微生物降解edta

RESEARCH NOTE MICROBIAL DEGRADATION OF EDTA IN AN INDUSTRIAL WASTEWATER TREATMENT PLANT U. KALUZA, P. KLINGELHO FER and K. TAEGER* BASF Aktiengesellschaft, Speciality Chemicals, 67056 Ludwigshafen, Germany (First received May 1997; accepted in revised form January 1998) AbstractFor the fi rst time it is shown that EDTA is ultimately biodegraded under practical industrial wastewater treatment conditions, involving a Finnish plant dedicated to treat the e?uent from a paper mill. Monitoring measurements on the infl uent and the treated e?uent showed an EDTA elimination of about 80%. The mean EDTA concentration in the infl uent was 23.8 mg l?1and in the corresponding e?uent 5.8 mg l?1 . The biodegradability of EDTA was verifi ed in the laboratory with activated sludge from the treatment plant. Using a combined CO2/DOC method the total mineralization of EDTA was indicated by 80% CO2formation and r99% DOC removal. # 1998 Elsevier Science Ltd. All rights reserved Key wordsEDTA, biodegradability, CO2/DOC-combination test, industrial wastewater treatment plant, chlorine-free bleaching INTRODUCTION In the pulp and paper industry totally chlorine-free bleaching (TCF) is increasingly being adopted. This process employs hydrogen peroxide (H2O2) instead of chlorine compounds. The disadvantage is the rapidly catalyzed decomposition of the bleach by the manganese and iron ions contained in wood. Therefore hydrogen peroxide is stabilized by adding metal chelating agents such as EDTA. But it is commonly known that EDTA is poorly degradable in natural compartments despite the fact that there are several investigations showing the biodegrad- ability with mixed cultures under defi ned laboratory conditions (Klu ner et al., 1994; Henneken et al., 1995). The advantages of the TCF process would be even greater if EDTA could also be broken down biologically in wastewater treatment plants. MATERIAL AND METHODS Operating data of the treatment plant Hydraulic loading rate: ca. 10000 m3d?1 pH of infl uent: 5.35.8; pH of e?uent: 7.67.9 Sludge retention time: 9 d Temperature: 35408C over the whole year Mean hydraulic retention time: about 1 d Infl uent load: BOD: 10 t d?1; COD: 20 t d?1 Urea was added as a source of nitrogen in order to avoid bacterial growth from being curtailed by a lack of nitrogen. 700 kg of sludge was generated per tonne of BOD. Sampling and analysis Fifty separate samples of infl uent and treated e?uent were taken daily over a period of two weeks. The daily samples taken for determining EDTA were unfi ltered and preserved with 1% formaldehyde. The samples taken for determining the heavy metal content were stabilized with 0.5% HNO3. EDTA was determined in the form of its iron(III) complex by HPLC on RP 18 phase (Randt et al., 1993) withanUVdetectorat320 nm(detectionlimit R0.5 mg l?1). The heavy metal content was determined by means of ICP-AES (inductive coupled plasma-atomic emission spec- trometry). The sample was oxidized with perchloric acid and dissolved in hydrochloric acid and water (detection limit = 1 mg l?1). Biodegradability tests in the laboratory Biodegradability tests were performed with the activated sludge from the above industrial wastewater treatment plant using a combined CO2/DOC method that allows the simultaneously determination of the formation of CO2and of the DOC removal (dissolved organic carbon) (updated ISO 9439, 1998, Strotmann et al., 1995). The activated sludge was incubated at 358C with a concentration of 150 mg l?1dry solids. The incubation vessels were kept in the dark to exclude any photochemical degradation pro- cesses. Blank controls were proved to show real biological EDTA degradation. Wat. Res. Vol. 32, No. 9, pp. 28432845, 1998 # 1998 Elsevier Science Ltd. All rights reserved Printed in Great Britain 0043-1354/98 $19.00+0.00PII: S0043-1354(98)00048-7 *Author to whom all correspondence should be addressed. Tel: +49-621-6058015; Fax: 049-621-6058043. 2843 RESULTS EDTA removal in an industrial wastewater treatment plant EDTA concentration expressed as H4EDTA was measured in the infl uent and the e?uent of the wastewater treatment plant. The results indicate thatabout80%oftheEDTAwasremoved (Table 1). The results in Table 1 are reproducible because an earlier investigation indicated a removal degree of 87% at average EDTA infl uent and e?uent con- centrations of 43.5 mg l?1and 5.5 mg l?1. Biodegradability of EDTA in a laboratory test The evidence of high EDTA removal degrees in the described industrial treatment plant prompted us to confi rm the removal of EDTA was due to a biological mineralization process. Therefore exper- iments were performed according to the combined CO2/DOC method (Strotmann et al., 1995). This method allows a clear distinction between biodegra- dation and physical removal. According to the elev- ated temperature in the wastewater treatment plant the standard procedure (Strotmann et al., 1995) was performed at 358C. The result shows 80% CO2- formation and r99% DOC removal, obviously due to the biodegradation of EDTA (Fig. 1). EDTA test concentration: 20 mg l?1DOC. The biodegradability of EDTA is shown during an incu- bation time of 28 d at a temperature of 358C. Concentration