Effect of system variables and particle size on physical characteristics of air sparging plumes

Abstract

Air was injected through a well in a thin transparent tank filled with saturated glass beads to study how the size and air saturation of air sparging plumes are affected by particle size and gradation; operational parameters such as injection pressure, well depth, injection pressure pulsing; and well outlet configuration. V-shaped air plumes with an apex between 408 and 608 were obtained for all tests. The air pressure required to initiate sparging agreed closely with the sum of the air entry pressure and the hydrostatic pressure, with higher initiation pressures required in the fine and wellgraded beads. Higher air flow rates and air saturations were obtained in coarser beads at a given pressure, and the variation in flow rate was consistent with estimated air permeabilities. Peak average air saturations were 28-56% for the coarsemedium beads, 10% for the well-graded beads, and 8% for the fine beads. Air saturation and the radius of influence increased modestly (<40%) as the normalized injection pressure exceeded 0.1. Radius of influence increased by approximately a factor of two as the well depth increased, but leveled off once the ratio of radius of influence to well depth reached 0.60-1.05. Pulsing of injection pressure had no effect on the initiation pressure, air flow rate, or air saturation, but increased the size of the air plume and the radius of influence slightly (<15%). Well outlet configuration had only a slight affect the radius of influence (<10%), air saturation (<10%), or air flow rate (<12%). Dye testing showed that water surrounding the air plume circulated during continuous and pulsed sparging. However, pulsed sparging resulted in greater and more defined circulation of water within and adjacent to the air plume, which should reduce mass transfer limitations during sparging.

Effect of Temporal Changes in Air Injection Rate on Air Sparging Performance Groundwater Remediation

“…This can be explained by the air channel “memory”: during subsequent sparging cycle, trapped air provides less resistance to flow than the original water filled pores. Thus, an initial higher injection pressure lowers the entry pressure in the following cycles (Baker and Benson ).…”

“…Previous studies pointed out pronounced advantages applying AS in a pulsed operation rather than using it in a continuous operation mode (Shah et al 1995;Johnson et al 1999;Suthersan 1999;Kirtland and Aelion 2000;Heron and Gierke 2002;Yang et al 2005;Baker and Benson 2007;Balcke et al 2009). A field scale study, reported by Heron and Gierke (2002), showed that applying AS in a pulsed mode accelerated the time weighted average mass removal by 40% to 600% (depending on the "aggressiveness" of the pulsing).…”

“…This can be explained by the air channel "memory": during subsequent sparging cycle, trapped air provides less resistance to flow than the original water filled pores. Thus, an initial higher injection pressure lowers the entry pressure in the following cycles (Baker and Benson 2007). We conducted preliminary experiments and observed that the characteristic time of reaching steady state in flow in the experimental tank after initiating air sparging was T ∼ = 20 [s].…”

“…In the third stage, upon reaching steady state conditions, contaminants within the MTZ, in the immediate vicinity of the air channels, are rapidly removed, while beyond this zone, contaminant diffusion from the bulk toward the MTZ becomes the limiting factor for the remediation process (Elder and Benson ; Braida and Ong , ; Kirtland and Aelion ; Peterson et al ; Yang et al ; Baker and Benson ). Mei et al () showed that in the third stage, water motion within the ZOI is negligible.…”

Bounds to Air‐Flow Patterns during Cyclic Air Injection into Partially Saturated Soils Inferred from Extremum States

“…Many studies have demonstrated improved air distribution using pulsed (periodic) air injection below (Shah et al, 1995; Johnson et al, 1999; Kirtland and Aelion, 2000; Heron et al, 2002; Yang et al, 2005; Baker and Benson, 2007; Balcke et al, 2009; Ben Neriah and Paster, 2017) and above (Rathfelder et al, 2000) the water table. The positive effects of step‐pulsed or harmonically changing air‐injection rates have been attributed to enhanced air mixing, which in turn increases the contact of the injected fresh air with the volatile contaminants (Ben‐Neriah and Paster, 2016), and to the reduced restrictive effect of preferential flow and fingering on the air's horizontal spread (Thomson and Johnson, 2000).…”