Table 1. Experimental conditions for all the batch reactors and control reactors in the batch test.

	pH	COD conc. (mg/L)	SO42− conc. (mg S/L)	Cr (VI) conc. (mg/L)	Biomass conc. (mg VSS/L)
Batch Reactor 1	6.0	150	75	50	488
Batch Reactor 2	7.0	150	75	50	472
Batch Reactor 3	8.0	150	75	50	466
Batch Reactor 4	9.0	150	75	50	484
Non-sludge reactors
Control Reactor 1	6.0	150	75	50	–
Control Reactor 2	7.0	150	75	50	–
Control Reactor 3	8.0	150	75	50	–
Control Reactor 4	9.0	150	75	50	–
Non-COD/sulfate reactors
Control Reactor 5	6.0	–	–	50	459
Control Reactor 6	7.0	–	–	50	441
Control Reactor 7	8.0	–	–	50	466
Control Reactor 8	9.0	–	–	50	447
Non-sulfate reactors
Control Reactor 9	6.0	150	–	50	494
Control Reactor 10	7.0	150	–	50	508
Control Reactor 11	8.0	150	–	50	482
Control Reactor 12	9.0	150	–	50	498
Non-Cr (VI) reactors
Control Reactor 13	6.0	150	75	–	462
Control Reactor 14	7.0	150	75	–	443
Control Reactor 15	8.0	150	75	–	452
Control Reactor 16	8.0	150	75	–	458