Anaerobic co-digestion of desugared molasses with cow manure; focusing on sodium and potassium inhibition

Desugared molasses (DM), a syrup residue from beet-molasses, was investigated for biogas production in both batch and in continuously-stirred tank reactor (CSTR) experiments. DM contained 2-3 times higher concentration of ions than normal molasses, which could inhibit the biogas process. The effect of sodium and potassium concentration on biogas production from manure was also investigated. Fifty percent inhibition occurred at sodium and potassium concentration of 11 and 28 g/L, respectively. The reactor experiments were carried out to investigate the biogas production from DM under different dilutions with water and co-digestion with manure. Stable operation at maximum methane yield of 300 mL-CH₄/gVS-added was obtained at a mixture of 5% DM in cow manure. The biogas process was inhibited at DM concentrations higher than 15%. Manure was a good base substrate for co-digestion, and a stable anaerobic digestion could be achieved by co-digesting DM with manure at the concentration below 15% DM.     

Detection and quantification of long chain fatty acids in liquid and solid samples and its relevance to understand anaerobic digestion of lipids

A method for long chain fatty acids (LCFA) extraction, identification and further quantification by gas chromatography was developed and its application to liquid and solid samples collected from anaerobic digesters was demonstrated. After validation, the usefulness of this method was demonstrated in a cow manure digester receiving pulses of an industrial effluent containing high lipid content. From the LCFA analysis data it was showed that the conversion of oleic acid, the main LCFA fed to the reactor, by the adapted biomass became faster and more effective along the successive pulses. Conversely, the accumulation of palmitic acid in the solid phase suggests that degradation of this LCFA, under these conditions, is less effective.     

Influence of carbon source and inoculum type on anaerobic biomass adhesion on polyurethane foam in reactors fed with acid mine drainage

This paper analyzes the influence of carbon source and inoculum origin on the dynamics of biomass adhesion to an inert support in anaerobic reactors fed with acid mine drainage. Formic acid, lactic acid and ethanol were used as carbon sources. Two different inocula were evaluated: one taken from an UASB reactor and other from the sediment of a uranium mine. The values of average colonization rates and the maximum biomass concentration (C_max) were inversely proportional to the number of carbon atoms in each substrate. The highest C_max value (0.35 g TVS g⁻¹ foam) was observed with formic acid and anaerobic sludge as inoculum. Maximum colonization rates (v_max) were strongly influenced by the type of inoculum when ethanol and lactic acid were used. For both carbon sources, the use of mine sediment as inoculum resulted in a v_max of 0.013 g TVS g⁻¹ foam day⁻¹, whereas 0.024 g TVS g⁻¹ foam day⁻¹ was achieved with anaerobic sludge.     

Biological kinetics evaluation of anaerobic stabilization pond treatment of palm oil mill effluent

Biological kinetic (bio-kinetic) study of the anaerobic stabilization pond treatment of palm oil mill effluent (POME) was carried out in a laboratory anaerobic bench scale reactor (ABSR). The reactor was operated at different feed flow-rates of 0.63, 0.76, 0.95, 1.27, 1.9 and 3.8 l of raw POME for a day. Chemical oxygen demand (COD) as influent substrates was selected for bio-kinetic study. The investigation showed that the growth yield (Y_G), specific biomass decay (b), maximum specific biomass growth rate (μ_max), saturation constant (K_s) and critical retention time (Θ_c) were in the range of 0.990 g VSS/g COD_removed day, 0.024 day⁻¹, 0.524 day⁻¹, 203.433 g COD l⁻¹ and 1.908 day, respectively.     

Recovery strategies for tackling the impact of phenolic compounds in a UASB reactor treating coal gasification wastewater

The impact of phenolic compounds (around 3.2 g/L) resulted in a completely failed performance in a mesophilic UASB reactor treating coal gasification wastewater. The recovery strategies, including extension of HRT, dilution, oxygen-limited aeration, and addition of powdered activated carbon were evaluated in batch tests, in order to obtain the most appropriate way for the quick recovery of the failed reactor performance. Results indicated that addition of powdered activated carbon and oxygen-limited aeration were the best recovery strategies in the batch tests. In the UASB reactor, addition of powdered activated carbon of 1 g/L shortened the recovery time from 25 to 9 days and oxygen-limited aeration of 0-0.5 mgO₂/L reduced the recovery time to 17 days. Reduction of bioavailable concentration of phenolic compounds and recovery of sludge activity were the decisive factors for the recovery strategies to tackle the impact of phenolic compounds in anaerobic treatment of coal gasification wastewater.     

