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Combining grey water + solar still + bio sand filter

Posted: Sun Dec 17, 2017 1:28 am
by zombieapocalypsegame
Hey all

I'm looking for some reference links on DIY'ing an automatic grey water distillation setup for rural residential use.

I've done a 5 gallon bio sand filter at home. I have found how to build a solar still although I haven't made one yet. And I've seen a number of videos of people catching grey water from the house such as from a washing machine. I am thinking about how to connect them all together.

I envision the following setup:
  • Grey water from the house (shower, kitchen sink, bathroom sinks, washing machine, dishwasher) but no black water nor garage/shop washout
  • 55 gallon steel drums to receive the effluent (or perhaps the plastic 275-330's usually used for rainwater collection)
  • Solar panel powered pump to transfer to still array set up in parallel or series
  • Still array needs to be sized to handle ~320 to ~400 gallons per day (typical household volume)
  • After collection from stills, pumped to bio sand in 55 gallon or another 275-330 to filter any other evaporated contaminants (alcohol, for example, but some soaps, etc too)
  • Collection from bio sand filters to long term storage containers (same as huge rain harvest tanks)
I believe this will alleviate the vast majority of pathogens & particulates in the water early on by not permitting the grey water to pool for significant time, high temperature, evaporation itself, secondary filtration, etc.

I'm trying to determine how much square footage I'd need to handle typical household volume of water use. The big limitation on the solar side is the volume of water distilled per sq ft of distillery. I can't buy a piece of equipment that can handle 3 gallons per day. I am looking for what I could affordably build DIY that has the capacity.

And I am considering other alternatives such as creating a steam turbine for power, capturing the steam as clean(er) water, possibly including a stage where I could add fuel/heat to boost or even replace the solar heating of the water during winter, etc. Then there are other considerations, including how automated is it? How often does the solar still array need to be cleaned of debris (soap scum, for one). How to ensure the still array cannot overflow and contaminate downstream storage, etc.

Does anyone in this group have a system such as this? I see lots of little pieces of this on the web, but nothing integrated. Once I have the solar still part figured out, I can see what else is do-able in terms of space & what it would cost to do.

Re: Combining grey water + solar still + bio sand filter

Posted: Sun Dec 17, 2017 4:53 am
by Halfapint
I like the idea, there are problems though. If you're talking solar still, like shallow pools with tarps or something over them to use the sun to evaporate the water. You're going to need a LOT of sq ft. I've seen people make solar stills, it gets you a mouthful of water ever few hours. Honestly I think you're talking half an acre or more? Just look into making sea salt. They have MASSIVE pools to evaporate all the water, it takes weeks. If you're in AZ maybe you could do it.

I think you're better choice is going with a collection pond that's graded down on the end where the contaminates will settle. Having plants and other organisms on there to filter most the nasty stuff out and using that water as irrigation.

I honestly like your idea, but without some sort of heat source you're not going to get enough evaporation out of the sun on a scale that works for most people.

Re: Combining grey water + solar still + bio sand filter

Posted: Sun Dec 17, 2017 9:42 am
by Benbrutal
Also you would have to insure any cleansers do not kill your bio-sand filter. Several types of hand and dish washing soaps are antibacterial and would kill off your beneficial microbes.

Re: Combining grey water + solar still + bio sand filter

Posted: Sun Dec 17, 2017 10:29 am
by raptor
Dbl post.

Re: Combining grey water + solar still + bio sand filter

Posted: Sun Dec 17, 2017 10:44 am
by raptor
I was also going to say the biggest issue will be the detergents in the washing machine and dishwasher. That said you could either by pass this effluent and treat it sepatately or simply call it black water and use it to dilute the black water.

The solar still would be the most difficult thing to incorporate. If the scale is large enough you could simply use a pool or spa sand filter. Though that would require a pump.

Still I could see the gray water going into a holding tank to let it settle and the solids to drop out and then when there was enough volume pumping the water through the sand filter into another process tank. You could then recirculate the water through the filter if necessary. Once clean enough dump that water into your sanitary sandfilter for further processing or simply use it for gray water use.

