Grantee Research Project Results
Hydrolysis of Particulate Organic MatterEPA Grant Number: F5A20174
Title: Hydrolysis of Particulate Organic Matter
Investigators: Dimock, Rachel
Institution: University of Illinois Urbana-Champaign
EPA Project Officer: Packard, Benjamin H
Project Period: August 1, 2005 through August 1, 2008
Project Amount: $111,172
RFA: STAR Graduate Fellowships (2005) RFA Text | Recipients Lists
Research Category: Academic Fellowships
This research project is a study on the effects of particle characteristics on the rate of hydrolysis of particulate organic matter. In addition, this project will examine the physical mechanisms involved in hydrolysis, including how the particles and organisms interact with each other. A better understanding of hydrolysis has applications in biological nutrient removal from wastewater, where particles could potentially be used in these processes in place of external substrates. Hydrolysis also affects sludge production and understanding it has the potential to reduce the total amounts of solids from wastewater treatment plants that require land or other disposal.
The goal of this project is to quantify how particle size affects hydrolysis rates, how particle composition affects hydrolysis rates, and examine the mechanisms involved in hydrolysis. These objectives are best expressed by the following five hypotheses:
- When particles of uniform composition are hydrolyzed by activated sludge, particle size will determine rates of hydrolysis, with smaller particles utilized faster, because of their larger specific surface area.
- Particles will disintegrate as they are hydrolyzed, exposing a greater surface area available for hydrolysis over time.
- Particle composition will also affect hydrolysis rates. Carbohydrates will be used the fastest, followed by proteins and then lipids.
- In order for hydrolysis to take place in activated sludge systems, physical contact is needed between the particles and the activated sludge flocs.
- The rate of hydrolysis will be identical under aerobic and anoxic conditions.
The effects of particle size and composition will be studied using oxygen uptake rate experiments, which are a commonly-used tool in assessing wastewater biodegradability. These experiments will be batch tests, where particles of a known size and composition are added to activated sludge and the oxygen uptake rate is measured over time as these particles are consumed. Particles will be artificially manufactured using potatoes to represent carbohydrates, hard-boiled egg whites to represent proteins, and beef tallow to represent lipids. Real particles from a wastewater treatment plant's primary clarifier will also be used in these tests. The oxygen uptake rate curves from these batch tests will be mathematically modeled in order to quantify any differences observed.
In addition to the oxygen uptake rate experiments, the protein particles and activated sludge flocs will be observed microscopically, using a protein dye and a nucleic acid stain in order to differentiate the two. These microscopic observations will be made for two reasons. First, they will reveal the spatial interaction of the particles and the sludge flocs - whether or not direct contact or particle enmeshment is required for hydrolysis. Second, they will show the changes that particles undergo over time as they are hydrolyzed - whether they break into smaller particles or single particles reduce in size over time.
Finally, tests similar to the oxygen uptake rate experiments, except made under anoxic conditions will be used to study whether or not hydrolysis rates differ under aerobic and anoxic conditions. As there is no oxygen present in an anoxic system, nitrogen gas production rate will be measured in a denitrifying system, where organisms are converting nitrate to nitrogen gas. Again, the results will be mathematically modeled and compared to the oxygen uptake rate experiments.
These experiments are expected to provide a comprehensive picture of hydrolysis in activated sludge at the floc scale. The oxygen uptake rate experiments will determine how the particle characteristics of size and composition affect hydrolysis rates and the accompanying mathematical modeling will quantify the difference between different types of particles. The microscopy experiments will not only show how particles and flocs interact during hydrolysis, but will reveal the changes that a particle undergoes as it is hydrolyzed. Combining this information will illuminate the mechanisms involved in hydrolysis, which will not only direct further research into hydrolysis, but will also provide a basis to make decisions regarding the use of particles typically removed in primary clarification for nutrient removal. Increasing wastewater treatment efficiency by making rational decisions in plant design will reduce not only the cost of wastewater treatment, but the energy consumption involved in it, so that societal benefits of this work will not only include nutrient-free water, but also reduction in monetary and energy costs.