Field Demonstrations of Mycoremediation for Removal of Fecal Coliform Bacteria and Nutrients in the Dungeness Watershed, Washington
Consulting Report for the Dungeness River Watershed Final Workplan , 2009
Thomas, S.A., Aston, L.M., Woodruff, D.L., Cullinan, V.I.
This study focused on the development and demonstration of an innovative biotechnology—mycoremediation—used in conjunction with bioretention cells, as a potential best management practice for the removal of fecal coliform bacteria and nutrients from surface waters in the Dungeness watershed of Washington State. The study is part of a larger body of work that has been conducted under a U.S. Environmental Protection Agency (EPA) Targeted Watershed Initiative in the Dungeness watershed and Bay to encourage innovative community-based solutions to protect and restore clean surface waters. Mycoremediation is a form of bioremediation that uses conditioned native fungi and fungal mycelium applied to surface soils to remove and degrade contaminants. In this particular application, mycoremediation was used in combination with a bioretention cell (e.g., rain garden), incorporating native vegetation, a soil media mix, and natural microbial assemblages to remove and degrade fecal coliforms and nutrients. The mycoremediation treatment incorporated a layer of fungal mycelium-enhanced alder chip mulch and mycorrhizal fungi applied to plants. For this demonstration, a field site was constructed and flowing surface water was directed to a bioretention cell (control) and a mirror image mycoremediation-treated bioretention cell (treatment) for a comparative study of the bacteria and nutrient removal effectiveness at the field site. Once the field site was constructed, three phases of the study were implemented. The first phase looked at the fecal coliform and nutrient concentrations in the source water and two outflow pipes from the control and treatment cells after the water was treated. Fecal coliform and nutrient samples from this phase were analyzed on a monthly basis after construction of the cells, plants had been established and a permanent source of water was in place. A dye study was conducted during the second phase of the study in order to better understand the retention time and attenuation rate of water moving through the site. Finally, the third phase involved an inoculation or spike experiment that introduced a one-time inoculation of dairy lagoon waste into the source inflow at the site. During this phase, fecal coliform and nutrient concentrations were analyzed at selected time periods from the two cells based on the results of the dye study to further assess the functionality of the system(s) to remove greater concentrations of bacteria and nutrients. Fecal coliform bacteria were reduced to a significant degree in both the bioretention cell and the mycoremediation cell, based on the results of the monthly sampling conducted during Phase 1 and the Phase 3 spike experiment. During the Phase 1 experiment, the fecal coliform concentrations were reduced from a mean of 30 colony forming units (CFU)/100 ml in the inflow to 10 CFU/100 ml in the bioremediation (control) cell outflow and 3 CFU/100 ml in the mycoremediation (treatment) cell outflow. Although these inflow concentrations are relatively low, fecal coliform was reduced by 66% in the control cell and 90% in the treatment cell. During the Phase 3 spike experiment, a 5-ml spike of untreated dairy lagoon waste (259,000 CFU/100 ml) was introduced every minute for 15 minutes for a total addition of approximately 194,250 CFU into the site inflow. The bioretention cell outflow showed an initial spike of 376 CFU/100 ml at 1 hour, then dropped steadily over time, whereas the mycoremediation outflow never had concentrations greater than 10 CFU/100 ml and remained relatively constant throughout the duration of the experiment with a mean of 5 CFU/100 ml. An exponential decay model was used to evaluate the difference between the treatment and control fecal coliform concentration response for the 17-day duration of the experiment. There was a statistically significant difference between bioretention and mycoremediation cells between 1 and 28 hours, however after 29 hours a steady state was reached, where the fecal coliform concentrations were reduced from a mean of 172 CFU/100 ml in the source water to a mean of 13 CFU/100 ml in the control cell and 5 CFU/100 ml in the treatment cell. Once this steady state was reached, fecal coliform was reduced by 92% in the bioretention cell and 97% in the mycoremediation cell. In both Phase 1 and Phase 3 experiments, fecal coliform bacteria were decreased significantly in the bioretention cell, and to a greater degree in the mycoremediation cell. This is likely due to the enhanced predation of bacteria through the extensive mycelial network that is associated with the fungal species in the alder chip mulch as part of the mycoremediation treatment. The nutrient results were more difficult to evaluate, primarily because the data showed varying trends of nutrient export or removal over time. During the Phase 1 experiment, total nitrogen (TN) was exported from both the bioretention and mycoremediation cells (i.e., higher concentration in the outflow compared to the inflow) between July and October 2007; however, concentrations were reduced in the outflow of both cells compared to the inflow between October and January 2008. During the Phase 3 spike experiment, TN concentrations were reduced in both cells for the duration of the experiment (24 days), and to a greater degree in the mycoremediation cell. Alternatively, total phosphorus (TP) was consistently exported from the bioretention and mycoremediation treatment cells during both the Phase 1 and Phase 3 experiments, although the export was less in the mycoremediation cell during the Phase 3 experiment. In general, the varying trends in the nutrient data are consistent with results obtained from other field and laboratory studies of bioretention cell effectiveness. Although nutrient reduction can be achieved with bioretention and mycoremediation treatments, careful attention must be paid to the design of the field site. Other studies have shown that nitrogen reduction can be achieved if an anaerobic zone or water saturation layer is incorporated into the bioretention cell design and an organic carbon source is supplied to the site to enhance de-nitrification and removal of nitrates. In our study, the bioretention and mycoremediation cells contained zones that were submerged in water for frequent but intermittent time periods. These shifted as flow rates changed and seasonal fluctuations occurred. In the mycoremediation cell, it is likely that nutrient removal was increased by the addition of mycorrhizal fungi to the plants, which can enhance plant establishment by increasing the nutrient absorption capacity of root systems and improving soil structure. The application of a mycoremediation treatment to a variety of field settings is relatively straight-forward and, given the appropriate landscape conditions, is appropriate for the reduction of fecal coliform bacteria. We designed a comparative field study and examined the functionality of a bioretention cell compared to a mycoremediation-treated bioretention cell as an enhanced treatment for the removal of fecal coliform bacteria and nutrients. While the bioretention cell itself performed well at reducing fecal coliform bacteria, the mycoremediation treatment provided a greater reduction of bacteria. This was particularly evident during the spike experiment where a higher concentration of bacteria and nutrients were introduced into the cells. Unfortunately, funding did not support a more thorough and quantitative evaluation of the technology (e.g., independent application of mycoremediation treatment without a bioretention cell, controlled laboratory/mesocosm settings, or rigorous replication across numerous bioretention cells). Hence, an application of a mycoremediation treatment alone would need to be evaluated on a site-specific basis taking into consideration the contaminants of interest, landscape characteristics, soil type, and hydrology. In general, bioretention cells require moderate to extensive site preparation and are viewed as somewhat permanent installations, whereas the mycoremediation treatment can be considered a temporary installation requiring no excavation and is less expensive to deploy than a bioretention cell. The application of either or both biotechnologies is highly dependent on the specific site needs being addressed.