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DISINFECTION: APPROPRIATE TECHNOLOGIES FOR WASTEWATER TREATMENT KA SAMSON

DISINFECTION: APPROPRIATE TECHNOLOGIES FOR WASTEWATER TREATMENT KA SAMSON Presented at the APPROPRIATE TECHNOLOGY CONFERENCE BMW CENTRE, CAPE TOWN, 3-4 SEPTEMBER 2007 Kevin.samson@capetown.gov.za. INTRODUCTION

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DISINFECTION: APPROPRIATE TECHNOLOGIES FOR WASTEWATER TREATMENT KA SAMSON

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  1. DISINFECTION: APPROPRIATE TECHNOLOGIES FOR WASTEWATER TREATMENT KA SAMSON Presented at the APPROPRIATE TECHNOLOGY CONFERENCE BMW CENTRE, CAPE TOWN, 3-4 SEPTEMBER 2007 Kevin.samson@capetown.gov.za

  2. INTRODUCTION WASTEWATER TREATMENT IS ONE OF THE FEW INDUSTRIES WHICH HAVE LIMITED INFLUENCE OVER THE QUALITY AND QUANTITY OF THE INCOMING RAW MATERIAL THE PRIMARY PURPOSE OF WASTEWATER TREATMENT IS TO ENSURE THE SAFE DISCHARGE OF THE TREATED EFFLUENT INTO THE ENVIRONMENT IN ORDER TO PROTECT PUBLIC HEALTH AND THE ENVIRONMENT

  3. IMPORTANCE OF DISINFECTION: it is the last barrier protecting the receiving water bodies and/or users from pathogenic organisms • Disinfection can be achieved through the application of heat, light, oxidizing chemicals. Some technologies are: • Sunlight (natural disinfectant) • Oxidizing chemicals: chlorine, ozone, chlorine dioxide, • hypochlorites (calcium & sodium), hydrogen peroxide • UV (Ultra-violet light) using mercury vapour lamps • Membranes

  4. Effective disinfection of wastewater is influenced by: • contact time (dependent of type of disinfectant) • concentration and the type of disinfecting agent/facility • wastewater demand (e.g. FSA) • flow rate (average vs peak) • concentration of the interfering substances (TSS,COD,FSA) • e.g. typical Cl2 dosagefor ww is 2-10mg/l vs 0.2 to 2 mg/l for potable • water

  5. To determine the appropriateness of the disinfection • technology for a specific WWTP, the following needs • to be considered: • influent wastewater characteristics • effectiveness of the treatment process • impact on the receiving environment • risks associated with the technology • costs (O&M and CAPEX) • simplicity of operation • reliability and effectiveness • maintenance & the degree of skills required

  6. DISINFECTION WITH SUNLIGHT CAPE FLATS WWTP MATURATION PONDS (1.2km2) FOR 10 -12 DAY RETENTION

  7. CALCIUM HYPOCHLORITE CHIPS

  8. Another disinfection system with operational issues Calcium hypochlorite

  9. Gas chlorination

  10. MATURATION PONDS (90 000 m2) FOR 1.25 DAY RETENTION ATHLONE WWTW

  11. Assessing final effluent characteristics for possible UV disinfection technology

  12. Membrane Filtration Membrane Solids Virus Treated effluent Air 0.04-0.4um Bacteria

  13. MEMBRANE TECHNOLOGY

  14. The reason why disinfection is so important!

  15. THE END

  16. COMPONENTS OF THE DIFFERENT UV LAMP TYPES Source: UV Technology for Municipal WWTPs in Canada (2003)

  17. UV DISINFECTION(… in general) • One installation in Cape Town - at the Potsdam WWTP • Principal parameter controlling the effectiveness is the UV dose • UV Dose (mW.s/cm2 ormJ/cm2)= Intensity (mW/cm2) * contact time (s) • Recommended dose = > 30 mJ/cm2 or UVT > 50% • Usually installed in the effluent channel eliminating the need for a • contact tank - short contact time required  2 sec to 15 sec • Lamp technologies: low pressure/low intensity (LP/LI), LP/HI, MP/HI • Power consumption: 87.5W per lamp • Lamp operating life: 12000 hrs

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