Anaerobic Digestion Plants Research Articles

Logistical considerations and challenges in deploying virtual biomethane pipelines to serve on-farm biogas plants

On-farm anaerobic digestion plants served by virtual biomethane pipelines may be used in areas with no gas grid infrastructure access to improve manure (slurry) management and to produce and deliver renewable gas. A modelling analysis of a simulated virtual biomethane pipeline is presented whereby gas is collected from 100 on-farm biogas plants fed with slurry and grass silage feedstocks and delivered to a market entry point (depot). In total, 7 scenarios are presented in the analysis. In scenarios 1–4, the biogas is upgraded on-site by the digester operator, the biomethane is collected by the haulage vehicle(s) and transported to a single depot. The impact of an additional depot on vehicle routing is investigated in scenarios 5 and 6. Scenario 7 investigates the use of a mobile-upgrading and compression unit, which would allow biogas plant operators to forego the installation and operation of biogas upgrading facilities. In scenario 3 (which considers the largest capacity biomethane haulage vehicles and a single delivery depot) all 100 anaerobic digestion plants are visited over the course of one week using 4 routes, with a total aggregated distance travelled of 205 km. Scenario 7 requires a total routing distance in excess of 613 km to visit all 100 biogas plants and requires long routing times and periods of downtime at each site due to the slow upgrading speed of the mobile unit. The weekly greenhouse gas emissions due to vehicle routing from each scenario are calculated. Assuming diesel-fuelled haulage vehicles, scenario 7 routing results in 431 kg CO2-eq week−1, a 167% increase in vehicle route emissions compared to scenario 3 (161 kg CO2-eq week−1). Additionally, whilst the mobile-upgrading unit may alleviate financial challenges, they carry significant logistical challenges, and their resultant higher routing emissions will impact the sustainability of the collected biomethane. Biomethane fuelled haulage vehicles may address this concern if the biomethane is sustainably sourced.

Integration of photovoltaic panels and solar collectors into a plant producing biomethane for the transport sector: Dynamic simulation and case study

In the current energy and environmental framework, the environmental impact of the road transport sector and the urban waste management and disposal are extremely important for highly crowded cities. This work assesses the energy, economic and environmental performance of an innovative paradigm for the full decarbonisation of the road transport sector. This problem is integrated with the management of the organic fraction of municipal solid waste. In particular, the proposed technology is based on an anaerobic digestion plant coupled with a biogas upgrading unit, for the production of biomethane. In addition, photovoltaic panels and solar thermal collectors are also considered for matching electrical and thermal demands, in order to achieve a fully-renewable system. To this scope, the system also includes suitable thermal and electric storages. The economic analysis also considers specific public funding policies, currently available for this technology. This system aims to be a novel paradigm in the energy scenario of waste disposal and road transport sector refurbishment. TRNSYS software was adopted to perform an accurate dynamic simulation for a one-year operation of the system. The anaerobic digestion model is developed by the authors in MatLab and integrated in TRNSYS, for dynamic simulation purpose. Results show that the plant is almost self-sufficient due to the integration of storage systems for both the thermal and electric energy. The photovoltaic system is able to reduce by 45% the energy dependence from the grid. Energy and environmental analyses show a Primary Energy Saving of 126% and a reduction of CO2 equivalent emissions by 112%. The economic feasibility analysis shows a promising Simple Payback period of 6 years.

Use of Microbial Fuel Cells for the Treatment of Residue Effluents Discharged from an Anaerobic Digester Treating Food Wastes.

One of practical challenges in anaerobic-digestion (AD) technology is the cost-effective treatment of residue effluents containing high concentrations of organics, nitrogen and phosphorus (CNP). In order to evaluate the utility of microbial fuel cells (MFCs) for treating anaerobic-digester effluents (ADEs) and generating power from them, laboratory-scale single-chamber MFCs were filled with ADE obtained from a commercial AD plant treating food wastes and thereafter operated by routinely supplying ADE at different hydraulic residence times (HRTs, 5 to 20 days). It is shown that MFCs were able to reduce not only organics in ADE but also nitrogen and phosphorus. For instance, data demonstrated that over 50% of CNP was removed in MFCs operated at an HRT of 10 days, at which the maximum power density reached over 200 mW m-2 (based on the projected area of anode). Metabarcoding of 16S rRNA genes showed that some bacteria were specifically enriched in anode biofilms, suggesting their involvement in power generation. Our study suggests that MFCs are applicable to reducing CNP in ADEs at reasonable rates, and provides subsequent work with fundamental data useful for setting targets for further developments.

