Past HRD students
Influence of biosolids processing on the production of odorous emissions at wastewater treatment plants
Supervisors : Prof Richard M Stuetz, Dr Juan Pablo Alvarez-Gaitan, Stephen Moore
Project summary: Odours from wastewater treatment facilities can cause nuisance impacts in the community and erode public acceptance, while odorous emissions from biosolids can limit opportunities for their beneficial reuse via land application. The aim of this research was to understand how odour emissions throughout wastewater treatment plants are affected by the configuration and operation of biosolids processing. Odour emissions can be more effectively managed if reasons for the presence of different types of odorants and their sensorial impacts are known. Odorants in emissions throughout the biosolids processing at eight wastewater treatment plants were quantified using methods specifically targeting volatile sulfur compounds (VSCs), which are thought to be key odorants in wastewater treatment. In addition, a range of volatile organic compounds (VOCs) and their sensorial properties were studied using gas chromatography coupled with an odour detection port (GC-MS/O). Intra and inter site variations in emissions were compared to the different biosolids processing operations over the eight sites. VSCs such as hydrogen sulfide, methyl mercaptan and dimethyl sulfide were identified as dominant odorants due to their high concentrations and low odour detection thresholds. In addition, certain VOCs such as p-cresol, trimethylamine and volatile fatty acids were detected at sensorially perceptible levels. Anaerobic digestion and dewatering were studied to determine their influence on nuisance emissions from the biosolids product. Temporal variations in biosolids emissions were studied over an eight week period at one WWTP showing significant variations in biosolids iron, aluminium and sulfur content which appeared to be related to certain emissions. Optimisation of a full scale dewatering centrifuge showed weir plate height and feed flow affected emissions of ammonia and dimethyl sulfide as the biosolids aged. GC-MS/O analysis was used to identify odorants based on their sensorial properties; which highlighted the range of human variability in odour perception. While models were produced for the prediction of odour concentration based on odorants, limitations to this approach were identified. Alternatively, the odorants identified throughout the eight sites formed the basis of biosolids processing Odour Wheels. The use of Odour Wheels links odour perception to odorants and process conditions, which can assist onsite odour management.
Foul Air Contaminant Removal in Sewer Odour Control Systems
Supervisors : Prof Richard M Stuetz, Ian Evanson
Project summary: Odour control systems in wastewater collection systems are typically designed to remove hydrogen sulfide (H2S); however other compounds in sewer related foul air also lead to odour complaints. Methyl mercaptan and dimethyl sulfide are rarely investigated for performance in these treatment systems despite being key odorants. Volatile organic compounds readily occur and rarely contribute substantially to odour impact, but could affect the removal of other more odorous compounds. The most common odour control systems are biologically based (biofilters or biotrickling filters) or adsorption based (predominantly activated carbon). Samples on the inlet and outlet of 10 activated carbon systems, 5 biofilters and 3 biotrickling filters across Sydney, Melbourne and Perth in Australia were taken approximately every month for 18 months. Samples were analysed for a wide range of volatile organic and sulfurous compounds as well as H2S. The collected data were filtered for warm and non-warm periods, wet weather, and for those where data points were greater than three times the standard deviation over the average (known as ‘spikes’). Performance oftreatment systems were analysed under these conditions. An analysis of the most common volatile organic and sulfurous compounds on the inlet samples found that there was no clear relationship between any compounds, meaning that when sampling sewer foul air, all key odorants needed to be tested. All treatment system types perform well at H2S removal. Activated carbon systems exhibited the poorest and most variable treatment of non-H2S based compounds, particularly halogenated volatile organics; however treatment of most compounds improved during spike conditions. Biofilters generally showed the most stable and greatest removal of non-H2S based compounds; however treatment deteriorated during spike conditions. In selecting an odour treatment technology, the concentration and variability of contaminants, treatment required and the space available, allow the most efficient technology selection to be made. Two stage processes are generally required for high level treatments whilst single stages are appropriate for lower treatments. Biofilters are generally preferred as the first (or only) stage, with biotrickling filters used where space is constrained. Activated carbon is suitable for low load scenarios or as a polishing filter.
