Archive for the ‘Water treatment’ Category

Farm dam water filter – the results are in!

Saturday, March 11th, 2017

On our farm we require good quality water for jobs like cleaning in the dairy. We built a water filter that would be capable of treating a large volume of dam water so that it could be used to top up our rain water tank through dry periods. The design can be seen Low tech farm dam water filter.

In a slow media filter water passes slowly down through a filter medium. In our filter we used rockwool. The rockwool acts as a trap for sediment. Over time a layer of micro-organisms, mainly bacteria, builds up on top of the media. These trap and digest organic contaminants in the water. So it is a type of biological filter. Slow media filters have a simple design and have been used in many places mainly as a cheap and easy to make filter to improve drinking water. Studies have shown that they are effective in reducing turbidity and reducing bacteria and organic matter contamination in water.

A new filter needs to have water run through it for some time to condition the filter. This allows the biofilm to develop and for the filter to become effective.

Test results:

At the time of testing the dam water entering the filter was of reasonable quality. The turbidity was slightly elevated and fresh organic matter was in the low to moderate range. Coliform bacteria and total aerobic bacteria levels were elevated.

We tested before filter and after filter samples starting from day 2 after the filter was started. The tests were for coliform bacteria, total aerobic bacteria, turbidity, humic material by UV absorption and fresh or readily degradable organic matter by permanganate oxidation. Humic materials often give water from dams or creeks pale yellow or brown colours.

On day 2 before and after coliform and total aerobic bacteria counts were high and showed very little difference.

After operating for 8 days, filtered samples showed a 68% reduction in coliform bacteria.

After 18 days there was a 96% reduction in coliforms and 50% reduction in total aerobic bacteria.

At day 20 there was a 21% reduction in turbidity, 44% reduction in fresh organic matter and 15% reduction in UV absorbance.

Coliform bacteria are a large group of bacteria that are naturally present in water and soils. The group also includes some species that can cause illness. Therefore they are often used as indicators of water quality with higher than normal levels indicating possible contamination.

Slow media filter supplying water on a dairy farm

A slow media filter made from 2 x 200 L barrels on a dairy farm. The filter treats over 1000 L of dam water each day which is then used to top up a rainwater tank.

Maintenance: Our filter has now run for 6 weeks without any problems. We expect that at some later time the biofilm may build up and perhaps restrict the flow of water. There is a drain plug installed just above the biofilm layer which will allow some of the biofilm to be removed.

How the idea can be extended: If more filtered water is required then another filter with its own float valve and connection to the source water could be added. Both could then feed into the one collection barrel. A slow media filter could also be used to maintain the quality of water in a tank. In this case the filter would continuously take water from the tank, treat it then put the water back into the tank. The same type of filter could be installed in a gravity fed farm water supply. If the source water can be fed in by gravity and the treated water can be run off to below the filter then no pressurised water or pumps are needed.

A slow media filter is a low cost and low tech but effective way to improve the quality of surface water such as creek and dam water on farms.

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.

Effluent management on a dairy farm

Saturday, November 9th, 2013

For the last few weeks I’ve been visiting a dairy farm in West Gippsland to learn a bit more about how dairy farms work. It’s also an opportunity to apply some ideas about soil and water management in a practical context.

Cows can deposit around 8 – 10% of manure and urine output around the milking shed and yards. Manure and urine contains significant amounts of major nutrients including nitrogen, phosphorous and potassium.

On many farms this manure is often washed directly into specially contructed waste retention dams. A typical setup is a sedimentation dam sometimes followed by an aeration dam.

Sedimentation dam for dairy waste on a farm in West Gippsland. Water is washed into the dam from the milking shed and yards without treatment.

Sedimentation dam for dairy waste on a farm in West Gippsland. Water is washed into the dam from the milking shed and yards without treatment.

The picture shows a sedimentation dam on the WG farm. There is a thick crust of manure on top which means that conditions in the dam are most likely anaerobic. At this dam I didn’t want to get too close in case I became part of the waste system! Therefore I didn’t get a sample!

In an anaerobic dam the organic matter itself provides oxygen to help drive the other processes that eventually break down most of the organic matter into methane, hydrogen, carbon dioxide and ammonia. But the disadvantage of this method is that energy in the organic matter is lost (as methane) and importantly nitrogen is lost (as ammonia).

