Grantee Research Project Results
Final Report: Additively manufactured novel media for the enhancement of biological in situ stormwater remediation
EPA Grant Number: SU840413Title: Additively manufactured novel media for the enhancement of biological in situ stormwater remediation
Investigators: Kardel, Kamran , Cubas, Francisco , Jones, Michael , Wolf, Nickolas , Collins, John , Fluker, Corina , Roberson, Brandon , Ray, Tyrec
Institution: Georgia Southern University
EPA Project Officer: Harper, Jacquelyn
Phase: I
Project Period: July 1, 2022 through June 30, 2023 (Extended to December 30, 2023)
Project Amount: $24,908
RFA: 18th Annual P3 Awards: A National Student Design Competition Focusing on People, Prosperity and the Planet (2021) RFA Text | Recipients Lists
Research Category: P3 Awards , P3 Challenge Area - Safe and Sustainable Water Resources
Objective:
The goal of this project is to develop and test a biofiltration module that uses a novel 3D-printed media that provides a very high surface area for microorganism attachment and development, which can be used as part of an existing or new biofiltration device to enhance nutrient (nitrogen and phosphorus) removal in runoff from urban or agricultural watersheds.
Background: Unmanaged runoff from urban and rural watersheds is still a major contributor to nonpoint source pollution (NPS), deteriorating the water quality in streams, lakes, and estuaries across the U.S. Nutrients, such as nitrogen and phosphorus, carried by stormwater runoff are still a major NPS pollution problem because treating stormwater is currently an unsustainable practice. Biologically driven processes are a promising sustainable alternative to achieve high nutrient removal from runoff. However, biological processes as part of best management practices (BMPs) rely on a well-developed diverse community of microorganisms capable of thriving in biofilm environments, which are subject to variable environment conditions. Under certain circumstances, having variable environment conditions (e.g., variable nutrient inflow or ratios) may hamper the removal capacity of biofilters resulting in poor water qua. In addition, biofilters deployed in watersheds are subject to excess biofilm growth if not maintained properly, leading to poor water treatment, and increased organic matter and nutrients in the effluent. Maintaining BMPs is not cost effective as there is no additional benefit or return of doing this regularly. In the case of biofilters, constantly cleaning or replacing media to improve treatment performance may be a costly activity especially if the biofilters are placed in remote areas. Hence, the need for a more sustainable option to address NPS pollution problems in watersheds.
The objective of this project was to design, build, and test a novel 3D printed media having a high surface area to volume ratio that may offset some of the limitations of having variable environment conditions by providing a surface area that would promote improved nutrient storage (adsorption) and transport, and a better biofilm attachment media that will promote microorganism growth. This novel media was used to design and test a biofilter setup containing the designed media. The performance of the biofilters (three configurations were tested in total) was assessed by measuring their capacity to remove nutrients under common environmental conditions. As part of the project objectives, the reactors were designed to provide an easy way to replace the media when needed. As an incentive to make this operational procedure sustainable, the attached algae grown in the media was designed to be easily removed, while the clean media can be reinstalled and reused in the biofilter configuration. A team of senior undergraduate students designed, developed, and tested the novel media under different environmental conditions (e.g., nutrient inflows, and light availability) in a laboratory setup as part of the educational objectives. Students presented the results in the Expo session in Washington D.C. in June of 2023.
Summary/Accomplishments (Outputs/Outcomes):
Most commercial biofilter media provide a specific surface area that is less than 1000 m2/m3 (with most popular media ranging between 200-500 m2/m3). The findings in Phase I produced a cubical Gyroid media design that achieved 1195 m2/m3, more than 20% improvement over standard commercial media. This design was proved feasible via fabrication and testing in biofilters with water from local ponds. Furthermore, preliminary refinement of the media design has shown that this area can be modulated and further improved significantly. The resulting media was built upon to create a specific shape that could be used in a biofilter setup. The resulting media and shape provided an excellent environment for biofilm development and attached algae growth. The synergy between the biofilm and the algae grown in the media improved nutrient removal in the biofilters containing the media compared to a control filter not having the media in it.
Biofilter performance – Reactor design: Three reactors in total, all designed under same specifications, were designed to be installed in a semi-urban small size watershed, aiming to treat moderate flows corresponding to normal precipitation conditions in southeast GA. The reactors had a hydraulic retention time (HRT) of 4 days, a volume of ~ 0.25 m2 and flowrate of 2.4 L/hr during the experiment duration. As part of the design, the reactors were dived into two main treatment areas. The first half of the reactor worked as plug flow system (PFR), while the second part worked as a completely stirred tank reactor (CSTR). The PFR part of the reactor contained 3D-printed media, evenly distributed through the flow path. No media addition in this part was needed in this experiment. A computer flow simulation confirmed a homogenous flow distribution within the system and no short circuit or no-mixing zones seemed to develop in the reactors. The bioreactors were designed to have media cartridges that could be easily swapped by the user to increase ease of operation. Reactor 1 having no media served as a control. Reactors 2 and 3 included the 3D-printed media. Additional lighting was used for reactor 3 to assure algae growth. Water from a Georgia Southern campus retention pond was used to feed the reactors. Samples for dissolved oxygen (DO), pH, oxidation reduction potential (ORP), total organic carbon (TOC), total nitrogen (TN) and nitrogen and phosphorus species were collected twice a week for the duration of the experiment.
