In Israel, solar radiation is higher in the spring and summer than in the winter. This radiation causes the effluent reservoir water surface to heat up due to continuous and high sunray
exposure throughout the day. Since the warm water in the reservoir’s upper layer (between one and two meters) is less dense and “lighter” than the cold water in the deeper
layers, it does not penetrate the deeper layers. This prevents transference and the reservoir’s “natural” water mixing. Water temperature differences between the
upper and bottom layers can be considerable, reaching up to 10 degrees Celsius and sometimes higher.

Even the night’s relatively cooler temperature during warm seasons is insufficient to lower the upper layer’s temperature to match the deeper layers.

Thus, “natural” water mixing doesn’t even occur at night. Due to these considerable temperature differences, even strong winds cannot generate adequate water
mixing in the reservoir during warm seasons.

In fact, without treatment, two distinct and separate layers are formed in the reservoir during warm seasons (a phenomenon known as “thermal stratification”).
The epilimnion layer is the upper, high temperature layer that absorbs light and oxygen from the reservoir’s water surface and creates algae photosynthesis.
The hypolimnion layer is the lower layer, and, as mentioned, is significantly cooler and is not penetrated by light (since the distance from the
water surface and the algae in the upper epilimnion layer cast a “shadow” that blocks light from penetrating the water surface) .

The conditions generated in this layer are anaerobic.
The thermal stratification causes a significant decline in the reservoir’s water quality partly due to the water’s lower oxygen level, algae, pathogenic bacteria overdevelopment, and a
delay in sludge absorption processes.
The thermal stratification can be prevented during spring and summer; thus, the reservoir’s water quality can be maintained by continuously mixing the reservoir’s water.
Mixing the reservoir’s water has numerous benefits:
1. Improving the oxygen balance – mixing the reservoir water enhances the oxygen balance in the lower levels. It prevents oxygen emission into the atmosphere during the day
(when the oxygen concentration in the hypolimnion layer is higher than the saturation). In addition, increasing the reservoir’s organic load is feasible due to an improved oxygen balance.
2. Reducing the development of algae – water mixing helps prevent green algae overdevelopment since the algae are relocated to a shadier area for several hours daily. Moreover, the oxygen dispersed throughout the water body precludes the release of phosphorus from the bottom of the reservoir, thereby encouraging the growth of algae-eating crustaceans. Furthermore,
preventing thermal stratification by mixing helps eliminate cyanobacteria growth that is toxic or has a foul odor and other algae that can clog irrigation systems.
3. Improving pathogenic bacteria removal – in the upper layer (epilimnion), pathogenic bacterial mortality is generated naturally, among other reasons, due to solar radiation, changes in oxygen levels, and high formation.
Water mixing generates an active oxygen-pH, and the upper layer conditions are then developed in the reservoir’s deeper layers, thus enhancing pathogenic bacteria removal in all
reservoir layers.
4. Improving and extending sludge absorption at the bottom of the reservoir – starting in March, the reservoir’s water temperature rises at the start of spring. In untreated reservoirs that generate
thermal stratification, the lower layer’s temperature increases slowly, and the hypolimnion remains colder all summer compared to the reservoir’s upper layer. This phenomenon persists until the fall when thermal stratification ceases. Thus, the anaerobic sludge absorption, accumulated throughout the year, is delayed until the end of summer and occurs only in August and September. During this short period, these conditions cause a sudden release of dissolved substances into the water, damaging the effluent quality. Preventing thermal stratification by mixing the water allows the temperature of the reservoir’s lower levels to rise from the beginning of spring, causing the sludge absorption period to extend over many months, thereby improving the reservoir water quality.

What system can be employed for general efficient water mixing in the effluent reservoir at reasonable costs and minimal energy?
Madan Technologies’ RIO series floating mixers can provide a proper and effective solution to thermal stratification in the summer months and prevent the phenomenon at a reasonable cost and with maximum efficiency. These are submersible mixers installed on a stainless-steel construction, which includes fiberglass buoys. The RIO series floating mixers of Madan Technologies from
Kibbutz Ma’agan Michael have a rotation capacity of up to 3,000 m3/h – the ability to move 72,000 cubic meters of water per day while utilizing only 2.5 horsepower!
Madan Technologies’ RIO series floating mixers have been installed and have been operating regularly in dozens of reservoirs in Israel for over 15 years with great success.                    Experience demonstrates that the installed mixers effectively prevent thermal stratification in the reservoirs, significantly improving the water quality.
This is achieved while utilizing minimal energy and at a nominal initial cost when assessing accomplishments over time. In addition to effectively preventing thermal stratification during the summer season, the floating mixer from the Madan Technologies Rio series has other possible uses:

When spraying algae, the RIO mixers can efficiently disperse the spray in the reservoir’s water body. The Rio mixers’ efficiency in swiftly mixing large quantities of water in the reservoir
generates homogeneity of the spray agents and enables their effective dispersal. The spray agent distribution is executed by connecting a spray container placed on the bank of the
reservoir via a hose to the RIO mixer installed
inside the reservoir. RIO mixers are a superior alternative to using expensive methods to disperse the spray, such as aerial spraying – another reason it’s an efficient and economical product.
Moreover, installing solar systems above reservoirs is an increasingly common practice, eliminating the option of using aerial spraying to treat algae growth. With these solar systems,
the only feasible method to treat algae in the reservoir is by dispersing the spray agents using the RIO mixers.
Another benefit of RIO mixers is their ability to remove sand and sludge that accumulates in the reservoir’s pumping areas, thus successfully unclogging the system or preventing the
obstruction that can be caused for various reasons. Thus, for example, if the reservoir exterior wall was damaged and generated an accumulation of sand that caused a blockage in
the reservoir’s pump, the clogging substances will be pushed away by the Rio mixers, thus enabling the operation to proceed successfully at a minimal cost.
In addition to its usage in effluent reservoirs, Madan Technologies’ RIO mixing systems can also provide an excellent solution for balance pools, operative pools, and irrigation                  reservoirs – enabling water movement in the reservoirs and thus significantly enhancing water quality.
In conclusion, the floating mixers from Madan Technologies offer high energy efficiency solutions at low cost, providing an overall and comprehensive response to the water
quality concern in effluent and other water reservoirs. In addition, the system also offers an excellent solution to other requirements related to the proper management of
water reservoirs, such as dispersing spraying agents and moving sludge at the bottom of the reservoir – with maximum efficiency and at a reasonable cost.