Hey guys, I been working on a project, and I think I have it almost figured out, but would love some feedback.
As everyone is now well aware, things are VERY bad in western NC. I believe I have a cheapish solution for water purification.
The problem:
People need water. I have witnessed literal tons of water being hauled in from donations. I estimate around 20 gallons of diesel would be required to haul 1 ton of water from east TN to the nearby towns in WNC. That equates to roughly 1 gallon of diesel per 25ish gallons of water. The real cost lies in the cost of water by the case at the grocery store. It costs 80$ for the diesel, but 600$ for the water. Sounds inefficient to me.
The solution:
1 IBC tote as a 250 gal reservoir
1 5gpm diaphragm pump
3x 4040 membranes and housings
Tubing and fittings to pipe it all together
Total: ~1k-1300$
I estimate around 2gpm with this setup, which would take ~2.5hr to fill the IBC tote completely. The pump would require around 200w, which puts the energy requirements down to less than a gal of gas per hour through a generator.
My plan was to have a 55gal drum to pump river or dirty water into as a buffer, and have the diaphragm pump draw from the drum through the membranes into the IBC tote.
Now, we have clean water, now what? I planned to use a cheap bottle filler pump to draw from the tote into a 1 gallon spout pouch which can be had as low as 0.91$/unit. Still kinda expensive when compared to 1.16$/gal purified water, but you can transport way more of those up a mountain than you can gallons of water.
Anyone have any thoughts, critiques, ideas that I have not considered?
Here are some pictures for reference. Pardon my drunken napkin scritchins!
Id pre filter your water if you want any kind of decent life span on those membranes, theres a reason most over the counter RO filters use a carbon and sediment filter before the membrane itself
Id also run a test to see what pressure is required to get permeate on those membranes before commiting to a pump, 70 psi might be enough but its hard to say without running trials
You could also run something that low of wattage on solar if you really wanted to
It probably depends on what is in the water in the first place. Flood waters are generally considered to be toxic. I dont think a filter would remove everything. You could make a sand filter, carbon if you had it, and then distill it as a final step.
Depending on what your potential contaminants are, hollow fibre membranes will run much faster than RO membranes, and are an effective filter for bacteria, viruseses, etc, to below 0.2 um, and can produce drinkable water.
They also don’t need high pressure to operate - some have a maximum operating pressure of 30 psi. I’d suggest a centrifugal pump, not a diaphragm.
It’s the same technology used by most backcountry water purification systems.
However, they do need to be back flushed occasionally if you want them to continue to work without clogging.
If nothing else, they’re an effective pre-filter for before your RO system.
It will be incredibly turbid for one. Ton of suspended sediment. High amount of biological contamination including E. coli from septic systems getting washed out. Heavy metals are a safe bet as well.
If suspended solids and biologicals are the primary concern a hollow fibre of 0.2 um or smaller will remove the “will immediately make you sick” stuff.
As far as I know, there aren’t any that will remove heavy metals, but they will definitely remove particulate/turbidity, bacteria, and viruses.
A single 4040 module rated to 0.02 um - an order of magnitude smaller than a “sterile” filter - should produce something like 100-300 gph per element.
They’re available from companies like MSR for personal sized versions, and DuPont/3M/Dow and a thousand other manufacturers or white labellers for 1812, 2540, and larger sizes. They could even be fed in gravity flow configuration so a pump isn’t necessary.
I wouldn’t be surprised if local(ish) water supply companies had a few on hand, they’re a pretty common technology for water filtration.
A carbon filter after the HF should remove most or all of the trace hydrocarbons and other contaminants that may make the water less palatable to drink than it might be otherwise.
HF is what I’d reach for if I were in a situation where I needed to be confident that my water supply wasn’t going to make me sick, and needed something as simple and cheap as possible.
RO is definitely going to filter to a lower level, remove more stuff, and produce more palatable water. But also requires much more $ and equipment.
