以c-di-GMP評估生物膜之生成潛力並探討MBR操作參數對生物膜積垢之影響

Abstract

Water is regarded as the origin of life and one of the most important resources on the earth. In Taiwan, owing to difficult water acquirement and unlimited water usage which caused by topographic limitation and unsuitable water price, respectively. Such higher fresh water stress would generate more wastewater treating and recycling requirement. In typical, the construction cost and area requirement of traditional wastewater treatment plant is high, because it needs secondary sedimentation unit to complete solid-liquid separation. Furthermore, several types of wastewater are not treatable through traditional wastewater treatment process. Therefore, we pay much attention to a noval technique membrane bioreactor(MBR). MBR has a lot of advantages such as high treating efficiency, low treating cost and comprehensive wastewater treatment application. However, the major obstacle of MBR is membrane fouling. And biofilm which formed by microorganism on the membrane also contribute to biofouling level. Recently, people found a special second messenger called bis-(3'-5')-cyclic diguanosine monophosphate(cyclic-di-GMP) in eubacteria. Cyclic-di-GMP can control “life style” conversion in microorganism and correlate to biofilm forming ability. Therefore, we measure membrane fouling and cyclic-di-GMP level in cell under different condition(food to microorganism ratio–F/M and dissolved oxygen–DO) to evaluate biofilm forming propensity in MBR. Under different F/M, suspended biomass growth would increase while F/M increases from 0.2 day-1 to 10 day-1. Besides, cyclic-di-GMP concentration, biofilm content, sCOD removal rate and Rp would also increase while F/M increases in most situations. Although microorganism would not generate large amount of cyclic-di-GMP and biofilm under starvation(F/M = 0.2 day-1), but total resistance become highest at the end of all experiments. It probably due to conversion of biofilm components or structure. Making it more resistant to permeate and causing severe fouling under substrate stress. Under different DO, cyclic-di-GMP concentration, biofilm content and total resistance would increase when DO is unlimited. Because the enzyme MorA of Pseudomonas putida can control flagella synthesize and mediate cyclic-di-GMP concentration by GGDEF and EAL domain(Choy et al., 2004). Therefore, we suppose that Pseudomonas putida would decrease flagella synthesis and increase cyclic-di-GMP concentration to enhance biofilm forming ability for retaining at DO sufficient environment. Cyclic-di-GMP concentration is correlated to biofilm content and fouling level under different DO but not F/M. Because Pseudomonas putida would response to environmental stresses in different level. It seems that it is more sensitive to DO than F/M. Moreover, because Rc and Rp also contribute to total resistance. It makes prediction of biofouling more uncertain.