“The winter of 1831-1832 was mild, the spring not too warm and the general state of health was excellent. Then, on 24 June 1832, the scourge of cholera  – like a bolt from the blue – struck down the seaside village.[…] Cholera has arrived in Scheveningen; but how did it get there?”[1]

That was the big question to which no one knew the answer.
Originally, this killer disease had occurred only in India, in the Ganges delta. From 1817 however, ‘Cholera Asiatica’ had been spreading worldwide. In 1830, infections reached Europe. After Scheveningen, the epidemic swept through the whole of the Netherlands with the number of deaths growing rapidly.[2] 

The panic was huge because the disease struck at an alarming rate. People whose bodies were in the perfect of health in the morning may have completely succumbed by the evening. Equally frightening was the fact that the disease could suddenly appear anywhere and everywhere without people coming into contact with each other. This caused widespread confusion and numerous theories about causes and remedies began to circulate. 

The spread of cholera across the world between 1817 and October 1831. (source: Leiden University Libraries)

Cholera in a tram in Hamburg at the end of the 19th century. (source: private collection)


On the basis of ‘cholera maps’ (town plans on which incidences of death were drawn in), the London-based doctor John Snow was the first to devise a theory which claimed that a ‘germ’ had to be the cause of cholera and was being spread by infected water.[3] Nevertheless, the idea persisted that poisonous fumes (miasmas) caused cholera and other diseases. It was only at the end of the 19th century when it was established that a bacterium (Vibrio cholerae) was the pathogen.[4]

Hygiene by engineers

Statistics - a new discipline - showed there were links between hygiene problems and high mortality and morbidity rates. Doctors (hygienists) argued for a major clean-up of polluted and overcrowded industrial cities and put forward recommendations for technical solutions.[5] Clean water supplies and separate disposal of waste and faeces played a key role in this. This included ‘pipes, conduits, pumps, steam pumping stations, dustcarts, composting processes, barrels and filtering equipment’.[6] Now, engineers came onto the hygiene scene. They embraced health education and came up with a new infrastructure of sanitary measures and systems. What was striking in the Netherlands was that all towns and cities chose to adopt their own approach.[7]

Amsterdam’s (now municipal) drinking water supply system near the Sprenkel canal in 1901– with water extracted from the coastal dunes. (source: stadsarchief Amsterdam/ Archief van de Dienst Riolering en Waterhuishouding Amsterdam)

Johan van Hasselt and Amsterdam’s Duinwater

Shortly after Johan van Hasselt and Jacobus de Koning founded their engineering firm, Van Hasselt also became chief engineer at the first waterworks in the Netherlands, the Amsterdamse Duinwater Maatschappij. This company extracted water from the coastal dunes close to the capital.[8] He had started this ‘secondary job’ in 1888 to ‘enable himself to establish closer connections for his firm’.[9] However, it soon became clear that Van Hasselt would have to devote all his time to this task. In 1893, he left his engineering firm – very much against his will. 

The intended commercial effect of his job for the waterworks remained modest, as is apparent from a 1905 list of projects, which contains only 7 assignments in the field of waterworks and drinking water supplies, out of a total of 121.[10] In addition to drinking water projects, J. van Hasselt en De Koning also produced reports and plans for sewerage from 1894 onwards. At the end of the century, in the Western world the discharge of faeces via sewers had become ‘big business’ both for municipalities and engineering firms.[11]

Recently constructed discharge pipelines from Amsterdam to the Zuiderzee, ca. 1911. The principle was to discharge wastewater as far as possible outside the city. (source: stadsarchief Amsterdam/Gustaaf Oosterhuis)

The sewage systems of Dwars, Heederik & Verhey

From 1919 onwards, the firm of Dwars, Heederik & Verhey provided advice on sewage systems under the flag of Technisch Adviesbureau (TAB) - which they founded and managed - on behalf of the Association of Netherlands Municipalities (VNG). Bastiaan Verhey had acquired the necessary know-how during a study trip to England, but the real expert and the key person behind the development of sewage systems was Adriaan Dwars.[12] By the end of 1941, the firm had issued no fewer than 94 advisory reports to municipalities: this amounted to a quarter of all the TAB assignments that had been carried out by them. ‘Sewage plans’ were followed by plans for culverts; control, inspection and overflow wells; discharge pipes and the design of installations so that a pumping station could function fully automatically.[13] It was a fantastic business with huge growth potential, in terms of both numbers (municipalities) and technological developments. Once again, bacteria turned out to be the driving force behind all of this. This time however, not in terms of them causing the contamination, but in the actual purification process. 

