Posts Tagged ‘Water filters’

Low tech filter for farm dam water

Friday, March 10th, 2017

Farm dam water is challenging to treat because it typically has high overall bacteria levels, is often discoloured by humic materials, has elevated turbidity and often has elevated levels of fresh organic matter.

On our dairy farm we rely on dam water through the dry months. The dam water is pumped to a holding tank near the dairy and is used as wash down water in the dairy and for drinking water for cows.

Dam on dairy farm in South Gippsland

Dam on a dairy farm in South Gippsland. The dam collects water from surrounding paddocks that are grazed by dairy cows. In this water bacteria levels are elevated and fresh organic matter is slightly elevated.

Water from a rain water tank is used to wash cows, clusters and to do the final rinse and clean. During summer the rainwater tank is occasionally topped up with the dam water. We needed a filter to treat about 1000 L each day of the dam water to improve the quality of the top up water.

Slow media filters are a simple low-tech method for treating poor quality water. We built a slow media filter out of two plastic 200 L barrels.

The main barrel has a few inches of clean gravel in the bottom. Horticultural grade rockwool was added up to about 2/3 the barrel height. The rockwool sits on a piece of woven shademesh to stop it mixing with the gravel. A manifold of PVC pipe with multiple drill holes sits within the gravel layer. It is glued to a riser pipe inside the barrel that exits just above the rockwool layer.

The filter is kept full of water by a float valve that lets in pressurised dam water. A valve on the outlet restricts the flow of water out of the filter. This both slows the flow of water in the filter and maintains a ‘head’ of water above the rockwool.

Slow media filter on a dairy farm.

Dam water enters the filter through a float valve. A valve on the outlet is opened just enough to allow a small flow through the filter. There is always water above the biofilm layer.

Over time a layer of microorganisms called a biofilm mainly made up by bacteria develops on the surface of the rockwool. Our filter has a biofilm surface area of 0.25 sq meters and has an output of 0.8 L each minute. Most of the work in a slow media filter is done by the biofilm layer which catches particles and digests organic material.

The second barrel catches the treated water. It has an automatic sump pump that periodically pumps the treated water out into the dairy rainwater tank. Even running at this low rate the filter treats around 1150 L each day.

The total cost of setting up the filter including fittings, rockwool and sump pump was under AU$200.

References:

Guchi, Ephrem. “Review on Slow Sand Filtration in Removing Microbial Contamination and Particles from Drinking Water.” American Journal of Food and Nutrition 3.2 (2015): 47-55.

My tank drinking water smells, what can I do?

Monday, December 31st, 2012

One of the frequent problems seen in water tanks is smelly water. This can occur in above and below ground tanks and includes rain water tanks. People often describe the smell of their water as musty, decaying or like ammonia or rotten eggs. It can be just a little bit off-putting or in some cases can be very unpleasant. In any case its hard to drink and wash in smelly water.

The ammonia or rotten egg smell is a give away for anaerobic conditions. In other words poorly aerated water.  The first test to do when investigating smelly tank water is a redox test. Redox or oxidation reduction potential is an indicator of oxygenation and unlike oxygen level tests redox can also show very anaerobic conditions.

Tests from one underground tank with smelly water showed that redox was 145 mV just below the water surface. Generally redox in the 200 – 250 mV range is commonly seen and acceptable for drinking water. Below 0 mV is definitely not good. So 145 mV was a little low but not too bad. However at the kitchen tap where water is drawn from deep in the tank the redox was -58 mV. Now that is bad! It indicates anaerobic water. This water had an unpleasant ‘eggy’ smell.

testing being carried out on a below ground concrete rain water tank. The tank is dug into a slope with no barrier to stop runoff running onto the tank.

Testing being carried out on a below ground concrete rain water tank. The tank is dug into a slope and risks contamination because the tank is level with the ground on the uphill side.

Checklist for smelly tanks:

  • is there runoff entering the tank?
  • have you been on holidays or have you just bought the property?
  • do the downpipes from the roof go underground then come back up before the tank?

