Activated sludge is a domain that most pure microbiologists avoid, and most wastewater engineers have grown to love, although they don't really understand it.

Activated sludge? What in the world is activated sludge? Activated sludge is what engineers call the biological culture that is used to treat wastewater in most domestic and many industrial treatment plants throughout the United States and in many regions of the world. It is a heterogeneous mixed culture of microorganisms containing a broad range of bacteria (primarily) along with some protozoa, metazoa, fungi, and algae. The activated sludge bacteria are responsible for removing organic, and some inorganic, pollutants from wastewater.

For organic pollutants, the overall reaction is: organic wastewater compounds + O2 ?> CO2 + H2O + new cell mass, where bacteria are the catalysts for this reaction.

Seems simple and safe, right? If only it were that easy. You might be surprised to know that environmental engineers do not know which bacteria are largely responsible for treating wastewaters. Some believe as many as 90 percent of the bacterial species present in wastewaters are unculturable when traditional methods of isolation are used (such as plating on selective solid agar media). Additionally, it is not uncommon for synthetic organic chemicals (SOCs) from industrial activities to make their way into wastewaters that are largely from domestic sources. Many SOCs are difficult for bacteria to biodegrade, and some can even harm activated sludge cultures, making it difficult for these cultures to biodegrade even the easiest to degrade compounds. This can lead to incomplete treatment of wastewaters, which eventually end up being discharged to rivers.

Whereas most environmental engineers refer to bacteria as "bugs" and have never looked at an activated sludge culture under a microscope, the environmental engineering students working in the Fralin Biotechnology Center environmental laboratory at Virginia Tech are a new breed of engineer. Through the guidance of research associate and microbiologist Kathy Terlesky and civil engineering assistant professor Nancy Love, the students are:

• extracting DNA from isolates obtained from activated sludge using novel enrichment techniques and are determining the phylogeny of the organisms based on the 16S rDNA sequence;

• extracting RNA from activated sludge cultures exposed to different treatment methods and using selective genetic probes (called oligonucleotide probes) to determine the activity levels of selected genera and species in the cultures; and

• extracting and characterizing indicator proteins generated by activated sludge cultures that are exposed to shock loads of toxic wastewaters.

Although most environmental engineers consider the operation and design of activated sludge systems to be comparable to working with a "black box," the research team working in the Fralin Biotechnology Center environmental laboratory are trying to understand the structure and function of activated sludge cultures so that the discipline can move beyond the "black box." Engineers make design and operational decisions everyday with activated sludge treatment systems that influence the physiology of the microorganisms present in the system. By influencing the physiology, they impact the performance of the treatment system. The research ongoing within the Fralin Environmental Biotechnology Laboratory will help engineers to understand how their decisions influence treatment process performance by considering the impact on the microorganisms doing the work in the system.

In short, this collaborative research effort that integrates molecular biology, microbiology, and engineering will help us to move beyond the "black box" approach to wastewater treatment design and operation.

For more information about biotechnology research at Virginia Tech, visit: The Fralin Biotechnology Center

— Written by Nancy G. Love