Air Products also is helping customers to reuse their own wastewater, especially when significant quantities of organics or nutrients are present and use of oxygen is a good fit. There's a strong focus on MBRs because they are high-intensity, have a small footprint and produce very high quality water that can be reused in a number of on-site applications such as cooling-water makeup.
"However, while you get a lot more treatment/volume with an MBR, the use of high sludge concentrations can lead to limitations getting sufficient oxygen into the wastewater using conventional air-based aeration. So we believe that the optimum MBR design would run on pure oxygen. We have a couple of these up and running now in industrial applications and are close to commercializing a further optimized system," he reveals.
Overall, the company sees an increasing drive from industry to do more wastewater treatment in less space, reduce waste disposal costs and extract value in the form of water reuse and energy. "We are working to make our oxygen technologies more efficient and, with partners, are developing complete treatment systems designed to take advantage of the benefits of oxygen," he says.
At its Rotterdam site in the Netherlands, Akzo Nobel has cut fresh water consumption while increasing the concentration of saline water that its treatment plant can handle. Salt concentration has risen from its original maximum concentration of 2% as process intensification and expansion projects took place.
"Our first choice, an anaerobic biological system, did not work. But we found we could use an aerobic system instead. By slowly creating and maintaining a biomass that was adjusted to the higher salt concentrations, we were able to operate at 3% salts. Large water savings were realized and we could operate the installation at a higher total capacity," notes a spokeswoman.
At its Delfzijl, the Netherlands, site, Akzo has installed an efficient co-generation plant to generate steam for a multi-effect evaporation process, with condensate purified and reused in a continuous recycling system.
Half a world away, the BP refinery in Kwinana, Australia, (Figure 3) now sends its wastewater to a water recycling plant instead of discharging it into the Cockburn Sound. In addition, the company is taking in treated sewage water from a nearby effluent plant. This water, treated by intense microfiltration and RO, is so pure that it would leach metal from standard piping. So BP has installed glass-reinforced epoxy pipelines.
Seán Ottewell is Chemical Processing's Editor at Large. You can e-mail him at email@example.com.