Comments on a Graywater Reuse Demonstration in Bangalore

I stole this link from the Rainbow Water Coalition site (thanks to Todd Jarvis).  It is a great little demonstration of how easily kitchen sink water can be reused.  If my math is correct this will treat up to about 30 gallons per day, easily accommodating what comes from a typical single family residence.  How many of you know people with water features in the back yard?

Bangalore graywater reuse video

There are a couple of things to think about here depending on if you are in a big municipal sewer context or in the little septic system context.  The big municipal sewer might really like these diversions because in the sense of total volume these kinds of installations will "buy" them sewer treatment plant capacity, probably at no cost to the municipality (assuming that homeowners install them on their own dime).  The other issue that municipalities may face if there is a very large proportion of graywater flow being redirected is a change in the quality of the sewage reaching the plant.  Depending on the proportion of commercial/industrial/residential contributions in the community waste stream, changes in the sewage quality may cause a change in the treatment process.  Not necessarily in all cases, and the change may be so gradual that little tweaks to the system can accommodate the change in incoming quality to still meet discharge standards.

In terms of small septic systems, particularly those that serve one house, the change in water quantity through the system can have a significant impact, positive and negative, depending on the kind of system in use.  A simple septic tank and trench kind of system will probably benefit from having graywater removed from the flow going to the septic tank because the remaining blackwater will be retained in the septic tank (primary digester) for a longer period, allowing more anaerobic digestion to take place.  In addition, the flow going to the trenches that distribute the water to the environment have to take less water and therefore, the life of the trenches is prolonged.  And that leads to lower costs to the homeowner, etc. etc.

With more mechanized (i.e. pumped) systems, you would hope and pray that the homeowner is working with a professional to make sure that the pumping cycles are lowered in this system to account for the lowered flow to the septic system because the septic tank will have a higher concentration of solids that could start moving towards the trenches.  These kinds of systems are supposed to have water levels sensors and alarms on them that help protect the system and alert the homeowner to the presence of a problem, but homeowners have been known to quietly cut the electrical connection to the alarm.  If this is done before the graywater diversion is installed or if the mechanized system is otherwise malfunctioning, then the effects on the treatment systems could be bad.

There are new kinds of septic systems permitted by the DEQ currently and some of these produce very high quality effluent, which is worthy of its own reuse discussion.  In these cases, why take only part of the water when all of it is potentially reusable?  This presents another opportunity to "buy" municipal treatment system capacity:  allow homes in urban areas to install an individual system and reuse the water on site.  Each home taken off the grid in this manner means treatment capacity to the city treatment works.