The effects of organic loading rate on the performance and stability of anaerobic co-digestion of municipal biomass waste (MBW) and waste activated sludge (WAS) were investigated on a pilot-scale reactor. The results showed that stable operation was achieved with organic loading rates (OLR) of 1.2-8.0kgvolatile solid (VS)(m(3)d)(-1), with VS reduction rates of 61.7-69.9%, and volumetric biogas production of 0.89-5.28m(3)(m(3)d)(-1). A maximum methane production rate of 2.94m(3)(m(3)d)(-1) was achieved at OLR of 8.0kgVS(m(3)d)(-1) and hydraulic retention time of 15days. With increasing OLRs, the anaerobic reactor showed a decrease in VS removal rate, average pH value and methane concentration, and a increase of volatile fatty acid concentration. By monitoring the biogas production rate (BPR), the anaerobic digestion system has a higher acidification risk under an OLR of 8.0kgVS(m(3)d)(-1). This result remarks the possibility of relating bioreactor performance with BPR in order to better understand and monitor anaerobic digestion process.
"Cumulative biogas production decreased at higher organic loading due to VFAs accumulation in digesters. These results are in accordance with other studies where higher risks of VFA accumulation and low biogas yield at higher organic loading rate have been reported (Alvarez and Lidén, 2008; Liu et al., 2012). Digester at an S/I ratio of 0.25 yielded highest biogas among all other digesters (Fig. 2b). "
[Show abstract][Hide abstract] ABSTRACT: Aim of this study was to find out suitable mixing ratio of food waste and rice husk for their co-digestion in order to overcome VFA accumulation in digestion of food waste alone. Four mixing ratios of food waste and rice husk with C/N ratios of 20, 25, 30 and 35 were subjected to a lab scale anaerobic batch experiment under mesophilic conditions. Highest specific biogas yield of 584L/kgVS was obtained from feedstock with C/N ratio of 20. Biogas yield decreased with decrease in food waste proportion. Further, fresh cow dung was used as inoculum to investigate optimum S/I ratio with the selected feedstock. In experiment 2, feedstock with C/N ratio 20 was subjected to anaerobic digestion at five S/I ratios of 0.25, 0.5, 1.0, 1.5 and 2.0. Specific biogas yield of 557L/kgVS was obtained at S/I ratio of 0.25. However, VFA accumulation occurred at higher S/I ratios due to higher organic loadings.
"From the 35 th day until the end of the experiment, the total VFAs concentration in the bioreactor increased from 10 to 40 g/L. With increasing OLRs, the anaerobic reactor suffered from an increase of VFA concentration, resulting in inhibition of the methanogenic bacteria . Forbes et al.  reported that an OLR of 9 g COD/L.day at a hydraulic retention time (HRT) of 1 day made the thermophilic bioreactor unstable , shown by a high concentration of VFAs in the effluent. "
[Show abstract][Hide abstract] ABSTRACT: A bioreactor including encased digesting bacteria for biogas production was developed, and its performance in toxic media and under high organic loading rates (OLRs) was examined and compared with traditional digestion reactors. The bacteria (3 g) were encased and sealed in 3 x 6 cm2 PVDF (polyvinylidene fluoride) membranes with a pore size of 0.1 microm, and then several sachets were placed in the reactors. They were then examined in toxic medium containing up to 3% limonene as a model inhibitor in batch reactors, and OLRs of up to 20 g COD/L.day in semi-continuous digestions. The free and encased cells with an identical total bacterial concentration of 9 g in a medium containing 2% limonene produced at most 6.56 and 23.06 mL biogas per day, respectively. In addition, the digestion with free cells completely failed at an OLR of 7.5 gCOD/L.day, while the encased cells were still fully active with a loading of 15 g COD/L x day.
"MFCs may be competitive to anaerobic digesters in terms of primary sludge treatment, especially in reducing volatile solids (VS). A few examples of AD treatment reported in the previous studies include a 56% reduction in VS at an HRT of 15 days (Tchobanoglous et al., 2002), 35% reduction in VS from primary sludge at an HRT 20 days (Ghyoot and Verstraete, 1997), 61.7% reduction in VS from waste-activated sludge at an HRT 15 days (Liu et al., 2012), and 40– 50% reduction in VS from sewage sludge (Cao and Pawłowski, 2012). In our study, MFC-1 could reduce 68% of VSS in 9 days in Phase I, and about 50% of VSS in 7 days in Phase II. "
[Show abstract][Hide abstract] ABSTRACT: The long-term performance of sludge treatment in microbial fuel cells (MFCs) was examined by operating two MFCs for almost 500days. In Phase I, one MFC fed with primary sludge removed 69.8±24.1% of total chemical oxygen demand (TCOD) and 68.4±17.9% of volatile suspended solids (VSS); the other MFC with digested sludge reduced 36.2±24.4% of TCOD and 46.1±19.2% of VSS. In Phase II, both MFCs were operated as a two-stage system that removed 60% of TCOD and 70% of VSS from the primary sludge. An energy analysis revealed that, although the total energy in the MFC system was comparable with that of anaerobic digesters, the electric energy had a minor contribution and methane gas still dominated the total energy production. The results suggest that MFCs may not be suitable for treating primary sludge for energy recovery, but could potentially be used to polish the effluent from anaerobic digesters.
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