Alexander Szabo and Oscar Engle - Svenskt Vatten

3. Pond Hydraulics
3.1 Retention time
When dimensioning a pond, the water flow behavior is crucial. One of the key parameters is the
“retention time”, or “hydraulic retention time” HRT, which occurs as a key parameter in almost
every calculation. The retention time tells us how long the water, on average, stays within the
pond. The formula for retention time is:
θ= pollutant concentration (mg/l)
r is in the form of ammonium (ay be necessary to add. There is also extra sludge produced from
this method.
Sludge treatment
Sludge created from waste water treatment could easily become a public-health hazard if not
handled properly. What to do with the sludge is today considered as one of the main problems in
waste water treatment. Still, there are several methods to choose from when selecting
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