As clean-water plants strive to become resource recovery facilities, energy neutrality is a key goal. There are two components to get there: using less energy (through efficiency) and producing more energy (by using biogas).

An example of the first component is ZeeLung membrane aerated biofilm reactor (MABR) technology from GE Power & Water. The system is designed to use oxygen much more efficiently than conventional fine-bubble aeration in the activated sludge process.

The technology transfers oxygen by diffusion through a membrane to a biofilm that grows on the outside membrane surface. The microorganisms in the biofilm then metabolize the nutrients and organic compounds in the wastewater. The manufacturer says the process uses one-fourth the energy required for fine-bubble aeration, which typically accounts for about 60 percent of a treatment facility’s electricity usage.

The ZeeLung system can be installed in new plants or retrofitted to existing aeration basins, increasing treatment capacity or performance without increasing the plant’s footprint. Jeff Peeters, senior product manager for water and process technologies with GE Power & Water, talked about the process in an interview with Treatment Plant Operator.

TPO: What market need drove the development of this technology?

Peeters: Energy is increasingly important in water treatment. There’s a need for energy-saving technologies and energy recovery processes. We are developing a suite of products to fill that need. ZeeLung addresses the largest energy consumer in wastewater treatment plants, which is the aeration process.

TPO: How have you documented the potential energy savings?

Peeters: We’ve been testing the technology for about three years at different scales. We started with proof of concept testing in our lab. We scaled that up to small-scale versions of the product in the lab and then went to pilot testing at a customer site. Most recently, we’ve been testing a commercial scale module at the Metropolitan Water Reclamation District of Greater Chicago’s Terrence J. O’Brien Water Reclamation Plant.

TPO: What makes this process more efficient than conventional aeration?

Peeters: Until now, the game in aeration has been how to make smaller and smaller bubbles, because that increases the surface area of air in contact with the liquid. That has limitations in transfer efficiency, as typically 60 to 70 percent of the oxygen that goes into the basin comes out at the surface and isn’t used. With the ZeeLung MABR, we use a membrane to diffuse oxygen directly into a biofilm.

TPO: What does the membrane system consist of?

Peeters: It consists of bundles of membrane fibers deployed into cassettes and installed in the aeration basin. It looks exactly like our ZeeWeed membrane filtration system, except that the membrane is different. The membrane does not filter water. We chose a membrane material that has an affinity for diffusing oxygen.

TPO: How exactly does the aeration process work?

Peeters: We push air into the membrane fibers. This creates an oxygen concentration gradient so that molecular oxygen diffuses from the inside of the membrane through to the outside. On the outside of the membrane a biofilm grows. The bacteria in the biofilm are in direct contact with the medium that provides the oxygen they need.

TPO: Besides the membrane, what are the other key components of the technology?

Peeters: You still need a blower, but that blower can be significantly smaller. You also need mixing in the tank. Some mixing is integral to the cassette. If the tank is large or wide or deep, it may need some supplemental mixing to get good contact between the substrate in the wastewater and the biofilm on the membrane.

TPO: What are the most promising applications for the technology?

Peeters: Most opportunities we’ve looked at have been retrofits into conventional activated sludge systems that have bioreactor tanks and secondary clarifiers, but need to upgrade to meet new regulatory requirements or to expand capacity.

TPO: How does this process perform in applications that require nutrient removal?

Peeters: The biofilm includes bugs that remove BOD as well as bugs that remove ammonia — the nitrifiers. So we get very good nitrification performance. Then if the customer needs total nitrogen removal — denitrification — that can happen in the bulk solution around the membrane.

 

TPO: Can the process provide biological phosphorus removal as well?

Peeters: Some applications we’ve looked at are existing plants that want to do biological phosphorus removal but are at capacity and don’t have enough tankage to introduce an anaerobic zone. We could add ZeeLung cassettes to concentrate the aerobic portion of the system, and in that way free up space for an anaerobic zone for bio-P.

TPO: What is involved in retrofitting the technology to existing tankage?

Peeters: We designed the product to simplify installation to existing tanks. After installing the cassettes in the aeration basin, you simply plumb the air supply to them. Of course, you need to look at the plant hydraulics and, if you’re adding capacity, make sure the secondary clarifiers can handle the increased flow.

TPO: How has this technology proven out at commercial scale?

Peeters: Chicago is our first commercial demonstration. We’re testing a full cassette of commercial modules operating in a sidestream configuration with a nominal capacity of 0.5 mgd. We pump a mixture of primary effluent and return activated sludge to a separate tank that houses the ZeeLung cassette and monitor its performance. The effluent from that tank goes back into the main plant. The focus there is on ammonia removal. We are seeing consistently greater than 30 percent ammonia removal by the membranes, which is the target for this particular plant.

TPO: What other GE technologies can help plants achieve energy neutrality?

Peeters: ZeeLung is one of four products in our Energy Neutral portfolio. Another is LEAPprimary, an enhanced primary treatment process designed to remove as much of the organics as possible and minimize the load to secondary treatment. The MONSAL advanced anaerobic digestion process improves digester gas yield. And the Jenbacher gas engine converts that gas to electricity and heat.