This work was undertaken to investigate the feasibility of reusing the process effluent from fermentation processes to minimize the liquid waste. Two fermentations with different characteristics were chosen as model fermentations for development of principles. The first was a yeast fermentation that requires high levels of carbon substrate for production of intracellular lipid. The second was a bacterial fermentation requiring high levels of nitrogen in the medium for production of lysine. The latter is used for commercial production of lysine;In the study of the first model fermentation, Apiotrichum curvatum, an oleaginous yeast, was used as the working culture. Spent broth from a defined medium was recycled to replace as much as 75% of the water and salts for subsequent batches and this was repeated for seven sequential batches without negative effect on cell mass or lipid production. A 64% volume reduction of wastewater was achieved in this manner. However, when using whey permeate as the medium, lipid production dropped after three consecutive recycle operations at 50% recycle, and after two consecutive recycle operations at 75 and 100% recycle. Accumulation of ions in the broth appeared to be responsible for the inhibition. An ion exchange step was able to eliminate the ion buildup and restore fermentation performance;In the second model fermentation study, we investigated a strategy of recycling to the subsequent fermentation a large fraction of the broth effluent from the cation exchange column used for lysine recovery. This was done on a lab-scale process with Corynebacterium glutamicum ATCC 21253 as the lysine-producing organism. Broth effluent from a fermentation in a defined medium was able to replace 75% of the water for the subsequent batch; this recycle ratio was maintained for three sequential batches without affecting cell mass and lysine production. Broth effluent was recycled at 50% recycle ratio in a fermentation in a complex medium containing beet molasses. The first recycle batch had a somewhat lower final lysine production, but somewhat higher maximum cell mass. In addition to reducing the volume of liquid waste, this recycle strategy has the additional advantage of utilizing the ammonium desorbed from the ion-exchange column as a nitrogen source in the recycle fermentation. The major problem of recycling the effluent from the complex medium was in the cation-exchange operation, where column capacity was lower for the recycle batch. The loss of column capacity probably results from the buildup of cations competing with lysine for binding;A zero liquid discharge strategy which utilizes sequential ultrafiltration and reverse osmosis with purified water regeneration for an industrial lysine fermentation process was also examined. Ultrafiltration of a stream sample obtained from an industrial production plant suggested that the high solid content of the stream was the major cause of rapid flux decline while the high osmotic pressure of the ultrafiltration permeate limited water recovery by reverse osmosis to about 38%.