The odour of digested sewage sludge--determination and its abatement by air stripping.

This paper describes a project to investigate the odour of sewage sludge after anaerobic digestion. The impact of air stripping on the odour of liquid sludge and on the quality of the dewatered product was evaluated at a full-scale sludge treatment installation. A continuous and a batch air-stripping mode were tested. Odour samples were collected during air stripping from the liquid sludge and from the biosolids surface during long term storage. The biosolids were also analysed for hedonic tone and for their potential odour expressed as an odour unit per unit mass. The odour emission profiles for continuous and batch air stripping demonstrated a reduction in the overall (time weighted) emissions during a 24 hr-period compared with emissions from the quiescent liquid storage tank. The averaged specific odour emission rate (Esp) of the biosolids derived from the continuous process was only 13% of the Esp of the biosolids derived from unaerated liquid sludge during the first month of storage. The results of the total potential odour and the hedonic tone of the biosolids underpin the beneficial effects of the air stripping. Odour dispersion modelling showed a noticeable reduction in overall odour impact from the sludge centre when air stripping was applied. The reduction was primarily associated with the reduced odour from stockpiled biosolids. The continuous air-stripping mode appeared to provide the greatest benefits in terms of odour impact from site operations.     

Control of odour emission in wastewater treatment plants by direct and undirected measurement of odour emission capacity

Odour emissions from wastewater treatment plants (WWTPs) are considered to be the main causes of disturbance noticed by the exposed population and have relevant impacts on both tourism economy and land costs. Odour impact from WWTPs is generated by primary and secondary odour emissions. Primary odour emissions are related especially to the wastewater type and variability discharged into the sewer and directed to the WWTP, and to the wastewater collection and sewage system. Secondary odours are related to the treatment units of the plant. Several studies describe the key role of primary odour emissions and how they are strongly related to odour impacts of WWTPs. In this way, a opportune characterization of the emission capacity of primary odour could be an effective way to control odour emission in the WWTPs. In this study the odour emission capacity (OEC) of different domestic sewers was described and investigated; a correlation between the OEC and the main physical-chemical parameters of wastewater quality was also carried out. Results of this study identify the optimum conditions for sampling and measuring OEC in wastewaters and define its dependence by wastewater quality. These results can contribute to setting the standards for the maximum odourant content of wastewater that are discharged into the publicly owned sewage system.     

Odour emission inventory of German wastewater treatment plants--odour flow rates and odour emission capacity.

Wastewater Treatment plants can cause odour emissions that may lead to significant odour annoyance in their vicinity. Thus, over the past 20 years, several measurements were taken of the odour emissions that occur at WWTPs of different sizes, treatment technology, plant design and under different operating conditions. The specific aspects of odour sampling and measurement have to be considered. I presented some of the results of my odour emission measurements 11 years ago. However, it is now necessary to update the figures by evaluating newer measurement results obtained from measurements taken from 1994 to 2003. These are presented in this paper. Also, the paper highlights the odour emission capacity (OEC) measurement technique which characterises liquids and can be used to assess the results achieved by different types of treatment in the liquid phase, e.g. in a sewerage system. In addition, the OEC is a suitable parameter to set standards for the odorant content of industrial wastewaters that are discharged into the publicly owned sewerage system.     

Identification of the odour and chemical composition of alumina refinery air emissions.

Alcoa World Alumina Australia has undertaken comprehensive air emissions monitoring aimed at characterising and quantifying the complete range of emissions to the atmosphere from Bayer refining of alumina at its Western Australian refineries. To the best of our knowledge, this project represents the most complete air emissions inventory of a Bayer refinery conducted in the worldwide alumina industry. It adds considerably to knowledge of air emission factors available for use in emissions estimation required under national pollutant release and transfer registers (NPRTs), such as the Toxic Releases Inventory, USA, and the National Pollutant Inventory, Australia. It also allows the preliminary identification of the key chemical components responsible for characteristic alumina refinery odours and the contribution of these components to the quality, or hedonic tone, of the odours. The strength and acceptability of refinery odours to employees and neighbours appears to be dependent upon where and in what proportion the odorous gases have been emitted from the refineries. This paper presents the results of the programme and develops a basis for classifying the odour properties of the key emission sources in the alumina-refining process.     

Monitoring of biological odour filtration in closed environments with olfactometry and an electronic nose.

