breakdown at loadings higher than 1200 g S/(m(3) day), 1800 g N/(m(3) day), and 900 g C/(m(3) day) by the following mechanism: high sulfide first inhibits heterotrophic denitrifies (Bacillus sp. and Pseudomonas sp.), thereby accumulating nitrite in the system; then, the accumulated nitrite inhibits autotrophic denitrifiers (Thiobacillus sp., Azoarcus sp., and Sulfurovum sp.) to complete breakdown of the system.