Current Solutions

Although harmful algal blooms have been known for more than 40 years (Shilo, 1967), presently available solutions are uneconomical, impractical in large scale reservoirs and present an ecological hazard.

The result is a global annual economic loss estimated at more than US$5 billion caused by harmful algal blooms.

The available treatments are mostly used in artificial small ponds, pools and small shallow lakes where the ecological aspect of overdosing is not crucial. These treatments are certainly not adequate for large water bodies nor are they suitable for repeated use due to their toxicological and ecological impact, their high cost of application, and their requirement for high doses to ensure uniform dispersal.

 

Several means for treating algal blooms are presently employed:

Copper sulfate (CuSO4・5H2O)

Copper(II) sulfate pentahydrate (CAS # 7758-99-8)  is an odorless and a very potent algicide approved under the US EPA for water reservoirs including potable water sources. It is used in large quantities in aquaculture and contained artificial ponds, where toxicity is a minor issue.

The Lake Guard Blue™ is designed to minimize the dosage  as well as the operational costs associated with the application of copper sulfate to a fraction of their current levels.

Sodium Percarbonate (2 Na₂CO₃ · 3 H₂O₂))

Sodium Percarbonate (aka ‘Sodium Carbonate Peroxyhydrate’; CAS# 15630-89-4) is an odorless algaecide composed of Soda Ash and Hydrogen Peroxide (H₂O₂) which is considered to be the most environmentally friendly algaecide commercially available for the treatment of cyanobacteria. However, and although approved under the US EPA, its overall usage is quite limited. The major reason this compound did not establish itself as a viable solution are high operational costs. In addition, and unlike copper or chlorine-based compounds, its active oxygen concentration is relatively low, badly impacting its potency – especially in the context of a full lake treatment and the potential for dilution.

Moreover, the use of liquid H₂O₂ poses serious dangers, as large quantities of the compound have to be carried on boats where they may cause significant safety issues, including combustion or physical exposure to leaks.

In contrast, the Lake Guard H₂O₂ dramatically reduces the operational costs associated with the application of hydrogen peroxide, as the product travels independently on the currents along the cyanobacteria. Its ability to effectively target the cyanobacteria spatially as well as vertically, further reduces the overall input required to achieve effective concentrations of H2O2 where needed. Coming in dry, granular form, it requires no special preparation or equipment reducing unneeded exposure by operators to a minimum.

Calcium Hypochlorite (Ca(ClO)₂)

Calcium Hypochlorite (CAS# 7778-54-3)  is commonly used as an algicide (under NSF/ANSI 60 where it is limited to 15 mg/l), as well as a bactericide, deodorant, disinfectant, fungicide and so on.

Hypochlorite is widely used in the  cooling-water systems of power plants. These facilities have been authorized by regulators worldwide to treat the systems with chlorine in order to avoid biofouling. Free chlorine is later being discharged in massive quantities to adjunct water bodies. This method is regarded as ‘the best available method’ in terms of biocidal efficiency and cost effectiveness (Hergott et al., 1978). The US Code of Federal Regulations (40 CFR 423) dictates limitations on the concentration of free-chlorine and the permissible amount of chlorinated water discharge to be released into a water body per day per reactor. And yet, a power plant with a standard daily flow of five million cubic liters can release up to 200,000 kg of free-chlorine into the adjacent pond on an annual basis (see Table 3.1 in Pacey et al., 2011). Comprehensive environmental studies that have been conducted by various environmental protection agencies showed that this mass discharge of chlorine had insignificant adverse effects on fauna and flora (e.g. Brungs, 1973; Hergott et al., 1978; Sung et al., 1978; Pacey et al., 2011; Ma et al., 2011). Moreover, studies also showed that residual chlorine byproducts from these practices, such as trihalomethanes, were found below harmful levels (Hollod and Wilde, 1982; Jenner et al., 1997; Jenner and Wither, 2011).

Nevertheless, hypochlorite of any type has never been registered as an algaecide for freshwater bodies and therefore is currently not approved for use as an algaecide in surface water.

BlueGreen’s past field trials with this compound have confirmed that treatment with chlorine concentrations of under 5 g/m2 had no effect on fish, seabirds or turtles.

Moreover, our hypochlorite-based formulation (Lake Guard White™) was found to fully release its chlorine content within 60 minutes from application and to interact with the existing organic load in the water, after which total-chlorine could not be detected in the water (<0.01 ppm). In contradiction to in-vitro tests done in purified water (i.e. Clasen and Edmondson, 2006) this rapid interaction released all bound chlorine regardless of the pH range in the ponds (~pH 8.0).

Phosphate Binders

Phosphate is a well known factor in cyanobacterial succession over other microorganisms in aquatic habitats.  It is therefore logical that eliminating phosphates from the water leads to a decline in cyanobacterial infestations. Compounds such as aluminum sulfate and Phoslock efficiently bind to phosphates and sink to the sediment. In some cases, treatment of a whole lake with these compounds may prevent a few seasonal blooms.

Similar to treatments with copper sulfate and hydrogen peroxide, treatments with phosphate binders are applied subsurface, thus limiting the feasible scale for treatment, making it extremely expensive.

While considered a “preventative” measure against cyanobacterial blooms, the treatment is only effective to the extent it is able to bind with sufficient amounts of phosphate in the water. Given the abundant sources of phosphates from catchment areas, the effect of these  treatments is usually short-living. In addition, and although seldom addressed, treatment with phosphate binders include drastic amounts of binders, which in turn “rains” over the  sediment and chokes it. It is important to remember that bound phosphates remain in the ecosystem and under some conditions (heavy storms and water mixing)  can be re-released into the water column. Worse off, the bound phosphates are regularly consumed by “bottom feeders” such as carp and are easily disturbed and compromised by normal wind and wave action in shallow lakes.

Considering the overall (limited) demand to treatment with alum salts, BlueGreen is currently developing an alum-based product, the Lake Guard Alum™, which will  remove all operational obstacles associated with aluminum treatment for end users wishing to implement it.

Barley / Rice Straw

Placing barley or rice straw into aquatic ecosystems has been practiced in some places with an inconsistent effect. A recent discovery of the active compounds released from the straw (flavonolignans salcolin A and B) did demonstrate a lytic effect on Microcystis aeruginosa. However, these active compounds are not commercially available and have yet to obtain the required environmental and regulatory clearances which are likely to require long-term toxicology and environmental-impact studies.

Herbicides

Herbicides such as diuron, simazine and atrazine are rarely in use due to their high price and the grave environmental consequences they are associated with.

Cyanophages or Viruses

Algal viruses or cyanophages (lytic viruses that specifically attack cyanobacteria) have been hypothetically suggested, although to date, none has been identified for commercial use.