Between 1919 and 1933, A.W.C. Dwars, co-founder of Dwars, Groothoff & Verhey, was responsible for the firm’s sewage treatment projects. (source: Royal HaskoningDHV company archives)

Bacteria become flocs 

After experimenting with various methods of wastewater treatment, in the 19th century the idea emerged that ‘organisms’ might achieve this naturally.[14] In 1913, two British chemists working in a laboratory managed to create small flocs in wastewater after aerating the water for a period of time. Bubbles of oxygen set the process in motion. The flocculated bacteria (or ‘activated sludge’) sank to the bottom and what was left was purified wastewater.[15]

This activated sludge process became the crux of a purification treatment which, in a short space of time, would become extremely popular worldwide. In 1938, the United States looked back on the first quarter of a century: “This astounding growth […] is unparalleled in the history of sewage treatment, and must be ascribed to the fact that the activated sludge process is in harmony with the speed and science of modern life. Sewage treatment works in our modern cities […] must be free from odor, occupy limited area and be amenable to scientific control”.[16]

Sewage treatment plant in Heiloo with a sewage pumping station, an aeration tank, a final clarifier, sludge drying fields, settling ponds and storage ponds. Jobless workers were first called on to lay 10,000 metres of sewage pipes, ca. 1937. (source: Royal HaskoningDHV company archives)

Pasveer’s oxidation ditch

At the beginning of the 20th century, all pipelines and pumping stations constructed in the Netherlands primarily ensured that the problem of effluent was shifted elsewhere. Sewers in larger cities hardly ever discharged locally anymore, into their canals for example, but they did so into the sea or into major rivers via kilometres of discharge pipes.[17] Outside the towns and cities, household and industrial wastewater ended up in ditches. Over time these would become increasingly filthy and smelly, primarily as a result of increasing industrial pollution.

However, wastewater treatment plants were expensive. For this reason, in 1954 the agricultural engineer Aale Pasveer (1909-2001)[18] devised a simple and affordable solution: the oxidation ditch. The whole treatment process worked on the basis of the activated sludge principle and took place in one and the same compactly constructed ditch. A rotor set the water in motion, produced aeration and mixed the activated sludge in the sewage water. As soon as the rotor stopped, the sludge sank to the bottom and after a few days the purified water could be removed. 
Pasveer’s solution meant that the primary settling tank, sludge digestion and final clarifier – until now necessary elements - became completely unnecessary. His invention provided a solution for smaller municipalities, which – from now on - would be able to carry out wastewater purification a lot more cheaply. Small-scale wastewater treatment plants were being quickly constructed everywhere. DHV also developed a whole series of these Pasveer ditches.[19]


Aale Pasveer in the laboratory at TNO where he worked in the Water, Soil and Air department of the Instituut voor gezondheidstechniek (institute for health technology). (source: TNO)

Pasveer ditch with raw sewage in 1954. Left the rotor canopy, in the background a control building. (source: Royal HaskoningDHV company archives)

DHV invents the Carrousel

There was a disadvantage to the inexpensive Pasveer ditches however. Given they were shallow ‘by design’, a great deal of extra space was needed for larger scale purification. The solution to this came in the person of DHV engineer R.J. Klein. His initial enquiries were small in scale: “The first experiments were carried out in a washing-up bowl, in which a partition was placed in a longitudinal direction and a surface aerator cut from tin on the front side of the partition, driven by a toy motor.” After a series of tests, he achieved the improvements to the Pasveer ditch and this became known as the Carrousel®.[20] 

The DHV-patented design proved a huge success, not least as a result of the Dutch Surface Water Pollution Act which came into effect in 1971. This obliged industry and local authorities to carry out wastewater treatment. It was no longer just health that was the sole purpose of water treatment, ecosystems too needed a healthy future.[21]  

