Two-phase Reactor System Research Articles

The anaerobic co-digestion of fruit and vegetable waste and horse manure mixtures in a bench-scale, two-phase anaerobic digestion system

In this study, the anaerobic digestion of mixtures of food waste (FW) and horse manure was investigated using a bench-scale two-phase reactor system. Both phases were maintained at 35°C for the duration of the 30-day study period. The first phase reactors were prepared with biomass mixtures in deionized water such that each mixture had an initial total solids (TS) concentration of 6 wt%. The second phase reactors were inoculated with cow manure in water two weeks prior to the study period at 3 wt% TS. The biogas from all second phase reactors contained greater than 60 vol% methane in the biogas before they were used in the study, thus indicating the presence of active methanogens. Filtrate (5 mL) from the first phase was used as feed to the second phase reactor. The chemical oxygen demand (COD), total organic carbon, and volatile solids (VS) of the feed from Phase 1 increased with FW content in the biomass mixture, and so the organic loading rates (OLRs) to the Phase 2 reactors also increased. Accordingly, the volume of biogas and methane generated from Phase 2 also increased with FW content. The low OLR (<0.2 g VS/L/day), the use of a two-phase system, and the use of filtrate from Phase 1as feed to Phase 2 allowed for high utilization of the feed; the observed specific methane yields (mL/g COD) were greater than 80% of the theoretical yields for all mixtures. The methane yields were statistically similar to within a 95% confidence interval.

Textile Dye Removal in Single-Phase and Two-Phase Anaerobic Biotreatment Systems

This research compares performances of an anaerobic two-phase reactor system and a conventional single-phase reactor system in treatment of a synthetic dye wastewater. The two-phase reactor setup used four anaerobic reactors based on upflow anaerobic sludge blanket technology as acid reactors and an expanded granular sludge bed (EGSB) reactor as a methane reactor. An anaerobic reactor based on EGSB technology constituted the single-phase reactor setup. The reactors were operated at different hydraulic retention times (HRTs). The acid reactors removed up to 67% of the influent chemical-oxygen demand (COD) and 77% of the influent dye or color. An average of 10–25% acidification was achieved, and acetic acid, propionic acid, and butyric acid were the major volatile fatty acids produced in the acid reactors. The organic loading or the influent dye concentration did not have any significant effect on acid production or its speciation. The two-phase system could be operated at a HRT as low as 7.5 h with at leas...

Phase Modifiers Promote Efficient Production of Hydroxymethylfurfural from Fructose

Furan derivatives obtained from renewable biomass resources have the potential to serve as substitutes for the petroleum-based building blocks that are currently used in the production of plastics and fine chemicals. We developed a process for the selective dehydration of fructose to 5-hydroxymethylfurfural (HMF) that operates at high fructose concentrations (10 to 50 weight %), achieves high yields (80% HMF selectivity at 90% fructose conversion), and delivers HMF in a separation-friendly solvent. In a two-phase reactor system, fructose is dehydrated in the aqueous phase with the use of an acid catalyst (hydrochloric acid or an acidic ion-exchange resin) with dimethylsulfoxide and/or poly(1-vinyl-2-pyrrolidinone) added to suppress undesired side reactions. The HMF product is continuously extracted into an organic phase (methylisobutylketone) modified with 2-butanol to enhance partitioning from the reactive aqueous solution.

Continuous Fermentative Hydrogen Production Using a Two-Phase Reactor System with Recycle

The effects of effluent recycle were examined in a two-phase anaerobic system where the first phase was operated for fermentative hydrogen production and the second for methanogenesis. The hydrogen reactor was operated as a chemostat at 35 degrees C and pH 5.5 with a 10 h hydraulic retention time, and the methane reactor was operated as an up-flow reactor at 28 degrees C and pH between 6.9 and 7.2. Two recycle ratios were examined: 0 and 0.98. Effluent recycle reduced the required alkalinity for pH control by approximately 40%. The H2 productivity metric, with a basis in electrons and incorporating both gaseous and dissolved H2, was developed as a more fundamental reporting method than the molar H2 yield. Without recycle, the H2 productivity was 0.115 g of H2 COD/g of feed COD, but decreased to 0.015 q of H2 COD/g of feed COD with recycle (COD = chemical oxygen demand). Mass balances indicated the lower H2 productivity during recycle was due to electrons being partitioned to methane and less-oxidized soluble constituents such as propionic acid, ethanol, and butanol. The results indicated that achieving high H2 productivity with nonsterile wastewaters will be challenging and membrane filtration of the recycle liquid may be required to exclude the return of hydrogen-consuming organisms.