Air treatment with a compact biological membrane filter, and air quality monitoring with an electronic nose were tested in the laboratory on air from a cage containing six mice. Additional analyses of air to and from the filter were performed using olfactometry and ammonia and hydrogen sulphide gas detection tubes. The biological air filter is a module containing biofilm-coated membrane fibres that separate a closed liquid loop from a gas phase. Odour compounds and oxygen diffuse through the membranes from the gas phase to the biofilm, where they are degraded to carbon dioxide and water. The prototype "ENQBE" electronic nose is based on an array of eight thickness shear mode resonators (TSMR), also known in the literature as quartz microbalance sensors. The chemical sensitivity is given by molecular films of metalloporphyrins and similar compounds. Chemical interaction of compounds in the air with the vibrating sensors induces a frequency change of the vibration that can be measured as a signal. The air from the mouse cage had a strong odour (3490 OUE/m3). The biological membrane filter performed well, achieving over 80% odour and ammonia reduction. The electronic nose signal could be correlated with the inlet and outlet air-quality of the biological filter, making it a promising method for monitoring air quality in closed environments.     

Olfactory and toxic impact of industrial odour emissions

This paper describes the approach adopted for the evaluation both of the odour impact and of the non-carcinogenic health effects relevant to odours in the city of Terni, Italy. The first part of the study focused on the quantification of emissions by means of dynamic olfactometry and chemical analyses. Dispersion modelling was then applied for the evaluation of citizens' exposure both to odours and to their non-carcinogenic toxicity. The results show that, on one hand, the odour impact is considerable, actually affecting almost the whole city of Terni. On the other hand, the toxic impact, expressed in terms of the Hazard Index (HI), is about three orders of magnitude lower than the level that is expected to bring adverse effects, over a lifetime exposure, for human health.     

Evaluation of a novel wind tunnel for the measurement of the kinetics of odour emissions from piggery effluent.

A novel laboratory wind tunnel, with the capability to control factors such as air flow-rate, was developed to measure the kinetics of odour emissions from liquid effluent. The tunnel allows the emission of odours and other volatiles under an atmospheric transport system similar to ambient conditions. Sensors for wind speed, temperature and humidity were installed and calibrated. To calibrate the wind tunnel, trials were performed to determine the gas recovery efficiency under different air flow-rates (ranging from 0.001 to 0.028m3/s) and gas supply rates (ranging from 2.5 to 10.0 L/min) using a standard CO gas mixture. The results have shown gas recovery efficiencies ranging from 61.7 to 106.8%, while the average result from the trials was 81.14%. From statistical analysis, it was observed that the highest, most reliable gas recovery efficiency of the tunnel was 88.9%. The values of air flow-rate and gas supply rate corresponding to the highest gas recovery efficiency were 0.028 m3/s and 10.0 L/min respectively. This study suggested that the wind tunnel would provide precise estimates of odour emission rate. However, the wind tunnel needs to be calibrated to compensate for errors caused by different air flow-rates.     

The effect of two ammonia-emission-reducing pig housing systems on odour emission.

Odour nuisance from agricultural activities is increasing in densely populated countries like the Netherlands. To develop adequate regulations, a large-scale, government-financed monitoring programme was started in the mid-1990s to establish odour emission levels for both conventional and low ammonia emission housing systems for cattle, pigs and poultry. The results indicate that high- and low-odour emission housing are difficult to distinguish because of the large variation within housing systems. Measurements on different farm locations within the same housing system show both a large variation between locations and within one location (in time). The latter, however, is significantly smaller, which suggests that farm management is an important determinant in odour emission that interferes with the effects of housing systems. The current research was aimed at determining the effect of two common ammonia-reducing pig-housing systems on odour emissions compared to conventional housing systems under similar management conditions. The respective reduction principles of these systems are reducing the emitting surface of the manure pit and cooling of manure in the manure pit (both pits beneath slatted floor). Five farms that combined conventional housing with one low-ammonia system (three reduced emitting surface and two manure cooling) were selected for a direct, pair-wise comparison of (olfactometric) odour emission measurements. The results show a highly significant effect (p < 0.01) for two of the three reduced emitting surface systems and for one of the two manure cooling system. The average odour reduction percentages of these systems are 35% (from 24.9 to 16.0 OUE/s per animal) and 23% (from 30.1 to 24.0 OUE/s per animal) respectively. Although odour emission reduction through the type of housing system is possible, management factors interact with the system and thereby determine whether the system reduces odour emission or not.     

