Grey water treatment, why is it so important nowadays for organic farming ?
For the moment, at most Nepalese farms, including at the Spiral Farm House, the greywaters (from the bathroom and washing the dishes, clothes etc) are released directly onto the land, often being under cultivation. That means the substances, including synthetic chemicals in soaps and detergents, enter the soil untreated, which is problematic when trying to grow organic food such as bananas, papayas, and others. Also, these chemicals are harmful in the long run as much for the soil, as for the plants grown for our consumption.
The objective of the project is to start collecting the greywaters and make them pass through a “plant bed” based filter system of Canna indica, also known as Indian Shot, which after they may be used safely for irrigation purposes.
As we mentioned above, the chemical substances present in soaps and other detergents are harmful for the soil because they accumulate and modify the soil structure, depleting its quality. To our fortune some plants have the property of having a special root system called “rhizomes”. The rhizomes release organic compounds into the soil, but the exact nature of those is still under study. What we know is that those organic compounds include phytohormones who have a role in the degradation process: they are capable of degrading chemicals and heavy metals such as phosphorus, iron, aluminium, etc. Moreover, the structure of the rhizomes allow an essential oxygen flow to the soil. This promotes the growth of beneficial soil bacteria colonies and increases their degrading capabilities. The combination of these two factors is the key to degrade soaps and detergents. Once the chemicals are degraded, they are used by the plants as nutrients.
Plant bed filtration systems are currently used in several places in Nepal and we visited two of them during our stay at Kathmandu University. They are usually made with Reed (Phragmites karka) and it is the most well known plant for greywater filtration. However, this species of plant is extremely invasive and has a tendency to spread very fast and easily, causing extra maintenance work to avoid them spreading and taking over the surrounding vegetation plots as a weed. It is also not particularly aesthetic and does not produce anything interesting to use furthermore. For these reasons, we chose to use Canna Indica instead, which has similar roots but also nice flowers and does not spread uncontrollably. It is also a very common plant in tropical regions.
The grey water treatment unit :
The unit is composed of three basins, each with a specific purpose and connection tubes for autonomous water flow. For this to work autonomously, water must always be placed to set off from a higher point to a lower, firstly to take advantage of gravity to make the water flow and secondly to avoid electrical dependency.The first step is to collect the grey waters in the first basin, the “settling tank”. The waters come from a pipe linked to the shower and another from a laundry station that we built next to the pump (see picture below). The purpose is to let big and heavy particles sink and sediment. This first tank will then pour out into the second, larger tank, which is the actual plant bed. It is made out of several layers : gravel for drainage, sand to withhold suspended particles, soil to aliment the rhizomes and some pebbles on the top to maintain the soil layer during heavy monsoon rains and protect it from other plants invasions. The third basin is adjacent to the plant bed and allows a water harvest of up to 75 liters. The surplus water will evacuate into the banana plantation which has, until now, been irrigated with untreated greywater.
The first few days after building, the different compartments will need to be filled up by passing a large volume of greywater, for the water to reach the level of evacuation. Once this is accomplished, the water flow at the outlet will be continuous as long as the water provisioning is continuous too. Otherwise, for any punctual input going into the system, an identical volume of water will evacuate through the outlet. That way, there is a constant stock of 75 liters of filtered water available for any use such as irrigation.
As a lot of sand and dirt can flow into the settling tank, there will be some cleaning up required, depending on the charge of solid particles the water carries. This cleaning up will be manual and have to be done at a regular rate, which will be determined by usage volume. Although the settling tank will require some attention, the plant bed itself won’t as Canna indica is a local perennial plant, an evergreen.
The cost and labour
Event though that system could be made of buckets (as we first planned), we decided to go for a heavier plan using proper construction material : bricks, cement, sand, PVC pipes, gravel, pebbles. Also, we went for a larger scale installation than needed, because the farm is planning on expanding.
Even though those are common and available almost anywhere, they can be costly for the locals, as the selected farmers from the ScaleSchool program told us during the first lesson we gave. Lucky for us, we were able to use material on site as there were constructions around. That’s why using a smaller installation made of plastic containers is an affordable alternative to most farmers to start with.
We’ll present the total amount in a follow up article of the project as we have to estimate the actual price of everything we used, using local material prices.
Finally, concerning labour, the labour intensity depends on the choice of materials. In the case of Spiral Farm House, the seven of us are planning to finish the building phase in a total of ten days. But we have to admit that we only work in the morning (due to the bashing midday heat) and there is a maximum of four of us working full time.
The team has been building the unit and it will be tested in the upcoming few days. Those were ten days of team working, sometimes hard but always rewarding! We’ll test the water quality before and after treatment onsite and in the laboratories of Kathmandu University. You will be able to read about the process and the results in an upcoming article.