A few years ago sand filters were being presented, very effectively I must add, by a company that manufactured sand filter kits, as a panacea that would solve the world's onsite wastewater treatment problems. Engineers, contractors and regulators were offered "classes" in a traveling side show of sorts providing them everything they needed to specify, permit and build God's gift to mankind's need to treat onsite wastewater. Detailed gradation curves describing the size and composition of the sand were developed and distributed giving the illusion that a lot of hard thought went into the design of these sand filters. I remember the pages of plans that were made available to engineers so that they could simply make copies and insert them into their plan set. Sand filters were sold as easy to install, easy to maintain, reliable and inexpensive.
There were many problems with sand filters that resulted in them being a nightmare to install, impossible to maintain, expensive and when they failed....they went all at once.
In my opinion one first must look at the treatment media. Sand works great, right up to the point where it doesn't. Then you have this mess to deal with:
There was a poster presentation at a NOWRA conference a few years ago relating hydraulic conductivity of the media to clogging potential. It was shown, and this should not come as a surprise, that low hydraulic conductivity media had a much greater probability of failing due to biological fouling than media with higher hydraulic conductivity.
During a recent presentation, Tchobanoglous stated that the size of the particles in the wastewater being applied had a significant effect on the bio-fouling potential of the media. If the particle size is close to the media pore size...clogging is likely. This explains, in part, why manufacturers are requiring larger and larger primary tanks and recirculation tanks for their systems; to try to reduce the size of the suspended solids so their media does not foul.
The sand filter shown above has already been rebuilt and the owners have decided to install an Eliminite system in its place. Our MetaRocks media has been proven over time and hundreds of installations to reduce the potential for biological clogging to near zero. The extreme efficiency of the media allows us to use smaller and fewer tanks while dramatically improving reliability and treatment characteristics.
Hydraulic acceptance rate of MetaRocks: >250 gal/min/ft^2.
Our goal has been to identify aspects of an onsite treatment system critical to its performance and optimize those aspects. The fundamental starting point is the media. If the media is not right, the system either will not work, or it will be a maintenance nightmare.
Highly robust media allows the system operation to be varied and optimized because there is no concern that the media will be overloaded. This fact leads to a variety of possible configurations and allows the designer to target constituents in the wastewater for treatment. Rather than treating the system with kid gloves, it handles dynamic conditions to the point of abuse. Isn't that what you really want in an onsite system?
We just received several Montana Cold Winter sample results for nitrogen, total nitrogen........The "worst" result was 12 mg/L TN. Montana cold, dead of winter, inspection not maintenance, no telephone link, just great results.
The best?...it was 4 mg/L TN.
