[QUOTE=Tellie;480060]Actually Jim, unless I'm missing the math approach Minggat is using, typical boat type watermakers are roughly a ten to one ratio. Usual brine discharge will be nine gallons to one gallon of product water made. Commercial
RO systems use multiple membranes thus gaining multiple passes of the same concentrate over many membranes before being discharged.
One could reverse a boat watermaker system and dump the product water overboard
. Then retain and re-cycle the brine discharge in the tub passing it again through the watermaker several times to achieve higher concentrations of salinity.
OK, I gave a sloppy response.
99% reject pertains to the salts. So what is rejected by the membrane (concentrate) then is going to leave the pressure vessel in the brine flow. While the recovery in small pleasure craft units may be less than 40%, 10% sounds way low. But, for purposes of this conversation, using the brine to make a seawater spa is not so wonderful.
I don't think Tellie was trying to say reverse the RO, but rather where the different streams are going. Thus capturing the brine. I would NOT recycle the brine though.
As far as multipal membranes to get multipal passes goes,.. well, sort of. Multipal membranes in a single
pressure vessel (typically 40 ft long with 6 membranes inside). I think it would be more accurate to say that the feed becomes more saline after passing thru each membrane, but it would not be ready to be called concentrate just yet because it is diluted with the feedwater. But I don't want to debate word choices.
SWRO designs just don't not bother with multipal passes systems anymore. Seawater is too plentiful for that. There are lots of non seawater applications where the actual recovery rate is 98 + % of the feedwater flow. They will take the reject of a first stage and feed it directly to the second stage.
Bottom line. Don't bother using RO brine stream to fill the spa.