Toward the Transition of Agricultural Anaerobic Digesters into Multiproduct Biorefineries

Anaerobic digestion allows for the proper management of agro-waste, including manure. Currently, more than 18,000 anaerobic digestion plants are under operation in EU, 80% of which are employed in the rural context. Tariff schemes for power generation from biogas produced during anaerobic digestion of agricultural feedstocks in Germany, Italy and Austria are coming to an end and new approaches are needed to exploit the existing infrastructures. Digesters in the rural context can be implemented and modified to be transformed into sustainable multi-feedstock and multi-purpose biorefineries for the production of energy, nutrients, proteins, bio-chemicals such as carboxylic acids, polyesters and proteins. This paper describes how the transition of agricultural anaerobic digesters into multi-products biorefineries can be achieved and what are the potential benefits originating from the application of a pilot scale platform able to treat cow manure and other crop residues while producing volatile fatty acids, polyhydroxyalkanoates, microbial protein material, hydrogen, methane and a concentrated liquid stream rich in nitrogen, potassium and phosphorus.

Assessment of economic viability and production costs for the innovative microfiltered digestate

This paper assesses the economic viability of the production process of an innovative form of digestate known as “microfiltered digestate”, suitable for use as a fertilizer in driplines for permanent crops. A Break-Even Analysis was performed to determine the Break-Even Point which identifies the minimum quantity of products necessary to cover production costs at a certain selling price. Our results show that the production of microfiltered digestate provides positive economic viability for anaerobic digestion managers, providing them with an attractive market outlet and, at the same time, a new form of income.The experimental study was stated in Sicily, but it is replicable in any territorial context with anaerobic digestion plants. The results are in line with the principles of circular economy and are very current with reference to the use of organic fertilizers instead of chemical ones.

Enhancement of sustainable bioenergy production by valorising tomato residues: A GIS-based model

In order to increase the utilization of renewable energy sources, the biomethane production through anaerobic digestion has notably developed over the last years. Although, it is worldwide recognized, that valorising waste resources (i.e., by-products) is an opportunity to improve the efficiency rate of the agro-industrial chains, by reducing economic and environmental impact, it is necessary to support the strategic planning development of a future sustainable biomethane chain in line to circular economy. In this study, by adopting network information technologies, the importance of a strategic planning for sustainable developing biomethane sector was highlighted, since feedstocks logistic and supply phase is a key-aspect of any bioenergy project. The developed Geographic Information Systems (GIS) – methodology, that could be applied in any territorial area considering any type of biomass, allowed to define suitable locations for allocating new anaerobic digestion plants with the aim of developing a sustainable valorisation of tomato residues, by minimising the economic and environmental impacts.The achieved results provided advanced knowledge for the literature on the topic, helping to develop an operational GIS-tool for defining sustainable strategies for planning new plants, and proved that the development of integrated approach to define sustainable strategies for resource management along the whole supply chain is crucial.

Development of an artificial intelligence-based framework for biogas generation from a micro anaerobic digestion plant

Despite the advantages of the Anaerobic Digestion (AD) technology for organic waste management, low system performance in biogas production negatively affects the wide spread of this technology. This paper develops a new artificial intelligence-based framework to predict and optimise the biogas generated from a micro-AD plant. The framework comprises some main steps including data collection and imputation, recurrent neural network/ Non-Linear Autoregressive Exogenous (NARX) model, shuffled frog leaping algorithm (SFLA) optimisation model and sensitivity analysis. The suggested framework was demonstrated by its application on a real micro-AD plant in London. The NARX model was developed for predicting yielded biogas based on the feeding data over preceding days in which their lag times were fine-tuned using the SFLA. The optimal daily feeding pattern to obtain maximum biogas generation was determined using the SFLA. The results show that the developed framework can improve the productivity of biogas in optimal operation strategy by 43 % compared to business as usual and the average biogas produced can raise from 3.26 to 4.34 m3/day. The optimal feeding pattern during a four-day cycle is to feed over the last two days and thereby reducing the operational costs related to the labour for feeding the plant in the first two days. The results of the sensitivity analysis show the optimised biogas generation is strongly influenced by the content of oats and catering waste as well as the optimal allocated day for adding feed to the main digester compared to other feed variables e.g., added water and soaked liner.

