zahn-wellens test in industrial wastewater biodegradability assessment

Biodegradability of pollution contained in examined industrial wastewater was assessed according to methodology based on Zahn-Wellens (OECD 302B) test. The following kinds of wastewater were examined: - metal industry wastewater from aluminium pressure foundry; - wastewater from industrial waste treatment processes, such as: filtration waste, chemical reagents, coolants, water emulsions, oil wastes and other industrial wastes, galvanising waste treatment processes sludge. Samples COD value decrease in the subsequent days of the experiment proves that organic substances contained in the examined wastewater undergo gradual biodegradability in aerobic conditions. The highest biodegradability degree of aluminium pressure foundry wastewater equal 65.7% was noted during 28 day of the experiment. However, the minimum biodegradability degree equal 80% after 13 aeration days, which in Zahn-Wellens test allows to determine the examined substance to be biodegradable, has not been achieved. Meanwhile, Zahn-Wellens test conducted for wastewater from industrial waste treatment processes showed that in the day 14 of the process, high (87.1%) organic substance degradation degree, measured with COD value decrease, was achieved. Further aeration of the samples did not increase biodegradability, which equalled 87.9% after 28 days.