Anaerobic biodegradability of organic compounds in digested sludge

This Test Guideline describes a screening method for the evaluation of potential anaerobic biodegradability of organic chemicals under specific conditions. Washed digested sludge, containing low (<10 mg/L) concentrations of inorganic carbon (IC), is diluted about ten-fold to a total solids concentration of 1 g/L to 3 g/L and incubated at 35 °C ±2°C in sealed vessels with the test substance at 20 to 100 mg C/L for up to 60 days. The activity of the sludge is measured by running parallel blank controls. To check the procedure a reference substance (phenol, sodium benzoate, polyethylene glycol 400) is tested in parallel. At least triplicate test vessels for the test substance, blank controls, reference substance, inhibition controls and pressure control chambers are prepared. The increase in headspace pressure in the vessels resulting from the production of carbon dioxide and methane is measured. The inorganic carbon is measured at the end of the test. The amount of carbon (inorganic plus methane) resulting from the biodegradation of the test substance, is calculated from the net gas production and net IC formation in the liquid phase, in excess of blank control values. The extent of biodegradation is calculated from total IC and methane-C produced as a percentage of the measured or calculated amount of carbon added as test substance.