Anaerobic digestion plays a crucial role in the transition toward a circular economy. Incorporating system supervision through mathematical modelling can enhance control and resilience. This study aims to assess the impact of scheduled digester maintenance on the effectiveness of modelling as a tool for monitoring and control. Data from a pilot-scale plug-flow digester were analyzed using an adapted ADM1 model. The maintenance involved halting the digester and removing sedimented solids. Model calibration indicated solid retention in the first two zones of the reactor, while the hydrolysis coefficient and biogas potential remained at 0.122 d−1 and 100.4 mL CH4/gVS, respectively. The average biogas production decreased from 156 to 109 mL/gVS pre- and post-maintenance. Simulations showed a decline in the model’s predictive accuracy after maintenance. To improve model fit, the initial conditions, solids retention, and kinetic parameters were adjusted. Optimal performance was achieved with khyd at 0.045 d−1 and B0 at 52.28 mL gVS−1, revealing an issue with the digester’s heating system. In conclusion, maintenance can significantly alter digester conditions, requiring model recalibration to maintain its effectiveness as a digital copilot for process supervision.

Accurately characterizing the substrate used in anaerobic digestion is crucial for predicting the biogas plant's performance. This issue makes particularly challenging the application of modeling in codigestion plants. In this work, a novel methodology called substrate prediction module (SPM) has been developed and tested, using virtual codigestion data. The SPM aims to estimate the inlet properties of the substrate based on the reverse application of the anaerobic digestion model n1 (ADM1). The results show that, while the SPM can estimate some properties of the substrate based on certain output parameters, there are limitations in accurately determining all required variables.

The application of organic amendments is an increasingly widespread practice, which allows fertilizing and restoring soils in a sustainable and environmentally friendly way. Improving the quality of amendments through the application of microorganisms has been a challenge in recent years. The objective of the study was to determine the effects of microalgae+compost (1:1) mixture on the yield of cauliflower (Brassica oleracea L. var. botrytis L.) plants grown in a sandy loam soil with low nutrient availability. Yields were compared with the application of compost, cattle manure and two chemical fertilizers. The treatments applied were: T1 prepared with urea (NPK 46-0-0), triple superphosphate (NPK 0-46-0) and potassium saltpeter (NPK 15-0-14); T2 commercial fertilizer (NPK 12-11-18); T3 microalgae biomass (T3); T4 compost; T5 1:1 microalgae+compost mixture; T6 cattle manure; and T0 control (no fertilization). The experiments were conducted in 30 L pots using 40 g soil per plant and 4 g N as a reference to standardize fertilizer application. The results showed that the fresh weight (FW) and dry weight (%DW) of T5 and T6 were not significantly different from those of T1 (p > 0.05), on the contrary, FW of T5 and T6 was 43.8% and 40% higher than in T2, as well as the %DW was 0.59% and 0.6% w w-1, also higher than in T2. These results suggest that the microalgae+compost mixture is an alternative fertilizer, equivalent to chemical fertilizers and manure, presenting the advantages of being more stable, sustainable, and environmentally friendly. However, further studies are needed to determine the necessary dose per cultivated plant species.

Conventional agriculture has important challenges to guarantee soil fertility and sustainable food production. Many agricultural soils in the world are degraded and multiple strategies are currently being developed to restore them. The study of beneficial soil microorganisms has attracted increasing interest due to their relevant role in sustainable agricultural development. The balance and maintenance of ecosystem services, such as biomass transformation, nutrient cycling, plant growth, and health, are directly dependent on soil microbial activity. Therefore, it is important to promote its establishment and propagation. An ancient technique that favors soil biodiversity is the production and application of compost. While numerous studies have focused on the benefits of plant cultivation, fewer studies have focused on the benefits for soil microbiota. The objective of this review was to elucidate the role of the microbiota in the composting process and its impact on soil microorganisms in agriculture. The review presents the advances in the knowledge and importance of microorganisms involved in the composting process and how compost promotes the maintenance and multiplication of beneficial microbial consortia and their ecosystem functions in agricultural soils, shifting towards a more sustainable and resilient agriculture.

Modelling in anaerobic digestion will play a crucial role as a tool for smart monitoring and supervision of the process performance and stability. By far, the Anaerobic Digestion Model No. 1 (ADM1) has been the most recognized and exploited model to represent this process. This study aims to propose simple extensions for the ADM1 model to tackle some overlooked operational and metabolic aspects. Extensions for the discontinuous feeding process, the reduction of the active working volume, the transport of the soluble compound from the bulk to the cell interior, and biomass acclimation are presented in this study. The model extensions are included by a change in the mass balance of the process in batch and continuous operation, the incorporation of a transfer equation governed by the gradient between the extra- and intra- cellular concentration, and a saturation-type function where the time has an explicit influence on the kinetic parameters, respectively. By adding minimal complexity to the existing ADM1, the incorporation of these phenomena may help to understand some underlying process issues that remain unexplained by the current model structure, broadening the scope of the model for control and monitoring industrial applications.

