Sonolytic degradation of volatile pollutants in natural ground water: conclusions from a model study

Dedicated to the 60th birthday of Prof. Dr. Ralf Miethchen
https://doi.org/10.1016/S1350-4177(01)00080-3Get rights and content

Abstract

In order to evaluate the possibilities of an ultrasound-based cleaning technology, the effects of sonication on pollutants in a contaminated natural ground water were investigated. After the discussion of the results from this model study on the sonolytic degradation of volatile organic compounds, some consequences are reported and the important role of water components is described. Furthermore, the use of sonication as a cleaning technology for polluted water is discussed based on the conclusions from this study.

Introduction

The treatment and cleaning of contaminated ground water is a costly process. In recent years, there has been an increased number of rehabilitation cases and sites in Germany involving volatile chlorinated compounds. The existing cleaning technologies are already effective but the efforts and costs do dramatically increase if the contaminant concentrations are very low or high. Moreover, some of the remediation technologies (e.g. adsorption to active carbon, air stripping) do not solve the problem completely as the contaminants are only transferred (bound to a host) and not degraded. Combustion of the contaminants adsorbed on activated carbon may cause new pollution problems due to by-products and is therefore questioned as a benign technology. Oxidation technologies are a good alternative, but require the addition of chemicals. Therefore, improved procedures and technologies are of interest. These facts together with public discussions and legislation demand new and innovative remediation technologies. (cf. discussion in Refs. [1], [2]).

One group of hazardous contaminants are volatile chlorinated compounds. From an environmental point of view the following compounds are relevant (common trivial names in parentheses): dichloromethane (DCM), chloroform, carbon tetrachloride (Tetra), 1,2-dichloroethane (1,2-DCA), 1,1,1-trichloroethane, 1,1-dichloroethene, cis- and trans-1,2-dichloroethene, trichloroethene (Tri), tetrachloroethene (Per) and vinyl chloride (VC). Owing to their toxic properties to humans they may damage the function of the kidney, liver and nerve system. Furthermore, they are reported to be carcinogenic. The extended and in part careless use of volatile chlorinated compounds especially as solvents, technical cleaners and degreasing agents in the past has resulted in numerous rehabilitation problems at present. Thus, the amount of volatile chlorinated hydrocarbons applied only as solvents sums to 246 000 tons in Germany for 1985 [3]. The worldwide and extended use of these compounds makes this class of compounds practically ubiquitous in air, soil and water. The concentration found in non-contaminated ground and rainwater is lower than 0.1 μg/l, whereas contaminated surface, ground and seepage water contains up to 101–105-fold higher concentrations. Due to their physicochemical properties, volatile chlorinated hydrocarbons can penetrate concrete, reach the ground water level vertically, are horizontally mobile and very persistent. In a consequence of this behaviour, large contaminated areas may be formed which can extend to several kilometres. The destruction in the soil and water proceeds extremely slowly. Moreover, rehabilitation measures have to take into account that very often contaminant mixtures are present due to the nature of the technical cleaners.

The World Health Organization (WHO) guidelines for drinking water quality involve limit values for single components: chloroform (30 μg/l), carbon tetrachloride (3 μg/l), 1,2-dichloroethane (10 μg/l), 1,1-dichloroethene (0.3 μg/l), trichloroethene (30 μg/l), tetrachloroethene (10 μg/l) [4]. The German drinking water regulation (TrinkwVO) outlines a sum limit value for chlorinated organic compounds (including trichloroethene, 1,1,1-trichloroethane, tetrachloroethene, carbon tetrachloride, dichloromethane) of 0.01 mg/l and gives a single value of 0.003 mg/l for carbon tetrachloride [5]. Moreover, there are guidelines for drinking water quality of the Environmental Agency of the State of Hamburg. The latter is of importance for the study described in this chapter as the contaminated ground water investigated was taken from a rehabilitation site near Hamburg.

