Bacterial sulfide production from sulfate‐enriched spent distillery liquor. III.

Abstract Semicontinuous sulfide fermentation has been conducted with distillery spent liquor as the source of carbon employing a strain similar to Desulphovibrio rubentschikii . Mineral barites and gypsum have been used as the hydrogen acceptors during the studies. Results reveal that mineral barites can also react very favorably as hydrogen acceptors. Sulfates have been used both in powdered (200 mesh) and lumpy (1/4‐1/2 in. size) forms. When applied in lumpy form in a packed tower, both the mineral sulfates produced higher yields of sulfide compared to their corresponding finely pulverized states. Thus, under similar conditions, fermentation conducted with pulverized gypsum showed a yield of 450–550 p.p.m. hydrogen sulfide, whereas the yield was as high as 750–1025 p.p.m. when gypsum lumps were used as a packing. Corresponding figures with barites are 300 and 540 p.p.m., respectively. Continuous sulfide fermentation has also been conducted in a packed tower containing lumpy gypsum as the packing under total recirculation. Daily buildup of sulfide was observed to be as high as 180 mg./l. of fermenting medium. Appreciable reduction in COD of the effluent was observed during the above studies. Thus, with barites, per cent COD reduction values were 30–35, 45–50, 60–65, and 75–80 with retention periods of 10, 15, 25, and 35 days, respectively. With gypsum, per cent COD reduction was 50–70 with 10 days's residence time. The effects of the retention period on sulfide yield and volatile acid content were also studied. The longer the retention period, the higher is the sulfide yield and the lower the volatile acid content of the discharge becomes. Studies were also conducted to find the correct composition of volatile acids in the discharge, as well as the levels of their concentration during continuous feeding and discharge over a number of days. It has been observed that during 18 hr. of fermentation in a batch, volatile acid concentration increased from 6.76 m. to 15.01 mmoles per liter of medium of which 10 mmoles are acetic, 0.833 mmoles butyric, and 4.16 mmoles propionic acid. Studies on soluble and insoluble sulfate balance have also been made in a synthetic medium containing calcium acetate as the substrate. Unaccounted for sulfates were negligible and a deviation between the actual and calculated sulfide yield did not exceed 2%. It is also observed that, when fermentations are conducted in sulfate packed columns, the color of the effluent becomes paleyellow containing very little suspended and volatile matter compared to the deep‐black color of the emuent emerging from a ferrnenter fed with pulverized sulfates. This liquor contains 0.5271% soluble ash (computed as potash) and might be a good source of potash.