Catalytic ozonation for odour removal of high temperature alumina refinery condensate

Odour emissions from aluminium processing can cause an impact on local communities surrounding such facilities. Of particular concern is fugitive odours emitted from the handling and use of refinery condensate streams, particularly the digestion condensate. This study evaluated the application of using catalytic ozonation to treat alumina refinery condensate in order to remove the potential emission of odourous compounds from the industrial wastewater. The technical challenges in treating the alumina refinery condensate are the high pH and temperatures of the wastewater effluent (over 80 °C and pH above 10) due the industrial process. The odour removal efficiencies for different catalysts (FeCl(3), MnO, and MnSO(4)) under experimental conditions in terms of controlled pH, temperature and ozone dosage were determined before and after ozone treatment using dynamic olfactometry. The result demonstrated that the addition of both FeCl(3) and MnO catalysts improved odour removal efficiencies during the ozonation of alumina condensates at similar pH and temperature conditions. FeCl(3) and MnO had similar enhancement for odour removal, however MnO was determined to be more appropriate than MnSO(4) for odour removal due to the colouration of the treated condensate.     

Odour monitoring of small wastewater treatment plant located in sensitive environment

Small wastewater treatment plants are often localized nearby tourist areas. Odour emissions are a major environmental issue in these plants and are considered to be the main cause of disturbance noticed by the exposed population. Odour measurement is carried out using analytical or sensorial methods. Sensorial analysis, being assigned to the "human sensor", is the cause of a considerable uncertainty.In this study, a novel procedure based on highly innovative analytical tool was used to identify and characterise the odour sources and the volatile substances that cause annoyance in a SWWTP located in a sensitive area, with the aim to remove the subjective component in the measure of the odours and define the induced impact. At the same time key odour compounds are detected, and the relationship between their concentration and the performances of the plant are investigated.The sources and the main chemical substances responsible for the olfactory annoyances were identified. Results highlight the applicability of the highly innovative tool in odour emission monitoring. Around 39 different substances were detected, with almost half being smell relevant components as well as responsible. Dimethyl disulphide was identified as key compound connected to the efficiency of the process.     

Integrated odour modelling for sewage treatment works.

Odours from sewage treatment works are a significant source of environmental annoyance. There is a need for tools to assess the degree of annoyance caused, and to assess strategies for mitigation of the problem. This is the role of odour modelling. Four main stages are important in the development of an odour problem. Firstly, the odorous molecules must be formed in the liquid phase. They must then transfer from the liquid to the gaseous phase. They are then transported through the atmosphere to the population surrounding the odour source, and are then perceived and assessed by that population. Odour modelling as currently practised tends to concentrate on the transportation of odorants through the atmosphere, with the other areas receiving less attention. Instead, odour modelling should consider each stage in an integrated manner. This paper describes the development of integrated odour models for annoyance prediction. The models describe the liquid-phase transformations and emission of hydrogen sulphide from sewage treatment processes. Model output is in a form suitable for integration with dispersion models, the predictions of which can in turn be used to indicate the probability of annoyance. The models have been applied to both hypothetical and real sewage treatment works cases. Simulation results have highlighted the potential variability of emission rates from sewage treatment works, resulting from flow, quality and meteorological variations. Emission rate variations can have significant effects on annoyance predictions, which is an important finding, as they are usually considered to be fixed and only meteorological variations are considered in predicting the odour footprint. Areas for further development of integrated odour modelling are discussed, in particular the search for improved links between analytical and sensory measurements, and a better understanding of dose/response relationships for odour annoyance.     

Characterisation of odour masking agents often used in the solid waste industry for odour abatement.

Odours from waste management facilities, wastewater treatment plants and composting areas have become a major nuisance issue for operators. In addition to facing regulations which tend to become more stringent, operators are also facing increased public pressure due to complaints from neighbours resulting in the temporary shutdown of such plants, therefore the elimination of atmospheric odours is becoming a major industrial objective. Many commercial odour control products are available on the market, however, very little is known concerning their real efficiency and mechanism of action. This paper will present the results from the study of 19 agents collected in various countries. The products were first characterised both in terms of their chemical composition and sensory properties. Selected products with different modes of application were then submitted to a study of their efficiency at the pilot-scale level. The results from one product test showed no significant difference in their odour removal efficiency as determined by olfactory and chemical analysis of the emission before and after application of the odour control product.     

Water Environment Research Foundation (WERF) anaerobic digestion and related processes, odour and health effects study.

