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Change of toxicity during secondary treatment of industrial sludge containing nitroaromatics
Örebro University, Department of Natural Sciences.
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Wastewater treatment plants in Sweden are facing a great challenge due to the prohibition of depositing organic waste which gained legal force in January 2005. Biological and commercial available alternatives to disposal are composting and anaerobic digestion. A promising technique for wastewater and sludge treatment is the use of constructed wetland.

In this thesis we have looked at the sludge from a wastewater treatment plant receiving wastewater from industries manufacturing pharmaceutical substances, chemical intermediates and explosives. The wastewater and sludge contains high concentrations of nitro-aromatic compounds and amino-aromatic compounds, both original compounds and degradation products. The degradation of nitroaromatics under different oxygen conditions is well examined and several studies have reported the alteration of nitroaromatics to more potent cytotoxic and genotoxic compounds after degradation. The use of bioassays is a practicable approach to estimate the toxic potency of complex samples such as sludge, since it is difficult to analyse all toxic compounds in a sample by using chemical analysis.

The aim of this study was to follow change in toxicity in three different sludge treatment methods; aerobic composting and anaerobic digestion and constructed wetland to follow change in general and mechanism-specific toxicity.

In order to detect both lipo- and hydrophilic compounds, different extraction and bioassays are necessary. We used organic solvents and multi-layer cleaned-up samples in the DR-Calux assay to detect the persistent lipophilic compounds causing dioxin-like activity. We also used both water and acetone extracts in the umu-C assay to detect genotoxicity and in the fishegg assay to detect embryotoxicty of water and semi-water soluble compounds in low concentrations.

The results showed that anaerobic treatment is less suitable for this particular sludge, since the anaerobic residues showed high induction in all toxicity tests compared to the residues of the aerobic treatment. The anaerobic treatment also transformed the toxicants in the sludge to more lipophilic and persistent forms as well as to more water soluble, genotoxic compounds. This makes the treated material difficult to handle due to the toxic potential of the material as well as of the leachate. The aerobic treated material also showed an increased toxic potential of the material but the leachate showed no toxicity. However, high concentrations of nitrite were formed during both aerobic and anaerobic treatment, which is of environmental concern.

The constructed wetlands eluated a non-toxic effluent and had a bed material with lower toxicity than expected considering the sludge concentrations and loaded sludge amount. The bed material contained concentration of TEQ considered as acceptable levels for sensitive ground use such as parks, lawns and other grounds without groundwater protection.

However, all three treatment methods need to be optimised and the residual needs further evaluation in order to establish a suitable biodegradation method.

Place, publisher, year, edition, pages
Örebro: Örebro universitetsbibliotek , 2005. , p. 45
Series
Örebro Studies in Environmental Science, ISSN 1650-6278 ; 7
Keyword [en]
Anaerobic, aerobic, AhR agonists, CALUX, constructed wetlands, Danio rerio, embryotoxicity, genotoxicity, nitroaromatics, sludge
National Category
Other Environmental Engineering
Research subject
Enviromental Science
Identifiers
URN: urn:nbn:se:oru:diva-181ISBN: 91-7668-453-9 (print)OAI: oai:DiVA.org:oru-181DiVA, id: diva2:135515
Public defence
2005-10-28, Hörsal P1, Prismahuset, Fakultetsgatan 1, 70182 Örebro, 10:00
Opponent
Supervisors
Available from: 2005-10-07 Created: 2005-10-06 Last updated: 2017-10-18Bibliographically approved
List of papers
1. Changes in toxicity and genotoxicity of industrial sewage sludge samples containing nitro- and amino-aromatic compounds following treatment in bioreactors with different oxygen regimes
Open this publication in new window or tab >>Changes in toxicity and genotoxicity of industrial sewage sludge samples containing nitro- and amino-aromatic compounds following treatment in bioreactors with different oxygen regimes
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2004 (English)In: Environmental science and pollution research international, ISSN 0944-1344, E-ISSN 1614-7499, Vol. 11, no 5, p. 313-320Article in journal (Refereed) Published
Abstract [en]

GOALS, SCOPE AND BACKGROUND: From 2005, deposition of organic waste will be banned in Sweden. Likewise, in Germany and Austria, similar bans are being planned, and further countries will probably follow. Thus, there is a need to develop new methods and to refine established techniques for sludge management in the whole of the European Union. For this end, there is also an urgent need for appropriate ecotoxicological approaches to elucidate and assess the hazard potential of sewage sludge. Therefore, the present study was designed to assess the capacity of various established sludge treatment methods using different oxygen regimes to degrade recalcitrant nitro-substituted organic compounds and reduce their toxicity. Sewage sludge samples from a wastewater treatment plant in Sweden (Cambrex Karlskoga AB, industrial area Björkborn) receiving wastewater from industries manufacturing pharmaceutical substances, chemical intermediates and explosives were processed with different sludge treatment methods. Among other treatment methods, bioreactors (for anaerobic and aerobic sludge treatment) were used. In the present investigation, a battery of in vitro bioassays was employed to compare the cytotoxic and genotoxic potentials of different fractions of sludge samples in order to elucidate whether the treatments were suitable to reduce the toxicity of the sludge.

