Water Recycling in Australia: February 2009

I’ve just returned from an interesting field trip at the Old Bar sewage treatment plant (STP) not far from Taree on the mid-coast of NSW.

One of our research group’s PhD students, ‘Nhat’ is investigating the fate of some antibiotic drugs during biological sewage treatment processes. In doing so, he is comparing how well the drugs are removed during conventional activated sludge treatment with removal by an experimental membrane bioreactor.

Old Bar STP is operated by MidCoast Water, with whom we have an on-going research relationship. So in order to characterise the performance of the STP and simultaneously obtain some useful data for Nhat’s project, we decided to undertake a ‘diurnal investigation’ of the plant.

This means that we monitored the performance of the STP in removing a wide range of chemical contaminants (mainly pharmaceuticals, hormones and pesticides) over a 24-hour period. This can be a useful step in characterizing an STP since a number of factors can change over this diurnal period.

For example, the flow of water into the plant changes according to community sleeping habits. We see a peek flow around 7-8am when people are showering and another later in the evening for bath-time and dishwashing. We have also previously observed that the concentration (and the ‘load’) of pharmaceuticals in sewage changes over 24 hours, presumably as a consequence of factors such as when particular drugs are taken, the rate of metabolism and when people go to the toilet.

We collected samples from the influent to the STP every two hours and samples from the effluents of the activated sludge process and the membrane bioreactor every other hour. Since we were sampling in triplicate, this meant that we had to collect, filter and extract over 100 samples during the 24 hour period.

It will probably take a month to analyse the samples and process the data, so we won’t have any results until then. However, I took the opportunity to take some slightly unusual ‘sewage treatment plant by night’ photographs, which I thought I’d like to share... Who would have guessed that an STP could look so pretty by night!?