Specialist Group on Use of Macrophytes in Water Pollution ... - IWA

Do you see treatment wetlands as an ultimate solution for waste water? And if so, in
general or just occasional, i.e. when no sewer system is available?
I think the ultimate solution for wastewater would be to stop using water as a means to convey
our waste away from us, but I don‘t expect much headway on that in our lifetimes, so we are
kind of stuck with the system we have, at least in the developed world. Otherwise it depends on
the goals. I think treatment wetlands are the best option when flow rates are small enough that a
conventional system, i.e. activated sludge with advanced nutrient removal and anaerobic sludge
digestion, is too expensive. I don‘t think any other ‗alternative‘ or ‗natural‘ or extensive‘ or
‗low tech‘ system can compare performance-wise (BTW I don‘t like any of those terms, but
have never been able to come up with a better one). But for big flow rates or applications in
highly urbanized areas, I think the trade-off on land requirements for TWs makes conventional
systems the more logical option. I do worry about the carbon footprint cost for power required
to run a conventional system though. It would be an interesting exercise to do a life cycle
analysis between wetlands and conventional systems, hum ... next project �?
Here’s a daring question for you! Do you think the horizontal system is superior to the
vertical or is it the other way around or do we simply need them both?
Let‘s not forget our free water surface or floating island friends in this debate! I think there is
an appropriate application for everyone of those systems. But since you asked, for domestic
wastewater I like the hybrid system with a vertical flow (two stage??) followed by a
horizontal flow system, especially in the USA where we typically have nitrate limits as well
as TN and BOD and SS and …. everything else. The idea of taking raw WW to US discharge
standards using nothing but a wetland is really intriguing to me. And if we could do it in a
climate like Montana‘s, well even better.
Is there, to your knowledge, a TW that is an example for us all?
I think I just answered that. I like the hybrid systems with a primary first stage that I have
seen. I have to admit that I was a complete sceptic when I first heard them described at our
conference in Arusha, Tanzania, as I couldn‘t see how a system like that could possibly work
without plugging. But when I had the chance to see a few on the tour during the Avignon,
France conference, I was completely convinced. That is what made me realize that a TW
could be the complete system, raw wastewater to surface discharge.
Well, here you get close to what I actually meant: What physical wetland is an example
for us all? Are you talking about the Roussillon wetland, built by SINT (Dirk Esser) in
1998, we visited during that conference?
Ha, you are really trying to put me on the spot for my favourite system, and there are so many
good ones to choose from! But yeah, I do like the system I saw in Roussillon but I think for
US discharge standards we need to add an HF component on the back end to knock down the
nitrate that is generated, and there is also that sticky issue of long-term phosphorous removal.
One concern for that type of system to meet Montana discharge standards would be whether
there is enough organic carbon carryover from the VF component or production in the HF
component to drive denitrification. My research group is currently looking into that.
And the last question: who would you like to be interviewed the next time?
I would really like to know more about the views of one of our more experienced group
members: Paul Cooper. And finally, I want to thank you for the opportunity to ‗chat‘ with
you. I think this is great addition to the newsletter.
Interview by Frank van Dien
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10 IWA <strong>Specialist</strong> <strong>Group</strong> on Use of Macrophytes in Water Pollution Control: Newsletter No. 37