Biogas Digester Research Articles

Experimental evaluation on the effect of biochar addition with anaerobic digestion of the tannery wastewater to improve biogas production

Abstract The use of biochar as an additive material in various compositions to the anaerobic digestion of the tannery wastewater was investigated. Pyrolytic biochar made from Khat waste with different compositions was added to anaerobic batch digesters in laboratory-scale experiments. Biogas digesters of 500 ml volume were used to explore the effects of biochar on anaerobic digestion in the ratios of 5, 10, 15, and 20% (w/w) at constant mesophilic temperature (38 °C). The results show that for five experimental tests in digesters (D0, D1, D2, D3, and D4), which contains 0, 5, 10, 15, and 20% of biochar, the cumulative methane and biogas yields were, respectively, 17.04, 41.2, 43.8, 51.6, 48.6% and 150, 520, 680, 760, 690ml. Compared to the cumulative methane production efficiency of the digester without biochar (D0), the addition of 5, 10, 15, and 20% biochar had more favorable effects and increased the efficiency by 58.6, 61.1, 66.98, and 64.94%, respectively. From these results, adding 15% of biochar to anaerobic digestion causes a three-fold increase in methane compared to the control and more positive effects than all other biochar compositions. According to this result, the right dose of biochar must be added to maximize biogas production.

Biochemical assays of intensified methane content in biogas from low-temperature processing of waste activated sludge

Anaerobic digestion (AD) is implemented as an important ‘waste to energy’ approach for converting organic-rich byproducts such as sewage sludge into biogas and nutrient-rich digestate. Sewage sludge consists of primary sludge and waste activated sludge (WAS), and low biodegradability of WAS limits methane production. This study presents the influence of the low-temperature pretreatment (LT-PT) of WAS on the efficiency of AD. Different conditions of LT-PT process were tested in terms of temperature (45 °C/50 °C/55 °C/60 °C) and exposure time (24h/48h). LT-PT caused the increase of biomethane potential, which was even 43% higher if compared with the untreated WAS; 90% of all methane production was reached between 6 and 12 day of the LT-PT process. The highest improvements were observed in samples pretreated at 55 °C and 60 °C for 48 h (198.8 ± 5.5 NmL CH4/g VS and 194.3 ± 4.2 NmL CH4/g VS, respectively). Changes in the microbial community during LT-PT of WAS showed an oxygen-driven decrease among the predominant phyla except for Firmicutes. Taxonomic diversity and numerous rare taxa with the potential for functional compensation were observed. It was also proved that AD of pretreated WAS, combined with the heat recovery, achieved a positive net energy balance (improved by over 40%) and better energy performance, than AD without LT-PT.

Water lettuce (Pistia stratiotes L.) increases biogas effluent pollutant removal efficacy and proves a positive substrate for renewable energy production.

Aquatic plants play a crucial role in nature-based wastewater treatment and provide a promising substrate for renewable energy production using anaerobic digestion (AD) technology. This study aimed to examine the contaminant removal from AD effluent by water lettuce (WL) and produce biogas from WL biomass co-digested with pig dung (PD) in a farm-scale biogas digester. The first experiment used styrofoam boxes containing husbandry AD effluent. WLs were initially arranged in 50%, 25%, 12.5%, and 0% surface coverage. Each treatment was conducted in five replicates under natural conditions. In the second experiment, WL biomass was co-digested with PD into an existing anaerobic digester to examine biogas production on a farm scale. Over 30 days, the treatment efficiency of TSS, BOD5, COD, TKN, and TP in the effluent was 93.75-97.66%, 76.63-82.56%, 76.78-82.89%, 61.75-63.75%, and 89.00-89.57%, respectively. Higher WL coverage increased the pollutant elimination potential. The WL biomass doubled after 12 days for all treatments. In the farm-scale biogas production, the biogas yield varied between 190.6 and 292.9 L kg VSadded-1. The methane content reached over 54%. WL removed AD effluent nutrients effectively through a phytoremediation system and generated significant biomass for renewable energy production in a farm-scale model.

Artefacts in Field Trial Research—Lateral Ammonia Fluxes Confound Fertiliser Plot Experiments

Agricultural ammonia (NH3) emissions can have serious environmental impacts, lower fertiliser nitrogen-use efficiencies, and cause economic losses. NH3 losses may not only occur directly from organic fertilisers such as biogas digestates when applied to crops, the crops themselves may also be a source of ammonia emissions. Wheat yields from 14 years of an organic small plot fertiliser trial fertilised with biogas digestate were analysed to determine if there was significant lateral N transfer between plots. A simple NH3 loss/gain model was developed to calculate possible N gains and losses via NH3 volatilisation from the applied digestate. This model was tested using NH3 volatilisation measurements. In addition, 15N isotope measurements of crop biomass were used to analyse plant N uptake. While digestate fertilisation increased wheat yields, yield patterns indicated that NH3 emissions from plots fertilised with biogas digestate affected yields in neighbouring unfertilised plots. Measurements of ammonia losses and gains in the field validated our modelling results, showing that 55% of digestate NH4+-N was volatilised. 15N isotope analysis indicated that crops took up as much as 30 kg ha−1 NH3-N volatilised from digestate, and that plots closer to fertilised plots took up more of this NH3-N than crops further away from fertilised plots. Our results imply that neither the results from the fertilised plots nor from the unfertilised plots are without bias. To avoid inadvertently introducing artefacts into fertiliser field trials, plot sizes need to be increased and treatments situated further apart.

