Odour and ammonia removal from pig house exhaust air using a biotrickling filter.

Odour from agricultural activities, such as the spreading of manure and the housing of animals, is increasingly being considered a nuisance in densely populated countries like the Netherlands. The objective of this research was to study the odour removal from pig house exhaust air by a biotrickling filter that had been implemented for ammonia abatement. At a regular pig production farm, the performance of a running full-scale biotrickling filter was studied for 72 days. Ammonia and odour removal efficiency were on average 79% and 49% respectively. Ammonia removal appeared to be based on an unintended accumulation of ammonium and nitrite in the system, instead of on production and discharge of nitrate. The odour removal efficiency showed a large variation that, for a major part, about 80%, could be attributed to actual changes in the performance of the biotrickling filter. These changes were probably caused by variations in the composition of the air that were not completely reflected by the olfactometrically measured odour concentration, as the many different components that make up the odour each have different removal characteristics. It seemed that the biotrickling filter was operated below its maximum absolute odour removal capacity [OUE/(m3 filter)/s], which means that the absolute odour removal will probably rise at increasing load. It was, however, not possible to distinguish between the influence of either the odour load or the odour concentration on the odour removal, because of a positive correlation between the odour concentration and the air flow. To increase the odour removal efficiency (%), the design of the filter probably needs to be optimised for both well and poorly water-soluble odour components.     

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.     

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.     

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.     

Anoxic control of odour and corrosion from sewer networks.

Anoxic processes can effectively control odour and corrosion in sewer networks. However, the absence of fundamental knowledge on the kinetics of anoxic transformation of sewage prevents the engineering applications of anoxic control in sewers. This paper focuss on a basic understanding of the anoxic transformations needed for a conceptual simulation of the water phase processes. Experiments conducted in batch reactors have shown that nitrite builds up in wastewater during denitrification. Part of the nitrate-reducing biomass is capable of utilizing nitrite after nitrate is depleted. Compared with aerobic transformation, anoxic processes have low values of maximum growth rate of the biomass and also a low endogenous respiration rate. Heterotrophic yield determined under anoxic conditions, at level of 0.25 mmol e-eq (mmol e-eq)(-1), accounted for less than 40% of the corresponding aerobic values.     

Evaluating odour impacts from a landfilling and composting site: involving citizens in the monitoring.

The City of Montreal operates a large sanitary landfill site within a densely populated urban area. Adjacent to the landfill site is a yard waste composting facility that processes 10,000 metric tons per year using the windrow technique. Over the years, numerous complaints have been received from citizens in the surrounding area regarding odours, particularly during the fall period. Aware of this nuisance, the City of Montreal wanted to identify odour sources, management operations leading to odours, and weather conditions accentuating odours, as well as to quantify actual odour impact. Forty-three (43) citizens living adjacent to this site were recruited and trained to make odour observations during the fall of 2000. This paper presents the methodology used to select and train the citizens chosen to make odour observations, to quantify and to identify odours. It also presents the main results of the study.     

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.     

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.     

Ambient odour testing of concentrated animal feeding operations using field and laboratory olfactometers.

The Missouri Air Conservation Commission regulations include regulations that limit the amount of acceptable odor from confined animal feeding operations (CAFOs). The regulations concerning odor designate the use of a scentometer as a screening tool. The rules dictate that if an odor is detectable by an investigator at a dilution ratio of 5.4 using a scentometer then an air sample should be collected and sent to an olfactometry laboratory for an odor panel to determine the detection threshold and the intensity of the odor sample. The detection thresholds are determined following ASTM E679-91 and EN13725. The intensity is determined following ASTM E544-99. If the olfactometry laboratory determined the detection threshold of the sample to be above seven, then the CAFO would be in violation. If the olfactometry laboratory determined the intensity level to be above a level equivalent to 225 ppm of n-butanol, then the source of odor would be in violation. The CAFO odor rules came under scrutiny by representatives of the largest hog producer in the State of Missouri. Specifically, they argued that the detection threshold limit of seven in the CAFO portion of the rule was too low for the rule to realistically identify a violation. This paper presents the results of a study to find the appropriate regulatory level of odor as determined by laboratory olfactometry. The study took place from November 2001 to October 2002. Samples were collected from field locations that exhibited odor produced by confined animal feeding operations and from areas exhibiting no apparent odor. The odors were categorized based upon the scentometer level at which the odors were detectable, and then samples were sent to an odor evaluation laboratory for analysis by olfactometry.     

Characterisation of high-rate acidogenesis processes using a titration and off-gas analysis sensor.

