Methane production in a 100-L upflow bioreactor by anaerobic digestion of farm waste

Manure waste from dairy farms has been used for methane production for decades, however, problems such as digester failure are routine. The problem has been investigated in small scale (1–2 L) digesters in the laboratory; however, very little scale-up to intermediate scales are available. We report production of methane in a 100-L digester and the results of an investigation into the effect of partial mixing induced by gas upflow/recirculation in the digester. The digester was operated for a period of about 70 d (with 16-d hydraulic retention time) with and without the mixing induced by gas recirculation through an internal draft tube. The results show a clear effect of mixing on digester operation. Without any mixing, the digester performance deteriorated within 30–50 d, whereas with mixing continuous production of methane was observed. This study demonstrates the importance of mixing and its critical role in design of large scale anaerobic digesters.     

Methane production in a 100-L upflow bioreactor by anaerobic digestion of farm waste

Manure waste from dairy farms has been used for methane production for decades, however, problems such as digester failure are routine. The problem has been investigated in small scale (1-2 L) digesters in the laboratory; however, very little scale-up to intermediate scales are available. We report production of methane in a 100-L digester and the results of an investigation into the effect of partial mixing induced by gas upflow/recirculation in the digester. The digester was operated for a period of about 70 d (with 16-d hydraulic retention time) with and without the mixing induced by gas recirculation through an internal draft tube. The results show a clear effect of mixing on digester operation. Without any mixing, the digester performance deteriorated within 30-50 d, whereas with mixing continuous production of methane was observed. This study demonstrates the importance of mixing and its critical role in design of large scale anaerobic digesters.     

Biomethanation of a mixture of salty cheese whey and poultry waste or cattle dung

This paper describes the results of a study aimed at improving the efficiency of anaerobic digestion of salty cheese whey in combination with poultry waste or cattle dung. Best results were obtained when salty cheese whey was mixed with poultry waste in the ratio of 7:3, or cattle dung in the ratio of 1:1, both on dry weight basis giving maximum gas production of 1.2 L/L of digester/d with enriched methane content of 64% and 1.3 L/L of digester/d having methane content of 63% respectively. Various conditions such as temperature and retention time have been optimized for maximum process performance.     

Biogasification of Green and Food Wastes Using Anaerobic-Phased Solids Digester System

The performance of a laboratory-scale anaerobic-phased solid (APS) digester system treating food and green wastes was evaluated at thermophilic condition. The APS system comprised of four hydrolysis digesters and one biogasification reactor. The hydrolysis reactors were operated batchwised at a 12-day retention time, while the biogasification reactor was continuously operated at different hydraulic retention times (HRT). The biogas and methane yields from green waste were determined to be 0.438 and 0.252 L/g volatile solid (VS), respectively, with VS removal of 78%. The biogas and methane yields from food waste were 0.596 and 0.379 L/g VS, respectively, with VS removal of 85%. Hydrogen was produced from hydrolysis reactors during the digestion of food waste. Its content was 30.1% and 8.5% of the biogas produced on the first and second day of digestion, respectively. Hydrogen yield from the whole system was determined to be 0.029 L/g VS representing about 4.9% of the total biogas production from the system. The ratio between the volumes of biogasification and hydrolysis reactors (BR/HR) was found to be a factor that affects the process performance and stability.     

Improved efficiency and stable digestion of biomass in nonmixed upflow solids reactors

A nonmixed upflow solids reactor (USR), which permitted longer solids than hydraulic retention times, was used to study the anaerobic digestion performance of sea kelp (Macrocystis pyrifera). The performance of the USR was compared to that of the continuously stirred tank reactor (CSTR) at different organic loading rates in terms of methane yield, methane production rate, and process stability. Results showed that, although digester performance was markedly affected by kelp compositional variability, methane yields and production rates in the USR were significantly higher than those observed with the CSTR. Results also showed that volatile acid concentrations, which are generally inversely related to digester stability, were significantly lower in the USR than in the CSTR.     

