Treatment of Industrial Wastewater

1. M. Kolb, Fachhochschule Aalen Treatment of Industrial Wastewater 1. Chemical Industry 1.1 Biological treatment Because of the enormous adaptation ability of bacteria biocenosis waste- water of the chemical industry can often be biologically treated (aerobically). The following points must however be considered: In few cases the wastewater is treated anaerobically.

2. Schematic diagramm of the BASF Ludwigshafen wastewater-treatment plant Daily influx 700.000 m3 BOD5 load 375.000 kg/day BOD5 removal 97 % COD removal 89 % Nitrate removal 98 %

3. Special Bioreactors used in chemical industry Advantages: O2-Exploitation better21 % (air)  5 % (off-gas) ; normal activated sludge process: 21 %  16 % Lesser requirement of area Closed reactors  no emission of aerosols and odour

4. The Hoechst tall bioreactor (Biohochreaktor) process

5. Hoechst tall bioreactor (Biohochreaktor)

6. 1.2 Extraction Examples: Phenol can be extracted from wastewater with butyl acetate, cumene or diisopropylether. The remaining concentration is between 20 and 500 mg/l which is not toxic for the bacteria in the activated sludge tank. Phenol and the extraction solvent are separated in a following distillation process. The extraction solvent is reused in the process. Acetic acid can be extractedwith ethyl acetate, again the extraction solvent is recycled for the process and acetic acid is a valuable substance

7. 1.3 Adsorption (very important also for the purification of drinking water and waste gas) Adsorption processes are used for waste water generally, but mostly for individual wastewater streams. Adsorbents: Activated carbon Lignite coke Aluminium oxide Adsorber resins

8. Regeneration: Activated carbon can be thermally reactivated, i. e. the adsorbed substances are combusted Lignite coke is burned Aluminium oxide is thermally regenerated Adsorber resins can be regenerated with methanol or acetone Applications: Aniline is adsorbed from alkaline solutions, desorption by acid solutions Phenol is adsorbed from acidic solutions, desorption by alkaline solutions Landfill leachets (Deponie-Sickerwasser) can be treated biologically followed by ultrafiltration and activated carbon adsorption (for non-biodegradable substances) Special Application: Addition of activated carbon into the activated sludge basin  growth surface for microorganisms causes higher biomass concentration.

9. 1.4 Wastewater incineration (“Abwasserverbrennung”) • Combustion of organic substances, water matrix is simultaneously vaporized • Suitable if: • substances present are poorly biodegradable or biologically toxic • high organic load → heat of combustion is sufficient for vaporation of water • the wastewater contains a multicomponent mixture in which concentrations vary in a large amount • salts shall be recycled • Applications: • icincineration of wastewater from terephthalic production • incineration of wastewater which contains lignosulfonic acids • emulsified organic matter Problems: - metal corrosion by acids -  incrustination by salts -  flue gas treatment Combination with combustion of waste gases and solids is possible

10. Wastewater incineration Clariant AG, Gersthofen plant reasonable from ca. 50.000 mg/l COD, therephthalic acid (the combustion energy of the organic compounds meets the evaporation energy of the water)

11. 1.5 Wet Oxidation (Nassoxidation) Oxidation with O2 at higher temperature and higher pressure, water not vaporized Often followed by biological treatment Characteristics: -    for not degradeable or slowly degradeable or toxic substances -     for partial streams -     for high concentrations of contaminants -     some tolerance for salts and acids -     corrosion problems (Ti, PTFE)

12. Low pressure wet oxidation T < 200 °C, p = 5 – 20 bar At COD > 6.000 mg/l: heat recovery from enthalpy of oxidation is comparable to the total energy requirement of the process SO32-/HSO3-, phenol, amino- and hydroxyl substituted phenols, waste water from dye manufacturing AOX decreases, COD decreases, BOD5 increases High pressure wet oxidation T > 200 °C, p > 20 bar At COD > 50.000 mg/l: heat recovery from enthalpy of oxidation is comparable to the total energy requirement of the process

