Anaerobic and Aerobic Treatability of High-Yield Sulphite Spent Liquor

Abstract

Abstract Several higher-yield sulphite pulp mills in Canada discharge untreated spent cooking liquor containing substantial amounts of dissolved organic pollutants. The Wastewater Technology Centre has conducted a study on the chemical characterization and biotreatability of spent liquor from a high-yield sulphite (HYS) and an ultra-high-yield sulphite (UHYS) pulping operation. Batch bioassays revealed a high degree of aerobic treatability, including filterable COD removals of 60-65% and 70–75% from HYS and UHYS waste liquor, respectively. Anaerobic treatment was found to be much less suitable as evidenced by severely inhibited methane production rates and impaired treatment efficiencies during batch serum bottle testing of 5-20% v/v spent liquor. Anaerobic bioassays over a 70-day incubation period with 5% HYS waste liquor produced relatively low filt-COD and filt-BOD5 removals of 30% and 75%, respectively. Even poorer performance results were observed at increased test concentrations. Although the degree of anaerobic treatment was somewhat better for the lower-strength UHYS liquor, a high level of dilution (i.e., 10-20 fold) was still required. The elevated concentrations of total sulphur and particularly sulphite-sulphur of 13.5 and 4.8 g/L respectively in HYS spent liquor, and of 3.6 and 1.3 g/ L in UHYS liquor, were apparently responsible for much of the toxic effects on the unacclimated anaerobic biomass.