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Waste Water RO (WWRO) plants operate under significantly different conditions to those of SWRO and BWRO plants. The main difference lies in the ability of the bacteria to reproduce rapidly, and the presence of nutrients.  In WWRO we have a combination of bacteria able to reproduce rapidly, and a high concentration of nutrients: a combination that does not allow the control of bio-fouling without the continuous presence of chloramine in contact with the RO membranes.

Current WWRO technology is based on the presence of chloramine because UF, or MF, pretreatment is unable to remove dissolved nutrients in the form of Assumable Organic Carbon (AOC).

Chloramine in the RO permeate significantly diminishes the UV transmittance and reduces the effectiveness of advanced oxidation processes (AOP) treatment.  Chloramine slowly damages membrane flux and within a relatively short time, almost 80% more pressure is required to maintain the designed permeate production.

The addition of significant amounts of harsh chemicals for period CIP and CEP cleaning cannot be avoided with UF or MF pretreatment. Ultrafiltration pretreatment is expensive from both Capex and Opex aspects, due to the costs of chemicals and of membrane replacement. Significant manpower is required for the maintenance of complicated equipment.

Our approach is based on sand filtration, without chlorination, where a large amount of biological life consumes AOC and produces an extracellular matrix that absorbs suspended and dissolved matter. This pretreatment process does not requires the addition of coagulant or flocculant.

This pretreatment technology cannot be implemented without controlling (dehydrating) bacteria on the RO membranes by high osmotic pressure shock, which is actually Drawing Solution (DS) that transfers the Reverse Osmosis process to Forward Osmosis.  A short injection of DS increases the osmotic pressure from about 2 bar to 60 bar (7% TDS) for few seconds, a few times day. This injection provides several short changes in the desalination process:

  •  Bacteria dehydrates by 'salt curing'
  • Forward osmosis provides membrane backwash
  • Sharply increased shearing velocity
  • Scaling proto-crystals dissolute by the FO permeate backflow and the high ionic strength of the DS
  • Particles are removed frequently, before a strong van-der Waals interaction is created with the surface

In addition to the RO-FO osmotic processes presented above, the new technology applies a series of pulsed water strokes, simultaneously with the osmosis backward flow, causing superposed membrane directional shaking and detachment of fouling.  The pulsed water stroke is provided by a water stroke generator as several momentary sharp changes in the brine and permeate gauge pressure, during pumping of the permeate flow into the permeate enclosure by energy included in a pulse-wise discharge of brine flow. The pulsed water strokes ideally induce resonance in the membrane drums. Permanent oscillation of membrane drums prevents quorum sensing - the formation of bio-film - and prevents the attachment of particles to the membrane.

Main Topics to be discussed: 

Waste Water RO (WWRO) involves the rapid reproduction of bacteria and a high concentration of nutrients: not allowing for control of bio-fouling without the continuous presence of chloramine in contact with the RO membranes.

Current technology includes chloramine because UF/MF pretreatment is unable to remove dissolved nutrients in the form of Assumable Organic Carbon (AOC).

Chloramine in the RO permeate significantly diminishes the UV transmittance and reduces the effectiveness of advanced oxidation processes (AOP) treatment whilst slowly damaging membrane flux requiring almost

Presenters

Dr. Boris Liberman

VP & CTO Membrane Technologies

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Dr. Liberman joined IDE in 1993, and held various position in the company prior to assuming his current position as VP and CTO for membrane technologies. As CTO he leads the company's R&D activities in the RO field. Dr. Liberman is responsible for several industry technological breakthroughs including the Pressure Center Design, the patented Direct Osmosis Cleaning enabling membrane cleaning without stopping the RO train, green desalination allowing desalination without the use of chemicals, and 16” membranes in a vertical array. He is extremely well known and respected in the desalination field and regularly speaks at leading industry conferences and events. Dr. Liberman holds a B.A. and M.S from the Civil Engineering Institute Rostov-on-Don, USSR and a Ph.D. from the Institute for Scientific Research in Water Supply, Moscow.

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