The characteristics of the glucose degradation by acidogenesis processes were investigated both in a long-term operating laboratory-scale continuously stirred tank reactor and in short-term experiments utilising a titration and off-gas analysis (TOGA) sensor. The results obtained from continuous-flow experiments in both reactors demonstrated that the TOGA sensor can be applied as a useful tool for the study of acidogenesis processes under steady-state and dynamic conditions. No significant effect from the culture transfer could be detected in the study with the TOGA sensor. Furthermore, the variation of gas production rate could be monitored at real time by the TOGA sensor. The experiments showed that the distribution of acidogenic products in the liquid and the gas phase was significantly influenced by the hydraulic retention time at least in the short term.     

Determination of nanogram level of VSCs using GC-SCD and an adsorption tube.

A quantitative analytical method was used for detection of low level of volatile sulfur compounds (VSCs) using GC with a sulfur chemiluminescence detector (SCD) in this study. A linear response over the range of 2-90 ngS injected was obtained with a good repeatability or reproducibility. Equimolar response for H2S, DMS, MeSH, and EtSH was obtained by use of SCD and the response of the SCD is nearly equimolar for different sulfur compounds. It was possible to quantify the total VSCs as well as individual VSC using one of the standard VSCs. VSC recovery was measured with respect to some storing methods. An adsorption tube packed with molecular sieve 5A showed almost perfect recovery for both H2S and dimethyl sulfide (DMS) during 6 days at a dark state below 2 degrees. Whereas, with a gas tight pyrex vial or tedlar bag, it was impossible to obtain the recovery of 50% after 6 days. It is strongly recommended to use the adsorption tube for determination of nanogram levels of volatile sulfur compounds and for storing and concentrating VSCs effectively with a minimum experimental error.     

Study of the effect of DMSO on VOS odour production in a wastewater plant.

Odours caused by volatile organic sulphides (VOS) have a history spanning over 20 years for Philadelphia's Northeast Water Pollution Control Plant (NEWPCP). A "canned corn" type of odour has caused residential complaints. Traditional odour control approaches based on hydrogen sulphide failed. This study confirmed that dimethyl sulphoxide (DMSO) from a chemical facility was the dominant cause of the "canned corn" nuisance odour in the form of dimethyl sulphide (DMS). During a discharge, DMSO concentrations up to 12 mg/L were found in the influent of the NEWPCP. Each DMSO concentration peak induced a DMS peak. DMS concentrations increased from less than 50 microg/L to 6 mg/L with a corresponding decrease in DMSO. Approximately 79% of DMSO from the primary sedimentation influent was passed to the effluent, and to downstream processes, such as the aeration tanks where the DMS was volatilised by the aeration. The DMS partial pressure in ambient air of NEWPCP can be between 0.03 and 0.18 x 10(-3) atm during a DMSO discharge. From the above information, the potential of VOS production is estimated and a practical plan for remediation can be designed.     

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.     

Needs and perspectives of odour research in the aquatic sciences.

Over more than four decades odour research in the aquatic sciences has increasingly focused on cyanobacteria and the common odour-causing compounds, geosmin and 2-methylisoborneol. Success in future research requires a long-term perspective. Key areas for investigation are secondary metabolites and cyanobacteria, regulatory mechanisms for geosmin and other compounds' synthesis; understanding their spatial and temporal distribution (particularly relating to the food web in a habitat); and molecular mechanisms for liberation of geosmin by microorganisms.     

An analytical method for shipboard extraction of the odour compounds, 2-methylisoborneol and geosmin.

Extractions for the analysis of geosmin and 2-methylisoborneol (MIB) were carried out on board a research vessel by extracting water samples in the collection bottles with dichloromethane. The extracts are stable and can be stored for up to two months with no apparent loss of analytes. Workup and analysis could be done at the rate 15-20 samples per week. Approximately 150 samples from Lake Ontario were analyzed in 2000 and 120 samples in 2001. Concentrations as low as 1 ng/L could be detected, but reliable determination was only attained above 5 ng/L (> 80% qualifier ion match within +/- 50%). Reproducibility between duplicates was generally better than 10%, and recovery of surrogate standards from reagent water averaged ca. 80% and from lake water ca. 60%. In early September, 2000, geosmin concentrations in Lake Ontario ranged from 1-13 ng/L and MIB from 1-31 ng/L. In 2001, the ranges were 1-47 and 1-56 ng/L for geosmin and MIB, respectively. Lowest concentrations occurred in the western and central regions and highest concentrations in the eastern region and St Lawrence River.     

The use of an odour wheel classification for the evaluation of human health risk criteria for compost facilities.