The overflow from the sedimentation dam on the farm enters a second aeration dam. What can we expect the water quality to be in this type of dam? There shouldn’t be much nitrogen but what other nutrients will be present?

Dairy farm aeration dam in West Gippsland. Water flows into this dam from an uphill sediantation dam that takes waste directly from the dairy.

Dairy farm aeration dam in West Gippsland. Water flows into this dam from an uphill sedimentation dam that takes waste directly from the dairy.

The aeration dam is just below the sedimentation dam. The overflow pipe can be seen in the picture. The water has a brown colour and a slightly unpleasant smell. Here are some water quality tests done in the Apps Labs lab: Dissociated carbon dioxide 13.5 ppm (elevated); Turbidity (unfiltered) 57 FTU (high); Turbidity filtered (0.45 micron) 19.8 FTU (still high); pH 7.1 (very slightly on the alkaline side); UV absorbance 99.2% (very high dissolved humic materials); Conductivity 1459 microS/cm (elevated salts); redox potential (ORP) -44.7 mV (anaerobic, and that’s at the surface).

Nitrate and nitrite were checked using screening tests. Both were at low levels or absent. That’s expected anyway because nitrates usually don’t exist in low oxygen conditions and nitrites usually form from nitrates under reducing conditions. Phosphate was checked using two different test kits. One showed phosphate over 30 ppm. The other showed phosphate as 43 ppm. Both these levels are very high.

There may be significantly more phosphate present in the two dams than the amount measured as some is likely to be held in the sediments.

What about nitrogen? Ammonia – nitrogen in the aeration dam was 0.44 ppm. This is higher than normally found in natural waters but is not excessive. At pH 7 around 0.4% of this nitrogen can be expected to be in the ammonia form as opposed to the ammonium form. This is not good for water life because the ammonia form is harmful. In general as water becomes more alkaline, an increasing amount of any total ammonia nitrogen present is likely to be in the ammonia form. This same amount of ammonia nitrogen, is roughly equivalent to 2 ppm nitrogen as nitrate. This is slightly elevated for natural waters so the nitrogen in the ammonia form probably doesn’t account for all the nitrogen in the original manure entering the two dams.

What is the best way to use dairy effluent to capture maximum nutrient value?

The following web resource provides detailed figures on tests done on dairy effluent dams and suggests way to reuse the nutrients in the effluent:

DPI Victoria 2013, Using dairy effluent as a fertilizer. Downloaded from http://www.dpi.vic.gov.au/agriculture/dairy/pastures-management/fertilising-dairy-pastures/chapter-13, November 2013.

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.

Reducing water hardness by lime softening

Wednesday, November 28th, 2012

Water hardness is caused by high calcium and magnesium levels. However a water test is needed to find out how much hardness is accounted for by bicarbonates, called temporary hardness and how much is composed of sulphates and chlorides (permanent hardness). For a discussion of alkalinity and hardness please see Water test interpretations.

Lime softening uses calcium hydroxide to raise the pH of the water to reduce temporary hardness. At around pH 10 calcium is precipitated and at around pH 11.5 magnesium is precipitated.

Laboratoriy trial of lime softenin.

Calcium hydroxide ready to be added to a sample of hard water in a laboratory trial.

The theoretical dose of lime can be calculated from water test results. In practice the dose of calcium hydroxide and final pH adjustment needs to be tested on actual samples in laboratory trials. Too little lime will only reduce calcium. Too much will create an imbalance of calcium and magnesium in the final sample and will make pH adjustment more difficult.

In the Apps Laboratories lab we were successful in significantly reducing the hardness in a bore water sample from a rural property. After several trials we arrived at a lime dose that achieved a good final balance of salts and hardness.

EC Hardness Calcium Magnesium
microS/cm ppm CaCO3 mg/L mg/L
Untreated 1630 769 72 139
Treated 586 162 34 18.5

Calcium and magnesium precipitate formed after dosing with lime. If the dose is right the 'fluffy' precipitate settles quickly.

Calcium and magnesium precipitate formed after dosing with lime. If the dose is right the 'fluffy' precipitate settles quickly.

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.