High-rate Reactor Research Articles

Treatment of sugarcane vinasse in AnMBR and UASB: process performance and microbial community comparison

Vinasse is a by-product of sugarcane processing which is often used in fertigation; however, the direct use of vinasse harms the environment and reduces soil productivity due to its physicochemical properties. Anaerobic digestion (AD) offers an alternative to mitigate part of the negative effects. Anaerobic high-rate reactors, which mainly rely on sludge granulation, are mostly used in AD of vinasse wastewater. However, the composition of vinasse such as high concentration of solids and organic matter, high salinity, low pH, and high concentrations of sulfate, affect granule formation, leading to sludge washout. Anaerobic membrane bioreactors (AnMBR) present an alternative for vinasse treatment, eliminating the need for sludge granulation and producing a nutrient-rich effluent with minimal residual organics and no suspended solids. Research on sugarcane vinasse treatment using AnMBRs is limited. Most studies have employed submerged internal membrane modules, highlighting the need for further research with different reactor configurations to enhance process performance. In this study, an AnMBR equipped with an external inside-out crossflow ultrafiltration membrane was compared to an upflow anaerobic sludge blanket (UASB) reactor for the treatment of sugarcane vinasse. At a volumetric organic loading rate of up to 6 g COD. L-1.d-1, the UASB reactor reached 75% ± 7% of COD removal efficiency whereas the AnMBR generated a solids-free effluent and reached 88% ± 2% of COD removal efficiency. Microorganisms such as Clostridia, Bacteroidia, Mesotaga, Syner-01, Dehalococcoidia, Bacteroidia-DMER64, and Methanolinea were found as the most abundant. The results highlight the AnMBR potential as an effective alternative for treating sugarcane vinasse while overcoming the challenges posed by unsatisfactory sludge granulation.

Innovative system to maximize methane production from fruit and vegetable waste.

Anaerobic digestion of fruit and vegetable waste (FVW) offers an environmentally friendly alternative for waste disposal, converting it into methane for energy recovery. Typically, FVW digestion is conducted in a continuously stirred tank reactor (CSTR) due to its ease of use and stability with solid concentrations between 5 and 10%. However, CSTRs are limited to organic loading rates (OLRs) of about 3kg COD/m3.day, resulting in large reactor volumes, low methane productivity, and costly wet digestate handling. This work introduces a novel method for methane production from FVW using a high-rate reactor system. The proposed approach involves grinding, centrifuging, and/or pressing the FVW to separate it into liquid and solid phases. The liquid phase is then digested in an up-flow anaerobic sludge blanket (UASB) reactor, while the solid phase undergoes digestion in a dry methanization reactor. A model incorporating all biological reactors was implemented in the Anaerobic Digestion Model 1 (ADM1) to provide a theoretical basis for the experimental development of this system. The current simulation scenarios offer initial references for operating the experimental system, which will, in turn, generate data for further model refinement. For instance, constrained liquid-gas mass transfer was considered for dry fermentation, with additional potential biochemical kinetic limitations to be incorporated following on experimental evidence. The success of this system could enable energy recovery in 72 Central Wholesale Markets across Brazil, offering a critical tool for planning, operating, and optimizing such systems.

Two problems in one shot: Vinasse and glycerol co-digestion in a thermophilic high-rate reactor to improve process stability even at high sulfate concentrations

Anaerobic co-digestion (AcoD) of sugarcane vinasse and glycerol can be profitable because of the destination of two biofuel wastes produced in large quantities in Brazil (ethanol and biodiesel, respectively) and the complementary properties of these substrates. Thus, the objective of this study was to assess the effect of increasing the organic loading rate (OLR) from 2 to 20 kg COD m−3 d−1 on the AcoD of vinasse and glycerol (50 %:50 % on a COD basis) in a thermophilic (55 °C) anaerobic fluidized bed reactor (AFBR). The highest methane production rate was observed at 20 kg COD m−3 d−1 (8.83 L CH4 d−1 L−1), while the methane yield remained stable at around 265 NmL CH4 g−1 CODrem in all conditions, even when influent vinasse reached 1811 mg SO42− L−1 (10 kg COD m−3 d−1). Sulfate was not detected in the effluent. Bacterial genera related to sulfate removal, such as Desulfovibrio and Desulfomicrobium, were observed by means of shotgun metagenomic sequencing at 10 kg COD m−3 d−1, as well as the acetoclastic archaea Methanosaeta and prevalence of genes encoding enzymes related to acetoclastic methanogenesis. It was concluded that process efficiency and methane production occurred even in higher sulfate concentrations due to glycerol addition.

