By Tanner Devlin and Philip Wiebe
A Canadian-made wastewater treatment innovation could be part of a long-term sustainable solution for the removal of contaminants of emerging concern (CECs) in extreme cold climates.
“With increased pressure on water resources, the issue of pharmaceuticals, personal care products, and pesticides in wastewater continues to grow,” says Nexom’s Dr. Pouria Jabari. “CECs are increasingly being detected at low levels in surface water, and there is concern that these compounds are affecting aquatic life.”
It was this growing concern that prom-pted Jabari to join with the University of Winnipeg and Red River College in Manitoba in evaluating the removal of these types of compounds, using the fully-aerated submerged gravel bed technology known as SAGR.
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The risks posed by CECs
Contaminants of emerging concern refer to many different kinds of chemicals, including medicines, personal care or household cleaning products, lawn care and agricultural products, among others. These chemicals make it into water bodies and have a detrimental effect on fish and other aquatic species. They have also been shown to bioaccumulate up the food web, putting even non-aquatic species at risk when they eat contaminated fish.
One strain of CEC is known as endocrine disruptors (EDC), which alter the normal functions of hormones, resulting in a variety of health effects. EDCs can alter hormone levels leading to reproductive effects in aquatic organisms.
Figure 1: Percentage removal of detected CEC in SAGR at LPFN and MCN.
A substantial challenge related to CECs is determining what is safe in the long term. Evaluating these effects may require testing methodologies, not typically available, along with endpoints not previously evaluated using current guidelines. The effects of exposure to aquatic organisms during the early stages of life may not be observed until adulthood. These chemicals may also have specific modes of action that may affect only certain types of aquatic animals (e.g., vertebrates such as fish).
Setting up the study
“For this study, we wanted to evaluate the removal of CECs in one or more communities under extreme cold winter conditions,” says Jabari, “Since the submerged attached-growth reactor itself was initially created for cold-climate ammonia removal, it was important that the study was conducted during the cold season under the harshest conditions for biology for which the system is designed.”
SAGR is a Canadian innovation now installed at more than 70 sites across North America. It consists of a fully aerated coarse gravel bed, in which wastewater from sewage lagoons flows horizontally through the porous media. The gravel bed is insulated at the surface and continuously aerated, allowing the system to grow and maintain sufficient nitrifying biomass even at near-freezing temperatures of <1°C.
Two existing sites with SAGR treatment systems were selected for this study: Misipawistik Cree Nation (MCN) and Long Plain First Nation (LPFN).
LPFN had installed their SAGR system in 2012 in order to reach assigned total ammonia nitrogen (TAN) limits as low as <1 mg/L. MCN followed suit for the same concerns in 2013.
“We chose these two sites due to their relatively close proximity to the University, which allowed for ease of travel to the sites for everyone involved,” explains Jabari. Both sites are among the oldest SAGR installations at nearly 10 years old, but they are still successfully achieving their original purpose of ammonia removal, which was also important for the study.
For the purpose of the study, water samples were collected biweekly over the course of the three-month project (January to March 2019, inclusive) for a total of seven samples per site. They were then sent to an accredited lab for testing wastewater parameters (e.g., N, P, TSS, and BOD, E. coli), as well as to the University of Winnipeg to measure for CECs.
“The contaminants that we looked at were diclofenac, naproxen, atenolol, carbamazepine, clarithromycin, metoprolol, sulfamethoxazole, sulfapyridine, and trimethoprim,” says Jabari, adding that testing samples were taken from raw sewage, as well as the SAGR influent and effluent.
Of the 14 samples taken over the course of the study, laboratory testing showed both the TSS and BOD levels in SAGR influent were well below the 25 mg/L assigned limits in both categories, for each site. This information was not included in the reporting for the study, as there was no deviation from expectation.
Additionally, the results of ammonia and total coliform showed the SAGR could deliver effective nitrification and disinfection performance at water temperature of <1°C, which has been previously documented. What wasn’t previously documented was how well it could remove CECs.
“Of the 32 known target CECs, only eight were detected in the SAGR influent on both sites,” says Jabari, adding that atenolol was detected only at MCN. Out of those eight, he says, testing of the effluent showed the SAGR had removed the detected CECs at different levels, ranging from low to high treatment.
“We see different levels of treatment for different CECs, because of the speed that each chemical breaks down in water,” says Jabari. The anti-seizure drug carbamazepine was not well removed by the SAGR at either site, possibly due to its low biodegradation rate at low temperatures. By comparison, he adds, the antibiotic trimethoprim was removed at a rate of 75% at both sites. Atenolol, which is used to treat high blood pressure and was only found at MCN, had a removal rate of 80%.
Jabari postulates that the CECs are mainly removed from wastewater via the bacterial activity in the SAGR. One 2014 study entitled “A review on the occurrence of micropollutants in the aquatic environment and their fate and removal during wastewater treatment” compared various treatment technologies and their effectiveness against CECs from 14 different countries and regions. Its authors suggested nitrifying bacteria, which are responsible for the removal of ammonia in biological treatment, would positively affect the removal of CECs.
The other potential mechanisms are less likely, says Jabari. “The SAGR surface is covered with insulation, meaning there is no light available for direct photolysis. The SAGR has a long solid retention time and so almost complete solid digestion. This means that CECs that are physically adsorbed in the SAGR bed, if not broken down by biology, would be released back to the effluent.”
What Does it Mean for the Future?
Rural Canadian sites, including Dead Horse Creek, Manitoba, and Cambridge Bay, Nunavut, have been the focus of similar studies that have found CECs within their respective wastewater treatment systems.
Jabari believes the ability of the SAGR to remove these compounds would be beneficial to many communities like these, having been tested at water temperature below 1°C. These are typical winter conditions for Canada’s lagoon-based wastewater treatment plants, particularly on the prairies and further north.
Despite seeing success in that environment, the removal of CECs in biological treatment processes is also negatively affected by the cold. Cold weather means less bacterial activity. With that in mind, the removal of CECs in warmer climates, where the biodegradation would be greater due to increased bacterial activity, has yet to be investigated.
“What we can say for now is that results have shown that a technology already in place at many small Canadian municipal plants removes CECs at moderate level while also providing designed treatment performance, even in the extreme cold,” concludes Jabari.
Tanner Devlin and Philip Wiebe are with Nexom. For more information, email: email@example.com
Read the full article in ES&E Magazine’s April/May 2020 issue below.