Feasibility of biogas production from anaerobic co-digestion of herbal-extraction residues with swine manure

The objective of this work was to examine the feasibility of biogas production from the anaerobic co-digestion of herbal-extraction residues with swine manure. Batch and semi-continuous experiments were carried out under mesophilic anaerobic conditions. Batch experiments revealed that the highest specific biogas yield was 294 mL CH₄ g⁻¹ volatile solids added, obtained at 50% of herbal-extraction residues and 3.50 g volatile solids g⁻¹ mixed liquor suspended solids. Specific methane yield from swine manure alone was 207 mL CH₄ g⁻¹ volatile solid added d⁻¹ at 3.50 g volatile solids g⁻¹ mixed liquor suspended solids. Furthermore, specific methane yields were 162, 180 and 220 mL CH₄ g⁻¹ volatile solids added d⁻¹ for the reactors co-digesting mixtures with 10%, 25% and 50% herbal-extraction residues, respectively. These results suggested that biogas production could be enhanced efficiently by the anaerobic co-digestion of herbal-extraction residues with swine manure.     

Nitrogen removal from wastewater with a low COD/N ratio at a low oxygen concentration

The goal of the study was to determine the effectiveness of nitrification and denitrification and the kinetics of ammonia removal from a mixture of wastewater and anaerobic sludge digester supernatant in an SBR at limited oxygen concentration. In addition, the COD removal efficiency and sludge production were assessed.In the SBR cycle alternating aerobic and anaerobic phases occurred; in the aeration phase the dissolved oxygen (DO) concentration was below 0.7 mg O₂/L. The low DO concentration did not inhibit ammonia oxidation-nitrification and the efficiency was ca. 96-98%. However, a relatively high COD concentration in the effluent was detected. The values of K_m and V_max, calculated from the Michaelis-Menten equation, were 43 mg N-NH₄/L and 15.64 mg N-NH₄/L h, respectively. Activated sludge production was almost stable (0.62-0.66 g MLVSS/g COD). A high net biomass production resulted from a low specific biomass decay rate of 0.0015 d⁻¹.     

Enhanced methane production in a two-phase anaerobic digestion plant, after CO2 capture and addition to organic wastes

Cost-effective technologies are needed to reach the international greenhouse gas (GHG) reduction targets in many fields, including waste and biomass treatment. This work reports the effects of CO₂ capture from a combustion flue gas and its use in a newly-patented, two-phase anaerobic digestion (TPAD) process, to improve energy recovery and to reduce CO₂ emissions. A TPAD process, fed with urban wastewater sludge, was successfully established and maintained for several months at pilot scale. The TPAD process with injection of CO₂ exhibits efficient biomass degradation (58% VSS reduction), increased VFA production during the acidogenic phase (leading to VFA concentration of 8.4 g/L) and high biomethane production (0.350 Sm³/kg_SSV; 0.363 Sm³/m³_react·d). Moreover, CO₂ intake in the acid phase has a positive impact on the overall GHG balance associated to biomethane production, and suggests an improved solution for both emission reduction and biomass conversion into biomethane.     

Nitrogen removal performance of a hybrid anammox reactor

The anaerobic ammonium oxidation (anammox) process has attracted considerable attention in recent years as an alternative to conventional nitrogen removal technologies. In this study, an innovative hybrid reactor combining fluidized and fixed beds for anammox treatment was developed. The fluidized bed was mechanically stirred and the gaseous product could be rapidly released from the anammox sludge to prevent washout of the sludge caused by floatation. The fixed bed comprising a non-woven biomass carrier could efficiently catch sludge to reduce washout. During the operation, nitrogen loading rates to the reactor were increased to 27.3 kg N/m³/d, with total nitrogen removal efficiencies of 75%. The biomass concentration in the fluidized bed reached 26-g VSS/L. Anammox granules were observed in the reactors, with settling velocities and sludge volumetric index of 27.3 ± 6.5 m/h and 23 mL/g, respectively. Quantification of extracellular polymeric substances revealed the anammox granules contained a significant amount of extracellular proteins.     

