Reducing generation of biogenic hydrogen sulfide in sugar wastewaters

Abstract

In the manufacture of beet sugar, improving discharge water quality is a key objective for effective reuse of water for irrigation purposes. Problems associated with the discharge water includes generation of odors from biogenic hydrogen sulfide and ammonia, sludge buildup in ponds used for water retention and treatment due to precipitation of metal sulfides, and inadequate water discharge quality, in terms of total nitrogen, ammonia, fecal coliforms count, and phosphorus concentrations. Methods used to improve water quality have focused mainly on either adding chemicals to minimize odor generation, which cause toxicity issues in the discharge water or to add external aeration, which increases dissolved oxygen concentration in the water and improves aerobic treatment rates, but increases power expenditure and hence operating cost. In this paper, use of a biocatalyst solution containing enzymes has been tested in the laboratory and at field-scale. Enzymes function by inhibiting the growth of sulfate reducing bacteria (SRBs) which are responsible for biogenic hydrogen sulfide generation. Experimental and field results show that the enzyme solution tested, ZymeOut, virtually eliminates the generation of biogenic hydrogen sulfide and introduces no water toxicity, unlike conventional biocides. It also reduces the occurrence of biofilms, improves water clarity in lagoons and significantly reduces metal sulfide sludge precipitation.