Filtering river water for irrigation

Hi everyone,

Long time lurker, first time poster here. I manage a 25 year old organic farm in the south of Taiwan and we have roughly 20 acres of land planted out with mango, lychee, curry trees, guavas, bananas and many speciality fruit trees. There are three large ponds, a market garden and we use/have experimented with liquid composts, natural farming techniques, permaculture design, local pruning techniques, aquaponics, grey water systems, green manures, crop rotation etc.

Currently, we have a pressing issue with our irrigation system and I would appreciate any help or advice. We have a powerful (5bar or roughly 70psi) electric pump in a nearby river which was previously used to irrigate the market gardens. Unfortunately, the river is full of sediment, algae and all the neighbours spray their mango trees rather freely. There is a 20,000L (5,000G) rainwater tank (not refilled for many months of the year due to the dry season) which I am considering using as a settlement/filtration tank. The tank input could have an in-line filter attached. This would then have a submersible pump floating on the surface of the water in the tank which would, in turn, pump to the sprinkler system.

My questions - would a clay/sand/charcoal filter work adequately in only one tank which would fill under high pressure? How long would the water have to stay in the tank before pumping out again? Does anyone have any suggestions for a low-tech and effective solution for filtering out muddy and potentially chemically affected water that would be suitable for our situation?

Thanks in advance and I'm happy to share feedback on our progress

To summarise:

20 acre mixed organic farm
tropical/subtropical climate with distinct wet and dry seasons
Nearby river is turbid, has algae, and a high potential of being polluted with chemicals
20,000 litre tank
70psi electric water pump

A few things will need to be determined:

Actual water consumption needs in LITRES PER DAY - seasonal
Water analysis – how ‘dirty’ is it really
Soil analysis – chemical content (see below)
Define ‘organic’ in the Taiwan context because countries differ according to their regulations

General:

If not already done, there are ways to improve the water holding capacity of soil to reduce, and sometimes remove, the need for irrigation; especially with trees

Even using drip irrigation, 20,000 litres is nowhere near enough to irrigate 20 acres – it’s barely enough to do one acre under full crops in that climate. So, the storage tank would need to be filled and emptied several times a day to ensure soil moisture is maintained at a consistent level

It seems the major problem with the river water is the chemical content rather than the sediment/algae load – though sediment and algae aren’t good for pumps or storage tanks.

Removing debris like algae and sediment is pretty straightforward for most filtration systems e.g. settling tank or tanks, screens, and regular maintenance to remove the resulting sludge. However, in a non-commercial context, the removal of heavy metals and chemicals used in insecticides, fungicides and fertilisers is much harder for large volumes of water.

Typically, the filtration system is only as good as the filters/membranes being used and the frequency of maintenance. There’s two basic ways: carbon filters and reverse osmosis. The latter removes chemicals.

Both systems are expensive to implement and maintain so they work effectively, the reverse osmosis option is most likely overkill depending on just how polluted the river water actually is.

If river water was previously used for irrigations, and neighbours continue to spray, the soil is most likely already contaminated to some degree. I acknowledge you probably want to reduce further contamination and, besides, in that climate most chems will eventually leech out or breakdown over time.

I suggest filtering chemicals out of that volume of water is not practical, so, have you considered a bore or well?

Collect all the minute sediments 'dissolved' in the turbid/murky river water and add it to your land. It is the most fertile of soil. but no need to go dredging.
Collect all the duckweed from the river it adds 600lbs of nitrogen per acre.
Collect all the green manure/algae/invasive aquatic life from the river, it's like chop and drop+liquid compost.
Collect all the free nitrogen and phosphorous that the neighbors are throwing in the river for you to use.
You could probably even charge some money for all the hard work you are doing for the 'community'.
Most people wish they have this 'unlimited' gift that you are talking about.
Find a better pump that doesn't get clogged easily. or some how emulsifier the algae/etc so as not to clog the sprinkler.

Another idea is to build a pond (preferable at the top of the property).
Have that pond filter/collect as much of the green manure from the river, returning the rest of the water back to the river.
You can use weekly flood irrigation to water the soil/plants. The soil will naturally filter and breakdown the horrible stuff in the river water.
You can use your existing pipe infrastructure to dump water into irrigation ditches on contour (swales).
You can even add liquid/organic compost to this water.

To breakdown pesticides/etc just inoculate the soil/water/liquid compost with as much wild mushroom slurries.
Traditionally we would welcome the start of the season river flood for their deposits of fertility. And mushrooms esp oyster mushroom will break down the organic based pesticides in just a few weeks turning it into carbon dioxide without it accumulating. Arsenic/heavy metal based ones (these are no longer really made/sold) are a bit different but even those are reduced to a form that is less bio-available.

