Process Control as Ecosystem Management: Using the History of Sewage Treatment Plants to Analyze Ecosystem Management Practices

Industrial ecosystems are fruitful sites for examining ecosystem management. Sewage treatment plants, breweries, biotechnology reactors, and ethanol production plants are all ecosystems—complex biophysical systems in which communities of bacteria, yeast, fungi, and other organisms are maintained to extract services or resources. The industrial analog to ecosystem management is “process control”, where the industrial operator is the ecosystem manager. Process control is the management of a production process through the careful measurement and adjustment of its physical and chemical conditions. By analyzing the history of process control in activated sludge sewage treatment plants, I show the importance of craft knowledge in ecosystem management. Sewage treatment plant workers, through their experience in operating the plants, developed means of evaluating process conditions based on sight and smell rather than laboratory analysis. These craft techniques developed and persisted in spite of concerted efforts on the part of sanitary scientists to institute “scientific” control of the process based on laboratory analysis and models of microbial kinetics, suggesting that craft knowledge of ecosystem function can contribute to successful management. The craft knowledge of sewage plant workers is a kind of adaptive management, in which workers constantly adjust ecosystem parameters and observe the results. This approach is contrasted to “command and control” approaches to treatment plant automation, which have met with uneven success.