(140d) Pressure Cycles of Ozonation and Aeration for Activated Sludge Solubilization

Authors: 
Hong, A., University of Utah
Cheng, C., University of Utah


Waste activated sludge from wastewater treatment plants is a universal problem. Traditional disposal methods such as composting, land application, and incineration post environmental and cost issues. Anaerobic digestion has been most common for excess waste sludge; however, retention time is often extensive because of kinetic limitation in the hydrolysis step. Ongoing researches have shown considerable benefits of solubilizing sludge prior to anaerobic digestion in solids reduction as well as biogas formation.

We tested a new sludge solubilization technique to obtain increased yields of soluble cell materials. The new technique incorporates rapid, successive compression and decompression cycles using ozone and air only. During compression, steepened gas concentration gradient across the cell membrane drives dissolved gas into the cell, increasing the gas concentration within the cell. When the pressure is rapidly reduced, gas formation and expansion occur within the cell, causing the formation of gas pockets in the cell (as transport across the membrane is slower than decompression). Gas accumulation in the cells during repeated pressure cycles leads to eventual rupture of the cells. Microscopic pictures of activated sludge were taken prior to pressure cycles, after 10 pressure cycles with air reaching 1000 kPa, and after 10 pressure cycles with 0.06% O3 reaching 1000 kPa. Prior to treatment, an abundance of filamentous bacteria and floc along with discernable microbes was present as in typical activated sludge. Pressure cycles with air show similar but diluted biomass with ciliated stalks broken into smaller pieces, while pressure cycles with ozone reveal little biomass but disperse nondescript flocs and seemingly gluey patches in the liquid. The application of pressure cycles resulted in disintegration of activated sludge. In its final form, this paper will present solubilization results under different rupturing conditions as characterized by TS, TSS, TDS, VDS, VSS, sCOD, tCOD, BOD, as well as confirmatory identifications of DNA and protein in the slurry before and after treatment.