and removal of heavy metals In wastewater EDTA is usually present in form of its metal complexes. The biodegradability of EDTA depends on the stability of the existing and/ or newly formed metal complexes (Henneken et al., 1996). For this reason it is important to determine the metal concentrations in the infl uent and e?uent (Table 2). As a result it could be shown that out of eighteen heavy metals only iron and manganese were present in concentrations above the detection limit and that a stoichiometric excess of the sum of these ions over EDTA was given. All metals were removed below the detection limit during the wastewater treatment. DISCUSSION There are several investigations showing the bio- degradability of EDTA with mixed cultures under defi ned laboratory conditions (Lau? et al., 1990; Gschwind, 1992; Klu ner et al., 1994; Henneken et al., 1995, 1996). Now it has been shown for the fi rst time that EDTA is about 80% biodegradable in an industrial wastewater treatment plant under techni- cal operating conditions. Evidence of the biodegra- dation was confi rmed by formation of 80% CO2 and r99% DOC removal in the combined CO2/ DOC test. Table 1. EDTA removal in an industrial wastewater treatment plant Infl uent concentrationE?uent concentration H4EDTAmg l?1mmol l?1mg l?1mmol l?1Removal degree Mean23.80.08145.80.0276% Standard deviation2.32.07 Maximum28.00.0969.00.03168% Minimum18.00.0623.00.0183% Fig. 1. Biodegradability of EDTA in the combined CO2/DOC test. Research Note2844 In wastewater EDTA is usually present in form of its metal complexes. The biodegradability of EDTA depends on the stability of the metal com- plexes (Henneken et al., 1996). The total concen- tration of iron and manganese ions in the infl uent was in stoichiometric excess against EDTA. It can be assumed that EDTA is discharged in the form of its iron and manganese complexes. This obviously has no detrimental e?ects on the biodegradation of EDTA nor on the removal of heavy metals, as is shown by the decrease of the Fe and Mn concen- trations in the e?uent. In laboratory experiments and by defi ned mi- crobial cultures (Henneken et al., 1996) iron com- plexes and other relatively stable complexes of EDTA are more di?cult to break down than mag- nesium or calcium complexes. If Ca and Mg ions exist in a stoichiometric excess, the composition of the metal complexes is slowly displaced in favor of the more degradable Ca and Mg complexes (Xue et al., 1995; Henneken et al., 1996). This process can be accelerated by increasing the pH as occurs between infl uent and e?uent of the treatment plant reducing the stability of FeEDTA and increas- ing the stability of other metal complexes (BASF, 1988). The phenomenon to improve biodegradation by increasing the pH is shown by (Van Ginkel et al., 1997). However, there is also evidence that the pure ironEDTA complex is biodegradable (Lau? et al., 1990). Furthermore it is known that the ironEDTA complex is unstable when exposed to sunlight and it is easily broken down directly by photolysis (BUA- Sto?bericht, 1996). This is an e?ective way to elim- inate EDTA, especially in receiving waters that con- tain little suspended solids (Kari et al., 1995). The results presented are a major improvement on those that have been obtained with specially selectedculturesunder defi nedlaboratorycon- ditions(Lau?etal.,1990;Gschwind,1992; Henneken et al., 1996). They illustrate very clearly that EDTA does not necessarily have to be persist- entunder conditions likewastewater treatment plants. REFERENCES BASF, Brochure Chelating Agents Trilon11988. BUA-Sto?berichtEthylendiamintetraessigsa ure/Tetrana- triumethylendiamintetraacetat(H4EDTA/Na4EDTA); BUA-Report ethylenediaminetetraacetic acid/tetrasodiu- methylenediaminetetraacetate(H4EDTA/Na4EDTA), 168,S.Hirzel,WissenschaftlicheVerlagsgesellschaft, Stuttgart 1996, ISBN 3-7776-0699-5. Gschwind N. (1992) Biologischer Abbau von EDTA in einemModellabwasser:Biologicaldegradationof EDTA in a model waste water. Wasser Abwasser 133, 546549. Henneken L., No rtemann B. and Hempel D. C. (1995) Infl uence of physiological conditions on EDTA degra- dation. Appl. Microbiol. Biotechnol. 44, 190197. HennekenL.,Bru ggenthiesA.,No rtemannB.and Hempel D. C. (1996) Teilstrombehandlung EDTA-halti- ger Abwa sser mittels Biofi lm-Wirbelbettreaktoren, treat- mentofpartialstreamcontainingEDTAwitha moving-bed biofi lm reactor. Chemie-Ing. Tech. 68, 310 314. ISO 9439, Water quality Evaluation in an aqueous med- ium of the ultimate aerobic biodegradability of organic compounds Method by analysis of released carbon diox- ide, updated ISO/DIS 9439 annex D, published 1998. KariF.G.,HilgerS.andCanonicaS.(1995) Determination of the reaction quantum yield for the photochemicaldegradationofFe(III)EDTA: Implications for the environmental fate of EDTA in sur- face waters. Environ. Sci. Technol. 29, 10081017. Klu ner T., Henneken L., Gehle M., Bru ggenthies A., No rtemann B. and Hempel D. C. (1994) Katabolismus von Ethylendiamintetraacetat (EDTA), Catabolism of ethylenediaminetetraacetate (EDTA).BIOforum 17, 284288. Lau? J. J., Steele D. B., Coogan L. A. and Breitfeller J. M. (1990) Degradation of the ferric chelate of EDT