Mesocosm-Scale Constructed Wetland Design for Wastewater Treatment

Our research investigates the use of constructive wetland treatment systems as a passive cost-effective approach to treat oil sands process effective water, focusing on removing naphthenic acid fraction compounds through mesocosm-scale experiments, and identifying key optimization factors. Recent advancements in constructive wetlands for OSPW include genomics-based methods to enhance the efficacy of constructive wetlands, integrating toxic NAFCs. Additionally, our research outcome will inform the optimization of plant selection and system design for improved contaminant removal. Mesocosm studies bridge lab to field constructive wetland treatment system gaps by testing plant microbe interactions and design factors under semi-realistic conditions to assess treatment efficacy and guide pilot scale implementation.

Our protocol allows for replication and manipulation of variables while still incorporating ecological complexities, making mesocosms ideal for identifying wire treatment mechanisms, testing system design, and predicting scalability with reduced risk and cost. Our findings will advance OSPW treatment research by demonstrating how mesocosms scale constructed wetland treatment systems can effectively reduce toxic compounds, like NAFCs, while also identifying the specific biotic and abiotic mechanisms at play.

[Narrator] To begin, place Carex aquatilis seeds into standard styroblock containers filled with peat as plug stock. Once the seedlings have germinated, fertilize them three times a week using water soluble plant food. Reinforce the greenhouse tables with plywood to support the weight of the mesocosms. Distribute the mesocosms evenly across the greenhouse bay tables. Position the plumbing to hang off the edge of the table. Next place a 57 liter open top plastic industrial drum under the drainage plumbing. Install a submersible power head circulation pump between the middle and bottom of the tank for continuous mixing. Secure the power cord to the outside of the tank. Now spread the substrate evenly in the mesocosm and tamp it down with moderate pressure to reach the desired height. Fully saturate the substrate with reverse osmosis water. Measure the volume of water added as it is equivalent to the volume of porewater in the substrate. After selecting a retention time based on prior studies and study objectives, calculate the total water volume in the mesocosm using the formula shown. Then calculate the flow rate. Position one pump between two adjacent mesocosms. Link all the pumps together using a male-male USB cable, ensuring the last pump is connected to the controller. Now place the in-valve tubing in the reservoir and secure it down to keep it in place. Secure the out-valve tubing to the back top corner of the mesocosm, keeping it above the waterline. Wrap the tubing in aluminum foil to help prevent algae growth. Set up and calibrate the pumps, power bar and controller according to the manufacturer's instructions. Then adjust the pumps to the calculated flow rate. Then adjust the temperature and LED grow lights to optimal levels for plant growth while conditioning plant species to the mesocosm. Evenly plant six to 12 individual plant species to ensure equal biomass per unit area in the mesocosm. Fill the reservoir with reverse osmosis water. Gradually raise the reverse osmosis water level, maintaining each level for one to two days, and replace the PVC pipe as needed to match the water level. Turn on the pumps with the final desired flow rate. Once the desired water level is reached, adjust the greenhouse light and temperature to experimental settings and allow the plants to acclimate for approximately 35 days. To drain and flush the system. Remove the PVC standpipe and open the ball valve to completely drain the system. Then flush the system with OSPW and ensure complete drainage. Once flushed, close the ball valve and add the PVC pipe to match the desired water level. Carefully pour OSPW into each mesocosm to avoid disturbing the substrate or plants. Filling until the desired water level is reached. Now, fill the reservoir tank with OSPW leaving approximately five centimeters of space from the top. Manage evaporation by refilling the reservoir tank with OSPW water as needed. Maintaining the water level approximately five centimeters below the top. During every retention time cycle. Measure plant health and growth metrics. Assess plant health based on visible signs of stress, such as chlorosis and insect damage. Measure plant growth metrics including mortality, height, and percentage cover. Before adding substrates or OSPW to each mesocosm, conduct baseline characterization by measuring the on-screen parameters. During the first retention cycle, collect substrate and water samples from random locations in each mesocosm to establish a baseline for general chemistry. Measure substrate oxidation reduction potential using an appropriate ORP probe during every retention time cycle. At the end of the experiment, collect substrate samples from each mesocosm, and measure the same parameters recorded during baseline characterization. After adding OSPW, collect initial OSPW samples from each mesocosm at the end of the first retention cycle, allowing sediment to settle and filling the porewater space. Then collect the samples from the front of each mesocosm. During each retention time cycle. Measure dissolved oxygen, ORP, pH, electrical conductivity, and temperature using the referenced instrument. At the end of the experiment, collect final water samples to analyze general chemistry. The height of Carex aquatilis increased steadily reaching approximately 150 centimeters by day 40 before plateauing. Dissolved oxygen levels were consistently higher in unplanted mesocosms compared to those with aquatilis with levels above five parts per million in both conditions. Soil redox potential in unplanted mesocosms remained between 50 millivolts and 100 millivolts. Whereas implanted mesocosms, it occasionally approached zero millivolts. Total naphthenic acid fraction compounds implanted mesocosms showed a 76% reduction from 72.1 milligrams per liter to 17.1 milligrams per liter over 82 days, whereas unplanted mesocosms only showed an 8.5% reduction.