A non-partisan, neutral perspective supporting diversity in the color of water

Tuesday, May 8, 2012

Yet Another Great Greywater Thesis

I recently proposed to teach a class titled "Geography of Greywater" at Oregon State University based on my experience with the Rainbow Water Coalition. I have been pleasantly surprised at how global greywater reuse is regardless of the reason for reuse, whether it be due to water scarcity, thus pressing the need to get the most out of water when one can, to the connection to the notion of greywater reuse as part of one of the many definitions of "sustainability", whether it be to leave more water in rivers for salmon, or to reduce greenhouse gas emissions associated with first treating the water that is delivered or to treat the wastewater before discharge. Heck, if we follow the lead of Oregon, we apparently reuse water because according to one of the advisors to the Oregon Graywater Advisory Committee, it makes us "feel good". We will revisit that good feeling in later posts.

But to bolster the notion that an entire course can be developed around global greywater reuse, consider the many great graduate theses that have been discussed in the Rainbow Water Coalition. They are easy to find by simply typing "thesis" in the blog search engine. The latest find is a Master of Science in Engineering from the University of Guelph in Canada titled Appropriate Technology and Adoption of Water Conservation Practices: Case Study of Greywater Reuse in Guelph by Matthew John De Luca.


This study investigates the appropriateness of greywater reuse technologies in Canada. To design a technology to appropriately meet a user’s needs the approach must conform to existing technical, cultural, economic, environmental, and social conditions. The appropriateness of two greywater reuse systems (GWRS) were investigated according to three criteria; reliability/soundness/flexibility, affordability, and sustainability. The GWRS reduced water consumption from 9-20% of total household use, and often met required fecal coliforms concentrations at several sites. However, the study revealed that neither GWRS met all the appropriate technology criteria and significant barriers preventing greywater reuse were identified. Both GWRS produced effluent that largely did not meet current regulations, were prone to mechanical failure, and did not provide any financial benefits, resulting in a varied level of acceptance among users. In addition, the systems resulted in increased green house gas emissions. The study also concluded that the regulations governing greywater quality for toilet flushing and the technology’s robustness must be further refined.

This is one remarkable piece of work. I won't reproduce the conclusions or ideas future research (well worth reading), but will reproduce the recommendations:

1. When greywater is meant solely for non-potable purposes such as toilet flushing the exposure to the greywater is small. Regulations may need to be modified to reflect the fact that greywater is not meant for drinking. The health risk of using greywater to flush toilets is minimized if simple precautions are taken to prevent cross contamination with municipal supplies. In addition, some greywater-fed toilets were found to have lower concentrations of fecal coliforms than a typical toilet that were flushed with potable water. More specifically, the maximum turbidity and BOD values could be increased by a factor of 2-4 so that the new maximums are in the range of 10-20NTU and 40-80mg/L, respectively. Greywater at such turbidity and BOD ranges still met the fecal coliform requirements during this study. A minimum chlorine residual of 0.5mg/L was found to provide a level of disinfection that met the HCG for fecal coliforms.

2. Greywater reuse technology needs further improvement to ensure that the systems are robust. Equally important is the design of toilets working in conjunction with GWRS. Toilets need to be redesigned to accommodate the use of non-potable water, keeping in mind the clogging, pressure loss, and corrosion issues that are known to occur with recycled water. Utilizing energy efficient pumps or reducing the need for pumps altogether is also recommended. More passive treatment systems such as engineered wetlands could provide a less energy intense method of treatment; reducing the GHG associated with system operation.

3. There is little financial benefit of buying a GWRS as the pay back on investment period (POI) is extensive (in the best case, 14 to 26 years for GWRS supplying just toilet water). To improve the POI the following were considered:

  • Water and wastewater policy needs to better reflect the value of this service. Increasing water and wastewater rates is one means (others include alternative pricing structures, and quantifying externalities) which would achieve this, while reducing the POI for any water conservation technology.
  • Greywater reuse needs to be expanded beyond toilet flushing to more wide scale landscape irrigation systems, and even for gardening purposes if the right precautions are taken. With more greywater applications there is more opportunity for conserving water, thus improving the financial benefits of owning a GWRS.
  • The use of backflow prevention devices and their testing requirements may need to be revised. Devices other than reduced pressure backflow preventers that are less costly to install and do not require an annual inspection should be considered. Removing this barrier would improve the GWRS financial benefits.

4. Lack of effective communication between stakeholders was identified as an important issue during this pilot study. This included communication between the homeowners, tenants, landlords, builders, contractors, and the municipal government. A centralized greywater reuse centre could provide a stronger support network for users as well as endorse other water conservation approaches. This space could also provide further community awareness and education on water conservation practices.

5. Focus should be directed towards reaching the select green and renovation audiences first. People who are highly concerned about environmental conservation and/or have a do-it-yourself ability are likely to have a greater acceptance for greywater reuse. For those not interested in water conservation and/or do not have mechanical knowhow, a GWRS will only be considered a burden, and is less likely to be perceived as providing any benefits.

6. Further greywater reuse pilot studies should be conducted on an apartment and/or neighborhood scale in Canada. This may provide a setting where greywater can be reused close to where it is produced while being more cost effective.

Great greywater advice and an outstanding piece of work!
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When I'm in Canada, I feel this is what the world should be like. 
~Jane Fonda

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