Assessing technological feasibility for wastewater reclamation based on early life stage toxicity of Japanese medaka (Oryzias latipes)

Abstract

To assess technological feasibility for reuse of secondary effluent from sewage treatment plant, the effects of raw sewage (RW) water sample and effluents samples from secondary treatment (SS), ultrafiltration treatment after SS (SS-UF), micro-filtration treatment after SS (SS-MF), activated carbon column adsorption after SS (SS-AC), as well as reverse osmosis treatment after SS-UF (SS-UF-RO) were assessed using embryo larval development of Japanese medaka (Oryzias latipes). Samples of RW and effluents from secondary treatment were taken from Beixiaohe sewage treatment plant (STP) in Beijing, China. Newly fertilized embryos (<5-h-old) were exposed to these water samples at different concentration gradients (including 100, 50, 25, 12.5, 6.25% effluent concentrations) in a 24-h static renewal system at 25 ± 1 °C for 15 day post-hatch. The assay considered both acute toxicity using endpoint of 96-h larval morality and chronic toxicity using endpoints including the time to hatch, hatching success, deformity, growth rate, swim-up failure, accumulative mortality and sex ratio. In the 96-h larval mortality test, 96h LC50 for RW, and effluents from SS, SS-UF and SS-MF on medaka larval were 33.7, 62.9, 60.0, 64.4% concentrations, respectively. However, no acute toxicity was observed for effluents from SS-AC and SS-UF-RO. No embryos exposed to 100% RW effluent hatched. Most of the endpoints were alternated when the fish was exposed to effluents from SS, RW, SS-UF, SS-MF that were 50–100% concentration, except those of growth and time to hatch (P < 0.05). The sex ratio of the larvae was alternated when exposed to 25% effluents from RW and 50% effluents from SS, SS-UF and SS-MF. Sex ratios in treatments with effluents from SS-AC and SS-UF-RO were not significantly different with the controls. However, embryos lesions and swim-up failure were still significantly different from the controls for 100% effluent from SS-AC (P < 0.05) and swim-up failure and larval growth could be observed for 100% effluent from SS-UF-RO (P < 0.05). We conclude that acute toxicity was present in the sewage water and secondary treatment could remove only part of the toxicants. As advanced treatment technologies, membrane technologies could not further remove trace toxicants and endocrine disruptors. Activated carbon adsorption and reverse osmosis were effective in removing most of the toxicants, but discharge without dilution could still manifest potential ecological risk on receiving aquatic biology. We conclude that activated carbon adsorption and reverse osmosis are relatively feasible technologies for reuse of secondary effluents from sewage treatment plant.