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Isaac Volschan Jr. Water Resources and Environmental Engineering Department Federal University of Rio de Janeiro

Brazilian separate sewerage systems expansion faces the challenge of new alternative engineering solutions: how to deal with grit contribuitio from storm sewers ?. Isaac Volschan Jr. Water Resources and Environmental Engineering Department Federal University of Rio de Janeiro.

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Isaac Volschan Jr. Water Resources and Environmental Engineering Department Federal University of Rio de Janeiro

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  1. Brazilian separate sewerage systems expansion faces the challenge of new alternative engineering solutions: how to deal with grit contribuitio from storm sewers ? Isaac Volschan Jr. Water Resources and Environmental Engineering DepartmentFederal University of Rio de Janeiro

  2. Population Attendance

  3. Rio de Janeiro rainfall regime Summer season 30 days acum Max 1 hour Winter season • large difference between summer wet period and winter dry period • 30 days accumulation rainfall during wet periods achieves values 3.5 x higher than dry periods • during summer wet periods, 1 hour rainfall event reaches up to 50-80% of 30 days accumulation rainfall  very high rainfall 1 hour events are not frequent

  4. large structures would be required • be optimized for dry, but also for very high wet flows • present low frequency use, just for few high rainfall events COMBINED

  5. Brazil applies separate system SEWERAGE STORM Partially treated = pollution

  6. Deficient separate systems pollute Irregular dwelling connections & interconnections Irregular housing = irregular connection Decentralized bad performance First flush water quality

  7. How to improve separate efficiency ? IF COMBINED AREN’T REASONABLE IF SEPARATE AREN’T EFFECTIVE DRY-WEATHER FLOW WATER INTAKE 1 DRY WET WET DRY

  8. How to improve separate efficiency ? IF COMBINED AREN’T REASONABLE IF SEPARATE AREN’T EFFECTIVE DRY-WEATHER FLOW WATER INTAKE 2

  9. It will improve separate efficiency, but concerns about GRIT … 860 L/s 852 L/s 218 L/s 18.0 x 10-5 m3grit/m3 (WEF, 1992): 13.3 + 3.4 + 13.4 t grit/d 5.0 m³/s

  10. CONCERNS ABOUT GRIT – 1 GRIT DEPOSITION IN PUMP SUMPS • Interruption of pump operation • Material accumulation and even equipment grounding • Inside equipment devices or inside suction and discharge pipes • Higher hydraulic headlosses and even in clogging • Bad odours may occur • Designed to optimize geometrical sump volume and pumping efficiency • Grit removal mechanical equipments must be part of the enginnering solution in order to avoid excess grit accumulation

  11. CONCERNS ABOUT GRIT – 2 GRIT ABRASIVE INJURIES • Potentially abrasive due to the large amount of silica and its high hardness • Progressive loss of material, loss of equipment efficiency, and operational disruption • Pump impeller vanes, suction entrance devices and the initial section of discharge pipes • Ceramic coating on the pump metal surface, especially at the volute and impeller. • Steel mechanical parts with high chromium content and much higher abrasion resistance

  12. CONCERNS ABOUT GRIT – 3 GRIT DEPOSITION IN PIPES Brazilian guidelines design TRACTIVE TENSION  1,0 - 1,5 Pa Avoid deposit of organic solids < 0.2 mm, anaerobic degradation, hydrogen sulfide and odors Gupta, 2008 • frequent cleaning and unclogging should be required • main pipe: dia 2,000 mm and 13 m deep • mainholes are up 300 m apart • difficult and costly operation

  13. CONCERNS ABOUT GRIT – 4 GRIT DEPOSITION AT WWTP • To prevent sedimentation in primary clarifiers • Alegria WWTP: 5 grit chambers, square type • 3 years operational data: 90t grit/month • 1.5 t/m³ = 60 m³/month • Q=1.38 m³/s (36.3x105m³/m): 1.65x10-5m³ grit/m³ • Q=5.0 m³/s (129 x 105 m3/month): 214 m³ of grit/m • just due to sewage from separate sewerage network • QDWWI total flow= 50 x 105 m³/month • 18.0 x 10-5 m3 of grit/m3: 900 m³ of grit/m • 4 times the regular removal at Alegria WWTP • Wouldn’t disturb mineral discrete sedimentation • Would affect scrapers operation and effective removal • Sedimentation in primary clarifiers • Anaerobic Digestors may soon become overloaded.

  14. CONCERNS ABOUT GRIT – 5 URBAN AND ENVIRONMENTAL IMPACTS • Negative visual aspects at important sites of the city • Vehicles for operation and maintenance services, in special for removal of grit, may impact local traffic • Risk to odour generation.

  15. How to improve separate efficiency ? IF COMBINED AREN’T REASONABLE IF SEPARATE AREN’T EFFECTIVE IN RIVER WATER TREATMENT ?

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