Guest Author: David C. Kennedy, Ph.D
A Look Into the Wastewater Testing Process and its Potential Impacts
Treating domestic wastewater (sewage) to remove harmful contaminants is thought to be the single greatest contribution to the improvement of human health in the past 200 years. In our modern era, it is an established and regulated process featuring a combination of biological and physical treatment steps that remove >99.9% of the contaminants present.
Although modern treatment processes are quite effective, trace contaminants can still be present in the treated wastewater, because there is no such thing as 100% removal. However, even with the presence of such trace contaminants, the Environmental Protection Agency (EPA) still considers such treated wastewater sufficiently safe to be discharged. But, discharged to where? As it turns out, the “where” makes a substantial difference.
Generally, treated wastewater is discharged into a river or stream. Consider a location in the United States where there is abundant rainfall and a large river nearby, like in the City of St. Louis, Missouri on the banks of the Mississippi River.
The average flow of the Mississippi River in May at St. Louis is 2,250,000 gallons per second. The discharge from a large wastewater treatment plant on that river might be on the order of 10,000,000 gallons per day.
That sounds like a lot of wastewater until you do the math and realize that the discharge is only 115 gallons per second. The resulting dilution factor—owing to the flow of the river—translates to about 20,000 to 1. As a result, a few parts per billion of some contaminant in the discharge would be rather difficult to detect when diluted by all that river water. Certainly, any harmful effects of a pollutant would be mitigated as well.
Now, the above illustration is not meant to justify the discharge of pollutants, even at the part-per-billion level. However, what if there isn’t some great big river nearby to receive the treated wastewater flow? What if there isn’t a river at all?
In such a case, we might want to reconsider the thought process about those pesky trace levels of contaminants in the treated wastewater. Many consumers would probably want to know what is in their water, the percentage of contaminates, and where it is all going? The old expression that “dilution is the solution to pollution” doesn’t seem to cut it anymore.
This is the precisely the situation in much of the arid Southwestern United States. For example, in Los Angeles, California, the average rainfall is about 15 inches per year. If you look at a map of the area you will notice that there appears to be a number of rivers, but they are dry most of the year. So, this is not the ideal location to discharge wastewater, even after treatment.
So, what do Angelinos do with their treated wastewater? Well, the bulk of it is discharged into the Pacific Ocean and some is recycled for non-drinking water purposes, like irrigating golf courses. However, some is used to recharge the underground drinking water aquifers. Hard numbers are difficult to come by, but a reasonable estimate for the Los Angeles region might be that 70% of the treated wastewater currently ends up in the Pacific Ocean, 30% is recycled, and 10% is used for groundwater recharge. This percentage used for groundwater recharge is quite low, but it can be expected to increase in the future owing to the combination of population growth and climate change impacts on water supplies.
That said, recharge makes a great deal of sense. As water is pumped out of an aquifer for drinking water purposes, the aquifer must be recharged or the wells will run dry. With insufficient rainfall to recharge the aquifers, the only significant additional source of recharge water is treated wastewater. Although recharge does not take place directly near the drinking water wells themselves, the aquifer is interconnected so the treated wastewater does eventually become part of the drinking water supply.
You might be slightly disgusted by this notion, but this heavily treated wastewater is safe to drink. Furthermore, additional purification takes place as the treated wastewater filters down through the soil to the aquifer and additional dilution does take place, even underground. A more rational concern is the presence of trace levels of synthetic organic chemical that are difficult to remove in the wastewater treatment process and are not removed by filtration through the soil.
For example, it is known that certain pharmaceutical and personal care products (PPCPs) are present in domestic wastewater (i.e. birth control estrogens, caffeine) and can pass through the treatment process and end up in the aquifer. The same possibility exists for commonly used pesticides and herbicides that might enter the wastewater through runoff and remain in the treated wastewater (pyrethroids, for example).
Full Technical Application on Rapid Extraction and Analysis of PPCPs from Sediments by QuEChERS and LC-MS/MS
Full Technical Application on Rapid Extraction and Analysis of Pyrethroids from Sediments by QuEChERS and LC-MS/MS
Full Technical Application on Rapid Extraction and Analysis of Steroid Hormones from Sediments by QuEChERS and LC-MS/MS
The question is, what specific and amount of trace contaminants are there and could they possibly present a long term health risk? These are important questions if we want to consider the possibility of using recharged groundwater for future drinking water use in arid climates.
To answer those questions requires the application of some very sophisticated analytical testing involving advanced techniques such as LC-MS/MS and preparative techniques such as Solid Phase Extraction (SPE) and QuEChERS. This advanced testing is routinely carried out by public agencies and by private testing laboratories in Southern California to ensure the safety of the drinking water supply.
The Sanitation Districts of Los Angeles County collaborated with Phenomenex to develop new methods for analyzing contaminants in sediment samples. Syljohn Estil, a chemist at LACSD, has been working to make sure that the process used to treat waste water is in line with regulations, and that the effluent produced complies with various environmental mandates.
Treated wastewater reuse and recharge will inevitably become more common in the future, even in areas where rainfall is prevalent, as the growth of large metropolitan areas collide with diminishing water supplies. Add to the mix the fact that new refractory pollutants are continually being discovered in water and wastewater (e.i. polyfuorinated-alky substances (PFAS)). Consequently, this type of advanced testing is certain to become more common and ever more sophisticated tests will be required. Phenomenex stands ready to work with our customers to meet these challenges.