By Darrell Corkal, Prairie Farm Rehabilitation Administration, Saskatoon, Joanne Sketchell, Sask Water, Saskatoon, and Jim Kidd, Sask Water, Nipawin
Conventional water treatment chemicals be applied directly into farm ponds to improve the water quality? That's the question Sask Water, Saskatchewan ADD Boards, PFRA and the Saskatchewan Research Council have set out to answer with an ongoing study.Liquid aluminum sulphate is commonly used to treat drinking water in many towns and cities throughout the world. The chemical works like a magnet by colliding with dissolved matter suspended in the water. At correct dosages, it binds with the dissolved matter, forms a denser and larger particle known as a flocculant and settles or precipitates to the bottom of the water column. In a water treatment plant, the settled matter, known as sludge, is pumped away for disposal.
In recent experiments, liquid aluminum sulphate has been applied to dugouts as large as 5 million litres. In addition, one storm water retention pond of nearly 13 million litres has been treated.
Prior to treatment, the dugout water was analyzed in laboratories at the Saskatchewan Research Council. Various dosages of aluminum sulphate were used in jar testing to select an optimum treatment concentration. Field experiments over 21 to 50 days on 300-litre cells of water confirmed field response. Finally, the full dugout was treated.
To date, about 12 sites have been treated by the aluminum coagulation method, some with very dramatic improvements and others with less dramatic but nevertheless beneficial changes in water quality. This process can reduce dissolved organic carbon, turbidity, colour and phosphorus. In a dugout, it is believed to be beneficial to leave the sludge at the bottom since the aluminum will bind with the soft sediment and help to minimize the release of phosphorus back into the water column.
Treatment dosage is regulated in the field by a pH meter, with optimum reactions generally occurring in the range of pH 5 to 6 with aluminum salts. However, field applications did not lower pH below 6.5 in order to prevent the killing of aquatic life.
Some limitations will occur on sites high in alkalinity as chemical costs could increase. On the opposite end of the spectrum, low alkalinity sites may be difficult to treat as a rapid drop in pH could kill aquatic life. Since a dugout is an ecosystem, the treatment technique chosen should also strive to keep the desired aquatic life alive. For example, zooplankton will eat algae (phytoplankton) and are therefore an important part of the dugout ecosystem.
In terms of potability, some concerns exist with regard to the residual of aluminum after treatment. If levels are high, the water should not be used for human consumption unless it is first passed through a distiller or reverse osmosis membrane.
Batch coagulation of dugouts may be a promising way to improve water quality in dugouts, if due care is taken and the water is monitored properly. Results will be presented in more detail when research is complete. Costs to treat one dugout could range from about $500 to $1,000. The treatment would likely last one year, if there is no new inflow of low quality raw water to the site.
This project is supported by the Canada-Saskatchewan Agriculture Green Plan, SRC, Sask Water and PFRA.