Title page for ETD etd-09112007-110256

Type of Document Master's Thesis
Author Sibler, Sabine
Author's Email Address sibler@vt.edu
URN etd-09112007-110256
Title Enhanced Microbial Activity and Energy Conservation through Pneumatic Mixing in Sludge Systems
Degree Master of Engineering
Department Environmental Engineering
Advisory Committee
Advisor Name Title
Boardman, Gregory D. Committee Chair
Little, John C. Committee Member
Novak, John T. Committee Member
  • microbial activity
  • Activated sludge
  • aeration
  • mixing
  • energy consumption
Date of Defense 2007-08-28
Availability unrestricted
The primary goal of this study was to evaluate a new device and system, designed to optimize the performance of standard low pressure air diffusers in two types of aerated systems (activated sludge and aerobic sludge digestion) and to decrease overall energy consumption.

Aerated treatment systems are very important in the treatment of wastewaters and management of sludges. The activated sludge process is widely used to treat wastewater from both industrial and municipal sources. However, they are costly to operate because oxygen is marginally soluble in water and standard low pressure (8 psig) diffusers provide marginal mixing and minimum retention.

The newly patented device is referred to as TotalMix and is a type of pneumatic mixing system. TotalMix introduces air under high pressure at regular fixed intervals. During the tests the frequency of air delivered, the pressure, and the period of pressured air delivery was varied manually or through feedback control to optimize oxygen transfer and the interaction with a regular aeration system. Various chemical parameters, most importantly dissolved oxygen, were measured and compared to the new approach, using the TotalMix in combination with standard diffuser systems.

The new System was tested in different sized tanks (17,000 L and 380,000 L), different concentrations of total solids (TS), using different airflow rates and different diffusers (membrane fine bubble diffusers, ceramic fine bubble diffuser, and course bubble diffuser). The statistical evaluation of the experiments indicates an increase in oxygen transfer rate with a concomitant decrease in energy consumption at low airflow rates.

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