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

3. 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

4. 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

5. 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 Cl 2 dosage for ww is 2-10mg/l vs 0.2 to 2 mg/l for potable water

6. 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

7. CAPE FLATS WWTP MATURATION PONDS ( 1.2km 2 ) FOR 10 -12 DAY RETENTION DISINFECTION WITH SUNLIGHT

9. CALCIUM HYPOCHLORITE CHIPS

10. Calcium hypochlorite Another disinfection system with operational issues

11. Gas chlorination

16. ATHLONE WWTW MATURATION PONDS ( 90 000 m 2 ) FOR 1.25 DAY RETENTION

17. Assessing final effluent characteristics for possible UV disinfection technology

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

20. MEMBRANE TECHNOLOGY

25. The reason why disinfection is so important!

26. THE END

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

28. 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/cm 2 or mJ/cm 2 )= Intensity (mW/cm 2 ) * contact time (s) Recommended dose = > 30 mJ/cm 2 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