Optimization of PW Plant

Clean, disinfect and rinse the RO membrane properly and on a regular basis to maintain the required PH . Check and adjust water temperature and pressure to match membrane specifications. You may also need to add pre-filtering stage, lower than 5 micron level you have now. Your RO membrane may not be the proper or right type for the available water conditions in your area???

Filtration is like a car.

If you want the best filtration, it will be expensive, up front, and expensive to maintain.

This is RO. It will only work properly if maintained properly and not overworked.

Operate the system per the manufacturer's recommendations. Cut corners and you will get poor performance.

You still get what you pay for.

Do Raw water analysis regularly. Consider to provide suitable dosing system to reduce scaling of membrane. Cheek and regulate the operating valves for its optimum performance regularly.

Hi Bashir,

It is generally accepted that RO is currently the most cost effective method of purifying water. This depends on your specific situation (as if you had waste heat or very cheap fuel source, other methods such as MSF or MED may be more cost competative).

With RO, the technology limit is the point where the reject water (brine or waste) is so concentrated with salts, any further concentration (or brine reduction) will simply crystallise salts within your system (and you don't want that). So you physically can't decrease the rejection flowrate. It is necessary for the system to operate correctly.

This is assuming your system is operating to it's optimum performance. And I'd need alot more information to assist you with that.

Basically it's a trade off. the higher performaing a system, the more cleaning is required to maintain that performance. This has the effect of reducing membrane life, and the water quality peroduced. As always ... higher performance = higher operating costs & reduced asset life.

But I gather from your question you are trying to reduce waste water. Have you considered looking at the pre-treatment to the plant. You have a multimedia filter, a Softener and carbon filter. Each of these filters requires regular backwashing, to maintain performance. In my experiance significant water savings can be made by looking at the duration & frequency of the backwash of these filters, and comparing to the operating performance. This is because they are almost always installed and commisssioned according to manufacturers (generic & conservative) recomendations. Optimise these parameters and you'll save alot of water.

In addition there are more effective technology that could replace these assets all together.

The optimum method of filtering suspended solids for RO pre-treatment is Micro (or Ultra) filtration. Thes plants can have up to 95% water efficientcy (only 5% waste). But they are expensive, and especially when you already have existing plant onsite. Unless you are paying serious amount for water, it might be hard to justify upgrade.

The Carbon Filter can be replaced with SMBS (or SBS) dosing for neutralisation of Chlorine in the feed water. This is far better (than carbon vessels) for many reasons including water efficiency.

The softener may or may not be actually needed depending on your specific water chemistry, and the antiscalant you are using for prevention of scale. Often this can be managed by a higher grade antiscalant & manipulation of the pH (to avoid scaling) - again depends heavily on your specific water chemistry.

You mention, plant optimisation. In my discussion above, I've assumed this is for water savings. Are you (or have you) considered the overall plant cost (including running costs, asset maintenance and replacement costs etc). Work I've done recently has made major cost savings taking a wholistic view of the plant. 5-10 years ago, plants were desinged to protect the membrane (at all cost). Nowdays the membrane cost has reduced significantly, so by accepting some comprimised with regard to membrane life can lead to major savings elsewhere.

Hope this helps.

Anthony

Is the second stage reject blended with the incoming feed as a supply to the first stage? If not, why not?

What are the infeed raw water characteristics, in terms of Hardness, silica, TDS, SS etc? What is your source of water?

Hi, Thanks to all.

I am unable to attach the lay out drawing and Raw water test report as most of you want to check. We are using under ground water as our raw water and at first we add Cl with a automatic dosing pump then it goes to underground water tank, then over head water tank then PW plant for treatment.

Just few data: pH: 6.41, Turbidity: 0.45 NTU, CO2: 62 mg/L, Alkalinity: 120 mg/L, Chloride: 19 mg/l, Total Hardness: 96 mg/L, Total Iron: 0.15 mg/L, Mn: 0.04 mg/L, Nitrate-Nitrogen: 0.3 mg/L, Fluoride: 0.29 mg/L, TDS: 234 mg/L, Arsenic: 0.002 mg/L, Sulphate: 1 mg/L, Silica: 70.2 mg/L, Mg: 10.83 mg/L, Copper: 0.04 mg/L, Zinc: 1.98 mg/L.

I can give you all the data as per your requirement but I need your e-mail ID or the procedure that I can attach drawings, file etc.

As per post number 8, the silica content of your water seems to be on the abnormal side. Silica is detrimental to R.O membranes & needs ban from entry into R.O systems. In that case you have go for prior removal of silica prior to R.O feed.

Please confirm with the membrane people, if they could install a nano filter prior to R.O. You can conduct laboratory trails with the membrane people who have supplied the systems to you.

Another simplest way is to dose mild quantities of EDTA solution & dilute lime along with chlrine so that the silica part can be precipitated & settled in the clarifier.

Hi,

How to use EDTA solution? I need some clarification. We are using water for pharmaceutical use, so the question is, does EDTA is OK for PW plant?

Simply dose with commercial grade Ethylene Diamine Tetra acetic acid- Tetra sodium or disodium salt as one to two gram per litre solution. The EDTA salt will form a chelate complex with silica/ silicate & settle down as a precipitate. Addition to EDTA disodum salt, you can also dose alum & lime solution in feeble quantities which can form Calcium silicate complex & settle down.

This you can confirm using a jar test prior & after the addition of the above above chelate complex agents, compare with untreated water sample for silica content & conclude for your self.

No additional dosing for antiscalant. Please re-view my first post and just add Cl dosing at the start of withdraw the raw water.