Roughing filter + "Daylight Drive" water delivery system

a practical, low-cost, off-grid option for removing sediment and sending water where you need it

A friend recently asked for my help solving an urgent water problem.

He’s starting an orchard and permaculture site in steep, hilly terrain in the Brushy Mountain province of the Blue Ridge Mountains (northwestern NC). Normally summers here are wet with plenty of rain. This summer has been different however. Our region has had very little rain - in some locales almost no rain at all - since mid-May.

Over the past couple of years my friend has been on a major tree-planting binge, trying to get his orchard project up-and-running. With very hot temperatures and drought conditions over the past two months his trees are mega-stressed in in danger of dying. So recently he asked me to come up with a plan to facilitate watering the trees, and “Put a hurry-up on it!”

He’s got a spring that flows through his property that at least so far into this drought is still producing water. But the stream runs down in the holler, of course, whereas he needs water way up at the top of his property above the orchards so that he can gravity-feed hoses or a drip irrigation system to his fruit and nut trees.

Now we’re seeing the stream under extreme low-flow conditions but it’s easy to tell from the catchment’s morphology that during periods of high rainfall the creek swells, carves up its banks, and carries and deposits significant loads of sediment.

So not only do we need to move water from a low point on the property to a high point, we also need to deal with episodic flow conditions and substantial amounts of sediment that could damage pumps, clog drip irrigation systems, etc.

So here’s what I came up with:

It’s an up-flow gravel roughing filter in a 200 L (55-gal) drum modified to have essentially a PVC pipe “borehole” in the middle of it. Down the simulated “borehole” we put a DC well pump driven by solar photovoltaic (PV) panels.

Water flows into the bottom of the gravel filter by gravity from the spring catchment. Sediment settles in the lower layers of gravel, and clear water spills into the “borehole” through holes in the PVC pipe. It’s then pumped to storage tanks at the top of the hill by the DC well pump.

Sediment is flushed from the filter on an as-needed basis by backwashing (reversing the flow direction) by simply opening the large cleanout valve near the bottom of the drum to expel the dirty water.

The criteria for this project was that it needed to be done pretty quickly, fairly cheaply, robustly and with low complexity, and off-grid (since my friend does not have power at his orchard site yet).

“Daylight Drive”

I designed this system to be as simple as possible - the DC well pump is wired directly to the solar panels (with only an On/Off switch in between). When the sun is shining on the panels (and the switch is On), the well pump runs. If there’s partial sun or shade, the well pump runs slower. It doesn’t run at night - hence “Daylight Drive,” a term I borrowed from friends who have pioneered the concept at Living Energy Farm.

There’s no inverter (to convert between DC and AC power), and no batteries for energy storage. The inverter and batteries are typically the most expensive components of solar electric systems so this approach saved a lot of money.

SYSTEM COMPONENTS AND SPECS

Except for the irrigation hose, HDPE drum, and large diameter PVC pipe, all plumbing and electrical components were purchased from amazon.

My friend already had an HDPE “pickle barrel” drum we used to house the filter:

The gravel depth is about 28” (about 70 cm) and the total volume of gravel used is about 5 cubic feet (about 140 L).

PLUMBING

For the “borehole” pipe I used a section of 6” inner diameter PVC electrical conduit I had laying around. I cut a hole in the lid of the pickle barrel to insert the PVC “borehole” pipe through, and epoxied the circle cut from the lid to the bottom of the PVC “borehole” pipe to close it. (This worked fine with what I had on-hand, but a better solution could be to use a section of PVC drain pipe with a proper slip-fit lid glued on the bottom end.)

The inlet and overflow lines are 1.25” diameter irrigation hose. They’re fitted to the drum using 1.25” bulkhead fittings and hose barbs (easy to find on amazon).

The cleanout is made using a 2” PVC threaded ball valve, a 2” threaded male-male close nipple, and 2” threaded bulkhead fitting (also easy to find on amazon).