Excellent. Some speedy and thoughtful responses. Let me first clarify a few of the questions that F Agricola raised.

In summary, your summary was pretty spot on. However, for now, I'm only looking at our market garden area rather than the whole 20 acre farm.

It's about 60m² of ditch and furrow cultivation. Lots of leafy greens, cabbages, radishes etc on the inner beds and peanuts, pineapples, rosella, corn etc on the outer beds. Thus, looking at the inner intensively irrigated area (40m²) and working on a rough estimate of 6.5L/m² I'm thinking about 250-300L of water per day. This is from Oct-Mar. I'm told that over many years here the dry season keeps getting drier and the wet wetter, and given that it's November and 30°C, these estimates may have to be raised. We are getting a well dug near to the river to take advantage of natural filtration, but it depends on the availability of the excavator driver and he's a very busy man. It's also on the other side of the whole property....

We have had the water tested and it's pretty good as far as heavy metals go. There are some infrequent fish die offs and it's definitely very turgid with a lot of algae.
The soil content is likewise low in heay metals, but also low in fertility with a pH around 7.5 - we are adding organic compost and animal manure at the time of planting.  
I'll go with defining organic in our context rather than speaking about Taiwan in general. It's a meditation and yoga retreat with an emphasis on sentient/yoga diets (no garlic,onion,egg,meat,mushrooms) and we have more than 10 people who live on the property, many volunteers who stay here and also many guests. It's not so realistic in this rural and agricultural environment to be overly demanding about organic purity. I want to do the best I practically can. We generate A LOT of food scraps and make hot compost, we use farm-grown mulch regularly - but it breaks down fast, we use farm-made enyzmes and liquid compost along with commercial organic fertilizers.
I absolutely agree about planting trees and shrubs around the perimeter of the garden.

As to S Bengi's suggestions. We already collect duck weed from the river and our ponds. Algae - not a bad idea, but also a lot of work. Sediment - I worry there would be more concentrated pollution in the silt. I'm not sure how many people wanting to keep their veggie plots clean would appreciate the free herbicides that the local mango farmers contribute, but I'll try to be grateful The pump is specially designed for river use, so it doesn't clog 'easily' but it certainly does clog. Regularly and at the bottom of a 10m ladder climb down a typhoon wall. I also agree on the ponds - it could be an option to pump into our pond and from there into the water tank. I will use a feeder tank for liquid compost and probably a weekly flood of the ditches would be very helpful. No need for swales on this section as it's very flat and, to be honest, we have a whole season where getting rid of excess water quickly is critical.

So, in conclusion, my thoughts for now...
1. Adding a foam sheet around the river pump will help prevent contamination, but will be a nightmare to regularly access and clean.
2. I'm looking at in-line filters, but they also have to be easy to screw in and out and cope with high pressure
3. A slow sand filter appeals to me, but I'm concerned it's not practical with a 20,000L tank to top up and the pump costing quite a lot to run if I reduce the incoming pressure into the tank and thus take much longer to fill it. Ideas?
4. Gravity feeding water down into the 20,000L tank from our lotus pond. Easier to access and filter. Might need to install a float valve
5. I'll certainly accept a better solution rather than an extremely expensive/perfect solution. I'd be very grateful to hear from anyone with any experience filtering river water into holding tanks for irrigation water. I'm also really pleased with the responses I have so far. Thanks for the suggestions

I would get the water and soil tested. You don't know what's going on until you do. I wouldn't spread biomass or sediment from the river until you do so. You might be taking contaminated sludge and spreading it all over your land.

I would assume ongoing contamination via the river and the aforementioned pesticides, and I would plan for the worst. This will help you put in place measures that will actively combat contamination over time.

I would first look to rejuvenating the banks of the river where it's on your property. I would look at placing any natural or artificial features you can perpendicular to the direction of flow on the shoreline, even fallen logs or small piles of boulders or rocks sticking out like fingers into the river, so as to divert water to the bank and encourage silt deposition, taking it out of the water.

I would plant these sedimentation areas with a complete local reed system, and I would ensure that whatever the local heavy-feeding riparian trees, perhaps willow of some sort, they are regularly planted to shade out the water, lowering solar heat gain in the shallows and preventing more algae growth.

