Sun-Kee Han

Performance of UASB reactor treating leachate from acidogenic fermenter in the two-phase anaerobic digestion of food waste.

This study was conducted to investigate the performance of the upflow anaerobic sludge blanket (UASB) reactor treating leachate from acidogenic fermenter in the two-phase anaerobic digestion of food waste. The chemical oxygen demand (COD) removal efficiency was consistently over 96% up to the loading rates of 15.8 g COD/l d. The methane production rate increased to 5.51/l d. Of all the COD removed, 92% was converted to methane and the remaining presumably to biomass. At loading rates over 18.7 g COD/l d, the COD removal efficiency decreased due to sludge flotation and washout in the reactor, which resulted from short HRT of less than 10.6 h. The residual propionate concentration was the highest among the volatile fatty acids (VFA) in the effluent. The specific methanogenic activity (SMA) analysis showed that the VFA-degrading activity of granule was the highest for butyrate, and the lowest for propionate. Typical granules were found to be mainly composed of microcolonies of Methanosaeta. The size distribution of sludge particles indicated that partially granulated sludge could maintain the original structure of granular sludge and continue to gain size in the UASB reactor treating leachate from acidogenic fermenter.

Performance of an Innovative Two-Stage Process Converting Food Waste to Hydrogen and Methane

Abstract This study was conducted to evaluate the performance of an innovative two-stage process, BIOCELL, that was developed to produce hydrogen (H2) and methane (CH4) from food waste on the basis of phase separation, reactor rotation mode, and sequential batch technique. The BIOCELL process consisted of four leaching-bed reactors for H2 recovery and post-treatment and a UASB reactor for CH4 recovery. The leaching-bed reactors were operated in a rotation mode with a 2-day interval between degradation stages. The sequential batch technique was useful to optimize environmental conditions during H2 fermentation. The BIOCELL process demonstrated that, at the high volatile solids (VS) loading rate of 11.9 kg/m3-day, it could remove 72.5% of VS and convert VSremoved to H2 (28.2%) and CH4 (69.9%) on a chemical oxygen demand (COD) basis in 8 days. H2 gas production rate was 3.63 m3/m3 ·day, while CH4 gas production rate was 1.75 m3/m3 ·day. The yield values of H2 and CH4 were 0.31 and 0.21 m3/kg VSadded, respectively. Moreover, the output from the post-treatment could be used as a soil amendment. The BIOCELL process proved to be stable, reliable, and effective in resource recovery as well as waste stabilization.

The optimisation of food waste addition as a co-substrate in anaerobic digestion of sewage sludge

Food waste has been regarded as the main source of various environmental pollution in Korea due to the high volatile solids (VS) and moisture content caused by the features of dietary habits. The feasibility of food waste as a co-substrate in anaerobic digestion of sewage sludge was investigated in mesophilic and thermophilic conditions using batch tests. Cumulative methane production, dissolved organic carbon (DOC) and volatile fatty acids (VFA) were monitored to find the optimal mixing ratios of food waste and sewage sludge for the enhanced performance of co-digestion. It was observed that adequately mixed food waste led to the enhanced methane production both at mesophilic and thermophilic conditions. However, a conventional linear regression conducted for the optimisation of co-substrate mixing ratios was not accurate in describing exact methane production trends of co-digestion because of the different biodegradability of substrates. Therefore, a remodified Gompertz equation showing nonlinear relationship between variables was developed to find exact information with the same experimental data obtained at 2g VS/l generally used in biochemical methane potential (BMP) tests. Based on an influential parameter, methane production rate (MPR), the optimal mixing ratios of food waste were 39.3% and 50.1% in mesophilic and thermophilic conditions, respectively. To confirm the application of the remodified Gompertz equation, secondary batch tests were conducted with the substrate concentrations of 1-4g VS/l. In overall range tested, the confident mixing ratios of food waste was adjusted to 30-40% and 40% in mesophilic and thermophilic conditions, respectively. The most significant factor for enhanced performance was the improved organic carbon content provided by additional food waste.

