Environmental engineering can trace its roots back to about 10,000 BC when humans began to develop agrarian societies which led to the development of villages and cities. This increase in population densities created a need to dispose communal waste and provide communal drinking water (and hopefully not use the same hole in the ground for each!). As ancient civilizations matured, so did their contributions to the practice of environmental engineering.

Around 2000 BC, ancient Egyptians developed the first known water treatment practices (which included UV irradiation, activated carbon filtration and heat sterilization!) and ancient Mesopotamians developed some of the earliest known drinking water and sewer lines. Around 1500 BC, the ancient Chinese were able to drill wells up to 1,500 feet deep and used alum to clarify their water supplies (a practice still used today). Finally, ancient Greeks and Romans developed such sophisticated water and sewer systems that they would still be effective in today’s 21st century cities.

With the fall of the Roman Empire and the start of the Dark Ages the practice of water and wastewater treatment was lost.  Without proper sanitation disease and plagues ran rampant throughout Europe.  By 1300, leprosy was endemic.  Between 1348 and 1350, bubonic plague ("Black Death") wiped out nearly one quarter of Europe's population (~60 million people).  Contaminated water supplies and poor sanitation continued to lead to death and disease until the development and advancement of the field of bacteriology. 

In the 17th Century, Anton van Leeuwenhoek invented the microscope which was used by Louis Pasteur to discover the existence of bacteria and their role in milk and beer spoilage.  In 1854, John Snow was able to use his "Ghost Map" to prove that the drinking water at the Broad Street pump was contaminated with sewage from a British soldier just returning from war in India (who had contracted cholera) and that this contaminated water responsible for the severe cholera epidemic that London was suffering.  This breakthrough was critical as it was the first time that water was shown to be a carrier for disease.  Previously, it was believed that disease could only be spread via the air or through human contact.  Finally, in the 1870's Robert Kolch proved that specific bacteria were responsible for specific diseases.  Kolch also discovered that hypochlorous acid (HOCl), aka bleach, is an effective disinfectant.  Today, hypochlorus acid addition is still used as a disinfectant at drinking water treatment and wastewater treatment plants.    

During the 1800's in the United States, environmental engineering was essentially hydraulic engineering (a branch of civil engineering).  Growing cities needed more water.  Hydraulic engineers were responsible for supplying the water through dam construction and building water distribution infrastructure.  Hydraulic engineers were also responsible for building sewers systems to remove sewage from the cities.  However, this often meant piping raw sewage into nearby rivers, lakes and bays.  As cities continued to grow so did the demand for water.  However, the dumping of raw sewage into the waterways made potable fresh water a diminishing resource.

To address the rising concern of deteriorating water quality and supplies, the Massachusetts Institute of Technology (MIT) combined the disciplines of engineering, chemistry and biology to form the field of Sanitation Engineering.  Sanitation engineers were responsible for developing the precursors to modern day wastewater treatment plants and drinking water treatment plants.  Advances made by sanitation engineers includes the development of activated sludge (a process that uses bacteria to removed dissolved organic matter) and the use of alum and sand filters in drinking water treatment plants to removed small particles and pathogens.  Environmental engineering was dominated by sanitation engineers until World War II and the "Chemical Revolution".

Many of the chemicals developed for the war were being applied in commercial applications and found their way into the environment.  Chemical detergents made their way to wastewater treatment plants and cause them to literally foam over like a broken dishwasher.  It was now possible to take nitrogen from the atmosphere and add it to agricultural fields as chemical fertilizers.  This led to huge increases in food production and the "Green Revolution" that has help feed billions of people.  However, excess fertilizer has led to river and lakes choked with algae and slowly dieing as the oxygen becomes depleted from a process known as eutrophication as well as the accumulation to toxic nitrates in groundwater supplies.  Synthetic pesticides further increased crop production and decrease in diseases as it was now possible to manage populations of mosquitoes that carry many deadly diseases.  However, in 1962, Rachel Carson documented the dangers of these pesticides to the environment and human health in her seminal work, "Silent Spring".  "Silent Spring" is credited with banning DDT (due to the unintended consequences of killing bald eagles by thinning their eggs shells to the point that they cracked when sat upon) and jump started the modern environmental movement.

In addition to agriculture products, the "Chemical Revolution" led to the production of plastics, leaded gasoline, nuclear power, chlorinated solvents and an insatiable demand for electricity and gasoline which led to an exponential increase in coal and oil consumption.  This led to the production of materials that cannot be broken down, an increase of lead in the environment and our blood streams, nuclear waste leaking into our rivers, carcinogens contaminating our groundwater supplies, acid rain pouring down on our lakes, smog choking the skies of our biggest cities and rivers so polluted that they started on fire. 

To address these environmental problems, environmental engineers had to evolve beyond basic sanitation engineering into the fields of bioremediation, air pollution technology, nuclear health and safety, environmental microbiology, alternative fuel development, contaminant fate and transport, environmental chemistry and toxicology.  Thus today's environmental engineer possess a wide range of skill and expertise that expands across traditional disciplinary boundaries to include not just traditional water/wastewater treatment and solid waste management but also pollution clean-up (in our soils, air and water), pollution prevention (through green chemistry and better waste treatment technologies), risk assessment (toxicity studies, tracking and modeling of contaminants and pathogens in the environment) and alternative energy development (wind, wave, solar and bio-based fuels).

The State of California has an excellent Detail Occupational Guide for Environmental Engineering that describes the duties of today's environmental engineer in more detail.  The guide can be found here.