Ardern and Lockett remembrance

Glen T. Daigger (USA)

1.1 INTRODUCTION

In this volume we recount the development of the AS process over the past 100 years. In so doing we also celebrate its contributions to enhancing human life and environmental protection and speculate about its role in the future. This is an ambitious task to say the least, but one which we hope will inform both the current generation about the future and future generations about the past. To do this it is necessary to go back to 'the beginning' and understand the circumstances which resulted in the initial development of the AS process. The reasons that it has been so transformational to the sanitary engineering profession, both throughout the past 100 years and especially as the sanitary engineering profession evolved into the environmental engineering profession in the late 1960s and 1970s, are also addressed.

Edward Ardern and William T. Lockett, pictured in Figure 1.1, are widely recognized as the 'discoverers' and 'inventors' of the AS process. Their paper before the Society of Chemical Industry on April 3, 1914 in Manchester, England is broadly recognized as the 'official' presentation of the AS process to the professional community. How did this come to pass and why was this such a momentous event in the history of the sanitary/environmental engineering profession? The answers to these questions require an understanding of the historical context for the development of the AS process – the circumstances which existed in society in general as the process was being developed. In English there is a common expression that states 'necessity is the mother of invention', so we might ask 'what was the necessity that drove this invention?' Addressing this question is essential for setting the stage for all that follows, both in the following chapters of this book and as we collectively look at the future of the process. Why is this the case? It is because, as in the past, it is 'necessity' that will drive the further practical advancement of the process.

To accomplish this task I will:

• Review the social, economic, scientific, and environmental context of the late 19th and early 20th century when the AS process was developed.

• Briefly summarize the principal events which led to development of the process.

• Discuss the role that Ardern and Lockett specifically played in development of the process.

• Discuss the subsequent implementation of the process, which set it on the path to become the dominant technology that it is today.

• Identify the key characteristics of the process which have allowed it to remain so dominant for such a long time.

It is clear that the AS process has had a major impact on the sanitary/ environmental engineering profession in its approach to addressing human health and environmental protection over the past 100 years. Each quarter century or so of AS process's existence has brought with it a review of its historical development (Mohlman, 1938; Sawyer, 1965; Alleman & Prakasam, 1983). It will be interesting to see if yet another major review and assessment is prepared in about 2040.

1.2 INVENTION OF AS

1.2.1 The context

The late 19th and early 20th century was a time of significant change. Roughly 100 years following the initiation of the first industrial revolution in the UK and the USA, and at the conclusion of the second industrial revolution in which technological, economic, and population growth gained increased momentum, the living standards of a rapidly increasing population were, likewise, rapidly increasing. Millions of people were literally being lifted out of poverty into a standard of living never before experienced by so many (a situation not unlike what is occurring in developing countries such as China today). The urban population was also increasing exponentially (a trend which continues today) as the economic wealth created by the industrial revolution was concentrated there.

While a tendency exists to romanticize this period, the actual situation was far from idyllic (Bettmann, 1974). Indeed, the increased urban population suffered from unsanitary conditions that adversely impacted their health, comfort, and standard of living, and negative environmental impacts were broadly felt. The average life span during this time period was roughly 45 to 50 years, compared to the 75 to 80 years that it is today. Infant mortality was a principal contributor to reducing the lifespan in the late 19th and early 20th century. It is thought by many that two of the three decades of additional life span now enjoyed in the developed world are due to the water and sanitation systems installed during the 20th century. Indeed, a survey of public health researchers and professionals in the British Medical Journal indicated that the implementation of modern water and wastewater systems was the most significant step that improved public health over the past 150 years (Anon., 2007). Observations such as these led the US National Academy of Engineering to list modern water and sanitation as one of the significant engineering accomplishments of the 20th century (Constable & Sommerville, 2003).

