Evapotranspiration rates for reed beds

[ashtree]

I am looking for some evapotransporation rates for reed beds processing wastewater.

I know there are many variables but i am looking for some approximate ranges (or even a % of pan rate evaporation) as a starting point to see if this technology would be appropriate for one of the treatment plants i work at.

Google so far has not thrown up anything that has been useful.



Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

 

[bimr]

Beware the invasion of non-native Phragmites, as it has been a problem.

Evaporation rates are generally governed by meteorological conditions and soil water availability. The Natural Resources Conservation Service has maps showing precipitation and potential evaporation.

The first link lists the pied piper of reed beds who should be able to answer any questions that you have on reed beds.

Link 1

Link 2

Link 3

Reed bed technology may feature low construction costs if land is free and construction costs are low. The operation and maintenance costs may be high or low. Some operators do not bother with the necessary maintenance with the resulting low O&M costs.

 

[ashtree]

Thanks bimr.

The plant involved has been the subject of a EPA violation simply because the existing reed bed basically had no basis for design and has had nothing done to it for years.
The bed handles effluent as a final polishing process and ultimately disposal via evapotranspiration and ground infiltration to end up as a zero discharge site.
However it does none of this very well and appears to be regularly discharging off site.
So I am attempting a reverse engineering of what is there already, and what needs to be there, as well as deciding how it should be operated.

Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

 

[bimr]

For some reason, people think that these wetland type systems require zero maintenance when in reality one is growing a crop that has to be managed and harvested.

This reminds me of a project a while back. I had an industrial project in Kentucky where the wastewater department manager wanted an environmental showcase for busloads of school children to visit. The original plant was zero discharge but was constructed on a site with clay hardpan. The first line operator told me that the discharge spray nozzle was moved around on the large site until they found a sinkhole that the wastewater disappeared into.

When the plant expanded, they hired an engineer who constructed a 7 section zero discharge wetland. The plant wastewater contained salts which of course would build up over time in the wetlands so it did not make any sense. Being in a part of the country where the rainfall exceeds the evaporation rate, I could not understand how it could be zero discharge. The State permitted it for 500 gpm intermittent discharge. I don't even know what intermittent discharge means.

In the interest of economic development, the State sometimes will permit this type of nonsense without much review and oversight, but it is not right.

 

[ckeller]

Depending upon the location, wetland ET may be very similar to lake evaporation (or about 80% of pan evaporation). Arid, windy areas produce higher ET rates in wetlands.

Zero discharge wetlands can be designed and operated successfully in regions where rainfall exceeds ET. Performance is usually controlled by the long-term saturated hydraulic conductivity of the soil profile. If the infiltration rate > (application rate - ET), then there should be no surface discharge. Some maintenance may be required depending on solids loading and other factors. Plant harvesting is not typical.

 

[bimr]

The zero discharge facilities, sometimes called evapotranspiration systems or 100% evapotranspiration systems, resemble constructed wetlands insofar as they are contained, planted areas used for effluent management, not treatment. However they are differentiated from treatment wetlands in that they are designed specifically to contain and then evaporate all of the effluent introduced and not have any discharge point.

On the other hand, treatment wetlands require harvesting since the pollutants of concern that are being removed in the treatment process (phosphorus, dissolved salts, etc.) will accumulate without some type of harvesting.