REMOVING PHOSPHORUS IN SEPTIC TANKS BY USING AQUA STONE

The university of Oulu, Green Rock Ltd and Kemira Plc carried out a joint research on the suitability of Aqua stone for retaining phosphorus in septic tanks. The research period was from November 7, 2000 to March 28, 2001. There were altogether six research sites in the municipalities of Haukipudas and Kempele in Northern Finland. Wastewater samples, about 100 in total, were taken from the third septic tank on each house, about ten centimetres below the wastewater level by using a pump sampler. This sampling method proved to give a good sample on the quality of wastewater leaving the septic tanks. The solubility rests on the chemical stones were carried out under test conditions at a toilet.

According to solubility tests the sawed chemical pieces lasted for about 100 flushes, whereas the compressed pieces lasted for about 150 flushes. The solubility of the compressed pieces was rather constant.

Observations showed that Aqua stone primarily affected on the content of phosphorus in wastewater and the state on phosphorus. The average phosphorus content in different septic tanks varied between 5-7 mg/l or between 10-12 mg/1 depending on the dosage of Aqua Stone. The chemical dosages used in the research were 150 g/m3 and 250 g/m3 respectively.

Before Aqua Stone was used, the ph-levels of wastewater were rather high, i.e. between 7.3 and 8.3, which weakens the precipitation of aluminium sulphate and increases the need of chemical. The ideal precipitation pH of aluminium sulphate is between 6.2 and 6.5.

Aqua stone is an affordable way to reduce phosphorus loading on the environment. Further research is needed on the application of Ekoteko Aqua Stone for other fixtures, such as a floor drains and kitchen pipes. The method must be as simple to use as the device in a toilet.