Enhanced biological phosphorus removal

Abstract

PolyHydroxyAlkanoates (PHA) and Poly-β-HydroxyButyrate (PHB) in particular has become a compound which is routinely investigated in wastewater research. The PHB analysis method is only recently applied to activated sludge samples where PHA contents might be relatively low. This urges the need to investigate the reproducibility of the gas chromatographic method for PHB analysis. This was evaluated in a Round-Robin test in 5 European laboratories with samples from lab-scale and full-scale enhanced biological phosphorus removal systems. The basic method was direct solvent extraction of lyophilised cells, depolymerisation (hydrolysis) of the polymer and alkylation of the alkanoates. All steps take place in one tube with the necessary incubation time generally being 2 hours. The concentration of the (propyl)ester is then analysed by gas chromatography. Each lab used slightly modified methods. It was observed that the use of an internal standard improved the reproducibility of the method, that using dichloro(m)ethane as solvent instead of chloroform improves the GC analysis and that shaking the reaction tubes during heating improves the esterification reaction. It was shown that the standard deviation of measurements in each lab and the reproducibility between the labs was very good. Experimental results obtained by different laboratories using this analysis method can be compared. Sludge samples with PHB contents varying between 0.3 and 22.5 mg PHB/mg sludge were analysed. The gas chromatographic method allows for PHV, PH2MB and PH2MV analysis as well. The gas chromatographic analysis of PHA is important for kinetic modelling of EBPR processes. Moreover, with the publication of the Activated Sludge Model No3 and the general acceptance that storage polymers are of prime importance for non polyphosphate accumulating organisms as well, analysis of internal storage components becomes a prerequisite for modelling the activated sludge processes.