Surface Water Treatment, high color

[pgustavson]

Hello,
I am working on a system that draws surface water from a creek in a redwood forest. The source will only be used for utility water; however, it is the color of medium tea and contains a large amount of floc or other solids even after a succession of 5-, 1- and 0.35-micron cartridge filtration.

As it stands, the system is overly complicated for the staff to run, and they do not want additional chemicals or other consumables integrated into the system. In fact, they want the removal of the filtration units due to frequent clogging. A company is proposing a 2.5 cubic foot sand filter, with chlorination in a storage tank as the entire treatment process; however, I do not feel entirely confident in that recommendation.

An abbreviated chemical analysis was performed and here are some of the main points:
Iron: 0.84 ppm
Manganese: 0.015 ppm
Corrosivity (Langlier): -2.6
pH: 7
Tannin and Lignin: 0.28
TDS: 79 mg/L

If tannins are the main culprit, we can live with that and not use ion exchange. I know the iron concentration is over the secondary MCL; however, we are not necessary trying to get it to drinking water standards. If iron is to be removed, would a greensand filter be appropriate? I am interested if anyone has a different approach/evaluation and other ideas on treatment methods.
Thank you for your time!

 

[itsmoked]

What's the flow rate needed?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[bimr]

You will need some type of clarification process. Alum is a chemical commonly used for this application and it will remove the color which is probably seasonal.

 

[ashtree]

It will be difficult to treat to any sort of standard without the use of additional chemicals or some degree of complexity. Can you post the whole chemical analysis results?

Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

 

[MFJewell]

Look at an Actiflo high rate, modular clarifier.

 

[bimr]

Actiflo technology is more appropriate on applications where 95% removal of high (10,000) TSS is required than applications for low solids waters where 100% removal is required. Actiflo is also not likely to be approved for a potable water application.

 

[MFJewell]

I agree, you won't get 100% removal, but we used it pretty well treating Mississippi river water to get steam cycle make-up quality water. It was the first step in the process. We also had disk filters and RO to get quality where we wanted it. I also might be remembering incorrectly, it may have been TSS, not TDS that was our main factor for clarifying.

 

[bimr]

Yes, it is for TSS. Some of the Mississippi River water treatment plants have two clarifiers in series, the first one being a roughing unit.

The use of alum is crucial or the removal of color.

 

[pgustavson]

Thank you for the replies. I have been out in the field for the last few days, so I apologize for not responding sooner.

The intake pump operates in the 50-60 gpm range, but use is only very sporadic (ie washing trucks). A 10,000 gallon tank provides storage of the treated water.

As for the full chemical analysis, other than nutrients (ND), calcium (4 mg/L), magnesium (2 mg/L), and alkalinity (15 mg/L) there were no other analytes.

The tannin portion of the color is not necessarily a concern for this system. I am mainly interested in treatment options for the metals contribution to color and solids. Alum addition, while potentially effective, would likely not work in the operational scenarios that this system experiences (limited annual budget, short staffing, sometimes no staffing, and sporadic untrained use). Without any pilot tests, it's difficult to be definitive, but is greensand a valid option for this surface water?

Also, with the corrosivity high and alkalinity fairly low, it is possible that the water is corroding some of the piping in the system...leading to higher iron concentrations. Though I find it strange that the pH is 7. Any thoughts on this?

The goal is for a very simple system that doesn't have to treat to potable standards, but with a finished product that isn't quite so objectionable.

Thank you again for your time!

 

[ashtree]

Given that the OP is looking for something that is simple and does not require high performance, maybe river bank slow sand filtration might be adequate for the job.

Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

 

[QualityTime]

I made a correction to my post, now it should read as follows

Use of potassium permanganate or higher doses of chlorine is required for iron removal. The time it will take is pH and water temperature dependant. Alum is the easiest way to get rid of the turbidity and color. You will need to add alkalinity to the water if you plan on using alum. Your raw water alkalinity is very low to begin with. Becasue the alkalinity is so low the water is unstable and pH will fluctuate. The water is corrosive at a pH of 7. Your Langlelier Index says that. People wrongly equate a pH=7 (neutral) to be non corrosive. This is what happened in Flint Michigan

Even if you use greensand filters to take out the iron you need to recharge the greensand filters. For that you will be using potassium permanganate

 

[bimr]

If all that you are doing is washing trucks with this water, use a cartridge filter. You may need to change the cartridges frequently. You will need to increase the pH of this water to eliminate the corrosion.

 

[hydrae]

You are looking for Low cost easy to maintain
do you have land?
A slow sand filter is low operating cost and easy to maintain but you need a fair amount of land
50 gpm will require 1000 square feet for drinking level treatment, double that for an uninterrupted supply during cleaning operations, which can take a day or so for the filter to ripen
May not remove all the ferrous iron though. though aeration can convert the ferrous to ferric.
Slow sand filters work well with forested streams except during heavy storms, although sometimes they can fail or take a long time to ripen if the water is too clean or too cold. If that is the case, a little seeding may be needed from another slow sand filter.

It sounds like you do not need 50 gpm continuously though, if you can get by with 2.5 gpm average, that can be set up in a 8ft dia x 8ft 2500 gallon plastic water tank for the slow sand filter and a pond pump to move the water from the filter tank to the storage tank.

 

[Teju100890]

Recommended flow rate for maximum filtration performance is :5GPM For more information please visit this website:

http://watersedge.co.in/