Evaluation of toxicity and estrogenicity in UASB - Treated municipal sewage

Abstract

This study was undertaken to assess the capacity of the upflow anaerobic sludge blanket (UASB) reactor, one of the most commonly used systems in Brazilian sewage treatment plants, to remove municipal sewage toxicity using different Danio rerio life stages (embryo, embryo-larval, larval, adult), and estrogenicity using in vitro (yeast Saccharomyces cerevisiae) and in vivo (vitellogenin induction in D. rerio) assays. Sensitivity of chronic fish assays were compared to the chronic Ceriodaphnia dubia assay. UASB-treated sewage met Brazilian legal limits for BOD and COD removals, but did not remove toxicity, and treated sewage remained extremely toxic to D. rerio larvae and C. dubia, and highly toxic to D. rerio embryos. The 4-day embryo assay had the same sensitivity as the adult acute toxicity assay, and could safely replace it, avoiding the need to sacrifice adult fish. No significant differences were identified in vitellogenin induction among organisms exposed to sewage or control. However, the in vitro test showed that anaerobic treatment increased sample estrogenicity from 27 to 40 ng equivalents of 17-β estradiol per liter, a result corroborated by the greater induction of vitellogenin in male fish exposed to 5% (2.73 μg/g) and 20% (2.12 μg/g) treated sewage compared to the same concentrations of raw sewage (0.174 μg/g at 5% and 0.188 μg/g at 20%). Thus, UASB reactor should be followed by post-treatment to reduce risks of sewage discharge to receiving waters.