Odour concentrations prediction based on odorants concentrations from biosolid emissions.

Biosolids storage areas are a significant contributor to wastewater treatment plant (WWTPs) odour emissions which can cause sensorial impact to surrounding communities. Most odour impact regulations are based on odour concentration (COD) measurements determined by dynamic olfactometry. Understanding the relationship between odorants concentrations and COD in the biosolids emission is important to identify how the measurement and monitoring can be conducted using analytical rather than sensorial techniques. Some of the odorants are unknown in biosolid emissions, increasing the uncertainty in predicting COD. In this study, emissions from 56 biosolid samples collected from two WWTPs located in Sydney, Australia, were analysed by analytical and sensorial methods, including olfactory detection port (ODP) and dynamic olfactometry. Concentrations of 25 odorants and two ordinal variables represented odour events detected by ODP assessors were linked to COD values. Bayesian Model Averaging and Variable Selection with Bayesian Adaptive Sampling were applied to model the relation between COD and odorants concentrations. Results indicate the usability of the probabilistic methods and nonlinear transformations in modelling the odour concentrations based on odorants concentrations from biosolids emission and the accuracy of a small dataset.

Identification of odorant characters using GC-MS/O in biosolids emissions from aerobic and anaerobic stabilisation.

Malodorous emissions from biosolids limit potential re-use opportunities. Emissions from anaerobically stabilised biosolids have been widely studied. In contrast, emissions from aerobically stabilised biosolids have not been well documented. Individual odorants in complex emissions can be detected using sensorial analysis methods, such as gas chromatography mass spectroscopy coupled with an odour detection port (GC-MS/O) where assessors sniff the GC effluent to identify odorants present. In this study, GC-MS/O was used to study and compare emissions from biosolids produced from aerobically and anaerobically stabilised biosolids from different wastewater treatment plants (WWTPs). The WWTPs varied in size, catchments and dewatering technology. Three GC-MS/O assessors were used for the sensorial analysis. The identified odorants varied significantly between the two sites using aerobic stabilisation, in number of odour characters detected, as well as their intensity. Different odour characters were noted from biosolids generated at the aerobic digestion sites compared to characters from biosolids generated at the anaerobic digestion site. Biosolids from the aerobic digestion sites had medicinal, acrid or putrid type odours not noted from the anaerobic site. However, descriptors of biosolids emissions were commonly noted as: rotten vegetables, seaweed, garbage, garlic, or bad-breath. Many of the descriptors were associated with the presence of sulfur-type compounds. The importance of assessor variability was also highlighted in the paper where certain characters were not detected or were described differently by assessors.

Variations of odorous VOCs detected by different assessors via gas chromatography coupled with mass spectrometry and olfactory detection port (ODP) system.

Odorous volatile organic compounds (VOCs) were analysed via a thermal desorption gas chromatograph coupled with a mass spectrometer and olfactory detection port (TD-GC-MS/ODP) to characterize odour emissions from a wastewater treatment plant (WWTP). Three trained ODP assessors, screened according to the European dynamic olfactometry standard (EN: 13725), were used for the olfactory analysis. Their sensitivity to n-butanol varied within the acceptable limits. VOC samples from the WWTP were collected onto Tenax TA sorbent tubes in triplicate and each assessor analysed one tube in the same sample desorbing and analysing conditions. Intensities of odours detected from ODP were scaled from 1 to 4. The ODP assessors used their own odour descriptors based on their own experience as well as referenced descriptors on published compost and wastewater odour wheels. The ODP assessors detected a total of 32 different odorous VOCs; however, the intensities assigned by each assessor to particular VOCs varied. Moreover, some odorous VOCs were not detected by all assessors. For example, geosmin was detected by only two assessors. The use of a TD-GC-MS/ODP system for the analysis of odorous VOCs is valuable when analysed by different assessors, allowing a range of responses to specific odorants in a populations to be investigated.

Comparison of different measurement methods of odour and odorants used in the odour impact assessment of wastewater treatment plants in Poland.

The aim of this study was to compare sensory and analytical methods used to measure odour and odorants concentrations for odour impact assessment on municipal wastewater treatment plants (WWTPs). A range of sources and odour or odorants concentrations were used to compare the methods. Four different odours and odorants measurement methods were compared: field olfactometry using Nasal Ranger® field olfactometer, dynamic olfactometry according to PN-EN 13725:2007 standard, colorimetric assays (hydrogen sulphide, ammonia) and gas chromatography-mass spectrometry (GC-MS) methods (methanethiol, ethanethiol, dimethyl sulphide). Mechanical-biological and mechanical-biological-chemical WWTPs were chosen. Receptor points were selected inside of 'closed' facilities of the technological line (screening rooms, mechanical thickening and dewatering building) and downwind at 'open' facilities (collection chambers, sand trap, mechanical thickeners) which were the most significant regarding the potential for odour nuisance. By the research, it is not possible to specify explicit dependencies between results obtained from different research methods used in the odour impact assessment of WWTPs. A strong correlation (Pearson's correlation coefficient was equal R = 0.79) was determined only once between odour concentrations measured by dynamic olfactometry and methanethiol concentrations in the screen room at the WWTP No. 3.

The use of gas chromatography combined with chemical and sensory analysis to evaluate nuisance odours in the air and water environment.