A natural microalgae consortium for the biological nutrient removal in a upflow photobioreactor as tertiary wastewater treatment

A natural microalgae consortium from a eutrophic lagoon was used and evaluated for the tertiary treatment in a upflow photobioreactor. The photobioreactor was continuously fed with the effluent of a UASB high-rate reactor. The photobioreactor average concentration of the inflow pre-treated wastewater in terms of chemical oxygen demand (COD), nitrogen (N), and phosphorus (P) was 125 mg/L, 49 mg/L, and 8 mg/L, respectively. The operation variables of the photobioreactor include a hydraulic retention time (HRT) of 1 day and 2 days of solids retention time (SRT). The photoperiod in the photobioreactor was 24 h at a light illuminance of 5000 lx. The highest nutrient uptake rates in the photobioreactor were 14 mg TN/L·d and 2 mg TP/L·d. Environmental conditions in the photobioreactor favour the cyanobacteria dominance over the microalgae taxonomic groups. In addition, the outcomes established CO2:N ratios of 9:1 to ensure the N removal in wastewater microalgae treatment systems.

Zeolite addition to improve biohydrogen production from dark fermentation of C5/C6-sugars and Sargassum sp. biomass

Thermophilic biohydrogen production by dark fermentation from a mixture (1:1) of C5 (arabinose) and C6 (glucose) sugars, present in lignocellulosic hydrolysates, and from Sargassum sp. biomass, is studied in this work in batch assays and also in a continuous reactor experiment. Pursuing the interest of studying interactions between inorganic materials (adsorbents, conductive and others) and anaerobic bacteria, the biological processes were amended with variable amounts of a zeolite type-13X in the range of zeolite/inoculum (in VS) ratios (Z/I) of 0.065–0.26 g g−1. In the batch assays, the presence of the zeolite was beneficial to increase the hydrogen titer by 15–21% with C5 and C6-sugars as compared to the control, and an increase of 27% was observed in the batch fermentation of Sargassum sp. Hydrogen yields also increased by 10–26% with sugars in the presence of the zeolite. The rate of hydrogen production increased linearly with the Z/I ratios in the experiments with C5 and C6-sugars. In the batch assay with Sargassum sp., there was an optimum value of Z/I of 0.13 g g−1 where the H2 production rate observed was the highest, although all values were in a narrow range between 3.21 and 4.19 mmol L−1 day−1. The positive effect of the zeolite was also observed in a continuous high-rate reactor fed with C5 and C6-sugars. The increase of the organic loading rate (OLR) from 8.8 to 17.6 kg m−3 day−1 of COD led to lower hydrogen production rates but, upon zeolite addition (0.26 g g−1 VS inoculum), the hydrogen production increased significantly from 143 to 413 mL L−1 day−1. Interestingly, the presence of zeolite in the continuous operation had a remarkable impact in the microbial community and in the profile of fermentation products. The effect of zeolite could be related to several properties, including the porous structure and the associated surface area available for bacterial adhesion, potential release of trace elements, ion-exchanger capacity or ability to adsorb different compounds (i.e. protons). The observations opens novel perspectives and will stimulate further research not only in biohydrogen production, but broadly in the field of interactions between bacteria and inorganic materials.

Anaerobic Biodegradation of Biodiesel Industry Wastewater in Mesophilic and Thermophilic Fluidized Bed Reactors: Enhancing Treatment and Methane Recovery.

