Slowsand Filter on Groundwater source
Slowsand Filter on Groundwater source
(OP)
I recently reviewed a set of plans for a slowsand filter. The source water is ground water and is not under the influence of surface water. I am concerned with the use of slowsand with groundwater. I do not believe that a schmutzdecke will form. Has anyone heard of using slowsand on groundwater. What concerns would you have. Thanks for any information you can provide.
Confused reviewer
Confused reviewer





RE: Slowsand Filter on Groundwater source
Presumably, groundwater is acceptable as is without filtration. If the groundwater contains suspended matter, then the well should be repaired or replaced.
RE: Slowsand Filter on Groundwater source
RE: Slowsand Filter on Groundwater source
A few observations. Pretreatment has to be considered very carefully when using RO. There are all sorts of things that will foul RO membranes.
Without knowing anything further, I would guess that the black material is oxidized sulfur. If it is sulfur, then the usual course of water treatment is an aearation step to oxidize the sulfur, chlorination to oxidize the remaining traces of sulfur, and then filtration.
You may want to suggest an alternatives to RO. Water softeners are commonly to remove radon for example. Not sure that an RO system is necessary. Whatever is in the water analysis will be the deciding factor.
RE: Slowsand Filter on Groundwater source
Bimr raises a valid question: Why choose RO for gross alpha reduction? RO is typically viable when TDS reduction is required in combination with high gross alpha levels.
High gross alpha readings are typically caused by either radium or uranium isotopes (but not radon, which is a volatile gas). If radium is the source, then a simple cation exchange resin system operating in the sodium form is highly effective. If uranium isotopes are the source, then a simple anion exchange system operating in the chloride form is highly effective. If the source is a combination of both, then cation followed by anion will work.
I agree with Bimr. You need to look at the total water chemistry and weigh all of the options. Try to get outside advice from someone other than the RO system vendor. Your state's drinking water approval authority should be able to comment on technologies and experiences at similar sites.
S. Bush
www.water-eg.com
RE: Slowsand Filter on Groundwater source
Tanisdad
RE: Slowsand Filter on Groundwater source
Some possible sources for “black” fouling are: metal oxides such as manganese oxides, sulfate reducing bacteria, and naturally occurring organic matter which can be gray to black in color.
You cannot proceed with a pretreatment scheme, until you know precisely what you are dealing with. Once you have identified the contaminants, then take your problem to an experienced professional engineer. Since the RO vendor has not exhibited these qualifications, thus far, I suggest you look elsewhere. There are several consulting firms in the U. S. who specialize in membrane-based water treatment. Peter S. Cartright is one of these firms that has been around for 25+ years. Although I have not used them personally, I believe they could help you. A search of the Internet may turn up others as well. The key to unbiased assistance is to find an independent consultant who is not an equipment vendor.
S. Bush
www.water-eg.com