Varieties of gas chromatography (GC) combined with chemical detection (CD) and sensory analysis at the odour detection port (ODP) for the evaluation of environmental odorants has steadily increased in application and sophistication; this has given rise to a plethora of techniques that cater to specific tasks. With this diversity of approaches in mind, there is a need to assess the critical points at which these approaches differ, as well as likely risks and factors that may affect them. These critical points explained within this review include sample preparation, GC separation techniques (with associated co-elution risks), how the elute is separated between CD and sensory analysis, the type of CD, the type of sensory analysis (with particular attention paid to its factors and guidelines), integrative data techniques, as well as how that data may be used. Additionally, this review provides commentary on the current state of the research space and makes recommendations based on how these analyses should be reported, the standardisation of nomenclature, as well as the impediments to the future goals of this research area. By careful consideration of the critical points of varying analytical processes and how best to communicate these findings, the quality of output within this area will improve. This review provides a benchmark for how GC-CD/sensory analysis should be undertaken and reported.

Identification of volatile sulfur odorants emitted from ageing wastewater biosolids.

Volatile sulfur compounds (VSCs) are important sources of unpleasant odours in biosolid emissions. However, the study of VSCs may be limited by complications in their gas phase measurements due to reactivity, transformations and varying reported odour detection thresholds. A range of methods were used to quantitatively analyse VSCs in wastewater biosolid emissions. VSCs were identified in aged biosolid emissions by gas chromatography (GC) with a sulfur chemiluminescence detector (SCD) and mass spectrometry coupled with olfactory detection port (MS/O). In total, 10 VSC's were identified with two volatile organic sulfur compounds (VOSCs), allyl methyl sulfide and methyl propyl sulfide being reported for the first time in biosolid emissions. The emission patterns of different VSCs varied as the biosolids aged. Initially, the median concentrations of H2S, dimethyl sulfide (DMS), dimethyl trisulfide (DMTS), methanethiol (MeSH) and ethanethiol (EtSH) were orders of magnitude greater than their reported odour detection threshold, suggesting they would contribute to the odorous impact of the biosolids. The maximum H2S value was equal to 59.9 × 103 µg/m3 and was at least one magnitude higher compared to VOSCs, such as dimethyl disulfide (DMDS) (3.8×103 µg/m3), DMS (4.53 × 103 µg/m3), EtSH (2.83 × 103 µg/m3) and MeSH (3.25 × 103 µg/m3). Among the identified VSCs, H2S was the prominent odorant in terms of the magnitude and the frequency of detection, both initially as well as throughout storage. However, DMTS should be considered as a high priority or key odorant due to its odour activity value (OAV) and frequency of detection (sensorially detected in more than 75% of samples, with an OAVs higher than 1).

Monitoring of odors emitted from stabilized dewatered sludge subjected to aging using proton transfer reaction-mass spectrometry.

One of the potential emission sources of odorous compounds from wastewater treatment plants is sludge processing. The odorous compounds released from dewatered sludge can result in odor nuisance. This study concerns the use of flux hood chamber combined with proton transfer reaction-time of flight-mass spectrometry (PTR-MS) technique for periodical monitoring of odorous compounds emitted from aged, stabilized dewatered sludge samples from 2 different wastewater treatment plants located in Pomeranian Voivodeship, Poland. Based on determined concentration of the chemical compounds and olfactory threshold values, theoretical odor concentrations (known also as "odor activity value" or "odor index") were calculated for 17 selected odorous compounds. As a result, sulfur compounds such as diethyl sulphide, dimethyl sulphide, methanethiol, and ethanethiol were estimated as the most significant chemical compounds responsible for malodorous effect (average results, e.g., methanethiol, 178 ou/m3; diethyl sulphide, 184 ou/m3). Based on Pearson correlation coefficient, we revealed a correlation between odorous substances emitted from aged, stabilized dewatered sludge cakes. It was revealed that stabilized dewatered sludge still possessed significant amount of odorous compounds and applied measurement technique could be used for monitoring of odor concentration level of selected malodorous compounds.

Framework for the use of odour wheels to manage odours throughout wastewater biosolids processing.

Odorous emissions from wastewater biosolids processing can cause nuisance impacts to the surrounding community. Odour Wheels are an effective tool for environmental odour management, but have yet to be provided for wastewater biosolids processing. Emissions throughout the biosolids processing from eight wastewater treatment plants, each with different unit operation configurations, were surveyed to identify odorants present and their olfactory properties. Chemical and olfactory methods identified a range of odorants and odours emitted throughout biosolids processing. Within the biosolids processing locations studied Sulfur type odours, described as rotten eggs or cabbage, were typically encountered. However, there was also a varying presence of Rancid/putrid and Faecal/manure type odours. Odour Wheels were generated to communicate both the olfactory and chemical components of emissions which were measured throughout biosolids processing. Examples based on the operation of the eight wastewater treatment plants were used to demonstrate how the Odour Wheels can be used as an onsite odour management aid. The paper demonstrates how Odour Wheels can be prepared using chemical and olfactory measurements and then used to communicate olfactory properties, as well as identify the causes of nuisance emissions throughout biosolids processing at wastewater treatment plants. The linking of odours and odorants to process conditions throughout biosolids processing facilitates effective abatement and management practices.