Full-Scale Biological Treatment of Industrial ... - ACS Publications

Chapter 11

Full-Scale Biological Treatment of Industrial Effluents Containing EDTA

Downloaded by CORNELL UNIV on October 24, 2016 | http://pubs.acs.org Publication Date: July 21, 2005 | doi: 10.1021/bk-2005-0910.ch011

Cornelis G. van Ginkel and Roy Geerts Akzo Nobel Chemicals Research, Velperweg 76, 6824 B M Arnhem, The Netherlands ([email protected])

In Europe, the ability of microorganisms to biodegrade E D T A aerobically under slightly alkaline conditions in existing full-scale activated sludge plants has been applied. The use of alkaline conditions in activated sludge plants is spurred by increasingly stringent environmental regulations. This process has been implemented in plants treating wastewater from pulp and paper mills at negligible costs. High removal of EDTA has also been observed in full-scale activated sludge plants treating wastewater from the dairy and beer industry. The results of monitoring studies of these full-scale activated sludge plants demonstrate removal efficiencies of more than 80%. The effectiveness of the activated sludge treatment is not only dependent on the pH level but also on the metal profile of the wastewater and the sludge retention time.

Introduction Ethylenediaminetetraacetic acid (EDTA) has numerous applications based on its ability to control the action of different metal ions. The pulp and paper industry and industrial and institutional cleaning are very important application areas. E D T A is used in the pulp and paper industry to stabilize the action of hydrogen peroxide on pulp by complexing with metals that catalyze the decomposition of peroxide. In industrial and institutional cleaners, E D T A is used to prevent precipitation of calcium and magnesium. As E D T A is water-soluble and not

© 2005 American Chemical Society Nowack and VanBriesen; Biogeochemistry of Chelating Agents ACS Symposium Series; American Chemical Society: Washington, DC, 2005.

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196 volatile, it is released mainly with wastewater effluents. In Europe, treatment of wastewaters containing E D T A is increasingly required because environmental regulations are becoming more stringent. Biological treatment of many industrial wastewaters has traditionally been based on methods successfully employed for processing domestic sewage. Aerobic processes, such as activated sludge systems, are the principle way in which naturally occurring microorganisms convert organic material into environmentally benign substances. E D T A has been reported to pass through conventionally operated biological treatment plante without notable degradation ( i , 2,3). However, the activated sludge process can be used to biodegrade E D T A under alkaline conditions (4, 5). Removal of E D T A in activated sludge systems also depends on sludge retention time (SRT) to ensure that EDTA-utilizing micro organisms do not wash out (4). Finally, it has been shown that the counter ions determine the treatability of E D T A (20 days (second). Part of the sludge of the second activated sludge plant is introduced into the first activated sludge plant. This system achieves a C O D removal of approximately 80%. B O D analyses show over 98% removal. The SRT of this 1

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Nowack and VanBriesen; Biogeochemistry of Chelating Agents ACS Symposium Series; American Chemical Society: Washington, DC, 2005.


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Figure 1. Removal of EDTA from wastewater derived from a dairy plant (V) in a CAS unit maintained at a pH of 8.7 to 8.9

activated sludge system could bring about E D T A removal. Under neutral conditions E D T A present in the effluent from the pulp and paper mill at concentrations ranging from 45 to 60 mg/L was not removed. However, at a p H of only 7.5 to 8.0 E D T A concentrations decreased to 2 mg/L at negligible costs. This represents >80% E D T A removal. The removal percentage can not be calculated with only the influent and effluent concentrations given because effluent from the paper mill is fed to the second reactor. The high E D T A removal percentages achieved at p H 7.5 to 8.0 have thus far only been obtained with wastewater from a dairy plant (4). M i l l Β producing T C F (totally chlorine free) bleached softwood paper, treats its wastewater in a reconstructed lagoon. The construction of a settling tank transformed the original biological treatment system into an activated sludge system. Since the reconstruction of the biological treatment plant was completed, discharges of C O D and B O D have fallen. The C O D removal of the activated sludge system averaged 77%. B O D removed amounted to 98 to 99%. The SRT of the plant is 30 to 50 days. The high SRT of the system allows E D T A removal (4). To obtain E D T A removal M i l l Β realizes alkaline conditions by 7

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reducing the concentration of sulfite in the influent of the activated sludge plant. At first a p H of approximately 8 was achieved using this approach. Under these conditions an average E D T A reduction of 70% was achieved. A further increase in E D T A removal was achieved by maintaining a p H of 8.5, resulting in an average E D T A effluent concentration of 4.5 mg/L corresponding to -85% removal of E D T A (Figure 2). Although the response of E D T A removal to the p H differs from one wastewater to another, an increase in the p H up to 8.5 usually leads to higher removal percentages (5). M i l l Β demonstrates that removal can be easily obtained at negligible costs.

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Time (weeks) Figure 2. Changes in EDTA concentration of influent (M) and effluent (Of) samples analyzed during full-scale activated sludge treatment of mill Β effluent. The pH was maintained at 8 from week 0 to week 8. From week 8 to week 43 the ρΗ was to 8.5

E D T A removal in activated sludge plants treating pulp and paper wastewater (approximately 80%) is lower than removal obtained with wastewater from dairy plants (over 90%). The different performance with respect to E D T A removal may be caused by different ratios of Fe and E D T A in the effluents since Fe-EDTA complexes have been shown to be recalcitrant (95% of the E D T A . The residual E D T A concentrations were therefore less than 5 mg/L of which, maximal 2 mg/L was complexed with Fe. This result demonstrates that high E D T A removal can be achieved by treating flows from bleaching plants separately.

Conclusions A few observations can be made from the monitoring studies. Slightly alkaline conditions are crucial to obtaining E D T A removal in activated sludge plants. The use of alkaline conditions proved to be a cost-effective and dependable technique for treatment of E D T A containing industrial effluents. Alkaline conditions exhibited no adverse effects on C O D and B O D removal during treatment. Available data suggest that the SRT should be more than approximately 20 days. Higher SRTs are a prerequisite when temperatures in the aeration tanks are lower than 15°C. E D T A removal may be determined by the ratio of E D T A and iron present in the wastewaters derived from the pulp and paper industry. Treatment options to reduce E D T A concentrations to acceptable levels in existing plants can be easily assessed in laboratory-scale C A S tests. 7

References 1. 2. 3. 4. 5. 6. 7. 8.

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