Nuisance microorganisms

                                                    Nuisance microorganisms

A group of microorganisms mainly bacteria, that are not pathogenic but they cause disturbances/nuisance such as changes in colour, odour, turbidity, taste of water. They are naturally found in the soil or water and are responsible for various chemical transformations or slime production or even production of some toxins. Some of the common examples found in drinking water are iron bacteria, sulfur bacteria, sulfate-reducing bacteria, slime producing bacteria etc. Relatively high amounts of biodegradable organic matter, warm waters and low residual concentrations of chlorine, facilitate growth of nuisance organisms in surface waters and during water distribution supplies.

Slime – forming organisms

When water is rich in organic matter, these organisms grow well and produce slime or mucilage. The gummy or slimy conditions can result in foul odours or turbidity eg. Pseudomonas species, Iron bacteria, algae etc

Sulfur bacteria

Sulfur oxidizing bacteria oxidize sulfur to sulfate producing sulphuric acid (H₂SO₄) eg., Thiobacillus which makes water very acidic and imparts foul odour. Sulfate-reducing bacteria (SRB) reduce sulfate to hydrogen sulfide (H₂S). eg., Desulfovibrio These products cause a foul odor and taste to the water. The hydrogen sulfide produced from the sulfate-reducing bacteria reacts with dissolved iron in water to form black insoluble iron sulfide. Precipitated S ions damage pipelines. Thus Sulfur bacteria can cause rusty water and corrosion of pipes.

Iron bacteria

Iron bacteria can transform soluble Fe compounds into insoluble form. They oxidize ferrous iron to ferric iron and cause the precipitation of ferric hydrate. The precipitation of ferric hydrate causes a foul odor and taste and reddish tinge to the water. It can also damage pipelines by causing an accumulation of deposits. Iron bacteria are seen in water with relatively high iron concentrations but may develop in water with low iron concentrations too if there is a continuous supply of iron. Eg., Gallionella, Spaerotilus

Algae

The top few meters of any water body of contain planktonic algae. They fix carbon dioxide into organic molecules that can be consumed by other organisms. They release oxygen (0₂) as a by-product of their photosynthesis. Though they are part of normal and beneficial flora, occasionally they cause disturbances such as turbidity, discolouration and unpleasant odour and taste.

Eutrophication and algal bloom

Seasonal changes in nutrients, light, and temperature cause fluctuations in algal populations; periodic increases in numbers of planktonic algae are called algal blooms. Algae thrive in high concentrations of organic materials that exist in sewage or industrial wastes. When algae die, the decomposition of the large numbers of cells associated with an algal bloom depletes the level of dissolved oxygen in the water.

By definition, Eutrophication is an enrichment of water by nutrient salts that causes structural changes to the ecosystem such as: increased production of algae and aquatic plants, depletion of fish species, general deterioration of water quality and other effects that reduce use of water body.

Biogradable detergents containing phosphates have a major role in eutrophication. Influx of nitrogen and phosphate rich matter into lakes and streams result in overabundance of nutrients or eutrophication. Algae and cyanobacteria get their energy from sunlight and their carbon from carbon dioxide dissolved in water. In most waters, only nitrogen and phosphorus supplies are the limiting factor for algal growth. When there is inefficient waste treatment, these nutrients enter water from domestic, farm, and industrial wastes and they cause algal blooms.

Many cyanobacteria can fix nitrogen from the atmosphere, so these photosynthesizing organisms require only traces of phosphorus to initiate blooms. Eutrophication results in blooms of algae or cyanobacteria, which occupy the surface layer of water body and can interfere with oxygen diffusion. This affects the growth of other life forms in water. These algae and cyanobacteria supply oxygen in the beginning which can be utilized by other life forms in water. However, they eventually die and are degraded by bacteria. During the degradation process, the oxygen in the water is used up, killing the fish. Undegraded remnants of organic matter settle to the bottom and add to the organic load of the lake.

Eutrophication is a serious environmental problem since it results in a deterioration of water quality. All water bodies are subject to a natural and slow eutrophication process, which in recent times is accelerated due to the presence of man and his activities (cultural eutrophication). The cultural eutrophication process consists of a continuous increase in the contribution of nutrients, mainly nitrogen and phosphorus (organic load) until it exceeds the capacity of the water body (i.e. the capacity of a lake, river or sea to purify itself), causing structural changes in the waters.

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