INTRODUCTION

Authors: Mark C.M. van Loosdrecht Per H. Nielsen Carlos M. Lopez-Vazquez Damir Brdjanovic

Wastewater treatment forms a crucial link in the services that the sanitation sector delivers to society. For centuries, sanitation largely consisted of transporting fresh, clean water to the cities, and using this water to transport the waste out of the city and discharge it into the natural environment. However, with the increase in human populations in cities as a result of the industrial revolution in the 19 century, this could no longer be maintained. The occurrence of epidemic diseases facilitated the development of wastewater treatment facilities and their implementation since the early 20th century. This development has been largely an empirical activity with theoretical approaches following experimental observations (Figure 1.1).

The discovery and development of activated sludge technology (described in detail in Jenkins and Wanner, 2014) was crucial as it triggered the rapid development and application of various analytical and experimental methods. Experimental work in the Lawrence Experimental Station in Massachusetts, USA, which at that time (1912) was a unique facility aimed at the experimental verification of different possible wastewater treatment procedures, inspired Gilbert Fowler to request Edward Ardern and William Lockett to repeat the experiments with wastewater aeration in the UK that he had seen in the USA. In 1913 and 1914 Lockett and Ardern carried out lab-scale experiments at the Manchester - Davyhulme wastewater treatment plant (Figure 1.2). Glass bottles were used to represent labscale aeration basins 'fed' by sewage from different districts of Manchester. Contrary to the experiments that Fowler saw in Massachusetts, in the Manchester aeration tests the sediment that remained after decantation was left in the bottle and a new dose of sewage was added to the sediment for the next batch. Lockett and Ardern soon found that the amount of the sediment increased with the increasing number of batches. At the same time the aeration time necessary for 'full oxidation' of sewage (full oxidation was a term used to describe the removal of degradable organics and for complete nitrification) was reduced. By using 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 a few weeks to less than one day, which made the process technically feasible. The sediment formed during the aeration of sewage was called activated sludge due to its appearance and activity. Lockett and Ardern published their results in a famous series of three papers (Ardern and Lockett 1914a, 1914b, 1915). This was the 'birth' of activated sludge, which is today the workhorse of wastewater treatment and the most widely applied sewage treatment technology in the world.

Wastewater engineering is a profession that is extremely experiment-based, and therefore it has always had the need to develop and standardise methods. This seemingly simple activity is strongly hampered by two factors, namely: (i) wastewater engineering is a typical interdisciplinary activity where chemical engineers, civil engineers, microbiologists and chemists interact to develop and understand the processes; the challenge here is to integrate methods and approaches from these disciplines, and, (ii) in addition, wastewater and its treatment processes are by their nature difficult to define with exactitude. It is for instance virtually impossible to measure all the individual compounds in the wastewater itself. Identifying all the relevant microorganisms in the processes has long been impossible and is still a complicated challenge. Defining all the potentially occurring chemical conversions is, due to the myriad of chemicals present, again an almost impossible task.

Due to the undefined nature of the experimental system, research has tended to progress slowly and it heavily depends on standardised methods that may not be exact but, when used in a standardised way, are very helpful and useful to compare experimental results. Examples are the commonly used chemical or biological oxygen demand tests. The iconic 'Standard Methods for the Examination of Water and Wastewater' (APHA et al., 2012, Figure 1.3) has for generations of sanitary engineers been the resource for analysing their experimental systems and full-scale operations. These methods focus heavily on the chemical characterization and measurement of specific microorganisms.

Societal demands on the efficiency of wastewater treatment plants have advanced, moving from public health protection to water resources and environmental protection and nowadays to integrated resource and energy recovery. Therefore the need to accurately characterize the microbial processes in the wastewater treatment processes has increased over recent decades. Certainly, it is a challenge to develop standardized methods for experimental work that can be easily repeated in different laboratories. In many cases, the exact handling is important, but it is not easy to be written down in a practical protocol.

Therefore, to avoid these problems, it was decided to develop not only a book describing all the experimental methods but also a video catalogue with the methods described in this book actually being demonstrated in the laboratory. This book and its associated video-based material are designed to support the research and development field with a manual for characterizing the biological processes in wastewater treatment. The editors have decided in this first edition of the 'Experimental methods in wastewater treatment' book to focus on the activated sludge process since this is worldwide by far the most applied technology. Nevertheless, most of the methods presented in this book can also be applicable to biofilm-based technologies or anaerobic digestion processes.

The decision to focus on experimental methods related to the activated sludge process has resulted in seven chapters...