a thought arise from an article of National Geographic:

In the last NG magazine of June there is an interesting article about solar storms written by Timothy Ferris:

Sun Struck - The space-weather forecast for the next few years: solar storms, with a chance of catastrophic blackouts on Earth. Are we prepared?

http://ngm.nationalgeographic.com/2012/06/solar-storms/nasa-photography

<A Carrington-class storm could fry more transformers than the power companies keep stockpiled, leaving millions without light, potable water, sewage treatment, heating, air-conditioning, fuel, telephone service, or perishable food and medications during the months it would take to manufacture and install new transformers. A recent National Academy of Sciences report estimates that such a storm could wreak the economic disruption of 20 Katrina-class hurricanes, costing one to two trillion dollars in the first year alone and taking a decade to recover from.

“We cannot predict what the sun will do more than a few days ahead of time,” laments Karel Schrijver of Lockheed Martin’s Solar and Astrophysics Laboratory in Palo Alto, California. 
(full text and video at http://ngm.nationalgeographic.com/2012/06/solar-storms/ferris-text).>>


In the underliner text you can read that everything that works with energy input may have problems.. also traditional sewage treatment!!!
Well, usually treatment wetlands do not have problems because the energy input is very limited!!! an horizontal flow bed doesn't require energy or pumps for his functioning... a vertical bed could be feeded with a mechanical syphoon!!!