Anaerobic co-digestion of swine manure and crude glycerol derived from animal fat - Effect of hydraulic retention time

Crude glycerol (CG), an abundant by-product of bio-diesel production, has been identified as a suitable co-substrate for improving the biogas production of livestock manure through anaerobic digestion (AD). In this study, the potential of utilizing CG generated from the esterification of animal fats for biogas production was studied in both batch and continuous AD experiments, with emphasis on the importance of the hydraulic retention time (HRT). Batch experiments showed that the limiting step in the methane production rate during CG mono-digestion was the 1,3-propanediol uptake. Additionally, biochemical methane potential tests indicated that the addition of 1% w/w CG to swine manure-AD is more efficient in terms of percent of theoretical amount of methane obtained than the addition of 3% w/w. However, in continuous experiments, co-digestion of manure with 3% w/w CG did not exhibit any sign of inhibition within the HRTs tested (17–22 days). Moreover, a 222% increase of biogas productivity was observed with 3% CG supplementation at an HRT of 17 days, in contrast to a 146% increase at an HRT of 22 days. Based on this, and on the similar efficiency of soluble COD removal among the processes (ca. 93%), it was shown that it is possible to reduce the HRT without affecting negatively the efficiency of conversion of manure. Moreover, it was shown that CG from 2nd generation biodiesel based on animal fat, is a suitable feedstock for boosting the methane production of manure-based biogas plants

Continuous Fermentation of Wheat Straw Hydrolysate by Clostridium tyrobutyricum with In-Situ Acids Removal

The present study focused on fermentative butyric acid production by Clostridium tyrobutyricum from pre-treated and hydrolysed wheat straw (PHWS) based on continuous operation mode and in situ acids extraction by reverse electro enhanced dialysis (REED). Different dilutions of PHWS in a synthetic medium (60–100 % v/v) were tested. It was found that continuous fermentation of PHWS greatly enhanced the sugar consumption rates and butyric acid productivity compared to batch tests, while application of REED enhanced them even further. Specifically, applying combined continuous operation mode and REED system for the fermentation of 70 % PHWS resulted in 19- and 53-fold higher glucose (1.37 g L(−1) h(−1)) and xylose (0.80 g L(−1) h(−1)) consumption rates, respectively, compared to those obtained by batch processing. Fermentation of 100 % PHWS continued unhindered with just urea and K(2)HPO(4) added with butyric acid production rate, yield and selectivity being 1.30 g L(−1) h(−1), 0.45 g g(−1) sugars and 0.88 g g(−1) acids, respectively. These results were also confirmed in a 20 L pilot plant bioreactor system