Information on the geoA and 2-MIB synthase genes involved in the biosynthesis of geosmin and 2-MIB is lacking. In this study, we analysed the geoA and 2-MIB synthase genes of the cyanobacterial isolates and environmental samples from water resources. In most isolates, the sequence similarities to those of already reported strains exceeded 99%, however in some isolates, sequence similarities were less than 90%. All geoA genes detected in the environmental samples affiliated with the geoA gene of Dolichospermum , showing geosmin producing Dolichospermum widespread in Japan. 2-MIB synthase genes detected from environmental samples affiliated with 2-MIB synthase genes of Pseudanabaena , Planktothricoides and Microcoleus , and were devided into 7 lineages in the phylogenetic tree. The development of a database of musty odor-causing substance synthase gene sequences will lead to the identification of the causative species and their habitats by analyzing the sequences in tap water source samples. This will be useful in predicting musty odor-causing substances and taking countermeasures in the future.

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In this study, we performed a nationwide questionnaire survey on incidents for water quality control caused by microorganisms and analyzed 1031 cases of incidents in 74 water suppliers in Japan during the fiscal years from 2012 to 2017, with comparing the cases from previous surveys. The annual mean cases of the incidents of taste and odor in this study increased compared with those in the previous surveys. Such incidents were reported in 34.5% of water purification plants in this study. In particular, the number of incidents of earthy and musty odors caused by Anabaena spp. increased compared with that in the previous survey. Major causative microorganisms for the incidents in coagulation-sedimentation, penetration, or clogging of filters were Bacillariophyceae (71%), picoplankton (33%), or Bacillariophyceae (84%), respectively, which were consistent with the results of previous surveys. The incidents in coagulation-sedimentation caused by fish eggs were also reported. In addition, the questionnaire in this study revealed that the water suppliers with at least one technical personnel in charge of microscopic examination have advantages in identifying the causative microorganisms for the earthy and musty odors.

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Pilot-scale experiments of ozone/biological activated carbon (BAC) process were conducted to reduce disinfection by-products and their precursors, especially trihalomethane formation potential (THM-FP). There were no organic indicators (ultraviolet absorbance (E260), fluorescence intensity, and total organic carbon (TOC)) that were related to the behavior of THM-FP in all treatment processes. Two indicators, E260 and fluorescence intensity, of water after coagulation and sedimentation were used to predict THM-FP after ozonation. It was shown that precursors of dichloroacetic acid and trichloroacetic acid could be controlled using chloroform as an indicator. The ozone consumption per TOC to reduce THM-FP sufficiently was about 0.6 to 1.0 mg/mg C. Bromate formation after ozonation was controlled by feedback control of 0.1 mg/L of dissolved ozone at the inlet of biological activated carbon treatment.

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