As with all transformations of the magnitude of the Industrial Revolution, there were both positive and negative effects. The principal negative impact was the absence of acceptable methods of managing human and industrial wastewaters. These circumstances resulted in intense studies by numerous researchers on both sides of the Atlantic. Schneider (2011) provides a thorough and interesting summary of developments in the late 19th and early 20th century in the USA and the UK. The problem of sewage arose in the 19th century in cities throughout the industrializing world as the modern potable water service was extended, thereby addressing one aspect of public health protection – the provision of safe drinking water. This led to the development of waterborne sewage, with the associated dramatic increase in volume which overwhelmed traditional waste management approaches. Identifying solutions to this problem was the subject in the UK of a number of Royal Commission studies, one of which in 1865 established land treatment as the only acceptable sewage treatment system (Congress on the Sewage of Towns, 1866). This finding led to the development of sewage farms to serve major cities throughout Europe. Sewage farms proved highly effective in some locations, with notable examples developing to serve Paris and Berlin (Schneider, 2011). However, in other locations, with poorly drained soils and rainy climates, they were less than successful. Moreover, the large land requirements became a practical constraint, especially as industrialization resulted in the rapid growth of urban areas. Thus, research into alternative sewage treatment methods was intense on both sides of the Atlantic. Schneider (2011) also discusses the ideological debate which developed concerning the 'nature' of an appropriate treatment system. Land-based systems were viewed as 'natural' and therefore appropriate by some proponents, in contrast to 'artificial' systems such as anaerobic septic and Imhoff tanks or contact and infiltration beds. Schneider (2011) discusses the development of modern sewage treatment processes as a leading example of the industrialization of biological process technology, which occurred during this same time frame. While this ideological debate continued through the second half of the 19th century, especially in the UK, it was largely resolved in the first decades of the 20th century (although, as we shall see, it reappears in subsequent decades).

By later in the 19th century various forms of anaerobic treatment, such as septic tanks and the Imhoff tank, were in practice, along with physical–chemical methods. Biofilm-based biological systems, such as intermittent filters, contact beds, and trickling filters, were also developed and transferred into practice in the later portion of the 19th century. At the same time, some researchers hypothesized that the provision of aerobic conditions would address the unpleasant and odorous conditions associated with anaerobic treatment, leading to experiments on blowing air through sewage. Experiments on the aeration of sewage were initiated as early as in 1882 by Dr Angus Smith, followed by several other researchers (Alleman & Prakasam, 1983). While obnoxious odors were avoided, effective sewage treatment was not achieved. Experiments providing direct aeration to biological filter systems conducted at the Lawrence Experimental Station, Massachusetts, USA were more successful. We understand today that this occurred because the system incorporated the provision of oxygen with a sufficient quantity of biomass to metabolize the biodegradable organic matter in the wastewater. It was the biomass which was missing from the earlier experiments on the aeration of the sewage. Based on our knowledge today, this sequence of events foreshadowed development of the AS process. In fact, during the later 1890s and early 1900s various researchers hypothesized the need for accumulated 'humus' to accelerate treatment. However, some such as Gilbert John Fowler thought that solids (particulates) must be fully solubilized and, consequently, considered accumulated humus to be contrary to the objective of sewage purification. Then, in the early 1910s, researchers coupled aeration with the accumulation of biomass on wooden slats in tanks – essentially an early embodiment of the current moving bed biofilm reactor (MBBR) process. Black and Phelps (1914) conducted successful full-scale tests of this concept in New York, while laboratory studies of the concept were conducted at the Lawrence Experimental Station. Of course, at this time the biological nature of wastewater treatment was not established, so the importance of maintaining a sufficient biomass was not recognized. Researchers were beginning, however, to document the importance of both aeration and the retention of solids required for treatment.

1.2.2 The discovery

At this point Fowler and the City of Manchester in the UK enter the picture. Fowler was both an academic and a researcher as well as a practitioner. While at the University of Manchester, he also served as Superintendent Chemist at the Manchester Sewage Works. In 1912 Fowler was enlisted to consult on the pollution problems in the New York Harbor. During this visit to the USA he also visited the Lawrence Experimental Station and observed the experiments on aeration of filters being conducted there. Fowler was well familiar with the previous work, including his own, on aeration of sewage. He later credited this visit with an 'illuminating idea' and referred to the Lawrence Experimental Station as the 'Mecca of sewage purification' (Alleman & Prakasam, 1983). The 'illuminating idea', was the concept of using a suspended biomass culture in an aerated bioreactor. What he observed in Lawrence were the results of experiments by Clark and Gage (1912) who inoculated bottles of sewage with algal suspensions and aerated them. Upon return to the UK, Fowler initiated studies using a mixture of iron salts and a selected bacterial seed added into an aerated tank followed by a clarifier. Unfortunately, he did not recycle the solids which settled in the clarifier back to the aerated tank. Thus, while purification occurred, the rate was not sufficient. Alleman and Prakasam (1983) point out that, at this point, thirty-one years had passed since the first experiments on sewage aeration. Researchers had also empirically identified the need for a sufficient mass of treatment solids, such as those that were retained by biofilms developing on media provided in contact beds, and so on. Or through their direct addition. However, no one had disclosed the idea of retaining the solids produced through treatment by sedimentation.