Kinetics of LCFA Inhibition on Acetoclastic Methanogenesis, Propionate Degradation and β-Oxidation

Abstract Kinetics of long-chain fatty acids (LCFAs) inhibition on acetoclastic methanogenesis, propionate degradation and β-oxidation were studied with granular sludge under mesophilic batch conditions. Mathematical expressions used for reaction rates were as shown below: The simulated results revealed that the methane production rates from acetate decreased with an increase in both concentration and the number of double bonds of LCFAs. The concentrations of oleate (C18:1), linoleate (C18:2), palmitate (C16:0), and stearate (C18:0) were 0.54 mM, 0.11 mM 1.62 mM, and 2.58 mM, respectively, at which the methane production rates from acetate dropped 10%, and 3.10 mM, 0.72 mM, 5.71 mM, and 5.37 mM, respectively, at which the rates dropped 50%. The inhibitory effects of LCFAs on propionate degradation showed a similar tendency with acetoclastic methanogenesis; however, were less severe. The concentrations of oleate, linoleate, palmitate, and stearate were 1.02 mM, 0.18 mM, 2.34 mM, and 1.92 mM, respectively, at which the propionate degradation rates dropped 10%, and 4.38 mM, 1.17 mM, 5.88 mM, and 5.18 mM, respectively, at which the rates dropped 50%. The observed maximum β-oxidation rates of oleate, linoleate, palmitate, and stearate were 0.21 mmol (g VSS)−1 d−1, 0.09 mmol (g VSS)−1 d−1, 0.12 mmol (g VSS)−1 d−1, and 0.08 mmol (g VSS)−1 d−1, respectively. The lag-phase times in β-oxidation were also dependent on LCFA concentrations. The concentrations of oleate, linoleate, palmitate, and stearate, at which the lag-phase times became 5 days, were 5.93 mM, 2.24 mM, 4.02 mM, and 2.81 mM, respectively.

Enhanced acidogenic fermentation of food waste in a continuous-flow reactor

This study was performed to improve acidogenic fermentation of food waste in a continuous-flow reactor. The fermentation of food waste is affected by the fermentation constraints such as the biodegradability of substrate, the degrading capability of microorganisms and the environmental conditions. The key factors were, therefore, examined to control the fermentation constraints, such as the effect of seed inoculation and the effect of adjusting dilution rate. Acidogenic fermentation of food waste employing rumen microorganisms resulted in the enhanced efficiency (71.2%) as compared with that (59.8%) employing mesophilic acidogens. In addition, the fermentation efficiency increased from 71.2 to 82.0% by adjusting dilution rate from 3.0 to 1.0 d-1 depending on the state of the fermentation. The main component of the acidified product was shifted from butyric to acetic acid. This meant that the increase of the fermentation efficiency was mainly caused by the enhanced degradation of vegetables and meats. The control of the fermentation constraints was, therefore, very effective in improving the fermentation efficiency of food waste.

Response Surface Optimization of Substrates for Thermophilic Anaerobic Codigestion of Sewage Sludge and Food Waste

Abstract This study investigated the effects of food waste constituents on thermophilic (55 °C) anaerobic codigestion of sewage sludge and food waste by using statistical techniques based on biochemical methane potential tests. Various combinations of grain, vegetable, and meat as cosubstrate were tested, and then the data of methane potential (MP), methane production rate (MPR), and first-order kinetic constant of hydrolysis (kH) were collected for further analyses. Response surface methodology by the Box-Behnken design can verify the effects and their interactions of three variables on responses efficiently. MP was mainly affected by grain, whereas MPR and kH were affected by both vegetable and meat. Estimated polynomial regression models can properly explain the variability of experimental data with a high-adjusted R2 of 0.727, 0.836, and 0.915, respectively. By applying a series of optimization techniques, it was possible to find the proper criteria of cosubstrate. The optimal cosubstrate region was suggested based on overlay contours of overall mean responses. With the desirability contour plots, it was found that optimal conditions of cosubstrate for the maximum MPR (56.6 mL of CH4/g of chemical oxygen demand [COD]/day) were 0.71 g of COD/L of grain, 0.18 g of COD/L of vegetable, and 0.38 g of COD/L of meat by the simultaneous consideration of MP, MPR, and kH. Within the range of each factor examined, the corresponding optimal ratio of sewage sludge to cosubstrate was 71:29 as the COD basis. Elaborate discussions could yield practical operational strategies for the enhanced thermophilic anaerobic codigestion of sewage sludge and food waste.

