The rise of process intensification: Big gains with small footprints
October 07, 2022
October 07, 2022
Intensification holds the key to sustainable wastewater treatment—smaller, cleaner, safer, and more energy-efficient technologies
Over the past two decades, three major trends in wastewater treatment have emerged. Nutrient removal and recovery, energy conservation and production, and process intensification.
We’ve talked about the first two previously, now let’s tackle the third. So, what exactly is process intensification, and why is there so much focus on it today? Is it just a fad? Or is it the new normal for wastewater treatment?
Process intensification is not actually a new idea. In fact, it originated in the chemical manufacturing industry. The first formal use of the term was published in a technical journal in Poland in 1971. For that industry, it meant devising a strategy for manufacturing processes, associated equipment, and methods that would push a company toward key performance indicators (KPIs) that improved economic growth. This is especially true for those in the treatment of domestic and industrial wastewater by publicly owned treatment works.
In wastewater, intensifying a process means increasing product mass transfer and throughput. It results in a more sustainable path in times of growth. Critically, it puts a focus on changing regulations and squeezing more out of existing infrastructure.
So, why would a public utility be interested in process intensification? Here are some reasons:
To ensure this purpose is achieved, the wastewater treatment process engineer is focused on four principles. First, we want to maximize intra- and intermolecular interactions and events. This correlates to the stoichiometry and kinetics associated with biological activity. Second, we want to give each molecule the same process experience, correlating with system hydraulic retention time and solids retention time. Third, is optimizing the driving forces at every scale of the system and maximizing the exposure microorganisms have to the application of those forces. This relates to the gradients of substrate concentration and mass transfer diffusion. Finally, the fourth principle is to boost the synergistic effects from the influences of partial processes. This means correlating with process configuration environments (anaerobic, anoxic, aerobic), side stream processes, recycle streams, and more.
The greatest benefits come when the solution is simplistic and practical.
When all these principles are enacted, KPIs for process intensification in a public utility differ from those of private industry. Here, the value is more about operational efficiency, rather than economics. Efficiency gains to the municipal operator include the following:
And you can see these are all signs of efficient operation and wins for any utility manager. Some argue that increased mass throughput is another indicator for measuring process intensification success, but this is still debatable.
One of the main reasons process intensification has gained so much momentum in municipal wastewater treatment in recent years is the number of tools available to measure the impacts. These tools include:
What’s more interesting is when you can see all these tools working together. By bundling the applications of these tools, the benefits of intensifying process can be magnified.
To better understand the benefits of process intensification, let’s examine a couple of examples where there is little doubt that the answer is yes.
At a project in Ontario, Canada, we used process intensification to help us address capacity and strict regulatory limits. How? By deploying the membrane aerated biofilm reactor technology. This enabled the plant to unlock double its current 13.6-million litres per day (MLD) process capacity to re-rate the facility to 26 MLD. This was done with less than half of the footprint usually needed for a conventional solution, consuming 30% less energy, and at half the capital cost. The key to this success was maximizing the use of existing assets coupled with a technology to capitalize on the benefits of immobilizing bacteria in biofilms.
Another example is when our teams designed the conversion of a high purity oxygen (HPO) activated sludge plant into an aerobic granular sludge (AGS) process in Alberta, Canada. This allowed the facility to convert to an ultimate capacity of 60 MLD from its current 23 MLD rating, while achieving higher process performance. Again, the key to this was repurposing 6 existing secondary clarifiers to AGS batch reactors—essentially reconstructing them as a “tank within a tank.” This advanced technology allows for complete nutrient removal, an action not possible with the existing HPO process. It also performs these functions within one reaction environment. The benefits of this type of technology are once again realized in the physics of biofilms, via granules. As such, robust performance is achieved in the challenging times of chilly winter weather. By using the existing footprint, this led to significant cost savings versus a standard biological nutrient removal process facility.
It’s important to remember that process intensification will always demand three things of us.
First, it requires we relentlessly push back on convention. In this case, convention favors the incumbent solution. Nothing stymies the benefits of process intensification more than a fixation on the status quo. Secondly, this requires that we view system solutions holistically. Finally, the greatest benefits come when the solution is simplistic and practical. Introducing too many complex parameters into the process flow diagram can backfire. At the end of the day, the operator must fully grasp the range of reliable operability of the intensified process. The more complicated the intensification, the more its practicality wanes. When practicality wanes, an operator’s interest—and even confidence in that process—fades as well.
Without doubt, process intensification within municipal wastewater treatment is a breakthrough for the industry. And to date, its benefits to the wastewater industry are being delivered as promised. It is not a fad for the wastewater treatment industry. Just as process intensification became the norm in the chemical manufacturing industry, it is the new normal for wastewater treatment, and it’s here to stay.