May 16, 2002

NC State Civil Engineering Researchers Use Fluorescent Techniques to Aid Wastewater Treatment

This fluorescence micrograph depicts Microthrix parvicella, an organism that causes foaming and bulking in activated sludge.

As more and more people crowd into cities and towns worldwide, wastewater treatment becomes a greater challenge. Researchers at NC State University are studying a down-to-earth problem, designing efficient wastewater treatment systems, using cutting-edge technology.

Effective wastewater treatment involves a complex, multistep process. At one point in the process, sludge is treated, or activated, to encourage decomposition of solids by microorganisms. Then the sludge and the liquid are pumped into a settling tank, where the sludge is supposed to settle to the bottom and the liquid can be removed for further treatment such as chlorination.

Bulking— a problem caused by filamentous microorganisms — can arise in the settling tank when the solid component won’t settle out well. According to Dr. Francis L. de los Reyes III, assistant professor of civil engineering, bulking is the most common problem in wastewater treatment.

De los Reyes and NC State graduate student Jiangying Liao are studying this problem using a unique fluorescent microscopy technique called Fluorescence In Situ Hybridization (FISH). This technique helps them identify the filamentous organisms, an essential step in learning to control their growth. “If you can’t identify the filament, then you can’t relate the organism to operating conditions, and you don’t know what caused the filament to grow,” said de los Reyes.

Traditional staining methods using a light microscope don’t provide enough information to distinguish different species of filamentous organisms. Another problem is quantification of the amount of filaments in a sample. “Identification and quantification go hand in hand,” according to de los Reyes.

“With FISH we use a very specific probe for each organism,” explained Liao. “Then we can establish curves with computer analyses that relate cells of volatile suspended solids (VSS) concentrations to filament lengths.” This is important because, for the first time, engineers can figure out how much of a specific species is present in an environmental sample based on the VSS concentration.

“Now we have data to quantify the effect of filamentous biomass on bulking,” said de los Reyes. “This will help us determine which species are most important and which ones relate to operational conditions of the wastewater plant.” In addition, FISH techniques can help scientists understand the ecology of filamentous species in the wastewater treatment plant environment.

The current research is funded from a five-year National Science Foundation (NSF) Faculty Early Career Development (Career) grant. Future applications of this work include using VSS concentration curves for modeling purposes as scientists and engineers study the relationships among species of filamentous organisms in sludge. “We hope to relate this work to operation of the wastewater treatment plant,” said de los Reyes. “Very few engineers are using FISH probes in this way.”

— rudd —

Media Contacts: Dr. Francis L. de los Reyes III, 919/515-7416, fldelos@eos.ncsu.edu
Linda E. Rudd, 919/515-3848, linda_rudd@ncsu.edu

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