Multi-Step Sequential Batch Two-Phase Anaerobic Composting of Food Waste

This study was conducted to evaluate the newly devised process, called MUlti-step Sequential batch Two-phase Anaerobic Composting (MUSTAC). The MUSTAC process consisted of several leaching beds for hydrolysis, acidification and posttreatment, and a UASB reactor for methane recovery. This process to treat food waste was developed with a high-rate anaerobic composting technique based on the rate-limiting step approach. Rumen microorganisms were inoculated to improve the low efficiency of acidogenic fermentation. Both two-phase anaerobic digestion and sequential batch operation were used to control environmental constraints in anaerobic degradation. The MUSTAC process demonstrated excellent performance as it resulted in a large reduction in volatile solids (VS) (84.7%) and high methane conversion efficiency (84.4%) at high organic loading rates (10.8 kg VS m−3 d−1) in a short SRT (10 days). Methane yield was 0.27 m3 kg−1 VS, while methane gas production rate was 2.27 m3 m−3 d−1. The output from the post-treatment could be used as a soil amendment, which was produced at the same acidogenic fermenter without troublesome moving. The main advantages of the MUSTAC process were simple operation and high efficiency. The MUSTAC process proved stable, reliable and effective in resource recovery as well as waste stabilization.

Enhancement of methane production in anaerobic digestion of sewage sludge by thermal hydrolysis pretreatment

This study was performed to optimize thermal hydrolysis pretreatment (THP) of sewage sludge for enhanced anaerobic digestion (AD). Using the response surface methodology (RSM), the optimal conditions were found 180 °C of reaction temperature and 76 min of reaction time. Through THP under optimal conditions, high molecular substances in sewage sludge such as soluble microbial by-products (SMPs) and extracellular polymeric substances (EPSs) were hydrolyzed into low molecular ones without the generation of refractory compounds. The microbial community analysis revealed that relative abundances of Methanomicrobia such as Methanosarcina, Methanosaeta (acetoclastic methanogens), and Methanoculleus (hydrogenotrophic methanogens) in AD with THP were higher than those in conventional AD.

Evaluation of Characterization During Start-up of Anaerobic Digestion Via Various Seeding Methods

>> This study was performed to evaluate the characteristics of start-up of anaerobic digestion from food waste with different inoculum ratios. The hydrogen yield was similar with different inoculum ratios. The hydrogen production rate increased with increasing inoculum ratio. But the specific hydrogen production rate decreased with increasing inoculum ratio. Total volatile fatty acids composition analysis showed that butyrate and acetate were the prevalent products in all reactors, followed by lactate and propionate. The acetate was most prevalent product in reactors at X0/S0=0.080 and 0.159. But in reactors at X0/S0=0.239 and 0.318, butyrate accounted for greater than 50% of the total volatile fatty acids.

Production of Biofuels and Biochemicals by Biorefinery

>> The authors reviewed information about biorefining of biomass by using academic information databases. Feedstocks were classified into triglycerides biomass, sugar biomass, starchy biomass, lignocellulosic biomass, and organic waste biomass. Biorefinery is an integrated system converting biomass into biofuels and biochemicals by various physical, chemical, biological, and thermochemical technologies. This paper presented a comprehensive summaries of opportunities, recent trends and challenges of biorefinery. A brief overview of promising building blocks, their sources from biomass, and their derivatives were also provided. In conclusion, this paper demonstrated the feasibility of biorefinery producing biofuels and biochemicals from biomass.