1. Passive treatment of agro-industrial wastewater to meet stringent environmental and reuse requirements Passive treatment of agro-industrial wastewater to meet stringent environmental and reuse requirements Len Dekker and Mynhardt Theron

2. Wastewater characteristics ParametersUnits Raw wastewater After treatment Volume m 3 /day 1 600 1 400 pH 4.5 – 7.5 5.5 – 9.5 CODmg/L 5 500 73 Suspended solids mg/L < 2 000 21 ConductivitymS/m 120 – 180 150 Nitrogenmg/L 20 – 100 4 Phosphorusmg/L < 15 8

3. Conceptual design Rotary screen Raw tomato wastewater ANAEROBIC POND FACULTATIVE POND Venturi aerators ALGAL STABILISATION PONDS CONSTRUCTED WETLAND Sludge & alkalinity recycle Recycle for pH control 40% river discharge Chlorine dioxide 60% reuse by factory Settling tanks Sand filtration

4. Settling tanks Rotary screen

5. Anaerobic Pond

6. Facultative Pond

7. pump venturi

8. Algal Stabilisation Ponds

9. Algal biomass on surface

10. Constructed wetland divided into 4 cells

11. Operating details and cost per annum Electricity:60 kWh Labour:1 semi-skilled operator Chemicals:R20,000 per annum (Lime dosing during start-up) Sludge removal:no secondary sludge Maintenance:R50,000 per annum Operational complexity:conventional pumps utilised no complex PLC-controls Capital cost:R8 million (20% less than conventional system)

12. Benefits SLUDGE-FREE SYSTEM low maintenance + easy operation = SUSTAINABILITY Treatment components based on proven technology Effective water reuse not dependant on high-tech

13. Project Team Consultants:Dr. Len Dekker Mynhardt Theron Engineers:SKCM consulting engineers ldekker@mweb.co.zaldekker@mweb.co.za 083 309 7056