Grantee Research Project Results
Final Report: Advanced Bioreactor
EPA Grant Number: SU836138Title: Advanced Bioreactor
Investigators: Skardon, John
Institution: California State University - Monterey Bay
EPA Project Officer: Page, Angela
Phase: I
Project Period: September 1, 2015 through August 31, 2016
Project Amount: $15,000
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2015) RFA Text | Recipients Lists
Research Category: P3 Awards , Pollution Prevention/Sustainable Development , Sustainable and Healthy Communities , P3 Challenge Area - Safe and Sustainable Water Resources
Objective:
The purpose of this research was to design and test an “advanced bioreactor” that will reduce incoming nitrate contaminated water from 100 ppm at the inlet to less that 10 ppm in the effluent with a hydraulic residence time of less than 1 hour. The operating cost of the proposed system was targeted at $1.25 or less per pound of nitrate-nitrogen removed. This cost target is well below any existing technology. We had five objectives for this project. First, we wanted to design and demonstrate a bioreactor that can meet the performance targets for denitrification. Our second objective was the creation of a mathematical model that would enable users to estimate the size, cost, and performance of the reactor. Third, we planned to take as much data as possible using our on-campus unit and then move the unit out into the local agriculture fields to take denitrification data at a variety of locations. Fourth, we want to develop an operating cost model that would demonstrate, as close as possible, the costs to the farmer/grower for purchasing and operating one of these reactors. Finally, our fifth goal was to develop a new public-private partnership business model for deploying the reactor technology. Our operational focus was the Salinas river valley and adjoining watershed(s). The reactor design was focused on removing nitrate from agricultural surface and sub-surface tailwater, rather than remediating ground water. However, there is no reason why our design could not be used to remediate nitrate contaminated wells in the local area or other types of nutrient rich runoff from other types of agriculture.
Summary/Accomplishments (Outputs/Outcomes):
Our final prototype was an anaerobic, upflow moving bed biofilm reactor (MBBR)(Rusten, Eikebrokk, Ulgenes, & Lygren, 2006). The bioreactor was a 200 gallon tank, 31” W x 71” L. The bioreactor tank was filled with 120 gallons of 18 chamber MBBR media. These MBBR media are similar to the well known Kaldnes K1 style media used in wastewater treatment plants. The reactor diameter and flow rate were designed to maintain plug flow conditions inside the reactor. Our synthetic wastewater, about 450 gallons, consisted of tap water with the appropriate amounts of water soluble nitrate and phosphorus to maintain ideal C:N:P ratios for denitrification. Our external carbon substrate was denatured alcohol, available locally at Home Depot. The supply pump flow rate was controlled with a pulse width modulated control board. The external carbon was metered into the bioreactor separately, using an off-the-shelf peristaltic pump. Once all of the water in T1 had flowed to T3, a sump pump in T3 (not shown) moved the water to a upflow sand and gravel filter fabricated from 55 gallon drums. The filtrate from the sand filter was returned back to T1.
We calculated the denitrification coefficient (grams of NO3-N removed per day per cubic meter of “filter”) by using the following formula: DNR = ΔC ∗ Flow/Volume
Where:
DNR= denitrification rate coefficient (g NO3-N/Day-M3 )
ΔC= change in concentration, Cin-Cout from inlet to outlet (grams/M3 )
Flow= flow rate (M3 /Day)
Volume= volume of MBBR media in bioreactor tank (M3 )
Note: the term “ MBBR media” is a generally accepted term in industry for biofilm support matrix.
The inlet concentration sample was taken from SP1 at approximately 30 minutes after P1 and P2 were started. The outlet concentration was taken approximately 120 minutes after the inlet concentration sample. Each test run took approximately four hours to complete.
We initially calculated the denitrification coefficient using a commercially available ISE style nitrate probes. However, in an unrelated experiment, other faculty members at CSUMB found some problems with the nitrate ISE sensors they had purchased from the same manufacturer. While we did not see the kind of problems the other team did, we stopped using our nitrate ISE probe. Because of this, we switched to a commercial analytical lab to measure nitrates. Our last runs before the project shut down gave us a denitrification coefficient values from 1300 to 1700 g NO3-N/Day-M3
. Findings
1. The MBBR style reactor was extremely efficient at removing nitrate and easy to maintain and manage throughout the testing period of 60 days.
