Zupanc Paper

7/29/2019 Zupanc Paper

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Hydrodynamic cavitation: a technique for augmentation ofremoval of persistent pharmaceuticals?

Mojca Zupanc1,2, Tina Kosjek1, Boris Kompare3, eljko Blaeka4, Uro Jee5,Matev Dular5, Brane irok5, Ester Heath1,21 Department of Environmental Sciences, Jozef Stefan Institute, Ljubljana, Slovenia

2Jozef Stefan International Postgraduate School, Ljubljana, Slovenia

3 Faculty of Civil and Geodetic Engineering, University of Ljubljana, Ljubljana,Slovenia4 Ecological Engineering Institute Ltd, Maribor, Slovenia5 Faculty of Mechanic Engineering, University of Ljubljana, Ljubljana, Slovenia

[email protected]

Abstract. Pharmaceutical residues enter the environment mainly due to

insufficient wastewater treatment. Many pharmaceuticals are not readily

degraded during conventional wastewater treatment, therefore advanced

technologies to remove them need to be investigated. In our study we

examined the removal of six pharmaceuticals (clofibric acid, ibuprofen,

naproxen, ketoprofen, carbamazepine and diclofenac) using a combination of

hydrodynamic cavitation and hydrogen peroxide. We performed the

experiments in distilled water under different operating conditions (initial

pressures set at 6, 5, 4 bar). The results showed good removal of naproxen (up

to 86%) and satisfactory removal of both carbamazepine (up to 72%) and

diclofenac (up to 77%), which are only moderately removed during biological

water treatment (21% and 48%, respectively). Removal of clofibric acid,

ibuprofen and ketoprofen by cavitation was lower and inconsistent

(45%35%, 48%31% and 52%27%, respectively).

Keywords: pharmaceuticals, hydrodynamic cavitation, removal

1 IntroductionAwareness of the presence of pharmaceuticals in the environment began around 30

years ago [1]. Since then the scientific community has made a significant effort into

understanding fate, behaviour and the risks posed by pharmaceuticals in the

environment [2], [3], [4]. Pharmaceuticals are developed for human and veterinary
mailto:[email protected]:[email protected]:[email protected]


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use [5] and after their application they reach wastewater treatment plants mostlyvia

the domestic sewage system [6]. Their concentrations detected in different

environmental compartments are in the ng L-1to g L-1 range [1], [3]. Since many

pharmaceuticals are not readily degradable by conventional treatment schemes [6],

research into and development of alternative methods like advanced oxidation

processes is important [7].

Cavitation is a physical phenomenon where the formation, growth and subsequent

collapse of small bubbles and bubble clusters occurs simultaneously releasing high

amounts of energy [7]. Cavitation belongs to a group of advanced oxidation

processes (AOP), the basis of which is in situ formation of hydroxyl radicals that

can oxidise recalcitrant organic compounds [7], [8]. In hydrodynamic cavitation, the

inception and collapse of small bubbles and bubble clusters is the result of an

increase of the fluid velocity and the decrease of static pressure, which occurs when

the fluid passes through a constriction [7]. The destruction of organic compounds

can occur viatwo pathways: free radical attack and pyrolysis, and which of the two

predominates depend on the properties of the compound and on cavitation

intensity [7]. The addition of hydrogen peroxide enhances the amount of free

radicals.

The main objective of our study was to test a series of techniques that could be

coupled to biological treatment to enhance overall removal efficiency. For this

purpose we investigated the removal of six pharmaceuticals (clofibric acid: CLA,

ibuprofen: IBP, naproxen: NP, ketoprofen: KTP, carbamazepine: CBZ and

diclofenac: DF) with hydrodynamic cavitation under different operating conditions

including the addition of hydrogen peroxide.

2 Experimental setupThe hydrodynamic cavitation reactor (HC-reactor) setup included two reservoirs

connected by a symmetrical venturi pipe with a constriction of 1 mm height and 5

mm width. As the flow passes through the constriction, it accelerates, causing a

drop in the static pressure resulting in cavitation. The sample is introduced into the

left reservoir (Figure 1), while the right reservoir remains empty. The pressure in

the left reservoir is then increased to the desired level, while the pressure in theright reservoir is kept at 1 bar. When the regulating valve is opened, the reactor


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contents are transferred from the left reservoir to the right one in about 10s. The

process is then reversed (cycled) for a given number of times. Figure 1 shows a

schematic of the reactor set up.

Figure 1: HC-reactor set up and cavitation phenomenon

In our experiments we observed the effects of cavitation in 1 L of distilled water

spiked with a mixture of the model pharmaceuticals (clofibric acid, ibuprofen,

naproxen, ketoprofen, carbamazepine and diclofenac) at environmentally relevant

concentrations (1 g L-1). The operating conditions were selected in previous

experiments (data not shown) and were as follows: cavitation time (30 minutes) and

H2O2 addition (30%, 20 mL). As a variable, we selected initial pressure since this

parameter defines flow velocity and the intensity of cavitation. Experiments were

made at 4, 5, and 6 bar. In order to ascertain the repeatability of cavitation, we

performed the experiments under optimum conditions (6 bar) in 10 parallels.


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3 Results and discussion

The results show that highest removal of all six pharmaceuticals was achieved at 6

bar (Figure 2). This was in agreement with the presumption that a higher initial

pressure results in an increase in cavitation intensity. The removal of

pharmaceuticals at 5 bar was slightly better than at 4 bar.

