University of Vermont
Mentor: M. Robin Collins, Associate Professor of Civil Engineering and T. Taylor Eighmy, Research Associate Professor of Civil Engineering
Distinguishing the Differences Between Biological Degradation and Adsorption of Natural Organic Matter In a Biologically Active Sand Filter
The focus on Disinfection byproducts such as Trihalomethanes (THM's) and distribution bacterial growth has increased as a result of recent EPA water restrictions. Natural organic matter (NOM) has been determined to be the cause of these byproduct formations. Biological treatment has been deemed an alternative in order to reduce levels of biodegradable organic carbon (BDOC).
The chief mechanisms involved in such processes have been suggested to be biological degradation and adsorption. However, in a biologically active sand filtration system, the quantity of BDOC reduction as a result of either degradation or adsorption has yet to be characterized.
This research has been conducted to reveal what portion of BDOC is reduced as a result of degradation or adsorption. By utilizing biological inhibitors (sodium azide: NaAZ, mercuric chloride: HgCl2) in a readily biodegradable media (glucose/glutamic acid) and raw water samples (Portsmouth Treatment Plant Raw Water), the quantity of BDOC reductions were measured. Since glucose/glutamic acid is readily biodegradable, it is believed that an inhibitor should have blocked all BDOC reduction. Preliminary results using the inhibitor sodium azide were unsuccessful.
The current experiments utilized mercuric chloride and cold temperatures to inhibit biofiltration of a raw water source and glucose/glutamic acid. The environmental conditions were 20 and 5 degrees C. Preliminary results indicated an increase in NOM (measured as Total Organic Carbon, TOC) but in later stages of the experiment than with the use of sodium azide. This indicated that the biofilms within the sand media were stunted in the earlier stages of the experiment and released organic carbon into the environment when later killed.
Future analyses will include Scanning Electron Microscopy (SEM) micrographs of selected biofilm samples gathered from the sand medium surfaces. Future experiments will include increases in inhibitor pre-exposure times to ensure complete death of all microbiological activity. Future experiments will also include variances in water flow rates and extended research of other known biological inhibitors.