Waste stabilisation Ponds or Oxidation Ponds Flashcards
1
Q
Advantages of WSP in Today’s Society
A
- Use of solar and wind energy
- Excellent disinfection if short circuiting is minimised
- Potential to use new technologies to improve effluent quality
2
Q
Current Design of WSP - Best Practice
A
- Fine Screeening
- Anaerobic or settlement zones
- Mechanical aerator/mixer assistance
- Avoidance of localised over loading
- Mixing essential in calm conditions to bring algae to surface for sunlight
- biofilm surface
- Multiple ponds-in-series for greater efficiency
- To reduce short circuiting, position inlet and outlets with flow against prevailing wind
- Flat floors reduce wind driven current short circuits
- Stub baffles effective in smaller ponds but not in large ponds
- Primary ponds can be nearly square to allow complete mixing and encourage algae growth
- Design for 84kgBOD/ha.d
- 2/3 primary ponds in parallel to give flexible loading
- Maturation ponds can be elonganted to approximate plug flow
3
Q
Improvement Options
A
WSP Variations
- Anaerobic/aerobic
- Facultative ponds
- Multi maturation cells in series
- AIPS
- High rate add-ons e.g. PETRO
Rock filters or trickling filters for ammonia reduction
Wetlands
4
Q
Add-on Improvements
A
- UV disinfection
- Chemical dosing
- Dissolved Air Flotation
- Sand Filtration
- Membrane Filtration
5
Q
Indicator/Pathogen Reduction
A
- Normally used indicators are all reduced by ponds-in-series
Concentrations
6
Q
Good Natural Pathogen Removal in Christchurch WWTP Ponds
A
- Sunlight
- Dissolved Oxygen
- Temperature
- Retention time
- pH
- Predation
- Settlement
7
Q
Sunlight Inactivation
A
- Photobiological damage
- Internal photo-oxidation
- External photo-oxidation
- Adequate dissolved oxygen is important >4g/m^3
8
Q
Sludge Management
A
- Deeper ponds to allow for more sludge and greater depth of overlying liquid to control odour
- Creating deeper pit near inlet will store incoming solids and create ideal conditions for anaerobic digestion
- Sludge removal needed every 15-30yrs
- Economic to construct extra primary pond so pond can be drained and sludge air-dried
- Sludge can be air dried and removed by excavator
- Sludge can be removed as a slurry using suction cutter dredge or by pumps on pontoon
- Slurry can be dewatered using portable belt press or centrifuge with polymer dosing
- Sludge disposal can be to on-site landfill or regional landfill or forests
9
Q
WSP are sustainable because
A
- Utilise green energy
- sunlight provides excellent disinfection
- Multiple ponds-in-series or baffles reduce short circuiting
- Add-on processes can reduce ammonia, phosphorus and pathogens
- Sludge can be processed using solar and air drying but extra space required
