Correction of cyanobacterial blooms
1.Convencional approaches in cyanobacterial blooms removal
Contemporary technological solutions, used for cyanobacteria blooms management, match the given criteria only to a limited extent. Very expensive solutions, such as sediment removal, are effective only if external source of nutrients is removed as well, effectively preventing nutrient-rich sediment creation. Another way is blocking (immobilizing) nutrients in these sediments using chemical substances. Alternative mechanical removal of the biomass should only be considered when there is a temporary gathering of cyanobacterial biomass on the surface. There is a problem with their subsequent storage and associated drying, however, which leads to amorphous crusts formation and subsequent problematic disintegration. Removal of cyanobacterial biomass using herbivorous fish species does not bring the desired results either. Some laboratory observations even prove that, although these fish receive fodder plankton easily, they do not posses the ability to break down and digest the blue-green algae in their digestive tract (tested fish are usually silver carp and Bighead Aristichtis nobilis).
One of the few solutions, which can remove cyanobacterial biomass, is the usage of chemicals such as coagulants, flocculants and algaecides. However, they are still facing the problem of inaccurate application and thus, unnecessarily large dose concentrations used. These interventions are not only uneconomical, but environmentally unfriendly as well. Among the most commonly used substances are: copper sulphate (bluestone), ferrous sulfate (copperas), ferric chloride, aluminum compounds, calcium hydroxide, etc... An effective and environmentally friendly solution would be the utilization of enzymes, though they´re deployment is hampered by limited use (only removes sediments containing nutrients) and price.
2.Electrocoagulation, an alternative to the common practise
Thus a demand for technology, that will be able to use and combine different solutions according to the actual conditions of each water body, has emerged. The aim was to develop technology, that will allow these interventions. The principle of the technology is based on the Ejector jet application, which is under development since year 2000. Technical solutions are currently protected by four patents and two industrial designs.
Electrocoagulation technology is based on the principle of water electrolysis in the reactor cell assembly, which comprises aluminum, iron, or combined blades, which receive low-voltage direct current electricity. An optimum concentration of electrolyte is reached, during witch the potential of dispersed particles is reduced and coagulation reaches it´s activation threshold.
The effect of the reaction is accompanied by formation of oxygen, ozone and hydrogen microbubbles and simultaneous formation of positive aluminum ions Al3 +. When in contact with water molecules, these react with negatively charged ions, colloidal particles and subsequently flocculate. The water is separated not only from mechanical colloidal particles, but also from dispersed organic impurities and particulates. An advantage is, that this approach allows one to control the current density depending on the detected amount of impurities in treated water.
Another equally significant advantage is the absence of contemporary chemicals used for coagulation. The electrolysis induces a significant cyanobacterial reduction and simultaneously a partial water disinfection, due to the biocidal effect of the released medium from the process of electrolysis. Electrocoagulation is thus a friendly alternative to chemical products (PAX, vitriol,... ). The technology eliminates the need to transport tens of tons of commonly used materials on the site of application, and in particular, significantly reduces the environmental burden of unnatural ingredients. Price of the intervention is thus further reduced by the cost of substances and logistics costs. Unlike common coagulants like aluminum sulfate or polyalumuiniumchlorid (PAU, PAX) this approach does not cause nutrient immobilization (phosphorus, nitrogen) in sediments, making them unavailable for bio-degradation. Concurrently, the amount of aluminum exported into the water and sediment is virtually zero.
Up to this date, this technology has undergone several trial applications on various locations in the Czech Republic (Jablonec, Máchovo jezero, Klabava, Orlík). Brief conclusions of the interventions, listed on these sites, state that generally positive results have been achieved. Technical reports are available and distributable by SILFOR (www.silfor.cz).
The technology, which is constantly under development, successfully utilizes several synergistic effects: an adjustable ejector nozzle capable of deploying various substances into the water column. Water is evenly treated with targeted application, operated through the ejector jet. The aim is not to affect the characteristics of water in the entire water column, but to cover the part of a reservoir layer with an increased incidence of cyanobacteria. The electrocoagulation method is aimed on cyanobacteria zeta potential neutralization, causing coagulation and floculation of particles and colloids. The process is accompanied by active aluminum hydroxide Al (OH) 3 ion release, which occurs on the reactors and causes a secondary biocidal effect. Intervention by electrocoagulation can be specifically applied whenever there is an excessive development of algae. In some cases it is possible to further increase the effectiveness of the intervention by enzymes, either applied in pure form or as a bio-preparation.
3. Ejector application
Ejecting application allows controlled application of a variety of media (including binary and polyfactorial substances) in trophogenous layers of the water column, where the blue-green algae are found in actual time. The effective interaction occurs only after their incorporation into the treated water. Targeted applications bring maximum effect, and they are very environmentally friendly. We can also apply substances into the reservoir sediment, which is especially suitable for biological products application, for sediment organic fraction reduction and to reduce the release of bottom nutrients. Ejecting applications are managed in real time based on GPS and sonar; they are very accurate and the effect is easily verifiable. An output report is presented after the intervention.
The device is composed of two parts: a DC voltage source, with the parameters being dependent on the volume and the contamination of the treated water. The second part of the device is a laminated reactor; the sizing is determined by the duration of exposure time.
Application is carried out in form of a targeted incorporation of electrolytically treated water into the water column.
- The equipment itself is integrated on board of the application vessel. Application conditions allow for sensitive setting of a combination of two main technologies used – a generator and applicator tech.:
- The electrodes are located on the rear side of the vessel, electrolytically treated water is fed into the trophogenic layer using appropriately sized ejector nozzle; the main propulsion is carried out by the vessel itself.
The electrolyte is generated in tanks on board of the ship and injected into the nozzle applicator.