We are currently at one of the most important crossroads in human history. Since the onset of agriculture 12,000 years ago in the Neolithic period, mankind’s primary habitat has been the village. 126 years ago, in 1890, a mere 200 million humans lived in cities - somewhere between 10 and 15 percent of the world’s population at the time. By 1950, this proportion had risen to one third, and currently, more than 50% of all people live in urban areas. This includes 28 mega cities, each with a population greater than 10 million. According to the Food and Agriculture Organization of the United Nations, by 2050, around three quarters of the world’s population will live in cities - an increase of 2.5 billion urban dwellers.
To cope with mass urbanization, we need to invent ways to make living in cities more sustainable. A big source of energy intensive infrastructure in cities is the transportation of water and food from farm to home. Hydroponics is a solution to transporting food from distant farms. You can use hydroponics to grown food all year round in the comfort of your living room. Recycling wastewater from sinks and taps known as "greywater" is a way to eliminate the haul of water out of the city to the waste treatment plant. We propose a simple hydroponics system that is fed by recycled greywater after it passes through an easy gravel filter.
The materials used in the construction of this project are valued at $80. However, we found almost everything we needed by scavenging around a college campus in Minnesota.
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Step 1: Materials
In the spirit of sustainability, we put almost our entire system together using scavenged materials; most notable was our use of red Solo Cups.
To find leftover PVC pipes and buckets, we recommend traveling to the facilities HQ of a nearby campus, for example a university or office complex.
The size of pipes and tubes in our materials, tools, and prices chart (above) were arbitrary - dependent on what we found scavenging. Whatever you end up using, just remember to adjust your hole and connector sizes accordingly!
Step 2: Cut 1” PVS Into Specified Dimensions
Starting with your 35 ft of 1” PVC pipe, use a hacksaw or other appropriate tool to cut into the following lengths, which are also shown in the above diagram:
4 x 5”, 5 x 4”, 2 x 10”, 2 x 11”, and 4 x 20”
Note: The left half of the structure is 1” shorter than the right (10” vs. 11”). This is purposeful. In hydroponics, the suggested slope is one inch down for every 30” to 40” across.
Step 3: Assemble Frame With 1” PVC
Use 8 elbow and 6 tee PVC connectors to put the frame together in the order shown in Figure 4.
Step 4: Drill Holes Into 4” PVC
Use a circle saw to cut 5 holes in the wider 4” pipe, spaced evenly apart.
Step 5: Place Into Frame
Insert the 4" PVC pipe with 5 drilled holes into the frame made from 1" PVC.
As explained earlier, one side of the frame is one inch taller than the other, so there should be a natural tilt, allowing for easy water flow.
We found that you can squeeze the frame into the PVC connectors so that the tilted pipe is naturally held in place. But, super glue or another adhesive wouldn't hurt as well.
Step 6: Block Open Ends
We found that the use of hot glue to attach extra plastic cups worked best for this step (see the horizontal cups in in the diagram in Step 1).
Step 7: Drill Holes Into the Cups for Plants.
Holes in the bottom of a cup allow roots from a plant to escape from the substrate and into the nutrient solution.
Step 8: Place the Plant-cups Into the Five Big Holes
Step 9: Complete the Hydroponics System
Connect pump to one plastic tube.
Connect that tube to the higher horizontal plastic cup (above, left).
Connect lower horizontal plastic cup to second tube without pump (above, right).
Place connected pump and open tube in central reservoir bucket, fill with nutrient solution, and turn on pump.
Nutrient solution should ender from the reservoir via the tube connected to the pump (left). Nutrient solution should flow back into reservoir via gravity (right).
Step 10: Incorporating Recycled Greywater System
Unlike any other hydroponics system that has instructions available on the internet, ours is meant to run on recycled greywater.
Do do so, we include here the instructions for a greywater gravel filter that feeds into the above described hydroponics system.
First, take your second bucket and use a hole saw or hole punch to create a 1" drain hole at the bottom.
Second, collect many different types of sand and gravel from your neighborhood and local park(s). Create layers of sand and gravel in the bucket, with coarser gravel on the bottom and finer sand on the top.
Third, connect the grey water filter to the indoor hydroponics system. Use a 1” plastic tube (or whichever size is appropriate for your bucket's drain hole) to connect the greywater filter to the indoor system. This is the black tube coming out of the blue bucket on the windowsill in the above picture.
Finally, this end product is just a mockup of the "Greywater Recycling Hydroponic System" that could one day be incorporated into your home. In it, more than one greywater filters could be connected and dually serve as massive hydroponics basins. Above is a sketch of such a system:
1) Water is recovered from an indoor source, such as a sink, and directed outside to the first large plant. 2) The large plant is supported by substrate, such as gravel, that acts as a filter for the water. The water flows through the filter, feeding the plant as it goes. 3) The process is repeated in another large plant. There could be just one large plant or as many as desired. 4) The water flows back toward the house, either relying on gravity or requiring a pump so that it can 5) re-enter the house and the small hydroponic system. 6) The filtered greywater cycles through the small hydroponic system. In order to avoid overwhelming the indoor reservoir, the outside section and indoor section would occasionally have to be disconnected.