During the first expansion of their wastewater treatment plant, the city of Eugene, Oregon needed to comply with a regulation that required raw sewage sampling. Their plant inlet sewer was fairly deep and treatment plant recycle flows were returned into the influent sewer prior to the influent pump station. Therefore raw sewage samples needed to be taken upstream of the pump station.
The pump station was equipped with very large axial-flow propeller pumps and did not utilize bar screens, so there was no place in the wet well that a conventional sampler could be installed. As a result, the city was faced with the probability that a costly new underground chamber to house sampling equipment would be required to be located upstream of the pump station wet well.
In searching for a more cost-effective solution, Gene Suhr devised an automated sampler that required no below-ground parts except a copper pipe connection to the influent sewer. His watching a vacuum truck clean a catch basin and his ownership of a Volkswagen Beetle triggered the idea for the sampler he devised.
Drawing on the Beetle’s two-compartment gasoline tank, he designed a 6-inch-diameter Plexiglas sample collection tube with a shorter, smaller-diameter copper tube inside. As the outer larger tube filed, it finally overflowed into the inner tube. In filling the inner tube, a representative aliquot of suspended solids settled into the inner tube. The sample was aspirated into the outer tube by a vacuum pump. After filling the sample tube, the outer tube was emptied by use of compressed air and the inner tube was then drained into a refrigerated sample container. Needed valves were solenoid operated and an adjustable timer controlled the sampling frequency. The sampler automatically reset itself after each sample and was largely self-cleaning.
It proved to be very reliable and much less costly than other solutions that were then available. Later models of the Suhr Sampler incorporated sold-state controllers, but the essential operating principles remain unchanged to this day.