Electricity production by a microbial fuel cell fueled by brewery wastewater and the factors in its membrane deterioration

Electricity production from brewery wastewater using dual-chamber microbial fuel cells (MFCs) with a tin-coated copper mesh in the anode was investigated by changing the hydraulic retention time (HRT). The MFCs were fed with wastewater samples from the inlet (inflow, MFC-1) and outlet (outflow, MFC-2) of an anaerobic digester of a brewery wastewater treatment plant. Both chemical oxygen demand removal and current density were improved by decreasing HRT. The best MFC performance was with an HRT of 0.5 d. The maximum power densities of 8.001 and 1.843 μW/cm2 were obtained from reactors MFC-1 and MFC-2, respectively. Microbial diversity at different condi-tions was studied using PCR-DGGE profiling of 16S rRNA fragments of the microorganisms from the biofilm on the anode electrode. The MFC reactor had mainlyGeobacter,Shewanella, andClostridium species, and some bacteria were easily washed out at lower HRTs. The fouling characteristics of the MFC Nafion membrane and the resulting degradation of MFC performance were examined. The ion exchange capacity, conductivity, and diffusivity of the membrane decreased significantly after foul-ing. The morphology of the Nafion membrane and MFC degradation were studied using scanning electron microscopy and attenuated total reflection-Fourier transform infrared spectroscopy.     

Pretreatment of swine wastewater using anaerobic filter

Efforts were made to assess the efficiency of an anaerobic filter packed with porous floating ceramic media and to identify the optimum operational condition of anaerobic filter as a pretreatment of swine wastewater for the subsequent biological removal of nitrogen and phosphorus. A stepwise decrease in hydraulic retention time (HRT) and an increase in organic loading rate (OLR) were utilized in an anaerobic filter reactor at mesophilic temperature (35°C). The optimum operating condition of the anaerobic filter was found to be at an HRT of 1 d. A soluble chemical oxygen demand (COD) removal efficiency of 62% and a total suspended solids removal efficiency of 39% at an HRT of 1 d were achieved with an OLR of 16.0 kg total COD/(m³·d), respectively. The maximum methane production rate approached 1.70 vol of biogas produced per volume of reactor per day at an HRT of 1 d. It was likely that the effluent COD/total Kjeldahl nitrogen ratio, of 22, the COD/total phosphorous ratio of 47, and the high effluent alkalinity >2500 mg/L as CaCO₃ of the anaerobic filter operated at an HRT of 1 d was adequate for the subsequent biological removal of nitrogen and phosphorus.     

Amelioration of methane yield in cheese whey fermentation by controlling the pH of the methanogenic stage

A two-stage, no-mix anaerobic digester of 145 L capacity was used to investigate the effect of controlling the pH of the methanogenic stage on the biogas production and the pollution potential reduction of acid cheese whey. The digester was operated at a 15-d hydraulic retention time, and a temperature of 35°C. Controlling the pH of the methanogenic stage increased the biogas production rate and methane yield by 77.77 and 289.00%, respectively. Reductions of up to 32.19, 44.44, and 35.86% in the COD, solids and nitrogen were achieved.     

Inhibition mechanisms of ammonia and sulfate in high-solids anaerobic digesters for food waste treatment: Microbial community and element distributions responses

The horizontal flow anaerobic digester indicated that high ammonia (2923 mg/L) and SO₄^2? (3653 mg/L) would influence the performance of methane production with food waste as substrates. Therefore, bottle anaerobic digestion reactors were carried out to investigate the effect of ammonia/sulfate concentrations on the methane production. Experimental results manifested that the anaerobic digesters with an ammonia concentration of 3500 mg/L or sulfate of 1600 mg/L showed the best performance of methane production, with an average methane yield of 0.32 and 0.33 L (g VS)^?1 d^?1, respectively. Specifically, a higher ammonia (6500 mg/L) or sulfate (1600-3500 mg/L) level hindered the bioconversion of C from liquid to gas phase (2.68% or 1.73% CH₄-Gas, respectively), while insignificantly for the hydrolyzation of C and N from solid to liquid phase. Similar to sulfate, high ammonia nitrogen seriously inhibited the methanation process, leading to a significant carbon accumulation in the anaerobic reactor, especially for propionic acid. The predominant archaea Methanosarcina at genus level indicated that aceticlastic methanogenesis was the major methanogenic pathway. Meanwhile, high ammonia level suppressed the activity of Methanosarcina, while modest sulfate improved H₂-consuming methanogens activity. A large fraction of unclassified bacteria within the Firmicutes (43.78%-63.17%) and Bacteroidetes (24.20%-33.30%) phylum played an important role in substrates hydrolysis.     