Honestly if you simply segregate the water for gray water use that would be the easiest and best use. That would simply require a holding tank and appropriate piping.

Now if you had free btus ,say from waste heat as you say, a steam distillation process would treat all of the water without issues. That said if the heat source is not free then the cost of steam distillation is very high.

If you Google steam distillation you can find lot of information especially in the marine world. The process is simple though there is a lot of art in the application.

Re: Combining grey water + solar still + bio sand filter

Posted: Sun Dec 17, 2017 9:52 pm
by boskone
I think it's a cool idea...but Halfapint's hit the nail on the head. Some napkin math (based on a solar still that produced 2/3gal per day from a 24-inch sphere) indicates you'd need at least 1,700 sq ft to clean 325 gal on the summer solstice; ignoring temperature concerns, you'd need around 5k sq ft in to produce 325gal in the winter.

Probably better with rainwater catchment and RO or such at whitewater outlets.

Re: Combining grey water + solar still + bio sand filter

Posted: Mon Dec 18, 2017 8:51 pm
by zombieapocalypsegame
I'm in TX and we get some pretty darn strong sunshine here. :)

I'll also use a physical filter (likely mesh netting & paper liner) when pumping into the initial reservoir from the house. I forgot to mention that, as it is particularly useful re: water from the kitchen.

I am planning toward constructed / installed units, not a pond or ground level pool of some kind. I am thinking basic 2x4 and plywood or aluminum legs & plywood with window frames & glass tops secured on an angled orientation, in series or parallel.

I might put a black hose or copper line solar water heater in front of the stills to increase temperature and therefore minimize time in the stills. And of course the storage tanks themselves would be painted black to absorb as much heat as possible.

I want to move the water to these solar still units as quickly as possible, as grey water can begin to have issues at ~24 hours. If I tried going to the bio sand first, I'd have to have a TON more sand filters due to the slower rate of flow they can handle vs the stills. The 5 gallon bucket version of the bio sand filter I built would only handle 3-5 gallons in 1 hour. That's ~120 gallons per day, max. The 55 gallon version would handle more, but not by much more because the goal is to not disturb the sand and allow the bacterial layer to work unmolested. Area, not volume is the determining factor.

Plus, the bio sand drums will be WAY heavier and a logistical nightmare to move, so I'd like to keep those to a minimum. Also, this way the majority of suspended particles will get dealt with via paper filtration, high heat then evaporation vs clogging up the bio sand filter. And it's certainly a LOT easier to clean the stills than the filter sand.

The point of this effort is to clean the water from the site wells so it can be re-used for ANY purpose at the site. I can legally just disperse the grey water throughout the property as long as this is outside city jurisdictions. But to use slightly soapy / oily / bacteria contaminated water that way will only invite problems in general, let alone for anything consumption related. The RO method is FAR more expensive for such capacities AND requires much more energy.

The biggest $$$ for any household would be watering the lawn, just in sheer number of gallons required. But, if I could direct nearly all the 300-400 gallons used inside the house to be re-used again outside without real reservations, that would be a BIG win. Especially for vegetable gardening, etc.

The common US residential lot size is 8,600 sq ft or 1/5 acre. Subtract the average home itself and you have 6,000 sq ft that might normally be grass (leaving out the driveway anyway). That would require 3720 gallons per week just to water the grass. Which is essentially identical to the tomatoes. So even with a household of 4 people estimated at 400 gallons per day - you can just barely cover 2800 gallons per week of water recovered, no loss best case. So watering the lawn isn't really a viable option even with a SMALL lawn. Maybe with 6 people in the family and increased water usage that comes with the size, but then there's no water for anything else either.

Here in TX, beginning in May the sun can be so intense that tomato plants easily die within 1-2 days. The same is true for many edibles. If I could water them with purified water I have already paid for & used, I can water them daily without any extra cost aside from the passive equipment & one or two reasonably small pumps.

