Flux optimization in passive membrane systems with air sparging and relaxation

Abstract

Traditional membrane filtration plants for drinking water require uninterrupted electricity for pumps and fouling control, thus making it unsuitable for small/rural communities and developing countries. Gravity driven passive membrane filtration systems can be a possible solution to this problem. Previous studies demonstrated that frequent air sparging is beneficial to maintaining a high permeate flux in passive membrane systems. Previous studies also reported that forward flushing after relaxation is also beneficial to maintaining a high permeate flux. Air sparging is an alternate solution to forward flushing after relaxation and considered in the present study. Four different air sparging rates were considered: no air sparging, continuous air sparging, 5 min/day and 5 min/2 days. Periodic air sparging significantly increased the steady-state permeability (0.39±0.003 B/Bi and 0.37±0.007 B/Bi for 5 min/ day and 5 min/2 days respectively) compared to conditions with no air sparging (0.21±0.006 B/Bi). The highest permeability (0.56±0.036 B/Bi) was achieved with continuous air sparging. Three different relaxation periods prior to periodic air sparging (5 min/day) were tested (1 hr, 4 hrs and 8 hrs). Relaxation prior to periodic air sparging increased the steady-state permeability (0.47±0.012 B/Bi and 0.41±0.023 B/Bi for 1 hr and 4 hrs relaxation period respectively) compared to condition without relaxation prior to air sparging (0.39±0.003 B/Bi). However, lower permeability was observed when a longer relaxation period (0.25±0.002 B/Bi for 8 hrs relaxation period) was considered.