In the past few years, the extraction of value-added compounds from the anaerobic digestion of glycerol has been an option to add value to this waste because biodiesel production is increasing worldwide. The evolution of research on glycerol valorization by anaerobic digestion has reached the use of high-rate reactors. However, no study has evaluated glycerol digestion in an anaerobic fluidized bed reactor (AFBR), a configuration with potential advantages in methane production. Still, the best operating temperature for high-rate glycerol digestion remains unclear. To clarify these gaps, the present study aimed to compare glycerol digestion in mesophilic AFBR (30 °C) and thermophilic AFBR (55 °C). In both reactors, glycerol concentration was increased from 1.0 to 7.0 g L-1 at a fixed hydraulic retention time of 24 h, resulting in an increase at the organic loading rate from 1.2 to 7.6 kg COD m-3 day-1. Thermophilic digestion of glycerol achieved superior removals of organic matter (67.7-94.2%) and methane yield (330.8 mL CH4 g-1 COD) than the mesophilic digestion (48.6-93.0% and 266.6 mL CH4 g-1 COD). Additionally, the application of the kinetic model of substrate utilization (modified Stover-Kincannon model) indicated a higher substrate utilization coefficient in the thermophilic AFBR (23.09 g L-1 day-1) than the mesophilic AFBR (7.14 g L-1 day-1). Therefore, the application of glycerol concentrations higher than 7.0 g L-1 in thermophilic AFBR should be further investigated. Also, given only operational results, the application of the AFBR in the two-stage anaerobic digestion of glycerol is recommended.

Soybean molasses as feedstock for sustainable generation of biomethane using high-rate anaerobic reactor

Anaerobic digestion of agro-industrial wastes is an environmentally friendly green biotechnology of significant interest in order to facilitate sustainable development of bioenergy production. Thus, it becomes important to invest in management processes for agro-industrial wastes, particularly low-cost ones. In this paper, the main purposes were to investigate the performance of a high-rate reactor and biogas generation potential by anaerobic digestion of soybean molasses, which is a viscous liquid of brown color obtained as a byproduct from processing of the soy protein industry concentrate. A lab-scale up-flow anaerobic sludge blanket reactor (UASB reactor), with a total volume of 12 L, was operated at six different organic loading rates (OLR) ranging from 0.28 to 6.98kgCODm−3d−1 (COD of 500–4000 mg L−1). The reactor was fed with soybean molasses for 134 days and maintained under mesophilic conditions. Different values were tested for the hydraulic retention time (HRT of 48, 24 and 12 h). After the fast startup period (52 days), the mean values of removal efficiencies (CODTotal) ranged from 70% to 83% in all experimental periods. In a UASB reactor, a higher organic loading rate of 6.98kgCODm−3d−1 could be tolerated, but it resulted in a lower biomethane yield of 356.1mLCH4gCOD−1. In addition, for all the tested COD concentrations and HRT, high concentrations of methane in the biogas were obtained from 72.5% to 82.1%. Based on the experimental results, it can be verified that this high-rate anaerobic configuration can be used for the biomethane generation of soybean molasses and the produced effluent can be reutilized in the dilution of soybean molasses for reactor feed.

Hydrogenotrophic activity: A tool to evaluate the kinetics of methanogens

Anaerobic-digestion-based technology is key to achieving sustainable water management and resource recovery. It is essential to understand the material flux and kinetics involved in methanogenesis to optimize the organic matter removal and methane production. In this sense, specific methanogenic activity is a cost-effective tool to characterize the biological activity of anaerobic biosludge, to monitor the performance of reactors, and study the kinetics of acetate and H2 conversion to methane. Established protocols are applied for the acetoclastic activity test. However, hydrogenotrophic activity assay remains less widespread and is not standardized. In this work, the assay design for hydrogenotrophic activity is discussed and full calculation is presented, based on the kinetics for the H2/CO2 conversion to methane. An equation to calculate the inoculum size is proposed, suitable for a wide variety of types of biosludge: from a wastewater treatment plant to solid digesters, from a high-rate reactor to lagoons. The applied zero-order model fitted adequately to data for pilot-scale and full-scale anaerobic reactors: the p-values from the ANOVA F-test were below 1E-03; standard deviations for triplicate experiments were between 3 and 12%, coherent with the values found in the literature. Microbial growth during the test was negligible, below 1.2% of the biomass dosed in the vial. As a complement, acetoclastic activity was determined for each sample. The use of both acetoclastic and hydrogenotrophic activity is relevant for the study of the methanogenesis and gives a better characterization of the performance of the biosludge in anaerobic reactors rather than only using the specific acetoclastic methanogenic activity.

