Biofiltration Dominates Discussion at 2016 WateReuse Research Conference

At the recent WateReuse Research Conference in Denver, I had expected much of the discussion to be around the use of membranes (low and high pressure) for wastewater reuse applications, but was surprised that much of the research focus was on biological filtration. Perhaps since there are a lot of full scale membrane systems already installed and in the pipeline for water reuse, this is starting to be considered as a more mature technology and not needing as much research. If that is the reason I think it is mistaken, but I will come back to that later in this post.

I haven’t been keeping up with recent developments in biofiltration, so I was very interested in what was presented at this conference. Around 10-15 years ago when I was working in ion exchange I recall there was interest in looking at biofiltration for nitrate and perchlorate removal from drinking water as an alternative to IX but this treatment generally wasn’t seriously considered for full-scale systems, due to the perhaps misguided concern about using bugs to treat the water when you were also trying to pull them out to protect public health. This did not take into account that many existing filters were probably operating in biological mode to some degree anyway.

Wastewater Reuse Helps Acceptance of Biofiltration

Today the landscape has changed significantly with the current drought on the west coast and the recent drought in Texas helping the public to be more accepting of direct and indirect potable reuse of wastewater and with reuse becoming an essential component of the water supply. If the public will accept potable reuse of biologically treated wastewater, acceptance of biological filtration should be a walk in the park!

Wastewater reuse has also opened up new opportunities for biological filtration, where micropollutants (MPs) not removed in wastewater plants need to be removed if the treated water is to be used for drinking directly or indirectly. In combination with pre-oxidation to break down the MPs to biologically assimable components, biological filtration can be an attractive alternative to high pressure membranes where it has a significantly lower waste volume and does not produce a saline waste, which is a considerable benefit in non-coastal areas where NF/RO waste disposal options are limited and/or expensive.

Wastewaters Ain’t Wastewaters!

There are plenty of technical articles today about potable reuse, so you don’t need to read another one from me. I do think it is important to mention that I believe the use of membranes for wastewater reuse is not yet a mature technology and is worthy of further research. We have all read a lot about Orange County Water District’s Groundwater Replenishment System that has been using membranes for decades for treating wastewater to drinking water standards and maybe some think you can just throw membranes at the end of any secondary wastewater treatment plant and start making high quality recycled water….but wastewaters ain’t wastewaters and membrane treatment is not that simple…. The quality of secondary effluent can vary significantly, from inland WWTPs with stringent nutrient removal requirements to ocean discharge WWTPs with less stringent requirements. This can result in widely varying cleaning requirements which also varies by membrane type. While there have been a lot of pilot studies on different secondary effluent sources, I haven’t yet seen a dedicated study evaluating the impact of specific secondary effluent constituents and the impact on low pressure membrane permeability and cleaning effectiveness.

Perhaps with all of the recent reuse pilot studies, this information will start to come together. Or maybe the key results will be kept from the public as a competitive advantage for those with the pilot experience, which is understandable when OEMs and/or engineering firms have generated this knowledge. This is where no-strings-attached research can help the reuse industry. After being involved in several recent pilot studies my take-away is that wastewaters ain’t wastewaters and don’t assume you can simply take the performance of a membrane at one WWTP and apply it to another.