Abstract
An evaluation of 5 and 8 pH-point titrimetric methods for determining volatile fatty acids (VFAs) was conducted, and the results were compared for tap water and primary treated wastewater at the laboratory scale. These techniques were then applied to full-scale primary sludge hydrolysate, and the results were compared with those obtained via gas chromatography.The comparison showed that the VFA concentrations measured with the two titration methods were higher than those obtained via gas chromatography, differing by 9 and 13 mg COD∙ℓ-1 for the hydrolysate and by 5 and 6 mg COD∙ℓ-1 for the ordinary primary settler effluent. No improvement in the accuracy of VFA concentration measurement was obtained from applying the 8 pH-point titration method instead of the 5 point method. The 5 pH-point method was successfully applied to determine VFA in full-scale primary sludge hydrolysate and was shown to be equally efficient to the methods that are routinely-used for this purpose.Keywords: Multiple pH-point titration, volatile fatty acids, wastewater, full-scale, primary sludge hydrolysis
Highlights
At wastewater treatment plants (WWTPs), the addition of various external carbon sources to serve as energy source for the denitrifying heterotrophic bacteria, such as ethanol, methanol and acetic acid (AcOH), is used for extended nitrogen removal (Henze et al, 2002)
The titration experiments were conducted to determine the recovery of known volatile fatty acids (VFAs) concentrations in tap water and primary wastewater
Compromised and shown to depend more on the nature of the sample’s matrix than does TITRA5. Both titrimetric methods showed high reliability and accuracy when used to analyse standard VFA solutions prepared with tap water or wastewater matrices, TITRA5 showed higher credibility than did TITRA8 when analysing hydrolysate samples, enabling the practical applicability of TITRA5 for the daily laboratory routine of WWTPs in monitoring primary sludge hydrolysis
Summary
At wastewater treatment plants (WWTPs), the addition of various external carbon sources to serve as energy source for the denitrifying heterotrophic bacteria, such as ethanol, methanol and acetic acid (AcOH), is used for extended nitrogen removal (Henze et al, 2002). The multiple pH-point titrimetric technique has attracted considerable attention, mainly because of its robustness, wide range of application, cost efficiency and user-friendliness (Moosbrugger et al, 1993; Buchauer, 1998; Lahav et al, 2000, 2002, 2004; Feitkenhauer et al, 2002; Vanrolleghem et al, 2003) Another pronounced advantage of titrations is the potential of simultaneously measuring alkalinity and VFA concentrations. The precision and applicability of the two selected methods were assessed by measuring the VFA content in hydrolysate obtained from a full-scale hydrolysis of primary sludge. The results from the latter experiment were compared with those obtained via gas chromatography (GC) analysis. The VFA results obtained from the TITRA5 and TITRA8 protocols were converted into COD units to facilitate comparison with the GC results
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