The Overlooked Importance of the Equalization Tank at the Start of the Treatment Process

Industrial activities generate numerous pollutants, and industrial wastewater is a major contributing factor.

Following the tightening of standards for the discharge of industrial wastewater into municipal infrastructure, many industries have had to install pretreatment plants for their wastewater before it can be discharged into a city’s sewer system.

However, we can observe that in many industries, an important aspect is overlooked when designing these pretreatment plants: the fundamental role of the equalization tank upstream of the physicochemical treatment.

As a matter of fact, to ensure the stability of the physicochemical treatment process, it is essential to homogenize the various types of wastewater generated by the plant before it enters the treatment equipment.

For example, in the case of the agri-food industry, it generates wastewater during production hours, but also during sanitation hours. These two types of wastewater differ significantly in terms of pollutant loads and pH (sanitation water has a highly alkaline pH). Furthermore, the volume of the wastewater produced during sanitation is often greater than that produced during production.

The presence of a buffer tank with a 24-hour storage capacity at the beginning of the treatment process has very beneficial effects on the system’s hydraulic balance as well as on the efficiency of the physicochemical treatment. Furthermore, operating the treatment equipment becomes less complex by balancing the pH and the influent load, as the chemical dosages remain more stable throughout the day and require fewer adjustments in response to variations in the wastewater’s pollutant load.

This tank must be, at a minimum, agitated to prevent dead zones and the sedimentation of suspended solids. Ideally, if this tank is aerated, it will result in a better reduction of the soluble load prior to the physicochemical treatment, as the tank will then function as a bioreactor. In fact, if the tank is aerated, aerobic bacteria will naturally develop within it and consume a portion of the pollutant load.

We were able to observe these benefits with a client in the agri-food industry who followed our recommendation to aerate their equalization tank upstream of their DAF.

Within a few weeks, the organic load (total COD and BOD5) at the end of treatment had been reduced by half when compared to before the equalization tank was aerated, as a large portion of the soluble fraction was now being consumed by the bacteria proliferating in the equalization tank.¹

¹ https://aquasan.ca/articles/removal-of-organic-load-from-wastewater/