Electron beam pretreatment of sewage sludge before anaerobic digestion

The pretreatment of waste-activated sludge (WAS) by electron beam irradiation was studied in order to improve anaerobic sludge digestion. The irradiation dose of the electron beam was varied from 0.5 to 10 kGy. Batch and continuous-flow stirred tank reactors (CFSTRs) were operated to evaluate the effect of the electron beam pretreatment on anaerobic sludge digestion. Approximately 30–52% of the total chemical oxygen demand (COD) content of the WAS was solubilized within 24 h after electron beam irradiation. A large quantity of soluble COD, protein, and carbohydrates leached out from cell ruptures caused by the electron beam irradiation. Volatile fatty acids production from the irradiated sludge was approx 90% higher than that of the unirradiated sludge. The degradation of irradiated sewage sludge was described by two distinct first-order decay rates (k ₁ and k ₂). Most initial decay reaction accelerated within 10 d, with an average k ₁ of 0.06/d for sewage sludge irradiated at all dosages. The mean values for the long-term batch first-order decay coefficient (k ₂) were 0.025/d for irradiated sewage sludge and 0.007/d for unirradiated sludge. Volatile solids removal efficiency of the control reactor fed with unirradiated sewage sludge at a hydraulic retention time (HRT) of 20 d was almost the same as that of the CFSTRs fed with irradiated sludge at an HRT of 10 d. Therefore, disintegration of sewage sludge cells using electron beam pretreatment could reduce the reactor solid retention time by half.     

Temperature and Inoculum Origin Influence the Performance of Ex-Situ Biological Hydrogen Methanation

The conversion of H₂ into methane can be carried out by microorganisms in a process so-called biomethanation. In ex-situ biomethanation H₂ and CO₂ gas are exogenous to the system. One of the main limitations of the biomethanation process is the low gas-liquid transfer rate and solubility of H₂ which are strongly influenced by the temperature. Hydrogenotrophic methanogens that are responsible for the biomethanation reaction are also very sensitive to temperature variations. The aim of this work was to evaluate the impact of temperature on batch biomethanation process in mixed culture. The performances of mesophilic and thermophilic inocula were assessed at 4 temperatures (24, 35, 55 and 65 °C). A negative impact of the low temperature (24 °C) was observed on microbial kinetics. Although methane production rate was higher at 55 and 65 °C (respectively 290 ± 55 and 309 ± 109 mL CH₄/L.day for the mesophilic inoculum) than at 24 and 35 °C (respectively 156 ± 41 and 253 ± 51 mL CH₄/L.day), the instability of the system substantially increased, likely because of a strong dominance of only Methanothermobacter species. Considering the maximal methane production rates and their stability all along the experiments, an optimal temperature range of 35 °C or 55 °C is recommended to operate ex-situ biomethanation process.     

Single-stage anaerobic codigestion for mixture wastes of simulated Korean food waste and waste activated sludge

Korean food waste was treated with a single-stage anaerobic codigester (SSAD) using waste activated sludge (WAS) generated from a municipal wastewater treatment plant. The stability and performance of the system was analyzed. The C/N ratio was improved with increasing food waste fraction of feed mixture. The pH, alkalinity, and free ammonia nitrogen concentration were the parameters used to evaluate the digester’s stability. The experimentally determined values of the parameters indicated that there were no methane inhibitions in the digester. Digester performance was determined by measuring the total chemical oxygen demand TCOD), volate solids (VS) removal, methane content in biogas, methane production rate (MPR), and specific methane productivity. Methane content in biogas and MPR were significantly dependent on hydraulic retention time (HRT) and ratio of food waste to WAS. The methane content in biogas decreased at shorter HRT or higher organic loading rate (OLR) with increased food waste fraction. Concerning the performance of the codigester, the optimum operating condition of the SSAD was found to be at an HRT of 10 d with a feed mixture ratio of 50% food waste and 50% WAS. A TCOD removal efficiency of 53.6% and a VS removal efficiency of 53.7% were obtained at an OLR of 5.96 kg of TCOD/(m³·d) and 3.14 kg of VS/(m³·d), respectively. A maximum MPR of 1.15 m³ CH₄/(m³·d) and an SMP of 0.37 m³ CH₄/kg of VS_feed were obtained at an HRT of 10 d with a methane content of 63%.     

