Treatment of Hydroponic Glasshouse Waste: Temperature and Carbon Limitations

 

Situation: In addition to removing nitrate-N from tile drains, denitrifying bioreactors can also treat a range of wastewaters. In these situations, bioreactors are used as a polishing step after pre-treatment to remove remaining nitrate-N before discharge to land or water. Wastewater from hydroponic glasshouses are one such source. To ensure that bioreactors are constructed at the appropriate size, we need to understand nitrate-N removal rates and the factors controlling this removal.

 

Actions: A large denitrification bioreactor (176 m long by 5m wide and 1.5 m deep) was constructed in Karaka, New Zealand to treat wastewater from a hydroponic glasshouse. Coarse wood chips were used to fill a plastic lined pit. A series of studies led by Drs Sören Warneke and Louis Schipper measured rates of nitrate removal as temperature varied through the year. 

denitrification bed next to glasshouse

Take-home message: 

  • Nitrate inputs to the bioreactor were greater than 100 g N m-3 and substantially reduced as nitrate moved through the bed.
  • Nitrate removal from ranged 4.6 to 11.2 g N m-3 d-1 and was never limited by nitrate concentration but highly dependent on temperature. In broad terms, the rate of nitrate removal doubled for a 10°C increase in temperature.
  • Nitrate removal rates were also limited by the availability of carbon from degrading wood chips in the bioreactor.

 

For more information:

  • Warneke, S., Schipper, L.A., Brusewitz, D.A., McDonald I.R., Cameron S.G., (2011) Rates, controls and potential adverse effects of nitrate removal in a denitrification bed. Ecological Engineering. 37: 511-522.
  • Warneke, S.; Schipper, L.A.; Matiasek, M.G.; Scow, K.M.; Cameron, S.; Bruesewitz, D.A.; McDonald I.R. (2011) Nitrate removal, communities of denitrifiers and adverse effects in different carbon substrates for use in denitrification beds. Water Research 45: 5463-5475.
  • Warneke, S.; Schipper, L.A.; Bruesewitz, D.A.; Baisden, W.T. (2011) A comparison of different approaches for measuring denitrification rates in a nitrate removing bioreactor. Water Research. 45: 4141-4151.
  • Email Dr. Louis Schipper at schipper@waikato.ac.nz