Many environmental monitoring programmes require the determination of volatile organic compounds (VOCs) emitted from large areal sources including liquid surfaces. A study was carried out to compare existing sampling techniques. Both the isolation chamber method (static technique) and the wind tunnel method (dynamic technique) were examined. A review of the mechanisms suggested that static techniques would not be appropriate for determining emissions from liquid surfaces which result from gas phase controlled volatilisation processes. A portable wind tunnel developed at the University of New South Wales and an isolation chamber built to USEPA specification were used in an experimental study of emissions from aqueous liquid surfaces. An acetone solution was chosen to represent gas phase controlled volatilisation processes. Toluene and methyl ethyl ketone in aqueous solution were chosen, respectively to investigate (1) liquid phase controlled volatilisation processes, and (2) combined gas and liquid phase controlled volatilisation processes. It was found that the use of the isolation chamber method resulted in different degrees of underestimation of the emission rates for the above three compounds. The wind tunnel method is suitable for sampling all VOC emissions from areal sources.

Wind-tunnel systems are widely used for collecting odour emission samples from surface area sources. Consequently, a portable wind-tunnel system was developed at the University of New South Wales that was easy to handle and suitable for sampling from liquid surfaces. Development work was undertaken to ensure even air-flows above the emitting surface and to optimise air velocities to simulate real situations. However, recovery efficiencies for emissions have not previously been studied for wind-tunnel systems. A series of experiments was carried out for determining and improving the recovery rate of the wind-tunnel sampling system by using carbon monoxide as a tracer gas. It was observed by mass balance that carbon monoxide recovery rates were initially only 37% to 48% from a simulated surface area emission source. It was therefore apparent that further development work was required to improve recovery efficiencies. By analysing the aerodynamic character of air movement and CO transportation inside the wind-tunnel, it was determined that the apparent poor recoveries resulted from uneven mixing at the sample collection point. A number of modifications were made for the mixing chamber of the wind-tunnel system. A special sampling chamber extension and a sampling manifold with optimally distributed sampling orifices were developed for the wind-tunnel sampling system. The simulation experiments were repeated with the new sampling system. Over a series of experiments, the recovery efficiency of sampling was improved to 83-100% with an average of 90%, where the CO tracer gas was introduced at a single point and 92-102% with an average of 97%, where the CO tracer gas was introduced along a line transverse to the sweep air. The stability and accuracy of the new system were determined statistically and are reported.

This investigation was aimed at developing an acceptable technology for using secondary effluent as cooling water makeup for inland manufacturing industry in Australia. Approximate economic evaluations were made for a number of pretreatment alternatives and for internal treatment with chemical conditioning agents. Internal treatment with biocide dosing appeared to be the most promising option. A portable pilot plant scale cooling tower/heat exchanger unit was constructed. The unit incorporated an on-line, differential pressure biofilm monitor together with automated control and data acquisition systems. The pilot plant was installed on site at a sewage treatment plant near Sydney. It was demonstrated that the use of TSE for cooling water makeup is technically feasible. The rate of biofilm growth observed using chlorinated secondary effluent directly from the sewage treatment plant as makeup water was similar to the rate of biofilm growth observed when potable water was used and supplementary chemical treatment was not introduced in either case. Excellent control of biofilm growth was observed in subsequent experiments when supplementary additions of simple chlorine or bromine chloride treatment systems were carried out. The pilot plant was operated successfully at 5 cycles of concentration without any other supplementary treatment being required.

Odour impact from a sewage treatment plant has been predicted using a Gausian plume atmospheric model (Ausplume). A wind tunnel system was used to determine the odour emission from processing units. An improved technique for odour emission rate modelling is proposed to take account of wind speeds and atmospheric stability classes. A new technique is proposed to define odour impact criteria for sewage treatment plants. The dispersion model was calibrated using two years of odour complaint data. An odour concentration of 23 OU/m3 as a one hour averaged 99.5th percentile was found to be appropriate to minimise adverse community impacts, assuming lognormal human nose response to odours and a “zero complaints” community objective. The proposed method can also be used to develop odour impact criteria for other industries.

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