Grantee Research Project Results
Final Report: Coupled Anaerobic Digester: Wetland System for Dairy Waste and Stormwater Treatment with Biogas Production
EPA Grant Number: SU834334Title: Coupled Anaerobic Digester: Wetland System for Dairy Waste and Stormwater Treatment with Biogas Production
Investigators: Reinhold, Dawn , Ahlquist, Joseph , Faivor, Louis , Haan, Mat , Crook, Michelle , Triscari, Patrick , Henderson, Shannon , Safferman, Steve , Liao, Wei
Institution: Michigan State University
EPA Project Officer: Page, Angela
Phase: I
Project Period: August 15, 2009 through August 14, 2010
Project Amount: $10,000
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2009) RFA Text | Recipients Lists
Research Category: P3 Challenge Area - Air Quality , P3 Challenge Area - Safe and Sustainable Water Resources , Pollution Prevention/Sustainable Development , P3 Awards , Sustainable and Healthy Communities
Objective:
The objective of the research was to evaluate the benefits of duckweed addition to anaerobic digester performance and other factors that would affect those benefits in order to develop a model for a combined anaerobic digester and wetland treatment system to be used by dairy producers to treat waste from dairy operations. Experiments were carried out to test the methane production of lab-scale anaerobic digesters with varying concentrations of added duckweed. Duckweed was grown in anaerobic digestate to determine if it would a) inhibit the growth of the duckweed and b) affect the benefit of duckweed addition. The methane production of anaerobic digesters containing duckweed that had been grown in anaerobic digestate was recorded and analyzed. Single frond toxicity tests as well as toxicity tests on full surface coverage populations were performed. In the single frond tests, surviving fronds were counted after a week of exposure in Petri dishes. In the study on full surface-coverage, the chlorophyll and oxygen production rate were measured after one week of exposure in Erlenmeyer flasks.
Summary/Accomplishments (Outputs/Outcomes):
Experiments were conducted to determine: (1) the benefits of duckweed addition on digester performance, (2) the effects of duckweed growth in anaerobic digestate on (1), and (3) inhibition of duckweed by growth in anaerobic digestate. Duckweed additions were tested from 0-3%, and there was a significant difference in methane production when duckweed was added, with 2 and 3% having significantly higher methane production than 0.5 or 1%. There was no significant difference in methane production when duckweed was grown in varying concentrations of anaerobic digestate. The growth of the duckweed in digestate did not affect the benefits of duckweed addition on digester performance, but it did inhibit duckweed growth under full surface coverage significantly at concentrations greater than 30%, and at concentrations as low as 2% in the single frond tests.
Conclusions:
Design Recommendations
The design consists of a concrete tank with a total volume of 205 cubic meters, which would result in 55,929 cubic meters of biogas during the winter months, and if blended with duckweed during the summer, 17,664 cubic meters of biogas. The daily duckweed requirement would be 0.6 cubic meters per day at a fresh weight for the summer months and 2.4 cubic meters would be needed per day for the winter months, if possible. The treatment wetland model will provide estimates to the feasibility of duckweed yield. Biogas from the digester can be used for many purposes, including the heating of the digester. Separating the solids and liquids of the digestate using a screw press is recommended to reduce cleaning and maintenance of the wetland, as well as to make use of the digestate solids. After going through the screw press, the liquied digestate would still have a high solids concentration, and would first go into a storage lagoon to reduce the solids content further through settling. Sampling of the manure and duckweed prior to design of the system is recommended, specifically performing a biogas assays through the Anaerobic Digesetrer at MSU. This is in order to characterize the manure so as to make the best possible design for each specific site.
Conclusions
The goal of this project was to identify and address the waste management needs of a pasture based dairy farm in a manner that balanced people, prosperity and the planet, which was done in the sense that a preliminary design was constructed that fulfilled the set objectives. This project has implications for many different situations that are not necessarily restricted to agriculture. Waste and water need treatment from industrial and domestic domains as well. This project reduces the environmental impact of dairy operation waste by reducing the nutrient load to an acceptable level. This affects not only the farmer, but the entire community. Anaerobic digestion and treatment wetlands are not new technologies, but the manner in which they are used is under constant evaluation. Although there is much research on both technologies, there are constant variations on them, including the idea of combining the two systems, on which there is not much literature yet.
Supplemental Keywords:
Duckweed, methane, bioenergy, water qualityThe 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.