Posts Tagged ‘rural water’

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.

Farm water supply investigation

Saturday, January 25th, 2014

A preliminary investigation was carried out on the quality of water in two dams on a dairy farm in West Gippsland. The dams are a short distance apart in the same gully. The Upper dam is spring fed and can overflow into the Lower dam. The water was tested during summer. At that time the flow into the Upper dam had decreased and the water level was falling. The Lower dam was still fairly full.

The dams are in an elevated position and drain approximately 10 ha. The surrounding land is pasture.

Farm dam in West Gippsland. The Upper dam in this study. Water is pumped around the farm for drinking water for stock and also for washdown water in the dairy.

Farm dam in West Gippsland. The Upper dam in this study. Water is pumped around the farm for drinking water for stock.

There are many waterbirds on the dams – mainly ducks. Cows have access to both dams and commonly drink at the water’s edge. The water in both dams has a pale yellow-brown colour. There is significant attached bacterial – fungal mats clearly visible in shallow water.¬† One significant observation was that were no visible micro crustaceans.

Dam CO2 EC Turbidity Reactive C ORP*
ppm microS/cm FTU mg/L mV
Upper 18 289 11.5 0.5 207
elevated sl. elevated sl. cloudy moderate OK
Lower 5.8 738 3.5 0.5 205
moderate elevated clear moderate OK
* oxidation reduction potential

Some key findings are: Dissociated carbon dioxide was high in the Upper dam. The water is fairly clear in both dams with the Upper dam water just slightly cloudy. Overall salts as conductivity are elevated in the Lower dam. Both dams have oxidizing potential (a surrogate for oxygen level) within the desirable range.

Reactive or relatively fresh organic matter was estimated by permanganate digestion. In both dams reactive organic matter was in the moderately elevated range. Humic material in dams can be measured indirectly by UV absorbance. In both dams the UV absorbance was high, around 65%.

The pH of the Upper dam was 7.2 and pH of the Lower dam was 6.8. A pH buffer system analysis of the Upper dam gives a calculated pH of 6.7. This suggested the scenario of a falling pH (water becoming more acidic) as the carbon dioxide level rises. In this case the rise in carbon dioxide is being most likely caused by increasing organic matter decomposition. See organic matter figures below.

A pH buffer system analysis for the Lower dam gives theoretical pH of 7.84. This suggests that carbon dioxide level in this water is falling and this will cause the pH to slowly rise (the water will become more alkaline).

Farm dam in West Gippsland. This is the Lower dam in the study. Some physical and chemical factors show some improvement compared to the Upper dam. However there levels of the 3 key bacteria water quality indicator groups are twice the levels compared to the Upper dam.

Farm dam in West Gippsland. This is the Lower dam in the study. Some levels of physical and chemical factors are more favourable compared to the Upper dam. However the levels of 3 key bacteria water quality indicator groups are around twice the levels of the Upper dam.

Dam E. coli coliforms TC*
CFU’s / 100 ml CFU’s / 100 ml CFU’s / 100 ml
Upper 440 3317 53281
elevated** high moderate
Lower 960 7119 118274
elevated** elevated** sl. elevated
* aerobic plate count
** indicates contamination

For both dams the high  E coli level taken along with the high coliform levels indicate some fecal contamination of the water. Total aerobic bacteria level is approximately in the moderate range for exposed waters.

The main quality issue in both dams is elevated reactive organic matter levels and elevated E coli bacteria levels. There is some evidence that processes in the Lower dam are at least slowing deterioration of water quality. However on the negative side, levels of bacteria are significantly higher in the Lower dam.

Ideally in a study like this it would be useful to test the source water, in this case the spring water entering the dams. Unfortunately the spring was not accessible. There was also no other dam on the property to provide a comparison.

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.