Introducing AWWA Manual M7 Next Chapter 2: Iron-oxidizing Bacteria

Over the decades of my “life of slime,” I have had the privilege of working on three editions of AWWA Manual M7, Nuisance Organisms, first with Dr. Jennifer Clancy and most recently with Dr. David Emerson on Chapter 2, Iron-Oxidizing Bacteria, bringing the cutting-edge #geomicrobiology in various environments to complement my more ultra-applied perspective. I also weighed in on the sulfur bacteria chapter. After literally over a decade of revision, the next edition of M7 is coming out. An introducer article in AWWA OpFlow is in press. This article is a modification of a “crib notes” summary of Chapter 2, submitted as a contribution to that article. I encourage you to purchase the most recent edition of Manual M7 when it comes out.

What are “iron-oxidizing bacteria? #Iron-oxidizing bacteria (#IOB) are a diverse group of bacteria, historically referred to as the ‘iron bacteria’; however, ‘#ironbacteria ' would now encompass two functionally separate groups, the iron-oxidizing and iron-reducing bacteria, parts of an important geochemical cycle.

The IOB of interest in this chapter are those that live in circum-neutral (near 7) pH, distinct from acidophilic (‘acid-loving’) IOB that cause acid mine drainage (#AMD, a sometimes separate, daunting challenge). Circum-neutral IOB prefer low-O2 environments, or where there is high flux of Fe2+ ions, such as at well screens or in trickling filters.

IOB are very widespread globally in aquatic environments, including wetlands and aquifers, but also marine environments. Some of them may precipitate #manganese as well, with this process considered in a separate chapter. All that manganese and other minerals on the ocean floor? These same geomicrobiological processes.

Biofouling: Because they transform iron (and sometimes manganese) to insoluble forms, they can cause severe fouling problems (referred to as #biofouling) in wells, infiltration galleries, pressure relief drains in dams, water treatment plants, water distribution systems and other downstream apparatus. They can enhance #biocorrosion, but also ….

Not always “nuisance” organisms: … when managed properly, they can also serve to filter Fe, Mn, As, and other metals coprecipitating with Fe oxides, so not always a nuisance. Note also, these are the sources of “bog ores” historically important in iron manufacture in the eastern USA and elsewhere.

Back to biofouling: Several “types” are associated with Fe biofouling in relatively fresh water environments, including sheathed bacteria such as Leptothrix and Sphaerotilus, the stalk former Gallionella (and related ‘stalk-free’ bacteria), and members of the genus Pseudomonas and related bacteria. Some Leptothrix spp. also precipitate Mn oxides, and the Zetaproteobacteria group of bacteria perform many of the same functions in marine environments (see photos from the Titanic ship wreck).

The major factors creating iron biofouling include:

?????The presence of the bacteria

?????The presence of dissolved or complexed iron (and/or manganese)

?????An environment that encourages bacterial survival and growth

·?????Aggravating factors that encourage biofouling include features of system design and operation.

Analyzing IOB and iron biofouling: IOB may be analyzed by light and electron microscopy, by culturing, as described in Standard Methods Section 9240 and scientific literature. In recent decades, such culturing has become much more convenient with packaged testing such as BART kits (but must be interpreted with some expertise).

Because many IOB belong to unique genetic clades, the use of DNA-based methods for their sensitive and accurate detection holds much promise for the future. Indeed, the authors have used these methods in a limited way currently in troubleshooting the impairment of wellfield performance and water quality. Section 9240 also describes sampling methods that improve collection success, such as biofilm collectors.

Preventing iron biofouling: ?While options to manage aquifer characteristics are limited, the effects of biofouling are controllable by sound engineering, construction, and operating practices. Controlling the following factors will limit the impact of iron bacteria on a well and its connected system:

?????????????Well design, construction, and use

?????????????Water system design and construction

?????????????Choices in water treatment

This is where our “applied” view of iron biofouling comes into play: Experts like us recognize the biofouling potential and consequences and influence design, materials and construction accordingly. Also, we design treatments.

Rehabilitation: Additionally, wells may be rehabilitated using combinations of mechanical surging, jetting and impulse tools and the appropriate use of treatment chemicals designed for removing iron biofouling.

Prevention and catching biofouling as early as possible are very important.?The key to catching growth before it causes problems is ongoing, preventive monitoring and testing.