Comparison of DMF and UF pre-treatments for particulate material and dissolved organic matter removal in SWRO desalination

Abstract

Dissolved air flotation (DAF) followed by dual-media filter (DMF) and ultrafiltration (UF) membrane pre-treatments were run in parallel in a seawater desalination pilot plant in order to compare performances in terms of particles and dissolved organic matter removal. Results indicate that both processes exhibit a high elimination of particulate and microbial contaminants. Both treatments successfully maintain the water turbidity to values <0.1 NTU and SDI15 <2. UF, however, fulfills its purpose by securing almost 100% elimination of algal content while DMF demonstrates an average algae removal of only 60%. Raw seawater shows very low dissolved organic matter content (DOC≈0.9mg C L−1), and LC-OCD technique revealed that the DOC is mainly composed of humic compounds with size range of 0.3-10kDa and low molecular weight (LMW) substances smaller than 0.3kDa (47% each). LC-OCD analyses of the DAF+UF and DAF+DMF filtrates give a proportion among the constituents almost constant. Biopolymers in raw seawater were partially removed by both pre-treatments tested (41% removal in UF permeate and 18% removal in DMF filtrate). Lower impact in LMW (6% removal by UF, 1% removal by DMF) and humics (removals of 8% by UF and 2% by DMF) was observed.