Ammonia Recovery with Sweeping Gas Membrane Distillation: Energy and Removal Efficiency Analysis

Abstract

Membrane distillation (MD) is a thermally driven phase separation process. In sweeping gas membrane distillation (SGMD), an air stream is utilized to capture and remove volatile compounds on the sweeping gas stream. SGMD is an attractive, compact, and efficient process to replace conventional ammonia removal processes such as air stripping or to reduce energy consumption related to nutrient removal of existing processes in wastewater treatment plants. In this study, we present an energetic analysis of humidity-assisted SGMD to remove ammonia from wastewater. We developed a numerical simulation to optimize the design and operating conditions (inlet feed temperature, air flow rate, brine flow rate, and humidity level of the sweeping gas stream) of the process. We show that operating under multiple stages in series the process can achieve an ammonia removal rate greater than 90% at high air-to-water ratios while maintaining low energy consumption. SGMD is a promising way to separate ammonia from wastewater compared to conventional ammonia stripping processes.

Understanding Ammonia and Water Transport in Direct Contact Membrane Distillation toward Selective Ammonia Recovery

“…As illustrated in eq 8, the mass transfer for ammonia molecules can be considered as transition diffusion, involving both molecular diffusion and Knudsen diffusion, wherein ammonia molecules collide with each other as well as the pore wall. 15,53 In addition to the molecular diffusion term and the Knudsen diffusion term present in eq 8, our fitted equation includes a constant, denoted as C. In our experiments, the values of C were found to be specific for different concentrations of NH 4 Cl: −8.722 × 10 7 kg −1 •m −1 •s•mol for 50 mM NH 4 Cl and −1.772 × 10 7 kg −1 • m −1 •s•mol for 170 mM NH 4 Cl. We hypothesize that this constant C is likely related to the interaction between ammonia molecules and water molecules within the air gap of the membrane.…”

“…The ammonia mass transfer coefficient in the MD process is calculated based on the ammonia flux and the ammonia concentration gradient between the MD membrane: normalk normalA = normalJ normalA / ( C Af − C Ac ) where k A is the ammonia mass transfer coefficient and C Af and C Ac are the ammonia concentrations at the feed side and the collector side, respectively.…”

“…where k A is the ammonia mass transfer coefficient and C Af and C Ac are the ammonia concentrations at the feed side and the collector side, respectively. The water mass transfer coefficient in this MD process is calculated based on the water flux and the water vapor pressure gradient between the MD membrane: 15 k J /(P P )…”

Solvent-driven aqueous separations for hypersaline brine concentration and resource recovery

“…By tuning the membrane pore size distribution and porosities, FO, nanofiltration and ultrafiltration have been used to remove trace amounts of dissolved organic solvents, using a variety of counter-solvents as draw and osmotic agents [22,33]. Variants of conventional MD have recently been investigated for the recovery of low molecular weight organics, such as ammonia [110][111][112]. Pervaporation is also an effective means to remove trace organics from an aqueous solution [113][114][115].…”

Membrane Distillation–Crystallization for Sustainable Carbon Utilization and Storage

“…Sweeping gas membrane distillation (SGMD) is a less common MD configuration, in which flowing air is swept across the distillate side of the membrane. SGMD is advantageous for heat utilization efficiency because convective heat losses into the distillate stream are minimized. , This is an important consideration because the duration of active mass transfer, or the feed solution concentration rate, in the MDC process is limited by the amount of heat available in the system.…”