When the bulking was caused not only by filamentous bulking, but also by other reasons such as dispersed microorganisms, the addition of the surfactant could not work out perfectly. In this case, adding the inorganic powder to the bulking sludge resulted in an overall increase in density and thereby an increase in the settling velocity. It was proved that the addition of the inorganic powder after lysing filamentous bacteria by the nonionic surfactant were efficient to solve compound bulking in the activated sludge process.

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The submerged type membrane bioreactor has been tried to treat wastewater containing formaldehyde which is currently used as disinfectant and preservative in medical facilities. The concentration of formaldehyde in the wastewater was set at 0, 50, 100, 250, 500, 1000 mg/l respectively. The treatment processes of total organic carbon (TOC) and formaldehyde and the growth process of microbes were observed. The experimental results showed that filamentous microbes grew dominantly and formaldehyde could be treated well by those microbes when the concentration was under 250 mg/l. It was also shown that the reactor could be operated well in spite of dominant growing of filamentous microbes. When formaldehyde concentration was over 500 mg/l, the growth of microbes was much inhibited by formaldehyde, and the treatment characteristics was found to be quite different from that when formaldehyde concentration was under 250 mg/l.

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