Process Stability of Enhanced Biological Phosphorus Removal in Wastewater: The Effect of Varying Influent QualityEPA Grant Number: U914804
Title: Process Stability of Enhanced Biological Phosphorus Removal in Wastewater: The Effect of Varying Influent Quality
Investigators: Schuler, Andrew J.
Institution: University of California - Berkeley
EPA Project Officer: Michaud, Jayne
Project Period: January 1, 1995 through January 1, 1996
Project Amount: $102,000
RFA: STAR Graduate Fellowships (1995) Recipients Lists
Research Category: Academic Fellowships , Engineering and Environmental Chemistry , Fellowship - Engineering
This research will address questions regarding the process of enhanced biological phosphorus removal (EBPR).
Phosphorus is a limiting nutrient in many receiving water ecosystems, and eutrophication can occur when phosphorus is discharged to these systems. Phosphorus is therefore a regulated pollutant in many inland locations. Sources of phosphorus in municipal wastewater systems include human waste and commercial and industrial sources such as detergents and phosphate buffers. Although source reduction of the condensed phosphate builders in household detergents has reduced influent wastewater phosphate concentrations, typical secondary treatment plants cannot meet discharge requirements in areas with sensitive receiving waters. Typical biological wastewater treatment processes can remove only about 1 mg of phosphorus for every 100 to 150 mg of BOD5 removed.
Previous work has shown that the activated sludge process can be modified by incorporating an initial anaerobic zone ahead of the aeration basin, which selects for microorganisms with a high phosphorus content in the form of polyphosphate. The wasting of such organisms from the system provides increased phosphorus removal. Further research is required of EBPR because:
· Reliable removal of phosphorus to regulated levels (commonly 1 mg
P/L) currently is difficult by EBPR alone.
· Chemical precipitation, the alternative to biological removal, is more expensive and generates a larger volume of waste solids.
· Important issues remain unresolved in the current body of EBPR research.
In the proposed research I will address specific questions that have not yet been clearly answered:
· Which microorganism(s) are responsible for EBPR? Members of the genus Acinetobacter have been widely studied and advanced as the primary causative organisms responsible for EBPR. They have been isolated from many EBPR plants and are able to store polyphosphate and PHB, which are important storage products in EBPR. However, Acinetobacter is a heterogeneous group, and not all strains store polyphosphate. Other organisms in activated sludge have been found that also accumulate polyphosphate—indeed, the only pure culture experiment in which EBPR has been induced was with a gram-positive organism (Ubukata, et al., 1994), and Acinetobacter is gram-negative. Additionally, one of the metabolic models for EBPR includes the use of glycogen as a source of reducing power, which most Acinetobacter strains are unable to metabolize. The determination of the causative organisms is important to EBPR operation because different plant design and operations may favor different organisms.
· Which (if any) of the proposed EBPR metabolic models are correct? The currently proposed "standard" EBPR model. The centerpiece of debate over this model is whether glycogen is used for reducing power storage for the anaerobic conversion of acetyl-CoA to PHB. The answer to this question is important in assessing the amount of phosphate released per unit amount of dissolved organic matter removed in the initial anaerobic zone.
· What enzymes are active in EBPR and how are they regulated? The search for enzymes that are induced during EBPR has met with little success. The determination of the relevant enzymes will further elucidate the correct metabolic model. Few theories have been advanced on EBPR regulatory mechanisms. Knowledge of EBPR regulation is fundamental to plant operation because a poorly performing plant may either be selecting against EBPR organisms, or these organisms may be presented but not performing EBPR.