Microbiological Endogenous Processes in Biological Wastewater Treatment Systems

Microbiological endogenous processes in biological wastewater treatment systems (BWTSs) refer to combinations of biological and ecological mechanisms and processes, including endogenous respiration/cell maintenance, cell decay, death-regeneration/cryptic growth, predation on bacteria by higher microorganisms, and cell lysis due to viral attack or adverse environmental conditions (pH, toxic substances, temperature and others), which have significant effects on almost all aspects of BWTSs. However, the current state of knowledge about endogenous processes is very limited. With this review article, the definition of endogenous processes is identified and summarized. Based on a review of the relevant literature, the endogenous processes in BWTSs are classified at two microbial levels, a cell level and a community level. At the cell level, each living microbial cell needs a certain amount of energy to satisfy cell maintenance; the community level reveals interactions between microorganisms and operating parameters. Processes such as uncoupling, programmed cell death (PCD), starvation, viral infection, and predation are reviewed, and state-of-the-art information about these processes is summarized. The development of determining maintenance energy and decay rate of bacteria in BWTSs is also outlined. Based on these reviews, further research aspects related to endogenous processes are proposed.