Power to gas plant for the production of bio-methane: Technoeconomic optimization

In this work, a power to bio-methane plant in which the biogas is produced from an anaerobic digester plant and the hydrogen is generated by using an electrolysis unit powered by a renewable plant (photovoltaic or wind-based), is designed and sized. The plant sizing is carried out by applying a techno-economic multi-objective black box optimization approach. A numerical code, built by using the Matlab software package, is used to evaluate components sizes and to assess plant costs. This code is implemented in an optimization workflow developed in the modeFRONTIER environment. This approach allows to identify the optimal size of the plants components with the aim of maximizing the annual bio-methane producibility and minimizing its levelized cost. The results show that for a low-price electricity scenario (45 €/MWh) the minimum levelized cost of bio-methane (LCOBM), equal to 84.6 €/MWh, is obtained adopting the PV-based configuration. On the contrary, considering an high-price scenario (135 €/MWh), the minimum LCOBM is obtained for the Wind-based plant and is equal to 34.9 €/MWh.

Economic Benefit Analysis of Anaerobic Digestion System

This paper aims to clarify the conditions and specific details of data collection by establishing an economic benefit analysis model, and provide corresponding economic analysis and support for the construction of anaerobic digestion plants and PTG facilities.With the implementation of China’s dual carbon policy, energy recovery and reuse and the development and use of clean energy have become hot issues. Through the corresponding literature reading, it was found that there is a new way to generate clean energy biogas abroad, and the biogas produced is used for power generation, that is, PTG facilities. At present, PTG facilities have not been studied in the literature. In order to consider the feasibility of establishing facilities, it is necessary to analyze the economic benefits, and the profits generated by the facilities can form a virtuous circle, so as to continue to invest in the construction, maintenance and construction of other supporting facilities.Based on the collected data, the calculation is carried out, considering the cost of labor, raw materials, and maintenance, and the final calculated profit is CNY4.33 109. Although it is necessary to increase the cost of maintenance and replacement of equipment inside the facility, the costs covered in this article account for only a small part of the total revenue, and the proportion of government subsidies in the income is much smaller than the proportion of power generation revenue, so the facility has great development prospects.

Effect of different-sized bulking agents on nitrification process during food waste digestate composting

ABSTRACT Food waste digestate (FWD) disposal is a serious bottleneck in anaerobic digestion plants to achieve a circular bioeconomy. FWD could be recycled into nitrogen-rich compost; however, the co-composting process optimisation along with bulking agents is required to reduce nitrogen loss and unwanted gaseous emissions. In the present study, two different-sized bulking agents, namely, wood shaving (WS) and fine sawdust (FS), were used to investigate their impact on FWD composting performance along with the nitrogen dynamics. The mixing of FWD with different bulking agents altered the physiochemical characteristics of composting matrix and the effective composting performance was observed through reduced ammonium nitrogen and increased seed germination index during 28 days of composting. The carbon loss of 19–22% through CO2 emission indicated similar carbon mineralisation with both types of sawdust; however, the nitrogen transformation pathways were different. Only WS treatment demonstrated the nitrification process, whereas the nitrogen loss was higher with FS. A total nitrogen loss of ∼15% was observed in treatments with FS, whereas WS treatments displayed a nitrogen loss of 12%. The outcome of the present study could significantly contribute to the practical aspect of the FWD composting operation with the promotion of the bio-recycling economy.

A positive observer for the chemostat model with biogas measurement

In anaerobic digestion plants, it is often crucial to measure state variables such as the substrate or biomass densities for monitoring the process. But, this task can be very difficult to achieve because the sensors are sometimes unavailable, unreliable or very expensive. For these reasons software sensors can be sought instead, using indirect measurements. In this paper, we design a new observer for the chemostat model with the single measurement of biogas flow rate. This observer is positive and we show its adjustable convergence. Through simulations we also show its robustness under noise measurements. The key point is to construct a non-linear observer using hidden symmetries in the framework of the theory of symmetry preserving nonlinear systems. The effectiveness of the proposed methodology is shown through simulations.

