North Dakota – The Porcelain State!

 

Two More Ceramic Membrane Projects Awarded in ND

With ceramic membrane systems recently selected for two more drinking water projects in North Dakota, we may soon be calling it the Porcelain State! By my count, that’s now at least four ceramic systems in ND, three are using Nanostone and one is with Metawater membranes. I think that currently has North Dakota with more ceramic membrane installations for drinking water treatment than any other US state. There are also a few drinking water systems retrofitted with ceramic membranes nearby in South Dakota.

What is driving the love of ceramic membranes in the Dakotas? Cold water is the reason for a few of the retrofits where existing polymeric systems had capacity challenges in winter. Cold water reduces the flux of polymeric membranes a lot more than ceramic membranes, so if a ceramic module can produce more water than a polymeric module then the capacity is increased – note, ceramic modules have a lot less surface area than polymeric modules, so just because you can get a higher flux with ceramic does not mean you will get a higher output per module – the math needs to be done to confirm this (see my previous post What the Flux!).

Most of the projects that bid in North Dakota allowed either polymeric or ceramic modules and ceramic membrane systems were selected based on an evaluation matrix, including a lifecycle cost comparison and other qualitative evaluation factors.

For two of the projects, despite the selection criteria, ceramic membranes were quite competitive based on capital cost alone. The major factor that allowed competitive capital costs for these bids was the allowed design flux for each type of membrane. On a surface water with coagulation and plate settler pre-treatment, the maximum flux allowed at 2 deg C for polymeric systems was 15 gfd and for ceramic systems was 90 gfd. Ceramic membranes were piloted to determine the design flux. As far as I am aware, there was no parallel pilot of polymeric membranes conducted and the design flux was based on a conservative design for an existing plant installed over 12 years ago. Notably, there are other polymeric membrane systems on the same water source (Missouri River) that have design fluxes over 40 gfd. 

With this spec, not surprisingly, some of the polymeric system OEMs decided not to bid because they had to bid with six times the membrane surface area. With the capital costs very close between polymeric and ceramic systems, based on the evaluation matrix, ceramic won by virtue of having a longer warranty period in both cases, which raises another concern about how these bids are evaluated – if you have a lifecycle cost comparison with the membrane replacement frequency based on the warranty period, why is there a separate evaluation scoring criteria for the warranty length? In that case you are penalizing polymeric membranes twice for a shorter warranty duration – there should not be a separate score for warranty period if there is a lifecycle cost comparison based on warranty length! Unless of course you want to make sure ceramic membranes are selected…

The most recent ceramic membrane project awarded in ND also had an evaluation matrix and while downstream reverse osmosis was also part of the evaluation, most of the evaluation criteria weighting was based on the MF/UF system. In this case, ceramic capital costs were significantly higher than polymeric, but lifecycle costs and non-cost evaluation factors resulted in the selection of ceramic membranes versus polymeric.

A water system owner is free to select a ceramic system if they want it and are happy to pay a premium for capital cost (and also operating cost if you do 21-year lifecycle – see post), just like someone can buy a Mercedes car ahead of a Lexus if that is their preference. If that is the case, flat spec ceramic membranes rather that have a flawed evaluation criteria against polymeric membranes just to get extra bids.

The comments and opinions in this post are my own and not those of my employer.