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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. - PowerPoint PPT Presentation
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7th International Conference on Sewer Processes and Networks
(SPN7)
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 ?
7th International Conference on Sewer Processes and Networks
(SPN7)
Population Attendance
7th International Conference on Sewer Processes and Networks
(SPN7)
Summer
season
Winter season
30 days acum
Max 1 hour
Rio de Janeiro rainfall regime
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
7th International Conference on Sewer Processes and Networks
(SPN7)
COMBINED 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
7th International Conference on Sewer Processes and Networks
(SPN7)
STORM
SEWERAGE
Brazil applies separate system
Partially treated = pollution
7th International Conference on Sewer Processes and Networks
(SPN7)
Deficient separate systems pollute
Irregular dwelling connections & interconnections
Irregular housing = irregular connection
Decentralized bad performance First flush water quality
7th International Conference on Sewer Processes and Networks
(SPN7)
How to improve separate efficiency ?
IF SEPARATE AREN’T EFFECTIVEIF COMBINED AREN’T REASONABLE
WET
DRY WET
DRY
DRY-WEATHER FLOW WATER INTAKE 1
7th International Conference on Sewer Processes and Networks
(SPN7)
How to improve separate efficiency ?
IF SEPARATE AREN’T EFFECTIVEIF COMBINED AREN’T REASONABLEDRY-WEATHER FLOW WATER INTAKE 2
7th International Conference on Sewer Processes and Networks
(SPN7)
852 L/s218 L/s
860 L/s
5.0 m³/s
It will improve separate efficiency, but concerns about
GRIT …
18.0 x 10-5 m3grit/m3 (WEF, 1992): 13.3 + 3.4 + 13.4 t grit/d
7th International Conference on Sewer Processes and Networks
(SPN7)
CONCERNS ABOUT GRIT – 1GRIT 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
7th International Conference on Sewer Processes and Networks
(SPN7)
CONCERNS ABOUT GRIT – 2GRIT 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
7th International Conference on Sewer Processes and Networks
(SPN7)
CONCERNS ABOUT GRIT – 3GRIT 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
Tractive tension requirements
Particle diameter d50 (mm)
0.1 0.2 0.5 1.0 2.0 5.0Without thin sediments 1.2 1.3 1.5 2.0 2.9 6.0Low quantity thin sediments
2.4 2.5 2.7 2.9 3.9 8.1
High quantity thin sediments
3.8 3.8 4.1 4.4 5.4 9.0 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
7th International Conference on Sewer Processes and Networks
(SPN7)
CONCERNS ABOUT GRIT – 4GRIT 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.
7th International Conference on Sewer Processes and Networks
(SPN7)
CONCERNS ABOUT GRIT – 5URBAN 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.
7th International Conference on Sewer Processes and Networks
(SPN7)
How to improve separate efficiency ?
IF SEPARATE AREN’T EFFECTIVEIF COMBINED AREN’T REASONABLE
IN RIVER WATER TREATMENT
?