ELECTRICAL

DC well pump According to the manufacturer’s specifications, it is a 12 Volt submersible pump with a maximum flow rate of 3.2 gallons per minute (12 L/min) and a maximum water lift of 230 feet (70 m). I estimated that the elevation difference between the streambed and the water tank at the top of the hill was about 80 feet, maybe 100 feet. For the design I planned (hoped) that this pump would be able to deliver 1-2 gal/min at that elevation. 1/2” irrigation hose was affixed to the pump outlet to transmit water uphill to the storage tank. The pump cost about US$150 from amazon.

PV array This designed used two 100 Watt, 12 Volt PV panels wired in parallel purchased as a two-pack for about $120 from amazon. I enclosed the electrical connections in a waterproof case using cable glands, and added a waterproof On/Off switch in-line between the panels and the pump (all purchased from amazon).

OVERALL COST ESTIMATE

Depending on how much water line is needed from the spring catchment source to the gravel filter, and from the pump to the water storage tank, this whole system can be constructed for around US$500.

Here’s a photo from the first test of the setup:

And here’s my friend happy to finally have water flowing to one of the empty tanks at the top of his orchard:

At that elevation above the filter/pump we measured a flow rate of just over 2 gal/min (>7.5 L/min).

On a clear sunny day he should be able to fill three of these ~300 gallon (~1,000 L) IBC totes.

VULNERABILITIES AND CONCERNS?

In trying to anticipate what might go wrong with this setup, I suspect our main source of potential trouble will be the water intake. If it gets clogged, or the steam level drops further with the continuing drought, then insufficient water (or no water) could be delivered to the gravel filter inlet.

During our first test pictured above, the flow rate of water coming into the filter was greater than the flow rate out from the pump when the panels were in full direct sun (at zero elevation, so the maximum possible pump flow rate). Even with the pump at max flow there was still water going through the filter overflow port. In this condition, the “borehole” would stay filled, avoid the risk of being pumped out and exposing the pump to drawing in air.

But if conditions change and the stream catchment provides insufficient flow to the gravel filter, then the pump could run dry. These pumps are supposed to have an automatic shutoff if they get too hot, but who knows if this will be ok to protect the pump from damage if flow to the filter stops or drops below the minimum needed to keep the “borehole” full.

Another big potential vulnerability comes from my electrical work! This is an area where I likely “don’t know what I don’t know.” But - hopefully that will be remedied soon as I am attending a “Daylight Drive” training at Living Energy Farm later this month! I’m sure Alexis et al. will be happy to critique my design and suggest improvements.

Let me know what you think of our “quick-n-dirty” roughing filter / Daylight Drive water pump solution! We’ll see what all goes wrong with this system and I will report back on our troubleshooting.

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As always, I/we we am/are very grateful for your enthusiasm and support of our work. I haven’t been posting here as often as I’d like to - this is generally because of being buried in various projects that are not at good points for summing up.

However, soon I should be able to report out on one big project I have been working on the past two months with Caminos de Agua. We are in the process of designing a facility for regenerating bone char used for removing excessive fluoride from groundwater. I wrote previously about bone char/fluoride treatment and the need for regeneration (extracting sorbed fluoride from spent bone char so that it can be reused).

Sorbent regeneration is key to the economic feasibility of fluoride treatment in low-resource settings, such as villages in rural Guanajuato, Mexico. Caminos received a generous grant to build a regeneration facility for their bone char filters. We’re now working to optimize the regeneration process and determine the quantitative specifications needed to design and build the full-scale facility. Construction is scheduled to begin late this year or early next year.

For the past six weeks I have been building a pilot-scale regeneration facility in my home lab. We’re using this for process engineering and optimization - in particular treatment of the wastewater stream so that it can be released safely (and legally) to the environment. I’d like to report out on that soon, once I have some of the kinks worked out of my pilot reactor setup.

Thanks again for you interest in our work! More to come…