Tomato plants need 1 to 1.5 inches of water per week. In a raised bed garden 8' x 4' that is ~30 gallons a week. This plan would allow for 10x that size - or 320 sq ft of tomato plants, and allow for 6 more plants at the same area needed if it has similar water needs. Cucumbers, water melon, squash, or even corn could be grown very effectively in large quantities with that amount of water on hand. Some plants need more water. Corn is +50% over grass/tomatoes, and watermelon is +100%.

During the winter, we'd certainly have a surplus of water that we don't need. That's when we should consider a stock tank type situation. It's a lot cheaper to dig a hole in the ground than to buy three 10,000 gallon tanks at $5k each. At say 2,000 gallons per week, we would max out capacity on a $5k tank in 5 weeks. Since winter is 3-4 months, we'd need 12-16 week of capacity while the water isn't being used. Paying to store potable water is one thing, but I certainly don't want to pay $15k for water storage that is destined for veggies or animals, let alone flowers or grass. Even if the storage tanks last 15 years, that's $1k per year - far more than the water would cost.

So, given say 2 acres of space, there would be PLENTY of room for such an array of solar stills. Normal atmospheric evaporation rates I have found to be 1 gallon per square foot of area per hour for many municipalities. That's a far cry from the amount typically collected by stills, so there is large loss to the atmosphere to be sure. To handle ~300 gallons by assuming 2 gallons generated per day for each 1 square meter / 10.7 sq feet - I'd need 150 individual stills or roughly 50 8' x 4' stills. That's just bigger than 7 x 7 tables which would be 56' x 28' with no spacing in between.

Assuming the supplies expenses would be:
  • Seven 96" 2x4 for main compartment & support (assuming 2' off the ground) $15
  • One 96" x 48" plywood $25
  • Plenty of PVC or similar pipe $10
  • Aluminum flashing / fin material
  • Labor to assemble
  • Recycled window glass from remodels etc (free)
Then the silicon
  • Black waterproof silicon roof rubber paint 5 gallons = 250 sq ft (good for 8 stills) @ $200 each
  • Clear silicon to seal glass (4 case @ $25 = $100)
I am ball-parking $80-$100 per table with hardware.

For $5,000 one-time cost, with occasional maintenance costs on top of that, plus a few pumps & other hardware, I can handle throughput of 300 gallons through this system. Each table handles 6 gallons per day, assuming just 5 hours solid sunshine according to the various research I have read. Automating it will cost a bit more with sensors for water flow etc.

It seems if you have the space, this is a no-brainer. Call it $7k for everything, being overly conservative. $7k would pay for 700,000 gallons of water at $0.01 each. In one year, a typical family uses 109,500 gallons at a cost of $1095. So that's around 7 years of water I'd be paying for. Even then well water is generally FAR less per gallon, but you likely had to pay much more for the deep well to keep it that way. This plan would provide me with ~219,000 gallons per year, essentially doubling my available water at the same cost. Yes, if I want to get 100% of those gallons I need some storage for portions of the year, but the self-sufficiency alone is worth $$$ too.

To compare, rainwater harvesting on a 65' x 40' roof (front & back gutters) would generate ~55,000 gallons per year in my neck of the woods. It gets half the water over the same period as the grey purification concept. And when rural and/or in a drought that well water might need to be the main source of potable water, let alone used for anything else. This has been a real problem in TX in the past 5-10 years.

Drilling a well - say $15,000, more for deeper etc. Harvest rainwater - say $2000 before storage and it is certainly not potable at that point. This plan seems to fall easily between those, could potentially share the fresh water storage costs, and makes FAR more use of the water.

Re: Combining grey water + solar still + bio sand filter

Posted: Tue Dec 19, 2017 4:13 pm
by boskone
Yea, my numbers were based on Texas (since it's where the two of us live). If you're willing to throw several acres and a few thousand bucks at it, though, it's doable.

I'm not sure I'd go with glass, though; aside from it's brittleness (which could suck after the first hailstorm), I think at least old glass used lead as a clarifying additive (glass is kinda green by itself, some portion of lead makes it clear) New glass might as well, since we don't usually consume food or water from windows. Since you'd have a lot of water-glass interface area, even a little bit of lead leaching could end up being a significant concern.

