However, his early fame was based on his work with aerobic treatment plants, i.e., facilities that work with microorganisms in the presence of oxygen. His work involving activated sludge systems, particularly the development of completely mixed activated sludge design equations, has resulted in a better understanding and the appropriate application of this widely used wastewater treatment process. McKinney has had a great influence on industrial and municipal treatment plants. More than 75 operating plants have been based on McKinney's research and design. In fact, one of the world's largest operating anaerobic industrial wastewater treatment plants, located in Puerto Rico, is based largely on McKinney's concepts.
Anaerobic treatment involves using microorganisms in the absence of oxygen.
They produce methane gas as a by-product, the main element in natural gas. This source may be of particular importance to underdeveloped nations because it is inexpensive. McKinney also has experience with many types of industrial wastes including pulp and paper, cotton, synthetic and wool textiles, food processing, meat-packing and petroleum refining. He has consulted with over 190 industries, consulting engineering firms, and federal, state and local governments on various pollution control projects. In addition, he has published over 200 technical papers, over 60 technical research reports and over 370 technical consulting reports.