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18 Cards in this Set

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waste stabilisation ponds Advantages

-low capital cost and easy to design


-low operating and maintenance cost


-high level pathogen kill


-robust system


-can deal with load fluctuations due to long retention periods.


- resource recovery via algae harvest


-bio-gas generation in anaerobic ponds

waste stabilisation ponds disadvantages

-large land area requirement


-inconsistent nutrient removal


-lack of engineering process control


-performance influenced by climate

Types of ponds

- anaerobic


-facultative


-maturation

Anaerobic

-first pond in series


-high organic loading


-40-70% BOD removal


-2-5m deep, no algae

Anaerobic pond

Facultative pond

- most common pond type


- primary or secondary pond


- 1.5m depth


- contains anaerobic and aerobic zones.

faculatative pond

Maturation pond

- last in series


- polishing treatment


- pathogen and nutrient removal


- 1.5m deep



Pond treatment: Organics

-Primary settling occurs in the first pond

- they get anaerobically decayed in sludge layer

Pond treatment: pathogen removal

- high pathogen removal


Due to


- long retention time


-high PH


-Exposure to sunlight


-Oxygen presence


-competition by microbes

Pond treatment: Nitrogen and phosphorus removal

-60-80% removal


-removed by assimilation, biological nitrification/denitrification, settlement an removal of solids




-chemical precipitation at high ph


-biological uptake by algae

anaerobic pond design


Facultative pond design

maturation pond design

Wetlands advantages

- low capital and operating cost


- ease of operation


- minimal mechanical and electrical components

types of wetlands

1. surface flow


2. sub-surface flow

surface flow

-water passes through stem of plants.


- larger than subsurface flow wetland.

Subsurface flow

-water passes through media and past root zone-Aesthetically pleasing