Archive for March, 2017

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.