The application of powdered activated carbon for MIB and geosmin removal: predicting PAC doses in four raw waters

Blooms of blue-green algae in reservoirs often produce the musty-earthy taste and odour algal metabolites 2-methylisoborneol (MIB) and geosmin. MIB and geosmin are not removed by conventional water treatment and their presence in the distribution system, even at low ng L-1 levels, can result in consumer complaints. Powdered activated carbon (PAC) can effectively remove MIB and geosmin when the correct dose is applied. The homogeneous surface diffusion model (HSDM) was used to predict PAC doses required to reduce MIB and geosmin concentrations to below 10 ng L-1 at four water treatment plants in Adelaide, South Australia. In jar tests, undertaken under treatment plant conditions, the predicted doses were found to produce water of the desired quality in three of the four waters. The poor predictions found in the fourth water, which had a considerably higher turbidity, were attributed to the incorporation of PAC in a larger, denser floc, leading to a reduced effective contact time of the adsorbent. It was found that higher doses of PAC were required for both compounds to produce acceptable quality water when turbidities rose above 26 NTU.