I would gather local mushrooms, and I would add to them oyster mushrooms, and make fungal slurries with which I would inoculate the riparian area, so that the whole bank area between the river and the rest of the land is essentially one big biological filter.

I would then dig a trench, on-contour, parallel to the river. It would be a secondary biological filter, a long, narrow pond, with more reed ecosystem for water treatment. This doesn't need to have any accessible water unless it's an advantage. It can be filled with large rocks if it is desired. I would put a layer of biochar along the bottom and sides of the trench, and put large stones atop it. I would make sure that the bottom of the trench extends down past the water line, so much of the groundwater is forced to flow through the biochar on its way to the next stop.

I would dig a well, then, with the riparian biofilter and the biochar trench between it and the river. It needn't be more than a hole extending to just above the depth of the biochar trench, itself also lined with biochar and held in place with large stones. The pump or the end of the pump's intake goes in the well, and out comes clean irrigation water, or at least as clean as biochar, microorganisms, fungi, and natural aquatic filtration can make it.

How to ascertain enough supply is another concern. I echo the suggestion about digging a pond at the height of land on your property, or as close to it as possible. You could pump water up from your new well site to the pond without worrying so much about contamination from pesticides and excess fertilisers. The riparian area of the pond would get the same treatment as the banks of the river, cleaning the water again.

If they are available as a resource, I would use wood chips or sawdust mixed with biochar as material for pathways. I would inoculate with fungal slurries as much as possible, and I would make oxygenated compost extracts to constantly bump up the levels of microbial activity in the soil. The more active the life in the soil is, the more any contamination is being broken down.

Incidentally, if you have a problem with contamination that you need to remedy, it can be as simple as growing a trap crop of sorts, something that grows a lot of biomass in a short time that also accumulates the pollutant in question. In this case, it sounds like that may be a heavy metal, and something like industrial hemp might foot the bill. If that's not possible, giant sunflowers, like the Russian Mammoths, might do as well. What also might work is belts of coppiced or pollarded woodlot. If you can grow poles for fenceposts or firewood, either way, the pollutants are going to be sequestered in a durable form, and as long as when they do break down it's either off-property or at high temperatures, you're remediating your land.

I would grow out the sequestering crop, grow a polyculture of chop-and-drop green manures in the spaces between, or situate a crop that would benefit from a little heavy metal, like fruit trees ( this depends on the specific contaminant and the levels). I would chop-and-drop the green manures just after they'd dropped their seed (as long as the remediation was ongoing, otherwise the last time or two, they'd get chopped beforehand), harvest the sequestration crop and either pelletise the biomass, use it for, say, paper or cloth-making, or turn it into biochar and add it to the riparian area and biochar reed filter trench.

If contamination really is a concern, I would harvest all fruiting bodies and either make biochar or dump them off-site. The fruiting bodies of the fungi along with the biomass from the remediation crops will be full of the stuff you want taken out of your soil, so it can't remain. If burnt in a rocket mass heater or rocketstove, the temperatures should get high enough to break down everything to carbon dioxide and water, though the little ash will likely be loaded with contaminants, so that would be best disposed of off-site.

What we need to know before we offer any further advice is as much as you can about where you are and what's upstream of you.

Please keep us posted, and I wish you the best of luck.

-CK

It really depends on the layout of your property and where things are located in relation to height, for example:

If you are concerned with the river water quality; its sediment load, algae and pump blockage issues, a suggestion is to stop using the river altogether, concentrate on getting that well dug - good and deep.

Then use the pump to extract water from the well, perhaps even have diversion valves so you can pump it to multiple locations e.g. into a tiered series of ponds to increase soil moisture over a larger area, to the 20,000 litre tank to create a pressure head for whatever, to the fruit trees, etc.

Water could then be diverted from the ponds to the market garden using gravity - free!

Having a series of interconnected ponds continuously flowing keeps even moisture levels (drought proofing) with the possibility to breed fish i.e. some species will only breed in running water.

You may find that pumping will become less time and energy consuming, and, the property remains green all year, and no more pump blockages or chemical worries.

We have had the water tested and it's pretty good as far as heavy metals go. There are some infrequent fish die offs and it's definitely very turgid with a lot of algae.
The soil content is likewise low in heay metals, but also low in fertility with a pH around 7.5 - we are adding organic compost and animal manure at the time of planting.  
I'll go with defining organic in our context rather than speaking about Taiwan in general. It's a meditation and yoga retreat with an emphasis on sentient/yoga diets (no garlic,onion,egg,meat,mushrooms) and we have more than 10 people who live on the property, many volunteers who stay here and also many guests. It's not so realistic in this rural and agricultural environment to be overly demanding about organic purity. I want to do the best I practically can. We generate A LOT of food scraps and make hot compost, we use farm-grown mulch regularly - but it breaks down fast, we use farm-made enyzmes and liquid compost along with commercial organic fertilizers.
I absolutely agree about planting trees and shrubs around the perimeter of the garden.