Performance evaluation and phylogenetic characterization of anaerobic fluidized bed reactors using ground tire and pet as support materials for biohydrogen production

This study evaluated two different support materials (ground tire and polyethylene terephthalate [PET]) for biohydrogen production in an anaerobic fluidized bed reactor (AFBR) treating synthetic wastewater containing glucose (4000 mg L⁻¹). The AFBR, which contained either ground tire (R1) or PET (R2) as support materials, were inoculated with thermally pretreated anaerobic sludge and operated at a temperature of 30 °C. The AFBR were operated with a range of hydraulic retention times (HRT) between 1 and 8 h. The reactor R1 operating with a HRT of 2 h showed better performance than reactor R2, reaching a maximum hydrogen yield of 2.25 mol H₂ mol⁻¹ glucose with 1.3 mg of biomass (as the total volatile solids) attached to each gram of ground tire. Subsequent 16S rRNA gene sequencing and phylogenetic analysis of particle samples revealed that reactor R1 favored the presence of hydrogen-producing bacteria such as Clostridium, Bacillus, and Enterobacter.     

The treatment of cheese whey wastewater by sequential anaerobic and aerobic steps in a single digester at pilot scale

The treatment of reconstituted whey wastewater was performed in a 400 L digester at 20 °C, with an anaerobic digestion step, followed by a step of aerobic treatment at low oxygen concentration in the same digester. In a first set of 48 cycles, total cycle time (T_C) of 2, 3 and 4 days were tested at varying organic loading rates (OLR). The COD removal reached 89 ± 4, 97 ± 3 and 98 ± 2% at T_C of 2, 3 and 4 days and OLR of 0.56, 1.04 and 0.78 gCOD L⁻¹ d⁻¹, respectively. The activity of the biomass decreased for the methanogenic population, while increasing by 400% for the acidogens, demonstrating a displacement in the predominant trophic group in the biomass bed. A second set of 16 cycles was performed with higher soluble oxygen concentration in the bulk liquid (0.5 mg L⁻¹) during the aerobic treatment at a T_C of 2 days and an OLR of 1.55 gCOD L⁻¹ d⁻¹, with a soluble COD removal of 88 ± 3%. The biomass specific activities showed a compartmentalization of the trophic group with methanogenic activity maintained in the biomass bed and a high acidogenic activity in the suspended flocs.     

Potential for methane production from anaerobic co-digestion of swine manure with winery wastewater

This work examines the methane production potential for the anaerobic co-digestion of swine manure (SM) with winery wastewater (WW). Batch and semi-continuous experiments were carried out under mesophilic conditions. Batch experiments revealed that the highest specific methane yield was 348 mL CH₄ g⁻¹ COD added, obtained at 85.4% of WW and 0.7 g COD g⁻¹ VS. Specific methane yield from SM alone was 27 mL CH₄ g⁻¹ COD added d⁻¹. Furthermore, specific methane yields were 49, 87 and 107 mL CH₄ g⁻¹ COD added d⁻¹ for the reactors co-digesting mixtures with 10% WW, 25% WW and 40% WW, respectively. Co-digestion with 40% WW improved the removal efficiencies up to 52% (TCOD), 132% (SCOD) and 61% (VSS) compared to SM alone. These results suggest that methane can be produced very efficiently by the co-digestion of swine manure with winery wastewater.     

A comparison study on the high-rate co-digestion of sewage sludge and food waste using a temperature-phased anaerobic sequencing batch reactor system

Assessing contemporary anaerobic biotechnologies requires proofs on reliable performance in terms of renewable bioenergy recovery such as methane (CH₄) production rate, CH₄ yield while removing volatile solid (VS) effectively. This study, therefore, aims to evaluate temperature-phased anaerobic sequencing batch reactor (TPASBR) system that is a promising approach for the sustainable treatment of organic fraction of municipal solid wastes (OFMSW). TPASBR system is compared with a conventional system, mesophilic two-stage anaerobic sequencing batch reactor system, which differs in operating temperature of 1st-stage. Results demonstrate that TPASBR system can obtain 44% VS removal from co-substrate of sewage sludge and food waste while producing 1.2 m³CH₄/m³_system/d (0.2 m³CH₄/kgVS_added) at organic loading rate of 6.1 gVS/L/d through the synergy of sequencing-batch operation, co-digestion, and temperature-phasing. Consequently, the rapid and balanced anaerobic metabolism at thermophilic stage makes TPASBR system to afford high organic loading rate showing superior performance on OFMSW stabilization.     

