Enhancing hyper-thermophilic hydrolysis pre-treatment of chicken manure for biogas production by in-situ gas phase ammonia stripping

Determination of effects of thermophilic and hyperthermophilic temperatures on anaerobic hydrolysis and acidogenesis of pig manure through a one-year study

Improving hydrolysis and acidogenesis through thermophilic and hyperthermophilic temperatures is critical for enhancing the anaerobic decomposition of organic waste like pig manure. However, whether higher temperatures can provide more enhanced performance has not been elucidated experimentally. This study, therefore, conducted a 375-day continuous operation experiment at 55 and 70 °C with a 5-day hydraulic retention time. The two temperature reactors entered a stable state after about 200 days and long-term microbial acclimation markedly changed their performances. In the thermophilic and hyperthermophilic reactor, the hydrolysis efficiencies were obtained at 29.7 % and 27.3 % respectively, whereas the acidogenesis efficiency was relatively low at 1.0 % and 3.1 %. Due to the occurrence of methanogenesis, the volatile fatty acid concentration in the thermophilic reactor was only 45 % of that in the hyperthermophilic reactor. The thermophilic reactor exhibited higher bacterial diversity; however, this difference between the two reactors apparently did not correlate with hydrolysis and acidogenesis performance.

Generation of High Concentration Free Volatile Fatty Acids from Continuous Anaerobic Digestion of Chicken Manure by Suppressing the Decomposition of Nitrogenous Components

Free volatile fatty acids (free VFA) play a crucial role in the inactivation of pathogens during the anaerobic digestion of animal manure. However, the decomposition of nitrogenous components can release alkaline ammonium-N, which might increase the pH and reduce the concentration of free VFA. In this study, continuous anaerobic digestion of high-solid chicken manure was conducted for 150 days. The results indicated the process stabilized at a pH of approximately 6.0, with total ammonia nitrogen (TAN) of around 7.0 g/L. The resulting concentration of free VFA was only about 3.1 g/L, which might not sufficiently effective for pathogen inactivation. On the 70th day, hydrogen chloride was added into the reactor to adjust the pH to 5.5. This led to a further decrease in pH to 4.3 and TAN to 2.3 g/L. As a result, the concentration of free VFA significantly increased, reaching up to 12.6 g/L. These findings support the potential for generating high levels of free VFA even for nitrogen-rich manure by implementing an appropriate process regulation.

Post-hydrolysis versus side-stream ammonia stripping in semi-continuous two-stage anaerobic digestion of high nitrogen feedstock

With the increased popularity of two-stage anaerobic digesters, post-hydrolysis ammonia stripping (PHAS) has resurfaced as a new possible treatment configuration. This study discusses for the first time the semi-continuous operation of PHAS and compares it with the most used stripping configuration nowadays, side-stream ammonia stripping (SSAS), under similar conditions using air or renewable natural gas (RNG) as stripping mediums. Ammonia stripping operating conditions were set to pH 9.5, 55 °C, and flowrate of 100 L gas/L/hour. RNG removed 50-58% of ammonia while air removed 70-78%. Interestingly, the PHAS system showed more flexibility and resilience than the SSAS system when testing parameters were changed. Volumetric and specific biogas production from PHAS and SSAS scenarios averaged up to 1.91 and 1.26 L/L/day and 831 and 701 L biogas/ kg VS/day under organic loading rates of 2.61 and 1.8 g VS/L/day, respectively.

Hyper-thermophilic anaerobic pretreatment enhances the removal of transferable oxazolidinone and phenicol cross-resistance gene optrA in enterococci

The extensive use of florfenicol in poultry industry results in the emergence of optrA gene, which also confers resistance to clinically important antibiotic linezolid. This study investigated the occurrence, genetic environments, and removal of optrA in enterococci in mesophilic (37 °C) and thermophilic (55 °C) anaerobic digestion systems, and a hyper-thermophilic (70 °C) anaerobic pretreatment system for chicken waste. A total of 331 enterococci were isolated and analyzed for antibiotic resistance against linezolid and florfenicol. The optrA gene was frequently detected in enterococci from chicken waste (42.7%) and effluents from mesophilic (72%) and thermophilic (56.8%) reactors, but rarely detected in the hyper-thermophilic (5.8%) effluent. Whole-genome sequencing revealed that optrA-carrying Enterococcus faecalis sequence type (ST) 368 and ST631 were the dominant clones in chicken waste, and they remained dominant in mesophilic and thermophilic effluents, respectively. The plasmid-borne IS1216E-fexA-optrA-erm(A)-IS1216E was the core genetic element for optrA in ST368, whereas chromosomal Tn554-fexA-optrA was the key one in ST631. IS1216E might play a key role in horizontal transfer of optrA due to its presence in different clones. Hyper-thermophilic pretreatment removed enterococci with plasmid-borne IS1216E-fexA-optrA-erm(A)-IS1216E. A hyper-thermophilic pretreatment is recommended for chicken waste to mitigate dissemination of optrA from animal waste to the environment.