Biosolids odour emissions can affect the ability of wastewater utilities to implement beneficial biosolids processing and reuse programs. Communities often become more sensitised and vocal about biosolids issues, once they experience odours emanating from a nearby site. Odour impacts from biosolids, including potential human health effects, have been targeted recently by many national and local newspapers, citizens' groups, and regulatory agencies, who have raised significant concerns, ranging from viable disposal methods/sites to outright bans. Many national and local regulatory agencies in the United States are considering biosolids disposal bans in their communities because of misinformation, poor science, and citizen pressure, but primarily because of odour impact concerns. The wastewater industry has a relatively poor understanding of the operations and treatment parameters that influence biosolids odour emissions. Thus, wastewater treatment plants are often unable to control the odour quality of the biosolids that are delivered into communities. A research study to demonstrate the influence of anaerobic digestion, mechanical dewatering, and storage design and operating parameters on the odour quality of the final product was performed and is the subject of this paper. Established and new sampling and analytical methods were used to measure biosolids odour emissions from 11 test sites in North America. By determining the impacts of these control variables on biosolids odour quality, design and operations of anaerobic digestion systems might be enhanced. This paper also summarises a corollary study performed as part of the WERF research study that addresses the health effects of biosolids odours.     

Modelling to assist in wastewater collection system odour and corrosion potential evaluations.

Odour emissions and corrosion concerns can be a constant focus for many wastewater treatment and collection system owners, usually from the first day that their collection systems begin operation. Many sewer systems are reaching the end of their useful life, or have experienced either odour or corrosion issues. This paper shows a link between odour generation and corrosion potential, and how modelling can be used to assist in odour/corrosion assessments of existing wastewater collection systems. A model has been developed that is capable of predicting liquid-phase sulphide generation and subsequent release to overlying sewer headspace as hydrogen sulphide (H2S), where it can be the source of either odour or corrosion problems. This paper presents an overview of the model, and uses a case study involving both odour and corrosion issues to demonstrate the utility in modelling. The model was used to identify potential locations within the system where odour/corrosion may be problematic, as well as assisting in the evaluation of potential odour control alternatives.     

Periphyton: a primary source of widespread and severe taste and odour.

In the last decade, a late summer-fall taste and odour problem has been a prolonged and annual event in the St Lawrence River (SLR). Earlier work identified the earthy/musty compounds geosmin and particularly, 2-methylisoborneol (GM-MIB), and ruled out Lake Ontario as a major source, but did not identify the biological origins. In 2000, we investigated the source(s) and underlying causes. We sampled littoral sites in the SLR near Cornwall, ON, and found that macrophytes (or associated biofilms) may be primary GM sources. Zebra mussel homogenate yielded low GM-MIB levels, but several associated actinomycetes generated high in vitro amounts. Periphyton from rocks showed significant yields, with cell-bound GM-MIB up to one hundred times the levels in overlying water. In 2001, we followed seasonal changes at some of these sites. Periphyton GM-MIB showed intriguing spatial and temporal patterns. Several cyanobacteria in these biofilms were identified as potential odour sources, notably Oscillatoriales. We conclude: i) periphyton is a major odour source in the SLR; ii) other biota such as macrophytes and mussels may also contribute; iii) seasonality in GM-MIB production and ratios indicate changes in cell production and/or taxa in response to environment. These results may account for the recent onset of the problematic odour events, which represent chemical signals of the increased water transparency and littoral surface area following the widespread dreissenid mussel invasion to the Great Lakes. Our data raise key questions about the processes that trigger the tremendous variability in biota and GM-MIB production in the SLR, the subject of our continued research.     

Sewer odour abatement monitoring - an Australian survey

Odourous emissions from sewer networks can significantly impact a local population causing odour annoyance. A survey of nine Australian wastewater utilities that serve over 8.4 million people and operate over 59,000 km of sewer networks was undertaken to summarise the current monitoring practices in Australia with the view to assist the water industry to further improve their practices in operating and monitoring sewer odour abatement systems. Results indicated that most odour abatement systems were monitored through complaints from the surrounding community, H(2)S is the dominant online and offline monitoring parameter and that a variety of different H(2)S instruments are used across the industry but the reported use is dominated by two manufacturers. The monitoring data were primarily used for decision making and diagnosis, and there was limited use of non-H(2)S odourant analysis. The water industry had several significant limitations in terms of its inability to provide gas flow data, process monitoring and complaint data as well as being able to link process monitoring data with maintenance information for instrumentation. The improved collection and management of this data would yield benefits to the water industry in terms of odour abatement design, performance and management.     