Following the installation of the very first Carrousel in Oosterwolde in 1968, by 1993 a further 650 Carrousel systems had been put in place worldwide. In order to maintain its independence as an engineering consultancy, other parties sold the product and paid royalties to DHV.[22]

Dick Theunissen alongside a steel model of the Carrousel (5 metres long, 1.2 metres wide and 0.4 metres deep).
A special area was reserved between the cloakroom and the drawing office of the new headquarters in Amersfoort for research into modelling, ca 1971. (source: Royal HaskoningDHV company archives)

The purifying granule

While DHV was still actively developing and designing new generations of its Carrousel system, environmental biotechnologist Mark van Loosdrecht (b. 1959) made a startling discovery in his laboratory. In the mid-1990s, together with his research team from the Delft University of Technology, he devised a process whereby different types of bacteria in wastewater no longer fluttered down (slowly) in flocculated form, but instead (more quickly) in granular form, without the need for any additional material. More importantly, the granules themselves formed a new material: a bioplastic. Moreover, this required less energy.

On the left the floc, on the right the granule. Showing a completely different configuration of similar particles. In the granule, the bacteria are surrounded by a new material: a gel-forming biopolymer (‘bioplastic’). (source: Winkler et al., "Microbial diversity differences", Appl Microbiol Biotechnol 97 (2013), 7447–7458)

Almost 80 years after the activated sludge process had been discovered, Van Loosdrecht's invention signalled the next breakthrough in wastewater treatment. He sought contacts in the world of business to further develop the process of bacterial purification with granules to create a marketable product. In a roundabout way he eventually met Helle van der Roest, a specialist in the field of wastewater technology at DHV. In 1999 the engineering firm and the Delft University of Technology formalised their partnership.[23]

Development of Nereda

Between 1996 and 2002 a series of small-scale experiments took place with systems for municipal and industrial wastewater respectively. In 2005 the first fully functioning industrial wastewater treatment system based on ‘Nereda® technology’[24] was put into use. 

The trick was to stay up to speed in a slow-moving market driven by depreciation periods for such systems. This proved possible as a result of an ingenious partnership between DHV, STOWA (Stichting Toegepast Onderzoek Waterbeheer), the Delft University of technology and six water authorities. In 2007 they entered into a public-private partnership for a period of 10 years.[25] Water authorities which were intending to replace their systems in around 2010 were allowed to join the collaboration. This helped ensure the availability of test environments for the necessary research and speeded up the adoption of the experimental technology.[26] The wastewater treatment plant in Epe, operationalised in 2012 and managed by the Vallei en Veluwe water authority, was the first in the Netherlands with a complete Nereda system for municipal wastewater.[27]

Wastewater treatment in three phases: in the granular sludge technique, all the purification processes take place in a single reactor tank that is periodically filled and emptied. The total process takes three hours.
(source: Royal HaskoningDHV company archives)

First full-scale demonstration of Nereda at a municipal wastewater treatment plant in Gansbaai, South Africa 2009. (source: Royal HaskoningDHV company archives)

Sustainable innovation

For Nereda, this moment marked the start of a huge upturn in demand. The installations are cheaper, quicker and more energy-efficient than traditional systems and require much less space. The former means savings for the water authorities, whereas the latter is valued by the provincial authorities who are responsible for spatial development in the Netherlands. In addition, the technology is also suitable for upgrading existing plants. Worldwide there are now more than 41 Nereda installations operating in 19 countries.[28] 

For his contribution to and innovation of methods of wastewater treatment and the development of the Nereda technology, Professor Mark van Loosdrecht has received a number of prestigious scientific awards.[29] Through their ingenious application of this ‘breakthrough technology of the decade’[30] , the water experts at Royal HaskoningDHV stand on the shoulders of science and those of their predecessors. Unlike in the time of Van Hasselt and Dwars, engineers, biotechnologists and software developers together are now helping to provide clean water. This they are doing in a way which is safer, more environmentally friendly and more sustainable than ever before. 



About this project

In October 2021 Royal HaskoningDHV will celebrate its 140th birthday. To mark this milestone, we have commissioned a series of striking stories highlighting key moments in the firm's history. We are proud of our heritage and this is a great opportunity to share our stories with a wider audience.