Filtering Suspended particles from water

[silentC]

We have a Supertreat onsite sewerage management system. The basis of this system is a pair of tanks, one of which is the septic tank and the second is the effluent treatment tank. The water that ultimately comes out of the system is not drinking quality but is OK for spraying on the garden, which is what we have been doing with it.

When we plumbed the house, we put in separate lines to the toilets, the ultimate aim being to use the treated effluent to flush the loos. We have set this up and it works fine. The only issue, and it is a minor one, is that the water is quite yellow. Our daughter flushed it three times last night before coming to Mum and saying "I've tried to flush it but the wee wont go away". Kids :o

The treatment removes all of the toxic stuff but it is quite heavy in various elements which are good for the garden but look a bit unsightly in the loo. What we would like to do is to filter it.

Over a few ales last night, the old man and I pondered the problem and I wondered if a sand filter from a swimming pool might not be the go. It can be backwashed to flush out the sediment and, in theory, should not need to be replenished like a cartridge filter would.

I suppose we could buy one, or maybe pick one up from the tip. However, on the off chance that someone here might know, can anyone suggest how one could be made from scratch? The main problem that I can see is how to stop the sand coming out of the vessel when you pump water through. There must be some trick, so if anyone has ever pulled one apart, how do they work, eh?

[Eddie Jones]

Why go to the trouble & expense of a filter? If the problem is only the colour, just get one of those hangy-thingies that go in the cistern and turn the water blue.

[silentC]

Why go to the trouble & expense of a filter
Because it's fun!!


just get one of those hangy-thingies that go in the cistern and turn the water blue
No offence, but that is a woman's solution to the problem ;) My wife's to be specific.

Now, do you know how they work or doncha?

[echnidna]

Maybe a bit of alum will settle the sediments in the holding tank
It will turn muddy damwater clear

Its not rocket science (nor expensive) to make a solar evaporator which theoretically would give you clear potable water. Should be examples on the web as they are used in many 3rd world countries.

[TassieKiwi]

Dunno how your system works but the big town systems use a 'flocculant' in the other end of the treatment systems, before it goes throught the sand filters. This causes the small particles to 'floculate' - have a group hug - and fall to the bottom. You might be able to dose the tank once a week. I think it's a lime product.

Sand filters have a series of graded sized layers on the base, coarse to fine, with a base peppered with holes underneath. When the filter 'blocks up' the pump is reversed and the wastwater from this dumped. The local wawter treatment operator would be proud to show off his equipment (!) as these guys are a breed apart - esp. wastwater plant operators!

The'res no reason why a sand filter wouldn't work, but it will always be a maintence thing. Would a large-volume settling tank be viable? Could be emergency fire storage too.

Go a googling.

D

[silentC]

a solar evaporator
I have thought of doing that. All you need is an old window, a bath tub, a bit of gutter and a pump. Will definately mess about with something along those lines one of these days. Will I be game to drink it? Hell yes!!

I have also been experimenting with distilling. I took a funnel and a bit of rubber hose on a coastal walk I did last year. The funnel goes over a billy full of seawater and the hose comes off the top and you coil it up inside a big mound of wet sand. The idea is that the sand absorbs the heat causing the steam to condense. It works OK but takes a lot of seawater and a lot of boiling to get a cup full because it's not very efficient. What comes out is pure water though. Next trip I'm going to try something enclosed with a lip around the inside of the funnel. You fill the top with cold water to help the steam condense and it runs down the sides of the funnel into the lip. You have a little spout out the side where the water runs out.

The filter would have a much faster turnaround. With a still, I would need enough storage capacity to keep the loos flushing while water is being distilled, which could take days to do a few litres at this time of the year.

[silentC]

The local wawter treatment operator would be proud to show off his equipment
Good idea. I ride past the local treatment plant every day. Might drop in one day and take a squizz.

[Rocker]

SilentC,

I would use alum, as suggested by echidna. I used to use it in the bush in Tanzania, when the only water I could access was muddy. The alum is very effective in flocculating the particulate matter in water and clearing it. At the time, I was not aware that alum in drinking water is suspected of causing Alzheimer's. This could account for difficulty I sometimes have in remembering what it was that I had gone to the other end of my shed to fetch. But if you are simply using the water for flushing toilets, it should be no problem.

It seems to me that using a sand filter to do the job would be using a sledgehammer to crack a nut.

