Laboratory-scale sequencing batch reactors (SBR) were used to examine the effects of adding dosage and ways of adding betaine on nitrogen and phosphorus removal from simulated pickled vegetables wastewater under two different concentrations of salt. The activated sludge was pre-acclimated in a salt environment prior to the experiment. Adding 0.5–2.0 mM betaine to the synthetic wastewater, all the levels were found to be effective at improving the ammonium nitrogen (NH4+-N) removal with increased salt concentrations from 8 to 16 g/L, in which 1.0 mM betaine was found to be the most effective. Rapid increase of salt concentration, however, showed to have a more pronounced negative effect on total phosphorus (TP) removal. Nevertheless, betaine-added enhanced TP removal was superior to that of NH4+-N in high salt content conditions compared with the absence of betaine. Both NH4+-N and TP removal rate were not significantly influenced by the ways of betaine-adding. Interestingly, the dynamic process on phosphate removal in a single cycle of SBR operation, was showed to have anomalous aerobic phosphorus desorption and anaerobic phosphorus absorption, the former could be caused by insufficiency of biodegradable organic matters and/or longer aeration time, and the latter may be attributed to the function of denitrifying phosphorus-accumulating bacteria in the sludge. As a result, a moderate betaine dosage can obtain a sufficient improvement effect for biological nitrogen and phosphorus removal even under high salt stress.

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