Energy-Cost Reduction in Starch Processing Using Aqueous Two Phase Reactor Systems

Saccharification is an energy intensive process of particular industrial interest in agribusiness. Considerable improvements to the energy costs of processing can be made by the elimination of multiple high temperature steps during liquefaction. To facilitate technology development for more energy efficient saccharification, the effectiveness of thermoseparating polymer-based aqueous two-phase reactor systems (ATPRS) in the enzymatic hydrolysis of starch was investigated. The partition behavior of pure α-amylase, and a recombinant, thermostable α-amylase (MJA1) from the hyperthermophile, Methanococcus jannaschii and amyloglucosidase in PEO-PPO/salt aqueous two-phase systems was evaluated. All of the studied enzymes partitioned unevenly in these systems. Hydrolysis of soluble starch and corn starch into glucose by thermostable α-amylase and amyloglucosidase was performed in an ATPRS coupled with temperature-induced phase separation. Use of the ATPRS reduced the hydrolysis time to half of that for single-phase processing, thus reducing energy inputs. The hydrolysis time was 18 hours for 20% soluble starch with an amyloglucosidase concentration of 2.18 unit mL−1 in the aqueous system, but only 11 hours in aqueous two-phase reactor system. The extent of product inhibition is greatly reduced. These results reveal the potential for polymer-enhanced extractive bioconversion of starch as a practical technology.

Kinetic enhancement of starch bioconversion in thermoseparating aqueous two-phase reactor systems

The extractive bioconversion of starch in an aqueous two-phase reactor system (ATPRS) was studied through experimentation and mathematical modeling. The phase-forming components included PEO-PPO-2500 (a random copolymer of ethylene oxide and propylene oxide with molecular weight of 2500) and MgSO 4. Partitioning of glucose and maltose in the PEO-PPO/MgSO 4 system was determined. Hydrolysis rates of soluble and corn starches in one-phase and aqueous two-phase reactor systems were compared. Starch consumption and glucose production kinetics were evaluated for α-amylase and amyloglucosidase separately as well as synergistically. A Michaelis–Menten kinetic model with product inhibition was employed to describe enzymatic hydrolysis. This model was expanded to include reaction with simultaneous partitioning for the two-phase system. Parametric studies of starch hydrolysis in the ATPRS with respect to the partition coefficient of the final hydrolysis product, glucose, were performed to simulate starch conversion profiles. The use of the ATPRS reduced the hydrolysis time to almost half of that for single-phase processing. These results were confirmed experimentally. The PEO-PPO-2500/MgSO 4 system enhanced the starch hydrolysis by decreasing the glucose inhibition. The hydrolysis reaction was completed in 10 h in ATPRS system while taking 18 h in one-phase aqueous system. The goodness of fit between model and experiments demonstrates that thermodynamic partition data, coupled with the lumped kinetic model for dual enzymatic hydrolysis and product inhibition are appropriate for describing the two-phase bioreactor system.

