Management of sewage sludge is an issue for Industry. Hydrothermal processing can be used to hydrothermally treat different kinds of sewage sludge such as primary, activated, and digested sludge and convert them into value added products such as hydrochar, biooil, aqueous phase and gas. This process will also be trialled on alum sludge and food and organic garden waste (FOGO). PFAS (Per and polyfluoro alkyl substances), another major concern of the water industry will be trialled to see if co-hydrothermal treatment can potentially degrade this emerging compound. This research will also investigate the techno commercial viability assessment of co-hydrothermal process.

PhD Thesis underway by Kamrun Nahar.

The occurrence of per- and polyfluoroalkyl substances (PFAs) in various environmental media is of great concern due to their potential adverse effects on living organisms. This project aims to investigate the feasibility of natural-occurring foams in aeration tanks for removal of PFAs and other contaminants of emerging concern from sewage.

PhD Thesis underway by Angel Chyi En We.

This study examined seedling emergence and early development growth responses of Spinacia oleracea L. (spinach) in per and polyfluoroalkyl substances (PFAS) contaminated soil. Results show that low concentrations of PFAS contaminated soil (50 ng/kg) can affect plant biomass and growth in young plants. Results also indicate that further testing and research is needed, which should include other PFAS as well as with a greater diversity of plant species and PFAS concentration exposures, to better understand the potency of fluorinated chemicals to terrestrial plants destined for food consumption. This study serves in improving the understanding of the behaviour and fate of these fluorinated compounds in the terrestrial environment.

Honours Thesis completed by Stephanie Wallace Polley in June 2018.

Biosolids, the main by product from wastewater treatment plants, have a high potential in agricultural applications because they contain important plant nutrients and they can function as soil amendments. However, there are limitations to direct soil application of biosolids due to odour, pathogens, PFAS, micro-plastics, pharmaceuticals, and high heavy metal concentration present biosolids. This project proposes co-pyrolysis of biosolids with other waste types as a technique to overcome these limitations. In co-pyrolysis process, biosolids are mixed with other types of waste feedstocks and then are transformed thermochemically to biochar, pyro-oil, and pyro-gas in oxygen free atmosphere. This process is expected to overcome existing barriers in biosolids management and soil applications by transforming biosolids into high quality biochar with low heavy metal content and destroy PFAS components present in biosolids. In addition, co-pyrolysis also evidently improves qualities of oil and gas products due to the synergetic effects between the feedstock materials.

‘PFAS’ are a large class of chemical compounds, some of which can bioaccumulate or be toxic to humans and animals. Three PFAS: PFOS, PFOA and PFAS3; have been comprehensively investigated. An earlier study (WaterRA Project 2046) found PFAS in recycled wastewater and this raised concerns that crops irrigated with recycled water might lead to long-term chronic toxicity or bioaccumulation in soils. This research used existing datasets about PFOS, PFOA and PFAS3 to build a predictive conceptual model: the PFAS Exposure Model for Irrigation (PEMI). This was used to derive ‘Trigger Points for Investigation’(TPI); the levels of PFOS or PFOA or PFAS3 that, when measured in soil or recycled water, are high enough to cause concern and trigger investigation and action. Levels lower than the TPI’s are considered ‘safe’, and the PFAS3 TPI was higher than the median concentration measured in recycled wastewater from 17 Australian treatment plants (Project 2046). While these TPI are an excellent start to ongoing environmental and safety monitoring, the authors note that more data and research about plant uptake, animal transfer, degradation and leaching of additional PFASs will help validate and improve the PEMI.

There are more than 3000 per- and poly-fluroalkyl substances (PFAS). They have unique chemical properties that makes them ideal for incorporating into stain and water-resistant materials, and for metal-plating, firefighting and medical imaging, but there are concerns that PFAS are persistent and toxic. The Australian federal government updated the PFAS National Environment Plan in 2020 and provided an aquatic and marine ecological guideline value of 1900 ng/L for a common PFAS, ‘PFOA’. This is a concentration that will NOT harm 99% of the species in those habitats. The safe guideline for ‘PFOS’ in drinking water is 2000 ng/L. This research measured 21 types of PFAS in 19 Australian wastewater treatment plants (WWTPs) and found that the WW treatment processes transformed small (short-chain) PFAS into stable ‘PCFA’ forms, and that when the concentrations of 21 common PFAS’s were added together there were, on average, only 142 ng/L in treated WW effluent. Although these concentrations are much lower than safe guideline values, it was concluded that ongoing monitoring is required to further understand the risk that effluent discharge might pose to aquatic ecosystems.