Transporting liquid waste is a continuously growing activity in several industries. This transportation is made in trucks and sea containers. Often, the liquid transported contains Volatile Organic Compounds (VOC) and odours. The process of washing and cleaning the truck tanks usually involves the emission of odours and VOCs. The aim of this study was to evaluate the odour abatement efficiency of a multistage hybrid approach consisting of alkaline scrubbing, condenser, adsorption with impregnated Al2O3 + active carbon (AC), and the injection of a deodorizing product to abate odour and VOC emission. In addition, the second aim of this study was to show that the use of these sequential technologies reduce VOC emissions below the limit of 100 mg/m³ set in the environmental authorisation.
Before the abatement system was installed, VOC concentration was measured over a week averaging 200 mg/Nm³. After the installation of the abatement system, the results showed that the average VOC concentration was always well below the legal limit. In addition, when washing activities took place, the odour concentration measured at the inlet, and outlet of the abatement system was 5000 ouE/m3 and 150 ouE/m3, respectively. This was a 97% odour abatement efficiency.
Competing interests: The author has declared that no competing interests exist.
Academic editor: Carloz N. Díaz
Content quality: This paper has been peer-reviewed by at least two reviewers. See the scientific committee here
Citation: Riccardo Snidar, Enrico Pieri, Enea Merlin, Silvia Rivilli, Jorge Vicente. 2021. Use of multistage hybrid technology for the treatment of emissions that present critical issues in terms of variations of the contained mixtures and volatility, 9th IWA Odour& VOC/Air Emission Conference, Bilbao, Spain, Olores.org.
Copyright: 2021 Olores.org. Open Content Creative Commons license. It is allowed to download, reuse, reprint, modify, distribute, and / or copy articles in Olores.org website, as long as the original authors and source are cited. No permission is required from the authors or the publishers.
ISBN: 978-84-09-37032-0
Keywords: odour, olfactometry, scrubber, liquid waste, routine controls
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Abstract
Transporting liquid waste is a continuously growing activity in several industries. This transportation is made in trucks and sea containers. Often, the liquid transported contains Volatile Organic Compounds (VOC) and odours. The process of washing and cleaning the truck tanks usually involves the emission of odours and VOCs. The aim of this study was to evaluate the odour abatement efficiency of a multistage hybrid approach consisting of alkaline scrubbing, condenser, adsorption with impregnated Al2O3 + active carbon (AC), and the injection of a deodorizing product to abate odour and VOC emission. In addition, the second aim of this study was to show that the use of these sequential technologies reduce VOC emissions below the limit of 100 mg/m³ set in the environmental authorisation. Before the abatement system was installed, VOC concentration was measured over a week averaging 200 mg/Nm³. After the installation of the abatement system the results showed that the average VOC concentration was always well below the legal limit. In addition, when washing activities took place, the odour concentration measured at the inlet, and outlet of the abatement system was 5000 ouE/m3 and 150 ouE/m3, respectively. This was a 97% odour abatement efficiency. The installation of the hybrid equipment demonstrated to be safe, robust and efficient, as it allowed obtaining significant abatement rates, chemical as well as olfactometric, at reasonable costs, ensured throughout time. Furthermore, odour concentration measured both on the inlet and outlet of the washing system, with open hatches and operating suction equipment, showed that there is no need to close hatches, which is; a useful information for future monitoring.
1. Introduction
Transporting liquid waste is a continuously growing activity in several industries. This transportation is made in trucks and sea containers. Often, the liquid transported contains Volatile Organic Compounds (VOC) and odours.
Once the liquid waste is delivered, the truck tanks must be washed and cleaned before loading another liquid. The process of washing and cleaning the truck tanks usually involves the emission of odours and VOCs. The odour release can be such that it can produce an odour impact if there are sensitive receptors nearby.
Single stage treatment technology, such as scrubbing, might not be a suitable technology because of the relative variety of chemical components that are emitted during these processes. The use of a multistage hybrid technology, combining scrubbing with other technologies can represent a solution as each stage works specifically on a group of chemical components and odour.
In this case study performed in a plant in central Italy dedicated to washing tanks we studied the use of a multistage hybrid combination of alkaline scrubbing, condenser, adsorcion (activated carbon, and Al2O3 pre-impregnated with KMnO4), and the injection of a deodorizing product to abate odour and VOC emission.