Anaerobic Digestion as a Component of Circular Bioeconomy—Case Study Approach

Current and future trends in the world population lead to the continuous growth of municipal waste volumes. Only in the EU-28 approx. 86 million tons of biowaste is produced yearly. On the other hand, the recent energy crisis calls for a fast transition towards more local and renewable energy sources. Most of this stream could be recycled through anaerobic digestion (AD) to produce energy and high-quality fertilizers. This paper presents a balance of dry anaerobic digestion of municipal biowaste based on three years of system monitoring in an industrial-scale AD plant. The results indicate that the average biogas production rate of 120 Nm3/ton of fresh waste can be achieved. Biogas utilization in combined heat and power (CHP) units leads to an overall positive energy balance at significantly reduced CO2 emissions. The overall CO2 emission reduction of 25.3–26.6% was achieved, considering that biogas utilization is environmentally neutral. Moreover, biowaste conversion allows digestate production to substitute mineral fertilizers in agriculture and other applications. It is beneficial for soil protection and a broader environmental perspective.

Management of classified municipal solid waste should focus on odor pollution and ozone formation potential caused by VOCs

VOCs, generated during municipal solid waste sorting, collection, transportation and treatment, are important causes of odor pollution and ozone formation. Sampling was conducted at 11 sampling sites in Suzhou waste stream 1 (other waste from a residential quarter, a transfer station, and a landfill) and waste stream 2 (kitchen waste from a residential quarter and waste from an anaerobic digestion plant). VOC emissions were mainly from the anaerobic digestion plant (31.8 mg/m3) and transfer station (22.9 mg/m3), while the emissions from the residential quarter and landfill were relatively small (from 113 to 982 μg/m3). Based on the theoretical value of odor potential, the anaerobic digestion plant and transfer station were also major sites of odor pollution, with ethanol, limonene, p-diethylbenzene and dimethyl sulfide as priority odor pollutants in the former and limonene in the transfer station. The anaerobic digestion plant and the transfer station also contributed most of the ozone formation potential. Ethanol, limonene and acetone were the priority pollutants of ozone formation in the anaerobic digestion plant, while it was toluene in the landfill, ethanol and limonene in the transfer station, and limonene in the kitchen waste. Anaerobic digestion plants and transfer stations should become the focus for management to reduce ozone formation potential and odor pollution. The study will provide information for theoretical value odor and ozone control of MSW and has reference value for MSW treatments in other developing areas and countries.

Does anaerobic digestion really help to reduce greenhouse gas emissions? A nuanced case study based on 30 cogeneration plants in France

Anaerobic digestion (AD) is often regarded as a promising option to substitute fossil fuel by renewable energy from biomass while sequestering carbon in soils through digestate spreading. Many studies have quantified the net greenhouse gas (GHG) emissions of AD plants. However, GHG assessments are often based on system delimitation that is not always comprehensive enough, leading to incomplete GHG budgets. This is especially the case for the baseline to which AD is compared. In this paper, we propose a thorough evaluation of the net GHG emissions of 30 cogeneration plants in France compared to a detailed definition and assessment of their related baseline, the latter being mostly based on direct biomass supply to agricultural soils. GHG emissions were quantified (i) from substrate supply to AD plants until the use of the produced heat and electricity and to the agricultural use of the produced digestate for the AD scenario and (ii) from substrate supply to their application on agricultural soils for the baseline scenario. Our results showed that on average, in the French energy context, AD plants do not provide significant GHG mitigation benefits, partly because fossil fuel substitution is offset by lower carbon storage in soils compared to the baseline. However, we also found large variability among AD plants in difference in net GHG emissions between both scenarios, a third of which are effective from a GHG mitigation perspective. This variability was contributed by (i) the efficiency of soil carbon storage in the baseline; the lower it is, the more AD displays interest for mitigating GHG emissions; and (ii) the efficiency of AD management, especially emission avoidance by digestate covering, leakage control and heat recovery. Additionally, based on a sensitivity analysis, we showed that direct injection would perform better than cogeneration, and that AD would better attenuate net GHG emissions in a European energy context rather than in the highly decarbonised French context. Finally, we showed that the implementation of optimal management of AD plants could significantly improve net GHG emissions from biogas production. This study highlighted the need for careful assessment of AD based on a rigorous definition of the baseline against which AD climate mitigation performances are compared.

Modification of Dietary Fibers to Valorize the By-Products of Cereal, Fruit and Vegetable Industry-A Review on Treatment Methods.