So, in conclusion, my thoughts for now...
1. Adding a foam sheet around the river pump will help prevent contamination, but will be a nightmare to regularly access and clean.
2. I'm looking at in-line filters, but they also have to be easy to screw in and out and cope with high pressure
3. A slow sand filter appeals to me, but I'm concerned it's not practical with a 20,000L tank to top up and the pump costing quite a lot to run if I reduce the incoming pressure into the tank and thus take much longer to fill it. Ideas?
4. Gravity feeding water down into the 20,000L tank from our lotus pond. Easier to access and filter. Might need to install a float valve

pH = 7.5, this is about + 0.8 from where most plants, and especially vegetables would prosper, it is also the same for overall nutrient availability. It is good that you know that heavy metals are low concentration.
Algae can be filtered out quite easily with a large quantity sand filter, this could be done in a pipe type or it could be done in an open tray type setup that feeds the tank you speak of.
If you went with a tray type filtration setup you could have it in three sections, pure sand at the inlet then a membrane separator, next would be a wood chip/sand  mix charged with mushroom slurry to get the mycelium growing for further water purification which would take care of any residual herbicide and pesticide as well as any heavy metals, next would be another membrane separator, the third section could be a pH adjustment section with some pure mineral sulfur mixed into the sand of this layer and finished off with a double layer of membrane just before the discharge tube that would go into the storage tank.

This system would allow you to not have to wait for sediment settling prior to usability of the water in the tank, if you use perforated plates at the filter system inlet, the water pressure could be dissipated enough to prevent filter material erosion.
Costs of such a system would be minimal as well, the containment box could be constructed of wood and if total collection of water was needed some sort of fiberglass containment could be constructed as the unit was being built, to fit under it or even made as the bottom of the filter materials container unit.
The use of pressure reducing plates means no need to reduce the pressure of the pump as well.
Your idea of gravity feed to the tank sounds great as well, taking the down hill side of the pond and turning it into your filter bed like I describe above is a good solution, the lotus plants would add a layer of pre-filtering sediment settling.

If you are promoting the sentient/ yoga diets, the closer you can get to true organic practices, the better for the chakra's of those participating.  
(with as much literature as their is about the definite immune system benefits  of garlic, onion and  mushroom consumption, I am surprised that these are no-no's to these diets).

Redhawk

Apologies for the delayed response. It's pruning season and I have had exhausting days of trimming the trees and hauling great quantities to the wood chipper to be recycled back to where they came from, but hopefully composted down, and with the borers and other insect problems substantially reduced. I'll be adding biochar, liquid compost and fungal slurries to these mulch piles. Any idea on how much slurry should be added to an adult mulberry or wax apple tree for example?

Regarding the above answers, thank you all very much and I'm going to post some pictures because I feel that my initial description was somewhat misleading.

Many rivers in Taiwan are monsoonal and are also completely empty during the dry season. During typhoons, they can quickly run 10m higher than usual with tremendous disturbance to both the banks and the river bed. For this reason, many of the rivers have concreted banks and the problem is deferred downstream.

We do have a well being dug on the property, but this is an expensive process and one is probably all we're going to have in the next few years. It's a long way from the vegetable garden and will hopefully be used in the near future to irrigate a lowland orchard. The problem with our ponds is that the soil here just isn't suitable for natural water storage. The soil particles don't bind adequately to create a naturally impermeable surface, so our ponds have liners and are then backfilled with earth to mimic natural conditions more closely. Sadly, this water obviously cannot move through the landscape. They do, however, have a substantial quantity of fish, lotus, water hyacinth and duckweed and are topped up with both rain water and some grey water from surrounding buildings.

I think Redhawk, that your suggestions are very applicable to our situation. Looking at the size and height of our tank, do you think one of the sand filters or tray type filters would be feasible to install on top of the tank? Adding the mineral sulphur to the tank, along with some of our liquid enzyme and beneficial bacteria (we also buy this commercially) would be a great way to fertilize and gradually balance the pH of the field without too much disruption.

