CO₂ Evolution Test (Sturm Test)

Principle

The „CO₂ Evolution Test“ is a method to determine the “ready” ultimate biodegradability of non-volatile chemicals in aqueous media.

Abstract

The amount of CO₂ produced by the biodegradation of substances is determined. The test item as sole source of carbon is incubated together with activated sludge of a municipal sewage treatment plant (30 mg/L) and a mineral media for 28 days. The test vessels are aerated with CO₂-free air. The resulting CO₂ is absorbed in NaOH in successively connected absorption bottles as NaHCO₃/Na₂CO₃. The amount of CO₂ bound in NaOH is determined as DIC (dissolved inorganic carbon) and is a direct measure for the mineralised carbon of the test substance, after subtraction of the blank values.

Criteria

A degradation extent of > 60% ThOD within 28 days and within a "10-days window" after the end of the lag-phase is defined as criterion for classifying a particular test substance as "readily” biodegradable.

Test substance properties

The CO₂ evolution test is applicable for soluble and insoluble substances as well as nitrogen-containing materials without disturbances caused by oxygen-consuming nitrification processes.