Comparison of two-phase and three-phase methanol synthesis processes

A comparison is made between the ICI (two-phase) methanol synthesis process and a three-phase slurry process based on a multi-stage agitated reactor. The process calculations are based on a complete reactor system consisting of the reactor itself, a recycling system and a gas-liquid separator. The basic kinetic and thermodynamic data were taken from previous studies carried out in our laboratory. The results show that both reactor systems produce comparable methanol yields under the same process conditions except for the reactor temperature. Carbon conversion to methanol values close to 100% can be achieved. The three-phase process is more efficient in terms of heat recovery and power consumption. This is primarily caused by the fact that the three-phase process generates high-pressure steam and the ICI two-phase process yields boiler feed water of 90°C. Furthermore, the pressure drop in the three-phase reactor is smaller than in the two-phase reactor, resulting in a smaller duty of the recycle compressor. However, for the present low energy prices, the annual financial savings, coupled with these energetic aspects, are not sufficient to compensate for the higher capital investment of the three-phase reactor system relative to the ICI two-phase reactor system. A relatively high natural gas price of US $4.1 per gigajoule is needed to reach the economical break-even point between the two processes. More active catalysts may be developed in the near future. Our results show that a relative increase in the catalyst activity by a factor of 1.5 or more (for both processes) will make the three-phase process of economic interest at a natural gas price of US $2.5 per gigajoule.

Anaerobic composting of crab-picking wastes for byproduct recovery

The objective of this project was to determine the feasibility of using two-stage anaerobic composting to stabilize crab-picking wastes, produce a residue amenable to byproduct recovery, and to compare flooded versus percolating operation of the leachbed. Crabpicking waste (CPW) was treated using duplicate, two-phase reactor systems consisting of 14-l leachbed reactors and 5-l hybrid sludge-bed filter reactors. Biochemical methane potential of the CPW, solids reduction, methane production and leachate pH, alkalinity, conductivity, volatile organic acids (run 4 only), and chemical oxygen demand were monitored. Methane yields approached or attained the BMP value (0.31 m 3 kg −1 VS −1), except for run 2, which was stopped at 20 days due to mechanical problems. Mean solids reduction was 80% (SD = 2). Residues were not odoriferous, had a low bulk density (85 g l −1) and were stored at ambient temperature with no vector attraction potential. There was no difference in methane yield or VS conversion between percolating and flooded operation of the leachbeds.

Anaerobic digestion of ice-cream wastewater: A comparison of single and two-phase reactor systems

The anaerobic digestion of ice-cream wastewater, a complex substrate which includes milk proteins, carbohydrates, and lipids, has received little attention. Work using an aerobic contact system showed that at a 7.5-d hydraulic retention time (HRT), with an organic loading rate of 1.7 g COD/Ld and influent TSS (total suspended solids) of 5870 mg/L, the effluent COD was 628 mg/L, BOD was 91 mg/L and TSS was 674. Anaerobic filters have also been used at organic loadings of 6 kg COD/m{sup 3}d applied at a HRT of 0.42 day, with COD removals of 80%. Goodwing showed that this waste was capable of being treated by the UASB process with granulation commencing after 60-70 days, and gas production ranging between 0.73 and 0.93 L CH{sub 4}/g COD removed with loading rates between 0.7 and 3.0 g TOC/Ld. Two-phase anaerobic digestion is an innovative fermentation mode that has recently received increased attention. The kinetically dissimilar fermentation phases, hydrolysis-acidification and acetogenesis-methanation are operated in two separate reactors; the first of which is maintained at a very short HRT. The effluent from the first, acid-forming, phase is used as the substrate for the methane-phase reactor which has a longer HRT or cell immobilization. The aimmore » of this work was to compare the methane production capability and performance of a single-phase upflow fixed bed reactor with a two-phase digestion system. The two-phase digestion system consists of a completely mixed reactor for the acidogenic reaction and an upflow fixed bed reactor for the methanogenic reaction. Because of the high lipid content and COD of ice cream wastewater off site disposal has proved to be both expensive and poses problems to the receiving effluent treatment plant. For this reason the potential for a rapid anaerobic stabilization of the waste, with energy recovery in the form of methane gas, has been investigated in an attempt to minimize plant size and maximize gas production. 9 refs., 2 tabs.« less

Extractive bioconversions in aqueous two-phase systems: Enzymatic hydrolysis of casein proteins

Partition coefficients in poly(ethylene glycol)/dextran aqueous two-phase systems are reported for mixed-casein and its components, alpha, beta and kappa casein. Rates of casein proteolysis by alpha-chymotrypsin and by trypsin are reported in single-phase and aqueous two-phase reactor systems. The advantages resulting from selective partitioning of substrates, enzymes, and products are examined in terms of relative volumetric reaction rates.