The agriculture and livestock industry generate waste used in anaerobic digestion to produce biogas containing methane (CH4), useful in the generation of electricity and heat. However, although biogas is mainly composed of CH4 (~65%) and CO2 (~34%), among the 1% of other compounds present is hydrogen sulphide (H2S) which deteriorates engines and power generation fuel cells that use biogas, generating a foul smell and contaminating the environment. As a solution to this, anoxic biofiltration, specifically with biotrickling filters (BTFs), stands out in terms of the elimination of H2S as it is cost-effective, efficient, and more environmentally friendly than chemical solutions. Research on the topic is uneven in terms of presenting performance markers, underestimating many microbiological indicators. Research from the last decade was analyzed (2010–2020), demonstrating that only 56% of the reviewed publications did not report microbiological analysis related to sulphur oxidising bacteria (SOB), the most important microbial group in desulphurisation BTFs. This exposes fundamental deficiencies within this type of research and difficulties in comparing performance between research works. In this review, traditional and microbiological performance markers of anoxic biofiltration to remove H2S are described. Additionally, an analysis to assess the efficiency of anoxic BTFs for biogas desulphurisation is proposed in order to have a complete and uniform assessment for research in this field.

Traditional plug-flow anaerobic reactors (PFRs) are characterized by lacking a mixing system and operating at high total solid concentrations, which limits their applicability for several kinds of manures. This paper studies the performance of a novel modified PFR for the treatment of pig manure, characterized by having an internal sludge mixing system by biogas recirculation in the range of 0.270–0.336 m3 m−3 h−1. The influence on the methane yield of four operating parameters (recirculation rate, hydraulic retention time, organic loading rate, and total solids) was evaluated by running four modified PFRs at the pilot scale in mesophilic conditions. While the previous biodegradability of organic matter by biochemical methane potential tests were between 31% and 47% with a methane yield between 125 and 184 LCH4 kgVS−1, the PFRs showed a suitable performance with organic matter degradation between 25% and 51% and a methane yield of up to 374 LCH4 kgVS−1. Operational problems such as solid stratification, foaming, or scum generation were avoided.

This study shows the implementation of the Anaerobic Digestion Model (ADM1) in an anaerobic plug-flow reactor (PFR) with two approaches based on the use of consecutive continuous stirred tank reactors (CSTR) connected in serie for considering non-ideal mixing. The two-region (TR) model splits each CSTR into two regions, while the particulate retention (PR) model adds a retention parameter. The models were calibrated and validated based on experimental data from a bench-scale reactor treating cow manure. The PFR conventional model slightly outperformed the non-ideal mixing approaches. However, the PR model showed an increase in biomass retention time treating high solid content substrate. Biogas production was not sensitive to variations of the mixing parameters. The liquid fraction content was better represented by the PR model than the PFR and TR models. The study shows how reactor modelling is useful for monitoring and supervising biogas plants.

This paper studies the application of calcium oxide (CaO), peracetic acid (PAA) and a combination of both in order to reduce lignin content and increase biogas potential of cow manure and maize straw. Changes in organic matter were mainly affected by the type of reagent use and the dosage, with minimum influence of exposure time and dilution. Changes in pH may limit the application of chemicals. Increase in biogas production with a combination of CaO and PAA, and separate application of PAA and CaO was 156.5%, 39.1% and 26.1% for cow manure and 125%, 137.5% and 37.5% for maize straw, respectively, compared to unpretreated samples. Pretreating cow manure with the aforementioned reagents does not increase the profitability of a biogas plant due mainly to the increase in operational costs from the intensive use of chemicals.

A link can be established in both the dairy and microalgae industries through the recycling of nutrients from dairy effluents (DE) in order to cultivate microalgae, using biomass on the farm or for commercial endeavors. This study assesses the development of Chlorella and Scenedesmus mixed cultures (CMC and SMC) in dairy farms using four different DE as culture media under ambient and laboratory conditions. Viability of the cultures for scaling up was determined based on biomass growth characteristics. CMC and SMC were able to grow in DE. Growth pattern was mainly affected by the type of effluent used, with almost no influence from culture conditions. CMC grew satisfactorily in effluents with high organic and ammonium loads such as cattle standing yard effluents (CSYE), reaching cell concentrations of 1.70 x 10(8) and 1.67 x 10(8) cel ml x 1 outdoors and indoors, respectively. Contrarily, SMC grew better on effluents with high chemical and detergent loads such as milking parlor effluents (MPE), reaching cell concentrations of 3.20 x 10(7) and 5.61 x 10(7) cel ml x 1 outdoors and indoors, respectively. Despite microalgal growth, there is a need of advance analysis for determining precisely nutrient reduction, since electrical conductivity could not be established as a remediation efficiency indicator. Overall, results show that there is a potential to treat DE through microalgae culture. (C) 2016 Elsevier Ltd. All rights reserved.