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Activated sludge

Colurella found in activated sludge.
 

100 years..

Aerated activated sludge tank.
 

.. and counting!

Aerated activated sludge tank.
 

Activated sludge

Fluorescence-marked filamentous bacteria.
 

100 years..

Rellinghausen WWTP the first activated sludge treatment plant on the European continent.

.. and counting!

Opercularia found in activated sludge.
 

Activated sludge

Aerated activated sludge tank.
 

100 years..

Fluorescence image of activated sludge.
 

..and counting!

Aerated activated sludge tank with internal final sedimentation tank.

History of activated sludge

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As generally known, the activated sludge process was invented in England at the beginning of this century. At that time England was the country with probably most urgent problems in water pollution because of dense population and advanced industry. Repeated hygienic problems in English towns and cities and the demand of industry for clean water led to the formation of appropriate institutions already in the second half of the 19th century. Thus in 1865 the first Royal Commission on River Pollution was established and re-established later on in 1874.

The activities of the Royal Commission on River Pollution resulted in the Rivers Pollution Prevention Act, issued in 1876. However, the act itself without proper technical measures could not stop and prevent further pollution of the rivers. From this point of view, the formation of the Royal Commission on Sewage Disposal in 1898 can be understood as the milestone in the development of wastewater treatment technology. This commission co-ordinated the activities leading to better understanding of factors affecting the water quality in receiving waters and to evaluation of new treatment procedures. One of the best known outputs of the commission is the BOD5 test recommended in 1908. The famous "30:20 + full nitrification" effluent standard was adopted in 1912 which was a great challenge for the development of wastewater treatment processes capable of meeting this standard.

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The effort of English engineers, chemists and microbiologists to improve the existing treatment techniques led finally to the invention of activated sludge process in 1914. The author of this article is lucky enough that he does not need to rely only upon the literature references in tracing the history of early days of activated sludge process. The author had the privilege to be a student and later on a colleague and friend of Professor Madera, one of the most outstanding persons in wastewater treatment in our century and one of the founding fathers of IAWQ.

During his frequent trips to England in the period between the World Wars, Madera met, inter alia, Dr. Fowler, the initiator of the first activated sludge studies in England. In lively debates with Madera, accompanied by numerous cups of strong coffee or tea and by unbelievable amount of cigarettes and pipes we smoked together, the author found that most of the written memories about the beginning of activated sludge process were not just a legend but a true story. Like in many other areas of human activities, the colourful days of the pioneers overshadow the prosaic reality of our days (I just hope that our descendants will be more lucky and will not need to say the same about our era).

Probably the greatest impulse for the invention of activated sludge process was the trip of Dr. Fowler to the USA in 1912. Dr. Gilbert Fowler from the University of Manchester undertook this journey in the position of consultant chemist to the Manchester Corporation. During this trip he visited the Lawrence Experimental Station˛ in Massachusetts, which was, at that time, a quite unique facility aimed at experimental verification of different possible wastewater treatment procedures. One of the processes studied there was the aeration of municipal wastewater in different arrangements. After his return to England, Dr. Fowler informed about his experience from the Lawrence Station experiments Mr. Edward Ardern, chemist at the Manchester - Davyhulme wastewater treatment plant, and his co-worker, Mr. William Lockett. Dr. Fowler suggested to them to repeat the experiments with wastewater aeration he saw in the Lawrence Experimental Station. However, the unforgettable contribution of those two gentlemen to the development of activated sludge process can be seen in the fact that Ardern and Lockett understood for the first time the active role of suspension formed during the aeration, known now as activated sludge.

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In 1913 - 1914 there were carried out lab-scale experiments at the Manchester - Davyhulme wastewater treatment plant. The experiments were prepared and performed by William Lockett according to the Dr. Fowlerąs recommendations. As the first reactors - lab-scale aeration basins - glass bottles were used. In order to prevent the growth of algae, the bottles were covered by brown paper to protect their content from day-light. Sewage from different districts of Manchester was used for those experiments.