Rocker

[Wildman]

You need to know what is causing the colour for the best results. You will need to get the water properly tested to determine this (I am sure we all have a fair idea, but you need to know chemically). Once you know what the colourant actually is, you can use the best flocculant for it to give filtration the best chance to remove the colour.

Some organic compounds breakdown in sunlight and all you need to do to remove the colour is store it in an open top tank in full sun. Fill a clear bottle with the water and leave it in the sun and see what happens.

Personally, I would just replace the pan with one the same colour as the water, might not fit with the bathroom theme but would solve your problem. I wish I had not replaced our pale yellowy mustardy apricoty pan with a white one, you need to clean it 5 times as often.....

Cheers
Ben

[silentC]

OK. Alum: I have that problem Rocker and, to the best of my knowledge, I have never been in contact with alum. Maybe they use alum to filter beer?

So what happens to the flocculated particles (can I say that here?). When I was a pool owner, there was a chemical you put in to remove particles and the clumps that formed would fall to the floor of the pool and had to be vacuumed up.

Ben, thanks. I'll try the water in a clear bottle idea and see what happens. My old man insists that the particles are not fecal. There's no odour, maybe a very faint urine smell. Our septic tank is only new and hasn't formed a decent crust (I trust you've all finished your lunch) and it is his opinion that things will clear up in due course.

All our pans are brand new and white. It would not be a popular decision to rip them all out now, seeing as we only moved in 2 weeks ago.

I have always found sledgehammers do an admirable job of cracking nuts, if that's all you want to do. Eating them afterwards is not always an option.

[Rocker]

SilentC,

The flocculated particles sink to the bottom, as in your pool. In fact I believe the pool flocculant chemical is alum, although I may be wrong.

Rocker

[TassieKiwi]

Ah yes - alum. What were we talking about again?

Question - have you spoken to the installers/designers of the system? They surely would've come up against the question before, maybe it will stop this in time.

[silentC]

The installer was my old man. To the best of our knowledge, no-one has ever tried to recycle the treated effluent this way. You're supposed to spray it on an area of medium density vegetation over an area of approximately 100 sq. metres and hang signs everywhere warning people not to come into contact with it. If the council knew we were doing this, they'd probably write us a harsh letter telling us to stop it at once.

The manufacturers of the system claim that it is perfectly safe, it's just not approved for anything other than irrigation of non-vegetable plants.

The local supplier has suggested a couple of ideas but that doesn't stop me from looking around for others. He reckons exposing it to sunlight will do the trick. It's a problem to solve, that's all. Gives me something to think about when I stand and/or lean.

[Clinton1]

i believe that fullers earth can be bought from a swimming pool supply shop and is a (one of many) flocculant (I really wanted to be the first to say flocculant, and missed out :( )

I'm sure you have Wik'd flocculant - maybe you should try putting some of your water in a drum with some fullers earth and see what happens.

Have a look at hydroponic farms that recycle their water, a fairly commonplace activity. They use flocculants and filters.

[ozwinner]

I think you are putting your familys health at risk by recycleing the water back through the dunny.

http://en.wikipedia.org/wiki/Pathogen.

Al :eek:

[echnidna]

I have thought of doing that. All you need is an old window, a bath tub, a bit of gutter and a pump. Will definately mess about with something along those lines one of these days. Will I be game to drink it? Hell yes!!

I have also been experimenting with distilling. I took a funnel and a bit of rubber hose on a coastal walk I did last year. The funnel goes over a billy full of seawater and the hose comes off the top and you coil it up inside a big mound of wet sand. The idea is that the sand absorbs the heat causing the steam to condense. It works OK but takes a lot of seawater and a lot of boiling to get a cup full because it's not very efficient. What comes out is pure water though. Next trip I'm going to try something enclosed with a lip around the inside of the funnel. You fill the top with cold water to help the steam condense and it runs down the sides of the funnel into the lip. You have a little spout out the side where the water runs out.

The filter would have a much faster turnaround. With a still, I would need enough storage capacity to keep the loos flushing while water is being distilled, which could take days to do a few litres at this time of the year.

I'm extremely rusty on the figures but from memory 1 sq metre of water will evaporate about 2 litres of water per hour in mid may in Melbourne.
So as long as you have a large enough surface area (say on top of the roof of your shed) you can get quite a good amount of evaporated water.
On sunny days there will be far higher evaporation.

