Membrane bioreactors can be an attractive wastewater treatment option, delivering high-quality effluent in a relatively compact footprint.

MBRs combine conventional activated sludge treatment with membrane filtration, delivering advanced removal of organic and suspended solids and, if so designed, significant nutrient removal as well.

At WEFTEC last October, Veolia Water Technologies & Solutions introduced a new version of its ZeeWeed 500 MBR for larger municipal applications. It is designed to enable expansion of capacity at low capital expense, reduce energy costs and provide long membrane life with simplified maintenance.

The ZeeWeed 500 series has a record of longevity and reliability and has some 2,500 users worldwide. The ZeeWeed 500EV reduces the membrane tank footprint by up to 50% and is designed to minimize plant construction or expansion costs.

The manufacturer says it also reduces energy costs by 20%, cuts usage of cleaning chemicals, has fewer parts to maintain, and has a robust membrane that meets the requirements of water reuse regulators. Jennifer Lim, product line director for the Veolia MBR product line, talked about the unit in an interview with Treatment Plant Operator.

TPO: What was the market rationale for creating this new version?

Lim: Our existing product, the 500D, was 20 years old last year, and we recognized that the market had shifted. When we talked to our customers, we heard five drivers. Capital cost of new builds and upgrades to existing conventional systems continued to go up, so they needed cost savings. Space is restricted in many places around the world, and so they needed a unit with a small footprint. Their budgets were not increasing while energy, technical and labor costs were going up, so they needed to minimize operating costs. They also wanted a system that would be easy to maintain with a long membrane life. And finally, as regulatory requirements become stricter, they wanted a product that could still comply if permit limits changed.

TPO: What are they key market niches for this system?

Lim: At present this product is focused on municipal applications, but as we expand factory capacity, we will expand it to our entire MBR portfolio. So this system would fit any MBR application with 10 mgd capacity or larger, whether industrial or municipal. There are systems that exceed 50 mgd in capacity that we are actively pursuing.

TPO: What are the capacity limits of individual ZeeWeed 500 EV units?

Lim: Depending on the temperature of the water, the capacity is anywhere from 0.5 mgd to 1 mgd per unit.

TPO: In brief, how does this system treat water?

Lim: A conventional wastewater treatment plant typically has primary clarifiers, a biological process feeding into secondary clarifiers, and potentially some type of tertiary filtration. In the MBR the primary clarification typically remains, but the biological process and secondary clarifiers are replaced with the MBR. The biological treatment process is smaller, and the secondary clarification step is replaced by the membrane filtration tanks. Unlike clarifiers, which can have upsets, the membrane is a 100% barrier that prevents anything from going downstream. That eliminates the need for tertiary filtration, except where a user might want a reverse osmosis process downstream in an industrial application.

TPO: What level of membrane filtration does this system use?

Lim: All of our units use ultrafiltration membranes.

TPO: What has enabled the significant capacity increase within the same footprint?

Lim: We started with the same footprint as the ZeeWeed 500D because we wanted the new product to be completely retrofittable for our existing customers. We achieved the 50% increase in capacity by optimizing the membrane packing density — the amount of membrane that is actually in the unit.

TPO: How was the energy requirement curtailed?

Lim: We didn’t change the amount of air we put in on a membrane basis, but the significant increase in membrane within the same footprint results in the 20% energy savings.

TPO: What was done to reduce the requirement for cleaning chemicals?

Lim: Our standard cleaning mode is what we call relax. We turn off the permeation and allow air to clean the membranes. We don’t actually backwash. For chemical cleaning, the way we achieve chemical reduction is twofold. First, while the membrane fibers have not changed between the two generations of ZeeWeed, we knew from more than 25 years of experience that we could reduce the chemical inputs. We surveyed our customers to understand how frequently they felt they needed to clean the membranes, and then we did a chemical optimization. Second, for the biennial soak-cleans, we reduce chemical usage because the tanks are smaller. 

TPO: What is the market reaction to this new version so far?

Lim: The reaction from customers and the consulting community is very positive. The drivers we selected resonate with them, and the demand is high. We have units operating at a number of plants, including two sites in North America, in Beaver Creek, Tennessee, and just outside London, Ontario. An additional three units will be started up in the near future.