Use of non-thermal plasma and UV-light for removal of odour from sludge treatment

Non-thermal plasma (NTP) systems can be used for abatement of odour nuisances. Odour reductions are achieved by radical-initiated oxidation and dust collection in the plasma reactor. For some emissions a sequence of NTP followed by UV-light can improve the odour reduction further. This study was conducted to evaluate the efficiency of NTP technology combined with UV-light towards odour emissions from sludge treatment. Air from a pilot sludge dryer was treated with a pilot NTP and a UV unit. The effect of using an acid scrubber upstream the NTP system was also tested. Thermal desorption gas chromatography and mass spectrometry (TD-GC/MS) was used to analyse samples taken from the inlet and the outlet of the NTP system. The TD-GC/MS used was also equipped with a sniffing port that made it possible to record odour-active compounds eluting from the column. Relative amounts of odour-active compounds in the inlet and the outlet flow from the NTP system were compared. Bag samples from inlet and outlet were also separately analysed by an external lab and by two operators using a one-man olfactometer, a modified NasalRanger(TM). These results indicated a significant odour removal efficiency of 70-90% depending on the settings and combinations of abatement equipment.     

The anatomy of odour wheels for odours of drinking water, wastewater, compost and the urban environment.

In the drinking water and air pollution fields, odour quality characterisation and intensity of each odour characteristic needs to be developed to evaluate the causes of the odours present. Drinking water quality characterisation has matured to the point where an "odour wheel" is described and the primary chemicals producing the odour are known and therefore a potential treatment can be defined from the odours reported. Sufficient understanding of the types of odorous compounds that can arise from wastewater and compost treatment processes and odours in the urban environment are starting to emerge. This article presents the anatomy of the odour wheels. It is hoped that the foundation of odour wheels will evolve as odour quality data are reported and linked with chemical causation. The compost and urban odour wheels are presented in print for the first time.     

Impact assessment of odours emitted by a wastewater treatment plant

Complaints from the Domingos Martins population about sewage odours in the city made the district attorney order an impact assessment of the odours emitted by the city wastewater treatment plant (WWTP). This study comprised various techniques, models and population surveys. In 2007, an odour emission model proved that the main hydrogen sulphide emitter was the aeration tank of the WWTP (13.5 g h(-1)) and such emissions, according to CALPUFF model, should be perceived in the whole Domingos Martins city centre area. In this area, 58% of those interviewed were annoyed by the WWTP odours. However, in 2009, the odour monitoring panel recorded few odour occurrences. A second population survey showed that hereafter only 20% of those interviewed were annoyed by the WWTP emissions. Odour emission and dispersion models run with 2010 data proved a drastic reduction of the WWTP aeration tank emissions and consequently the city centre was not bothered by WWTP emissions anymore. The odour emission reduction was due to the modification of the WWTP aeration tank system. Despite the odour emission reduction, houses located southeast of the WWTP were still annoyed by sewage odours. However, in this part of the town, other sources of sewage odours have been found.     

Variability and repeatability of olfactometric results of n-butanol, pig odour and a synthetic gas mixture.

For the purposes of a research project for the Flemish authorities, olfactometric measurements were carried out at six closed pig farms and six fattener farms. The results of these olfactometric measurements were compared with the olfactometric results of n-butanol samples and samples of a synthetic gas mixture of ethanethiol, methylacetate and 2-propanol in nitrogen, both analysed on the same days as the air samples from the pig farms. The results of the n-butanol tests for all panellists showed that nobody was qualified according to the CEN criteria, and that, consequently, these criteria are rather stringent. Comparing the variability of the results for the three different odours showed that the mean and standard deviation of the mean variance were not significantly different for the three odour types, which means that the repeatability of the panellist results was equal for the examined odour types. The principle of traceability was checked by comparing the variance of the n-butanol, pig odour and synthetic mixture ratio. For the complete dataset, the principle of traceability could not been proven for n-butanol. For the restricted dataset, the principle of traceability was more valid for n-butanol than for the mixture, but differences were small. Finally, normalization was looked for with regard to olfactometric measurements of air samples from pig arms based either on n-butanol or on the synthetic mixture. Both models had low determination coefficients, but the model based on the synthetic mixture gave better results than the one based on n-butanol.