13. wet oxidation plant T = 300 °C, p = 120 bar

14. 1.6 Oxidation with H2O2, H2O2/UV, O3 Often followed by biological treatment H2O2: hardening plants, tanneries Selfdecomposition, catalyzed by heavy metal ions is unfavourable H2O2/Fe2+ (Fenton’s reagent): H2O2 HO+ + HO- Fe2+ + HO- Fe3+ + HO· HO· + H+ + e- H2O from oxidized substances Best results at pH 3 Neutralization leeds to sludge formation

15. O3, O3/UV: two mechanisms: so called direct oxidation under acidic conditions, slow process – can be accelerated by UV-rays O3 + hν O· + O2 O· + H2O  H2O2 H2O2 + hν 2 HO· alkaline oxidation takes place also via the intermediate formation of hydroxyl radicals O3 + HO- HO2- + O2 HO2- + O3·O2- + O2 + HO· H2O+ O3 + ·O2- HO- + 2 O2 + HO· Organic halogen compounds are dehalogenated, but formation of new organic halogen compounds from inorganic halides is possible

16. 2. Breweries, tanneries, papermills, creameries, food- production Wastewater can be treated biologically (aerob) but BOD5 : N : P-ratio has to be checked. Danger: Wastewater can cause the formation of bulking sludge (Blähschlamm). The extent of activated sludge flocs is diminished relative to filament-like organisms

17. Microscopic pictures of activated sludge many filament-like bacteria bulking sludge, slow sedimentation (115x) strong bacteria flocs (90x) Sphaerotilus natans, filament-like Bacteria (1150x) Vorticella spec. (230 x)

18. 3. Anaerobic treatment of wastewater Sugar industry, starch industry, yeast manufacture, alcohol destillation BOD5-concentration > 2000 mg/l Compare anaerobic treatment of sludge in municipal wastewater treatment Subsequent aerobically biological purification is necessary

19. Anaerobic degradation of organic substances to biogas

20. Advantages: • No energy for supplying the process with air • Energy rich biogas is formed • Less production of sludge (ca. 10 % compared with aerobic degradation) • Disadvantage: • Residence time longer (> 2 days)  not for treatment of municipal wastewater

21. Two-stage anaerobic fluidized-bed reactor for treating wastewater from baker’s yeast manufacture by Gist Brocades, Delft, Holland Carbon balances in the (A) aerobic and (B) anaerobic microbial degradation of organic compounds

22. pilot plant for anaerobic treatment of textile waste water (right) and aerobic treatment of municipal + textile waste water (left)Aalen-Unterkochen

23. cation-exchanger anion-exchanger  Polymer resin -SO3- H+ 4. Electroplating industry Many electroplating facilities After electroplating the workpiece has to be cleaned from the adhesive solution; by this washing process wastewater occurs wastewater contains toxic components: cyanide (CN-), chromate (CrO42-), Metal-ions and slowly biodegradeable organic components (EDTA) Special treatment of wastewater is necessary separated facilities for treatment of chromate, cyanide and acidic bathes former: wastewater from flow-basin was led directly into the detoxification plants, today it is led into ion-exchange facilities and reused in the flow-basins After regeneration of the ion-exchanger (HCl, NaOH) the concentrated solutions are detoxified

24. Cyanide: CN- + OCl- + H2O  Cl-CN + 2OH- (pH = 10 – 12) toxic Cl-CN + 2OH- OCN- + Cl- + H2O Disadvantage: chlorinated compounds are formed (AOX) with organic additives of the bathes Therefore: oxidation with H2O2/UV, O3, H2SO5, H2O2/H2SO5 Chromate: Cr2O72- + 3 HSO3- + 8H+ 2Cr3+ + 3HSO4- + 4 H2O (pH ~ 2,5) Metal ions: Me2+ + 2OH- Me(OH)2 Me3+ + 3OH-­ Me(OH)3 Precipitation with polymers containing –SH-groups or Na2S also possible

25. Sludge: Filter press, hazardous waste site Newer developments: Recycling of metal ions: electrolytic deposition after -         reverse osmose -         electrodialysys -         ion-exchanger