Grantee Research Project Results

Final Report: Design of a Trap Grease Upgrader for BioFuel Processing - Phase I

EPA Grant Number: SU832486
Title: Design of a Trap Grease Upgrader for BioFuel Processing - Phase I
Investigators: Cernansky, Nicholas P. , Cairncross, Richard A. , Crawford, Douglas , Haas, Francis , Chapman, Jason , Letterle, Kenneth , Powell, Pamela , Doan, Thuyvan , Nguyen, Van-Anh
Institution: Drexel University
EPA Project Officer: Page, Angela
Phase: I
Project Period: September 30, 2005 through May 30, 2006
Project Amount: $9,065
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2005) RFA Text |  Recipients Lists
Research Category: Pollution Prevention/Sustainable Development , P3 Awards , P3 Challenge Area - Air Quality , Sustainable and Healthy Communities

Objective:

Trap grease is a heterogeneous mixture of grease, water, detergents, food particles, and other solids, which is intercepted between commercial/institutional kitchen drains and the municipal sewer system. Poor grease trap maintenance may lead to sewer line blockages; according to the U.S. EPA, approximately 70 percent of wastewater treatment plant blockages are grease related. Trap grease is a true waste product, currently having no secondary markets after generation; this is in part due to the variability and complexity of its composition. In order to utilize trap grease to make an engine-compatible biofuel, it must be pretreated to remove contaminants such as water and solids.

The objective of this study was to characterize some important engineering properties of trap grease, including grease, water and solids content; acid number; melting point; and density. These properties govern the methods and extent of pretreatment the trap grease must undergo prior to conversion into biofuel, but are not readily available in the literature. Laboratory evaluation of these parameters enabled a preliminary design and feasibility analysis of a ~2 million gallon per year municipal trap grease-to-biofuel process. A facility of this size has the potential to remove ~12 million gallons per year of as-pumped trap grease from municipal wastewater collection systems, and provide product to blend into up to 100 million gallons per year of B2 biodiesel (a blend required of nearly all diesel fuel sold in Minnesota, and soon to be required in Washington State).

Summary/Accomplishments (Outputs/Outcomes):

Important physical and chemical properties of trap grease relevant to its pretreatment were found for grease samples collected at Gloucester County Utilities Authority wastewater treatment plant (GCUA). Raw grease was separated to find its moisture, solids, and grease phase contents. Raw grease, even after initial gravity separation at GCUA, contained ~47 mass % water on average. An average of 49 mass % was grease, and the remaining 4 mass % was solids (on a dry basis). Specific gravity of the raw trap grease, including the water and solids, was ~0.91.

The grease-only phase was isolated to determine its chemical composition (fatty acid spectrum), acid number (free fatty acid content), meniscus point (incipient melting temperature), and specific gravity. Grease analyzed by gas chromatography at the USDA Eastern Regional Reaserch Center (ERRC), an institutional partner for this project, showed a fatty acid spectrum expected for an edible-oil based grease. Presence of short-chained fatty acids may indicate some microbiological, chemical, or thermal degradation of the grease, but the overall composition indicated that trap grease-derived biofuel may form less oxides of nitrogen and have better fuel stability than traditional soy-derived biodiesel. Acid number for the grease was measured by titration and averaged 182 mg KOH/g, or 91% free fatty acid (FFA) expressed as oleic acid. This is significant since traditional alkaline biofuel transesterification reactions (e.g., for soybean oil feedstock) are sensitive to even a few percent FFA. The meniscus point at which solid grease began to melt averaged 30°C (88°F), although in one trial it was measured as high as 36°C (97°F). This meniscus point temperature serves as a lower limit to which process equipment, piping, etc., must be heated in order for grease to flow. Specific gravity of the grease-only phase averaged 0.87.

These chemical and physical properties of raw and dry, solids-free grease, along with kinetic data from project partner Philadelphia Fry-o-Diesel, were used to design a ~2 million gallons per year trap grease-to-biofuel process. Laboratory data taken in this Phase I project are unavailable in the literature, and thus were instrumental in developing mass and energy balances for the process, selecting and sizing equipment, and completing the preliminary feasibility study. For example, sizing of the pretreatment centrifuge was enabled by determining the composition and density of raw trap grease (moisture, solids, and grease) as well as the density of dry, solids-free grease.

Conclusions:

This project was a successful fusion of existing technology and novel trap grease properties data into an innovative trap grease-to-biofuel process design. Expected outcomes from the Phase I proposal (publishable data on the composition of trap grease and student-led interactions with industrial and institutional partners) were met. Additionally, a portion of the project’s original Phase II objective (production of a demonstration-scale pilot plant for trap grease pretreatment) was also completed. Preliminary pretreatment system designs have been given to Philadelphia Fry-o-Diesel, which has used them as a basis to construct a pilot-scale 200 gallon-per-batch trap grease-to-biofuel facility; the ultimate outcome of this will be the production of 4,200 gallons of biofuel from roughly 42,000 gallons of raw trap grease.

A significant factor in the success of the project was Drexel’s relationship with its three external partners: Fry-o-Diesel, USDA ERRC, and GCUA. Their assistance in gathering samples, guiding process design, and assisting with laboratory analysis was invaluable, and complemented the multidisciplinary team of mechanical, civil & environmental, and chemical & biological engineers working on the project.

The P³ elements of people, prosperity and the planet were clearly balanced in this project. Society can benefit from potential project impacts such as a new sustainable energy source and improved water quality. Impacts from this project indeed represent a move towards sustainability from both an alternative fuels utilization and a waste reuse perspective, and the results are as applicable to developing nations as developed nations. Drexel University students and the project’s high school mentorship student benefited from non-traditional educational elements such as the conception, design and public defense of a process, as well as relationships with industrial and institutional partners.

A significant project outcome supporting prosperity includes direct application of project results to industrial research and development. Successful scale up from PFoD’s pilot operations could revolutionize the trap grease disposal industry and contribute to biofuel inventories, reduced emissions, and reduced dependence on foreign oil. Anticipated reductions in sanitary sewer overflows, among other consequences of grease carryover into sewers, can also alleviate municipal public works maintenance budgets, allowing funds to be applied to other programs.

Environmental benefits of reducing grease carryover and its consequences (i.e., BOD and pathogen loading from sanitary sewer overflow) are clear, as are the benefits of using an alternative fuel produced from waste rather than petroleum or other non-sustainable fuels.

Journal Articles:

No journal articles submitted with this report: View all 3 publications for this project

Supplemental Keywords:

Alternatives, biodiesel, biofuel, discharge, effluent, engineering, EPA Region 3, innovative technology, PA, Pennsylvania, pollution prevention, POTW, public policy, renewable, sustainable development, treatment, waste minimization, waste reduction,, Sustainable Industry/Business, RFA, Scientific Discipline, POLLUTION PREVENTION, INTERNATIONAL COOPERATION, TREATMENT/CONTROL, Technology for Sustainable Environment, Sustainable Environment, Environmental Chemistry, Chemicals Management, cleaner production/pollution prevention, Environmental Engineering, Technology, Energy, biofuel, alternative energy source, biotechnology, emission controls, environmentally benign alternative, energy conservation, renewable fuel production, waste to fuel conversion, bio-based energy, energy efficiency, biodiesel fuel, alternative to petroleum diesel fuel, alternative fuel, waste cooking oils, green chemistry, renewable energy