Grantee Research Project Results
Final Report: Climate & Community Friendly Wastewater Treatment
EPA Grant Number: SU839268Title: Climate & Community Friendly Wastewater Treatment
Investigators: Weber-Shirk, Monroe
Institution: Cornell University
EPA Project Officer: Page, Angela
Phase: I
Project Period: January 1, 2018 through December 31, 2018 (Extended to December 31, 2019)
Project Amount: $15,000
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2017) RFA Text | Recipients Lists
Research Category: Sustainable and Healthy Communities , P3 Awards , P3 Challenge Area - Safe and Sustainable Water Resources
Objective:
Over 80% of the world’s wastewater is estimated to be released to the environment without treatment (WWAP, 2017). Because wastewater contains biodegradable material, pathogens, and an excess of limiting nutrients (Nitrogen and Phosphorus), wastewater left untreated can lead to anoxic conditions within water bodies and can increase the risk of waterborne disease, thus damaging not only wildlife and ecosystems but also human health and industry. Current technologies to treat wastewater in the United States are expensive, energy intensive, and more commonly created for urban and suburban life. These systems are not applicable to smaller, rural communities. Thus, the objective of this research is to develop a small-scale Upflow Anaerobic Sludge Blanket (UASB) reactor, which can be designed to require no electricity and produce biogas which can be burned off for stovetop cooking.
Summary/Accomplishments (Outputs/Outcomes):
Over the course of the research period, the team successfully developed a design for a pilot scale Upflow Anaerobic Sludge Blanket (UASB) reactor. The reactor design was visualized using OnShape, an online computer-aided design (CAD) software system (Figure 1). The reactor was then fabricated and installed at the Ithaca Area Wastewater Treatment Facility (IAWWTF). In the process of designing the reactor, experiments were conducted with two main goals: 1) to determine the influence of plate settlers on solids retention, and 2) to determine the efficacy of a Submerged Gas Capture Lid (SGCL) at preventing methane loss to the atmosphere. The following sections describe the results and conclusions of these experiments, as well as key design considerations for the pilot scale UASB reactor.
Figure 1: A CAD model of the UASB reactor installed at the Ithaca Area Wastewater Treatment Facility (IAWWTF).
2.1.1 Settling Apparatus Analysis Initial experimentation demonstrated that including a settling apparatus (ie. plate settlers or a sloped exit pipe) improves solids retention and limits sludge granule escape through the effluent. However, this component was eventually eliminated from the design, because the average upflow velocity in the reactor is low compared to the settling velocity of the sludge granules, meaning that sludge washout is not a concern in this design.
2.1.2 Gas Collection and Storage System
A submerged gas capture lid (SGCL) (Figure 2) provides a gas-tight seal to eliminate the potential for gas bubbles to escape the sides of the reactors. After testing the SGCL design, the following conclusions were made: 1) A check valve would be required for continuous collection of biogas. 2) The backpressure, which is based on the spring constant of the check valve, must be lower than the air pressure under the lid for gas collection to occur. 3) The height of water above the ledge in Figure 2 depends on the relative magnitudes between the backpressure from the check valve and the gas pressure below the SGCL. 4) There is a minimum height of water above the ledge to make sure that biogas cannot escape up the sides of the SGCL.
Figure 2: Diagram of Designed Submerged Gas Capture Lid
2.1.3 Effluent Design
Since granule washout is not a concern in the current UASB reactor design, a horizontal exit pipe was chosen to maximize the allowable height of the sludge blanket in the reactor (Figure 3a). Water enters this pipe through holes along the top to prevent gas bubbles from flowing into the effluent stream. An open-ended vertical pipe (Figure 3b) also prevents biogas from being sucked into the effluent by maintaining atmospheric pressure inside of the reactor. A layer of bacterial growth can develop at the gas-liquid interface when gas bubbles transport solids to the top of the reactor. To prevent this scum from entering the effluent, the connection between the exit pipe and the main body of the reactor (Figure 3c)
was positioned 10 cm below the water level in the reactor. This positioning also assures that the gas-liquid interface will remain above the effluent line if the water level inside of the reactor were to drop.
Figure 3: A top view (left) and side view (right) of the effluent piping. (a) the horizontal exit pipe located inside of the reactor, (b) a vertical pipe open to the atmosphere, (c) the connection between the main body of the reactor and the exterior effluent piping, (d) tubing that leads to the drain line and sampling port (not pictured)
2.1.4 Influent Design
Non-uniform contact between the influent wastewater and the microbes in the sludge blanket results when water repeatedly follows the same pathway through the sludge granules. Eliminating these preferential pathways will improve the efficiency of the reactor by increasing the contact area between the microbes and organic content in the wastewater. The team hypothesizes that fluidizing the sludge bed with flow pulses will disrupt the formation of preferential pathways. The sludge bed is fluidized when water travels through it at a high enough velocity to counter the effect of gravity, and the solid sludge particles are briefly suspended and behave like a fluid. The team believes that a flat bottom geometry can generate the high velocity radial flow needed to lift the sludge bed. The concept of pulsated flow was incorporated into the UASB design using a tipping bucket system (Figure 4). Wastewater drips into the bucket until it reaches a volume predetermined by the placement of the pivots on the side of the bucket. Once filled, the bucket tips, sending a pulse of wastewater down the influent pipe.
Figure 4: Tipping Bucket Apparatus (releases wastewater to the reactor in batches)
Conclusions:
3.1 Evaluation of Economic Feasibility
The AguaClara program strives to provide sustainable water and wastewater treatment technologies that are accessible to any community. A large part of this mission involves making technologies affordable and low-maintenance. The current cost of the reactor is more than 500.00 USD per capita. This cost could be reduced by finding cheaper (locally sourced) alternatives to expensive parts, and removing unnecessary components from the design.
3.2 Future Work
One pilot scale UASB reactor was fabricated and installed at the Ithaca Area Wastewater Treatment Facility (IAWWTF) to test its performance with real wastewater. This reactor is currently in its startup phase. Once biogas and sludge production stabilize, reactor performance will be quantified in three ways: 1) efficiency of biogas production, 2) concentration of sludge in the sludge weir, and 3) Biological Oxygen Demand (BOD) and Chemical Oxygen Demand (COD) removal rates. In close cooperation with partner organizations, the UASB reactor will eventually be tested in a small community lacking wastewater treatment. The direct feedback from this community will be used to drive future iterations in the reactor design.
References:
Chen, Z. (2017). Upflow Anaerobic Sludge Blanket (UASB), Summer 2017 . AguaClara Cornell.
Retrieved from https://www.overleaf.com/project/5e47ee48580a4b0001012158
Narnoli, S. K. and Mehrotra, I. (1997). Sludge blanket of UASB reactor: Mathematical simulation. Water Research, 31(4):715–726.
WWAP (United Nations World Water Assessment Programme). 2017. The United Nations World Water Development Report 2017: Wastewater, The Untapped Resource. Paris,
UNESCO.
Journal Articles:
No journal articles submitted with this report: View all 3 publications for this projectSupplemental Keywords:
Wastewater treatment, UASB, GLS separators, plate settlers, scalable, phase separatorRelevant Websites:
AguaClara Cornell Webpage Exit
Progress and Final Reports:
Original AbstractP3 Phase II:
Environment and Community-Friendly Wastewater Treatment | 2019 Progress Report | 2020 Progress Report | 2021 Progress Report | Final ReportThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.
Project Research Results
- 2018 Progress Report
- Original Abstract
- P3 Phase II | 2019 Progress Report | 2020 Progress Report | 2021 Progress Report | Final Report