Let the Bugs Do It

A two-step biological treatment method offers an effective and affordable alternative for removing some troublesome groundwater contaminants.
Let the Bugs Do It
The system has a compact footprint and is designed to fit easily on well sites and in other locations with limited space.

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Traditionally, reverse osmosis (RO) and ion exchange have been used to treat groundwater for contaminants such as nitrate, perchlorate and hexavalent chromium, while VOCs are typically removed using granular activated carbon (GAC) adsorption or air stripping.

Now alternatives are emerging in the form of biological treatments. One of these is the BIOTTTA (Biologically Tailored Two-Stage Treatment Approach) from Carollo Engineers. It takes biological treatment concepts long proven on the wastewater treatment side and applies them — with major differences — to groundwater treatment.

Carollo has been running bench-scale testing and pilot plants using this process for more than 10 years. Pre-packaged and custom-designed systems are now ready for commercial application. The system combines environmentally friendly features with ease of operation and low operating cost, according to the company.

Chris Cleveland, Carollo vice president, and Jess Brown, research and development practice director, talked about the BIOTTTA system in an interview with Water System Operator magazine.

wso: What is the history behind this process?

Brown: The basic technology of using bacteria to degrade contaminants has been used for a very long time on the wastewater side and on the drinking water side for more than 30 years, notably in Europe. We have been working on a specific configuration of it for 14 years, honing it through bench and pilot scale testing.

wso: How would you describe the basic process?

Brown: The BIOTTTA system has two main unit processes. It includes a first-stage biological reactor that is analogous to a conventional granular media filter. Water passes through that system, and the second stage is almost a repeat of the first — it's also a fixed-bed biofilter. The difference between the two stages is that the first stage operates without oxygen (anoxic or anaerobic) and the second operates with oxygen (aerobic). Chemical-feed and biomass control systems bring it all together and enable the process to meet the desired drinking water requirements.

Cleveland: An interesting point is that we use bacteria already contained in the groundwater we're treating. We don't need to bring in any outside microbial community. We take advantage of naturally occurring microbes and put them into the right environment to treat what we're targeting. The bacteria grow on media inside the fixed-bed systems and form a biofilm.

wso: What would be a typical footprint size for these systems?

Cleveland: They fit on relatively compact well sites. If it's a typical well pumping 200 to 600 gpm, the water would be treated in pressure vessels each 6 to 10 feet in diameter.

wso: Would the system always be installed at the wellhead? Or could it be installed at a water treatment plant?

Cleveland: It depends on the community. If it's a small city in an agricultural area that has only a few wells in spread-out locations, they may put a wellhead treatment system at each site. For a larger community with well fields, it probably makes more sense to have a central BIOTTTA treatment facility.

wso: To what kinds of systems does this treatment serve as an alternative? And what are its advantages?

Cleveland: This system removes contaminants usually treated with RO or ion exchange. It destroys many of the contaminants, whereas RO and ion exchange concentrate them into high-strength waste streams. The process has a very high water recovery rate. The only wastewater we produce is from backwashing of the filters, and that's very infrequent.

The process is very robust and flexible — it can handle multiple contaminants. Suppose you have to deal with nitrate and we design a system for that. Then down the road, perchlorate or chromium 6 shows up into your well. This system, in most cases, will be able to handle that additional contaminant with just some operational adjustments — without having to add a second treatment process.

wso: How would this system destroy a constituent like hexavalent chromium?

Brown: It destroys nitrate, perchlorate and VOCs. For example, nitrate is converted to nitrogen gas, which floats off to the atmosphere. With chromium 6, we're not destroying it, but we're making it less toxic, and we're putting it into a solid form that is much easier to dispose of than a liquid concentrate. The process reduces chromium 6 to chromium 3, which is less soluble. It typically comes out of solution as a chromium hydroxide, which is filtered out in the system and removed during backwash.

wso: What are the energy inputs to this system?

Brown: The main energy inputs relate to pumping across the two-stage process, and occasional pumping during backwash. There is very low pressure loss across these systems. The aeration energy demand is quite low, as well. There isn't as big of an oxygen demand as in a wastewater treatment process. All we need is to get the water back to an oxic state — say, 3 to 8 mg/L dissolved oxygen. You can do that through an aeration process, or you can do that by addition of liquid oxygen or hydrogen peroxide.

wso: What chemicals need to be added to the process?

Brown: Right up front we add nutrients for the bacteria — they need an electron donor to reduce the contaminants. The other chemicals come in between the two stages. We condition the water coming out of the first stage with a polymer or some coagulant, so that the polishing filter in the second stage will remove biomass. If we add oxygen in a chemical form, that also happens between the two stages. Then there's a final chlorine disinfection step.

wso: What treatment results have you seen with this process?

Brown: We've treated a huge array of constituents. We have bench and pilot test results that show phenomenal removal of nitrate, perchlorate and chromium 6. In one pilot test, we're removing 80 mg/L of nitrate in a 4-minute contact time; perchlorate is also in that water and is removed to below detection.

We have bench-scale data that shows removal of environmentally relevant amounts of chromium 6 — from 10 to 100 micrograms per liter — to below detection. We have data on a number of VOCs being removed. We also have had success with uranium and arsenic.

wso: How does this process get designed, delivered and installed?

Cleveland: It's offered in a turnkey approach. We've done a lot of standardization so that we have the ability to deliver a solution that includes the design, manufacture and installation, with options for either technical support or full operation. For smaller projects, we have six to eight standard offerings to cover flows from 100 to 1,000 or 1,500 gpm. Larger systems can be custom-designed but still delivered as a package.

wso: Where do you see the most potential to deploy these systems in the field?

Brown: Anywhere you have agriculture, you're going to have nitrate contamination. Agriculture goes on at some scale in almost every state in the U.S.

Cleveland: Our process is the only biological treatment system of its type that has approval from the California Department of Public Health for groundwater treatment.

California is moving toward regulating chromium 6, and the current target is to have a draft maximum contaminant level (MCL) by next summer. The U.S. EPA is working on an MCL for chromium 6 as well.


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