The use of a microbubble dispersion to enhance a dissolved air flotation system in a wastewater treatment sludge media

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Virginia Tech

Colloidal gas aphrons (CGAs) are typically a 55 to 70% dispersion of 50 +/- 40 micron-sized air bubbles in water. Generation of CGAs has proceeded to allow continuous production of up to 80 liters per minute. Previous laboratory testing has demonstrated the effectiveness of CGA flotation for removing fine particulates, such as coal fines, food wastes, phosphate slimes, algae, as well as oils from contaminated solutions. This study involved comparing CGA flotation versus dissolved air flotation (DAF) in a wastewater treatment sludge media. Initially, laboratory tests were conducted to see if field testing was warranted, and to screen possible surfactant chemicals to be used in any such field testing. Three surfactants were tested individually; sodium dodecylbenzene sulfonate (NaDBS), alkyl dimethyl benzyl ammonium chloride (BTC-824), and cetyl pyridinium chloride (CPC). From the laboratory results and observations, it appeared that the CGA flotation tests using both NaDBS and CPC were more effective than DAF. Tests using BTC-824 were inconsistent due to bubble instability. Overall, the laboratory results and observations seemed encouraging, and field testing was initiated.

Next, four field tests were conducted at Pepper's Ferry Regional Wastewater Treatment Authority (PFRWTA) in which CGA flotation was used to try and enhance the performance of a DAF system. Tests were conducted by adding CGAs directly into the sludge influent line of PFRWTA's DAF system. Although CPC gave the best laboratory results, NaDBS was used in the field testing due to its availability and cost.

Results from all four field tests showed that a more concentrated effluent sludge was obtained when CGA flotation was used to enhance DAF. The field test results for the raffinates were inconclusive. Overall, the results from the field testing seem promising.

From these tests, CGA flotation appears to be an improvement over DAF in producing more concentrated effluent sludges when tested in a wastewater treatment sludge media. CGA flotation could enhance and/or possibly replace DAF in certain industrial applications.