What can be done about smelly water? If the smell can be traced to anaerobic conditions the simplest thing to do is direct the stream from a garden hose back into the tank. Just ripple the water and try to get a slow circulating movement happening in the water.  There’s no need to do anything too drastic like emptying the tank or throwing in handfulls of chlorine. All you need to do is get oxygen back into the water to reverse the reactions that created the smells in the first place. As a safeguard think about installing a cartridge water filter, one that has an activated carbon cartridge. That will help to remove some of the smells and will be good insurance against any future contamination. The Basic Water Quality Test from Apps Laboratories is designed to test water quality factors and can be used to trouble shoot water quality problems. Apps Labs also supplies rural and farm water filters.

Filters for farm water supplies.

Saturday, December 8th, 2012

Not all water quality problems for farm and rural drinking water can be solved by simple filters. However there is a lot that can be done to improve drinking water quality. Its often a matter of being proactive in case contamination occurs. Dual cartridge systems are easy to install and can often be fitted under the kitchen sink. The choice of cartridges depends on the source of the water.

Above ground or well protected rainwater tanks usually don’t build up bacteria levels but they can develop undesirable smells if poorly aerated. Use a sediment cartridge and a 5 micron carbon cartridge. At Apps Laboratories we have selected some dual cartridge combinations that can be applied to different situations. See them at Drinking water systems.

If you have to backup your water supply from a creek or dam then use a sediment cartridge plus a finer carbon cartridge, one that is designed to reduce waterborne protozoan pathogens. Your carbon cartridge should reduce some turbidity so that UV treatment can be added. UV is very effective against bacteria provided there is not too much dissolved organic matter in the water. Ask Apps Laboratories for a Basic water quality test.

Many farms source water from fairly protected situations like springs or bores. But there may be fine silt or sediment and a risk from bacteria. Again a fine carbon cartridge like the KX Matrikx Cr1 is recommended. The second cartridge will be a special ceramic cartridge such as the Doulton Sterasyl. Ceramic cartridges are very effective at reducing bacteria. At Apps Laboratories we have tested ceramic cartridges and the results are reported in Ceramic cartridge test.

Doulton Sterasyl ceramic cartridge for bacteria reduction.

Doulton Sterasyl ceramic cartridge for bacteria reduction.

For more details on Rural and farm drinking water systems please see Rural and farm systems.

Boosted reverse osmosis filter for farms

Friday, August 21st, 2009

One of the problems with many homes in rural areas is that there is not enough pressure from pressure pumps to run a reverse osmosis filter system. Reverse osmosis filters work by pushing water against a very fine membrane. Only a proportion of the water, usually 1/4 to 1/3 gets through, leaving behind most salts and other contaminants.  The rest of the water with the contaminants goes to waste.

A boosted RO system for rural homes.

A boosted RO system for rural homes.

RO systems are designed to remove a large proportion of most contaminants from water including salts and chemicals. The result is very clean water. RO works more efficiently with reasonably clean water like rain water tank or spring water.

The picture is of a boosted RO I made up. It is in the lab and produces rinsing water for the lab and also drinking water for the house. Output is about 108 l/d. It uses a 24 gpd membrane. 50 gpd membranes are also commonly used. The prefilter is just a 1 micron sediment cartridge. The second cartridge is a 1 micron carbon block cartridge. This cartridge is designed to reduce tastes, smells and protozoan pathogens. Here are some results for the lab RO system.

Before filter After filter
DOC* by UVA 254 nm 2.1 ppm 0
Conductivity 87 microS/cm 7.4 microS/cm

* DOC = Dissolved Organic Carbon. DOC is directly proportional to UVA at 254 nm for most waters. Here an estimate of DOC is made based on an approximate relationship derived from published data from a variety of waters.

There are no detectable dissolved organics getting through and the salts level has been significantly reduced. RO membranes can also reduce bacteria in the water but I haven’t tested bacteria reduction yet.

For a range of water filters to suit both town and country applications see Water Doctor water filters.