METHODS:

In order to investigate the cytotoxicity of the extracts of treated and untreated sludge samples, the acute cytotoxicity test with the permanent cell line RTL-W1 was used. Genotoxicity was tested by means of the comet assay (single cell gel electrophoresis) with RTL-W1 cells, and mutagenicity was assessed with the Ames test using the Salmonella typhimurium strains TA98, TA98NR and TA100. Sludge toxicity was tested in different fractions of organic extracts produced by acetone and hexane extractions. The subsequent clean-up procedure (silica gel chromatography and elution with hexane and dichloromethane) resulted in two fractions, a lipophilic hexane-fraction and a semi-lipophilic dichloromethane-fraction. For the genotoxicity and mutagenicity tests, these fractions were reunited at equal ratios.

RESULTS AND DISCUSSION:

The acute cytotoxicity test with RTL-W1 cells revealed a high cytotoxic potential for the semi-lipophilic DM-fractions of all sludge samples with NR50 values (= effective concentration for 50% cell death in the neutral red test) from 8.9 up to 20 mg sludge d.w./ml medium. A low cytotoxic potential for the hexane fractions of the untreated sludge samples (NR50 400 to > 400 mg sludge d.w./ml medium) was observed, whereas the hexane fractions of the treated sludge samples showed elevated cytotoxicity increasing further with treatment in the bioreactors. The comet assay indicated that three out of eight of the reunited fractions had a significant genotoxic potential. Whereas the genotoxic potential of one sample treated anaerobically was very high with an induction factor of 11.6, a similar sample (taken from the same anaerobic reactor four months later) and one untreated sample showed lower potentials. The samples treated in another anaerobic bioreactor as well as the samples treated aerobically showed no genotoxic potential. Results indicate that aerobic treatment was basically adequate for reducing the genotoxicity of the sludge, whereas anaerobic treatment was only partly useful for reduction of genotoxicity. The Ames test revealed a very high mutagenic potential for the reunited fractions of the untreated sludge samples with strain TA98 (maximum induction factors (IFmax) up to 45) and a relatively high potential for one of the samples treated aerobically (S2, IFmax = 18 (TA98, S9-)), thus documenting the suitability of both anaerobic and aerobic treatments to reduce the mutagenicity of the samples, however, with the aerobic treatment being less effective.

CONCLUSIONS:

Overall, none of the microbiological treatments for wastewater sludge in bioreactors was found to be ideal for general toxicity reduction of the sludge samples. Whereas cytotoxicity of the sludge increased or levelled off in most cases following either treatment, genotoxicity both increased or decreased after anaerobic treatment, depending on the specific sample. However, mutagenicity could generally be reduced by anaerobic treatment and, to a lesser degree, by aerobic treatment.

RECOMMENDATIONS AND PERSPECTIVES:

The complex modification of the diverse damage potentials of sludge sample extracts by use of an in vitro biotest battery following treatment for toxicity reduction in bioreactors showed that considerations of different toxicological endpoints is essential for an adequate hazard assessment. Whereas in the case of cytotoxicity reduction, the reactors proved ineffective, mutagenicity could be reduced significantly at least in some cases in this case study.

National Category
Other Environmental Engineering
Research subject
Enviromental Science
Identifiers
urn:nbn:se:oru:diva-2917 (URN)10.1007/BF02979645 (DOI)15506634 (PubMedID)
Available from: 2005-10-07 Created: 2005-10-07 Last updated: 2017-12-14Bibliographically approved
2. Fate of Ah receptor agonists during biological treatment of an industrial sludge containing explosives and pharmaceutical residues
Open this publication in new window or tab >>Fate of Ah receptor agonists during biological treatment of an industrial sludge containing explosives and pharmaceutical residues
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2004 (English)In: Environmental science and pollution research international, ISSN 0944-1344, E-ISSN 1614-7499, Vol. 11, no 6, p. 379-386Article in journal (Refereed) Published
Abstract [en]

GOAL, SCOPE AND BACKGROUND:

