Studies of the toxicological effect of aluminium compounds on the activated sludge biocenosis in aeration tanks

Summary

To provide for eliminating phosphorus from wastewater in the process of tertiary treatment in order to inhibit the eutrophication of the receiving water bodies iron- and alumunium containing chemical are used. At the wastewater treatment facilities operated by SUE «Vodokanal of St. Petersburg» chemical removal of phosphorus from wastewater was carried out with imported ferrous sulfate (III); beginning from 2012 domestically-produced aluminium sulfate has been used. Transfer to aluminium sulfate was supported with a series of experimental and research studies; one of them aiming at studying the toxic effect of aluminium and ferrous (III) salts on activated sludge in aeration tanks. The review of different assessments of the toxicity of aluminium compounds in relation to plants and animals in general is presented; the results of individual studies of the aluminium sulfate and ferrous (III) sulfate effect on the activated sludge biocenosis in aeration tanks are presented. During the analysis mixed liquor samples treated with different chemical dosages were fed with acetate ions and aerated for 18 hours under similar conditions; after that the sludge samples were subject to microscopic examination. The absence of any toxic effect of aluminium sulfate on the sludge biocenosis at the metal concentrations up to and including 64 mg/l was shown which exceeded the chemical dosages used in practice dozens of times. During the introduction of higher dosages of aluminium sulfate or ferrous sulfate the inhibition of aquatic life was caused by pH decrease; whereas at pH correction with alkali liquor no symptoms of the biocenosis inhibition was noticed. Further increase of chemical and alkali dosages up to 1000 mg/l as aluminium or iron caused the inhibition of aquatic life because of the total solids increase which is fatal for the fresh water biocenosis.

Key words

aeration tank , aluminium sulphate , aluminium , toxic effect , activated sludge resistance , resistance of indicator microorganisms of activated sludge