1 with 25 wt calcium hydroxide slurry spent filtrate was obtained from a preceding fermentation run spent filtrate was added to the fermentation media in a ratio of 1 1 and nutrient additions were adjusted accordingly table 7 summarizes results of a batch fermentation with recycle of filtrate the data showed a complete fermentation of dextrose unexpectedly a maximum substrate consumption rate of 5 5 g l hr is obtained with an overall productivity of 2 3 g l hr succinate yield for filtrate recycle fermentations was 87 the spent filtrate added to the recycle fermentations contains acetate thus a higher concentration of acetate was expected at the end of recycle fermentations because of the acetate initially present the results show that a very high rate of substrate fermentation was obtained by recycling spent filtrate without any adverse effects from higher acetate concentrations also the media cost was lowered because nitrogenous and other soluble nutrients were recycled and less needed to be added to the fermentation media table 7______________________________________succinate fermentation with spent filtraterecycle at ph 6 2 neutralized withcalcium hydroxide ex 13______________________________________dextrose initial g 49 2dextrose final g 0 3maximum substrateconsumption rate g l hr 5 5overall productivity g l hr 2 3productssuccinate g 43 0acetate g 10 6formate g 0 4succinate yield wt 87.