Hot Water

A bright future awaits chemengers in the water industry, say Richard Hill and Chris Short

WATER is fundamental to life, but it is a limited resource. Ensuring that people have access to clean water is a major global challenge. (Chemical Engineering Matters)

Has any other industrial sector benefitted from the arrival of chemical engineers as much as the water industry? Today in the UK the water industry delivers over 16bn L/d of 99.5% pure product to domestic, commercial and industrial consumers at a cost of less than £2/t (US$2.6/t) at point of use. The industry also processes about 20m t/d of wastewater for discharge to the environment. We use over a dozen different unit operations and have been using biotechnology for over a century and, taken over the last century and a half, our industry has probably made a bigger contribution to public health than the healthcare sector. In the UK, the introduction of chlorination of drinking water and the treatment of domestic sewage have virtually eliminated water-borne diseases like typhoid and cholera which were endemic in Victorian England.

All this makes water by far the UK’s biggest and most important chemical process sector. Chemical engineers are relative newcomers to the industry, but their arrival sparked a revolution.

When in Rome, China or the UK

The modern water industry traces its roots directly to the Romans who supplied water to Rome in lead pipes, thus inventing plumbing, and flushed their foricae into the Tiber via the Cloaca Maxima. These were massive infrastructure projects and so, from the Pont du Gard to the Thames Tideway, the industry has been dominated by civil engineers. But moving large quantities of liquid product and waste does not address the issue of product specification: this is where chemical, biochemical and process engineers can make a real difference.

The industry’s raw materials are natural water sources – rivers, lakes and aquifers – and domestic and industrial wastewater, and they contain a wide variety of contaminants. Unlike feedstock for other chemeng processes, ours varies in flow, composition and concentration seasonally, diurnally and even, in the case of some rivers and effluents, from hour to hour. Producing a consistent product from a variable feed is just one of the challenges for the chemical engineer. There are others. If your distillation column fails, you can stop processing crude oil: not so easy to turn off the feed to the sewage treatment works.

The unit operations used for water processing were, for centuries, simple solids separation technologies – sedimentation and filtration. In ancient times, the Chinese used alum to enhance the clarification of water in settlement tanks. The Romans had water filters but, in the UK at least, the technology disappeared when they left and did not reappear here until the mid-19th century. They knew about drinking water clarity, were aware of the health risks of lead pipes¹ and they didn’t have analytical chemists.