Combining submerged membrane technology with anaerobic and ...

(mg·L -1 )Denitrification with dissolved methane in an MBR after a methanogenic pre-treatment at ambient temperaturethat period ranged between 21 and 27 mg·L -1 . Figure 6.2 shows that N-NO x-concentrationwas almost zero in the first (anoxic) chamber. Thus, denitrification was limited by nitrateavailability. Nevertheless, during period IV, the absence of dissolved methane led to aprogressive increase of nitrate in the first (anoxic) chamber, indicating that the limitingfactor in this period was the carbon source (figures 6.2b and 6.3). From the data obtainedat the end of period IV (figure 6.3), a constant nitrogen removal rate of 73 mgN·L -1·d -1 wasobtained, whereas, considering the end of period III and the beginning of period IV, thisnitrogen removal rate was around 164 mgN·L -1·d -1 . The difference between both nitrogenremoval rates could be probably due to dissolved methane. From the 60% nitrogenremoval observed, DTN removal percentage due to the oxidation of methane couldaccount, at least, up to 33 %. Thus, the nitrogen removal percentage due to otherprocesses at the end of period IV was, at most, 27 %. It should be taken into account thatsome dissolved methane was still remaining in the UASB effluent (3-8 mg·L -1 ). 50% of thismethane was oxidized in the anoxic compartment during this period. When stripping ofmethane was stopped on period V, nitrogen removal increased again to the previousvalues observed during period III, up to 60 %, confirming the relevant role of methane indenitrification.50DTN, N-NH 4+ and N-NOx-403020100151 153 155 157 159 161 163 165 167 169Time (d)Figure 6.3. Evolution of DTN concentration in the UASB effluent () and the permeate(•) and N-NH 4+(•) and N-NO x-concentration (Δ) in the first MBR (anoxic) chamberduring period IV.The results presented show that denitrification, using methane as a carbon source iseffectively possible and feasible. Soluble COD concentration in the UASB effluent wasused for conventional heterotrophic denitrification. Nevertheless this low COD161