Mid Sweden University

The effect of fermented whey on the aerobic degradation of n-alkanes by a microbial consortium was investigated in an aqueous system. Microbial degradation of 100 mg n-alkanes (C12, C14, C16 and C18) in mineral nutrient medium was assessed by measuring the decrease in n-alkanes, production of CO2 and increase in biomass. The addition of fermented whey at a concentration of 5 mg dry weight to a nutrient medium receiving a small-sized inoculum (103.4 CFU ml-1)shortened the lag phase from 8 to 3 days, but the degradation rate during the degradation phase was not enhanced. The shortened lag phase at low initial concentration of microorganisms indicates that the fermented whey stimulates growth in the initial phase, without reducing the consortium's capacity for n-alkane degradation.

The objective of this work has been to investigate the possibility of using fermented whey as an organic growth supplement in order to enhance the aerobic degradation of n-hexadecane in soil. Fermented whey was added at different dosages to nutrient amended soil microcosms contaminated with 5000 mg diesel fuel kg-1 dry weight (dw). The target substance was 14C-labeled n-hexadecane, and the biodegradation was monitored by analysis of evolved 14CO2. Biodegradation curves were fitted to a three-half-order kinetics model. Enhanced biodegradation was observed in sand at 7 and 22C and in loamy sand at 22C but the effect was most pronounced in the sand soil at 22C. The addition of 6 or 60 ml fermented whey kg-1 soil dw, increased the degree of n-hexadecane biodegradation at the end of the experiment, 167 days, from 49% in the untreated sand to 60 or 67% respectively. This increase in biodegradation was characterized by an increase in the amount of substrate biodegradation by first-order kinetics despite a decrease in the first order rate constant, k1. The highest concentration of fermented whey, 60 ml kg-1, gave rise to substrate competition, diauxie, which resulted in an extended lag phase.

The effect of organic amendments on the biodegradation of n-alkanes and phenanthrene in diesel contaminated soil was evaluated. The organic amendments used were fermented and non fermented sweet milk whey and the mineralization was estimated by analysis of evolved 14CO from added 14C-hexadecane, 14C-octadecane and 14C-phenanthrene. The addition of 2100 mg dry weight (dw) sweet whey kg-1 soil dw at the start of the experiment increased the extent of mineralization after 184 days compared to a control, from 45 % to 61 % for n-hexadecane and from 35 % to 46 % for n-octadecane. The stimulation was characterized according to a three-half-order kinetic such as if a greater part of the substrates was mineralized according to first order kinetics. Similar stimulation was achieved from the fermented whey when 210 mg dw kg-1 soil dw was added to the soil every second week during the 184 days of incubation.