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Biodegradation in water and sediment: simulation tests

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According to REACH Annex IX a simulation test on degradation in surface water is not necessary if the compound is readily biodegradable. Formaldehyde is classified to be readily degradable.

The removal of formaldehyde in biological sewage treatment plants was studied in a lab-scale activated sludge unit (Eiroa et al., 2005). The test is comparable to OECD 303 A (Confirmatory Test). During the operation period of 160 days the influent concentrations were increased stepwise from 26 to 3168 mg/L. Removal of formaldehyde was calculated based on substance-specific and COD measurements. During the operation period, formaldehyde concentrations increased slightly when the influent concentrations were increased. Based on substance-specific measurements, high removal efficiencies of around 99.5% were maintained at all influent concentrations. However, ca. 18% of influent COD was present in effluent. The relative high COD content in the effluent can be explained by disproportionation of formaldehyde to methanol and formic acid. It was shown in previous experiments that degradation of methanol and formic acid began after exhaustion of formaldehyde in the medium. In the unit, ammonium was removed around 99.9%, indicating that there was no inhibition of nitrification. The hydraulic retention time (2.4 days) in the test unit is above the value (6 hours) proposed by the OECD guideline 303 A. Therefore, the resulting removal rate is assumed to probably overestimate removal in biological treatment plants.

In conclusion, in the wwtp simulation tests formaldehyde was removed to 99.5% under aerobic conditions.