Analysis of methods for estimating the emission rate of odorous compounds from passive liquid surfaces
Supervisors : Prof Richard M Stuetz, Dr Victoria Timchenko, Dr Jane Santos, Dr Eric Sivret
Project summary: The determination of the emission rate of odorous compounds from passive liquid surfaces is critical for the study and management of the environmental impacts associated with odour emissions from wastewater treatment plants (WWTPs). This research analysed two methods widely employed for estimating the emission rate of odorous compounds from such surfaces, namely, predictive emission models and direct sampling with a flux hood. Several theoretical and empirical models for the gas-side (kG) and liquid-side (kL) mass transfer coefficients in passive surfaces in WWTPs were evaluated against experimental data. The analysis of the compiled data set led to the development of an alternate approach for estimating kL which resulted in improved performance, particularly for longer fetches. Since the friction velocity (u*) is a critical input variable for the modelling of emissions, this work also evaluated different parametrisations of u* against available wind friction and wave data measured at wind-wave tanks with liquid surfaces of the same scale as WWTP units. For the first time, the most frequently used u* parametrisation was verified against representative data for WWTPs. Furthermore, new, alternative correlations were derived and combined in an approach that described the u* data set more accurately and in more detail, incorporating the size of the tanks together with the wind speed in the parametrisation of u*. A sensitivity analysis was conducted, in order to understand how different emission models are affected by the use of different u* parametrisations. The mass transfer of compounds inside the US EPA flux hood (one of the enclosure devices most commonly employed for the direct measurement of emissions) was studied by means of experiments that assessed kG and kL in the microenvironment created by the flux hood and the effects of concentration build-up in the hood`s headspace. The mass transfer of gas phase-dominated compounds inside the US EPA flux hood was found equivalent to conditions of very low wind speeds. A procedure was presented to scale the emission rates of these compounds to conditions of higher winds, by combining the application of emission models and the flux hood measurements.
The effect of arduous odours on the community
Supervisors : Prof Richard M Stuetz, Dr Richard Stevenson
Project summary: Environmental malodour remains a major source of complaints from communities. This factor is likely to increase, as the urban sprawl steadily encroaches into odour emitting industries. Within Australia, the efficacy of wastewater treatment and biosolids application are been undermined by community barriers due to malodour and its associated annoyance. This thesis is a study of the ways in which malodours and community satisfaction are understood within the context of wastewater treatment and biosolids. This involved a multiple-step research path which has incrementally provided information necessary to produce research and community interaction tools. This research path has centred on six wastewater treatment plants (WWTPs) that have provided a diverse set of industry-community interactions. The multiple-step research path has involved review of current literature, complaint management analysis, improving ecological validity of gas chromatography-mass spectrometry/olfactory (GC-MS/O), community and industry surveys, qualitative research for plant managers and land owners, before culminating in the application of online tool for dynamic community engagement. Foremost, a Literature Review assessing the effectiveness of odour and community assessment techniques within the context of community satisfaction guided the research plan. Complaint management procedures have been scrutinised with comparisons to odour report requirements as well as counterparts from other countries. We have also broadened methodologies for GC-MS/O in order to improve outcomes with community members who would not otherwise be represented. Community surveys at three community sites assessed the variation of response between WWTPs of high and low complaint levels, and have defined contributing factors of community satisfaction that have hitherto been disparate within research. We have also explored the under-researched area of industry culture through the use of surveys and plant manager interviews; this has revealed variations in industry attitudes and communicative relationships. These research landmarks have characterised gaps within industry-community engagement; namely establishing common language, appropriate inter-industry communication, appreciating community variance, as well as the adoption of techniques capable of defining malodour events. This thesis contributes both tools for community engagement as well as furthers research on the effect of malodours on communities.
