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Example questions

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• My feed TDS is 1500 mg/L and rejection is 99.4% — what is the permeate TDS?
• Feed TDS is 35,000 mg/L and permeate TDS is 210 mg/L — what is the salt rejection?
• Feed TDS is 35,000 mg/L and permeate TDS is 210 mg/L — what is the salt passage?
• Feed is 1000 m³/day, permeate 400 m³/day and concentrate 610 m³/day — does my water balance close?
• Feed flow is 1000 m³/day at 45% recovery — what is the concentrate flow?
• Feed TDS is 1500 mg/L at 25 °C — what is the osmotic pressure?
• Feed 100 m3/h at 45% recovery, 55 bar feed pressure and 80% pump efficiency — what is the specific energy?
• Recovery is 45%, feed TDS is 35,000 mg/L and feed flow is 100 m3/h — what is the concentration factor?
• pH 7.2, temperature 25 °C, TDS 35000 mg/L, calcium 400 mg/L as CaCO3 and alkalinity 150 mg/L as CaCO3 — what is the scaling risk?
• My feed flow is 1000 m³/day and permeate is 400 m³/day. Is this reasonable?
• What information is missing from my RO calculation?
• What should I check next in my RO calculation?
• My UF feed is 40 m3/h at a design flux of 55 LMH — what membrane area is required?
• UF feed is 2.5 bar, concentrate 2.2 bar and permeate 0.2 bar — what is the TMP?
• Design flux was 55 LMH and we now measure 41 LMH — what is the flux condition?
• NF feed is 50 m3/h at 1500 mg/L, 75% recovery and 95% rejection — what is the permeate TDS?
• NF needs 45 m3/h of permeate at 30 LMH — what membrane area is required?
• My IX unit treats 10 m3/h, resin capacity is 0.9 eq/L, bed depth 0.8 m and load is 2 meq/L — what is the resin volume?
• How much NaCl do I need to regenerate an IX bed after 40 m3 of breakthrough at 2 meq/L, using 10% brine?