Modern wastewater disinfection

2. Table of contents • Aims of wastewater disinfection • Indicator and target microorganisms • Modern wastewater disinfection methods • PAA, UV, Ozone, combinations Copyright © PAC-Solution Ltd. All rights reserved.

3. Aims of wastewater disinfection • Reach limits set by legislation (indicator microorganisms) • Protect publich health • Protect environment • Water reclamation (agriculture, potable water) • Image reasons: e.g. tourism Copyright © PAC-Solution Ltd. All rights reserved.

4. Indicator microorganisms • Are used instead of the actual pathogenic organisms • Reason: easier, cheaper and faster to analyze • Indicator organisms behave similarly to pathogenic organisms in disinfection • Indicators are not harmful to human themselves • Indicator organism don’t always give correct assesment of the situation: during a water epidemic indicator organism levels can be OK but there are still infections Copyright © PAC-Solution Ltd. All rights reserved.

5. Some generally used indicators • Escherichia coli: indicates fresh faecal contamination • Enterococcus faecalis and other Enterococci: indicates faecal contamination but non-intestinal species complicate interpretation • Faecal coliforms: indicates typically surface water run-off to wells and groundwater • Coliphages: virus parasitizing on E. Coli, indicates presence of enteric viruses, abundant in waste water (easy to analyse) Copyright © PAC-Solution Ltd. All rights reserved.

7. Bacteria removal during regular wastewater treatment (Source: Wastewater engineering, Treatment and Reuse, 2004) Process Percent removal (bacteria) Coarse screens 0 – 5 Fine screens 10 – 20 Grit chambers 10 – 25 Plain sedimentation 25 – 75 Chemical Precipitation 40 – 80 Activated sludge 90 – 98 → This is not usually enough, additional disinfection is needed! Copyright © PAC-Solution Ltd. All rights reserved.

8. Ideal disinfectant characteristics (Source: Wastewater engineering, Treatment and Reuse, 2004) • Availability: readily available and reasonable price • Deodorizing ability • Homogeneity: uniform composition • Should not be absorbed by organic matter other than bacterial cells • Nontoxic to higher forms of life • Penetration through surfaces • Safety: transport, store, handling and use • Solubility: soluble in water or cell tissue • Stability: low loss of germicidal action as a function of storage time • Toxicity to microorganism • Toxicity at ambient temperatures: also at low temperatures! Copyright © PAC-Solution Ltd. All rights reserved.

9. Modern / advanced wastewater disinfection methods: current status • Peracetic acid (PAA): IN USE • Performic acid (PFA): IN USE / RESEARCH LEVEL • UV: IN USE • UV / PAA: RESEARCH LEVEL • UV / hydrogen peroxide: RESEARCH LEVEL • Ozone: IN USE • Ozone / hydrogen peroxide: RESEARCH LEVEL • Chlorine dioxide: IN USE Copyright © PAC-Solution Ltd. All rights reserved.

10. Why chlorine is not involved? • Chlorine (NaOCl, Ca(OCl)2, Cl2) are not considered “advanced” because: • Formation of toxic and carsinogenic disinfection-by- products (DBP) • Corrosion • Toxicity of the chemical (especially Cl2 gas) and safety hazards • Increase of salinity in receiving water body Copyright © PAC-Solution Ltd. All rights reserved.

11. Peracetic acid (PAA) • Available as stabilized equilibrium solution (PAA-% typically 5 or 12): • CH3COOH + H2O2 ↔ CH3COOOH + H2O • Widely used by food industry, paper mills and medical facilities as a disinfectant. FDA certified in the USA. • Disinfection efficiency depends on wastewater characteristics, dosage, contact time • No (harmful) disinfection by-products and actually PAA can oxidize some DPB-type compounds • No re-activation of microbes after treatment Copyright © PAC-Solution Ltd. All rights reserved.

13. Peracetic acid: example of results from Mikkeli WWTP in Finland (summer 2011) 11000 0 3 3 0 0 12000 10000 8000 6000 4000 2000 0 16.5. 20.5. 24.5. 30.5. 6.6. 20.6. Colony forming units Copyright © PAC-Solution Ltd. All rights reserved. E.Coli Before PACS8 system PACS8 system in use

14. Scientific studies / pilot tests with PAA • In many scientific studies the used concentrations of peracetic acid were very high, for example: Reference Used PAA (mg/l) Salgot et al. Wat. Sci. Tech.: Wat. Supply, 2002, 2, 213-218. • With accurate control of dosing based on residual disinfectant and redox potential much smaller dosages can be used Copyright © PAC-Solution Ltd. All rights reserved. 15 - 30 Velasqueza et al. Enviromental Technology, 2008, 29, 1209-1217. 20 Liberti et al. J.CIWEM, 1999, 13, 262- 269. 1 – 500

17. Disinfection mechanisms of PAA 1. Release of “active” oxygen which disrupts sulfhydryl (–SH) and sulphur (S-S) bonds in proteins, enzymes and other metabolites. 2. Release of hydroxyl radicals (OH·) and superoxide anions (O2 Copyright © PAC-Solution Ltd. All rights reserved. -). 3. Double bonds of biomolecules are reacted. 4. Disruption of chemiosmotic function of lipoprotein cytoplasmic membrane and transport through the cell wall. 5. Protein denaturation. 6. Possibly inactivation of catalase enzyme.

18. PAA: Factors affecting disinfection • Temperature: higher temperature → better disinfection results • pH: greater activity at lower pH: this is because dissociation of peracetic acid: • CH3COOOH ↔ CH3COOO- + H+ (pKa = 8,2) • Protonated form (CH3COOOH) is considered biocidal • Optimal pH is 5 to 8 • Organic matter (COD, BOD, TOC) consumes PAA • Total suspended solids (TSS) protects microbes: higher the TSS the higher dose is needed Copyright © PAC-Solution Ltd. All rights reserved.

