rotating algal biofilm reactor for biomass growth and...

Rotating Algal Biofilm Reactor (RABR) for Biomass Growth and Nutrient Removal

Terence Smith, Ashik Sathish,

Reese Thompson, Dr. Ronald Sims

Algae Biomass Summit

10/1/2013

1

Outline

• Background

• Objectives

• Methods/Model

• Results

• Discussion/Conclusion

2

Background Wastewater Treatment

• Logan City Wastewater Treatment Facility – 460 acre facultative lagoon style wastewater treatment plant – Currently releasing excess phosphorus/nitrogen in effluent

• Average of 9.5 mg/L of Ammonia and 3.1 mg/L of Total Phosphorus – Requirements: Phosphorus and Ammonia = 1 mg/L, (Annual average, seasonal standards)

– Conventional retrofit is expensive • ~$110 million (activated sludge, nitrification/denitrification)

– 7,000 similar lagoon style wastewater treatment plants in the US

3

Background Wastewater Treatment

• Potential solution: Algae – Grow on excess nutrients

• C106H175O42N16P

• Remove algae, remove problem

– Use algal biomass for different valuable bioproducts

• Challenge: – How to grow and harvest enough

algae (cost effectively) to make this solution viable.

– Conventional system: Raceway

• Difficult/costly to separate algae from the wastewater

4

Potential solution: Rotating Algal Biofilm Reactor

(RABR) • Material details

– 74” diameter aluminum irrigation wheels

– ~60 inches in length

– ~4000 ft. of solid braid cotton rope (substratum)

– ~10700 L tank

– Wastewater drawn from final pond of treatment facility

• Data collection

– Biomass growth

– Nutrient removal

– Water temperature, pH, DO

– Weather conditions/Air temperature

• from local Campbell Scientific data logging station

– Photosynthetically active radiation

• from USU sensor

– Tested during different seasons, conditions

5

Objectives

• Objective 1: Develop a predictive model of the growth of algal biofilm biomass on the rotating algal biofilm reactor (RABR) • Task 1: Propose model based on variables including light, temperature,

nutrients, and cultivation area

• Task 2: Observe biofilm growth at pilot scale under natural conditions to compare to model

6

Objectives

• Objective 2: Develop a predictive model of nutrient removal by the rotating algal biofilm reactor (RABR) for wastewater remediation • Task 1: Propose nutrient removal model based on biofilm uptake of

nitrogen and phosphorus

• Task 2: Observe nutrient removal at pilot scale under natural conditions to compare to model prediction

• Application at other facilities/locations

• Maximize system efficiency

7

Model

Conceptual diagram of growth conditions

8

Biofilm Model

• Based on EPA Benthic Algae model

• Growth formula (photosynthetic rate):

𝑑𝐵

𝑑𝑡= 𝑢 − 𝑅𝑟 − 𝐷𝑟 𝑆𝑎

𝑢 = 𝑢max ∗ 𝐼 ∗ 𝑇 ∗ 𝑁 ∗ 𝐴

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Variable Identity Units

u specific growth rate (photosynthesis) g/m2/sec

u_max maximum growth rate (photosynthesis) g/m2/sec

I Light attenuation coefficient (photosynthesis) Dimensionless

T Temperature attenuation coefficient (photosynthesis) Dimensionless

N Nutrient attenuation coefficient Dimensionless

A Space attenuation coefficient Dimensionless

Rr Respiration rate 1/sec

Dr Death rate 1/sec

Sa Surface Area m2

Model Biofilm Growth

• Light attenuation coefficient (Steele’s equation)

– 𝐼 =𝐼𝑜

𝐼𝑠∗ exp(1 −

𝐼𝑜

𝐼𝑠)

• Temperature attenuation coefficient (Arrhenius equation)

– 𝑇 = 𝐺𝑡−20

𝑢=𝑢_max∗𝐼∗𝑇∗𝑁∗𝐴


Io Observed PAR intensity umol/m2/sec

Is Optimum PAR intensity umol/m2/sec


G Photosynthesis temperature coefficient Dimensionless

t Observed temperature Dimensionless

• Nutrient equation – Monod equation

– 𝑁 =𝑆

𝐾𝑠+𝑆

• Area equation (logistic)