In respect to the harmful character of organic water contaminants and the fact that sonication is a chemical-free technology, there has been a growing interest in the sonochemical destruction of organic contaminants in water in recent years. Thus, ultrasound has been proved to degrade several organic contaminants in water (e.g. chlorinated hydrocarbons, phenols, and pesticides [6], [7], [8], [9], [10], [11], [12]). An ultrasonic treatment may offer the following advantages: partial or complete destruction of pollutants, avoidance of disposal, recycling or combustion, full on-site process, physical treatment (i.e. no addition of chemicals) as well as the water has not to be translucent. Moreover, ultrasonic processing steps could also improve existing technologies. (e.g. advanced oxidation processes [13], [14]).

Previous studies using ultrasound in the destruction of water contaminants focused mainly on the effect of different parameters on the degradation of model contaminants in demineralized water under laboratory conditions (for detailed discussion of the literature cf. Ref. [1]) These studies showed that volatile chlorinated compounds were degraded inside the cavitation bubble by high temperature pyrolysis. Prolonged sonication gave an almost complete mineralization. The investigation of mixtures consisting of two or three single components showed that the degradation rates of the single components are independent of each other.

Section snippets

Model study parameter

In order to show the effects of ultrasound on pollutants in contaminated natural ground water, we investigated the effects of sonication on samples from a ground water rehabilitation site near Hamburg [1], [15]. Highly volatile chlorinated compounds pollute the ground water. The main component is 1,2-dichloroethane (1,2-DCA) in a concentration of about 350–390 μg/l whereas the other volatile organic compounds (VOC) amount to only 80–85 μg/l. The ground water also contained various natural

Transfer of sonolysis data from pure water to natural water

From the literature it is known that highly volatile halogenated hydrocarbons including 1,2-DCA can be destroyed by ultrasound [16], [17], [18]. In order to find reliable conditions for the sonication of the ground water samples, some initial experiments with pure 1,2-DCA in deionized water were performed under conditions that could be applied to the ground water samples.

The experiments were performed at different ultrasonic frequencies (206, 361, 620, 1086 and 20 kHz) and with sample volumes

Sonication of natural ground water

The decrease in concentration of the different VOC in the contaminated natural ground water depending on the sonication time is shown in Table 2, Table 3, Table 4 for three investigated frequencies at the same calorimetric power. 1,2-DCA as well as the minor highly volatile halogenated hydrocarbons were mostly destroyed within 60–120 min. Data for trans-1,2-dichloroethene show that halogenated hydrocarbons, which are formed during the destruction steps of 1,2-DCA, were also destroyed with

Conclusions

In view of the questions raised at the beginning of this paper, the results of our study lead on the one hand to some promising answers, but show on the other hand also a number of problems related to a commercial large-scale sonolytic water treatment process.

From the results obtained in pure and natural water contaminated by 1,2-DCA the following promising conclusions for a sonolytic process can be drawn:

  • It is possible to reproduce the degradation rates obtained with model contaminants by

References (27)

  • W.J. Catallo et al.

    Waste Mgmt.

    (1995)
  • M.R. Hoffmann et al.

    Ultrason. Sonochem.

    (1996)
  • D. Drijvers et al.

    Ultrason. Sonochem.

    (1996)
  • T.M. Olson et al.

    Water Res.

    (1994)
  • O. Krüger et al.

    Ultrason. Sonochem.

    (1999)
  • O. Krüger, FH Hamburg, Diploma Thesis,...
  • W.W. Eckenfelder, A.R. Bowers, J.A. Roth, Chemical oxidation: technologies for the nineties, Vol. 3, Technomic...
  • H. Brackemann et al.

    UWSF-Umweltchem. Ökotox.

    (1995)
  • L.H. Hütter, Wasser und Wasseruntersuchung, Reihe Laborbücher Chemie, Otto Salle Verlag, Frankfurt/M.,...
  • Handbuch Umweltchemikalien (Gesetze und Verordnungen: Trinkwasserverordnung), 12. Erg. Lfg. 10/91, Ecomed...
  • Y. Liu

    Huanjing Kexue Jinzhan

    (1995)
  • G.E. Orzechowska et al.

