Combining submerged membrane technology with anaerobic and ...

Chapter 6Denitrification with dissolved methane in an MBR after amethanogenic pre-treatment at ambient temperatureSummaryThe presence of dissolved methane, especially at low temperature, represents animportant environmental problem in terms of greenhouse gas (GHG) emissions ofwastewaters treated using methanogenic bioreactors. Methane has a global warmingpotential 25 times higher than carbon dioxide. For low strength wastewaters, dissolvedmethane might account up to 50% of the produced methane. The dissolved methane iseasily desorbed from the effluents, especially if these are either released in theenvironment or post-treated using aerobic bioreactors, increasing GHG emissions.The use of this dissolved methane as a carbon source for biological denitrificationhas been proposed as an alternative to reduce both GHGs emissions and nitrogen contentof the treated wastewater. In this study the effluent of a UASB reactor was post-treated inan MBR with a first anoxic chamber in order to use dissolved methane as carbon sourcefor denitrification. Up to 60% and 95% nitrogen removal and methane consumption wereobserved, respectively. The stripping of the dissolved methane present in the UASBeffluent led to a worsening of nitrogen removal in the MBR system. Batch experimentsconfirmed the presence of microorganisms capable of denitrifying using the dissolvedmethane as carbon source. Recirculation ratio between the anoxic and aerobic chambersof the MBR system, and either the presence of dissolved methane were shown as themain important parameters governing the denitrification process. The influence ofdenitrification with methane on membrane performance was also studied, showing aremarkable increase on biopolymer concentration when denitrification activity was affectedby the removal of dissolved methane from the UASB effluent.Parts of this chapter have been submitted for publication as:Sánchez, A., Rodríguez-Hernández, L., Buntner, D., Esteban-García, A.L., Tejero, I., Garrido,J. M. 2013. Denitrification coupled with methane oxidation in a membrane bioreactor after amethanogenic pre-treatment. Submitted to Water Research.149