Obviously, nobody before 1913 had the idea to increase the concentration of aerobic bacteria by sludge sedimentation after aerating the sewage in a bottle for several hours, to remove the solids-free water carefully and then add sewage again. The first persons to observe an increase in sludge by repeating this process several times were Edward Arden and William T. Lockett from the River Committee of the Manchester Corporation in 1914. They presented their results on the occasion of a
1.8 Early Experiments with the Activated Sludge Process 17
meeting at the Grand Hotel in Manchester on 3 April 1914 (Arden and Lockett 1914). It was of high importance that the glass bottles filled with 2.27 L of sewage were protected from light for the first time, so that algae could not grow. They filled their bottle with sewage from the Sewage Works at Davyhulme. If the sludge had a volume of 25% after sedimentation, "carbonaceous fermentation" and nitrification could be completed to a high degree within 24 h. It was very important that the sludge was mixed with the sewage and that sufficient air was added. The pH must be controlled by adding a small quantity of alkali. These published results are presented in Fig. 1.13.
In this figure, concentrations are given in "parts per million", which means approximately 200/106 = 200 mg L-1. The organics were measured as "Oxygen Abs.". The authors probably used KMnO4 as an oxidizing agent. The nitrification rate was slow compared to the removal rate for organics over the first 8 h. After this time, the situation changed.
Over the following years, this batch process was converted to a continuous process using an aeration tank, a sedimentation tank and sludge recycle system. After several experiments were performed in the UK and in the USA using pilot plants to study the process (Mohajeri 2002), the first technical-scale activated sludge plant was constructed in Sheffield, UK, in 1920 (Haworth 1922). The water flowed in open meandering channels and was aerated, moved and circulated by paddle stirrers. In Indianapolis, USA, compressed air flowed through perforated tubes arranged near the bottom at one side of a long channel, producing a spiral flow of air bubbles (Hurd 1923). The first surface aerator with a vertical shaft was constructed by Bolton. A conducting tube forced the two-phase flow near the bottom, resulting
Free & Saline Ammonia 4 Hours Oxygen Absorption Nitrite & Nitrate
Period of aeration
Fig. 1.13 First batch sewage aeration experiment with enriched activated sludge (Arden and Lockett 1914).
h in sufficient oxygen transfer and mixing of the water and sludge (Bolton 1921; Imhoff 1979). In Germany, the first large plants were built in Essen-Rellinghausen in 1926 (Kuhn 1927) and in Stahnsdorf near Berlin in 1929-1931 (Langbein 1930), the latter of which was designed and operated as an experimental plant for the study of different sedimentation tank designs (Mohajeri 2002).
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