Biological treatment of organic sulfate-rich wastewaters

Abstract

Many wastewaters have a high sulfate and organic carbon content, such as those generated by industrial processes that use sulfuric acid (fermentation industry), or sulfate-rich feedstocks (seafood processing industry). The use of sulfurous compounds less oxidized than sulfate in industrial processes, such as sulfide (tanneries, Kraft pulping), sulfite (sulfite pulping), or dithionite (pulp bleaching) also results in the generation of sulfate-rich wastewaters. Besides these organic wastewaters, some sulfate-rich effluents hardly contain any organic matter. These are generated during the leaching of sulfur-rich wastes (mine spoils and landfills, see Chapter 15) or during the scrubbing of sulfur-containing off-gases (see Lagas, 2000). Specific aspects of the treatment of these inorganic wastewaters are presented in Chapter 7. Aqueous sulfate emissions are generally considered safe. In humans, sulfate concentrations exceeding 500 mg L −1 can have laxative effects (US EPA, 1990), but the Drinking Water Standards of the U.S. Public Health Service proposed a maximum of 250 mg L −1 , based on aesthetic aspects. In the last decade, the water quality guidelines have included sulfur compounds in the protection of freshwater aquatic life. The Province of British Columbia (Canada), for instance, has set the maximum sulfate concentration between 128-429 mg L −1 (BC ME, 2013), depending on the water hardness (Elphick et al., 2011) to ensure aquatic life protection. This range was established based on toxicity assays with different