Ask the Expert Question-and-Answer Archive (Wastewater Treatment)
by Mike McGinness, EcoShield Environmental Systems, Inc.
February, 2003Automated Composite Sampling Systems
Q. Mike, I am looking at upgrading our sampling system to take our pretreatment effluent samples. I need a stationary refrigerated composite sampler, and also am considering installing a digital flowmeter of some sort to give us flow proportional capability. Do you have any recommendations on the brand, type, cost, and also the level of difficulty involved in getting good representation in a flow proportional setup? You may contact me if you need specific information; maybe I should mention we are currently discharging water in short intervals at 10-20 gpm for a daily flow of ~10,000 gallons.
A. I am making some assumptions about why you asking the question below in my reply here, so if I have missed the target with this reply please clarify your question.
I have found that automated composite sampling systems can leave a lot to be desired. They can be effective for verifying compliance if there is an adequate equalization storage capacity and a fairly constant flow rate in front of the sampler. They can also be useful for spot checking streams to see if there many be a problem. However, a very small flow rate with a very large concentration and little or no equalization capacity, when tied to larger more dilute flows can be a real problem.
I have found that it is sometimes simpler, and far more revealing data wise to back up into to each separate flow stream (or rinse tank) and collect separate samples to determine the actual contaminate sources and loads (maximums, minimums, and averages) on the waste water system. It can also remove some interferences in the lab methods. Also, by adding a separate water meter (positive displacement feed water meter that totalizes the flow) to the feed on each rinse tank you can collect individual flow rates and sample concentrations for each flowing stream. These flow meters (such as a city residential size meter, 3/4") are less than $100 each and are certified accurate to +/- 2%. In my experience if you are troubleshooting problems in the waste water feed or treatment system this method can be far more revealing that any composite sampler I ever used. You could consider using a composite sampler at each rinse tank or move the same one from tank to tank during the month.
I hope this was helpful to you. Please let me know of I can be of any further assistance. I am always looking for new challenges.
By the way, ISCO samplers are the only ones I have ever used, and they make a fine piece of equipment but as you can tell from my comments above, I do not use them very often now.
