Businesses and communities that produce and treat wastewater increasingly look for ways to recover resources from the waste streams — whether energy, nutrient-rich fertilizer and other valuable byproducts, or water for reuse.

Pentair, in partnership with Veolia Water, has developed a technology for treating high-strength, high-solids waste streams from industrial facilities such as dairies, distilleries, breweries and bioethanol plants in a way that yields high-quality effluent and maximizes production of biogas that can be used for heating fuel or electric power generation.

The Memthane anaerobic membrane bioreactor combines Veolia’s anaerobic biological wastewater treatment process with Pentair’s X-Flow ultrafiltration (UF) membrane separation. Its advantages include low energy consumption, a small footprint, low chemical usage and substantial reduction in biosolids volume, reducing handling costs.

Phil Rolchigo, vice president of technology with Pentair, talked about the process in an interview with Treatment Plant Operator.

TPO: What is the reason behind bringing this offering to market?

Rolchigo: Treating wastewater is generally considered an expense. The moment you start thinking of wastewater as a resource, as a feedstock, you can start thinking about wastewater treatment as a profit center. Our focus is around reimagining wastewater treatment plants as resource-recovery facilities. We found it exciting that by coupling a membrane with an anaerobic bioreactor we could change the efficiency of digestion such that we can get over 25 percent more methane out. The biogas generated through this process can help make the treatment plant energy neutral or even a net renewable energy producer.

TPO: So this process also functions as a treatment for the liquid side of the waste stream?

Rolchigo: Yes. COD is reduced by more than 98 percent. If you were to look at a sample of water coming out of an anaerobic digester versus water coming out of our process, you would see the latter coming out very low in color, whereas decant from an anaerobic digester would be colored from the presence of organics still in the water. So the net result is water suitable to be reused on site, treated further for more precise applications or at the very least cleaned to a level that makes it much easier to discharge to a sewer system.

TPO: So far, what are the primary applications for this technology?

Rolchigo: We’ve found really great traction in the food and beverage market because those waste streams tend to have very high BOD and require anaerobic digestion to treat the solids.

TPO: Are there potential applications in the municipal wastewater treatment sector?

Rolchigo: We are exploring new opportunities, and they include using this technology in municipal applications in what is traditionally the anaerobic digester part of a wastewater treatment plant. We see a significant opportunity there.

TPO: In basic terms, how would you describe the treatment process?

Rolchigo: It works in a manner similar to a kidney dialysis loop. You constantly circulate the solids and the liquid through the bioreactor. You concentrate the solids in the membrane filter and pull off purified water. Meanwhile, you’re continuously feeding the waste stream into the reactor. By significantly improving the digestion process, you convert more of the organic matter to methane while reducing the volume of solids and so reducing solids-handling costs.

TPO: How does the anaerobic bioreactor used in this process differ from a traditional anaerobic digester used in a municipal treatment system?

Rolchigo: The two are very similar in the way they are operated. The key difference is that while a traditional anaerobic digester tends to digest biomass that is near the end of its lifecycle, the anaerobic bioreactor actually digests a great deal of liquid organic mass — the carbohydrates, the proteins and the fats, oils and grease, which are the primary food source.

TPO: How does the UF membrane filter fit into the process?

Rolchigo: The UF membrane is outside the bioreactor. We constantly circulate the biomass across the membrane and back into the bioreactor. This yields a higher solids concentration in the bioreactor, making it more productive and enabling generation of more methane.

TPO: How do the UF membranes handle high solids loading without fouling?

Rolchigo: In designing UF membranes, you can change a number of parameters according to the flow being treated. With drinking water, you can use very fine fibers because the source water has low suspended solids. For our application, we use membranes shaped as tubes 1 mm to 2 mm in diameter. The material can flow through easily, and the flow velocity keeps the membrane surfaces clear. We also prevent fouling by making the membranes from PVDF material, which is similar to Teflon in that it repels oil, so you don’t have oil sticking to the membrane pores. There is also a periodic clean-in-place process that is fully automated.

TPO: How complex is this technology to operate?

Rolchigo: It’s no more complicated than a traditional solids treatment process, and in many cases it’s a little bit simpler, because in a classic application where you rely on settling to separate the liquid from the solids, there are many ways in which the process can be upset. In our process, the membrane performs a complete separation between liquid and solids and doesn’t rely on the density of biomass for separation. It’s a highly automated process.

TPO: How does this process limit the release of odors?

Rolchigo: Because it’s a closed system, there is no release of methane or any odorous gases. Our gas-recovery systems separate the CO2 from the methane to create two gas streams. The CO2 in some applications can be reused, such as to balance pH, and in other cases it is vented. The biogas is recovered and treated for use on site.