Chopper pump ends bad odours at paper mill.
A new aeration system has rescued a paper mill in El Salvador that was on the brink of million-dollar fines for causing major odour issues.
Changes to environmental regulations had put the paper mill into a crisis situation, despite the fact that it had already installed four 30HP surface aerators in its aeration tank in an attempt to quell the increasingly bad odour problems.
With the authorities set to take serious punitive measures, the paper mill called in the wastewater treatment business, Black Waters, to see if they could bring about 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). It was primitive in a bad way, resulting in the possibility of substantial fines that caught the paper mill completely off guard.
“The odours were awful, so we went straight into action with a sludge sampler to see what was going on, in order to establish a proper profile.”
Across the 23m length tank, which has a shallow end at 1.87m and a deep end of 4m, Roberto found that only five of the one-meter sections were free from sediment. The rest ranged from 2cm to as much as 45cm of sediment, varying from light brown towards the shallow end to thick dark grey at the deep end.
“At the deep end, it was septic because the surface aerators couldn’t mix the tank comprehensively,” added Roberto. “The slanted tank had become a biological reactor, but with the buildup of sediment, there just wasn’t enough oxygen to allow the bugs to do their job properly. They couldn’t ‘breathe’ and so would die.”
He continued: “It’s all well and good having some mixing, but this dire situation very much needed some oxygen. The wastewater from the paper, which in this case was from a process manufacturing tissue paper, is surprisingly abrasive. Surface aerators can make it appear as if there is a lot happening, but underneath the surface, it can be a totally different story. In a fairly short space of time, foul odours will soon tell you that something is seriously wrong.”
With a potential million-dollar lawsuit for violations on the horizon, Black Water urgently sought a rapid but long-lasting solution, consulting with contacts in the US and beyond to see what might be available.
“With a slanted tank,” added Roberto, “they all said they wouldn’t blame me if I walked away. But we are engineers, of course, so we’ll always want to find an answer, even in this case, where it might not be a perfect world solution. Additionally, the tank was divided into two halves by a concrete wall, so we had to cut 20cm holes across it to try to even out the flow distribution.”
The recommended solution certainly wasn’t the cheapest, but it came in the form of a simple design, combining a proven chopper pump with a venturi nozzle; the Landia AirJet. Simultaneously mixing and aerating, this system effectively keeps wastewater fresh; economically delivering dissolved oxygen to provide complete aeration.
The next challenge for Black Water was how to incorporate what would be six of the new Landia AirJets onto both sides of the tank.
“Landia helped us calculate the best positioning,” added Roberto. “The Landia AirJets had to be installed with middle guideline poles that had to be embedded in specially built concrete blocks. This allowed the aerators to be then slid to the bottom of the basin. The Landia Chopper Pumps that are part of the AirJet system do a great job and are very reliable. Everything is fine now. Thankfully, the horrible odours are no more.”