Sweden is meeting prohibition for deposition of organic waste from 2005. Since 1 million tons of sludge is produced every year in Sweden and the capacity for incineration does not fill the demands, other methods of sludge management have to be introduced to a higher degree. Two biological treatment alternatives are anaerobic digestion and composting. Different oxygen concentrations result in different microbial degradation pathways and, consequently, in a different quality of the digestion or composting residue, It is therefore necessary to study sludge treatment during different oxygen regimes in order to follow both degradation of compounds and change in toxicity. In this study, an industrial sludge containing explosives and pharmaceutical residues was treated with anaerobic digestion or composting, and the change in toxicity was studied. Nitroaromatic compounds, which are the main ingredients of both pharmaceutical and explosives, are well known to cause cytotoxicity and genotoxicity. However, little data are available concerning sludge with nitroaromatics and any associated dioxin-like activity. Therefore, we studied the sludge before and after the treatments in order to detect any changes in levels of Ah receptor (AhR) agonists using two bioassays for dioxin-like compounds.

METHODS:

An industrial sludge was treated with anaerobic digestion or composting in small reactors in a semi-continuous manner. The same volume as the feeding volume was taken out daily and stored at -20 degrees C. Sample preparation for the bioassays was done by extraction using organic solvents, followed by clean up with silica gel or sulphuric acid, yielding two fractions. The fractions were dissolved in DMSO and tested in the bioassays. The dioxin-like activity was measured using the DR-CALUX assay with transfected H4IIE rat hepatoma pGudluc cells and an EROD induction assay with RTL-W1 rainbow trout liver cells.

RESULTS AND DISCUSSION:

The bioassays showed that the sludge contained AhR agonists at levels of TCDD equivalents (TEQs) higher than other sludge types in Sweden. In addition, the TEQ values for the acid resistant fractions increased considerably after anaerobic digestion, resulting in an apparent formation of acid resistant TEQs in the anaerobic reactors. Similar results have been reported from studies of fermented household waste. There was a large difference in effects between the two bioassays, with higher TEQ levels in the RTL-W1 EROD assay than in the DR-CALUX assay. This is possibly due to a more rapid metabolism in rat hepatocytes than in trout hepatocytes or to differences in sensitivities for the AhR agonists in the sludge. It was also demonstrated by GC/FID analysis that the sludge contained high concentrations of nitroaromatics. It is suggested that nitroaromatic metabolites, such as aromatic amines and nitroanilines, are possible candidates for the observed bioassay effects. It was also found that the AhR agonists in the sludge samples were volatile.

CONCLUSIONS:

The sludge contained fairly high concentrations of volatile AhR agonists. The increase of acid resistant AhR agonist after anaerobic digestion warrants further investigations of the chemical and toxic properties of these compounds and of the mechanisms behind this observation.

RECOMMENDATION AND OUTLOOK:

This study has pointed out the benefits of using different types of mechanism-specific bioassays when evaluating the change in toxicity by sludge treatment, in which measurement of dioxin-like activity can be a valuable tool. In order to study the recalcitrant properties of the compounds in the sludge using the DR-CALUX assay, the exposure time can be varied between 6 and 24 hours. The properties of the acid-resistant AhR agonists formed in the anaerobic treatment have to be investigated in order to choose the most appropriate method for sludge management.

National Category
Other Environmental Engineering
Research subject
Enviromental Science
Identifiers
urn:nbn:se:oru:diva-2918 (URN)10.1007/BF02979656 (DOI)
Available from: 2005-10-07 Created: 2005-10-07 Last updated: 2017-12-14Bibliographically approved
3. Genotoxicity of nitroaromatic compounds in sludge after large scale biological treatment in aerated and nonaerated sacs
Open this publication in new window or tab >>Genotoxicity of nitroaromatic compounds in sludge after large scale biological treatment in aerated and nonaerated sacs
(English)Manuscript (Other academic)
National Category
Other Environmental Engineering
Research subject
Enviromental Science
Identifiers
urn:nbn:se:oru:diva-2919 (URN)
Available from: 2005-10-07 Created: 2005-10-07 Last updated: 2017-10-18Bibliographically approved
4. Reed beds receiving industrial sludge containing nitroaromatic compounds: effects of outgoing water and bed material extracts in the umu-C genotoxicity assay, DR-CALUX assay and on early life stage development in Zebrafish (Danio rerio)
Open this publication in new window or tab >>Reed beds receiving industrial sludge containing nitroaromatic compounds: effects of outgoing water and bed material extracts in the umu-C genotoxicity assay, DR-CALUX assay and on early life stage development in Zebrafish (Danio rerio)
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(English)Manuscript (Other academic)
National Category
Other Environmental Engineering
Research subject
Enviromental Science
Identifiers
urn:nbn:se:oru:diva-2920 (URN)
Available from: 2005-10-07 Created: 2005-10-07 Last updated: 2017-10-18Bibliographically approved

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