2. The calculated denitrification rate, in excess of 1500 grams NO3-N/Day-M3 , was achieved at an HRT of 96 minutes, about 30 minutes higher than our target of 1 hour.
3. Maintenance of the C:N:P ratio was essential for denitrification.
4. The denatured alcohol carbon source used in the test was very effective in growing biofilm and reducing nitrate
5. Conventional nitrate sensors have been and continue to be problematic for this application.
6. We were able to easily isolate denitrifying bacteria from our local agricultural drainage areas using a simple approach (Van Niel & Allen, 1952)
7. The MBBR media behaved per industry observations. As the biofilm attached to the media, the individual elements became neutrally buoyant, distributing through the vertical water column in the reactor.
Outcomes
1. Reactor design. The MBBR style up-flow reactor was very successful.
2. Mathematical Model. Initial spreadsheets created by students were updated during the summer.
3. Performance data. The limited data we were able collect over the June-July 2016 period showed very high rates of denitrification which dramatically reduce the size and complexity of a final design
4. Operating Cost Model. The estimated annualized cost of the equipment per 1000 gallons treated ranged from $0.75 to $1.2, much lower than any other solution. The variable or operating costs to the end user using a commercially available carbon waste byproduct were less than $1.25 per pound of nitrate-nitrogen removed.
5. Public-Private Partnership Model. Preliminary work was done on this but the model was not completed. A private company, Tailwater Systems, was launched in July of 2016 to further advance and commercialize the design. Tailwater will be installing first commercial systems in December 2016.
Discussion
1. No commercial MBBR style reactors have been proposed for this application. This is the first to our knowledge.
2. The MBBR design dramatically simplifies the system, and allows for the use of plastic water tanks instead of steel or reinforced fiberglass, resulting in a dramatic cost and weight savings.
3. Controlling the carbon:nitrogen ratio is the most important function for these systems.
4. Using a 25 GPM system as a reference, and reducing 100 mg/L NO3-N to less than 10 mg/L, results in a system that can fit on a 300 ft2 pad (concrete or packed earth/rock/sand).
5. The major cost challenge of this system and approach is the external substrate requirement. Many of these sources have been studied (Cameron & Schipper, 2010). The US EPA recommends several types of carbon sources including methanol and ethanol. In this report we found that an attractive price range for the reduction of nitrate was approximately $1.25 per pound of nitrate-nitrogen removed.
6. Reactor control should be done using existing ORP/pH sensors, as done in industry already. If the reactor conditions (ORP and pH) can be maintained, then simple nitrate test strips can be used to insure that the filtrate is below the MCL level in operation (Chang, Cheng, & Chao, 2004). 7. Dissolved oxygen levels are important in this application. We found that DO measurements made at P2 were about 1 ppm using a simple hand held meter.
Conclusions:
1. A compact, very efficient denitrifying MBBR style bioreactor can be designed using off the shelf technology and available expertise
2. The size of the reactor could be fit on the edge of field, taking up less than 150- 300 ft2 .
3. These reactors can be a key component in an overall nutrient management strategy because of their effectiveness, affordability, predictability, and ease of use.
References:
Cameron SG, Schipper LA. (2010). Nitrate removal and hydraulic performance of organic carbon for use in denitrification beds. Ecological Engineering 36(11):1588-1595. https://doi.org/10.1016/j.ecoleng.2010.03.010
Chang C-N, Cheng H-B, Chao AC. (2004). Applying the Nernst equation to simulate redox potential variations for biological nitrification and denitrification processes. Environmental Science & Technology 38(6):1807-1812. https://doi.org/10.1021/es021088e
Rusten B, Eikebrokk B, Ulgenes Y, Lygren E. (2006). Design and operations of the Kaldnes moving bed biofilm reactors. Aquacultural Engineering 34(3):322-331.
Van Niel CB, Allen MB. (1952). A note on Pseudomonas stutzeri. Journal of Bacteriology 64(3):413.
Journal Articles:
No journal articles submitted with this report: View all 3 publications for this projectSupplemental Keywords:
Denitrification, MBBRThe 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.