The aim of this study was to evaluate the odour abatement efficiency of multistage hybrid combination. In addition, the second aim of this paper is to show that the use of these sequential technologies reduce VOC emissions below the legal limit of 100 mg/m3.
2. Materials and methods
As mentioned before, the plant under study is located in central Italy. This plant works 6 days a week and washes tank trucks that transport over 400 various types of wastewaters containing a large amount of different chemical components. This plant has a limit of 100 mg/m³ of VOC as expressed in their environmental authorisation, that can not be exceeded during the cleaning operations. In addition this plant has odour complaints. The points identified as the main responsible of odour releases in this plant were the following.
1. Shed where the tank trucks were washed
2. Washing water recovery hall
3. Air lock
1) Shed where the tank trucks were washed
Washing of tanks takes place inside a dedicated track under a shelter where operators carry out the following operations: 1) opening upper hatches, 2) insertion of water jet washing heads, 3) closing hatches, and 4) beginning of washing sequence. All these processes produce odours and VOCs emissions.
A special conical shape was introduced in the tank truck manhole opening in order to collect gas emissions during the washing process. This device allowed an air tight connection for each of the 5 compartments in the tank trucks in order to extract emissions generated during the various washing steps. Each duct had a diameter of 80 cm. The system was designed to extract 80 m³/h of air from each tank opening, for a total flow rate of 360 m³/h ensuring the discharge of the whole volume (30 m³) contained in the tank in less than 5 minutes. That is 12 Air Changes per hour (ACh).
In addition, the shelter had an extraction point in order to collect fugitive emissions that could be released during the whole washing process. Flow rate normally sucked-in during plant operation was 700 m³/h. A valve allowed for the suction of environmental air to compensate for the lack of air flow from the washing area.
Photo 1-2-3: View of the tank truck washing, conical washing taps to extract air.
2) Washing water recovery hall
In addition, the washing water recovery hall was also responsible for some of the odour and VOC emissions. In this case, 300 m³/h air contained in the washing water recovery hall was brought to the odour abatement system. This way, this area got a ventilation rate of 6 ACh. The air extracted from the washing waters recovery hall was used to dilute the concentrated emission released during the first opening of tank trucks, in order to optimize the mitigation of the olfactive nuisance in this critical step. The suction circuit of the waters recovery hall was started only when the washing device was not operating.
3) Air Lock
The air inside the airlock was designed to be ventilated at 1 ACh considering the volume above liquid level of the water or equal to the flow rate of introduced water / steam). The air extracted in this area could range between 10 and 300 m3/h. The total flow to be treated was thus 1.000 m³/h. The following drawing shows the pipeline design and the location of local and ambient air collection points in this case study.
Fig. 3 : In violet: ventilation pipe line.
The extracted air was sent to a multistage hybrid approach consisting of alkaline scrubber, condenser, impregnated AC, and the injection of a deodorizing product. The following diagram shows the different steps of abatement treatment.
Fig. 1 : multistage hybrid combination
The abatement processes in detail were the following:
- Differentiated collection according to the washing status
- Oxidizing alkaline wet scrubber (with NaOH)
- Condenser to collect low vapour pressure VOCs and preserve filter media from humidity.
- DKFil® - Filter with 2 active masses: activated carbon, and Al2O3 pre-impregnated with KMnO4 (adsorption and oxidation)
- Zephiro UTS ® - Nebulization of deodorizing product (physical action with osmogenic barrier)
- Suction fan to avoid fugitive emissions
The whole abatement system was programmed by using an automatic system, in order to prevent washing to take place only when the suction system was activated.
Photo 4: pipe coming from washing air that is connected with hybrid abatement system
Fig. 4 Flow chart
Air suction of the washing area was in use only when washing operations were performed on tank trucks containing products that had a definite odour impact or when the staff in charge, after having evaluated the specific situation, felt that this was necessary. Odour impact polishing was achieved by spraying water with the addition of specific neutralizing products. Osmogenic barriers are non-polluting neutralizing products that modify the chemical structure of the constituent molecules of the foul-smelling substance.
