The growth of sulfate reducing bacteria (SRB) and filamentous sulfur bacteria was monitored on a laboratory scale in activated sludge reactors using acetate and peptone as the artificial wastewater. When the artificial wastewater contained acetate and peptone, filamentous bacteria increased in the sludge and the SVI values increased. There was a good correlation between sulfate reducing activity and sulfur oxidation activity in the produced sludge. The microbial community change of filamentous sulfur bacteria and sulfate reducing bacteria was analyzed using the fluorescent in situ hybridization (FISH) method. The tendency for the growth of filamentous sulfur bacteria Thiothrix eikelboomii following the growth of SRB was observed. The percentage of SRB385- hybridized cells and DNMA657-hybridized cells found in the total cell area increased from 2-3% to 7-10% when the filamentous bulking occurred.

Fluoride-containing wastewater is discharged from various industrial sites, including semiconductor, plating, and metal-treatment plants. To remove the fluoride, we treated wastewater with dicalcium phosphate dihydrate (DCPD, CaHPO 4 Á2H 2 O) to form fluorapatite [Ca 10 (PO 4 ) 6 F 2 ] crystals. We investigated the fluoride removal efficiency and the properties of the resulting sludge. For comparison, we also treated wastewater using conventional aluminum coprecipitation. The DCPD used in this study was a by-product of the gelatin industry. Nanoscale precursor particles were induced on the DCPD by treatment with warm water. After treatment of fluoridecontaining wastewater in batch experiments, the amount, particle size distribution, settleability, and filterability of the resulting sludge were measured to assess the usability of DCPD. We found that the amount of chemical additives required for the DCPD method was less than that for the conventional method. Additionally, the amount of sludge produced using the DCPD method was small and the final fluoride concentration was below 5 mg L -1 . In settleability tests, the sludge produced by the DCPD method was precipitated within 10 min. In filterability tests, most DCPD sludge was separated within 5 min. The settleability and filterability of sludge from the DCPD method were better than those of the conventional method. The release of fluoride from the DCPD sludge was below the levels stipulated by Japanese soil pollution regulations. Consequently, the sludge was considered unlikely to cause soil pollution, thereby facilitating landfill management. We concluded that DCPD can be used effectively to treat fluoride-containing wastewater and that the resulting sludge is unlikely to cause environmental damage.

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