I did some research on the perforated plates and believe that they will be very useful in this situation. The catch, often, is trying to purchase these items and get the corresponding fittings here in Taiwan. Rain water isn't collected here anywhere near as much as my home country Australia. I have installed a number of tanks, but try to what local people told me at first, the problem is with the boom and bust nature of the water cycle here. In a heavy rain even the biggest tanks are filled within a day or two. Then, while the rain continues to bucket down for weeks the tanks merely overflow. Once the rain stops, it stops, and then even 20,000L of water gets used up pretty fast. Also, much of the property is flat and thus pumps become a necessity to move this stored water around. Where feasible, I have installed gravity fed systems to passively move water to lower levels.

To be honest, I'm feeling very conflicted about how much we have installed in the way of PVC piping, pond liners, electrical wiring and metal storage tanks. If this infrastructure is done right, then the farm will have a solid basis on which to practice permaculture principles, but it seems very difficult to establish all this without using a lot of petrochemical products and processes. I'm intending to make some amends next year and plant a large section 5 woodlot on the further edges of the farm.

Oh, and about the sentient diet. I believe that there is acknowledgement of the health benefits of alliums, but they are held to have a negative effect on meditative practice. This belief is shared with the local Buddhist version of vegetarianism as well. Mushrooms? Well, that's more of a religious prohibition that is based on fungi growing on decaying matter and thus perceived as not clean.

In conclusion, I'm very happy with the suggestions presented so far. I'm still somewhat unsure how to divert the water through the suggested biological processes and then return it to the storage tanks for pumping. I'll look into Redhawk's suggestion of tray filters and pressure plates. The pond gravity-feed idea is one of the most feasible, but I wasn't aware previously that it is leaking.

It's not so realistic in this rural and agricultural environment to be overly demanding about organic purity. I want to do the best I practically can.

This is a very reasonable position. There is a saying "Perfection is the enemy of the good". There is a certain amount of hormesis that we disregard in our reach for absolutes. The plants you are growing will need some herbicide and pesticide exposure, they will have it intentionally or not. You cannot eliminate it due to the tragedy of the commons. What you can do is promote life in your little pocket. I love it!

I have no further input past what Dr Redhawk and others have mentioned, the only thing that truly accumulates in a vibrant system is heavy metals and radioactive isotopes. As long as you are not dousing the area in those, fungal life will be able to manage. It needs exposure time, so the effort is best geared to those, preferably long before it goes near vegetables. I suspect your pH is from limestone due to the geology of the island, and you have lots of sulfuric acid on the way from the mainland to fix it in the rain, unfortunately. That tends to have lots of cesium in it as well. There is no way to totally avoid contamination downwind from China and in a densely industrialized area. I put down wood chips that undoubtedly have some stuff in there that is not desirable. I lose more sleep over not having enough wood chips to make a vibrant ecology as soon as possible.

When I was a young pup I worked in Germany on a toxic waste rehabilitation project. The microbes (in this case bacterial due to the study design) were able to do almost unbelievable things. Every energy-rich bond has something that can  use it to maintain life, even benzene. Not saying we should spray it all over the place but promoting life is the key.

I appreciate your effort to work with what you have and not be paralyzed with what you haven't got.  

Thank you, that's a sincerely appreciated comment. I'm an idealist who has constantly had to learn to seek middle ground

This conversation is fascinating.  Thank you Busumatako for starting it.  I'm learning a great deal.

The use of reed beds for water filtration can be scaled according the volume of water you desire to treat.  It might be an interesting experiment to build a reed bed filtration system and see how effective it is pulling sediment and algae from the water, and how quickly it gets "gummed up".  Even a moderately sized reed bed system should be able to consistently process 10,000 liters of dirty river water a day.  

Would that supply all your water needs for the entire operation?  No, but in the drier months it would make a significant contribution to the overall needs of your operation.  If it works well, you could scale it up accordingly.

If the reed bed system were located down near the water source, then you wouldn't have to pump all that sediment and gunk all the way up to the top of your property.  You would pump the water to the top of the first reed bed, and then let it gravity feed through a series of beds until the purified water flows down to the catch point at the bottom, where a second pump then sends it up to your large sand filter/holding tank.  If the water is as dirty as you state, you'd probably need to rebuild that first reed bed every year—new sand, new plants, hauling away the accumulated sediment, etc.  But that's a small price to pay if you are getting a steady flow of purified water throughout the dry season.

Please keep us informed of your progress as you continue to innovate and experiment.  Pictures are always appreciated!

Best of luck.

You could also filter this water in a way similar to alot of sewer system.

Aeration Tank, Settling, Sand Filter, Green Filter, Mushroom Filter.