Ozonation of drinking waters containing algae sometimes has a beneficial effect on the process of coagulation. It is hypothesized that the extracellular organic matter (EOM) from the algae affects the flocculation process. The effects on algal particle stability and flocculation due to ozonation and the role of EOM were investigated. Four species of algae were cultivated and EOM from the algae extracted. Scanning electron micrographs (SEMs) of the algae indicated little cell lysing for ozone doses of 3 mg/L or less. Extensive cell wall alteration was observed. Lysis of algae cells was prominent at 8 mg/L ozone. Ozonation decreased the algae volume concentrations and cell sizes. Cyclotella and Scenedesmus produced ten times as much EOM per unit cell number than Chlorella. The EOM of Cyclotella and Scenedesmus was also of higher molecular size than that of Chlorella. Increasing the ozone dose to extracted EOM and alginic acid, a model EOM compound, resulted in decreasing molecular size, colloid charge and increasing hydrophilicity and functional group charge. Bench scale jar tests and flocculation kinetic experiments were performed. Ozonation was not effective in decreasing the polymer dose required to coagulate the algae. However, ozonation improved overall removals of Scenedesmus, Cyclotella and Synura. Ozonation also increased the flocculation rate of Scenedesmus and Cyclotella, but had a detrimental effect on the rate for Chlorella. Increasing calcium (up to 30 mg/L as CaCO$\sb3$) and ozone dosage increased the flocculation rate of Scenedesmus. Natural waters spiked with Cyclotella and Synura showed an increased flocculation rate upon ozonation.

The development of high rate anaerobic processes has reached a point where there is a need for better monitoring and control strategies. The general objective of this research was to evaluate the potential of headspace gas monitoring and control of fixed-film anaerobic digesters. Laboratory-scale fixed-film anaerobic digesters treating a synthetic soluble carbohydrate waste were used. Trace gases, hydrogen and carbon monoxide, and final gases, methane and carbon dioxide, were monitored on-line. The effects of liquid recirculation on the rate of gas transfer from the generation site to the headspace of the reactor were evaluated. It was found that liquid recirculation rates do not affect mass transport rates significantly. Gas transport was primarily taking place by rising bubbles. Methane and carbon dioxide were transported from the bubbles to the surrounding liquid, whereas hydrogen was transported from the liquid to the bubbles. The rate of substrate uptake by the biofilm was significantly affected by liquid recirculation rates. The responses of trace gases to toxic stress by cadmium and formaldehyde were evaluated. Trace gases proved to be sensitive indicators of toxic stress. Comparison with previous studies revealed that fixed-film digesters were several times more resistant to toxicity than suspended-growth digesters. Adaptation to formaldehyde was fast and degradation of the compound was consistently observed. On-line control of effluent COD concentration using headspace parameters was possible when changes in influent strength were imposed to the system. A new parameter for digester monitoring was proposed in this study. The new parameter was named the methanogenic activity index, MAI. The MAI provides a simple criterion to determine when the reactor is reaching its maximum loading rate and also, provides a clear signal of the occurrence of toxicity events in the process.

Dissolved air flotation (DAF) is an attractive solid/liquid separation process for highly colored, low turbidity water supplies. Low density floc is produced when these waters are coagulated, therefore DAF may be more effective than conventional gravity settling (CGS). Communities required to filter their supplies should consider DAF as an alternative pretreatment prior to filtration. Although DAF is a promising alternative to CGS, no rational basis has been developed for selection, design and operation of DAF facilities. The research objectives were: (1) to develop a fundamental basis for the application of DAF to water treatment, (2) to determine via experiment the key variables which affect DAF performance for the removal of clay turbidity and natural organic matter (NOM), and (3) to compare DAF to CGS. A conceptual model was developed based on colloidal stability and particle deposition and used to identify the variables which affect DAF. The variables which included pH, coagulant type and dose, temperature, DOC and clay concentrations, flocculation time, DAF detention time, and bubble concentration were studied using synthetic waters. Synthetic waters were used to compare DAF to CGS. Synthetic waters were prepared from extracted aquatic fulvic acid and research grade montmorillonite clay--their use allowed water quality variables to be carefully controlled. Synthetic water results were then verified using two natural waters. Modelling predicted that particle stability and size, bubble size and rise rate, bubble volume concentration, and detention time would affect DAF performance. Experiments indicated particles must be coagulated for successful flotation. Temperature and flocculation time affected DAF performance in experiments using alum. It is hypothesized that the effects of cold temperature on DAF performance are due to changes in coagulation mechanism and the physical and chemical stability of the particles as it relates to charge and bound water at the surface. In addition, bubble volume affected DAF performance for high DOC waters and waters containing clay. Comparisons of DAF to CGS indicated that the DOC, organic halide precursors, and dissolved aluminum after treatment were comparable for both. However, DAF produced significantly lower turbidities than CGS, particularly at colder temperatures.