Fate of Dissolved and Particulate Carbon in an Anoxic Biological Water Processor

The mineralization of organic carbon is one of the primary objectives in the operation of a biological water processor for long duration space missions. In order for the reactor to operate as efficiently as possible, an understanding of the various forms and mass balances of carbon and nitrogen is important, particularly in a modified Ludzak-Ettinger (MLE) process. Total organic carbon (TOC) is that carbon portion that can be oxidized eventually to CO₂. TOC is made up of two parts, dissolved organic carbon (DOC), which is easily utilized by microorganisms via absorption through the cellular membrane and particulate organic carbon (POC), which are organic aggregates that require extracellular enzymes to break the particulates down into smaller particles before they are used by the microorganisms.

The particulate fraction plays an important role in the overall efficiency of a reactor due to competition for space between the recalcitrant organic matter and the biofilm consortium in the reactor that degrades the influent. If a significant fraction of volume is POC, there is not sufficient viable biomass available to adequately degrade the influent. If a prefilter was added to the system, would performance increase and thereby extend the lifetime of a reactor? In order to determine the effect of a prefilter on performance and to determine the relationship between DOC, POC, sizing and lifetime in an anoxic system, three small bioreactors were operated with nitrate provided as an electron acceptor.