Many by-products originating from cereal, fruit and vegetable industries contain quite high amounts of dietary fiber (DF), which play an important role in maintaining the healthy state of the human body. Nevertheless, huge proportions of these by-products are still underutilized as feed ingredients, to generate energy within an anaerobic digestion plant or even landfilled. One of the biggest hindrances in the valorization of such by-products is their very low soluble dietary fiber (SDF) to insoluble dietary fiber (IDF) ratios, impairing their nutritional functionality, palatability and technological applicability. Therefore, it is of interest to develop methods that can enhance the SDF to IDF ratio and that can be applied to the by-product streams of the food industry, enabling better valorization perspectives for human nutrition purposes. In this regard, the review paper provides an overview of existing technologies to modify the SDF to IDF ratio in by-products of the food industry by means of physical, chemical and biological treatments. For each type of treatment, available data on application examples including achieved increases in SDF contents are given. Additionally, a comparative discussion regarding the advantages and disadvantages of these methods is provided.

Assessment of the Environmental Sustainability of Municipal Solid Waste Valorization by Anaerobic Digestion and by Composting in Sri Lanka

Municipal solid waste management (MSWM) remains a major concern in Sri Lanka, and various treatment methods have been deployed. Though both composting and anaerobic digestion have been effective in environmental decontamination, there are other environmental issues that should be assessed. This study aimed to evaluate the environmental impacts of a full-scale composting plant and an anaerobic digestion plant for managing the organic fraction of municipal solid waste (OFMSW) in Sri Lanka using life cycle assessment (LCA). The results show that OFMSW composting causes unfavorable environmental impacts on damage categories such as human health (6.77 × 10−4 disability-adjusted life years (DALY) tonne-1 OFMSW), ecosystem quality (1.90 × 10−6 species.year tonne-1 OFMSW), and resource scarcity (3.66 × 10−1 United States Dollar (USD) tonne-1 OFMSW). Anaerobic digestion also leads to unfavorable impacts on human health (2.13 × 10−4 DALY tonne-1 OFMSW) and ecosystem quality (6.46 × 10−7 species.year tonne-1 OFMSW). However, the impact on resource scarcity (-3.85 × 10−2 USD tonne-1 OFMSW) was avoided due to electricity production via anaerobic digestion. Specifically, the treatment of OFMSW by anaerobic digestion resulted in a reduction by 68.3% in the total environmental load as compared to composting. It can be concluded that out of the two existing systems investigated, anaerobic digestion has a more favorable environmental impact than composting.

Agricultural biogas plants as a hub to foster circular economy and bioenergy: An assessment using substance and energy flow analysis

Today's agro-food system is typically based on linear fluxes (e.g., mineral fertilizers importation) when a circular approach should be privileged. The production of biogas as a renewable energy source and digestate as an organic fertilizer is essential for the circular economy in agriculture. This study investigates the current utilization of biomass in agricultural anaerobic digestion plants in Switzerland in terms of mass, nutrients, and energy flows to assess its contribution to the circular economy and climate change mitigation through the substitution of mineral fertilizers and fossil fuels. We quantify the system and its benefits in detail and examine potential future developments using different scenarios. Today, agricultural anaerobic digestion provides 1300 TJ/a of biogas. Our results demonstrate that the system could be largely expanded and provide ten times more biogas by 2050 while saving significant mineral fertilizer amounts (over 10 kt/a of dry mass nutrients yielding 38 kt/a of CO2 equivalent).

Long-term inhibition of chlortetracycline antibiotics on anaerobic digestion of swine manure

This study aimed to identify whether chronic effects are present in the anaerobic digestion (AD) of swine manure (SM) containing chlortetracycline (CTC), which is one of the major broad-spectrum veterinary antibiotics, and to elucidate the long-term inhibitory effects and recovery from the inhibition based on AD performance and microbial community. Two continuous-stirred tank reactors treating SM with and without CTC spiking (3 mg/L) were operated for 900 days. Due to the degradation and transformation, the total concentration including CTC's epimer and isomer in the test reactor was 1.5 mg/L. The exposure level was determined according to probabilistically estimated concentrations with uncertainties in field conditions. Until the cessation of CTC exposure on day 585, the methane generation of test reactor continuously decreased to 55 ± 17 mL/g-VS/day, 53% that of control. The methane generation and organic removal were not recovered within 300 days after the CTC exposure was stopped. During the experiment, stability parameters such as pH, total ammonium nitrogen, the composition of methane and alkalinity were the same for both reactors. The concentration and composition of VFAs in the test reactor were different with those of control but not in inhibition level. Microbial profiles revealed that reduction in bacterial diversity and changed balance in microbial species resulted in the performance downgrade under the long-term antibiotic pressure. Since it is hard to recover from the inhibition and difficult to predict the inhibition using physicochemical indicators, continuous exposure to CTC needs to be avoided for the sustainable management of AD plants treating SM.