Odorants are released during the decomposition of organic waste at compost treatment plants. Composting releases volatile organic chemicals (VOCs), including alcohols, aldehydes, volatile fatty acids, ammonia and other nitrogen compounds, senobiotic solvents, and various sulphur compounds into the environment as categorised by a compost odor wheel. Each odorant possesses a characteristic odour signature--quality and threshold as well as a tosicity value. This paper presents data relating the human odour detection limit to human health threshold criteria developed by the National Institute for Occupational Safety and Health, Occupational Satety and Health Administration, the United States Environmental Protection Agency Region 9 and the World Health Organisation. This comparison indicates that: (1) the human odour threshold concentrations (OTO) for most compost odorants are far lower than their respective human health risk (regulatory) threshold values, (2) several compost odorants have OTC that are below some of their respective regulatory thresholds and above others (i.e. dimethyl amine, formic acid acetone, ethyl benzene and toluene) and (3) only the VOCs probably present as contaminants in the raw composting material have OTC greater than all of its regulatory thresholds (i.e. benzene). Benzene is the most hazardous VOC associated with compoating and should be monitored.     

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.     

A comparison of biofilms from macrophytes and rocks for taste and odour producers in the St. Lawrence river.

Given their widespread and prolific annual development in the St. Lawrence River (SLR), macrophytes (i.e. submerged aquatic plants) represent large surface areas for biofilm growth and potentially important sites for associated production of taste and odour (T&O) compounds. We therefore evaluated the importance of submerged macrophytes and their associated biofilms for production of T&O compounds, 2-methylisoborneol (MIB) and geosmin (GM), compared with biofilms from adjacent rocks. We also tested the hypothesis that production of these compounds would differ between macrophyte species, based on the premise that they are not inert substrates but directly influence the communities that colonise their surfaces. Samples collected from transects across the SLR between Kingston and Cornwall, ON were dominated by the flat-bladed Vallisneria spp., and the leafed Myriophyllum spicatum, Elodea canadensis, Chara spp., Potamgeton spp., and Ceratophyllum spp. Overall, MIB and GM levels in biofilms ranged widely between samples. Expressed per g dry weight of biofilm, median levels from macrophyte were 50 (range 1-5000) ng MIB g(-1) and 10 (<1 to 580) ng GM g(-1) compared with 50 (range 5-970) ng MIB g(-1) and 160 (1-1600) ng GM g(-1) from rocks. Based on non-parametric statistical analysis, levels of GM were higher on a g dry weight basis in biofilms from rocks than macrophytes (P = 0.02), but MIB levels were similar (P = 0.94). However, when normalised for differences in substrate surface area (i.e. ng cm(-2)), levels of both MIB and GM were higher in biofilms from rocks than from macrophytes (P < 0.01). There were no discernable differences in MIB and GM concentrations from biofilms of different macrophytes based on either g dry weight sample or surface area (P > 0.05). Overlying water (OLW) concentrations ranged between 2-45 ng L(-1) for MIB and 5-30 ng L(-1) for GM and were not correlated with levels in adjacent biofilms. However, OLW concentrations peaked in shallow, low energy embayments consistent with enhanced production and release of MIB and GM in nearshore areas. The results support our previous work showing the importance of biofilms on various surfaces (rocks, macrophytes and zebra mussels) for MIB and GM production in the SLR, but suggest that inert surfaces like rocks are more productive sites per unit surface area than macrophytes.     

Chlorophenols identification in water using an electronic nose and ANNs (artificial neural networks) classification.

Electronic artificial noses are being developed as systems for the automated detection and classification of odours, vapors and gases. In the food industry, such devices are used as aids for quality control or process-monitoring tools. An electronic nose (EN) is generally composed of a chemical sensing system and a pattern recognition system (e.g. artificial neural network). An EN based on a non-specific conducting polymer array was used to monitor chlorophenols in water samples. Operational parameters for the EN were optimized by a Plackett-Burman factorial design. The experimental parameters studied were: sample volume, platen temperature, sample equilibration time, loop fill time, sample pressurization time and injection time. Optimal experimental conditions were applied to chlorophenols determination and differentiation in ultrapure water samples spiked with the EPA listed chlorophenols. Data analysis was carried out using principal component analysis (PCA) and artificial neural networks (ANNs) to predict the chlorophenols presence in water samples. The obtained results showed that it was possible to differentiate the five chlorophenol groups: monochlorophenol, dichlorophenol, trichlorophenol, tetrachlorophenol and pentachlorophenol. Differentiation of chlorophenol groups was based on Mahalanobis distance between the formed clusters. This Mahalanobis distance is designated by the Quality Factor, a value >2 for this quality factor means a good differentiation between the clusters.