Quantifying poultry litter conditions and relationships with odour emissions
Supervisors : Prof Richard M Stuetz, Patrick Blackall
Project summary: Litter conditions are managed during poultry rearing to provide a comfortable environment for the chickens and reduce the potential of odour impact on surrounding communities. This study aimed to identify and quantify the properties of poultry litter in Australian meat chicken sheds that influence odour formation and emissions. Litter conditions were evaluated in terms of litter moisture content, pH, water activity and oxygen concentration. Litter samples collected from meat chicken sheds during the eight week grow-out period showed that litter conditions varied spatially, within the litter profile, during the grow-out and between grow-outs. Litter conditions were measured at discrete positions across the litter and within the profile to describe the full range, rather than measuring average conditions. Water affects many of the chemical, physical and microbial properties of litter and yet research revealed a lack of knowledge in terms of the water balance within meat chicken sheds and litter properties, especially moisture content, water holding capacity and water activity. An equation combining theoretical and empirical inputs was developed to estimate the water addition to litter during a grow-out. This was combined with experimental measurements of water holding capacity and evaporation rate to identify periods of the grow-out when litter conditions were at risk of deteriorating. Addition of manure during a grow-out was found to increase the water holding capacity of litter and reduced water activity, which is a measure of the availability of water within litter that affects friability and microbial growth. Odorant emission rates were measured for different litter conditions in meat chicken sheds and during a laboratory based study where meat chickens were reared in a pen with a litter floor. Emission rates of volatile organic compounds and sulfur compounds (VOC and VSC) from the litter surface were measured using flux hoods and analysed by a combination of TD-GC-MS, TD-GC-SCD and PTR-Tof MS methods. Emission rates of some odorants were found to be significantly affected by litter conditions (when litter was characterised as ‘wet’ or ‘dry’) and the length of the grow-out. Odour activity values indicated which individual odorants made the biggest contribution to wet and dry litter odours.
Chemical assessment of emissions from sewage collection
Supervisors : Prof Richard M Stuetz
Project summary: Sewage consists of a wide range of organic and inorganic constituents originating from domestic and trade waste discharges. Of particular interest are the range of odorous volatile organic compounds (VOCs) and volatile sulfur compounds (VSCs) produced by anaerobic reactions (such as fermentation and sulfate respiration) in the sewage, sediments and biofilms on the sewer walls. Complaints due to sewage odour are a major issue for wastewater utilities because the repeated release of unpleasant odours from a sewer network constitutes both a public nuisance and possible regulatory violation. However, the complex nature of sewer odours provides many challenges with regards to the management and control of these emissions. This thesis aims to improve understanding of the emissions of compounds and odorants from sewage collection facilities by developing and benchmarking analytical methodologies. A highly sensitive and reliable method using gas chromatograph was developed and evaluated for the analysis of full spectra of compounds that present at the headspace of sewer air. While identifying the emitted chemical species provides useful information, the key to understanding the odour is establishing which of the chemical species odorants are. The use of gas chromatograph with simultaneous mass spectrometer and olfactory detection port (GC-MS/ODP) provides a method of prioritising the chemical species present along with their odour potential. The VOCs identified within emissions included alkanes, aromatics, halogenated hydrocarbon and terpenes, esters, aldehydes and alcohols whiles non-H2S VSCs related were: methyl methanethiol (MeSH), dimethyl sulfide (DMS), Carbon disulfide (CS2), dimethyl disulfide (DMDS) and dimethyl trisulfide (DMTS). The spatial-temporal variability of VOCs and VSCs were clearly identified and evaluated. A similar range of VOCs and VSCs have been identified in sewer headspace air across diverse countries and climatic regions, demonstrating that the data and conclusions presented in this present work would extend to context out of Australia and is useful for identifying the odour implications of sewer headspace VOCs for the wider industry. However, measured VSC concentrations from the Perth sampling sites were significantly higher than those at the Melbourne and Sydney sites. This indicates the possibly important role of climatic conditions played for VSCs emission at sewer networks.
Fate of volatile sulfur compounds in odour bags
Supervisors : Prof Richard M Stuetz, Dr Eric Sivret
Project summary: Complaints due to odours are a major issue for many industrial as well as agricultural facilities. Repeated release of unpleasant odours from these facilities can constitute both a public nuisance and a possible regulatory violation. Amongst the most common odorous emissions, volatile sulfur compounds (VSCs) are the most malodorous, have very low odour threshold values, and in many cases are the dominant odorants. For odour assessment, VSC containing air samples are commonly collected using plastic bags. However, VSC odorants are unstable and often suffer losses during storage in the sample bags. The degree of VSCs losses depends on many factors such as storage time, bag materials, temperature, sample relative humidity, light exposure, and the presence of volatile organic compounds (VOCs).To assess the impact of storage factors on the stability of VSC odorants, laboratory-based experiments were performed according to a factorial experimental design. Linear mixed-effects models of the storage recoveries for 10 VSC odorants in 3 different bag materials were constructed. The 10 VSCs included hydrogen sulfide, methanethiol, ethanethiol, dimethyl sulfide, tert-butylthiol, ethyl methyl sulfide, 1-butanethiol, dimethyl disulfide, diethyl disulfide, and dimethyl trisulfide. The 3 bag materials chosen in this work were Tedlar, Mylar, and Nalophan. Analyses of the results suggested Tedlar as the material of choice for the storage of VSC odorants. This material is superior over Mylar and Nalophan in maintaining the stability of all the 10 VSCs as well as the integrity of the VSC compositions. Based on the outcome of the recovery projection from the mixed models, recommendations for the handling/storage of VSC containing air sample bags are produced. It is recommended that VSC containing samples in plastic bags should not be stored at a temperature higher than 20oC and be covered from light. Under those conditions, VSC samples in Tedlar bags can be stored up to 18 hours whereas in Mylar and Nalophan, the storage time should not exceed 12 hours.
