Combining submerged membrane technology with anaerobic and ...

Denitrification with dissolved methane in an MBR after a methanogenic pre-treatment at ambient temperature6.3. Material and methods6.3.1. Experimental set-up and operating strategyA schematic diagram of the experimental set-up can be observed on figure 6.1. A120 L volume UASB system was used for the first methanogenic stage. The effluent of theUASB reactor was led to an MBR reactor composed by two chambers: a first chamber (36L), with biomass growing onto plastic support and in suspension, and a second aerobicmembrane filtration chamber (20 L volume). 18.5 L (50% of the effective volume) ofsupport (Kaldnes® K3) were added in the first MBR chamber. An internal recirculation (R)from the filtration chamber to the first chamber was used to return suspended solids andnitrate to this chamber. A membrane ultrafiltration module Zenon ZW10 with a surfacearea of 0.9 m 2 was employed in the filtration chamber. This module consisted of PVDFhollow-fibre membrane, with a pore size of 0.04 µm. The membrane was operated incycles of 7.5 min with a permeation period of 7 min and a backwashing period of 0.5 min.The filtration chamber was aerated in order to minimize membrane fouling and promoteammonia oxidation. The specific air demand (SAD m) applied to the membrane was 0.7Nm 3·m -2·h -1 . The operation of the system was controlled by a PLC (Siemens S7-200)connected to a computer. Trans-membrane pressure (TMP) data was measured with ananalogue pressure sensor (Efector500 PN-2009) and collected in the PC via an analoguePLC module Siemens EM 235.The reactor was operated at ambient temperature (19-21.5 ºC) and fed usingsynthetic wastewater composed of diluted skimmed milk, NaHCO 3 and trace elements.COD concentration in the feeding was varied between 800 and 1300 mg·L -1 .The impact of recirculation ratio (R) and the presence of methane in the UASBeffluent were studied during six different periods (table 6.1). The first chamber of the MBRsystem was aerated during a first experimental period (period I) in order to establish abase base scenario for the emissions of dissolved total nitrogen and methane. Afterwardsit was maintained under anoxic conditions in order to promote denitrification (periods II, III,IV, V and VI). During periods II, III, V and VI the impact of the internal recirculation ratio onnitrogen removal in the MBR system was investigated. During period IV, methane presentin the effluent from the UASB reactor was stripped off by aerating this stream beforeentering in the MBR. The main objective of this period was to determine denitrificationcaused by the remaining biodegradable COD fraction of this stream.153