Black Waters and Landia Eradicate Odours at Paper Mill

A new aeration system has saved a paper mill in El Salvador from multi-million-dollar fines after serious odour problems put the company in crisis.

Changes to environmental regulations left the paper mill struggling, despite having already installed four 30HP surface aerators in its aeration tank in an attempt to combat the worsening odour issues.

With the authorities poised to take punitive action, the mill called in leading wastewater treatment specialists, Black Waters, to find a solution.

“This was a major challenge,” said Roberto Escalante, Principal of Black Waters.

“Nobody in our industry particularly relishes working with a slanted-floor rectangular tank (1,000m3), but I can tell you that the twisted face of the paper mill’s CEO was in far more pain than mine!”

“It was primitive in a bad way, creating the possibility of substantial fines that caught the mill completely off guard,” he added.

“The odours were awful, so we went straight into action with a sludge sampler to analyse the situation and establish a proper profile.”

Spanning 23 metres in length, with a shallow end of 1.87 metres and a deep end of 4 metres, the tank revealed serious sediment buildup. Roberto discovered that only five of the one-metre sections were free from sediment, while the rest had accumulations ranging from 0.8 inches to as much as 18 inches. The sediment transitioned from light brown at the shallow end to thick dark grey at the deep end.

“No wonder it stank so much,” Roberto added.

“At the deep end it was septic because the surface aerators couldn’t properly mix the tank. The slanted tank had become a biological reactor, but with the accumulation of sediment, there just wasn’t enough oxygen for the microbes to do their job properly. They couldn’t ‘breathe’ and so would die. It was nasty.”

‘Dire Situation Desperately Needed Oxygen’

He continued: “Mixing alone wasn’t enough – this dire situation desperately needed oxygen. Wastewater from paper production, especially tissue manufacturing, is surprisingly abrasive. Surface aerators can make it seem like there’s plenty of movement, but below the surface, it’s often a very different story. In a short space of time, foul odours make it clear that something is seriously wrong!”

With a multi-million-dollar lawsuit for environmental violations looming, Black Waters urgently sought a rapid yet lasting solution. Consulting with industry contacts in the US and beyond, they explored available options.

“With a slanted tank,” Roberto added, “they all said they wouldn’t blame me if I walked away. But as engineers, we always want to find a solution, even when a perfect answer isn’t possible. They told me I was crazy to take it on, but I already knew that! At least I’ll never be as crazy as the person who thought it was a good idea to design a slanted-floor rectangular tank for a paper mill’s wastewater! Additionally, the tank was divided into two halves by a concrete wall, so we had to cut eight-inch holes across it to try to even out the flow distribution.”

‘Simultaneous Mixing and Aeration’

The recommended solution wasn’t the cheapest, but it was simple and highly effective, combining a proven chopper pump with a venturi nozzle – the Landia AirJet. This system simultaneously mixes and aerates, keeping wastewater fresh and efficiently delivering dissolved oxygen for complete aeration.

The next challenge for Black Waters was integrating six Landia AirJets into both sides of the tank.

“Landia helped us calculate the best positioning,” said Roberto, “and I was really pleased that their vastly experienced Aftermarket Manager, Ken Jacobs, came over from the US to help ensure that the installation went smoothly. The Landia AirJets had to be installed with middle guideline poles embedded in specially built concrete blocks. This allowed the aerators to be slid to the bottom of the basin. The Landia Chopper Pumps that are part of the AirJet system do a great job and are proving very reliable. Everything is fine now. Thank goodness those horrible odours are no more!”

www.black-waters.com
www.landia.world.com