What’s happening in a wastewater lagoon when the TSS of the effluent is higher than the TSS of the influent? And more importantly, how does an operator fix it?

Excess sludge accumulation is often the cause of high effluent TSS and can be accurately diagnosed with a little time, observation and sampling.

The most obvious signs are visible sludge that is floating in the lagoon, or large deposits of sludge that rise close to the surface or above it. When operators sample the lagoon effluent they may notice a change in colour, reduced clarity and an abnormally high or non-compliant TSS level.

As sludge accumulates, storage capacity and retention time diminish, which can adversely impact nutrient removal. This can cause algae blooms and significant increases in TSS and BOD, potentially to levels that are higher than that of the influent.

Short circuiting is another symptom of excess sludge that can also contribute to high effluent TSS. When this occurs, channels form in the sludge that cause wastewater to travel relatively quickly through the lagoon from the inlet to the outlet, rather than dispersing and remaining for the optimal residence time. The shallow depth of the lagoon may also cause poor settling and carry over of sludge into the effluent.

Benthal feedback might also be the culprit of high effluent TSS, however this condition occurs primarily during the spring in non-aerated lagoons. As the water warms, it creates turbulence that stirs up the sludge blanket and releases accumulated hydrogen sulfide and nutrients. The condition is short-lived, but until the sludge settles, the lagoon could emit malodours and experience high TSS and nutrient levels in the effluent.

Sludge removal often solves the problem

A sludge survey is an important first step to measure the thickness of the sludge blanket and how it’s distributed throughout the lagoon cell. Following that, Bishop Water can discuss important sludge management considerations and actions including:

• Current lagoon capacity vs. design capacity
• Depth and distribution of sludge
• Location and volume of recommended sludge removal
• Available budget and operational objectives
• Partial vs. total lagoon sludge cleanout

Depending on the results, urgency and budget availability, a total cleanout might be the right approach, or a partial cleanout to remove sludge only from areas of concern and defer the full cost to a future fiscal year.

Once a plan is ready, our team can begin mobilizing sludge removal equipment and the Bishop Solids Management Solution. This process provides a simple and cost-effective way to collect, dewater and contain sludge and achieves a high level of dry solids using only polymer conditioning, Geotube™ containers and gravity.

Compared to alternatives like centrifuges and belt presses, the Bishop Solids Management Solution is less complex, more energy efficient and can collect and dewater sludge at a significantly higher rate, which means projects can be completed faster and more affordably.