Maximum removal rate of propionic acid as a sole carbon source in UASB reactors and the importance of the macro- and micro-nutrients stimulation

The maximum propionic acid (HPr) removal rate (R_HPr) was investigated in two lab-scale Upflow Anaerobic Sludge Bed (UASB) reactors. Two feeding strategies were applied by modifying the hydraulic retention time (HRT) in the UASB_HRT and the influent HPr concentration in the UASB_HPr, respectively. The experiment was divided into three main phases: phase 1, influent with only HPr; phase 2, HPr with macro-nutrients supplementation and phase 3, HPr with macro- and micro-nutrients supplementation. During phase 1, the maximum R_HPr achieved was less than 3 g HPr-COD L⁻¹ d⁻¹ in both reactors. However, the subsequent supplementation of macro- and micro-nutrients during phases 2 and 3 allowed to increase the R_HPr up to 18.1 and 32.8 g HPr-COD L⁻¹ d⁻¹, respectively, corresponding with an HRT of 0.5 h in the UASB_HRT and an influent HPr concentration of 10.5 g HPr-COD L⁻¹ in the UASB_HPr. Therefore, the high operational capacity of these reactor systems, specifically converting HPr with high throughput and high influent HPr level, was demonstrated. Moreover, the presence of macro- and micro-nutrients is clearly essential for stable and high HPr removal in anaerobic digestion.     

Bioenergy potential of Ulva lactuca: biomass yield, methane production and combustion

The biomass production potential at temperate latitudes (56°N), and the quality of the biomass for energy production (anaerobic digestion to methane and direct combustion) were investigated for the green macroalgae, Ulva lactuca. The algae were cultivated in a land based facility demonstrating a production potential of 45 T (TS) ha⁻¹ y⁻¹. Biogas production from fresh and macerated U. lactuca yielded up to 271 ml CH₄ g⁻¹ VS, which is in the range of the methane production from cattle manure and land based energy crops, such as grass-clover. Drying of the biomass resulted in a 5-9-fold increase in weight specific methane production compared to wet biomass. Ash and alkali contents are the main challenges in the use of U. lactuca for direct combustion. Application of a bio-refinery concept could increase the economical value of the U. lactuca biomass as well as improve its suitability for production of bioenergy.     

Influence of the ratio of the initial substrate concentration to biomass concentration on the performance of a sequencing batch reactor

Biomass behaviour and COD removal in a benchscale activated sludge reactor have been studied alternating anaerobic and aerobic conditions. Particular attention has been paid to the influence of the ratio of the initial substrate concentration (S ₀) to the initial biomass concentration (X ₀) on the reactor performance. Tests at very low ratios (S ₀/X ₀<2) demonstrate the existence of a threshold below which the reactor performance is seriously affected (S ₀/X ₀=0.5). Under conditions of total suppression of cell duplication, substrate maintenance requirements have also been calculated for the microbial consortium present in the activated sludges. The results obtained show that stressed biomass can survive conditions of substrate lack better than unstressed biomass.List of Symbols b h^–1 specific death rate - COD g/l chemical oxygen demand - DO g/l dissolved oxygen concentration - K _s g/l Monod saturation constant - MLSS g/l mixed liquor suspended solid concentration - P g/l phosphorus concentration - S g/l substrate concentration - S ₀ g/l initial substrate concentration - SS g/l suspended solid concentration - t h time - X g/l biomass concentration - X ₀ g/l initial biomass concentration - Y _SX g/g yield of growth on substrate - _max h^–1 maximum specific growth rate     

Bipolar effects of settling time on active biomass retention in anaerobic sequencing batch reactors digesting flushed dairy manure

Active biomass retention is a technical challenge in anaerobic digester treating dilute animal manure that contains solids particles. A strategy was tested using fibers in the dairy manure as biomass carriers by controlling settling time. Settling time ranging from 0.5 to 60 min were applied to eight anaerobic sequencing batch reactors to investigate their effects on active biomass retention in anaerobic digestion of flushed dairy manure. Results revealed that there existed a critical settling time at 2 min at which only minimum amount of active biomass was retained, and as settling time increased or decreased from this threshold, more active biomass could be retained. Gravity settling and selection pressure theories were suggested to account for the results. A model integrating these two effects was developed and verified with the experimental data. Knowledge derived from this study may lead to innovative bacterial retention technology for cost-effective anaerobic digestion of dairy wastes.     

