Concentrations requirements for lagoon effluent BOD5
range from 15 to 30 mg/l. Existing ponds exceed allowable concentrations
for different reasons such as:
Abscence of mechanical aeration (shallow wastewater stabilization
ponds)
Inadequate hydraulic retention time (HRT) in existing ponds as a result
of flows exceeding the original design or because of excessive
sludge accumulation
Unefficient aeration systems in existing aerated lagoons
Solution
The ADS fine bubble aeration system used in a
PNW aerated lagoon system supplies oxygen, reducing CBOD5
to carbon dioxide, water, and inert ash by natural bacteria. Optimum
CBOD5 reduction in newly constructed lagoons and retrofitting in existing
lagoon are obtained by opting for this highly effective aeration technology.
ADS aeration is ideal for improving year around CBOD5
reduction in new lagoons and ponds originally designed as unaerated
wastewater stabilization ponds because of exceptional oxygen transfer
efficiency and grid coverage.
A typical partially mixed lagoon system in cold winter (water temperatures
of 0.5°C) should have a minimum hydraulic retention time (HRT) of
30 days split into either 2 or 3 cells to ensure adequate CBOD5
reduction. In the case of warm climate ponds where minimum water temperature
is approximatively, 15°C the minimum HRT should be of 12 to 15 days.
The CBOD5 concentrations, the temperature and
the effluent requirements influence the exact retention time required.
The upgrade of a failing existing aeration systems because of inadequate
oxygen transfer and mixing is a simple procedure without the need
to dewater or interrupt lagoon service. Upgrades of complex lagoon
configurations are feasible thanks to various aeration technologies
and air header options.
Result
CBOD5 removal efficiencies are 90 to 95% with
10 to 20 mg/l effluent concentrations for PNW municipal wastewater
lagoon.
BOD
is Biochemical Oxygen Demand and is the amount of Dissolved Oxygen (DO)
consumed by microorganisms for the biochemical oxidation of organic
and inorganic matter. This is a five day test that's why it's a lot
of times shown as BOD5. Much has been written about BOD and by going
to any wastewater treatment site on the WEB, you can find information
about BOD. The BOD test was developed to predict the effect of wastewater
on receiving streams and to determine their capacity to assimilate the
organic matter.