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

• Two SWRO pre-treatment processes were operated in parallel and compared.
• The pre-treatment pilot plant consists of dual-media filtration and ultrafiltration.
• UF achieved almost 100% algal removal while DMF reached algal removal of only 60%.
• LC-OCD confirmed that both pre-treatments achieved low NOM removals.
• The fraction most efficiently removed was biopolymers (DMF = 18% and UF = 41%).

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 ≈ 0.9 mg C L− 1), and LC-OCD technique revealed that the DOC is mainly composed of humic compounds with size range of 0.3-10 kDa and low molecular weight (LMW) substances smaller than 0.3 kDa (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.