A Council Helath Inspector should be able to tell you the evaporation rates applicable to your region.

[wilco]

Swimming pools generally use a medium or high rate sand filter, these require pressure so may not suit your application.

An older style of filter still used on some pool today is a 'gravity sand filter' ive attached a pic for you to see how it works. this would not need very much pressure, just enough to get the water to flow over the 'wier wall' gravity does the rest, a benefit of this system would be sunlight hitting your water, UV light kills nasties so would be a bonus in this application, this could be built on a small or large scale... i can explain further if you need.

Thanks,
Luke

[Clinton1]

Oh, and the hydroponics setups I've seen use a clear pipe segment that has a UV light shining through it to sterilise the water.

Have a look at Tenix's website, they bought the intellectual property rights to Environmental Solutions International (share market listed then went bust). ESI used filtering and bacterial digestion techniques to treat water, and pioneered the use of sewage and bacteria to make bio-fuel. Perhaps Tenix have some info available on a web page.

I'm thinking that you might set up a gravity sand filter system (44 gallon drums is series) and charge the system with the bacteria mix that your local sewage treatment works uses. You'd need to add air to the mix to boost the bacteria (solar powered fish tank aerator). Then filter this and use a flocculant. I think it would be a fascinating project.

Or, set up a reed bed (a trench lined with a dam liner) and take water from the 'treated end'.

[Driver]

It's a problem to solve, that's all. Gives me something to think about when I stand and/or lean.

I urge you to caution, Brother Silent. If, in the course of thinking about this problem while standing and/or leaning, you should come up with a solution then the possibility exists that you will have completed a Work In Progress (WIP).

I would hate for a stalwart like yourself to inadvertently breach the Code. :eek:

Col the Cautionary.

[Sir Stinkalot]

Ok here are my views .....

Firstly I will qualify this with saying that I obtained a bach. Engineering (environmental) only a few years ago ..... this basically focuses on water treatment. Secondly ..... following graduation I have never used the information that I obtained and most of it is now gone. Luckily I kept some of my big books ...
"Wastewater Engineering - Treatment Disposal Reuse" Metacalf and Eddy
"Introduction to Environmental Engineering" Davis and Cornwell.

Ok now lets get into the problem ....

Substances that can exist in water fall into one of three classifications:
Suspended
Colloidal
or Dissolved.

A dissolved substance is one which is truly in solution, and is homogeneously dispersed in the liquid. The substance cannot be removed from the liquid without accomplishing a phase change such as distillation, precipitation, adsorption or extraction.

Suspended solids are large enough to settle out of solution or be removed by filtration. In this case there are two phases present, the liquid water phase and the suspended particle solid phase.

Colloidal particles are in the size range between dissolved substances and suspended particles. They are in a solid state and can be removed from the liquid by physical means such as very high-force centrifugation or filtration through membranes with very small pore spaces. Colloidal particles exhibit the Tyndall effect, when light passes through a liquid containing colloidal particles, the light is reflected by the particles. The degree to which a colloidal suspension reflects light is measured by turbidity.

Colour is not separate from the above three categories, but rather a combination of dissolved and colloidal materials. It is very difficult to distinguish "dissolved colour" from "colloidal colour". The most common cause of colour is the occurrence of complex organic compounds that originate from the decomposition of organic matter.

The particles in the colloidal range are too small to settle in a reasonable time period, and too small to be trapped in the pores of a filter. As this is the case a coagulant must be added in order for the colloidal particals to produce a flc. The coagulant is often alum.

To cut this short as the Stinkette wants the lapton :mad:
The floc makes the colloids of a size where the can settle, hopefully removing the colour problem.

The problem in silentC's situation is that the coagulant will need to be added often, mixed with the water, then given time to settle, prior to being used. This will be a labour intensive process and require a number of holding tanks. The other issue is if the water isn't fully treated and stored it will become septic again which will be worse than the colour problem.

Ahh hope this helps ..... got to go.

[silentC]

OK, all good stuff one and all. I will ponder it some more. Don't worry Col, there's no immmediate danger of WIP completion, plenty of other things on the boil that are more important than the colour of the water in the loo!

Might give the gravity sand filter a go as suggested by Luke. Easy to make and nothing to lose by trying it. I need to absorb some of that technical stuff a bit more. It might be worth getting it tested to see what's actually in it but that's dangerously close to doing a proper job of it!

