The operator of the RO unit that operates higher than 500 PSI is noticing low product water flow rate and high salt rejection flow rates caused by membrane compaction. What can be done to correct this problem?

•Begin cleaning of the membranes with citric acid

•Replace membrane elements when product water flow rate becomes unacceptable

•Immediately backwash the units, then clean with sodium tripolyphosphate

•Clean the membranes with sodium hydroxide first, flush the unit, then clean with sodium hypochlorite

Even under ideal conditions (pure feedwater, no fouling), there is a decline in water flux over time. This condition is known as what?

Membrane compaction

Pressure is applied to water at a higher PSI than its osmotic pressure and water flows from a more concentrated solution to a less concentrated solution is a definition of what?

Reverse osmosis

The percentage of feed flow recovered as product water is known as what?

Recovery

Calculate the percent recovery, %, of the RO treatment plant using the data given below:
Feedwater Flow = 2.95 mgd
Product Flow = 2.5 mgd

85%

What is an advantage of operating RO units in a 'Christmas Tree' layout?

Feedwater recovery rates of 85% are possible

Calculate the percent of mineral rejection for the RO plant using the following data:
Feedwater TDS = 2,200 mg/L
Product water TDS = 150 mg/L

93.2%

What increases the rate of hydrolysis of a cellulose acetate membrane?

Increased feedwater temperature and pH

Which statement about flux is true?

As feedwater temperature increases, flux increases

What is a limiting factor of using electrodialysis for demineralization of municipal water supplies?

Ineffective at removing organic material

Brackish water contains between 1,000 and 10,000 TDS and most can be found where?

•Inland reservoirs

•In groundwaters

•In the Gulf of Mexico

•Along the Mississippi River

What purpose does sodium hexametaphosphate serve in RO operation?

It is used to control scale on the membranes

In electrodialysis, the accumulation of particulate matter increases the electrical resistance of the membrane, damaging or destroying the membrane. What steps could the operator take to prevent this condition?

Add acid to the concentrate water stream to maintain a negative Langelier Index

What is the condition called when an operator of an RO system concentrates the brine to a degree that allows minerals to precipitate on the membrane surface?

Concentration polarization

What is an important operating guideline of a reverse osmosis system?

The average membrane flux rate

A reduction of flow through a membrane due to fouling can be remedied by what?

Backwashing and cleaning