Off-gas Nitrous Oxide monitoring for nitrification aeration control
Supervisors : Prof Richard M Stuetz, Dr William Peirson
Project summary: Effective control of nitrification processes employed at municipal wastewater treatment plants is essential for maintaining process reliability and minimizing environmental impacts and operating costs. While a range of process control strategies are available, they share a dependence on invasive liquid phase monitoring and are based on a periphery understanding of the metabolic status of the processes being controlled. Utilization of off-gas nitrous oxide (N2O) monitoring as a real-time indicator of the process metabolic status is a novel process control concept with the potential to address these concerns. This thesis details the development and evaluation of an off-gas N2O stress response based control technique. Examination of the stress response relationship demonstrated that it met the majority of the criteria of interest for process control. A simple feedback aeration control strategy was developed and evaluated through process simulation to determine the feasibility of implementation, cost effectiveness and associated environmental benefits. The off-gas N2O based control strategy provided better matching between aeration supply and metabolic demand, allowing the process to be maintained at the desired operating setpoints and avert nitrification failure. Performance was demonstrated to be similar to dissolved oxygen based feedback aeration control, although slightly more efficient at reduced dissolved oxygen concentrations. A technical, economic and environmental evaluation indicated that aeration control based on non-invasive off-gas N2O monitoring is technically feasible and has the potential to offer significant environmental and economic benefits including reductions in operating costs and process capital investment, as well as improved effluent compliance and reductions in emissions of gaseous pollutants including greenhouse gases. Overall, while off-gas N2O monitoring based aeration control techniques have the potential to provide significant economic and environmental benefits, a number of research questions remain to be answered. Future work in the form of long-term field trials is required to address these issues and allow quantification of economic and environmental benefits.
Intercomparison of headspace sampling methods coupled to TD-GC-MS/O to characterise key odorants from broiler chicken litter
Supervisors : Prof Richard M Stuetz, Dr Gavin P Parcsi
Project summary: Since limited studies exist on the emissions of odours from tunnel ventilated broiler sheds under the Australian climate, this research study aims to determine the key odorants in the headspace of litter at ambient temperature across the poultry production cycle in two seasons (winter and summer) using headspace sampling coupled to TD-GC-MS/O analysis. Dynamic dilution olfactometry analysis was performed on litter odour samples. Analysis of litter odorant composition employing headspace sampling coupled to TD-GC-MS/O provided a greater understanding of the fate of odorants in the litter during bird growth cycle. The study also showed that characterise odorous volatiles can be correlated with dynamic dilution olfactometry responses. The results revealed that the odorous contributions were ketones, volatile fatty acids, sulfur and nitrogen compounds that were highly offensive substances, which impose significant effect on the odour annoyance from the emissions compared to other chemical functionalities. The assessment of activated carbon, silica gel and zeolite as a potential odour reducing strategy was directly applied to litters. The studies exhibited mixed trends in chemical and sensory responses and selectivity in reducing the volatilisation of odorants attributed to the efficacy of the additive itself, heterogeneous condition of litter particles in contact with the reduction materials and the exposed surface area.
By: Gavin Parcsi
Supervisors: R.M. Stuetz, S. Khan
Project Summary: Population growth has increased pressures on primary producers, including poultry producers, to competitively produce greater amounts of produce, whilst reducing environmental impact. Additional rural encroachment has substantially reduced the distance between primary producers and neighbouring properties, yielding increased odour related complaints. This research project aims to improve understanding of the emission of odorous compounds from poultry facilities by benchmarking analytical methodologies. In particular this thesis focuses on methodologies for speciation of Non-Methane Volatile Organic Compound (NMVOC) and odorant emissions from mechanically ventilated poultry houses in Australia