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.

Measuring volatile emissions from biosolids: A critical review on sampling methods.

As a by-product of wastewater treatment, biosolids are a source of volatile emissions which can lead to community complaints due to odours and other pollution risks. Sampling methods play a significant role in collecting gas emissions from biosolids-related sources (i.e., pure biosolids, landfilling, land application and composting of biosolids). Though a range of different sampling techniques (flux hood, wind tunnel, static chamber, headspace devices) have been explored in many published papers, the management and best practice for sampling emissions from biosolids is unclear. This paper presents a comprehensive review of sampling methods for collecting gaseous emissions from biosolids. To account for the inconsistent terminologies used to describe sampling devices, a standard nomenclature by grouping sampling devices into five categories was proposed. Literature investigating emission sampling from biosolids-related sources was reviewed. Subsequently a critical analysis of sampling methods in terms of design, advantages, and disadvantages were compiled based on literature findings and assumed mechanistic understanding of operation. Key operational factors such as the presence of fans, purge gas flow rates, insertion depth, and incubation conditions were identified and their level of influence on the measurement of emissions were evaluated. From the review, there are still knowledge gaps regarding sampling methods used to collect gases from biosolids-related sources. Therefore, a framework for the management of emission sampling methodologies based on common sampling purposes was proposed. This critical review is expected to improve the understanding of sampling methodologies used in biosolids-related sources, by demonstrating the potential implications and impacts due to different choices in sampling methods.

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.

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).

Occurrence and risk assessment of trace organic contaminants and metals in anaerobically co-digested sludge.

Anaerobic co-digestion of sludge increases biogas production and maintains anaerobic digestion stability. However, it is unclear whether the addition of co-substrates may increase the concentration of trace organic contaminants (TrOCs) and metals, limiting potential resource recovery opportunities when applied to agricultural land. This study explored the occurrence of 20 TrOCs and 18 metals in wastewater sludge anaerobically co-digested with beverage rejects (cola, beer and juice) and food wastes. TrOCs results showed that cola reject caused an accumulation of caffeine in final digestate. Bisphenol A also significantly increased in food waste co-digestion when compared with the mono-digestion (control). No significant difference in TrOCs was observed in the juice reject co-digestion. Analysis of the metal composition revealed a significant increase in Cr and Al in juice reject co-digested sludge. While restaurant food waste increased concentrations of K and Ca, both of which may be beneficial when applied to land. All metals in this study were below the maximum permissible concentrations specified for agricultural land use in Australia. Environmental risk assessment of sludge when used as soil fertiliser, showed that caffeine, diuron, triclocarban, triclosan, Cu and Zn exhibited high risks, with the largest risk quotient (RQ) posed by caffeine. Estrone and naproxen implied medium risks, and ibuprofen implied a high risk except for the co-digestion using cola reject (RQ = 0.9, medium risk). The results emphasise the importance for wastewater utility operators to understand the impact of co-substrate selection on the quality of sludge to minimise environmental risk from the use of biosolids on agricultural land.

Investigation of non-community stakeholders regarding community engagement and environmental malodour.

Research into industry-community relationships have focused almost exclusively on the ways in which communities responds to actions from industries. This has led to a paucity of understanding with regards to how community engagement and malodour amelioration practices have been adopted by industry personnel, as well as the attitudes and beliefs of non-community stakeholders in general. In this study, a survey to water industry personnel was distributed to three Australian water utilities in South-Eastern Australia and a semi-structured interview process was carried out with plant managers at six wastewater treatment plants. It was observed that best practice has not yet been established with regards to community engagement and odour amelioration, and that water industry personnel in general had a poor understanding of these concepts. Recommendations for how this situation could be improved, and how non-community stakeholders investigated, are discussed.

Quantification of VOCs and the development of odour wheels for rubber processing.

The impacts of rubber variations (clonal, seasonal, and pre-treatment) were investigated to assess changes in the composition of volatile organic compounds (VOCs) emitted during rubber processing. VOC emissions from 14 different rubber types were evaluated by headspace micro-chamber (µ-TEC) extraction coupled with gas chromatography-mass spectrometry (GC-MS). Headspace extracted at 120 °C, which is equivalent to the drying temperature during rubber processing, revealed a significant number of odorants in terms of concentrations as well as odorant type. Volatile fatty acids (VFAs) such as acetic, propanoic, butanoic, pentanoic and hexanoic acids, were frequently detected at concentrations greater than their odour detection thresholds. Other odorous compounds including trimethylamine, p-cresol, butanone, indole, and phenol, were also detected. Emissions collected at ambient conditions represent odorants released during material storage (or maturation) and were dominated by benzene derivatives followed by ketones, aldehydes, esters, and acids. Emission composition during storage appeared to be governed by specific rubber properties such as protein and rubber moisture content. Seasonal variations revealed greater impacts on the concentration of VOCs for all studied clones, compared to pre-treatment variations, suggesting that the VOCs composition was seasonally dependent and may represents the 'potential' emissions from rubber as they are processed. A combination of sensorial and analytical measurements were used to produce odour wheels which may be used as tool to identify key malodours in onsite rubber processing. The linking of odours and odorants can facilitate communication between receptors (the public) and plant operators inorder to minimise odour impact and develop effective abatement and on-site management practices.

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.