I'd talk to maybe a glass shop to see a) if lead is still used, and b) if it's ever been used how to check for windows that might contain it. It might be as easy as finding windows that are slightly green, I dunno. Maybe talk to a chemist of some sort. Not sure who's specialty includes "how not to give yourself lead poisoning".

Re: Combining grey water + solar still + bio sand filter

Posted: Tue Dec 19, 2017 4:55 pm
by Halfapint
Being in TX it is doable as you said, however I think a bit of your math is wrong. As far as watering take the tomatoes you mention. You can get away with a LOT less water for the tomatoes if you water them at night, and not just spray it on top like grass. I know even up here in the PNW people say screw the grass in the middle of summer because unless you want to dump the 4k gallons a week on it it's going to die. But we get pretty intense sun (not nearly as bad as TX though) and most people I know have installed some sort of drip watering system for their gardens especially for tomatoes, peas, etc. Only use surface watering for things like carrots, and vegies you plant in huge parcels.

I'm not sure how much land you have but would you want to dedicate nearly the amount of land for something like this just to water a plot of land about 1/5 the size of this still set up? I mean you could probably spend the same amount of money on a simple filtration system. Two 55gallon drums filled with sand, 1 filled with charcoal, and another with sand, then some sort of store bought filter would probably get rid of everything you'd throw at it for at least a year and would cost maybe 100-200 a year in cost upkeep.

Re: Combining grey water + solar still + bio sand filter

Posted: Tue Dec 19, 2017 5:07 pm
by zombieapocalypsegame
I thought about plexiglass, but that alone would push my expense quite a bit higher. I too thought about the lead in old windows, so we are of like minds there. I could certainly cull out specific glass as possible. But the bio sand filters are excellent at removing lead, too.

The biggest advantage the glass has is clarity over plexi over time but it is more fragile. On the flip side I would have to collect old window glass for a long time vs get everything built at once.

Re: Combining grey water + solar still + bio sand filter

Posted: Tue Dec 19, 2017 11:54 pm
by zombieapocalypsegame
Those filters generally cannot deal with soap in large quantities, including the charcoal and bio sand drums. That's why I am looking at solar stills. Since every single water pipe coming out of the house will have soap, shampoo or detergent we need a solid plan on that front. And lots of soap we use is antibacterial in nature, which would tend to kill off the bio sand organisms. Then there's stuff like fat from the kitchen sink too. All that stuff will overwhelm the charcoal.

The other issue is capacity. Even the 55 gallon drums don't have enough throughput. I can't go from the house directly to the drums because of the soap issue. But even if they're in line after the solar stills, I have to have a bunch of them to handle the capacity. I want the minimum I can because these things are heavy and impossible to move around without heavy equipment once prepped.

I wonder if I heat the water with a concentrated beam from a fresnel lens pointed at a boiler, if we can speed up the rate of steam generated and then condensed in a smaller number of stills? The hard part there is keeping the fresnel lens focused for optimum effect throughout the day. I found a video on how to do that at and and

Using the passive solar water heater approach with black poly pipe to pre-heat the water + adding the Fresnel lens downline from there might be very useful and cost much less both in setup time and dollars. The same source has a video for the tubing at According to that video and part 2 of it, he generated 11 gallons @ 140 degrees per hour. The pump he used could handle 1000' of tubing instead of the 100' he had. So that capacity is 110 gallons @ 140 degrees per hour. And, that was water coming out of the well at roughly 70 degrees.

Typical solar panels & collectors optimize the day @ 5 hours of sunshine. That could put me at 550 gallons per day - IF the Fresnel lens could in fact flash the water to steam - i.e. provide enough energy to go from 140 to 212. Or, see if there is a better energy-free way to pre-heat to higher temps. The sun-tracking Fresnel lens would improve the 5 hours, but the black poly pipe might not keep the pre-heated water at 140 longer than that.

The system works in cold temperatures, too. I found videos showing some of these systems providing 80 gallons of water at 70-80 degrees when it's 25 outside. Granted that's a far cry from 300 gallons and it's only 80 degrees not 140. But it almost never gets anywhere near that cold in my neck of the woods.

I'm going to look into the Fresnel boiler idea further.