Anaerobic treatment of low-strength brewery wastewater in expanded granular sludge bed reactor

Anaerobic treatment of low-strength brewery wastewater, with influent total chemical oxygen demand (COD) (CODin) concentrations ranging from 550 to 825 mg/L, was investigated in a pilot-scale 225.5-L expanded granular sludge bed (EGSB) reactor. In an experiment in which the temperature was lowered stepwise from 30 to 12 degrees C, the COD removal efficiency decreased from 73 to 35%, at organic loading rates (OLR) of 11-16.5 g COD/L/d. The applied hydraulic retention time (HRT) and liquid upflow velocity (Vup) were 1.2 h and 5.8 m/h, respectively. Under these conditions, the acidified fraction of the CODin varied from 45 to 90%. In addition to the expected drop in reactor performance, problems with sludge retention were also observed. In a subsequent experiment set at 20 degrees C, COD removal efficiencies exceeding 80% were obtained at an OLR up to 12.6 g COD/L/d, with CODin between 630 and 715 mg/L. The values of HRT and Vup applied were 2.1-1.2 h, and 4.4-7.2 m/h, respectively. The acidified fraction of the CODin was above 90%, but sludge washout was not significant. These results indicate that the EGSB potentials can be further explored for the anaerobic treatment of low-strength brewery wastewater, even at lower temperatures.     

Thermophilic anaerobic digester performance under different feed-loading frequency

The effect of feed-loading frequency on digester performance was studied on a thermophilic anaerobic digester with a working volume of 27.43 m(3). The digester was fed 0.93 m(3) of chicken-litter slurry/d, containing 50.9 g/L chemical oxygen demand. The treatments were loading frequencies of 1, 2, 6, and 12 times/d. The hourly pH, biogas production, and methane percent of the biogas were less stable at lower feed frequencies. There was no statistical difference among treatments in methanogenic activity. The feed-loading frequency of six times per day treatment provided the greatest biogas production.     

Development of a novel laboratory scale high solids reactor for anaerobic digestion of processed municipal solid wastes for the production of methane

Economic evaluations of the capital costs for anaerobic digestion systems for gas production show that the reactor is a significant cost component. The successful application of high solids digestion of processed MSW (e.g., greater than 10% solids within the digester) would allow a decrease in reactor volume with maintenance of relatively high gas production rates. However, high solids slurries do not mix well in conventional stirred tank reactors. A horizontal shaft, hydraulically driven reactor was designed and fabricated to test the anaerobic digestion of high solids concentrations. Digester performance was evaluated as a function of experimental parameters such as nutrient requirements, feeding rates, pH control, and agitator design/ rotation speed; horsepower of mixing was also evaluated for the reactor. Several startup protocols were examined to obtain a biologically stable anaerobic fermentation at high solids levels.     

Mixed- and plug-flow performances of an anaerobic biofilter treating 2-ethylhexanoic acid

The performance of a 20-L anaerobic biofilter treating 2-ethyl-hexanoic acid (2-EHA) operating with the effluent recirculated was compared with that of the same biofilter operated without any recirculation. The recirculation of effluent was at a rate of 60 L/h through the biofilter. Tracer experiments were carried out to study the hydrodynamics in the biofilter under different modes of operation. The dispersion number (D/UL) obtained from these tracer experiments for the biofilter operated with and without effluent recirculation were 0.65 and 0.06, respectively. These values show that the recirculation was effective in achieving a mixed-flow pattern in the biofilter, whereas the biofilter operated without recirculation was essentially a plug-flow column with a moderate level of axial dispersion. The feed consisted of 2-EHA at a concentration of 8200 mg/L, which is equivalent to a COD of 20,000 mg/L. The optimal performance of the mixed-flow biofilter was at a hydraulic retention time (HRT) of 1.1 d, with a COD removal efficiency of 92.8% and a biogas production rate of 6.44 L/L biofilter vol/d. The biofilter failed at 0.83 d HRT, as a result of washout of biomass at this high hydraulic loading rate. By comparison, the optimal performance achieved for the plug-flow system was at 2 d HRT. The COD removal efficiency was 74.1%, and biogas production rate was 2.13 L/L biofilter vol/d. When the HRT was lowered to 1.5 d, failure occurred owing to inhibition as indicated by the low methane yield of 0.192 L/g COD removed. The superior performance of the mixed-flow mode can be attributed to the presence of the recycle stream, which diluted and evenly distributed the feed.     