– 𝐴 = (1 −𝑎

𝑎𝑚𝑎𝑥)

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Model

• Nutrient removal due to biomass:

•𝑑𝑁

𝑑𝑡= −𝑢𝑛𝑁

𝑆𝑎

𝑉+ 𝑁𝐹𝑖𝑛 − 𝑁𝐹𝑜𝑢𝑡

•𝑑𝑃

𝑑𝑡= −𝑢𝑝𝑃

𝑆𝑎

𝑉+ 𝑃𝐹𝑖𝑛 − 𝑃𝐹𝑜𝑢𝑡

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N Bioavailable nitrogen mg/L

n N content of biofilm biomass Dimensionless

P Bioavailable phosphorus mg/L

p P content of biofilm biomass Dimensionless

F Flow rate L/day

Sa Surface area m2

V Volume of tank L

Results Biofilm Growth

• Natural environmental conditions • Continuous flow • Different retention times

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Results for Objective 1 Modeling of Biomass

13

R2=0.907

Results for Objective 1 Modeling of Biomass

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R2=0.145

Results Observed Nutrient Removal

Results for Objective 2 Predicted vs. Measured

Comparison of projected uptake vs. measured uptake (Biofilm)

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Comparison of projected uptake vs. measured uptake (Biofilm)

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Results Observed Nutrient Removal

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Comparison of measured uptake (Biofilm) vs. nutrient removal from bulk fluid

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Environmental factors affecting nutrient removal: -pH (precipitation, volatilization) -DO (denitrification)

Comparison of measured uptake (Biofilm) vs. nutrient removal from bulk fluid

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Energy balance

40 g/m2/d

518.4 kJ/d

(Electricity)

Biomass

* Source: Christenson, L. B., & Sims, R. C. (2012). Rotating algal biofilm reactor and spool harvestor for wastewater treatment with biofuels by-products. Biotechnology and Bioengineering, 109(7), 1674-1684.

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RABR Effective area: 2.5 m2

RABR Productivity: 40 g/m2-day

RABR Power requirement*: 6 watts

Energy Consumption: 5184.00 KJ/kg Algae

RABR Productivity per unit: 100 g dry algae/day

Biomass energy content 21,400.00 KJ/kg Algae

Energy balance 16,216.00 KJ/kg Algae

Algae From RABRs

Discussion/conclusion

• Objective 1 - Develop a predictive model of the growth of algal biofilm biomass on the RABR

– Promising results for modeling biomass growth

• Objective 2 - Develop a predictive model of nutrient removal by the RABR for wastewater remediation

– Good agreement for biological uptake of nutrients into biofilm

– Environmental conditions dominant in observed nutrient removal • Future modeling needs to account for nutrient removal via pH and DO

• Current work – Lifecycle analysis (upstream and downstream)

• Clemson University and Dr. Jason Quinn (USU)

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Acknowledgements

– Special thanks to:

• Logan City Environmental Department

• WesTech Engineering

• Utah Water Research Laboratory

• Carollo Engineering

• US EPA

• Campbell Scientific

• Utah Science Technology and Research (USTAR)

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Sources

1. Ambrose, R. B., Martin, J. L., & Wool, T. A. U.S. Environmental Protection Agency, Office of Research and Development. (2006). Wasp7 benthic algae - model theory and user's guide (R600/R-06/106). Washington DC: U.S. Environmental Protection Agency.

2. Cerucci, M., Jaligama, G. K., & Ambrose, R. B. (2010). Comparison of the monod and droop methods for dynamic water quality simulations. Journal of Environmental Engineering, 136(10), 1009-1019.

3. Christenson, L. B., & Sims, R. C. (2012). Rotating algal biofilm reactor and spool harvestor for wastewater treatment with biofuels by-products. Biotechnology and Bioengineering, 109(7), 1674-1684.

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