Clean Energy Based Multigeneration System for Sustainable Cities: Thermodynamic, and Stability Analyses

This paper concerns the development and analysis of multigeneration systems based on hybrid sources such as biomass and wind. Industry requires different types of sources to provide several outputs, so the goal of this research was to fulfill the industrial requirement with optimization. The multigeneration cycle supplies enough power to satiate energy demands, i.e., power, cooling, hydrogen, air conditioning, freshwater, hot water, and heating. For this, the multigeneration cycle was modeled in the Engineering Equation Solver (EES) and Simulink to obtain optimized results for the industry. Energy and exergy for the multigeneration cycle were determined to assess the performance of the cycle and to investigate the optimized results for the overall system. This study shows that for configuration selection and design, different thermodynamic, economic, and environmental aspects should be considered. Based on the results, the selection of the best location for this multigeneration system was made. Power output from the wind turbine was around 7 MW and from biogas 0.6 MW. The overall exergy efficiency of the multigeneration system was found to be 0.1401.

Closing the Nutrient Loop-The New Approaches to Recovering Biomass Minerals during the Biorefinery Processes

The recovery of plant mineral nutrients from the bio-based value chains is essential for a sustainable, circular bioeconomy, wherein resources are (re)used sustainably. The widest used approach is to recover plant nutrients on the last stage of biomass utilization processes-e.g., from ash, wastewater, or anaerobic digestate. The best approach is to recover mineral nutrients from the initial stages of biomass biorefinery, especially during biomass pre-treatments. Our paper aims to evaluate the nutrient recovery solutions from a trans-sectorial perspective, including biomass processing and the agricultural use of recovered nutrients. Several solutions integrated with the biomass pre-treatment stage, such as leaching/bioleaching, recovery from pre-treatment neoteric solvents, ionic liquids (ILs), and deep eutectic solvents (DESs) or integrated with hydrothermal treatments are discussed. Reducing mineral contents on silicon, phosphorus, and nitrogen biomass before the core biorefinery processes improves processability and yield and reduces corrosion and fouling effects. The recovered minerals are used as bio-based fertilizers or as silica-based plant biostimulants, with economic and environmental benefits.

Volatile Fatty Acids (VFA) Production and Recovery from Chicken Manure Using a High-Solid Anaerobic Membrane Bioreactor (AnMBR)

Acidogenic fermentation of chicken manure (CM) for production and recovery of volatile fatty acids (VFA) is an interesting biological waste-to-value approach compared to benchmark organic waste management strategies. Considering the wide range of high value applications of VFA, a semi-continuous immersed anaerobic membrane bioreactor (AnMBR) was applied to boost VFA productivity and yield, while reducing downstream processing stages assisting the recovery of VFA. In this regard, the effect of parameters such as pH and organic loading rates (OLR) on the overall bioconversion and filtration performance was investigated. Thermal-shocked CM was applied both as inoculum and substrate. A very high VFA yield (0.90 g-VFA/g-VS) was obtained in the treatment with no pH control (~8.2) at an OLR of 2 g-VS/(L·d), presenting 24% higher yield compared to that of the controlled pH. Batch assays further demonstrated the enhanced hydrolysis and acidogenesis activities at weak alkaline conditions. A long-term (78 days) fermentation and filtration was successfully performed, where stable membrane filtration performance was experienced for about 50 days under high-solid (suspended solid of 37-45 g/L) and high flux (20 L/(m²·h)) conditions. Results suggest that AnMBR of CM is a feasible and promising process for VFA production and recovery.