The reed bed was one of my earlier ideas. I saw one on TV a couple of years ago and I liked the idea. Good thing we have plenty of un-landscaped land to play with.

Thanks for the input.

[silentC]

Luke,

In your diagram you show "collectors". I gather the purpose but what are they actually? Some sort of perforated pipe or...?

[wilco]

I believe a perforated PVC pipe would work fine, put a fine screen across it, flyscreen etc with aggregate surrounding it, then the sand on top.

Pool shops ,or i can give you a supplier, will sell you filter sand, you can get different 'grades' or sizes to suit the fine screen you have installed.

Does that make sense?

You'll also need a way to baskwash this, it could be as simple as a connector for a garden hose and tap water, you need enough pressure to expand your sand bed and carry away the crap but not enough to wash away your sand.

Its also good to note with these types of filters that generally the water is not totally filtered with one pass through the system, roughly speaking
1 pass will remove ~65% of the solids
2 passes 85%
3 passes 95%
4 passes 98% etc

Luke

[wilco]

Actually, with backwashing etc, a multiport valve, like on home pools and spas would make things easy for you to control backwashes once you have sorted out the pressures youll be using

[silentC]

When I was thinking of using a pool filter, my idea was that I would just circulate the water in the holding tank periodically. So the water would flow from the tank, through the pump, through the filter and back into the tank. For back wash, I would take water from the tank the other way through the filter and send it to the septic. That way the crap would go into the septic and we recycle the backwashed water as well. I don't know whether this would result in some sort of build up over time with the fine crap that normally goes on the garden ending up back in the tank.

I thought I would try some beach sand first. Got plenty of that nearby ;) A bit of aggregate in the bottom, maybe even some charcoal?

I'll see my mate at the pool shop and see if he can source me an old valve, or maybe even an old filter and pump.

[wilco]

When I was thinking of using a pool filter, my idea was that I would just circulate the water in the holding tank periodically. So the water would flow from the tank, through the pump, through the filter and back into the tank. For back wash, I would take water from the tank the other way through the filter and send it to the septic.

Perfect!

You could try this on a tiny scale with 2 buckets to see how it will work. Poke a hole the in bottom of bucket 1, cover with mesh, fill with a little aggregate then sand.

Place bucket 2 below bucket 1. Pour sample water into B1 and collect in B2. Circulate same water a couple of times and see if you get an improvement. Total cost should be 2 buckets :) Apples!

[wilco]

That way the crap would go into the septic and we recycle the backwashed water as well. I don't know whether this would result in some sort of build up over time with the fine crap that normally goes on the garden ending up back in the tank.


One of our backwash tanks (it holds the backwash water while it is being pumped into the sewers at a slow rate) is connected to 3 high rate sand filters at work. It takes all the backwash water from our 1.2million litre lap pool. After 7 years there is still only a small layer of sediment at the bottom. it should not be a problem :D

[jimc]

New Inventors on ABC has had a retrofitting treatment system to fit to existing septic tanks that use worms and other creepy crawlies to turn your sewage into clear water.

another alternative is do what nature does...build a marsh/swamp in an enclosed system...ie pond liner. As the dirty water drains into the system it will be cleaned and then pump it to whereever use you desire.

Add a UV lamp and you could drink it!...although I probably wouldn't.

There has been a lot of research into this process. Check out http://www.sustainablehouse.com.au/ They have a similar treatment system I have described.

[silentC]

Good idea. I've got plenty of buckets!

[silentC]

New Inventors on ABC has had a retrofitting treatment system
Saw that last night. Biolytix. Have already contacted them. The water that comes out of it is still tainted though, so I would have the same problem I have now. The advantage of that system is that it requires no pumps, or can be run on solar, and it uses no chemicals. The system I have now has a water pump for distribution and an air pump to help the bacteria do their job. It runs the treated effluent through chlorine on the way out and the tablets need to be replaced peridoically. The water is OK for above ground irrigation but as mentioned above it is brown.

[Clinton1]

Silent,
Here's another option - you've got me thinking...
a reed bed system that flows into an area that is wide and shallow and roofed over with the guttering on the inside of the roof edge - this being the evaporation system.

[silentC]

Let me know when you've built one and how it works!! :D

[Clinton1]

Naaah,
you let me know how it goes when you get it running.
:D