Black Waters and Landia eliminate odour problems at El Salvador paper mill

A new aeration system has come to the rescue of a paper mill in El Salvador, which was facing hefty fines due to severe odour issues. Despite having installed four 30HP surface aerators in an attempt to tackle the odour problem, changes in environmental regulations pushed the company to the brink of financial penalties.

With authorities preparing to impose significant fines, the paper mill turned to Black Waters, a leading wastewater treatment company, for a solution.

“This was a major challenge,” said Roberto Escalante, Principal of Black Waters. “No one in our industry enjoys working with a slanted rectangular tank (1,000m³), but I can tell you, the twisted expression on the paper mill’s CEO’s face was far worse than mine!”

Escalante explained that the situation had become critical. “The odours were unbearable, and it was clear the paper mill was caught off guard by the potential fines,” he added. “We immediately got to work, using a sludge sampler to determine what was going wrong and create an accurate profile of the problem.”

The tank, measuring 75.4’ (23m) in length with a shallow end at 6.2’ (1.87m) and a deeper end of 13’ (4m), showed that only five of its one-meter sections were free of sediment. The rest ranged from 0.8” to 18” of sediment, with the shallow end having light brown sludge and the deep end covered in thick, dark gray sediment.

“It’s no wonder it smelled so bad,” Escalante commented. “At the deep end, it was practically septic because the surface aerators couldn't mix the tank properly. The slanted tank had turned into a biological reactor, but with sediment buildup, there wasn’t enough oxygen to allow the bacteria to break down the waste. They were essentially suffocating, which created the foul odours.”

A dire need for oxygen
Escalante stressed the urgency of the situation: “While the surface aerators provided some mixing, the real issue was the lack of oxygen. The wastewater, which comes from tissue paper manufacturing, is surprisingly abrasive. The surface aerators might seem to work on the surface, but underneath, the conditions were deteriorating fast. The odours were a clear sign that something was seriously wrong.”

With the potential for significant financial penalties looming, Black Waters urgently searched for a lasting solution, consulting experts from the U.S. and beyond.

Despite the challenges of working with a slanted tank, Escalante was determined to find a solution. “Many people advised me to walk away, given the slanted tank, but as engineers, we always want to find a solution—even if it’s not perfect. While I may be crazy for taking this on, I’m certainly not as crazy as whoever thought a slanted-floor rectangular tank was a good idea for wastewater!”

Moreover, the tank was divided by a concrete wall, requiring Black Waters to cut eight-inch holes to improve flow distribution.

A proven solution: Simultaneous mixing and aeration
The solution that Black Waters implemented wasn’t the cheapest, but it was effective. The team chose a simple yet proven design: combining a chopper pump with a Venturi nozzle to create the Landia AirJet system. This system simultaneously mixes and aerates, economically providing dissolved oxygen to ensure thorough aeration of the wastewater.

The next challenge was fitting six Landia AirJets on both sides of the tank. Black Waters worked closely with Landia’s team to determine the best positioning. “Landia’s experienced Aftermarket Manager, Ken Jacobs, flew in from the U.S. to help ensure the installation went smoothly,” Escalante said.

To install the AirJets, special guideline poles were embedded into concrete blocks, allowing the aerators to be lowered into the bottom of the basin. The Landia Chopper Pumps proved to be highly reliable and effective.

“Now, everything is running smoothly,” Escalante said. “The horrible odours are gone, and the paper mill is no longer facing the risk of fines. Thanks to the Landia AirJets and our team’s hard work, the situation has been completely turned around.”