Low-Temperature Pretreatment of Biomass for Enhancing Biogas Production: A Review

Low-temperature pretreatment (LTPT, Temp. < 100 °C or 140 °C) has the advantages of low input, simplicity, and energy saving, which makes engineering easy to use for improving biogas production. However, compared with high-temperature pretreatment (>150 °C) that can destroy recalcitrant polymerized matter in biomass, the action mechanism of heat treatment of biomass is unclear. Improving LTPT on biogas yield is often influenced by feedstock type, treatment temperature, exposure time, and fermentation conditions. Such as, even when belonging to the same algal biomass, the response to LTPT varies between species. Therefore, forming a unified method for LTPT to be applied in practice is difficult. This review focuses on the LTPT used in different biomass materials to improve anaerobic digestion performance, including food waste, sludge, animal manure, algae, straw, etc. It also discusses the challenge and cost issues faced during LTPT application according to the energy balance and proposes some proposals for economically promoting the implementation of LTPT.

Sulfur containing mixed wastes in anaerobic processing by new immobilized synthetic consortia

Methanogenic biotransformation of unusual substrates (sulfur (S)-containing wastes: non-purified vacuum gas oil, straight-run gasoline fraction (Naphtha), gas condensate, and straight-run diesel fraction) coming from oil industry after their oxidative desulfurization was investigated. Nitrogen-containing wastes (hydrolysates of chicken manure and Chlorella vulgaris biomass) were added as co-substrates to mixture with oil industry wastes. The 100 % conversion of S-organic compounds to inorganic sulfide accumulated in the reaction liquid medium was achieved with simultaneous production of biogas containing high methane percent (greater than 70 %). Polishing of effluents from methane tank was carried out by denitrifying oxidation of ammonium (DEAMOX). The high process efficiency was due to use of original immobilized artificial consortia at the stage of methanogenesis and DEAMOX. This study reveals the real potential in the processing of very complex mixtures of large-scale wastes, usually inhibiting methanogenesis, by developing biocatalysts based on synthetic biology approaches.

Post-hydrolysis ammonia stripping as a new approach to enhance the two-stage anaerobic digestion of poultry manure: Optimization and statistical modelling

Post-hydrolysis ammonia stripping was investigated as a new approach to enhance the methane potential of high ammonia substrates, such as poultry manure. The objective of the proposed approach is to address some of the noticeable disadvantages in the existing ammonia-stripping techniques i.e., treatment of raw samples and side-stream stripping. Poultry manure (PM) and a co-substrate (mixed wastes from a cheese factory and a coffee house, referred to as MS) characterized by a high carbon-to-nitrogen ratio were mixed at five different ratios: PM:MS of 100:0, 75:25, 50:50, 25:75, and 0:100. Samples were hydrolyzed for six days to promote ammonia conversion from organic nitrogen and then the samples with higher ammonia levels (>2000 mg NH₃-N/L) were stripped with air at initial pH values of 9 and 10 and temperatures of 40 and 55 °C. Biochemical methane potential (BMP) test results showed that post-hydrolysis ammonia stripping had alleviated ammonia inhibition and improved methane potential up to 200% when compared with untreated samples. The ammonia removal efficiency was mostly affected by pH. On the other hand, methane potential was highest in the samples treated at a higher temperature as their biodegradability was enhanced when compared with the samples treated at lower temperatures. Post-BMP characterization showed that the proposed approach had also limited the increase of ammonia in the digestate which ensured proper growth of methanogenic microorganisms.

Enhanced biogas production from food waste and activated sludge using advanced techniques - A review

Biogas generation using food waste anaerobic co-digestion with activated sludge provides a cleaner addressable system, an excellent solution to global challenges, the increasing energy demands, fuel charges, pollution and wastewater treatment. Regardless of the anaerobic digestate end product values, the technology lacks efficiency and process instability due to substrate irregularities. Process parameters and substrate composition, play a vital role in the efficiency and outcome of the system. Intrinsic biochar properties such as pore size, specific surface properties and cation exchange capacity make it an ideal additive that enriches microbial functions and enhances anaerobic digestion. The pretreatment and co-digestion of food waste and activated sludge are found to be significant for efficient biogas generation. The advantages, drawbacks, limitations, and technical improvements are covered extensively in the present review besides the recent advancement in the anaerobic digestion system.

Stable, high-rate anaerobic digestion through vacuum stripping of digestate

This study coupled anaerobic digestion with vacuum stripping to achieve stable digestion at higher organic loading rates. Besides mitigation of ammonia inhibition, vacuum stripping of digestate improves solids solubilization and dewaterability due to vacuum-enhanced low-temperature thermal and mild-alkaline treatment under the vacuum stripping conditions (65 °C, 25-27 kPa, and pH 9). Batch vacuum stripping for 8 h removed 97.4-99.4% of ammonia, increased the dissolved fraction of volatile solids (VS) by 72.5%, and improved dewaterability with 30% decreases in time-to-filter and viscosity. The digesters having 2.9% of digestate replaced daily by vacuum stripped digestate were stable up to organic loading rate of 4.3 g-VS/L_reactor/d with biogas production at 3.15 L/L_reactor/d, while the digesters without stripping attained biogas production of 1.90 L/L_reactor/d at its highest stable organic loading rate of 2.5 g-VS/L_reactor/d. Acetoclastic Methanosaeta were the dominant methanogens, which became more resistant to ammonia stress in the digesters with vacuum stripping.

