Water Research Australia Water for the wellbeing of all Australians February 2015 Page 1

Fact Sheet 2 of 2Biological fi ltrati on potenti al

The Biological Filtrati on Potenti al (BFP) test was developed during WaterRA project 1021 to answer the questi on -

Can my � lters achieve successful biological � ltration for tastes and odours and algal toxins?

Research over the past 10 years has shown that the fi lters at the Morgan Water Treatment Plant in South Australia functi on as biological fi lters for the taste and odour (T&O) compounds MIB and geosmin, and it was hypothesised that other rapid fi lters could functi on in a similar manner under the appropriate conditi ons. However, at the full scale it is diffi cult to determine what processes in the plant are contributi ng to the removal of metabolites unless systemati c investi gati ve sampling is undertaken during a T&O or cyanotoxin event. A laboratory-scale procedure was developed to determine the extent of biological degradati on occurring in existi ng fi lters in treatment plants, and the potenti al for a biofi lm to develop that may be capable of degrading the metabolites. The rati onale behind this test is that full scale treatment plant fi lters have the potenti al to act as an eff ecti ve barrier for cyanobacterial metabolites if:

• They support a thriving biofi lm

• There are degrading bacteria present in the infl uent to the fi lters

• There is evidence from laboratory tests that the fi lter medium supports a degrading biofi lm

The procedure developed in the project was based upon testi ng samples of fi ltrati on media and water from fi ve treatment plants in Australia, aimed at identi fying the potenti al biological removal at the full scale of T&Os (MIB

and geosmin) and cyanotoxins (mLR and mLA, STXeq and cylindrospermopsin). The results are available in Secti on 3.2 and Appendix II of the fi nal report.

The BFP test is undertaken in four parts: laboratory scale fi ltrati on, batch testi ng, microbiological analysis and parti cle size observati on (shown in Figure 1). A descripti on of these tests is given below. For additi onal methodology details please refer to the fi nal report Secti on 1.4.2 and Appendix I.

Laboratory scale � ltration

Two laboratory columns are run in parallel, spiked with a range of metabolites. One column holds the fi lter medium as sampled (non-sterile) and the other holds a sterilised sample of the fi lter medium. The test is undertaken over a period of 12 days during which the inlet and outlet concentrati ons are monitored. From this test the removal to be expected from physical processes (such as volati lisati on, adsorpti on) is determined from the removal by the sterile media sample, and any biological removal is calculated from the diff erence in removal between the sterile and non-sterile samples.

Batch experiments

Two batch reactors containing infl uent water to the full-scale fi lters are run in parallel, spiked with a range of metabolites. One reactor is the water as sampled (non-sterile) and the other is sterilised. The concentrati on of the metabolites is monitored over a period of 15 days and any diff erence in the

Laboratory Scale Filter Column Testing

• Ability of full scale filters to biologically remove a range of cyanobacterial metabolites

Batch Testing

• Existence of degrading organisms in the inlet water to the filters and thus the potential to develop a biofilm capable of degrading the metabolites

Biofilm Characterisation and biological activity quantification

•Health / extent of biofilm, presence / absence of organisms capable of degrading the metabolites

• 16S rRNA gene abundance

• Presence of MlrA gene required

Particle size observation

•Surface area available for biofilm development

Figure 1: BFP test

Water Research Australia Water for the wellbeing of all Australians February 2015 Page 2

concentrati on between the sterile and non-sterile samples is att ributed to biological degradati on.

Microbiological analysis

Samples of the fi lter medium are analysed using two geneti c approaches: 16S rRNA gene abundance and presence of MlrA gene. DNA is extracted from the fi lter media using a commercially available kit (PowerSoil DNA Isolati on Kit, MO BIO Laboratories, USA). Each DNA extracti on is then screened for the abundance of the 16S rRNA gene fragment by using the primer set for qPCR amplifi cati on. Results of this test provide informati on about the total populati on of micro-organisms present in the fi lter media. The extracted DNA is also screened for a specifi c gene involved in microcysti n degradati on, mlrA, using a qPCR assay. The presence of this gene indicates the presence of potenti al microcysti n-degrading bacteria in the fi lter biofi lm.

Particle size observation

Dried fi lter media is photographed beside a 1 mm graduated scale to esti mate and compare parti cle sizes. The size of the parti cle has been shown to have an eff ect on the biomass, and potenti ally the biological fi ltrati on potenti al. A smaller parti cle has a larger surface area, and therefore can potenti ally sustain a higher biomass than the same volume of medium of a larger size. A comparison of sand media is shown in Figure 2 below.

Summary

This standardised testi ng procedure can give a good indicati on of whether existi ng fi lters can functi on in biological mode for metabolite removal, to provide an additi onal low cost barrier within the conventi onal drinking water treatment process.

In the absence of disinfecti on prior to fi ltrati on all fi lter media will sustain a biofi lm. The ability of the biofi lm to remove cyanobacterial metabolites will depend on:

• The number and the compositi on of the colonising bacteria, which in turn depends on

• The enti re biomass in the fi lter (which is dependent on the surface area available for sustaining a biofi lm), and

• The presence of degrading micro-organisms in the infl uent to the fi lter that can remain viable and thrive in a biofi lm.

From these tests, the conditi ons required for the establishment and maintenance of a degrading biofi lm may be established at a water treatment plant.

Reference: Sawade E, Ho L, Hoefel D, Newcombe G (2015) Implementati on of biological fi ltrati on for the treatment of cyanobacterial metabolites. Final report, project 1021.

Figure 2: Sand media particle size comparison (1mm graduated scale)