Development of water treatment technology for taste and odour removal in potable water

Abstract

The occurrence of taste and odour is one of the biggest problems faced in drinking water utilities. The geosmin and 2-methylisobornel (MIB) present in much surface water are thought to be the most common sources of taste and odour. They are responsible for two of the most frequently reported complaints, namely musty and earthy odours. Earthy/musty taste and odour problems related with geosmin and MIB are increasingly the focus of industry and academia, largely because both of the compounds are saturated cyclic tertiary alcohols and thus resistant to oxidation by conventional water treatment technology. Water treatment for tackling taste and odour problems alone can are generally considered not cost effective, however the paying consumer in countries with a reasonably high standard of living, expects to receive water that both tastes and smells good. Geosmin and MIB are not always sufficiently removed by conventional water treatment. The source of these and other compounds associated with taste and odour is the preliminary blue-green algae (cyanobacteria). Yantian reservoir was located in Dongguan city of China and has had taste and odour problems for many years, but the conventional treatment plant has proved ineffective in removing geosmin and MIB. The taste and odour problems seem to be increasing, especially during the early summer, extending well into late winter. In this research, water samples were collected from the Yantian reservoir of China. Levels of geosmin and MIB were determined. Geosmin and/or MIB producing species of cyanobacteria including Anabaena sp., Nostoc sp., Oscillatoria splendida, Oscillatoria cf. curviceps (LS184 and DVL902), Phormidium cf. inundatum (LP584), Oscillatoria Aplendida, Hyella Fontana, Phormidium sp. (LM494), Anabaena Scheremetievi Elenkin were also identified. This research study was divided into two stages. In the first stage, bench scale biofilters were set up to study the influence of biofilter carriers and the mechanisms of geosmin and MIB removal with synthetic water. Acclimation media was able to remove MIB and geosmin up to 20~89%, 11~40%, 16~62% for GAC, EC and sand media respectively. On the whole, the results of these experiments showed that biological filtration could be a method of geosmin and MIB removal. Additionally, these results showed the temperature impacts on the removal rate of both geosmin and MIB. Useful insights into the effects of media, empty bed contact time, ozone dosage and concentration of geosmin and MIB were also obtained. The use of design of experiment (DOE) also adopted in obtaining the best process parameters and parameter effect, sharply decreases the number of experiments from 81 to 9. In the second stage of the study, the biofilters with the best and worst process parameters were used to treat the surface water of the Yantian reservoir. The findings were in agreement with the biological degradation for synthetic water. Scaning Electron Microscope (SEM) and Microbial Identification Inc (MIDI) methods were used for the observation of the biofilm condition and determination of bacteria in the biofilm. Nine strains that existed in the biofilm had been identified; they were (i) Bacillus Cereus (ii) Pseudomonas-Aeruginosa, (iii) Salmonella-typhimunium-GC subgroup, (iv) Shigella-Flexneri, (v) Shigella-sonnei-GC subgroup B, (vi) Ewingella-americana, (vii) Morganella-morgarii, (viii) Serratia-plymuthica, (ix) Xenorhabdus-nematophila. During the last stage of study, the kinetic parameters of Bacillus Cereus, Pseudomonas-Aeruginosa and associated community were determined from the Monod model. The tastes and odour removal mechanism was demonstrated to be a feasible and economical alternative for water enterprises in tackling taste and odour problems. The results of this study have the potential to be used as a guide for the further improvement in design and operation of plant-scale taste and odour treatment.