Figure 2: Removals (%) of pharmaceuticals with hydrodynamic cavitation under

different initial pressures (6, 5 and 4 bars)

At 6 bar we achieved 86%8% removal of naproxen and 72%14% and

77%12% of carbamazepine and diclofenac, respectively. The removal efficiencies

of clofibric acid, ibuprofen and ketoprofen were lower and inconsistent compared

to naproxen. As mentioned before the destruction of organic compounds with

hydrodynamic cavitation is dependent on their structure and chemical properties

and the different chemical structure of the selected pharmaceuticals may be thereason for different removal efficiencies.

Since carbamazepine and diclofenac are not readily and consistently removed

during biological waste water treatment (21% and 48%, respectively), which we

established in our previous work and is in accordance with the literature [8], [9],

hydrodynamic cavitation could be a viable technique for augmenting their removal.

To authors knowledge few data exist regarding the removal of pharmaceuticals

using hydrodynamic cavitation. Since cavitation is a technique that is relatively easyto scale up [10], it should be given more attention.


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In the future we will combine hydrodynamic cavitation and Fenton process to

achieve better removal of recalcitrant pharmaceuticals (clofibric acid, ibuprofen and

ketoprofen) and further augment the removal of naproxen, carbamazepine and

diclofenac. After the determination of removal efficiencies and optimal operational

conditions for this combination in distilled water, we will transfer the technology to

more complex matrices (effluents of biological wastewater treatment plants). Last

but not least, our aim is to determine the best combination of different processes

considering removal of pharmaceuticals, feasibility and cost effectiveness, possibly

coupling AOP sequentially to biological treatment.

References:

[1]J. P. Bound, K. Kitsou, N. Voulvoulis. Household disposal of pharmaceuticals and perceptionof risk to the environment.Environmental Toxicology and Pharmacology, 21: 301307, 2006

[2]Halling-Srensen B., Nors Nielsen S., Lanzky P.F:, Ingerslev F., Holten Ltzhft, Jrgensen.Occurence, Fate and Effects of Pharmaceutical Substances in the EnvironmentA Review.Chemosphere, 36 : 357-393, 1998

[3]Ternes T.A., Giger W., Joss A. Introduction. In: Human Pharmaceuticals, Hormones andFragrances: The challenge of micropollutants in urban water management. Ternes T.A., Joss A., 2006.

[4]Farre M., Perez S., Kantiani L., Barcelo D. Fate and toxicity of emerging pollutants, theirmetabolites and transformation products in the aquatic environment. Trends in AnalyticalChemistry, 27 : 991-1007, 2008

[5]O.V. Enick, M.M. Moore. Assessing the assessments: Pharmaceuticals in the environment.Environmental Impact Assessment Review, 27: 707729, 2007

[6]A. Joss, S. Zabczynski, A. Gbel, B. Hoffmann, D. Lffler, C. S. McArdell, T. A. Ternes, A.Thomsea, H. Siegrist. Biological degradation of pharmaceuticals in municipal wastewatertreatment: Proposing a classification scheme. Water Research, 40: 16861696, 2006

[7]P.R. Gogate, A.B. Pandit. A review of imperative technologies for wastewater treatmentI:oxidation technologies at ambient conditions.Advances in Environmental Research, 8: 501-551,2004

[8]P. Braeutigam , M. Franke, R. J. Schneider , A. Lehmann , A. Stolle, B. Ondruschka.Degradation of carbamazepine in environmentally relevant concentrations in water byHydrodynamic-Acoustic-Cavitation (HAC). Water Research, 46: 2469-2477, 2012

[9]M. Ravina, L. Campanella, J. Kiwi. Accelerated mineralization of the drug Diclofenac viaFenton reactions in a concentric photo-reactor. Water research, 36: 3553-3560, 2002

[10]A.G. Chakinala, P.R. Gogate, A.E. Burgess, D.H. Bremner. Treatment of industrialwastewater effluents using hydrodynamic cavitation and the advanced Fenton process.Ultrasonics Sonochemistry, 15: 49-54, 2008


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For wider interest

To meet the ever growing demand for improved healthcare, pharmaceuticals are

being produced in increasing amounts. As a consequence, pharmaceutical residuesin the environment are becoming a concern. This is because many of these

compounds have been proven to be resistant to conventional microbiological

wastewater treatment. In response, new technologies are necessary to reach

increasingly stringent regulation on water quality.

In this study we investigated hydrodynamic cavitation which is a potent advanced

oxidation process (AOP) and is relatively cost-effective and easy for scale up.

Caviation is the term given to the formation and subsequent implosion of bubbles

that result when the partial local pressure in a fluid drops below vapour pressure.

The collapse of the bubbles can generate a significant increase in local pressures

and temperatures, called hot spots. Such extreme conditions can result in the

formation of free radicals, which are potent oxidising species capable of breaking

down organic compounds. Our intention is to make use of these free radicals by

deliberately cavitating the effluent flow from a wastewater plant. Additionally, our

idea is to increase the amount of free radicals formed by adding hydrogen peroxide.

Initial experiments have been carried out using a two reservoir system in which the

fluid can be transferred from one to the other by varying the pressures in each. As

the fluid passes from one reservoir to the other, it must pass through a

constriction, which creates a pressure drop in the fluid resulting in cavitation. We

tested the apparatus using six common pharmaceuticals: clofibric acid, ibuprofen,

naproxen, ketoprofen, carbamazepine and diclofenac at various pressures 4, 5 and 6

bar. A pressure of six bars was optimum. In the case of carbamazepine and

diclofenac, the results have been positive, improving the removal efficiency by 50%and 30 %, respectively, compared to conventional water treatment. In the case of

clofibric acid, ibuprofen and ketoprofen the results are less conclusive. Further

study will involve optimisation of cavitation process and its combination with

biological water treatment in order to improve overall removal of resistant

contaminants.

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