Ecotoxicological risk assessment of hospital wastewater: a proposed framework for raw effluents discharging into urban sewer network.

In hospitals a large variety of substances are in use for medical purposes such as diagnostics and research. After application, diagnostic agents, disinfectants and excreted non-metabolized pharmaceuticals by patients, reach the wastewater. This form of elimination may generate risks for aquatic organisms. The aim of this study was to present: (i) the steps of an ecological risk assessment and management framework related to hospital effluents evacuating into wastewater treatment plant (WWTP) without preliminary treatment; and (ii) the results of its application on wastewater from an infectious and tropical diseases department of a hospital of a large city in southeastern France. The characterization of effects has been made under two assumptions, which were related to: (a) the effects of hospital wastewater on biological treatment process of WWTP, particularly on the community of organisms in charge of the biological decomposition of the organic matter; (b) the effects on aquatic organisms. COD and BOD5 have been measured for studying global organic pollution. Assessment of halogenated organic compounds was made using halogenated organic compounds absorbable on activated carbon (AOX) concentrations. Heavy metals (arsenic, cadmium, chrome, copper, mercury, nickel, lead and zinc) were measured. Low most probable number (MPP) for faecal coliforms has been considered as an indirect detection of antibiotics and disinfectants presence. For toxicity assessment, bioluminescence assay using Vibrio fischeri photobacteria, 72-h EC50 algae growth Pseudokirchneriella subcapitata and 24-h EC50 on Daphnia magna were used. The scenario allows to a semi-quantitative risk characterization. It needs to be improved on some aspects, particularly those linked to: long term toxicity assessment on target organisms (bioaccumulation of pollutants, genotoxicity, etc.); ecotoxicological interactions between pharmaceuticals, disinfectants used both in diagnostics and in cleaning of surfaces, and detergents used in cleaning of surfaces; the interactions into the sewage network, between the hospital effluents and the aquatic ecosystem.

Kinetics of acetate, propionate and butyrate removal in the treatment of a semi-synthetic landfill leachate on anaerobic filter.

The kinetics of acetate, propionate, and butyrate removal was studied in conditions of leachate treatment in a plug flow anaerobic fixed-film reactor made of a sequence of seven perfectly mixed compartments. An original experimental procedure was followed under sequential feeding conditions so as to maintain the Bacteriol biomass in a quasi-steady state all along the study. With an appropriate computer program based on the least squares method, the apparent kinetic parameters of VFA removal were calculated within concentration ranges below the levels of salt inhibition. The models proposed are based on simple theoretical considerations. For acetate and n-butyrate removal, the best fits were given by the Michaelis-Menten equation with respectively: V(m) (spec) = 0.49 +/- 0.06 g CH(3) COOH g(-1) biomass h(-1)and 0.18 +/- 0.02 g n-CH(3)CH(2)CH(2)COOH g(-1) biomass h(-1) and: K(s) = 21.2 +/- 0.9 g CH(3)COOH L(-1) liquid phase and 8.2 +/- 0.9 g n-CH(3)CH(2)CH(2)COOH L(-1) liquid phase, Iso-butyrate was produced during n-butyrate catabolism and the apparent removal rate of (n + iso)-butyrate considered as a whole was also described by the Michaelis-Menten equation with V(m) (spec) = 0.14 +/- 0.02 g(n + iso)-butyrate g(-1) biomass h(-1) and K(s) = 9.0 +/- 1.2 g (n + iso) butyrate L(-1) liquid phase. On the other hand in the case of propionate, the best fit was obtained with a first-order equation with K(spec) = (0.88 +/- 0.05) 10(-2) L liquid phase g(-1) biomass h(-1). These constants were subsequently used to predict the removal of mixtures of the three major VFAs under study, at various feed concentrations. Three sets of concentrations were tested, and the experimental data were compared to the simulations. This study, together with other experimental observations previously reported, tends to show that under sequential feeding conditions the classical assumption of butyrate beta-oxidation should be rejected. Butyrate seems to be anaerobically decarboxylated, but propionate thus formed inside the biofilm is degraded as soon as its formation proceeds. It was therefore considered that butyrate degradation produces, through propionate intermediate, 1 mole acetate per mole butyrate removed. When propionate or butyrate concentrations were high, the same phenomenon was noted, to a much lower extent, for the degradation of acetate formed inside the biofilm.