Gas transfer is a key process in a wide range of water and wastewater treatment operations. It provides aeration in biological treatment processes such as the activated sludge process, transfers disinfectants during gas chlorination and ozonation, and strips volatile compounds in both water and wastewater treatment. This dissertation extends our understanding of three aspects of gas transfer in environmental processes. The first relates to the way aeration is quantified in a defensible way and describes the ASCE Standard for the Measurement of Oxygen Transfer in Clean Water and the ASCE Standard Guidelines for In-Process Oxygen Transfer Testing. Both have found widespread application and have reduced design variability and allowed operators and engineers to better evaluate process operation of existing treatment plants. The reasons for the Standard's success were described as well as the pitfalls of earlier approaches. Key new areas of the revised clean water Standard are highlighted and an analysis is presented that shows how the numerical treatment of the transfer data minimizes the impacts of gas-side oxygen depletion.

The second relates to mass-transfer characteristics and reaction kinetics of ozone in reclaimed water. Five columns were operated in series at an advanced reclamation plant, treating effluent from a trickling filter process. A mathematical model was developed to describe transfer rate and steady state ozone concentrations. Ozone decay was modeled accurately as a pseudo first-order reaction between ozone and ozone-demanding materials. A methodology is proposed and the observed decrease in oxygen transfer rate caused by contaminants in reclaimed water was only 10% to 15% compared to tap water.

The final area relates to the stripping of volatile organic compounds (VOCs) in wastewater treatment. Previous work, using oxygen as a tracer and combining the impacts of both liquid and gas films was extended to the high purity oxygen activated sludge process (HPO-AS). The model was sized to correspond to two large existing HPO-AS treatment plants. The psi factors, which are the ratio of volumetric mass-transfer coefficients of ozone/ VOCs to oxygen, were determined in each study for different types of aeration systems. The stripping of ten different VOCs was modeled and compared to stripping from conventional air activated sludge process. The results show that the covered aeration tanks can reduce stripping by more than 90%, depending on the specific VOC. If biodegradation is considered, the HPO-AS process degrades more than the conventional process due to the higher liquid phase concentrations that result because of reduced stripping. The increase in biodegradation depends on the VOCs degradability, but should increase to nearly 100% for highly volatile but biodegradable VOCs.