The treatment process called "osmogenic barrier" works by using dilution water and specific products. These products have within them sufficiently hydrophobic groups consisting of long chains of hydrocarbons which are capable of forming large molecular aggregates of various types, called aerosol phase micelles. The technology uses an ultrasonic membrane sprayer that is able to generate air with high humidity, capable of distributing the neutralizing properties of specific products.
Several monitoring campaigns were carried out over the whole period of the first year of operation. VOC and Odour concentration were measured in different parts of the system according to the UNI EN 12619 and the EN 13725, on a monthly basis, in order to evaluate output rates. VOCs were measured at the inlet and at the outlet of the abatement system; odour samples were taken at washing point (P1), at the outlet of the scrubber (P2), outlet of demister (P3) and at the outlet of the system (P4).
Fig.5 Odour sampling points
3. Results and discussion
Before the abatement system was installed, VOC emission was measured over a week during the washing process. Averaged VOC concentrations of 200 mg/Nm3 were detected. The legal limit for VOC emission is 100 mg/m3. After the installation of this multistage hybrid combination, regular measurements of VOC concentration were carried out each month. The following graph shows the average VOC concentration in the plant when there was no abatement system (in red) and the values obtained at the outlet of the system.
Figure 6. VOC concentration before the installation of the abatement system (red) and monthly concentrations measured at the outlet of the abatement system (blue)
The results show that the average VOC concentration was always well below the legal limit value of 100 mg/Nm3. When there were no washing activities, odour concentration measured at the outlet and at the inlet was 75 ouE/m3 and 70 ouE/m3, respectively. When washing activities took place the odour concentration measured at the inlet, and outlet of the abatement system was 5000 ouE/m3 and 150 ouE/m3, respectively. This is a 97% odour abatement efficiency.
Table 1: Measured odour concentration and abatement efficiency.
The scrubber was able to abate 76% of the odours, the demister tuned it further to 88% and after the adsorption the final efficiency of abatement was 97%, as mentioned before.
4. Conclusions
A plant dealing with washing tank trucks located in central Italy had odour complaints. The environmental regulator set a VOC concentration limit of 100 mg/Nm3 in its environmental permit. After studying different abatement methodologies, a multistage hybrid approach consisting of alkaline scrubbing, condenser, adsorption with AC + coated Al2O3, and the injection of a deodorizing product was selected to abate odour and VOC emission.
Before the abatement system was installed, VOC concentration and odour concentration measured was 200 mg/Nm³ and 5000 ouE/m3, respectively. After the installation of the abatement system, VOC concentration was always below the legal limit of 100 mg/Nm³, and odour concentration was significantly reduced to 150 ouE/m3. This is a 97% odour abatement efficiency.
5. References
Main data has been collected directly on the field.
[1] UNI EN 13725, 2004. Qualità dell’aria – Determinazione della concentrazione di odore mediante olfattometria dinamica. Ente Nazionale Italiano di Unificazione, Milano, Italia;
[2] Rivilli S., Snidar R., Mattiussi M., Soldati A., Trovarelli A. (2008), “Valutazioni di intensità e tono edonico delle emissioni olfattive in un impianto di trattamento rifiuti”, Emissioni odorigene e impatto olfattivo – Prevenzione e Trattamento, aa.vv, Geva Edizioni;
[3] Il Grande M. (2000) “L’olfattometria dinamica. Esperienze di applicazione per la determinazione degli odori dagli impianti di trattamento dei rifiuti”. In. Atti del seminario ANPA “L’inquinamento olfattivo”, 11 settembre 2000, Roma, Italy;
[4] K. B. Schnelle, Jr., C. A. Brown, (2002), Air Pollution Control Technology Handbook, CRC Press LLC;
[5] UNI EN 12619: 2013. Emissioni da sorgente fissa - Determinazione della concentrazione di massa del carbonio organico totale in forma gassosa - Metodo in continuo con rivelatore a ionizzazione di fiamma. Ente Nazionale Italiano di Unificazione, Milano, Italia;
[6] UNI 11806: 2021. Qualità dell'aria - Emissioni odorigene e impatto olfattivo - Vocabolario. Ente Nazionale Italiano di Unificazione, Milano, Italia;
After installation of this multistage hybrid combination, regular measurements of VOC concentration were carried out each month. The following graph shows the average VOC concentration in the plant when there was no abatement system (in red) and the values obtained at the outlet of the system.
