In spite of the significant advantages over aerobic processes, anaerobic processes are limitly used in industrial wastewater treatment as the bacteria system is very sensitive toxic or inhibitory substances present in some industrial wastewaters. As one of these toxic substances, sulfate is present in wastewater from various industries such as molasses, margarine, pulp and paper, and chemical industries.
To investigate the effects of industrial toxicants, several test methods for biochemical methane potential and anaerobic toxicity assays have been developed. However, most studies focused on the acetoclastic methanogens, and not much on the acidogenic bacteria. Therefore, it is necessary to improve the existing test method in order to understand the effect on acidogenic bacteria. And this study promotes understanding of toxic effect on whole anaerobic process and a new momentum for improving the stability of anaerobic process. Accordingly, anaerobic toxicity assay (ATA) was conducted by using phase separated anaerobes and mixed anaerobes for sulfate and sulfide effects. For inoculum in this ATA, two-phase and single-phase UASB systems were continuously operated for five months. Phase separation was successfully conducted by pH control in two-phase UASB system. 2,000mg/l of glucose, 1,000mg/l of acetate, and 1,000mg/l of glucose were used in the acidogenic phase, methanogenic phase, and mixed anaerobes, repectively.
The main objectives of this study were to investigate the effects of sulfate and sulfide on three types of anaerobes; acidogens, methanogens, and mixed anaerobes, and to compare the stability of single and two-phase systems added 100 $mgSO_4$-S/l.
Results of this study was obtained as follows;
1. Effects of sulfate and sulfide on acidogenic phase
Glucose utilization was first order reaction with 0.61$hr^{-1}$ of rate constant. Gas production and substrate utilization have a little effect with increasing sulfate 500 to 6,000 $mgSO_4$-S/l. However, substrate conversion to acetate might be retarded. The substrate utilization was retarded over 800 mgS/l and k value was decreased to 0.19 $hr^{-1}$ with increasing sulfide to 1,600 mgS/l. Methane production was severely inhibited in exess of 800 mgS/l. Glucose was completely utilized within only 9hrs and 40hrs in control and 1,600 mgS/l, respectively.
2. Effects of sulfate and sulfide on methanogenic phase
Methanogens were more sensitive than acidogens for sulfate and sulfide addition. Methane production was retarded in adding sulfate, but toxic effect on methnogens was not so high. Methane production was severly retared at 6, 000 $mgSO_4$-S/l and total methane production was inhibited 40% compare to control. Methane production has no inhibition up to 200 mgS/l, however, severly retarded in 400 mgS/l. Total methane production was inhibited 54% and almost 100% in 400 mgS/l and above 800 mgS/l, respectively
3. Effects of sulfate and sulfide on mixed anaerobes.
Effects of sulfate and sulfide on mixed anaerobes differed from that on phase separated anaerobes i.e. acidogens and methanogens. Methane production is slightly inhibited to 4,000 $mgSO_4$-S/l and 1,200 mgS/l. Total methane production was inhibited 32%, and 72% in 6,000 $mgSO_4$-S/l and 1,600 mgS/l, respectively
4. Continuous operation of two-phase and single-phase UASB process
In the results added 100 $mgSO_4$-S/l in two-phase and single-phase UASB processes, butyric acid was increased in acidogenic phase, and the effect of sulfate on methane production was reduced due to sulfate reduction in previous reactor. Meanwhile, the effluent COD increased in single-phase UASB process. Therefore, two-phase process is recommended to treating sulfate-rich industrial wastewater.
