Respirometric and titrimetric techniques for monitoring aerobic biodegradation of surfactant

Abstract

A titrimetric respirometer is an online biosensor that has been developed to elucidate the ongoing biological reactions which occur during a biodegradation processes. This paper describes the results of work with this biosensor to investigate the aerobic biodegradation of a surfactant, one of the emerging organic contaminants in wastewater which have complex chemical formulae and high molecular weights. Experiments used activated sludge based biosensors assembled with titrimetric respirometer. A series of batch experiments was conducted to observe the degradation process of the surfactant with varying initial concentrations and pH. The laboratory set-up had a respirometer to monitor the dissolved oxygen profile while the titrimetric unit kept the pH of the activated sludge sample at a constant value (7.8±0.03). The dissolved oxygen as well as the pH control data were logged over a period of time. Sodium dodecyl sulfate (SDS) was used as test anionic surfactant and compared to sodium acetate as a reference compound. The reference compound was chosen because it is readily biodegradable in nature. The activated sludge was acclimatized with SDS for 15 days before starting the current experimental program. Basic data interpretation was carried out for oxygen uptake rate (OUR) and proton production/consumption calculation. Respirometry showed that the biochemical oxygen demand increases proportionally with surfactant concentration and allowed the yield coefficient to be determined. The results confirm previous studies of the acetate biodegradation process where acid addition takes place. For the experiment with SDS, it is pointed out that protons are produced during the feast period of SDS biodegradation resulting in the need for base addition. The peak parameters such as peak slope, length and area of OUR describing the biodegradation rate, degradation time and short term BOD of SDS respectively were also studied to illustrate the effect of SDS concentration on respirographic characteristics recorded in the biosensor.