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ToastHater

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Posted: 09/29/20 05:05pm Link  |  Quote  |  Print  |  Notify Moderator

I'm working on a plan for a DIY RV build, and I wanted to incorporate a water filtration system. Specifically, with sustainable boondocking in mind. I'd like to be able to clean any incoming water to the freshwater tank, as well as recycle gray water if possible.

From the research I've done, there are two solutions that are very similar: reverse osmosis or ultraviolet light. Both incorporate or require a pre-filter. RO requires higher pressure. UV requires a lot more power.

My understanding is that RO is the most effective, but least efficient. And that the efficiency is related to the required PSI to run it. In-home units, needing 60-70 psi or more and being less efficient. Restaurant units, needing 100 psi or more and being more efficient.

[Gray Water/Water Intake Tank]
{High PSI Pump}
{5+ Stage RO System}
[Freshwater Tank]
{Low PSI Pump}
=Out to Sink/No-Tank Water Heater=
=Sink - Out to Grey Water Tank=

Trying to keep things tight, so it isn't all over the place. I also may not be incorporating a shower within the RV, and I'll be using a composting toilet. So the only thing going into the grey water system, would be water from the sink.

I'm curious if anyone has experience with either of these systems. More specifically, how frequently do they need to be maintained/replaced?

Would you trust either, to filter grey water?

Given the available power, could they be combined together? The RO system feeding the UV system. Would this be too redundant and over the top?

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Posted: 09/29/20 05:16pm Link  |  Quote  |  Print  |  Notify Moderator

Sustainable boondocking without a shower and needing mucho power to clean AND also recycle water?


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agesilaus

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Posted: 09/29/20 06:36pm Link  |  Quote  |  Print  |  Notify Moderator

I have industrial experience with RO systems and I doubt one would be appropriate for an RV. For one thing they generate a waste stream of the concentrated wastes from the material removed from the influent water. Also I would be surprised if they weren't major energy hogs. You need to determine the amperage draw for these units.

The household units placed under the sink to provide low volume supplies of drinking water are toys and I doubt will be filling your 50 gallon water tank. RO membranes have a definite lifespan measured in gallons passed thru them and on the quality of that water.

These days your enemy with untreated water is giardia spores. Along with other things like cryptsporidium. Usually chlorination or some other disinfectant is needed and even professionals running municipal water systems can fail to remove all of these microbes. And that's with the regulators breathing down their necks.

There is a low energy and fairly low tech method, sand filters when properly constructed and operated. Not very portable and the effluent still needs chlorine or ozone (high energy requirements). And knowledgeable monitoring.

Wiki

People credit doctors for curbing infectious diseases. But a big part of that reduction was derived from engineers constructing safe water sources for people to use.

My suggestion: buy some big water drums, 30 or 55 gallon plastic drums and get you water from a safe source.

* This post was edited 09/29/20 06:55pm by agesilaus *


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Posted: 09/29/20 06:51pm Link  |  Quote  |  Print  |  Notify Moderator

ToastHater wrote:

I'd like to be able to clean any incoming water to the freshwater tank, as well as recycle gray water if possible.

You won't (or shouldn't) be able to filter water from any source. There are too many pollutants for an amateur water filtration system.

Recycling gray water may be possible, but if you get it wrong . . .


ToastHater wrote:


From the research I've done, there are two solutions that are very similar: reverse osmosis or ultraviolet light. Both incorporate or require a pre-filter.

I use both in my RV's water filtration system. However, I don't boondock.

UV kills viruses and other pathogens, anything with DNA. RO filters out dissolved solids (harmful and non-harmful) like harmful metals.


ToastHater wrote:


RO requires higher pressure. UV requires a lot more power.

My RO works fine at 40 psi. My UV system is not a power hog. NSF-certified systems use more power.


ToastHater wrote:


My understanding is that RO is the most effective, but least efficient.

The main drawback of RO systems is waste water. An RO filter will "reject" a lot of water. However, I just plumb the RO waste water back into my RV's water tank.


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ToastHater

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Posted: 09/30/20 02:19am Link  |  Quote  |  Print  |  Notify Moderator

agesilaus wrote:

There is a low energy and fairly low tech method, sand filters when properly constructed and operated. Not very portable and the effluent still needs chlorine or ozone (high energy requirements). And knowledgeable monitoring.

Wiki


I've looked into doing a sand filter. It's not impossible to make portable, but still takes up a lot of space (and maintenance). Even went down the rabbit hole researching "Berky" filters to use as the carbon component...but the official claims are just that. "Claims." Berky filtered water still needs to be treated. So filtering non-potable water through a berky system or a repurposed berky filter isn't an option for my goals.

TechWriter wrote:

The main drawback of RO systems is waste water. An RO filter will "reject" a lot of water. However, I just plumb the RO waste water back into my RV's water tank.


