Development of a novel titration and off‐gas analysis (TOGA) sensor for study of biological processes in wastewater treatment systems

Abstract

The development of the new TOGA (titration and off-gas analysis) sensor for the detailed study of biological processes in wastewater treatment systems is outlined. The main innovation of the sensor is the amalgamation of titrimetric and off-gas measurement techniques. The resulting measured signals are: hydrogen ion production rate (HPR), oxygen transfer rate (OTR), nitrogen transfer rate (NTR), and carbon dioxide transfer rate (CTR). While OTR and NTR are applicable to aerobic and anoxic conditions, respectively, HPR and CTR are useful signals under all of the conditions found in biological wastewater treatment systems, namely, aerobic, anoxic and anaerobic. The sensor is therefore a powerful tool for studying the key biological processes under all these conditions. A major benefit from the integration of the titrimetric and off-gas analysis methods is that the acid/base buffering systems, in particular the bicarbonate system, are properly accounted for. Experimental data resulting from the TOGA sensor in aerobic, anoxic, and anaerobic conditions demonstrates the strength of the new sensor. In the aerobic environment, carbon oxidation (using acetate as an example carbon source) and nitrification are studied. Both the carbon and ammonia removal rates measured by the sensor compare very well with those obtained from off-line chemical analysis. Further, the aerobic acetate removal process is examined at a fundamental level using the metabolic pathway and stoichiometry established in the literature, whereby the rate of formation of storage products is identified. Under anoxic conditions, the denitrification process is monitored and, again, the measured rate of nitrogen gas transfer (NTR) matches well with the removal of the oxidised nitrogen compounds (measured chemically). In the anaerobic environment, the enhanced biological phosphorus process was investigated. In this case, the measured sensor signals (HPR and CTR) resulting from acetate uptake were used to determine the ratio of the rates of carbon dioxide production by competing groups of microorganisms, which consequently is a measure of the activity of these organisms. The sensor involves the use of expensive equipment such as a mass spectrometer and requires special gases to operate, thus incurring significant capital and operational costs. This makes the sensor more an advanced laboratory tool than an on-line sensor.

Anaerobic and aerobic metabolism of glycogen-accumulating organisms selected with propionate as the sole carbon source

“…Oxygen consumption and CO 2 production during a cycle were determined via the titration and off-gas analysis (TOGA) sensor with 2 h anaerobic and 3 h aerobic phases (Pratt et al, 2003).…”

“…A more detailed description of the TOGA and the determination of CO 2 production has been reported in the literature (Oehmen et al, 2005b;Pratt et al, 2003;Zeng et al, 2003b).…”

Sequential anode–cathode configuration improves cathodic oxygen reduction and effluent quality of microbial fuel cells

“…The Titration and Off-gas Analysis (TOGA) sensor system as developed by Pratt et al (2003) was used to determine the oxygen uptake rate (OUR) at the cathode of one of the reactors described above (MFC-1). The TOGA sensor allows mass balances to be determined on gas species by sending a gas with a known composition and flow rate through the reactor and monitoring the off-gas composition and flow rate with a mass spectrometer (Omnistar, Balzers AG, Liechtenstein).…”

Quantification of the effect of CO2 transfer on titrimetric techniques used for the study of biological wastewater treatment processes

“…An aerobic acetate oxidation experiment was carried out using a titrimetric and off-gas analysis (TOGA) sensor (see Pratt et al (2003) for details), which allowed measurement of both HPR and the CTR. Mixed liquor (3 ℓ) from a local domestic wastewater treatment plant was transferred to the TOGA reactor and aerated with a specialty gas, which was formed by mixing two gas streams: one stream with a flow rate of 140 mℓ·min -1 containing 95% O 2 , 0.48% CO 2 and 4.52%Ar, and the other stream, containing He only, had a flow rate of 675 mℓ·min -1…”

“…Invariably, the effect is a consequence of the action of acid-base buffering systems, whereby the biological consumption or production of components of these systems results in a change in hydrogen ion concentration (Pratt et al, 2003). For instance, when ammonia is consumed for biomass growth or oxidised during nitrification then dissociation of ammonium ions occurs, the result being an increase in hydrogen ion concentration; when volatile fatty acids (VFA) are produced/consumed during anaerobic digestion then acid dissociation/formation results in a change in hydrogen ion concentration ; and even when carbon dioxide is produced/ consumed during biological activity the carbonic acid concentration is altered, which again results in a change to the hydrogen ion concentration:…”