Catalytic Nitrate Removal in a Trickle Bed Reactor: Direct Drinking Water Treatment

Abstract

Palladium (Pd)-based catalysts hold promise as an alternative water treatment technology for nitrate (NO 3 -), but practical application requires a flow-through reactor that efficiently delivers hydrogen (H 2 ) from gas to water. A trickle bed reactor (TBR) packed with a 0.1 percent by weight (wt%) Pd-0.01 wt% In/-Al 2 O 3 (indium and porous aluminum oxide) catalyst was evaluated to address this challenge. Catalytic activity generally increased with H 2 superficial velocity (0.65-29.6 m/h) and liquid (deionized water) superficial velocities from 14.8 to 26.6 m/h before decreasing at 38.5 m/h. This decrease corresponded to a change in flow regime and suggests that optimal TBR performance occurs at the transition from pulse to bubble flow. An optimal TBR activity of 19.5 ± 1.3 mg NO 3 -/min-g Pd was obtained; this is only ~18% of the batch reactor activity as a result of H 2 mass transfer limitations, but three to 15 times greater than activities obtained with previous flow-through reactors. Catalyst deactivation occurred in the TBR after 41 days of operation, motivating the need for improved fouling mitigation strategies. 2017

Catalytic Denitrification in a Trickle Bed Reactor: Ion Exchange Waste Brine Treatment

“…Past work suggests that mass transfer rates should increase with gas flow rate (Metaxas & Papayannakos 2006), which was observed only when the TBR was at the high end of pulse flow or in the bubble flow regime (12 × 14: U r = 28.12 m/h, 12 × 30: U r = 20.7 and 28.12 m/h). However, both catalysts demonstrated a flat or downward trend in mass transfer rate in the trickle and early pulse regimes in agreement with results from the aforementioned companion study (Bertoch et al 2017). This unexpected result may be related to the very low U g‐H2 values tested.…”

“…This unexpected result may be related to the very low U g‐H2 values tested. The mass transfer rates achieved in Bertoch et al (2017) are similar to those obtained in this study using the 12 × 14 catalyst; the highest mass transfer rate in Bertoch et al (2017) is c. 40% of the highest mass transfer rate obtained using the 12 × 30 catalyst. In a prior study, the oxygen absorption rate into water was independent of oxygen gas flow rate between 1.77 and 7.1 m/h (Goto & Smith 1975), which is higher than the range tested here.…”

“…The NO 3 – reduction activity in studies of direct NO 3 – removal from freshwater using a TBR with alumina‐supported catalysts is also shown. The TBR activity with 12 × 30 catalysts is similar to that for the aforementioned companion study (Bertoch et al 2017), and 1,200% better than a TBR with 1.7 mm 1 wt% Pd–0.3 wt% Cu/alumina catalyst (Pintar & Batista 1999).…”

“…In a companion study (Bertoch et al 2017), a TBR reactor was developed and evaluated for reduction of NO 3 – in freshwater; the influent NO 3 – concentration was considerably lower (70 mg/L) than in this study (15,000 mg/L); an alumina rather than AC support was used; and a single pass instead of recycle flow configuration was used. In contrast to results in this study, the greatest NO 3 – reduction activity for the TBR treating freshwater was obtained under pulse flow conditions.…”

Treating Water by Degrading Oxyanions Using Metallic Nanostructures

“…Werth and co-workers have worked on developing Pd–In catalyst-based trickle-bed flow reactors (TBR) for nitrate treatment of drinking water and IX waste brine. ,, Gas and liquid flow rates, catalyst metal loading, and catalyst pellet size were varied to optimize TBR performance. Catalytic activity in the flow reactor was ∼18% that of the same catalyst tested in batch mode, which was attributed to H 2 mass transfer limitations.…”