ABSTRACT
Using Chl a removal rate as index, a 28 kHz/900w ultrasonic cleaning machine was applied to testify algal removal by ultrasonic irradiation from raw water of a pool, where Microcystis aeruginosa colonies is absolutely dominated with temperature being over 20oC, and the irradiation lasted for 5 min. PAC was used as flocculant at the dose of 60 mgl-1, jar tests were done to investigate the Chl a removal by flocculation. The results showed that ultrasound raised the water temperature instantly but did not lead to a regular pH change pattern in all the treated samples. Ultrasound could remove more than 90% of Chl a from raw water with temperature over 31oC, but less than 20% of Chl a or even increased Chl a concentration in some samples with temperature lower than 31 oC. Compared with the algal removal effects by direct raw water flocculation with PAC, ultrasound did not enhance markedly the flocculation effects on algae removal, which was not in agreement with the findings reported. The reason might be due to morphology and characteristics of natural algae differed greatly from that of algae cultured in laboratory.
ABSTRACT
Due to its potential to form toxic nitrogenous disinfection byproducts (N-DBPs), dissolved organic nitrogen (DON) is considered as one of the most important parameters in wastewater treatment plants (WWTP). This study describes a comprehensive investigation of variations in DON levels in orbal oxidation ditches. The results showed that DON increased gradually from 0.71 to 1.14 mg l-1 along anaerobic zone, anoxic zone, aerobic zone 1 and aerobic 2. Molecular weight fractionation of DON in one anaerobic zone and one aerobic zone (aerobic zone 2) was performed. We found that the proportion of small molecular weight (<6 kDa) decreased and large molecular weight (>20 kDa) showed opposite trend. This variation may have been caused due to the release of different types of soluble microbial products (SMPs) during biological processes. These SMPs contained both tryptophan protein-like and aromatic protein-like substances, which were confirmed by three-dimensional excitation-emission matrix (EEM) analysis.