Simultaneous removal of H2S and NH3 from raw biogas in hollow fibre membrane bioreactors

H 2 S and NH 3 are toxic, corrosive and odorous gases that often co-exist in gas streams emitted from industrial processes, including biogas produced in anaerobic digestion plants. A hollow fibre membrane bioreactor (HFMB) was tested for simultaneous biological removal of H 2 S and NH 3 from raw biogas. The HFMB achieved a removal efficiency (RE) > 99% for treating up to 1850, 915 and 1200 ppm v of H 2 S at an empty bed residence time (EBRT) of 187, 92 and 46 s, respectively. The RE of NH 3 was > 99% when the inlet NH 3 concentrations were up to 460, 355 and 750 ppm v at an EBRT of 187, 92 and 46 s, respectively. At an EBRT of 46 s, the RE of H 2 S and NH 3 was in the range of 85–97 and 73–95%, respectively, for inlet biogas laden with 1200–1700 ppm v of H 2 S and 750–1050 ppm v of NH 3 . The critical loading rates of H 2 S and NH 3 were about 150 and 40 g m −3 h −1 , respectively. S 0 (52%), SO 4 2 − (48%) and N 2 (92%) were the end products of the H 2 S and NH 3 bioconversion. Different sulfide oxidizers including aerobic (e.g. Smithella sp., Sulfuricurvum sp. and Thiomonas sp.) and anoxic (e.g. Rhodanobacter sp., Sulfuritalea sp. and Thiobacillus sp.) chemolithotrophs contributed to the H 2 S bioconversion. Aerobic (e.g. Pseudomonas sp., Stenotrophomonas sp. and Nitrosospira sp.) and Fe(III) dependent anaerobic (e.g. Clostridium_sensu_stricto_12 sp., Rhodoferax sp. and Dechloromonas sp.) ammonium oxidizers contributed to the NH 3 bioconversion. Denitrifiers including denitrifying phosphorus accumulating organisms (e.g Candidatus_Contendobacter sp.) contributed to the denitrification process. • Hydrophilic polyethersulfone HFMB simultaneously treated H 2 S and NH 3 from raw biogas. • Maximum H 2 S and NH 3 flux through membrane module was 1.94 and 0.55 g m -2 day -1 , respectively. • The critical loading rate of H 2 S and NH 3 was close to 150 and 40 g m -3 h -1 , respectively, at an EBRT of 46 s. • Outlet/inlet CH 4 ratio ( ∼ 0.99) confirmed low ( < 1%) biogas dilution in the HFMB. • Both aerobic and anoxic processes contributed to H 2 S and NH 3 bioconversion in the HFMB.

Fast and robust NIRS-based characterization of raw organic waste: Using non-linear methods to handle water effects

Fast characterization of organic waste using near infrared spectroscopy (NIRS) has been successfully developed in the last decade. However, up to now, an on-site use of this technology has been hindered by necessary sample preparation steps (freeze-drying and grinding) to avoid important water effects on NIRS. Recent research studies have shown that these effects are highly non-linear and relate both to the biochemical and physical properties of samples. To account for these complex effects, the current study compares the use of many different types of non-linear methods such as partial least squares regression (PLSR) based methods (global, clustered and local versions of PLSR), machine learning methods (support vector machines, regression trees and ensemble methods) and deep learning methods (artificial and convolutional neural networks). On an independent test data set, non-linear methods showed errors 28% lower than linear methods. The standard errors of prediction obtained for the prediction of total solids content (TS%), chemical oxygen demand (COD) and biochemical methane potential (BMP) were respectively 8%, 160 mg(O2).gTS−1 and 92 mL(CH4).gTS−1. These latter errors are similar to successful NIRS applications developed on freeze-dried samples. These findings hold great promises regarding the development of at-site and online NIRS solutions in anaerobic digestion plants.