Development of a pilot scale anaerobic digester for biogas production from cow manure and whey mix

This paper presents results from anaerobic digestion of cow manure and whey mix. A pilot scale anaerobic digester, 128 l in volume, has been developed, to operate under batch and fed-batch conditions. The versatile and unique characteristics of the instrument allowed testing the methane production directly in the farm. The digester performance was evaluated with two calibration tests, the main for a period of 56 days. The study test was divided into three phases, one for each type of feeding operation (batch, fed-batch, batch). The initial phase of digestion resulted in 57 l-CH₄/kg-VS, the second phase had a yield of 86.6 l-CH₄/kg-VS and the third one had a production of 67 l-CH₄/kg-VS. The total methane yield was equal to 211.4 l-CH₄/kg-VS. Using the obtained pilot plant results to a real scale diary production cycle, it was possible to evaluate an electricity production equal to 8.86 kwh per 1 t/d. The conducted tests did show that there is a good potential to the use of a cow manure and whey biomass mix for biogas production.     

Methane emissions from a full-scale A/A/O wastewater treatment plant

Methane (CH₄) emissions from a full-scale anaerobic/anoxic/oxic (A/A/O) wastewater treatment plant (WWTP) (Jinan, China) were investigated during spring and summer of 2010. Results showed that the major emission sources of CH₄ performed the following descending order: anaerobic tanks, oxic tanks, aerated grit chambers and sludge concentration tanks. The total annual fluxes of CH₄ emissions from the Jinan WWTP were 1.69 × 10⁴ kg yr⁻¹, with the emission factors of per capita emissions of 11.3 g CH₄ person⁻¹ yr⁻¹ and flow-based emissions of 1.55 × 10⁻⁴ g CH₄ (L of wastewater)⁻¹. The estimated source strength of methane for all WWTPs in China was 6.2 Gg yr⁻¹ (1 Gg = 10⁹ g). The most significant factors influencing methane emissions were dissolved oxygen concentration in aerated grit chamber and oxic tank and water temperature in high density settler tanks.     

Coupling of Mitochondrial Fatty Acid Uptake to Oxidative Flux in the Intact Heart

The coordination of long chain fatty acid (LCFA) transport across the mitochondrial membrane (V_PAL) with subsequent oxidation rate through β-oxidation and the tricarboxylic acid (TCA) cycle (V_tca) has been difficult to characterize in the intact heart. Kinetic analysis of dynamic ¹³C-NMR distinguished these flux rates in isolated rabbit hearts. Hearts were perfused in a 9.4 T magnet with either 0.5 mM [2,4,6,8,10,12,14,16-¹³C₈] palmitate (n = 4), or 0.5 mM ¹³C-labeled palmitate plus 0.08 mM unlabeled butyrate (n = 4). Butyrate is a short chain fatty acid (SCFA) that bypasses the LCFA transporters of mitochondria. In hearts oxidizing palmitate alone, the ratio of V_TCA to V_PAL was 8:1. This is consistent with one molecule of palmitate yielding eight molecules of acetyl-CoA for the subsequent oxidation through the TCA cycle. Addition of butyrate elevated this ratio; V_TCA/V_PAL = 12:1 due to an SCFA-induced increase in V_TCA of 43% (p < 0.05). However, SCFA oxidation did not significantly reduce palmitate transport into the mitochondria: V_PAL = 1.0 ± 0.2 μmol/min/g dw with palmitate alone versus 0.9 ± 0.1 with palmitate plus butyrate. Thus, the products of β-oxidation are preferentially channeled to the TCA cycle, away from mitochondrial efflux via carnitine acetyltransferase.