Bioreactors

Bioreactors — Key considerations

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• Overview
• Key considerations
• Planning and design
• Construction and operation
• Links and references

What makes a good bioreactor?

• Located to intercept regular water flows containing nitrate. Nitrate removal performance is related to the inflow nitrate concentration[3][4].
• Sized based on the water flow to be treated and the hydraulic residence time required to reduce nitrate by a given concentration (mostly relevant to bioreactor beds).
• Designed to maintain conditions suitable for denitrification, considering carbon source, low dissolved oxygen, suitable pH and sufficient nitrate to avoid nitrate-limited conditions[9].

Treatment processes

Suitability and limitations

Bioreactors are now being used in a variety of climatic and production settings for nitrate mitigation. Bioreactor beds are commonly used to treat tile drainage (i.e. ag pipe) from crops (mostly corn and soybean) in the US Midwest. Bioreactor walls and beds have been used to treat shallow groundwater or sub-surface water from dairy farms and glasshouses in New Zealand. They have also been trialled for treating aquaculture and urban wastewater. Bioreactor bed trials on a fish farm in North Queensland showed they were very effective at removing nitrate. Because aquaculture wastewater often contains ammonia, nitrification was conducted to convert the ammonia to nitrate before entering the bioreactor[9]. Recent results show that bioreactors are very effective at removing nitrate from intensive horticulture (blueberry) production systems in northern NSW with minimal nitrous oxide emissions[11][8].

Since 2017, bioreactors have been trialled on Queensland farms in South-East Queensland (pineapples) and North and far North Queensland (sugarcane and aquaculture) to test their effectiveness in tropical and sub-tropical Queensland climates and production systems. The Project Search Tool shows sites where bioreactors have been trialled in Queensland. They were found to be effective at removing nitrate in different production systems and climatic regions in Queensland, with performance related to nitrate inflow concentrations and water flow[3][4]. Their practical application in other production systems and regions in Queensland has yet to be tested and the design will need to be tailored to each site.

In addition to nitrate, bioreactors have the potential to reduce the concentration of some pesticides[6], although the main mechanism for this reduction is uncertain.

Bioreactors may produce nitrous oxide (a greenhouse gas) if denitrification is not complete, often due to low pH[1] or high dissolved oxygen[7]. If located and managed to ensure suitable conditions for denitrification, bioreactors will produce minimal amounts of N₂O[2] and less than that produced if nitrate-rich water entered natural waterways directly, without passing through a bioreactor[5]. Pollutant swapping such as sulphate reduction, leading to methane or hydrogen sulphide production can occur under nitrate-limited, saturated conditions, but can usually be minimised through careful site selection and design[2][10].

References

1. ^ Chapuis-Lardy, L, Wrage, N, Metay, A, Chotte, JL & Bernoux, M (January 2007), 'Soils, a sink for N2O? A review', Global Change Biology. [online], vol. 13, no. 1, pp. 1-17. Available at: https://onlinelibrary.wiley.com/doi/10.1111/j.1365-2486.2006.01280.x [Accessed 26 May 2022].
2. ^ a b Christianson, LE & Schipper, LA (2016), 'Moving Denitrifying Bioreactors beyond Proof of Concept: Introduction to the Special Section', Journal of Environmental Quality, vol. 45, pp. 757-761.
3. ^ a b Manca, F, De Rosa, D, Reading, LP, Rowlings, DW, Scheer, C, Layden, I, Irvine-Brown, S, Schipper, LA & Grace, PR (September 2020), 'Nitrate removal and greenhouse gas production of woodchip denitrification walls under a humid subtropical climate', Ecological Engineering. [online], vol. 156, p. 105988. Available at: https://linkinghub.elsevier.com/retrieve/pii/S0925857420302767 [Accessed 26 May 2022].
4. ^ a b Manca, F, Wegscheidl, C, Robinson, R, Argent, S, Algar, C, De Rosa, D, Griffiths, M, George, F, Rowlings, D, Schipper, L & Grace, P (15 December 2021), 'Nitrate Removal Performance of Denitrifying Woodchip Bioreactors in Tropical Climates', Water. [online], vol. 13, no. 24, p. 3608. Available at: https://www.mdpi.com/2073-4441/13/24/3608 [Accessed 23 May 2022].
5. ^ Queensland Bioreactor Network (2019), Nitrous oxide emissions from bioreactors, crops and waterways fact sheet. [online], State of Queensland. Available at: https://www.publications.qld.gov.au/dataset/treatment-system-technologies-to-improve-water-quality/resource/fd84d462-80f9-43ad-87c3-c8ba70ecce9e.
6. ^ Ranaivoson, A (14 August 2019), 'Acetochlor and atrazine dissipation in a woodchip denitrifying bioreactor: a comparison of experimental results with model estimates', International Journal of Hydrology. [online], vol. 3, no. 4, pp. 286-306. Available at: http://medcraveonline.com/IJH/acetochlor-and-atrazine-dissipation-in-a-woodchip-denitrifying-bioreactor-a-comparison-of-experimental-results-with-model-estimates.html [Accessed 26 May 2022].
7. ^ Robertson, WD (November 2010), 'Nitrate removal rates in woodchip media of varying age', Ecological Engineering. [online], vol. 36, no. 11, pp. 1581-1587. Available at: https://linkinghub.elsevier.com/retrieve/pii/S0925857410000340 [Accessed 23 May 2022].
8. ^ Wadnerkar, PD, White, SA, Morris, SA, Conrad, SR, Hessey, S, Woodrow, RL, Holloway, C, Sanders, CJ & Santos, IR (May 2022), 'Nitrate removal and nitrous oxide production from hothouse effluent draining to a pipe bioreactor', Ecological Engineering. [online], vol. 178, p. 106561. Available at: https://linkinghub.elsevier.com/retrieve/pii/S0925857422000222 [Accessed 26 May 2022].
9. ^ a b Wegscheidl, C, Robinson, R & Manca, F (2021), Using denitrifying bioreactors to improve water quality on Queensland farms. [online], Queensland Department of Agriculture and Fisheries, Townsville, Queensland. Available at: https://www.publications.qld.gov.au/dataset/treatment-system-technologies-to-improve-water-quality/resource/5a663c1c-9734-4367-9348-bf6e3f24b493.
10. ^ Weigelhofer, G & Hein, T (2015), 'Efficiency and detrimental side effects of denitrifying bioreactors for nitrate reduction in drainage water', Environmental Science and Pollution Research, vol. 22, pp. 13534-13545.
11. ^ White, SA, Morris, SA, Wadnerkar, PD, Woodrow, RL, Tucker, JP, Holloway, CJ, Conrad, SR, Sanders, CJ, Hessey, S & Santos, IR (May 2022), 'Anthropogenic nitrate attenuation versus nitrous oxide release from a woodchip bioreactor', Environmental Pollution. [online], vol. 300, p. 118814. Available at: https://linkinghub.elsevier.com/retrieve/pii/S0269749122000288 [Accessed 26 May 2022].

Last updated: 24 May 2022