November 1, 2022
Categories: Project News
A Multilayered Approach to Improving Industrial Effluent Quality
Morgan Crane, P.Eng.
Design Engineer, Municipal Engineering
MTE Consultants
As a supplier of over 500,000 tonnes of livestock feed annually, Wallenstein Feed and Supply (WFS) has been a staple of agricultural industry in Southern Ontario for 64 years. As their operations continued to grow, WFS found themselves in need of more space. They set forth with plans to expand their main mill site in the hamlet of Wallenstein, and enlisted our team to support their endeavour.
Through our efforts to obtain an Environmental Compliance Approval (ECA) for the expansion, we were able to develop a process water and stormwater management treatment plan that would meet the discharge criteria, as well as WFS’s sustainability goals.
Site and Water Conditions
The facility lays on the banks of the Conestogo River and is serviced by a series of wells and an onsite wastewater system. Since WFS uses well water exclusively, they are dependent on the groundwater’s natural characteristics. The raw groundwater in the area has extremely high hardness (>1500 mg/L CACO3) and a high sulphate concentration (98th percentile in the province). Due to the poor raw well water quality, alternate water sources were investigated, yet deemed unrealistic.
Current Raw Water Treatment Processes
Much of the process wastewater that WFS produces is from the treatment of the raw groundwater. There are several key components of the process, with reverse osmosis being the primary way that the water is treated. Water softener acts as a polishing step prior to water entering the boiler, while a media filter focuses on the removal of iron and manganese from the well water, and a boiler blowdown removes accumulation from the boiler to improve efficiency of the steam generation process. All of which have been optimized to reduce water consumption.
The process wastewater is combined in a settling tank before draining into a stormwater management pond, and then discharges to the Conestogo River. The settling tank serves to reduce the total suspended solids (TSS) and temperature of the process water prior to being conveyed to the stormwater management pond, which serves to treat the runoff on the property in addition to mitigating the effects of the raw process waters.
Challenges Characterizing Wastewater
Our team began the ECA application process by characterizing the wastewater. The discharges from the system are intermittent and variable in nature, which presented challenges during our sampling program. Due to the combination of runoff from the site, our team also had to consider the chloride concentration in the runoff during winter months and the possibility that chloride could be retained within the reservoir into the spring months. While WFS is mindful of the quantity and frequency of its winter salting operations, the feed trucks it operates can bring additional salt onto the property. To solve this, our team sampled the stormwater management pond throughout the year to determine maximum concentration and impacts of the interactions of the stormwater runoff through the winter months.
Our sampling solution involved collecting samples from the individual process streams in addition to combined samples throughout the process. Additional samples were collected with an autosampler to create a representative sample. Once characterized, it was determined that the process water had elevated levels of metals, chloride, sulphate, and formaldehydes, as well as Biological Oxygen Demand (BOD).
High BOD from Feed Dust
Due to the nature of the mill operations, dust from the processing of the feed is deposited over the property. This dust is collected in the storm sewer system before entering the stormwater management pond, resulting in elevated BOD concentrations in the runoff. The ensuing organic loading will be reduced through settling, separation and filtration in the treatment system. However, there is minimal guidance for BOD accumulation within existing guidelines. As such, a series of samples were collected from the pond and used as a basis for the expected BOD concentrations for the purpose of sizing the treatment system. The sampling results also showed that the site’s runoff to be impacted by toluene, metals and TSS.
ECA Discharge Criteria
Once the process water was characterized, we held a pre-consultation meeting with the Ministry of the Environment, Conservation and Parks (MECP) to set a series of acceptable discharge criteria. Objective and limit concentrations for metals, TSS, and BOD were determined using published discharge criteria. However, it was difficult to establish acceptable discharge criteria for the sulphate and chloride that would be realistic and attainable on a year-round basis. The raw well water contains sulphate concentrations in excess of the allowable discharge criteria. Additionally, the combination of process water and stormwater resulted in increased chloride loading during winter months when salt is applied to the parking lots and roads on which the WFS trucks travel. As a result, there were a number of factors outside of WFS’s control that led to increased chloride concentrations.
Our team joined forces with Hutchison Environmental to complete a series of toxicity tests to establish a safe discharge concentration for sulphate and chloride. Hutchinson also conducted an assimilative capacity study of the downstream receiver to ensure that the proposed discharge criteria would not cause harmful effects within the Conestoga River.
The toxicity testing resulted in a number of interesting findings. It confirmed that the effects of sulphate and chloride were additive. The combination of both parameters resulted in more toxic water and individual constituents. It also showed that the high hardness of the effluent had a buffering effect on the elevated chloride and sulphate concentrations. As a result, a series of toxicity tests were conducted with effluent from the settling tank and pond. Composite samples were used to obtain samples that would be representative of the process water.
Ultimately, the MECP accepted the results of the toxicity testing for guidance of the objective and limit concentrations for sulphate and chloride. A chloride limit was established at 640 mg/L for the summer and fall months, and 640 mg/L for the winter and spring months. These concentrations match the published discharge criteria. A year-round sulphate objective of 3,855 mg/L and a limit of 5,140 mg/L was established based on the results of the toxicity testing and assimilative capacity study.
Reservoir and Treatment Plant Design
Based on our findings, we determined that a reservoir was required to collect process and stormwater and pump it to a treatment system. The size of the reservoir was selected based on its ability to connect to the expanded internal storm sewer network and provide retention of a five-year storm event. Additional sizing considerations included being able to store over 30 days of process water discharges prior to overflow. The reservoir is hydraulically connected to an adjacent lift station via a 300-mm diameter storm sewer.
We worked with H2Flow to design a treatment system with the ability to treat the wide variety of parameters in the process waters and runoff. The lift station discharges directly into the treatment plant which will only function when the lift station is operating.
The treatment system will consist of coagulation, flocculation, clarification, macrolite media filtration and activated carbon adsorption. These processes serve to remove the parameters of concern prior to discharge. The team determined that formaldehyde could be treated to acceptable levels through extended detention times within the reservoir. Chloride and sulphate are also monitored to ensure compliance with the proposed objectives and limits. The ECA included two online chloride analyzers; one at the settling tank and one immediately prior to discharge. These analyzers will be able to detect abnormal changes in the process water chloride concentration.
In addition to the compliance limit and objective concentrations dictated by the ECA, MTE and the MECP agreed to additional sampling along the treatment process to guide the operation and compliance of the system.
Current Status
Our team continues to collect samples from the stormwater management pond to determine the historic seasonal patterns in the chloride and sulphate concentrations. Having received ECA approval, this project is currently under construction and it is expected to be fully operational for WFS in the spring of 2023.
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