On the Eve: Cities Drowned in Filth

In the early stages of the Industrial Revolution during the 19th century, major cities such as London and Paris experienced explosive population growth, while urban infrastructure remained largely medieval. Human waste, domestic wastewater, and slaughterhouse refuse were routinely discharged into open drains or directly into nearby rivers. The occupation of “night soil men” emerged to remove waste, yet much of what they collected was simply dumped further downstream.

At the time, the River Thames served both as London’s primary source of drinking water and its largest open sewer. Animal carcasses, decaying refuse, and human excreta floated in the river, fermenting and bubbling under the sun. Wealthier citizens often boiled their water before drinking, or substituted it with beer or spirits, while the lower classes had no choice but to consume untreated river water.

Catalysts: The Great Stink and the Map of Death

The year 1858 marked a decisive turning point with the outbreak of the “Great Stink”. An unusually hot summer accelerated the decomposition of organic matter in the Thames, releasing overwhelming hydrogen sulphide fumes that blanketed London and even seeped into the curtains of the Houses of Parliament. Lawmakers were forced to cover windows with lime-soaked cloth, and parliamentary proceedings were nearly brought to a halt.

Meanwhile, Dr John Snow was compiling his now-famous “cholera death map”. During the 1854 cholera outbreak in London’s Soho district, Snow conducted door-to-door investigations and traced the majority of deaths to a single public water pump on Broad Street. Defying prevailing opinion, he had the pump handle removed, after which the outbreak subsided dramatically.

Together, these events revealed a common truth: the mixing of wastewater with drinking water was causing mass mortality. The dominant “miasma theory”, which held that diseases were spread through foul air, began to lose credibility. Evidence supporting waterborne transmission steadily accumulated and, over the following decades, gradually displaced the miasma theory.

An Engineering Miracle: The Birth of the Underground Cathedral

In the aftermath of the Great Stink, London was finally compelled to act. Sir Joseph Bazalgette proposed an ambitious plan: to construct 132 kilometres of brick-built intercepting sewers along both banks of the Thames, collecting wastewater from across the city and conveying it eastward for discharge at Beckton.

This monumental project, completed over six years (1859-1865), employed more than 30,000 workers and consumed over 300 million bricks. The finished tunnels were large enough for horse-drawn carts to pass through and were later hailed as “underground cathedrals” of the Victorian era. The completion of London’s sewerage system marked the establishment of modern municipal drainage principles – moving away from reliance on natural dilution towards the active collection and controlled conveyance of pollutants.

The Emergence of Treatment: From Transfer to Purification

However, simple transfer merely shifted the problem downstream. By the late 19th century, early wastewater treatment technologies began to take shape:

In 1889, the world’s first wastewater treatment plant employing chemical precipitation was built in Salford, UK, using lime and iron salts to settle suspended solids.

In 1893, Exeter introduced the first biological trickling filter, spraying wastewater over beds of crushed stone where microbial films degraded organic matter. This system became the foundation of biological treatment technologies.

In the early 20th century, researchers at the Lawrence Experiment Station in Massachusetts observed flocculent, microbe-rich sludge forming during prolonged aeration experiments. This discovery revealed the remarkable purification capacity of microbial communities and, within the following decade, evolved into the now-famous activated sludge process.

Awakening: From Elite Privilege to Public Right

Looking back at this formative period, three fundamental shifts become evident:

In understanding, from viewing foul odours as a mere nuisance to recognising wastewater as a vector of deadly disease;

In responsibility, from individual disposal to government-led public accountability;

In technology, from passive discharge to active collection and treatment.

Early reform efforts were often driven by elites who directly suffered from the stench – London parliamentarians, Manchester industrialists, and Parisian municipal officials. Yet when it became clear that cholera did not discriminate by class, and that pollution ultimately returned to everyone’s table, public wastewater systems ceased to be a moral choice and became a necessity for survival.

Echoes: An Unfinished Journey

By the early 20th century, the first generation of wastewater treatment plants began operating, primarily serving large cities in industrialised nations. Vast portions of the global population, however, still lived without basic sanitation. Even so, a crucial foundation had been laid: civilisation is defined not only by its capacity to generate wealth, but by its responsibility to manage its own waste.

Today, standing in bright and orderly control rooms, watching data flow across digital screens, it is difficult to imagine the suffocating stench that once lingered along the Thames 160 years ago. Yet it was precisely that era, marked by filth and mortality, that triggered humanity’s first awakening in its relationship with wastewater – a shift from passive endurance to active governance.

Every modern wastewater treatment plant operating smoothly today continues this engineering revolution that began in the Victorian age. It reminds us that behind a clean environment lies continuous technological evolution and an enduring sense of responsibility.

History serves as the footnote of progress. From London’s sewers to today’s intelligent water treatment facilities, how has technology reshaped the fate of wastewater? In the next chapter, we will return to the present, focusing on the practical challenges and technological frontiers of municipal sludge dewatering, and explore how contemporary engineers continue to write new pages in this never-ending journey of purification.