Wastewater recycling in Antarctica: Performance assessment of an advanced water treatment plant in removing trace organic chemicals.

The Australian Antarctic Division (AAD) operates Australia's Davis Station in the Antarctic. In 2005, Davis Station's wastewater treatment plant failed and since then untreated, macerated effluent has been discharged to the ocean. The objectives of this study were to determine whether an advanced water treatment plant (AWTP) commissioned by the AAD and featuring a multi-barrier process involving ozonation, ceramic microfiltration, biologically activated carbon filtration, reverse osmosis, ultraviolet disinfection and chlorination was capable of producing potable water and a non-toxic brine concentrate that can be discharged with minimal environmental impact. The AWTP was tested using water from a municipal wastewater treatment plant in Tasmania, Australia. We used spot water and passive sampling combined with two multi-residue chromatographic-mass spectrometric methods and a range of recombinant receptor-reporter gene bioassays to screen trace organic chemicals (TrOCs), toxicity and receptor activity in the Feed water, in the environmental discharge (reject water), and product water from the AWTP for six months during 2014-15, and then again for three months in 2016. Across the two surveys we unambiguously detected 109 different TrOCs in the feed water, 39 chemicals in the reject water, and 34 chemicals in the product water. Sample toxicity and receptor activity in the feed water samples was almost totally removed in both testing periods, confirming that the vast majority of the receptor active TrOCs were removed by the treatment process. All the NDMA entering the AWTP in the feed and/or produced in the plant (typically < 50 ng/L), was retained into the reject water with no NDMA observed in the product water. In conclusion, the AWTP was working to design, and releases of TrOCs at the concentrations observed in this study would be unlikely cause adverse effects on populations of aquatic organisms in the receiving environment or users of the potable product water.

Scaling filtration time initial dependencies of wastewater sludges.

The filtration time, t(f), during constant pressure dead-end filtration testing of wastewater sludge is dependant on the initial height, h(0), and the initial solids concentration, phi(0). The theoretical dependencies of these initial conditions are explored: t(f) varies with h(0)(2) and cphi(0)(2), where c is a material dependant parameter that is also dependant on phi(0) and the applied pressure. Empirical values for c relative to a given phi(0) are determined from phenomenological filtration theory to give a qualitative scaling method to compare the filtration behaviour of highly compressible materials under differing initial conditions. The method is validated using filtration testing of municipal wastewater sludge. This new scaling method is applied to the filtration results of a range of different wastewater sludges, additives and treatments to illustrate its application for plant comparisons, polyelectrolyte comparisons, dose optimisation of polyelectrolyte and ferric chloride and combinations thereof, and the effects of two physicochemical treatments.

The fundamentals of wastewater sludge characterization and filtration.

The move to greater emphasis on the disposal of wastewater sludges through routes such as incineration and the added cost of landfill emplacement puts high demands on dewatering technology for these sludges. A clear problem in this area is that wastewater sludges are slow and difficult to dewater and traditional methods of laboratory measurement for prediction of filtration performance are inadequate. This is highly problematic for the design and operational optimisation of centrifuges, filters and settling devices in the wastewater industry. The behaviour is assessed as being due to non-linear behaviour of these sludges which negates the use of classical approaches. These approaches utilise the linear portion of a t versus V2 plot (where t is the time to filtration and V is the specific filtrate volume) to extract a simple Darcian permeability. Without this parameter, a predictive capacity for dewatering using current theory is negated.

Complete characterisation of thermally treated sludges.

As disposal options for sludges become more difficult to find and more expensive to operate, those relying on some form of thermal treatment are becoming more commercially attractive. The incentive, especially for more heavily populated countries, is the production of treated solids suitable for beneficial application to land. It is the level of treatment required to achieve this cost effectively which has been the focus of much of the research in this field. There are now several commercially available plants designed to thermally treat sludges and many have been in full scale operation for a number of years. One of the auxiliary claims often made by proponents of such treatments, is that the resultant sludges are more amenable to dewatering and therefore easier and cheaper to handle. In this work we have used a novel filtration rig to obtain complete sets of filtration data for different sludges. Historically sludge characterisation has been achieved by measurement of an empirical Capillary Suction Time (CST) parameter, however with the new filtration apparatus it is now possible to obtain fundamental sludge characteristics across a wide range of volume fractions in hours not days. We have applied this technology to characterise different sludge samples before and after thermal treatment under different sets of operating conditions (pH, temperature and pressure) to simulate some of the commercially available thermal treatment technologies. We have also examined the effects of various chemical oxidants (hydrogen peroxide and Fenton's reagent) used as pretreatments to the thermal process and attempted to compare their cost efficiencies. The results show that the physical structure of the sludge is irreversibly altered by decreasing the pH or heating to temperatures in excess of 150 degrees C in a way which significantly enhances the dewaterability of the material. The treated sludge not only has a higher permeability but also has a higher final per cent solids (often in the autothermal region). In contrast the amounts of chemical additives used in pretreatment to achieve similar effects are cost prohibitive.

Prediction of the dewatering of selected inorganic sludges.

There are a number of laboratory techniques traditionally used in the characterisation of sludges for the prediction of the efficient operation of dewatering processes such as centrifugation and filtration. In industry, capillary suction time and specific resistance to filtration measurements are common. Whilst useful in predicting trends, they do not assist in the design and optimisation of devices from first principles. Recent work in our laboratories has developed a technique for the fast measurement of the permeability and compressibility of sludge. This information, when coupled with first-principle models is useful for the prediction of the performance of solid-liquid separation devices. The work has shown that a single volume fraction dependent parameter, namely the solids diffusivity, calculated from permeability and compressibility, is able to fully characterise the dewaterability of sludge. This allows different sludges to be compared in an unequivocal fashion. Data will be presented for a range of sludges from different sources showing vastly different dewatering properties. The dewaterability of the different sludges is easily compared and the true role of flocculants in dewatering is highlighted.