2018 Charles and Mary O’Melia Lecture in Environmental Science
Re-Envisioning Wastewater Treatment for the 21st Century
Desmond Lawler, PhD
Nassir I. Al-Rashid Chair in Civil Engineering
Department of Civil, Architectural and Environmental Engineering
The University of Texas at Austin
Abstract: The philosophy of municipal wastewater treatment has changed only slowly in the past 100 years. From approximately 1920 to 1970, a wastewater discharge was considered acceptable if the dissolved oxygen level in the receiving stream did not dip below 5 mg/L downstream of the discharge. Protecting aquatic life, particularly fish, from immediate death due to low oxygen levels was the primary motivation and the goal. The passage of the Clean Water Act in 1970 reflected a broader view to include concerns about eutrophication by nutrients and ecological and human health concerns with the naming of “priority pollutants.” Nevertheless, the central concept was that discharge concentrations would be acceptable if they took advantage of the assimilative capacity of receiving waters; that is, if they limited the harm to acceptable values. Now we are embarking on a new philosophy, captured by the phrase “One Water” by the Water Environment Federation, in which we think of wastewater not as a problem for disposal but as a resource.
Why is this shift in philosophy happening? At least two major changes have occurred since the old philosophies were developed. First, a dramatically increased population has led to a substantial increase in “indirect potable reuse” of wastewater, whereby the effluent discharge from one city is a part of the drinking water source for a downstream city. In many areas of the arid Southwest, that “part” can often be nearly 100%. An extension of this trend, due to water shortages, is the drive toward direct potable reuse of wastewater. Second, not only do the chemical and pharmaceutical industries now produce tens of thousands of synthetic chemicals that were not dreamed of when the “priority pollutant” list associated with the Clean Water Act was developed, we now understand that some of these products are endocrine disruptors and others lead to microbial antibiotic resistance.
In this talk, I will try to make the case that wastewater treatment needs to be changed, perhaps radically, to reflect the new philosophy and to meet the needs of the 21st century. The thrust of the presentation will be to explore some possibilities for these radical changes and try to back them up with preliminary engineering calculations.