Contrary to the experiments Dr. Fowler saw in Massachusetts, in the Manchester aeration tests the sediment after decantation was left in the bottle and a new dose of wastewater was added to the sediment for the next batch. Lockett and Ardern found soon that the amount of the sediment increased with increasing number of batches. At the same time the aeration time necessary for "full oxidation" of sewage (full oxidation was a term used for description of removal of degradable organics and for complete nitrification). By this technique of repeated batch aeration with the sediment remaining in the bottle Lockett and Ardern were able to shorten the required aeration time for "full oxidation" from weeks to less than 24 hours which made the process technically feasible. The sediment formed during the aeration of sewage was called activated sludge for its appearance and activity. Lockett and Ardern referred about their experiments and results at the meeting of Society of Chemical Industry held on 3 April 1914 at the Grand Hotel, Manchester. The results were later on published in a famous series of three papers:

  • Ardern, E., Lockett, W.T. (1914a) Experiments on the Oxidation of Sewage without the Aid of Filters. J. Soc. Chem. Ind., 33, 523.
  • Ardern, E., Lockett, W.T. (1914b) Experiments on the Oxidation of Sewage without the Aid of Filters, Part II. J. Soc. Chem. Ind., 33, 1122.
  • Ardern, E., Lockett, W.T. (1915) Experiments on the Oxidation of Sewage without the Aid of Filters, Part III. J. Soc. Chem. Ind., 34, 937.

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Still in 1914 the activated sludge process was tested at the Manchester - Davyhulme wastewater treatment plant in a large scale, in a "mobile" pilot-plant. Although most parts of the pilot-plant unit were made of wood and the model was placed on the chassis of horse-driven wagon, this installation already exhibited most characteristic features of activated sludge process we know today. From the very beginning both basic arrangements of activated sludge process were tested, i.e., the continuous-flow arrangements with separate clarifiers and activated sludge recycle and the fill-and-draw arrangement, nowadays known as an SBR. The models at Davyhulme were equipped with the aeration by diffused air. The coarse-bubble diffusers were soon replaced with fine-bubble ceramic elements.

Simultaneously with the Manchester experiments in 1914 the SBR activated sludge process was tested in full-scale plant at Salford. The first full-scale continuous-flow activated sludge process was put into operation for the town of Worcester in 1916 by Jones and Attwood, Ltd. The diffusers used in aeration basins of first activated sludge plants suffered from rapid clogging. For this reason in 1916 Howarth, the manager of WWTP at Sheffield, replaced the aeration by diffused air with the mechanical aeration using vertically-rotating horizontal-shaft paddles. The first full-scale mechanical aeration system came into operation in 1920.This so-called Sheffield aeration system from 1924-1925 is still preserved and used at the Stockport WWTP, which is probably the oldest, still operated activated sludge plant in the world.

Howarth paddle aerators inspired Kessener to develop aeration brushes, used for the first time at the abattoir wastewater treatment plant in Appeldoorn, Holland, in 1927. At the same time Bolton in England was engaged in the development of aeration turbines. First łSimplex˛ turbines by Ames Crosta, Ltd. were installed at the Bury WWTP in 1925.

The activated sludge process found soon its application also outside the UK. The first experimental activated sludge plant in USA was built in Milwaukee in 1915 with the help of Dr. Fowler as a consultant. Imhoff performed the first tests with activated sludge process in 1924 and the first full-scale plant was built in 1926 at Essen-Rellinghausen. Even before World War II the activated sludge process reached other continents then Europe and America. Thus the activated sludge process was installed for instance in Bangalore, India; Adelaide - Glenelg, Australia and in Johannesburg in South Africa.

Kessener brush aerators at Stockport WWTP from 1935. Kessener brush aerators at Stockport WWTP from 1935.

The readers of the article, who are interested in the history of activated sludge process and can provide us with some pieces of interesting historical information or photographs, schemes, etc. from their countries, are asked to contact Jiri Wanner.

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