Friday, January 10, 2014

Graywater/Aquaponic Innovations

    Current centralized wastewater treatment technologies throughout the US remove roughly 80% of the macronutrients (heavy metals, nitrogen, phosphorus ... etc.) contained in wastewater streams before discharging the 'treated' wastewater into US waterways - streams, rivers, lakes.  One could argue that with greater technology comes greater treatment; however, when considering the energy necessary for current treatment, a more rational argument may point to the amount of wastewater originating from each private residence.  Consider the US EPA estimation of 100 gallons per person per day!

     We began research and development of graywater reuse combined with aquaponics in 2012.  Graywater is defined as wastewater stemming from household sinks, baths, showers, dishwashers, and clothes washers.  Aquaponics refers to a food growing system which utilizes an inhabited fish aquarium for irrigation and fertilization of edible plants.  Our pilot location was a 1920's apartment with twelve foot ceilings.  The concept was to capture wastewater exiting the kitchen sink in a bucket, then hoist the bucket to a high spot where we could slowly drain the bucket into a wetland system and ultimately into the fish tank.  Water from the fish tank, meanwhile, would be pumped up and into a series of grow beds above the tank, slowly draining excess water back into the tank.
The kitchen before system construction

Space within the apartment was extremely limited, thus we began devising a way to utilize vertical space.  With the concept in mind, we installed a 60 gallon fish tank complete with 4 koi.  Fish in aquaponics serve as the "canary in the coal mine" if you will.  If toxins are present in the system, or the pH is off, we will see it first in the health of the fish.  Healthy fish equal a healthy system overall.

Weight bearing ledgers installed
Our first order of business was to fully inspect the proposed area's structural integrity.  After poking around in the ceiling and walls, we were able to confirm that the   building was 'over built' -               structural timber was plentiful       and cheap in 1920s Missoula.  

By placing weight-bearing ledgers perpendicular to wall joists, we would be able to space the weight of the structure across the wall. Once the ledgers were up, it was time to create and install the wetland graywater system.

The wetland graywater system consisted of a series of specialized PVC pipes filled with medium, which would serve as a surface for bacteria and stability for the wetland plants.  Again, unfortunately, I did not think to take photographs as I was building the pipes or, as I like to call them, biofilters.  (The creation of this blog is helping me realize the necessary steps to have more valuable content.)  We utilized three types of biofilters, each having a slight difference in construction, but all having a very similar interior filter design.  By placing a stainless steel insert into the center of a tube, we were able to force the water down one side of the pipe and up the other.  We were able to modify this approach by simply adding a smaller diameter pipe inside the tube, forcing the water to travel down the inside pipe and then back up in the area between the two pipes.  In my opinion, this was the best filter model, as it requires little effort to build and lessens the chance for leakage.  Another model featured a smaller diameter pipe with a U shape; however, this filter proved to be the most troublesome of the bunch -  I'm not sure if it was the diameter difference or just an inappropriate attempt, but several times the pipe leaked.  If I were to set this system up again, I would certainly not include it.  Into each filter we fitted two outlets - a bib, or valve, near the bottom for draining and water sampling; and a barb adapter near the top for overflow.

Biofilters attached to the ledgers
Drain bucket, plants, and lights installed
We knew that we wanted aerobic bacteria so as to the limit unpleasant smells associated with anaerobic decomposition.  For this reason, we placed a large plastic wiffle ball in the bottom of each biofilter.  Inside each wiffle ball, we placed a bubbler and extended an air hose up and out of the biofilter.  While holding this air hose taunt, we filled the biofilter with large rocks, then more porous lava rock, followed by pea gravel. Finally, we planted wild harvested wetland plants in the pea gravel at the top of the tubes.  Once the filters were installed, they were filled with water from the aquarium in order to introduce beneficial bacteria and to feed the wetland plants.  We also added T5 grow lights above the filters to supplement lighting for the plants.

With the filters in place, we added a three-way valve under the sink that allowed us to divert water to a bucket or the sewer. Once the bucket was filled or, once a day, it was moved to the top of the system and allowed to drain into the first filter.   As the wastewater left the bucket, the incoming water displaced biofiltered water up and out of the first tube and into the next by way of the overflow adapter.  This water then displaces water in the next tube and so on until the bucket drains and additional overflow from the final filter enters the fish tank.

Unfortunately, or fortunately, depending on how you look at it, I was beckoned to a new location and the project halted after about 2 months.  We never installed the planter shelves that would support edible plants watered from the fish tank, as I made the decision to move into another house that was attached to a wonderful yard (and thus the food forest was born ... but more on that later). However, I wanted to share this experience with anyone interested as it was a successful means to treat household wastewater and we certainly would have been able to grow food, while decreasing the volume of wastewater leaving the house.  We'll pick this project back up again at some point, whether it be another in-home system or a larger greenhouse demonstration project.  Stay tuned!