That's exactly what I was thinking. I'm just not sure if that will cause more damage in the long run. Running all of the waste through the system repeatedly. Causing the maintenance/replacement cycles to be more frequent.

The other thing I want to make clear. There won't be any "human waste" in the gray water. It'll pretty much only be dish water (using some sort of "natural" biodegradable soaps/cleaners).

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Posted: 09/30/20 06:08am Link  |  Quote  |  Print  |  Notify Moderator

recirculating waste (dirty) water back into the feed water system would make that water dirtier and dirtier wouldn't it? what does that do for efficiency.
bumpy





way2roll

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Posted: 09/30/20 06:10am Link  |  Quote  |  Print  |  Notify Moderator

Under the sink RO systems aren't toys as previously suggested. They work and quite well in a home, under the sink, drinking water scenario. In an RV application they may not be practical. For starters they produce waste water. Depending on the quality of the unit it can be a higher than practical ratio of waste waster to drinking water. This can be recycled however but you would have to have a gravity capture and reintroduce into the system. Some RO systems use a powered pump to recycle waste waster but the energy consumption compared to the water saved is usually a wash - pardon the pun. The other challenge is pressure as you mentioned. Yet another issue is volume of water produced. Most drinking water systems are limited to about 3-6 gals over a few hours. Not practical for filling a water tank - but why would you? You really only need RO level filtered water for consumption. If just for a quick cleanup and washing dishes it's overkill. The other issue I can think of is power. An RO is going to need constant pressure to continue to produce water. That will require a water pump to run almost constantly. For that matter, any filtration system is going to require power, not just RO.

FWIW, I have installed RO systems in homes professionally for a few years. I am still working out installing a small RO system for drinking water in our RV. We don't really boondock however and I plan to incorporate cutoff switches so the pump doesn't constantly run and gravity waste water capture. Turn on as needed basically and use the waste water to clean bikes and outside stuff. My approach is really only to avoid carrying lots of bottled water which is so wasteful and has a large eco impact.

I applaud your efforts, it's an undertaking for sure.


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agesilaus

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Posted: 09/30/20 06:35am Link  |  Quote  |  Print  |  Notify Moderator

Bumpyroad wrote:

recirculating waste (dirty) water back into the feed water system would make that water dirtier and dirtier wouldn't it? what does that do for efficiency.
bumpy


I was assuming that we misunderstood what he meant to say, but you are correct, it would degrade the quality of the water in the tank.

way2roll

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Posted: 09/30/20 09:04am Link  |  Quote  |  Print  |  Notify Moderator

agesilaus wrote:

Bumpyroad wrote:

recirculating waste (dirty) water back into the feed water system would make that water dirtier and dirtier wouldn't it? what does that do for efficiency.
bumpy


I was assuming that we misunderstood what he meant to say, but you are correct, it would degrade the quality of the water in the tank.


Depends on the filter. Residential RO waste water is essentially water that isn't pushed through the system. Water at a certain PSI has to pass through a series of smaller and smaller filters , down to the bacterial micron level. So from 40-60 psi you end up with a trickle of water . That's why RO's have holding tanks and they take so long to fill. There is a relief valve for water than can't pass through so it doesn't cause back pressure on the supply line. It goes down the drain. So it's not "dirty" water, it's just the original water that didn't get passed through the system. It's like using a 5 gallon bucket to fill a 12 oz glass. What doesn't fit goes all over the floor - or in the RO's case, down the drain. It's called waste because it's wasted/rejected/never made it into the system (unless recycled). It's not waste because it's dirty. All the impurities are collected in the filter membranes themselves and stored until exhausted and then replaced. So by recycling the "waste" water in an RO system you are simply continually trying to push the same water through the system until it finally makes it. It's not any dirtier than it was to start with - it just never got polished.

I'll add another caution of RO systems in general for whole house or whole RV purpose. RO filters everything - including Chlorine and Chloramine which can kill bacteria that can live in your plumbing system and holding tanks. So while you don't want to drink them and it's good to filter them from drinking water, your whole house/whole RV should not be filtered from things that inhibit bacterial growth. RO is for drinking. But there are more pros than cons to filtering an entire house/rv.

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Posted: 09/30/20 12:06pm Link  |  Quote  |  Print  |  Notify Moderator

way2roll wrote:

All the impurities are collected in the filter membranes themselves and stored until exhausted and then replaced. So by recycling the "waste" water in an RO system you are simply continually trying to push the same water through the system until it finally makes it. It's not any dirtier than it was to start with - it just never got polished. .


if the waste water is returned to the supply tank or source that water will keep collecting reject material and get increasingly dirty and the efficiency of the membranes will suffer.
bumpy

* This post was edited 09/30/20 12:19pm by Bumpyroad *

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