Evaluation of bioenergy potential from citrus effluents through anaerobic digestion

At the global level, citrus production is around 92 million tons and citrus processing is about 22 million tons generating 28 million m3 of Citrus Effluents. In the last two decades, the generation of wastewater by the citrus industry has increased, and since earlier studies have focused mostly on solid citrus waste, there is inadequate information related to the potential energy value of these effluents. The main contribution of this work is the development of a methodology for conducting an energy analysis to determine the amount of electrical energy that can be derived from the biogas produced in the anaerobic digestion of citrus effluents at the global level. This determination was made through the operation of a novel, high-rate reactor, called the Anaerobic Hybrid Reactor. The aim of this paper was to evaluate the bioenergy potential of the effluents from the citrus industry by using anaerobic digestion to generate electrical energy. As part of the results of this evaluation, it was found that one ton of processed oranges generates 1.25 m3 of citrus effluents, 0.72 m3 of methane at standard temperature and pressure, 7.16 kWh of gross electricity, and 2.15 kWh of net electricity, which represents a cost of 0.17 USD. The worldwide bioenergy potential from citrus effluents by the main citrus processing countries is approximately 16 million m3 of methane/year at standard temperature and pressure, which is equivalent to approximately 159 GWh of gross electricity per year, about 48 GWh of net electricity per year, and about 111 GWh of thermal energy per year. The biogas that is produced can replace as much as 9% of the consumption of fuel oil and natural gas used in a citrus processing plant. Anaerobic digestion is a clean, simple energy technology, and it helps to minimize the social, environmental, and economic problems caused by poor management and the lack of alternatives for the treatment of the effluents from the citrus industry.

An innovative multistage anaerobic hythane reactor (MAHR): Metabolic flux, thermodynamics and microbial functions

Biohythane production from wastewater via anaerobic fermentation currently relies on two-stage physically separated biohydrogen and biomethane reactors, which requires closed monitoring, the implementation of a control system, and cost-intensive, complex operation. Herein, an innovative multistage anaerobic hythane reactor (MAHR) was reported via integrating two-stage fermentation into one reactor. MAHR was constructed using an internal down-flow packed bed reactor and an external up-flow sludge blanket to enhance microbial enrichment and thermodynamic feasibility of the associated bioreactions. The performance of MAHR was investigated for 160 d based on biogas production, metabolic flux and microbial structure in comparison to a typical anaerobic high-rate reactor (up-flow anaerobic sludge blanket (UASB)). A biohythane production with an optimized hydrogen volume ratio (10–20%) and a high methane content (75–80%) was achieved in the hythane zone (MH) and methane zone (MM) in MAHR, respectively. In addition, MAHR showed a stronger capability to accommodate a high organic loading rate (120 g COD/L/d), and it enhanced the conversion of organics leading to a methane production rate 66% higher than UASB. Thermodynamic analysis suggested that hydrogen extraction in MH significantly decreased the hydrogen partial pressure (<0.1% vol) which favored acetogenesis in MM. Metabolic flux and microbial function analysis further supported the superior performance of MAHR over UASB, which was primarily attributed to enhanced acetogenesis and acetoclastic methanogenesis.

Anaerobic treatment of LCFA-containing synthetic dairy wastewater at 20 °C: Process performance and microbial community dynamics.

Facilitating anaerobic degradation of long-chain fatty acids (LCFA) is key for tapping the high methane production potential of the fats, oil and grease (FOG) content of dairy wastewaters. In this study, the feasibility of using high-rate granular sludge reactors for the treatment of mixed LCFA-containing synthetic dairy wastewater (SDW) was assessed at 20 °C. The effects of the LCFA concentration (33-45% of COD) and organic loading rates (2-3 gCOD/L·d) were determined using three parallel expanded granular sludge bed reactors. For the first time, long term anaerobic treatment of LCFA-containing feed at 20 °C was shown to be feasible and was linked to the microbial community dynamics in high-rate reactors. During a two-month operation, a soluble COD removal of 84-91% and COD to methane conversion of 44-51% was obtained. However, granular sludge flotation and washout occurred after two months in all reactors without volatile fatty acids (VFA) accumulation, emphasizing the need for sludge retention for long-term granular sludge reactor operation with LCFA-containing feed at low ambient temperatures. The temporal shifts in microbial community structure were studied in the high-rate treatment of SDW, and the process disturbances (elevated LCFA loading, LCFA accumulation, and batch operation) were found to decrease the microbial community diversity. The relative abundance of Methanosaeta increased with higher LCFA accumulation in the settled and flotation layer granules in the three reactors, therefore, acetoclastic methanogenesis was found to be crucial for the high-rate treatment of SDW at 20 °C. This study provides an initial understanding of the continuous anaerobic treatment of LCFA-containing industrial wastewaters at low ambient temperatures.