19. Disinfection by-products Disinfection method Known DBPs and decomposition products Comments Chlorine (Cl2, NaOCl, Ca(OCl)2) Chlorinated organic compounds (e.g. trihalomethane) Carsinogenic, mutagenic, toxic DBPs Chlorine dioxide (ClO2) Chlorite, chlorate In proper conditions, no halogenated DBPs are formed. Chlorite and chlorate are however carsinogenic. UV No DBPs at dosages used for disinfection High UV doses can cause DBPs to form. Ozone Carboxylic acids, aldehydes, ketones, keto acids, brominated compounds Large increase in AOC, carsinogenic, mutagenic, toxic DBPs. Peracetic acid Acetic acid, hydrogen peroxide, oxygen, water, carboxylic acids No harmful DBPs in significant quantities, slight increase in BOD.

21. UV • UV radiation: 100 – 400 nm, germicidal action: 220 – 320 nm. Water must have high transmittance in this region. • Disinfection mechanism: damages DNA, inhibits transcription and replication Copyright © PAC-Solution Ltd. All rights reserved. (Source: Wastewater engineering, Treatment and Reuse, 2004)

23. UV of Fe and SS: a case example • Wastewater included Fe about 3 mg/l and SS about 30 mg/l → UV254 transmission only 32 %. → also singnificant fouling effects. • Source: Gehr, R., Wright, H. Water Science and Technology, 38, 15-23. Copyright © PAC-Solution Ltd. All rights reserved.

24. Emerging UV lamp technologies • Pulsed energy broad-band xenon lamp • High temperature plasma is produced by pulsing UV radiation. • Spectrum includes UV, visible, IR wavelengths. • 20 000 as intense as sunlight at sea level. • Rapid energy delivery and inactivation • Narrow-band excimer UV lamp • Excited dimers are produced and as they collapse, energy (radiation) is released. Radiation characteristics depend on used gas (e.g. Xe or Kr) • Very monochromatic radiation is produced (e.g. 172, 222 or 308 nm) Copyright © PAC-Solution Ltd. All rights reserved.

25. Photoreactivation • Some microorganisms have photorepair mechanism: • Enzyme-mediated (photolyase enzyme) • Happens when UV-damaged microbes are exposed to light of wavelenght 300 – 500 nm. • For example Legionella pneumophila can photoreactivate nearly completely after irradiation with low or medium pressure UV! • How to prevent photoreactivation? • UV dose that achieves complete cell inactivation is needed – difficult to determine in practice. Copyright © PAC-Solution Ltd. All rights reserved. Source: Maclean, M. et al Proceedings of the 2008 IEEE International Power Modulators and High Voltage Conference, PMHVC , art. no. 4743649, pp. 326-32

26. Dark repair • Another mechanism of certain microbes to recover from UV radiation • Also called nucleotide excision repair • Coordination of several proteins to excise and repair the damaged DNA segment • In practise not so important as photoreactivation (much slower kinetics) Copyright © PAC-Solution Ltd. All rights reserved.

27. Negative aspects of UV disinfection • Energy consumption (around 70 – 500 W / lamp) • Photoreactivation of microorganisms after UV treatment. • Colour, turbidity, suspended solids decrease UV transmittance and disinfection efficiency. • No odour control. • High investment costs. Copyright © PAC-Solution Ltd. All rights reserved.

28. UV / PAA • Synergistic system still at RESEARCH LEVEL. Lubello et al. Wat Sci Tecnol: Wat. Supply, 2002, 2, 205-212. Copyright © PAC-Solution Ltd. All rights reserved. UV (120 mW s / cm2) PAA 4,8 ppm + UV (120 mW s / cm2) E. Coli inactivation (log N0/N) 3,1 3,7 Faecal coliforms inactivation (log N0/N) 2,9 3,4 Total coliform inactivation (log N0/N) 3,0 3,6

29. UV / hydrogen peroxide • Hydrogen peroxide has relatively weak additional effect Lubello et al. Wat Sci Tecnol: Wat. Supply, 2002, 2, 205-212. Copyright © PAC-Solution Ltd. All rights reserved. UV (120 mW s / cm2) H2O2 4,8 ppm + UV (120 mW s / cm2) E. Coli inactivation (log N0/N) 3,1 3,2 Faecal coliforms inactivation (log N0/N) 2,9 2,8 Total coliform inactivation (log N0/N) 3,0 3,1

30. Ozone • Not widely used in waste water disinfection • Produced in-situ, usually via electrical discharge method. • Ozone decomposes to free radicals (HO2 and HO•) • Disinfection mechanism is cell wall disintegration (cell lysis) • Produces DPBs: brominated organic compounds (if bromine present) or aldehydes, ketones etc. Copyright © PAC-Solution Ltd. All rights reserved.

31. Energy requirements of ozonation Component kWh / kg ozone Air preparation (compressors and dyers) Copyright © PAC-Solution Ltd. All rights reserved. 4,4 – 6,6 Ozone generation (air feed) 13,2 – 19,8 Ozone contacting 2,2 – 6,6 Other 1,2 – 2,2 Total: 21 – 35,2 kWh / kg ozone Typical dosing: 1 – 40 mg/l depending on wastewater

32. Ozone / hydrogen peroxide (Peroxone) • Advanced oxidation process (AOP) • Two-step process: 1. Ozone dissolution 2. Hydrogen peroxide addition • Aim is to enhance the formation of radicals • Possible more effective than ozone itself • Still at RESEARCH STATE. Copyright © PAC-Solution Ltd. All rights reserved.

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