    Environ. Sci. Technol.

    (1995)
  • Y. Nagata et al.

    Chem. Express

    (1993)
  • Cited by (42)

    • A critical review of advanced oxidation processes for emerging trace organic contaminant degradation: Mechanisms, factors, degradation products, and effluent toxicity

      2021, Journal of Water Process Engineering
      Citation Excerpt :

      Contrary to this, hydrophobic and volatile TrOCs present in low viscosity stream can easily move from bulk to gas phase region of cavitation bubbles. As a result, they degrade due to thermolysis in core zone as well as by hydroxyl radicals attack in the bulk [163]. For example, Fu et al. [164] reported 80 % degradation of estrogens (initial concentration 10 μg/L) within 25 min.

    • A Review on Additives-assisted Ultrasound for Organic Pollutants Degradation

      2021, Journal of Hazardous Materials
      Citation Excerpt :

      Hc becomes dominant when Hc > 10 and DL can be negligible, indicating the mass transfer rate of VOCs only relies on Hc at this condition (Ayyildiz et al., 2007). It therefore comes as no surprise that some VOCs present little difference of degradation efficiency with the higher ultrasonic frequency or power input (Peters, 2001). The degradation reaction of NOCs is not zero-order in US systems because the NOCs degradation rates is concentration-dependent (Singla et al., 2004; Lu et al., 2019), indicating that a higher concentration of NOCs leads to higher degradation rates of NOCs.

    • Ultrasonic application in contaminated soil remediation

      2019, Current Opinion in Environmental Science and Health
      Citation Excerpt :

      The ultrasonic process can be used for compounds that are persistent with the environment and are able to degrade stable contaminants such as polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), pesticides, and other organochlorines adsorbed into soil particles [33]. In addition, there are many other organic pollutants that have been proven to be degraded by ultrasonic such as chlorinated aliphatic hydrocarbons, aromatic compounds, PCBs, PAHs, several phenol compounds, chlorofluorocarbons, pesticides, and herbicides and others [6,33–37]. These studies demonstrated that not only did sonication improve leaching, but it also destroyed contaminants.

    • Wastewater treatment using hybrid treatment schemes based on cavitation and Fenton chemistry: A review

      2014, Ultrasonics Sonochemistry
      Citation Excerpt :

      The limited diffusion of hydroxyl radicals out of the interfacial regions of the collapsing cavitation bubbles [61] may result in a decrease in the degradation rate with increasing pollutant concentration. Thus the better efficacy of Fenton chemistry and cavitation either operated individually or in combination, has been generally observed at lower initial concentrations [45,61,79–88]. Neppolian et al. [61] have reported a decrease in the reaction rate constant with an increase in initial concentration of MTBE over the range of 2.84 × 10−2–2.84 × 10−1 mM using ultrasound with fixed ultrasonic frequency of 20 kHz.

    • Recent development in the treatment of oily sludge from petroleum industry: A review

      2013, Journal of Hazardous Materials
      Citation Excerpt :

      Through sonolysis reaction by these free radicals, long-chain or aromatic petroleum hydrocarbons with complex structure and large molecular weight can be broken into simple hydrocarbons which have higher solubility and bioavailability. Ultrasound can be used to degrade many PHCs, such as chlorinated aliphatic hydrocarbons (CAHs), aromatic compounds, polychlorinated biphenyls (PCBs), poly aromatic hydrocarbons (PAHs), and various phenols [180–184]. Zhang et al. [185] utilized a combined process of ultrasonic and Fenton oxidation for the oily sludge treatment, and it was found that ultrasonic irradiation could enhance the Fenton oxidation effect on oily sludge degradation by improving the contact of hydroxyl radicals (OH) with PHCs compounds.

    View all citing articles on Scopus
    View full text