Biohythane production of post-hydrothermal liquefaction wastewater: A comparison of two-stage fermentation and catalytic hydrothermal gasification

Developing efficient methods to recover energy from post-hydrothermal liquefaction wastewater (PHW) is critical for scaling up hydrothermal liquefaction (HTL) technology. Here we evaluated two-stage fermentation (TF) and catalytic hydrothermal gasification (CHG) for biohythane production using PHW. A hydrogen yield of 29 mL·g−1 COD and methane yield of 254 mL·g−1 COD were achieved via TF. In comparison, a higher hydrogen yield (116 mL·g−1 COD) and lower methane yield (65 mL·g−1 COD) were achieved during CHG. Further, a techno-economic and sensitivity analysis was conducted. The capital cost and operating cost for TF varied with the different reactor systems. TF with high-rate reactors suggested its promising commercialized application as it had a lower minimum selling price (−0.71 to 2.59 USD per gallon of gasoline equivalent) compared with conventional fossil fuels under both the best and reference market conditions. Compared with TF, CHG was only likely to be profitable under the best case conditions.

Denitrification Kinetics of High‐Strength Nitrate in Granular Sludge Reactors

Biological denitrification of high‐strength nitrate is challenging due to building‐up of toxic nitrite to high levels. In this study, denitrification kinetics of high‐strength nitrate is investigated in a granular sludge reactor operated in sequencing batch mode. The nitrate concentrations are increased from 677, 1355, 2032, 2710, 3387, 4065–4742 mg L−1 NO3N in the reactor. Carbon and an electron source (acetate) are supplied at a fixed acetate‐carbon to nitrate‐nitrogen ratio of 1.5. At steady state, complete denitrification of 4742 mg L−1 NO3N in the feed is observed within the first 20 h of sequencing batch reactor (SBR) cycle. High denitrification rate constants are observed for NO3N concentrations from 677 to 2032 mg L−1. However, a decrease in denitrification rate constants is observed for nitrate‐N concentrations of 2710–4742 mg L−1, due to inhibition caused by transient accumulation of high levels of nitrite. Denitrifying biomass formed in the SBR is predominantly consisted of granular sludge, containing cocci, and rod‐shaped microorganisms. Cultivation of nitrite‐tolerant, denitrifying microbial community in granular sludge will help in the development of high rate reactors needed for process application.

Anaerobic treatment of blended sugar industry and ethanol distillery wastewater through biphasic high rate reactor

ABSTRACTThis study aimed to investigate the physicochemical properties of sugar industry and ethanol distillery wastewater and the treatment of the blended wastewater through a two-stage anaerobic reactor. For this treatment, different initial chemical oxygen demand (COD) concentrations (5–20 g/L) and hydraulic retention times (HRTs) (2–10 days) were applied. The sugar industry effluent characteristics obtained in terms of organic matter (mg/L) were as follows: 5 days biochemical oxygen demand (BOD5): 654.5–1,968; COD: 1,100–2,148.9; total solids (TS): 2,467–4,012 mg/L; and pH: 6.93–8.43. The ethanol distillery spent wash strengths obtained were: BOD5: 27,600–42,921 mg/L; COD: 126,000–167,534 mg/L; TS: 140,160–170,000 mg/L; and pH: 3.9–4.2. Maximum COD removal of 65% was obtained at optimum condition (initial COD concentration of 10 g/L and HRT of 10 days), and maximum color removal of 79% was recorded under similar treatment conditions. Hence, the performance of the two-stage anaerobic reactor for simultaneous removal of COD and color from high-strength blended wastewater is promising for scaling up in order to mitigate environmental problems of untreated effluent discharge.

Anaerobic digestion of citrus industry effluents using an Anaerobic Hybrid Reactor

Mexico is one of the main citrus producers, ranking fourth in the world with approximately 7.4 million tons per year, with oranges contributing 4.08 million tons to that total. The effluents from the citrus industry have high loadings of organic matter and low pH levels. These effluents also are suitable for treatment by anaerobic digestion to reduce the organic matter and to obtain a value-added product, such as biogas. The aim of this work was to perform the anaerobic digestion of effluents from the citrus industry by using a high-rate reactor, evaluating the biogas production and use as an alternative energy source. An Anaerobic Hybrid Reactor (AHR) was used to treat the effluent from a citrus processing plant in Martinez de la Torre, Veracruz, Mexico. The AHR was operated at an organic loading rate (OLR) of 8 gCODT/Ld at steady state, obtaining a total and soluble COD removal of approximately 85%, with methane yields around 0.15 LCH4 to STP/gCODrem. An inhibitory effect was observed by the presence of D-limonene in the citrus effluent, although no pretreatment was used for elimination of this essential oil, a decrease in the COD removal and methane yields was observed due to the higher OLR. An energy estimate was obtained with the biogas, and it was found that up to 2.2% of the electricity required for the operation of a citrus processing plant can be generated using anaerobic treatment.

