Performance Characteristics of Airlift Pumps with Vortex Induced by Tangential Fluid Injection

The effect of the swirl component of air injection on the performance of an airlift pump was examined experimentally. An airlift pump is a device that pumps a liquid or slurry using only gas injection. In this study, the liquid used was water and the injected gas was air. The effect of the air swirl was determined by measuring the water discharge from an airlift pump with an air injection nozzle in which the air flow had both axial and tangential components and then repeating the tests with a nozzle with only axial injection. The induced water flow was measured using an orifice meter in the supply pipeline. Tests were run for air pressures ranging from 10 to 30 pounds per square inch, gauge (psig), at flow rates from 5 standard cubic feet per minute (scfm) up the maximum values attainable at the given pressure (usually in the range from 20 to 35 scfm). The nozzle with only axial injection produced a water flow rate that wasequivalent to or better than that induced by the nozzle with swirl. The swirl component of air injection was found to be detrimental to pump performance for all but the smallest air injection flow rate. Optimum efficiency was found for air injection pressures of 10 psig to 15 psig. In addition, the effect of using auxiliary tangential injection of water to create a swirl component in the riser before air injection on the overall capacity (i.e., flow rate) and efficiencyof the pump was examined. Auxiliary tangential water injection was found to have no beneficial effect on the pump capacity or performance in the present system.

Sudden Increase and Regrowth of Fecal Coliforms and Escherichia Coli in Wastewater Biosolids After High Solids Centrifugation

Treatment plants that operate either thermophilic or mesophilic anaerobic digesters with centrifugal dewatering processes have consistently observed densities of fecal coliform and Escherichia coli, both indicator bacteria, that decrease during digestion but then increase after dewatering and storage. The increases have been characterized as two separate phenomena to explain this observation: 1) “Sudden Increase,” or SI, which is defined as the increase that occurs immediately after dewatering and 2) “regrowth,” which is defined as an increase during storage of cake samples over a period of hours or days. The SI observation appears to be more prevalent with biosolids that are generated with thermophilic processes and dewatered by centrifugation. Both thermophilic and mesophilic digesters with centrifuge dewatering processes have observed the regrowth phenomena. This research hypothesizes that the SI phenomenon is due to the presence of viable nonculturable (VNC) bacteria that are reactivated during dewatering. In other words, the bacteria were always present but were not enumerated by standard culturing methods (SCM). Analysis of the E. coli density in thermally treated solids by SCMs and quantitative real-time polymerase chain reaction (qPCR) indicated that E. coli densities are often underestimated by SCM. When analyzed with qPCR, the E. coli density after digestion can be 4-5 orders of magnitude greater than the non-detect levels identified by SCMs, which supports the non-culturable hypothesis. The VNC state describes a condition where bacteria are alive but unable to sustain the metabolic process needed for cellular division. Supplements added to culturing media were investigated to determine if the resuscitation of VNC bacteria could be enhanced. The autoinducer molecules Nhexanoyl- L-Homoserine lactone (C6-HSL), 3-oxo-N-octanoyl-L-Homoserine lactone (3-oxo- C8-HSL), and norepinephrine were unable to induce the resuscitation of VNC E. coli. Additional sampling was performed to determine if autoinducer molecules, peroxides, or other as of yet unknown inhibitory agents and toxins could be removed from biosolids during SCM. Culture media supplemented with the peroxide degrading compounds catalase, α-ketoglutaric acid, and sodium pyruvate was unable to resuscitate non-culturable E. coli. The additions of bentonite and exponential growth phase E. coli cell-free supernatant to culturing media were also unable to increase the culturability of E. coli. To remove inhibitory agents and toxins, a cell washing technique was employed prior to performing SCM; however, this cell washing technique may have increased cellular stresses that inhibited resuscitation since cell densities decreased. A novel laboratory-scale dewatering process was also investigated to determine if the SI and regrowth phenomena observed in full-scale centrifugal dewatering could be mimicked in the laboratory using a lab shearing device. Fecal coliform and E. coli densities in laboratory prepared cake samples were observed to be an order of magnitude higher than full-scale dewatered cakes. Additionally, the laboratory-scale dewatering process was able to resuscitate fecal coliforms and E. coli in stored sludge such that the density increased by 4-5 orders of magnitude from nondetect values. Lastly, the addition of aluminum sulfate during centrifuge dewatering at a full-scale utility produced an increased regrowth of fecal coliforms and E. coli that was sustained for 5 days.