CH2MBR

1. Using the Latest Data to expand MBR Technology’s Reach: Ask most engineers?at least those actively engaged in the design of wastewater treatment plants (WWTPs)?when membrane bioreactor (MBR)
technology makes sense and you will probably get the following response: “MBR technology should be considered
when the site footprint is small and when you are trying to produce high-quality effluent.”
Both are great reasons to think MBR, but the sentiment is lagging behind the facts and a growing trend.

MBR technology is routinely making more sense than sequencing batch reactors (SBR) and even moving bed bioreactors (MBBR);
and not just for postage stamp-size real estate conundrums. So, where does this lingering misperception about MBR
as a niche technology come from? Old ideas and dated facts on cost and energy.

In order to make the best available technology (BAT) truly available, we need to change outdated MBR paradigms.

2. Cost Competitiveness: By reviewing technical literature or surfing the Internet, one can
easily find the following comments associated with MBR costs:

· MBR operating costs are the same order of magnitude as alternative treatment.
· Membrane equipment costs have come down from $3 per gal to $0.75 per gal …
· Membrane prices have dropped eightfold in the last decade.

This growing body of information reflects a new reality that MBR technology is not only the BAT,
it also is competitive categorically in most WWTP applications.

The common theme is that MBR is now competitive with alternative technologies being considered
for mechanical plants. Despite higher equipment prices as compared to SBRs and other technologies,
MBRs make up ground in the following categories:

· Solids handling (more than 40% cost savings)
· Concrete/buildings (50% to 80% cost savings)
· Equalization (more than 50% cost savings compared to SBR)
· Constructability/phasing (more than 50% cost savings due to less site work).

Moreover, remote monitoring capabilities, pending nutrient limits and projected growth are examples of non-cost
factors that routinely favor the selection of MBRs, but there is still one question hindering the unfettered
use of MBRs anywhere and everywhere: Is MBR technology too energy-intensive? The answer is that it should not be.

3. The Energy Question: The idea that MBRs take more energy is not unfounded, but it is somewhat misguided in two key areas:
First, the notion that less membrane air scouring translates into lower energy bills is not consistent with energy data.
Second, reducing air scouring energy is not always the best or only way to make plants more efficient.

More to the point, industry data suggest that the best way to reduce energy bills is to improve turndown, simplify systems,
increase flux and hold system suppliers accountable for plant performance, not just air scouring.

An easy way to differentiate membrane technologies is to compare so-called air scour rates: Some take more and some take less.

· Make sure you have a method of controlling the dissolved oxygen concentration in each cell
    with an automatic air balance in each aeration cell, so that electrical energy is optimized and not wasted.
· Insure that you have a method of controlling the treatment process flow rate between
    banks or trains by automatically controlling weirs, valves, or gates. Often the loading rates vary among parallel treatment trains.
· Insure that the methods of cleaning the MBR membranes
    to minimize chemical and biological fouling are proven technologies.

4. Moving the Needle: A review of technical literature on how to improve MBR energy efficiency yielded some surprising results.
While air scouring reduction is a common theme, several other themes were just as important:

· Improving turndown (the ability to incrementally match energy input to demand);
· Simplifying systems (taking out parasitic loads such as pumps, mixers and blowers);
· Operating at higher flux rates; and
· Making the supplier responsible for plant performance.

5. Changing the Paradigm: MBR technology is a viable, affordable wastewater treatment technology that should be considered whenever
mechanical plants are on the table. While important innovations are being made at the commodity level,
operating at a plant’s best efficiency point, simplifying systems by removing unnecessary
equipment and improving operating procedures may have a greater impact on energy than air scouring rates.

In fact, industry data support that making suppliers responsible for plant performance?not
just theoretical air scouring targets?may move the needle the farthest toward lower energy bills.

ch2mbr