The Nautela pilot site is situated in Lieto municipality in Finland. The pilot site is established by the Turku University of Applied Sciences (TUAS) on a small agricultural ditch witch discharges to river Aurajoki. The size of the pilot sites´ catchment area is about 70 hectares and over half of it consists of fields. There is also a small part of residential area in the catchment basin.
The main purpose of the pilot site is to study the feasibility of chemical phosphorus precipitation in the treatment of agricultural ditch waters. At the site granular ferric sulphate is dosed to stream in relation to the water flow. The chemical doser is placed upstream from the previously created sedimentation pond. Purpose of the doser is to enhance the retention of the dissolved phosphorus in a pond. (The operational principle of the ferric sulphate doser is represented in Jokioinen pilots -web page.)
The functionality and effectiveness of the method are being monitored regularly by water samples and the water quality online monitoring system. The research on this site started in the fall of 2010 and it is meant to continue until the end of the year 2012. According to the water samples, this method reduces dissolved phosphorus load on average by half. However, there are big fluctuations in dissolved P removal efficiency between individual water samples (Figure 1).
Figure 1. Dissolved P concentrations in the ditch water before and after the treatment at the Nautela pilot site.
So far the monitoring results have not shown any significant effects on other water quality parameters than dissolved phosphorus. With applied ferric sulphate dosing, this method does not have a notable effect on nitrogen or suspended solid load. Nevertheless, the method influences on that part of nutrient load which is the most essential for surface water eutrophication and the blue-green algae blooms. Method also functions during the spring flow, when vegetation based nutrient removal is inactive.
Figure 2. The water quality online monitoring system installed at Nautela Pilot site before the Ferix-3 doser and sedimentation pond. On the left YSI 6000 multiparameter sonde and S:can Nitro::lyser probe to the right. Picture: TUAS.
Figure 3. The Ferric sulphate doser and the v-notch weir at Nautela. The iron chemical dissolves from a nylon netting cone, at adjustable rate according to the flow conditions, and precipitate phosphate from water in insoluble form. Picture: TUASFigure 4. Ferric sulphate doser and v-notch weir during spring flow at Nautela. Picture: TUAS
Figure 4. Ferric sulphate doser and v-notch weir during spring flow 2012 at Nautela. Picture: TUAS.
Figure 5. Ferric sulphate doser and v-notch weir in the autumn 2011 at Nautela. Picture: Antti Kaseva.