The Performance of Jatropha Curcas Linn. Capsule Husk as Feedstocks Biogas in One Phase Anaerobic Digestion

Jatropa curcas Linn. (JcL) capsule husk was not recommended as biogas feedstocks. However for biorefinery purpose, several technologies have been conducting to solve this problem. This research reported quantity and quality comparison of Dry Husk Jcl (DH-JcL) in one phase system of batch digester compare with semi continuous digester. HDPE drum of 80 L working volume used as digester with 40 days hydraulic retention time. Feeding of DH-Jcl and solvent water was mixed on concentration of 1: 8. Research conclusion showed that semi continuous digester was better than batch digester. Biogas quality showed that methane content can reach 66.61% to 83.15% and biogas quantity in semi continuous digester can reach 0.016 m³ · kg^–1 DH JcL. The result was not in optimize condition yet because ratio number of volatile fatty acids/ alkalinity showed 0.5, it was indicated unstable anaerobic degradation process of DH-JcL.     

Removal of high concentrations of NO3− from nuclear industrial wastewater by using a fixed-bed bioreactor

In this work, a down-flow fixed bed anaerobic biofilm reactor filled by biological ceramsites were prepared to remove the high concentration of NO₃^? (>?20 g/L) from nuclear industry wastewaters. The effects of hydraulic retention time, the concentration of NO₃^?, the molar ratio of C/N and temperature on the removal efficiencies of NO₃^? were investigated. The results showed that the removal rate of NO₃^? with the initial concentration of 6 g/L can reach 99% or more by controlling the hydraulic retention time at 0.75 h, the molar ratio of C/N at 1.5 and the temperature over 18 °C. In the process, the NO₂^? was not accumulated, and the autotrophic denitrifying bacteria grow well in anaerobic biofilm reactors, proving a usable method for removing the high concentration NO₃^? from nuclear industrial wastewaters.

     

Hydrolysis of starch with immobilized glucoamylase

Glucoamylase (E.C.3.2.1.3) covalently immobilized onto chitin particles (d_st = 0.37 mm) was examined in two types of continuous bench-scale reactors (180 mL) fed with hydrolyzed manioc starch (15%, w/v): a two-phase reactor (liquid expanded-bed) and a threephase reactor (air expanded-bed). Several conditions of continuous operation were investigated, varying the biocatalyst load (16.7, 37.2, and 54 g/L) into the reactor and the hydraulic residence time. The best results were achieved with the two-phase reactor, which operated continuously for 20 d and showed a decrease of only 6% in conversion (starch to glucose). Conversion levels of 96% were obtained with a hydraulic residence time of about 4 h. A simple mathematical model was able to describe the experimental results of the two types of reactors considering biocatalyst deactivation.     

Fumaric acid production in airlift loop reactor with porous sparger

Airlift loop reactors with porous spargers were investigated and used in the process of fumaric acid production byRhizopus oryzae ATCC 20344. In order to enhance oxygen mass transfer, which is very important for organic acid production, two kinds of porous spargers (stainless steel membrane tube and porcelain tube) were examined. Gas holdup, liquid circulation velocity, mixing time, bubble size, and bubble rise velocities were measured in a 50 L rectangular airlift loop reactor with different ratios of the cross-sectional area of the riser and downcomer. The local volumetric mass transfer coefficient (K_La) was also measured in the gas sparger zone. The results indicated that high K_La and excellent hydrodynamics can be obtained in the airlift loop reactor with a porous sparger. A 10 L laboratory airlift loop reactor was employed for the fumaric acid fermentation. Results showed that the turbulence of two-phase flow in the airlift loop reactor not only produced favorable conditions for mass transfer, but was also useful for forming and suspending small, well-distributed mycelial pellets (1ç2 mm). A production rate of up to 0.814 g/L/h and efficiency yield of 50.1% (w/w) was obtained in the airlift loop reactor. The performance was compared with the typical stirred tank fermentor fermentation results.