Beyond Clarifiers: How Advanced Primary Filtration Solves Wet Weather Capacity Challenges

Increasingly frequent and intense wet weather events pose a growing challenge for wastewater utilities. Whether operating combined or separate stormwater systems, facilities face the same issue: stormwater levels that exceed plant design capacity. When this happens, it can short-circuit clarifiers or overload storage tanks, resulting in untreated water being discharged into waterways.

To overcome this, many wastewater utilities are turning to advanced primary treatment using pile cloth media (PCM). Both the AquaPrime and AquaStorm Cloth Media Filters designed by Aqua-Aerobic Systems, Inc. can serve as alternatives to both clarifiers and stormwater storage, helping reduce costs, increase capacity, and improve treatment performance while minimizing footprint.

How Advanced Primary Treatment Works

Advanced primary treatment systems using PCM by Aqua-Aerobic Systems employ three distinct methods of removing suspended solids. First, heavier and faster settling solids particles are allowed to settle out via gravity as they would in a traditional clarifier into a solids removal zone. Second, the remaining solids are filtered through woven cloth media that is engineered to capture solids. Third, a scum weir at the top allows for removal of fats, oils, grease, and other floating solids. As water flows through the PCM, filtrate collected in the fully submerged disks and hollow center tube is discharged over an effluent weir, all via gravity. As the media starts to collect solids, the backwash process begins automatically based on the water level in the filter basin. Backwash shoes on either side of the disks make direct contact with the media and remove solids by pulling filtered water from inside the disks. This backwash waste can then be pumped back to the plant’s waste-handling facility.

Superior Alternative To Stormwater Storage

Stormwater storage systems present several critical drawbacks, including significantly high construction costs and intensive pre- and post-storm cleaning requirements. However, their greatest limitation is finite capacity.

Traditionally, stormwater is held until drier days, at which point the water is fed gradually into the wastewater treatment plant (WWTP) at a pace that will minimize disruptions to the biological processes. When extreme or consecutive storm events exceed the storage units’ limits, utilities must send excess flow to the treatment plant or discharge untreated water. Both scenarios can result in fines and regulatory action.

Advanced primary treatment eliminates or reduces the need for storage. Stormwater can be treated to required standards as it comes while minimizing compliance risk. Moreover, its compact footprint allows facilities to treat often three to four times more water within the same space, greatly increasing overall plant capacity.

Rethinking The Role Of Clarifiers

When used upstream of biological processes, advanced primary filtration using PCM boasts several notable advantages:

Improved removal efficiency. Studies have shown that PCM filtration typically exceeds 80% total suspended solids (TSS) removal compared to 40% to 60% for clarifiers. This approach can achieve up to 45% to 60% biological oxygen demand (BOD) reduction, whereas clarifiers rarely surpass 40%. In addition, advanced primary filtration does not suffer from short-circuiting during high-flow events, maintaining stable effluent quality at any flow rate.

Reduced footprint, increased capacity. Because cloth filters utilize vertical disks to provide a large surface area, advanced primary treatment can treat up to 30 million gallons per day (MGD) within same footprint as an 8 MGD clarifier, representing a 75% to 80% reduction in space. This is particularly valuable for operations that have limited land for expansion.

Saving Energy And Money

In addition to supporting downstream biological processes, advanced primary treatment can also help improve overall energy efficiency, as well as reduce costs. It does this through:

Reduced aeration demand. Aeration often accounts for between 40% and 60% of total energy usage at a WWTP. By cutting BOD, advanced primary treatment can trim aeration requirements by 15% to 30%.

Increased biogas production. While not all WWTPs capture solids for biogas production, those that do have found that higher solids captured with advanced primary treatment can produce about 30% more biogas, which can be converted for higher energy production.

Eliminated chemicals. Unlike clarifiers, PCM filtration does not require coagulants or flocculants to remove higher pounds of solids. In addition to saving money on these costly chemicals, this also reduces operational complexity and associated labor expenses.

Lower capital costs. With no need for large concrete tanks, advanced primary treatment systems have a fraction of the capital construction costs of a clarifier.

Minimized operational costs. Overall, advanced primary treatment using PCM requires less operator intervention. These fully automated systems utilize a special control strategy to initiate backwashing based on water levels or time, and the cloth media disks typically last four to five years, with longer lifespans in less demanding applications.

As wet weather events become more volatile, the limitations of traditional infrastructure — from the finite capacity of stormwater storage to the inefficiency of conventional clarifiers — are becoming increasingly apparent. Advanced primary treatment using PCM solutions like AquaPrime and AquaStorm systems offer a more resilient and cost-effective alternative. By enabling real-time treatment instead of simply storing it, these systems can help utilities ensure that even the most intense storms do not compromise their downstream process or the integrity of community waterways.