Using dolomitic limestone to replace conventional alkalinization in the biodigestion of rapid acidification cassava processing wastewater

Anaerobic digestion (AD) of rapid acidification wastewaters (RAW) in high-rate reactors is highly dependent on properly controlling the buffer capacity of systems, which is usually done by dosing alkalizing/alkali compounds. Although reliable, this strategy does not ensure complete effectiveness, depending on the chemical used, also affecting negatively the economic performance of the treatment plants. The aim of this study was to assess an alternative approach to conventional alkalizination in the AD of RAW by using dolomitic limestone as the alkalizing agent in single-phase continuous systems fed with cassava processing wastewater (CPWW). Two different amounts of limestone were used in horizontal-flow reactors subjected to increasing organic loading rates (OLRs). The effects of dolomite on the specific methanogenic activity (SMA) of the methanogenic sludge, as well as the fertilizer potential of the treated CPWW were also assessed. Limestone supplementation positively affected the SMA of the sludge by increasing methane production and decreasing the lag phase. Limestone also proved to be an adequate alkalizing agent for the horizontal-flow systems, continuously providing the systems with bicarbonate alkalinity at relatively high OLRs (up to 8.5 kg COD m−3 d−1), even during organic overloading periods. The availability of specific inorganic constituents, primarily K+, Ca2+ and Mg2+, also confirmed the biofertilizer potential of the treated CPWW, although higher organic matter removal levels would still be required for safer nutrient cycling.

Continuous production of biohythane from hydrothermal liquefied cornstalk biomass via two-stage high-rate anaerobic reactors.

BackgroundBiohythane production via two-stage fermentation is a promising direction for sustainable energy recovery from lignocellulosic biomass. However, the utilization of lignocellulosic biomass suffers from specific natural recalcitrance. Hydrothermal liquefaction (HTL) is an emerging technology for the liquefaction of biomass, but there are still several challenges for the coupling of HTL and two-stage fermentation. One particular challenge is the limited efficiency of fermentation reactors at a high solid content of the treated feedstock. Another is the conversion of potential inhibitors during fermentation. Here, we report a novel strategy for the continuous production of biohythane from cornstalk through the integration of HTL and two-stage fermentation. Cornstalk was converted to solid and liquid via HTL, and the resulting liquid could be subsequently fed into the two-stage fermentation systems. The systems consisted of two typical high-rate reactors: an upflow anaerobic sludge blanket (UASB) and a packed bed reactor (PBR). The liquid could be efficiently converted into biohythane via the UASB and PBR with a high density of microbes at a high organic loading rate.ResultsBiohydrogen production decreased from 2.34 L/L/day in UASB (1.01 L/L/day in PBR) to 0 L/L/day as the organic loading rate (OLR) of the HTL liquid products increased to 16 g/L/day. The methane production rate achieved a value of 2.53 (UASB) and 2.54 L/L/day (PBR), respectively. The energy and carbon recovery of the integrated HTL and biohythane fermentation system reached up to 79.0 and 67.7%, respectively. The fermentation inhibitors, i.e., 5-hydroxymethyl furfural (41.4–41.9% of the initial quantity detected) and furfural (74.7–85.0% of the initial quantity detected), were degraded during hydrogen fermentation. Compared with single-stage fermentation, the methane process during two-stage fermentation had a more efficient methane production rate, acetogenesis, and COD removal. The microbial distribution via Illumina MiSeq sequencing clarified that the biohydrogen process in the two-stage systems functioned not only for biohydrogen production, but also for the degradation of potential inhibitors. The higher distribution of the detoxification family Clostridiaceae, Bacillaceae, and Pseudomonadaceae was found in the biohydrogen process. In addition, a higher distribution of acetate-oxidizing bacteria (Spirochaetaceae) was observed in the biomethane process of the two-stage systems, revealing improved acetogenesis accompanied with an efficient conversion of acetate.ConclusionsBiohythane production could be a promising process for the recovery of energy and degradation of organic compounds from hydrothermal liquefied biomass. The two-stage process not only contributed to the improved quality of the gas fuels but also strengthened the biotransformation process, which resulted from the function of detoxification during biohydrogen production and enhanced acetogenesis during biomethane production.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-016-0666-z) contains supplementary material, which is available to authorized users.

