‘Krul, ‘De cholera in Scheveningen in 1832’, Nederlands Tijdschrift voor Geneeskunde (1892), 655-667. Rochus Krul was a doctor in Scheveningen who took a keen interest in the history of his profession.
 By October 1832, deaths had reached 3000, “frighteningly many” given the overall population of approx. 2.6 million. Auke van der Woud, Koninkrijk vol sloppen, 236.
 He was able to show this in 1854 at the time of a new outbreak of cholera. See also P.F. Cooper, ‘Historical aspects of wastewater treatment’ in Lens, P. N. L., Zeeman, G., & Lettinga, G. (2001). Decentralised Sanitation and Reuse - Concepts, systems and implementation. IWA Publishing. 19-21.
 The German chemist Robert Koch discovered the bacterium in 1882 on a study trip to Egypt and Calcutta.
 The name of this new multidisciplinary science was health education or hygiene. In Britain, this movement had got under way early in the 19th century. Van der Woud (2010), 242-250.
 This decentralised approach made for slow progress, astounding for a country whose engineers, working in central government service, had made huge hydraulic engineering achievements. The consequence of this was that the construction of pipelines and systems would not take place until long into the 20th century. By comparison, in London toilets, flushing systems and clean drinking water supplies were part of an integrated and properly functioning system by 1860. Van der Woud (2010), 271-272, 287 and 343-349.
 The private company was established in 1851 and passed into ownership of the city of Amsterdam in 1896.
 Pennink, ‘Ir. J. van Hasselt’, De Ingenieur 32, no. 16 (1917), 283.
 Van Sandick , ‘J. de Koning’, De Ingenieur 21, no. 50 (1906). Jan Schotel (1845-1912), the Rotterdam-based engineer for whom A.D. Heederik (1862-1937) worked, produced drinking water pipelines throughout the Netherlands and appeared to be the undisputed market leader. Sometimes the two firms’ paths crossed, such as in Apeldoorn, where the municipality was looking for a cheaper competitor to Schotel, ‘for example, Van Hasselt & De Koning’. Anonymous, Apeldoornsche Courant (6 September 1890).
 As director of Public Works in Amsterdam, in 1902, Van Hasselt drew up a plan for the construction of sewers in the city. This was never completed. The discharge of wastewater into surface water was cheaper. See Afvalwaterzuivering PIE rapport 10,(1994), 8.
 TAB was, to all intents and purposes, DHV. Formally established by the Association of Netherlands Municipalities (Vereniging van Nederlandse Gemeenten) in 1919, based on an idea by Bastiaan Verhey dating from 1917. A.W.C. Dwars and B.A. Verhey were its first directors. The work carried out for municipalities went further than sewerage alone, but also involved bridges, water supply systems, road building and expansion plans. See also story #4. Hillenius (1992), 25.
 DHV (1942), 28.
 Cooper in Lens et al (2010), 24.
 The sludge or slurry was stored in sludge pits and then transferred to sludge drying fields. See, for example, plans for sewage water treatment plant in Alblasserdam, 1920. Royal HaskoningDHV company archives.
 Mohlman, cited from Cooper (2010), 28. Worldwide, hundreds of activated sludge treatment plants got built, including in India, South Africa, the USA and the UK.
 Here the effluent was diluted, and the self-cleaning properties of the water ensured its eradication. In the Netherlands, untreated waste was still being discharged into the major rivers long into the 20th century. Groeneveld (1994), 20.
 A. Pasveer qualified as an engineer at the University of Wageningen in 1935 and was awarded a PhD in 1941 for his work on butter-making. He worked at TNO. https://www.kennisbank-waterbouw.nl/tresor/auteur.php?code=M&amp;naam=Pasveer
 At the end of 1960, the Netherlands had twenty oxidation ditches with capacities ranging in size from 200 to 4000 population equivalents (not all DHV’s!). Another 32 ditches were completed abroad. Koot, ‘Afvalwaterbehandeling en waterkwaliteitsbeheer; terug- en vooruitzien’, H2O 16, no. 19 (1983), 5.
 Together with his colleagues Schut and Veldkamp. The Carrousel was a new type of oxidation ditch in which the treated water was not aerated by a (horizontally rotating) brush, but instead by a so-called surface aerator (comparable to a vertically rotating hand blender) which churned the water and supplied it with oxygen. This invention enabled the construction of deeper and wider ditches than had proved possible with Pasveer’s original solution.
 Interview with Mark van Loosdrecht (22/4/2021), see also story 6 in this series about the emergence of environmental sciences.
 ‘Waternieuws Special 25 jaar Carrousel’. Company archives Royal HaskoningDHV. Carrousels were in great demand abroad after a colossal Carrousel designed by DHV was installed at BASF in Germany.
 Interview with Mark van Loosdrecht and Company archives Royal HaskoningDHV.
 Nereda is named after a Greek water nymph who is associated with purity and chastity.
 The partnership is still in existence today.
 From the start, the experimental granule technology was included as a fully-fledged alternative to the construction of new installations. When the pilots produced positive results, a great deal of groundwork for new construction had already been done.
 Interview with Andreas Giessen, Royal HaskoningDHV company archives. Its festive opening by HRH (then Prince) Willem-Alexander underlined the success of the public-private partnership. From a historical perspective, the first ‘full-scale demonstration’ in Gansbaai is at least as relevant. After all, the technology was already fully operational there in 2008.
 Interview with Van Loosdrecht. ‘General intro to Nereda Technology with timeline’, Royal HaskoningDHV company archives.
 Added to the awards received by water specialists at Royal HaskoningDHV between 2005 and 2019, the number of awards now stands at more than twenty in 2021.
 According to Global Water Intelligence Magazine in 2020 about Nereda.