Startup and initial operation of an MLE-MABR treating municipal wastewater.

A 630 m3/d pilot plant was installed at Subiaco WRRF to determine design and operational parameters of a hybrid Modified Ludzack-Ettinger - Membrane Aerated Biofilm Reactor (MLE-MABR) configuration. Two commercial ZeeLung MABR cassettes were installed in series in the anoxic zone and the pilot was fed with primary effluent (averaging COD 601 mg/L, TKN 68.5 mg/L and 17-29 °C). A nitrifying biofilm was developed within 3 weeks and the nitrous oxide (N2O) gas emissions from the MABR exhaust gas proved to be a reliable parameter to assess biofilm development. Both MABRs achieved the average nitrification rate (NR) of 3.7 gNH4-N/m2.d when air flow was 8.6 and 11.2 Nm3/h to MABR1 and MABR2 respectively, which reached a maximum oxygen transfer rate of 17.4 gO2/m2.d. Biofilm thickness was controlled via air scouring and intermittent coarse bubble mixing (90 s on/90 s off). This paper discusses the startup strategy, minimum requirements for process monitoring, impact of different air flow conditions, ORP and mixing patterns on performance efficiency over a 22-week period.

Method Development for Quantification of Bromochloramine Using Membrane Introduction Mass Spectrometry.

During chloramination of bromide-containing waters, the main brominated amine formed is bromochloramine (NHBrCl). To date, there is no analytical method, free of interference, allowing its accurate quantification. The major reason is that it is not possible to produce a pure NHBrCl solution. In this study, we report a method allowing the accurate quantification of NHBrCl with membrane introduction mass spectrometry (MIMS). First, the molar absorption coefficient for NHBrCl was determined by quantifying NHBrCl as 2,4,6-tribromophenol by HPLC-UV and comparing the results with the direct UV response at 320 nm. A molar absorption coefficient of 304 M-1cm-1 was obtained. The results obtained by direct UV measurements were compared to the MIMS signal recorded at m/ z 131 corresponding to the mass of the molecular ion and used to establish a calibration curve. A limit of detection of 2.9 µM (378 µg/L) was determined. MIMS is the only method enabling the unambiguous quantification of NHBrCl, as it is based on m/ z 131, while with other analytical techniques, other halamines can interfere, i.e., overlapping peaks with direct UV measurements and reaction of several halamines with colorimetric reagents or phenols. While the detection limit is not quite low enough to measure NHBrCl in actual drinking water, this analytical method will benefit the scientific community by allowing further mechanistic studies on the contribution of NHBrCl to the formation of toxic disinfection by-products.

Impact of brominated amines on monochloramine stability during in-line and pre-formed chloramination assessed by kinetic modelling.

In this study, a comprehensive kinetic model was developed and validated to predict the stability of monochloramine (NH2Cl) in presence of iodide and bromide for both pre-formed and in-line chloramination application in absence of organic matter. pH had the greatest influence on the stability of NH2Cl in waters containing bromide. For in-line chloramination, the NH2Cl decay over 3days was only 10% for pH9 and 58% for pH7 (400µgBr-/L and 3 mgCl2/L). Bromide also greatly affected the stability of NH2Cl by influencing the formation and speciation of the halamines produced during chloramination. In-line chloramination is commonly used since the pre-chlorination oxidises iodide to the non-toxic iodate. During pre-chlorination, brominated organics are formed from reaction between bromine and dissolved organic matter (DOM). In the case of the Colorado River DOM, 26% of the bromine was sequestered in only 4min, and therefore not available to form brominated amines during chloramination. Following ammonia addition, an immediate loss of oxidant was observed in water containing bromide at pH7 and 8. This is due to the reaction between NHBrCl and NHBr2, and the auto-decomposition of NHBr2 formed from NH2Br. Once NHBr2 was consumed, NHBrCl accumulated and then slowly decayed. Thereafter, the total oxidant concentration decayed slowly due to the auto-decomposition of NHCl2 and the reaction between NHBrCl and NHBr2. In the presence of DOM, the CHBr3 concentration increased, while the CHCl3 concentration (formed during pre-chlorination) was constant during chloramination, indicating that brominated-amines may continue to form disinfection by-products (DBPs).