Hazards Associated with Water Treatment

Despite a tendency to consider it as inert, mishaps or mal-operation of water and water treatment have resulted in fires, explosions, catastrophic failures, ill-health, environmental disasters and equipment failure. Particulars risks may be associated with the chemical reactivity of water and its properties as a universal solvent and disease vector.

Chemical Reactivity

Water can be considered to be chemically neutral, but it can behave as either an acid or a base and may react rapidly with many chemicals posing fire, toxic or explosion risks if admixture is uncontrolled. Importantly, metals which are less electronegative than hydrogen will displace it from water at different rates, and alkali metals such as sodium, potassium and lithium react so violently with water to generate hydrogen that the heat of reaction may ignite the gas and explosions may ensue.

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A major waste-transfer and treatment site contained a wide selection of chemicals including acids, caustic, flammable liquids and miscellaneous laboratory chemicals. A large fire, thought to have been initiated by ignition of pyrophoric lithium metal on contact with water, resulted in several explosions and acrid black smoke which drifted over the site. Residents in a town a mile away were instructed to stay indoors. Two firemen were hospitalised due to fume exposure. Standard practice should have been to segregate reactive, toxic and chemical wastes. The site had been the subject of previous enforcement actions.

Solvent Properties

Because of its polar nature, water is a “universal solvent” which will dissolve more substances than any other liquid. Many gases, similarly, also dissolve in water.

A confined explosion of methane gas in an underground water pumping station at Abbeystead caused the death of 16 people and injuries to 26 others. This resulted from ignition of a mixture of methane and air; the methane was displaced from a void formed in the end of a tunnel during a period of 17 days prior to the explosion when no water was pumped through the system. Most of the methane was of ancient geological origin and had percolated through the concrete walls of the tunnel between 2 and 2.5 km from the station either in gaseous form or in solution in water under pressure. The fact that significant quantities of methane might be dissolved in water had not been recognised.

Health/Environmental Hazards

Water may also act as a disease vector. Thus, chemical and microbiological impurities in water can increase the hazard when they enter the body through ingestion, for example.

Leakage of contaminated wastewater from cooling towers into unlined ponds at Hinkley, California over a period of years and its percolation resulted in hexavalent chromium being present in groundwater at 0.58 ppm which exceeded the maximum contaminant level of 0.10 ppm set by the Environmental Protection Agency. The Cr (VI) was in a compound used between 1952–1966 to minimise corrosion in the towers. Alleged contamination of drinking water, and the ensuing claims by local residents, led to the largest ever settlement of $333 million in a civil action lawsuit.

As evidenced, a range of industrial accidents and hazards are associated with water treatment services. Familiarity with processes does not necessarily result in a full appreciation of the potential accompanying risks. Accordingly, a thorough understanding of the physico-chemical properties of water and its process agents is essential for risk assessment and control.

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