Performance Assessment of Microfiltration Membranes for Backwash Water Reuse from Sand Filters

Area of Science:

• Environmental Engineering
• Water Treatment Technologies
• Membrane Science

Background:

• Utility-scale water treatment plants generate significant volumes of backwash water.
• Recycling backwash water is crucial for water conservation and resource management.
• Limited research exists on microfiltration performance using actual backwash water from diverse sources.

Purpose of the Study:

• To comparatively assess the performance of three distinct microfiltration (MF) membrane modules (spiral PVDF, capillary PP, capillary α-Alumina).
• To evaluate their efficacy in treating backwash water from surface water (SW) and infiltration water (IW) treatment plants.
• To analyze trade-offs between hydraulic performance, contaminant removal, and treatment costs.

Main Methods:

• Filtration cycles of 168 hours were conducted using three MF membrane modules (M1, M2, M3).
• Performance metrics included permeate flux, turbidity removal, dissolved organic carbon (DOC) removal, and total microorganism count (TNM) reduction.
• A simplified cost analysis was performed over two filtration cycles.

Main Results:

• Module M1 achieved the highest median TNM removal (97%), outperforming M2 (84%) and M3 (70%).
• Module M2 consistently provided the highest permeate flux rates across both water types.
• DOC removal efficiency varied by water type, with M2 excelling for IW and M1 for SW backwash.
• Ceramic membrane M3 showed the most variability in performance.
• Logarithmic models accurately predicted early-stage permeate flux (R²: 0.60–0.99).

Conclusions:

• Microfiltration is a viable technology for treating utility-scale water backwash, contributing to water reuse strategies.
• The choice of membrane module (M1, M2, M3) significantly impacts performance based on specific water quality and treatment objectives.
• While treatment costs for backwash water are higher than for raw water, it represents a valuable potential source amid increasing water scarcity.