Place: Lev Hanegev Reservoir, Israel
Date: May 2017
The “Lev Hanegev” reservoir is managed by Mekorot, Israel’s national water company, supplying reclaimed wastewater for irrigation purposes. The reservoir is prone to repeated algal blooms (diatoms or Chlorella-like sp) which clog irrigation pipes and mandate regular treatment.
Mekorot is currently treating the reservoir periodically with ~25-50 kg (50-100 lb.) of copper sulfate. The application requires two workers and takes approx. half a day.
The Lev Hanegev reservoir holds ~12,000 m2 (3 acres) of surface water. Being a man-made wastewater reservoir, approaching the water is only permitted from a single designated location at its northern end. This predetermined application location limits the operator’s ability to optimally apply the Lake Guard™ upwind – in accordance with the flow of the currents. At the time of application, wind and currents rendered the application point suboptimal, carrying the floating granules sideways (Western wind, see picture below), rather than deep into and across over the reservoir. Furthermore, intensive pumping during the treatment resulted in a rapid recession of water levels.
At the time of application, the water in the reservoir was infested with a bloom of green algae, Chlorella-like sp., that dominated the entire water column.
Based on the conditions in the reservoir, it was determined to treat the water with 12 kg (24 lb., theoretical concentration of ~0.35 ppm) of Lake Guard Blue™, which is 25-50% of the usual dose applied during regular treatments .
Measurements were taken at the surface of the water as well as at a pumping location at the intake [2-3m (~6-9f) deep]. Each measurement comprised of 3 biological replicates and included: temperature, pH, %DO, specific conductivity, phycocyanin concentration, chlorophyll-a concentration, total copper concentration as well as filter-clogging time.
The treatment was applied at the Northern access point of the reservoir, the only place to approach the water. The entire dose was applied manually from the shore within 5 min. Immediately after application, the floating granules were dispersed by a western wind.
Measurements were taken before treatment, as well as 24 hours and 48 hours after treatment.
- Measurements taken before treatment indicated the existence of a mild bloom dominated by green algae concentrating in the water column. Chl-A measurements from the intake showed 20 µg/l, while surface samples showed concentrations of 8 µg/l.
- Active copper ions in the water before treatment measured at 0.06 ppm. 24h post-treatment active copper ions count measured at 0.1 ppm, dropping below detection levels 48h after treatment.
- Chl-A levels in the water column dropped within 24h from treatment by ~60%.
- A similar drop was monitored in phycocyanin levels.
- Filter-clogging time taken from the intake indicated an improvement of 50% in the quality of the water within 24h, maintaining similar results 48h post treatment as well.
- All other parameters (temp., pH, DO) did not vary significantly over the 48h after the treatment. Relative conductivity levels reduced by 6% in comparison to 48h post-treatment.
- Efficacy of the Treatment with Lake Guard Blue™: the treatment proved to be efficacious in all relevant parameters within 24 hours from treatment, despite suboptimal conditions in terms of application location.
Water conditions remained at satisfactory levels for >3 weeks, which is in line with standard treatment.
- Reduction of Effective Dose: the treatment achieved its goals in treating a bloom while using 25-50% of the dose usually applied at this reservoir.
- Convenience of work and ability to operate prophylactically rather than in response to a bloom: Based on the work in the reservoir and the evident ease of implementing a Lake Guard Blue™ treatment, it is recommended to switch from a responsive treatment to a regular prophylactic treatment regime. A prophylactic treatment should include a periodical application of 3-6 kg (6-12 lb.) Lake Guard Blue™ (0.087-0.175 ppm) in the water, which is expected to prevent future blooms from developing altogether.
- Prevention of harmful algal blooms in the reservoir, avoidance of undesired suspension of operations throughout the season and reduction in complaints from end users.
- Time and cost savings: dramatically reducing the dose and the time needed to effectively treat the reservoir.
- Incidental cost savings associated with reducing the amounts of chlorine needed at the intake; pesticides needed for treating subsequent crustaceans nuisance; as well as reducing filters’ backwash.
- Safety: the treatment with Lake Guard Blue™ reduces dramatically the safety hazards associated with the current treatment regime to the field operators. This routine includes:
- exposure to high quantities of pesticides;
- preparing them for treatment;
- dangerous movement along the reservoir’s circumference in the attempt to spread the pesticides as evenly as possible.
- As mentioned before, the application of the Lake Guard Blue™:
- requires no preparation;
- allows the use of minute quantities in comparison with the alternative;
- can be applied from one point in the reservoir, even if suboptimal, while leaving the remainder of the spatial distribution of the compound in the water to winds and currents.
- has a superior environmental outcome, given the reduced copper levels and subsequent accumulation in the environment in absolute terms.