Pursuit of urine nitrifying granular sludge for decentralised nitrite production and sewer gas control

This study aims to develop a high-rate reactor for decentralised urine nitrification using granular sludge, which allows high biomass retention in a small footprint installation. The system incorporated alkalinity dosing to ensure full conversion of ammonia to nitrite for subsequent control of sewer gas production. The key operational parameters for granule formation such as feeding and settling duration were tested as well as environmental conditions including pH. Pulse feeding was found to be instrumental to both the treatment performance and development of well settling granule-like aggregates. These aggregates showed granular characteristics with a compact and well defined shape, excellent settleability and high strength. However, pulse feeding also led to increased pH and free ammonia concentrations which reduced heterotroph activity and aggregate growth. Furthermore, in order to prevent nitrification collapse and high pH and free ammonia associated with such an event the reactor nitrogen loading was limited. Due to the low organic to nitrogen ratio of urine this restrained the organics loading of the dominant heterotrophic community further limiting granule growth. Nevertheless, the development of compact well settling aggregates under pulse feed operation allowed the objective of high-rate nitrification to be achieved with sustained nitritation rates up to 1.1kg-N/m3d at a urine dilution of approximately 25%.

High-rate hydrogenotrophic denitrification in a pressurized reactor

Most conventional hydrogenotrophic denitrification reactors based on packed- or fluidized-bed present a similar H2 delivery scheme of continuous gas purging to the atmosphere in order to improve H2 transfer rates and enable discharge of N2 gas produced during denitrification. This operation results in a significant release of H2 gas to atmosphere with its related economic and safety concerns. The current research proposes a novel pressurized high-rate hydrogenotrophic reactor for denitrification without gas purging. The investigation performed refutes a prevalent notion that N2 gas accumulates in the headspace of a closed reactor during denitrification. Instead, this research shows that during continuous operation a gas–liquid equilibrium is established in the reactor according to Henry’s law and excess N2 gas is carried out by the effluent in dissolved form. Therefore, no gas purging is required and H2 loss is limited only to the dissolved H2 in the effluent. As a consequence, a simple low-cost and high-rate reactor with closed headspace can be designed for denitrification. The proposed reactor is operated as a trickling filter where water is recirculated over biofilm carriers with high surface area.The feasibility of the proposed reactor was shown for two effluent concentrations of 10 and 1mgNO3−-N/L. Average denitrification rates of 2.1±0.2 and 1.06±0.06gNO3−-N/(Lreactord) with H2 utilization efficiencies of 92.8% and 96.9% were measured for the two effluent concentrations, respectively. Higher denitrification rates of up to 5gNO3−-N/(Lreactord) were observed at higher recirculation flow rates and higher partial pressures of H2.

Biomethanation of fruit processing industry waste-water through high-rate reactor

The present paper reports a study conducted at Tamil Nadu Agricultural University, aiming at developing a highrate reactor for treating the food processing waste-water. It was found that the waste-water had low strength biodegradability by conducting batch experiment with and without mixing cattle-dung in different volatile solid proportion and cattle-dung ratio. The BOD and COD of the waste-water were found to be 540 and 2000 mg/L respectively and pH of the processing waste-water was 1.37 that lies in the acidic range. In the batch studies conducted, the maximum gas production was recorded per kg of Total Solid Content and Net Volatile Solid Content added was observed in crushed and over ripen sample as 87.95, 91.51 L and 82.05, 84.24 L respectively. The minimum gas production per kg of total solid content and volatile solid content added was observed in waste-water sample as 2.22 and 2.42 L respectively for the digestion period of 21 days. The high-rate reactor for treating the food processing waste-water was installed at a reputed firm. The COD removal efficiency, TS removal efficiency and VS removal efficiency was found to be about 50, 36 and 29% respectively. The biogas generation potential is estimated to be 60 m3/day. The industry saved not only electric power of 96 kWh/day, but also the sludge was used as manure, thus the waste disposal was in an environmentally friendly approach.