Passing it through a couple 25u/10u bag-style filters before passing through a HF filter will probably help a lot in preserving the life of them and reduce the amount of backflushing necessary
Yup, prefilters are useful, I’ve generally seen something between 250u and 100u recommended by most manufacturers.
Though I’ve found that if the situation requires it, you can be pretty abusive to HF filters for a rather extended length of time before the performance degrades all that much. I’ve seen HFs run high duty cycles with a 500u prefilter without backflushing and extremely heavily loaded feedstock for weeks before the performance started to drop off.
In an industrial setting, backflushing can be a significant pain in the ass. In a home/personal type setting, it’s much simpler - turn the fucker upside down.
Anything else before or after is going to extend the life of the system, but in an “I just need to make sure my water isn’t going to make me sick” type situation, the HF alone should get you there.
Maybe some clever use of hydrostatics could help you if power is limited. A 35m (115ft) column of water would get you 50 psi of pressure at the bottom. If you have a hill tall enough you could collect rainwater for contamination up top and have a 1/2" PVC pipe come down to whatever filter stages you want fill receiving barrels/totes.
If you wanted to do a grey water version of this, you may want a settling tank up top and pass thru UV sterilizing at the bottom before membranes. At the very least this will lower your power consumption if you want to add a booster pump.
I have calculated that at ~60psi, 1 Amazon 4040 membrane will produce ~0.66gpm. Higher pressure would obviously flow more. Allegedly they can produce 1200gpd. I was thinking 3 membranes would produce 2gpm at 60psi. Could probably get away with 2 membranes at 90psi, but gotta test that.
My question is, what would be the benefits of the HF filter over the membrane? From cursory googling, it seems to be the same price. I was under the impression that membranes would produce a cleaner product than the HF without the need for back flush.
My goal is not to maximize gpm. I don’t have the money to give everyone in Asheville a system that could run their home. My goal was to provide a system to a fire department or other municipality that was conveniently located near some body of water that could serve as a hub so to speak. So long as the system is producing more GPM than can reasonably be filled by 1 bottle filler in a given minute, it would remain net positive.
My other question is, I was under the impression that membranes removed basically everything harmful. As @Kingofthekush420 stated, it would be wise to implement a carbon pre filter to prolong membrane life as well as organic compound filtration. Am I incorrect in my assumption that the membrane would remove microbials and heavy metals? The carbon should remove chemicals that may have leached from basements/pollution.
Thank you to everyone that has contributed so far. I really appreciate the insights and feedback as I feel in my gut that this is needed.
On my way to work this morning I saw 6 full size pickemup trucks each loaded down with a pallet of bottled water (~1T each) headed up to Bristol. That’s ~600$ per pallet. At 6 pallets, that’s 3600$. That is roughly 3 systems which could produce that same 6 tons of water in ~12 hours using <10gal of fuel (if not using grid power). Those trucks could have been hauling other supplies. Water should be an easy problem to solve, but its always easier to shovel that money to Walmart and Nestle.
So margins are toight these days. I can set up a single system as a proof of concept, and then produce a distributable BOM and build guide that has been cost optimized as well as selling systems at cost plus 100$ (just to help lube the wheels), but ultimately the costs will come down to the unit cost of the spout pouch bags (1.14$ to 0.92$).
Would it be unethical to charge ~1.50$ per 1.3gal bag on a donation basis in order to recoup costs and build inventory of bags? I’d never turn down anyone who wanted water, but I simply don’t have the capital to give everything out for free. Would definitely appreciate feedback as I am wrestling with how to help people without going bankrupt.
I have powder packs of CLo2 LD55 1 packet make 55 gallons at 100ppm not sure how strong u need it to steriize water but certainly not 100ppm. We dilute it 100:1 to disinfect a grow room or spray on plants. so one pack potentially could disinfect 5500 gallons. You would want to run it thru pre filters to remove sediment 3 stage would work.