Alleviation of ammonia inhibition via nano-bubble water supplementation during anaerobic digestion of ammonia-rich swine manure: Buffering capacity promotion and methane production enhancement

Anaerobic digestion (AD) of ammonia-rich swine manure (SM) with nano-bubble water (NBW) supplementation was studied in this work with the expectation of ammonia inhibition alleviation, buffering capacity promotion, and methane production enhancement. Results indicated that cumulative methane yield was elevated by 12.3-38.7% in NBW groups. Besides, the reduced methane production rate and elongated lag phase under ammonia inhibition were increased and shortened by NBW supplementation, respectively. The rapid increase of total alkalinity (TA) and partial alkalinity (PA) could be observed with NBW supplementation, as well as the rapid decline of VFA/TA, thus improved buffering capacity and alleviated ammonia inhibition. Moreover, higher level of extracellular hydrolases and coenzyme F₄₂₀ could be detected in NBW groups. In conclusion, NBW with higher mobility and zeta potential (absolute value) could be a promising strategy for the alleviation of ammonia suppression during the AD of SM.

The effect of mono- and multiple fermentation parameters on volatile fatty acids (VFAs) production from chicken manure via anaerobic digestion

Although the high nitrogen content of chicken manure (CM) poses major challenges for methane production through anaerobic digestion, on the bright side, it has a great potential for production of value-added intermediate products, such as volatile fatty acids (VFAs). However, in order to enhance VFAs yield, methane formation should be substantially suppressed. In the current research, individual and multiple effects of initial pH, heat-shock pretreatment, chemical methanogens inhibitor and the inoculum to substrate ratio (ISR) on optimization VFAs fermentation from CM were evaluated via batch assays. In this regard, the highest net VFAs yield, 0.53 g-VFA/g-VS, was achieved at conditions with heat-shocked inoculum and CM at ISR 1:6 and pH uncontrolled. Acetate dominated the VFAs mixture, accounting for up to 75% of total. Increased inoculum content enhanced the bioconversion efficiency to 78% at ISR 1:3. The study results suggest that alkalinity is a key promoter of VFAs production from CM.

Upgrading the anaerobic membrane bioreactor treatment of chicken manure by introducing in-situ ammonia stripping and hyper-thermophilic pretreatment

The slow hydrolysis rate and ammonia inhibition effects significantly limit the performance of anaerobic digestion (AD) of nitrogen rich wastes. An innovative two-stage AD was therefore investigated for chicken manure by combining hyper-thermophilic (70 °C) pretreatment and a anaerobic membrane bioreactor (AnMBR). An in-situ stripping unit was assembled into the AnMBR to remove the ammonium-N, thus alleviating the inhibition effects. Through the 120-day experiment, the hydraulic retention time was optimized at 15 days for AnMBR with a constant retention 4 days for pretreatment. The hydrolysis efficiency and methane yield reached 72.4% and 352 mL-CH₄/g-VS_in respectively. About 3000 mg/L ammonium-N was removed through stripping, attributing to methane yield increased by 139 mL-CH₄/g-VS_in and volatile fatty acids decreased by 2683 mg/L compared to the control. No significant fouling was observed for the membrane. Conclusively, the combined two-stage AD process may offer an alternative approach for the treatment of nitrogen rich organic waste.

Pretreatment of Animal Manure Biomass to Improve Biogas Production: A Review

The objective of this research is to present a review of the current technologies and pretreatments used in the fermentation of cow, pig and poultry manure. Pretreatment techniques were classified into physical, chemical, physicochemical, and biological groups. Various aspects of these different pretreatment approaches are discussed in this review. The advantages and disadvantages of its applicability are highlighted since the effects of pretreatments are complex and generally depend on the characteristics of the animal manure and the operational parameters. Biological pretreatments were shown to improve methane production from animal manure by 74%, chemical pretreatments by 45%, heat pretreatments by 41% and physical pretreatments by 30%. In general, pretreatments improve anaerobic digestion of the lignocellulosic content of animal manure and, therefore, increase methane yield.