Results: Overall, results revealed that the reactor containing the 3D-media without additional illumination performed better than the other two. Specifically, results showed that the environmental conditions described with DO, pH, and ORP levels were similar in all reactors with minor differences in DO levels that can be explained by changes in microbial activity affecting oxygen consumption and reactor’performance. Higher productivity due to higher nutrient uptake rates in reactors 2 and 3 resulted in lower DO conditions and lower ORP measurements compared to reactor 1. Lower ORP levels in reactor 2 suggested a temporary reduce environment which may have exacerbated nitrate removal via denitrification. Reactor 3 (media with additional illumination) showed a rapid depletion of oxygen to the point where DO levels reached a concentration close to 0 mg/L after two weeks of operation. The high microbial productivity and biofilm growth in Reactor 3 resulted in poor water quality towards the end of the experiment. pH levels were closely similar in all reactors and slightly higher than 7, suggesting some algae activity throughout the experiment. TOC concentrations in the output were used to assess excessive algal growth, as higher amounts of biomass resulted in higher organic matter in the reactors effluent. The slight difference between the inflow and outflow TOC in reactor 1 suggested that no excessive biomass was produced in this reactor. TOC in reactor 2 higher in the outflow than in the inflow. The increase in TOC was due to a higher amount of biomass and algae produced in this reactor. However, organic matter production in this reactor was not excessive as it was only ~ 3 mg/L higher on average than in reactor 1. Outflow TOC in reactor 3 was approximately 3 times higher than in the inflow, which was also higher than in reactors 1 and 2. The higher outflow TOC mean concentration in reactor 3 was due to additional lighting promoting excess algae growth.
The reactors’ performance was assessed by measuring nutrient species concentrations in the inflow and outflow of each reactor. Overall, ammonia, nitrate and OP concentrations were similar in the inflow and outflow of reactor 1, suggesting a small removal of nutrients in the reactor that had no media (control). In reactors 2 and 3 these same constituents decreased as water moved through the 3D-printed media of the biofilters. As the biofilm and algae attached to media considerably increased in reactor 3, nutrient removal increased, but TOC and TN concentrations increased in the outflow suggesting excessive biomass growth in reactor 3. The ratio between outflow to inflow concentration was calculated for all reactors to further assess the nutrient removal performance. The Cout/Cin ratio for ammonia and OP in the reactors were as follows: reactor 1 – 0.92 and 0.95 respectively, reactor 2 – 0.69 and 0.86 respectively, and reactor 3 – 0.68 and 0.75 respectively. These results confirmed that reactor 3 was slightly better at removing ammonia and OP followed by reactor 2. The difference between the ratios from reactor 2 and reactor 3 was not significant, but greater than in the control. A similar trend was observed for nitrate. The Cout/Cin was 0.82, 0.42, and 0.22 for reactors 1, 2 and 3 respectively. These reactors showed that a significant amount of nitrate removal occurred in reactors 2 and 3. Nitrate removal in reactors 2 and 3 was probably the result of denitrification within the media and assimilation in the surface. Performance results suggest that the media in both reactors improved nutrient removal when compared to the control, suggesting that the visible biofilm that grew attached to the media was contributing to the enhanced removal in these two reactors. Analysis of the biomass samples yielded three conspicuous species of algae that were identified and occurred with relatively high frequency. Two species belonging to the division Chlorophyta was identified and appeared on about 70% of the samples. Another notable identified algae were in the division Ochrophytina for about 30% of species identified on samples. The most abundant species identified on all sections was the Spirogyra sp. found on 40% of the samples, followed by Microspora sp. and Tribonema sp. In general, results demonstrated that the biofilm and algae attached to the 3D-printed media enhanced nutrient removal in reactors 2 and 3. Reactor 1 experienced certain, but not significant, nutrient removal. In reactor 2, nutrient removal was significant after the establishment of a noticeable biofilm layer in the media. Reactor 3 had higher nutrient removal than the other reactors due to enhanced algae growth. It is possible that a better synergy between biofilm microorganisms and attached algae developed in this reactor resulting in higher nutrient uptake. However, as biofilm and algae biomass rapidly increased, there was a concomitant increase in organic matter resulting in poorer effluent water quality. Therefore, it is evident that there is an optimal biofilm and algae amount needed to support an ideal nutrient removal level. From a sustainability perspective, in the experiments the media was removed from the reactors at the end of the run and placed in a water tank having no nutrients. After a few days, biomass containing algae slowly and gradually detached from the media without adding any constituent or applying any mechanical force, resulting in settled detached biomass. After drying, the biomass containing algae was easily recovered from the media.
Conclusions:
Results have shown feasibility to the idea of using recent advances in 3D printing manufacturing techniques to develop and fabricate more efficient media designs that will improve biofiltration performance. Phase I efforts have produced biofiltration media designs that provide an increase of 20-200% of surface area for biofilm and algae attachment. Biofilter experimental results showed that the reactors having the media were able to develop environments favorable for nutrients depletion. Aerobic environments in the surface of the media and in water flowing outside the media are suitable for nitrification and nutrient assimilation. Conversely, environment conditions deeper within the media having lower DO concentrations are more suitable for denitrification and OP assimilation or storage. The reactors containing the 3D-printed media removed more nutrients (N and P) than the control. The reason for enhanced removal was the synergy formed between the attached algae and microbial biofilm. However, allowing excessive biomass growth may result in poorer water quality despite a better overall nutrient removal. Although nutrient removal was not 100% effective, there are external factors such as nutrient inflow or HRT that can be improved to develop an optimum operational setup that could result in better nutrient removal. Due to the nature of the media (material type), results showed that the biomass easily detaches from the media when not subject to a nutrient in flux, making the system a cost-effective and sustainable alternative for NPS pollution control.
Journal Articles:
No journal articles submitted with this report: View all 2 publications for this projectSupplemental Keywords:
Biofilters, 3D Printing, Nutrient Recovery, Biofilm, Additive ManufacturingProgress and Final Reports:
Original AbstractThe 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.