Then, on April 3, 1914 in Manchester, two of Fowler's students, Edward Ardern and William T. Lockett (Ardern & Lockett, 1914a), presented what Fowler himself characterized as the 'bombshell'. Employed at the Manchester Sewage Works, they presented the results of their experiments using aerated batch fill-and-draw reactors where they retained the settled solids following sewage purification. In their laboratory they aerated sewage in glass bottles that were covered with paper to prevent the growth of algae. Unlike previous researchers, they retained the sediment formed following aeration and fed subsequent batches of sewage. They found that the rate of purification (at that time defined as the removal of biodegradable organics and full nitrification) increased as they retained the settled solids over the course of several treatment cycles. The time required for purification was eventually reduced to less than 24 h, which made the process economically feasible. The solids were said to become 'activated' by retention and recycling. Today we understand that retention of settled solids allowed the development of the biomass needed for effective wastewater purification, but at the time, this was a novel concept. In this, their first paper, and in their two subsequent papers (Ardern & Lockett, 1914b, 1915) they provided a comprehensive treatment of many practical factors, such as energy considerations, sludge handling, sensitivity of nitrifiers to temperature and pH, continuous flow versus batch fill-and-draw operation, the effects of industrial wastes, aeration methods and levels, and the need to acclimate the 'activated sludge' to the subject wastewater.

While Ardern and Lockett are almost universally referred to as the inventors of the AS process, it appears obvious that they were able to do what they did because of the work of many others. They simply added the final concept, the last 'piece of the puzzle'. It would also appear obvious that their association with Fowler and his wide access to, and knowledge of the work of others, positioned them to make this highly significant contribution. In fact, Fowler suggested to Ardern and Lockett that they duplicate the lab-scale research that he had observed Clark and Gage conducting at the Lawrence Experimental Station in 1912. It is interesting that, at the same meeting in 1914 where Ardern and Lockett presented their second paper, Melling (1914) announced that he had already successfully applied the AS process in a 302 m3/d facility in Salford, England. This must have required some previous knowledge of the essential elements of the AS process, suggesting that others in the UK were considering similar concepts. Perhaps it was both the presentation of this last 'piece of the puzzle', as well as the fact that their three publications provided a comprehensive treatment of many of the relevant factors, that resulted in the widespread attribution of the invention of the process to them. In any event, the critical importance of the results presented by Ardern and Lockett were immediately recognized and acted on.

1.3 AFTERMATH OF THE INVENTION

1.3.1 Accelerated implementation

The substance of the 'bombshell' announcement by Ardern and Lockett was immediately adopted by practitioners who began implementing it. Just think, it was not necessary to buy and install all of the media needed in aerated biofiltration systems! Rather, just keep the solids produced as a result of treatment and the treatment rate accelerates. Elegantly simple! Engineers immediately began to explore and develop the equipment needed to implement this new process:

• Batch fill-and-draw, as used by Ardern and Lockett, or continuous flow? The practical answer in the early part of the 20th century was continuous flow due to the absence of automation for the valves and level controls necessary to implement batch processing. It would not be until the early 1970s, when programmable logic controllers became widely available, that the fill-and-draw operation needed for the now well-known sequencing batch reactor process was possible.

• Aeration devices to efficiently transfer the needed oxygen? Both mechanical and diffused air systems were developed and used. Practice quickly evolved to what we currently do today – mechanical aeration in smaller plants and diffused air in larger ones. However, practice in this regard differed somewhat between the USA and UK, with mechanical aeration becoming more popular in the UK in larger plants.

• Clarifier configurations? This is still a controversial aspect that will be addressed in Chapter 11 of this book.

• Sludge pumping (RAS and WAS) and treatment of excess sludge?