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Water Problems - Algae

Algae is a term referring collectively to a wide range of pigmented, oxygen-producing,
photosynthetic organisms usually present in surface waters. Virtually all aquatic vegetation
without true roots, stems and leaves is regarded as algae. Algae range from microscopically small unicellular forms, the size of bacteria, to larger filamentous forms which can be metres in length. Like other plants, algae are primary producers requiring light, carbon dioxide, water, nutrients such as nitrate and phosphate, and trace elements for growth. Algae are common inhabitants of surfaces water exposed to sunlight.

Algae play an important role in the natural purification of surface waters through the
assimilation of nitrogen species (ammonia and nitrate) during photosynthesis. Algal
photosynthesis also releases oxygen as a by-product into the aquatic environment. Algae
often form the basis for aquatic food webs. Algal overgrowths or the presence of noxious
algal species can, however, become a nuisance and interfere with the desirable uses of a
water body. 
Occurrence Algae can loosely be grouped into three types,
free floating algae (phytoplankton), attached filamentous algae and algae that coat rocks, plants and sediments (periphyton).
The classification of algae is extremely complex.

However, for the purposes of this guideline, the following groups are important:
! Blue-green algae: These typically dominate highly nutrient-enriched waters and are
sometimes referred to as cyanobacteria.
! Green algae: These are common summer residents of less enriched water bodies.
! Euglena: These are flagellate unicellular algae, typical of organically-enriched water.
! Diatoms: These are flagellate unicellular algae surrounded by a silica coating. This group
often dominates winter algal populations.
There are several types of algae which produce toxins, of which two types appear to be the most common. 
In fresh waters, the blue-green algae are often responsible for the occurrence of toxic algal blooms. In South Africa the most common bloom-forming toxic species are Microcystis spp and Anabaena spp, although a number of other species may also produce toxins on
occasion.
Blue-green algae produce a variety of neuro-, hepato- and lipopolysaccaride toxins. These toxins have been associated with a number of livestock and game deaths, and with widespread gastroenteritis in human populations.
These toxins have been known to penetrate standard water treatment processes,
but recent work has shown that chlorination which ensures a 0.5 mg/R chlorine residual after 30 minutes contact time is sufficient to destroy the toxins. This process may, however, give rise to by-products which are also potentially toxic.

Effective removal of algae in the treatment process depends on the species present. In
general removal requires coagulation, flocculation and/or sedimentation. Some species, for
example Microcystis spp, are buoyant and therefore lend themselves to dissolved air
floatation. Coagulants like aluminium sulphate or ferric chloride are conventionally used, with the addition of small doses of polyelectrolytes to assist flocculation, followed by deep bed or multimedia filtration.
The use of activated carbon, in particular granular activated carbon (GAC), is an effective means of removing the algal toxins and other algal by-products from treated water. In the absence of activated carbon treatment (which is expensive), care should be taken to remove whole cells before treatment with an oxidant, since oxidants cause cell lysis, and the release of toxins and other intracellular products. However, it has recently been indicated that a chlorine residual of 0.5 mg/R after 30 minutes contact time is sufficient to destroy acute toxicity of the hepatotoxins. Chlorination may, however, produce other potentially toxic by-products.

It is imperative that you filter your water to a quality that you can rely on and in a way that when municipal systems fail you will still be safe. Reverse Osmosis is best and most effective for this.