Bioreactors

Bioreactors — Construction and operation

Select from the tabs below

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

Approvals

A range of legislation and approvals may be required for the construction of a bioreactor. Contact your local government before any construction is undertaken to understand requirements.

Prior to construction, check for any existing infrastructure by contacting electricity, water and telecommunication providers. It is also recommended that local Traditional Owners are engaged to ensure no sites or items of cultural significance are disturbed during excavation.

Professional advice should be sought prior to construction to ensure the bioreactor is sized and sited appropriately, considering soil suitability, groundwater and local hydrology.

Construction

• Mark out the site and excavate a trench.
• Use a laser level to ensure the floor of the bioreactor is level or at the correct slope to avoid preferential flow paths or water ponding.
• For beds, install the inlet and outlet connected to a farm drain or subsurface drain.
• Install woodchip. Softwood woodchip is preferable as it has the same nitrate removal performance as hardwood, with reduced risk of dissolved organic carbon and greenhouse gas emissions[3]. Woodchip with a 50% fraction with a particle size >13mm[1] is recommended for improved hydraulic conductivity.
• Seal and cover with topsoil. Soil on top of bioreactors further minimises nitrous oxide emissions[2].
• Consider using geofabric on top of the woodchip to prevent sedimentation/clogging of woodchip media over time. This will also allow the woodchip to be exposed later in the project if desired[5].

Timelapse video of a bioreactor bed being built on a cane farm in the lower Burdekin

Time for establishment

A bioreactor can be constructed and operational within a few days, depending on the size of the structure and any associated pipe work or structures. Denitrification will commence within hours of nitrate entering the bioreactor. The denitrifying microbes are naturally present in the environment, so no ‘seeding’ is required.

Operation

Operational requirements are minimal. Bioreactors operate passively.

Monitoring and maintenance

Typical monitoring and maintenance of bioreactor beds will involve:

• Regularly check and clean out of the sediment trap to remove sediment, leaves and other material.
• Check and clear inlet and outlet structures if there is algal growth or blockages.
• Check that water is flowing out the outlet of the bioreactor.
• Check and repair any erosion or scour and replace or install diversion banks to minimise erosion.

Bioreactor walls require limited maintenance, other than slashing of grass at the surface. Soil may need to be replaced on the top of the bioreactor wall if subsidence or erosion occurs.

Monitoring of nitrate entering and leaving the bioreactor will help determine if the bioreactor is effectively removing nitrate as designed.

Monitoring regimes for quantifying the nitrate removal performance of bioreactors is outlined in Using denitrifying bioreactors to improve water quality on Queensland Farms. Videos on monitoring bioreactors are also available.

Lifespan/replacement time

The woodchips within the bioreactor bed or wall will gradually degrade over time and hydraulic efficiency will be reduced. Trials in Queensland suggest a 10-12 year lifespan for bioreactors, although this will depend on the woodchips used, site conditions (wetting and drying regime and temperature). After this time the woodchips will need to be replaced, although this should cost less than the original construction, especially for bioreactor beds as the inlet and outlet structures may not need replacing[4].

References

1. ^ L. Christianson, A. Castelló, R. Christianson, M. Helmers & A. Bhandari (2010), 'Technical Note: Hydraulic Property Determination of Denitrifying Bioreactor Fill Media', Applied Engineering in Agriculture. [online], vol. 26, no. 5, pp. 849-854. Available at: http://elibrary.asabe.org/abstract.asp??JID=3&AID=34946&CID=aeaj2010&v=26&i=5&T=1 [Accessed 26 May 2022].
2. ^ Laura Christianson, James Hanly, Neha Jha, Surinder Saggar & Mike Hedley (2013), 'Denitrification bioreactor nitrous oxide emissions under fluctuating flow conditions', 2013 Kansas City, Missouri, July 21 - July 24, 2013. [online], American Society of Agricultural and Biological Engineers. Available at: http://elibrary.asabe.org/abstract.asp?JID=5&AID=43448&CID=miss2013&T=1 [Accessed 26 May 2022].
3. ^ 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. ^ Schipper, L, Robertson, WD, Gold, AJ, Jaynes, DB & Cameron, SC (2010), 'Denitrifying bioreactors—An approach for reducing nitrate loads to receiving waters', Ecological Engineering, vol. 36, pp. 1532-1543.
5. ^ 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.

Last updated: 24 May 2022