APPLICATION OF FUZZY THEORY TO THE PERFORMANCE EVALUATION OF FINE BUBBLE DIFFUSED AERATION SYSTEMS IN A SHALLOW OPEN CHANNEL

When fine bubble diffused aerations run in shallow open channels, the performances of aeration systems are influenced by such factors: the relationship between the airflow rate of the aeration system and the water-flow rate of open channels, the layout and initial fine bubble diameters of the aeration systems, the sizes, the water depth and the flow state of the channels. And the following 6 parameters can be represented as the key indices of these factors: the air-water ratio (expressed as lambda) which is the ratio of air demand to the polluted water volume, the initial diameter of fine air bubble entering the aeration channels (d(0)), the layout parameters of the aeration systems (LPA), the ratio of the channels' length to its width (L/W), the water depth (H(c)) and the Reynolds number (Re) of the channels. To evaluate the performances of aeration systems, a new aeration performance index (API) is proposed. The relationship of API and the above 6 indices is established based on fuzzy theory, and weighted sums of the similarity degrees derived from the extensions of fuzzy c-means (FCM) are used to construct API. The performances of 4 different fine bubble diffused aeration systems evaluated by API are compared with those by conventional characteristic criteria, and their evaluation conclusions are consistent with each other. Moreover, API is demonstrated to be more remarkable for the evaluation of the performances of the aeration systems than the other characteristic criteria.