Monday, February 25, 2013

hybrid constructed wetlands

Hybrid systems are a combination of vertical flow and horizontal systems arranged in a staged manner. HF systems cannot provide nitrification because of their limited oxygen transfer capacity. VF systems, on the other hand, do provide a good conditions for nitrification but no denitrification occurs in these systems. In hybrid systems (also sometimes called combined systems) the advantages of the HF and VF systems can be combined to complement processes in each system to produce an effluent low in BOD, which is fully nitrified and partly denitrified and hence has a much lower total-N outflow concentrations (J. Vymazal, Ecological Engineering, Volume 25, Issue 5, 1 December 2005, Pages 478–490 . Constructed wetlands for wastewater treatment, abstract.

When I start to design a wetlands I always ask to myself "horizontal or vertical ? or hybrid?". Well, is not difficult to answer! I take into account the volume, the number of people treated, the available surface, energy input, and so on.
Usually I start with the horizontal, easy to be design, easy to be realized, no energy needed, and a lot of advantages.
If I have more than 50, 100 .. 450 cubic meters a day I'm sure I do an hybrid wetland with VF before and HF after. Yes, if we are in a place where the surface is free, and where there are no other problem I do an HF, sure. But usually for large volumes is better the hybrid wetland. As noted in the Vymazal abstract, the chemical reactions that occour in the two systems are different. in the hybrid system we have both, and the treatment  efficiency will be higher in less space!

For example you have to treat 100 m3 of municipal wastewater. 

1 Hp: only horizontal:
if you  build up only HF systems you need more or less 1800 square meters of treatment wetland

2 Hp: only vertical:
if you  build up only VF systems you need more or less 600 square meters of treatment wetland

3 Hp: hybrid system
if you  build up an hybrid wetland systems you need more or less 1200 square meters of treatment wetland

This comparison is not made for the capital cost of building and design, only to show you the difference between the design methods.
As you can see the VF surface is the lowest but usually you have to buy pumps systems and realize the tanks for the inlet pumping.
The HF have the highest surface but the lowest cost.
The hybrid is midway but be sure that will give you the best treatment performace you can reach because it combine aerobic and anaerobic environment.


jtcitrus said...

I'm thinking about running a traditional septic tank into a constructed wetland system where the treated effluent ultimately will empty into an aquaponics set up (pond w/ tilapia + grow beds for human consumption).

Therefore, I feel like I need to take the water quality up a notch from typical drain-field requirements?

The Constructed wetlands can be elevated with earth from digging out the pond.

I was thinking of a hybrid system using tidal flow CW's run by bell siphons with a Free Surface flow wetland as the polishing mechanism (effluent from the aquaponics grow beds would empty into the system at some point). What are your thoughts? Suggestions? Resources?

The septic will be fed by a family of four (to six; four bedroom house). Vegetation from constructed wetland will be used to supplement poultry feed.


Dave Toc PhD said...

Hello JTCITRUS, nice to meet you and thanks for contacting me. Write me at the email because is more fast. The project is good. With 4-6 persons you have probably 1 cubic meter a day of wastewater. With that volume you can easily build an horizontal flow treatment wetland. Then you can farm tilapia and then grow vegetbles. Usually we avoid the free surface wetland because the surface water could allow the growing of mosquitoes and grow wastewater odour. Why you use the syphon? Where are you located, in which Country?

jtcitrus said...

Other than the "follow by email" feature, I didn't see any functioning e-mail information.

I'm located near Houston, Texas in the United States.

I think perhaps that "tidal flow" was misnamed. Since the fish would be farmed for human consumption, I was thinking to take the water quality up a notch by doing a hybrid system, with the second stage being two flood/drain chambers in series with partial recirculation of the effluent to the first flood/drain chamber. I figured the drain cycle could be triggered by bell sipon or flout.

Here's a link to what I've been thinking. Don't know if it's over kill, over-priced, redundant or what! I hear you on the free-surface flow I was just, but you can see in the text where my mind was, though I'm all for simplifying things.

jtcitrus said...

And thanks for the response!

Dave Toc PhD said...

Hi, I think that the service "follow by mail" in the blogspot site doesn't work so well. I'm sorry. When I write a new post I think I'm the only one that receive the mail with the new post. Ok, go on with your project, but remember that you have more or less 1 cubic meter a day, and all the design must consider this.