Water being a need is key to the survival of humans, animals, plants, and all living organisms in general. Its usage among humans range from agriculture, industrial to domestic. The estimated volume of water on earth is about 1.4×1018 cubic meters. Approximately 3% of earth’s water is fresh, 0.3% is held on rivers, lakes, and reservoirs while the rest are held in underground water aquifers and glaciers. Domestic usage of water which entails water for drinking, cooking, and water used in households is of utmost importance with a requirement of about 50 liters per person each day. An adequate and safe supply of drinking water is required for healthy living.
Contamination of water as a result of human activity is a big challenge with surface water the most affected. The main contaminants are microbial contaminants from sewage effluents and wastewaters, chemical contaminants such as fluorides and heavy metals, agricultural waste, and oil spillage. Water quality and sanitation are closely related, contamination in most cases due to poor sanitation and hygiene. Globally, 2.5 billion people have no access to improved sanitation with the lowest levels of sanitation being in Sub-Saharan Africa and South Asia. This poses a health risk to many people since faecally contaminated water contains pathogens such as bacteria, viruses, and protozoa that cause diseases. These waterborne diseases affect millions with the majority of people affected being from developing countries such as African countries. Waterborne diseases are responsible for many deaths with the majority of the affected being children. Antibiotics were earlier used to treat such infections but the emergence of bacterial resistance has slowed down the efficacy of such drugs.
To prevent such mortality rates it’s essential to prevent faecal matter from entering water bodies or decontaminating drinking water by killing or inactivating pathogens in them. Several methods of water decontamination such as boiling, chlorination, and use of ozone are being used, with each method having its own limitation.
Photodynamic Antimicrobial Chemotherapy (PACT) has found its use in the clinical setup mainly as an efficient method of killing microorganisms in the body however its application can be extended to inactivating microorganisms in wastewaters and drinking water. PACT is based on the concept that a photosensitizer dye is able to penetrate a microorganism. The photosensitizer can then be activated by absorbing visible light at a sufficient wavelength. The excited photosensitizer then undergoes intersystem crossing to the long-lived triplet state. In the presence of oxygen, the photosensitizer is able to transfer energy to oxygen yielding reactive oxygen species such as the singlet oxygen and hydroxyl radical which are cytotoxic. Cell damage is caused by the destruction of cytoplasmic membrane and nucleic acids while cellular enzymatic and transport mechanisms are inhibited. Photosensitizers are aromatic molecules that absorb light at long wavelengths of the visible spectrum and are efficient in the formation of long-lived triplet excited state. They include phenothiazanium photosensitizers like methylene blue, natural products like furanocoumarins and tetrapyrrolic compounds like porphyrins.
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