Grey Water and Gravel Bed Hydroponic Reed systems

By Myles McCaulay

This blog post will investigate alternative methods of treating and disposing of wet waste, including grey water and gravel bed hydroponic reed beds. It will investigate how these techniques can provide wet waste disposal without infrastructure, how they can conserve water, and contribute to agriculture.

To begin, what is grey water? Grey water can also be called wash water, It typically makes up 50 - 80% of household waste water and accounts for everything except for toilet water. This includes waste water from sinks, showers, washing machines and dishwashers. It contains relatively few disease organisms in comparison to toilet water (termed black water), however it decomposes quickly and can rapidly degenerate to a state of septic sludge comparable to black water; meaning that this water can not be stored. Grey water makes up a significant portion of sewage and diverting it will greatly reduce stress on the sewage and septic systems that are going to face increased traffic in the future as a result of the booming population. Furthermore, the centralized collection of sewage for treatment creates toxic sludge; diverting grey water will not only reduce the amount of sludge created, but it will also provide an opportunity to capitalize on the many benefits that the effective use of grey water can provide. The best way for grey water to be handled is for it to be introduced to a layer of topsoil. This biologically active top soil will help break down the grey water, and its nutrients can be absorbed by plants and vegetation.

Basic Grey Water Treatment

For these reasons agricultural irrigation is an obvious application for grey water because it takes full advantage of its benefits and is also compatible in terms of size, soil and climate that are suitable for grey water irrigation. Grey water irrigation is not recommended in colder climates, or when there is not enough soil, or the soil is of a quality to poor, to adequately absorb and treat the grey water. Agricultural irrigation easily satisfies all of these requirements and can use grey water to conserve valuable fresh water resources, maintain soil fertility, and foster plant growth through the absorption of nutrients such as phosphorous, nitrogen and potassium. This process will not only benefit the crops but will effectively treat the grey water by removing organic pollutants (phosphorous, nitrogen and potassium) and replenishing ground water. Using grey water for agricultural irrigation is incredibly efficient, simultaneously treating waste water and replenishing natural water sources while conserving valuable fresh water that would otherwise have been used.

Although the use of grey water irrigation in the US has not been linked to any illnesses certain precautions should be taken. These include preventing contact and consumption; grey water is still sewage and should be handled as such. It can not be stored and the irrigation system can not be overloaded, excess grey water must be diverted through normal sewage lines. This will generally not be an issue for agricultural irrigation which in most cases will have the capacity to absorb any surplus grey water. Diversion through normal sewage channels is also necessary in the case of chemical contamination, care should be taken not to pour chemicals down sinks that are part of the irrigation system. Also, grey water can not be distributed through a sprinkler system, this will result in the presence of harmful microorganisms in the air that can be inhaled. Finally, these same microorganisms can be transferred to plants through irrigation and therefore grey water must be treated before being used in this manner, treatment can be mitigated by using cleaner sources of grey water (no food residue).

Clivus Greywater Filter System Constructed Wetland Drain to Mulch Basin

There are many different types and configurations of grey water irrigation systems, diagrams have been provided in this blog, however, more details are provided in their respective web pages; links can be found underneath the pictures and in the bottom link section. This blog will focus on the “anaerobic to aerobic” system as it is the most appropriate for agricultural irrigation, however, I encourage the reader to use the links provided to investigate alternate systems. The anaerobic to aerobic system is not the cheapest, but it is simple to maintain and is one of the most effective methods of onsite water treatment. It consists of a three stage septic tank that traps grease and sludge, followed by a sand filter and finished off with a planters bed. The final result of this treatment method is water that is near potable and ready to be used for irrigation. I will direct you to Sabrina’s post, where the irrigation process and methods are discussed in greater detail. It is also important to note that grey water alone will likely not be sufficient to support agricultural irrigation on its own and it would be most effective combined with rain water capture systems.

Anaerobic Aerobic Treatment System

The major problem with the grey water irrigation system previously discussed is that it requires access to basic plumbing infrastructure, which sadly excludes 2.5 billion people around the globe. Alternative methods are necessary to provide those without any plumbing infrastructure with the same services. Gravel Bed Hydroponic reed beds (GBH) are one example of a system that could be used to treat human waste water for use in agricultural irrigation. This idea was initially pioneered at the University of Portsmouth in the 1980’s and consists of a two meter wide forty centimeter deep drainage channel that extends for one hundred meters and is sealed by an impermeable material. This channel is filled with gravel and hydroponically grown reeds which waste water passes through. The presence of the reeds fosters the microbial activity that treats the sewage purifying the water to a level that is acceptable for restricted irrigation (can only be used to irrigate crops not eaten raw by humans). This method has been tested in Egypt and has proven to be an effective. While there may be some logistical difficulties (most notably the reliance on gravity and water flow in the absence of a pump) it is an affordable and relatively effective sewage treatment system that warrants further investigation and implementation.

In conclusion, the use of grey water and GBH treated waste water for irrigation is an extremely effective way to deal with wet waste without infrastructure. These two systems are able to provide water for agricultural irrigation thereby conserving fresh water supplies, in addition to treating waste water satisfactorily and in a way that replenishes ground water. Developing these already incredibly useful technologies is crucial in a crowded future where large scale infrastructure can not be relied on.

Links:

"DFID ENGINEERING THEME W4 SUMMARY - R4573: Gravel bed hydroponic wetlands for wastewater." Loughborough University. http://www.lboro.ac.uk/well/resources/consultancy-reports/task0065/htm/D4573.htm (accessed November 4, 2009).

"Greywater irrigation - grey waste treatment." Greywater irrigation - grey waste treatment. http://www.greywater.com/ (accessed November 4, 2009).

"Greywater Recycling." Composting Toilets. http://www.letsgogreen.com/greywater-recycling.html (accessed November 4, 2009).

"Planter Box." Tredyffrin. www.tredyffrin.org/pdf/publicworks/CH2%20-%20BMP6%20Planter%20Box.pdf (accessed November 4, 2009).

"Simple sewage solution could save millions living in third world." University of Technology, Sydney. http://www.uts.edu.au/new/releases/2002/November/11.html (accessed November 4, 2009).