Effects of solids and liquid flows on fermentation in continuous cultures. II. Nitrogen partition and efficiency of...

The effects of varying solids retention time (SRT) and liquid dilution rate (D) on N partition and microbial efficiency were studied in vitro with a dual flow continuous culture system. SRT's of 14.3, 22.0 and 29.7 hr and D's of .07, .11 and .15 volumes/hr were used. Ammonia N accounted for 2.69 to 7.30% of total effluent N. Highest values were observed with 29.7-hr SRT at .11 and .15/hr D's, and were associated with a slight decrease in microbial N. Between 1.17 and 2.50 g microbial N were produced per 24 hr, accounting for 31.34 to 50.49% of total effluent N. Daily output of microbial N increased (P less than .05) with increasing D at the lowest SRT but showed little or no change at the 22.0- and 29.7-hr SRT's. Feed bypass N was inversely related to microbial N and accounted for 44.91 to 65.10% of total effluent N. Microbial cell yields per mole ATP (YATP) ranged from 10.40 to 24.41 and tended to increase with decreased SRT more than with increased D, although responses were variable. Efficiency of microbial N synthesis ranged from 15.75 to 23.91 g microbial N/kg digested dry matter (DDM), with trends similar to those seen for YATP.