Anaerobic mono and co-digestion of agro-industrial waste and municipal sewage sludge: Biogas production potential, kinetic modelling, and digestate characteristics

Lignocellulosic substrates, including wastes generated from agro-industrial activities, are bio-residues evaluated to put an end to the energy needs and sustainable waste disposal problems that the world is trying to deal with today. However, the slow rate of hydrolysis of such lignocellulosic wastes limits the biogas production efficiency with the mono-anaerobic digestion (AD) process. Therefore, anaerobic co-digestion (AnCoD) of such wastes with secondary raw materials rich in microorganisms and various nutrients, such as sewage sludge, is an economical and useful method for both enhancing biogas production and disposal of more waste. In this study, AD and AnCoD processes for biogas and methane production were investigated on okra waste (OW) and municipal sewage sludge (MSS) by using cattle manure as inoculation, which constitutes only 8% of the total working volume. Five different substrate mixing ratios (100%OW, 75%OW-25%MSS, 50%OW-50%MSS, 25%OW-75%MSS, and 100MSS%) were prepared to observe the effect of C/N ratio, maximum biogas production potential, methane content, and organic matter removal efficiency on AD and AnCoD processes. All bioreactors were operated in a batch process with 8% TS in mesophilic temperature for 25 days. The amount of biogas produced in the 100%OW experimental set for the AD process was 44% more than 100%MSS. However, the AnCoD process was more efficient than AD, and biogas and methane production increased by up to 66% and 112%, respectively, compared to the mono-substrate experimental set. The highest biogas production value was 1060 mL (375 mL/gVSremoved) with 60% methane content in the bioreactor consisting of 25%OW-75%MSS. As a result of AD and AnCoD process, soluble carbohydrate, protein and COD removal for all bioreactors were between 62% and 79%, 28%-68% and 54%-70%, respectively. The FT-IR peaks seen in digestates were consistent with the presence of functional groups formed as a result of AnCoD. Monod, Cone, Transference function, and Logistic function kinetic models were used for the estimation of cumulative biogas production efficiency. In addition, the energy potential of the methane produced as a result of the AD and AnCoD processes and the financial gain that can be obtained from its direct sale were evaluated.

Positioning a Measurement System for Determining the Mixing Quality in Biogas Digesters

AbstractMixing quality in agricultural biogas plants is crucial for nutrition supply to the microorganisms and needs to be ensured by an energy‐efficient mixing strategy. Various approaches have been proposed to determine the mixing quality in biogas digesters. Among them are magnetic‐inductive or force sensors brought into vertical digesters through the concrete wall. This article presents an approach to locating these sensors effectively around the circumference of the digester to avoid positioning in dead zones and maximize information quality regarding flow and mixing behavior. Particle image velocimetry is used to measure flow fields in a transparent model digester. Finally, optimum measurement locations considering three widely used agitator geometries are suggested.

Effects of Substrate and Processing Conditions on Nematode Suppressiveness of Anaerobic Biogas Digestates

Biogas digestates produced from anaerobically processed food or dairy manure have demonstrated some potential to suppress different pathogens and pests. In this study, digestates from these two substrates processed mesophilically (20 to 40°C) or thermophilically (>40°C) were compared for their nematode-suppressive potential. In bioassays, the suppressive potential of Heterodera schachtii or Meloidogyne incognita was tested at different amendment rates. Testing was expanded to field microplot experiments with M. incognita and greenhouse tests with Pratylenchus vulnus. In the bioassay with H. schachtii, fewer nematodes penetrated radish roots after amendment with thermophilic than with mesophilic digestates. Root penetration was lowest after treatment with digestates of food waste and thermophilic dairy manure at the highest rate. In a watermelon bioassay with M. incognita, nematode-induced galling and egg mass production were reduced after amendment with food waste digestates compared with manure digestates and after thermophilic compared with mesophilic digestates in the case of egg masses. In a greenhouse experiment with peach rootstock ‘Nemaguard’, the numbers of P. vulnus in roots were diminished after amendment with digestates at the highest rate. In microplot experiments with bell peppers, plants initially were more vigorous after amendment with thermophilic digestates than after mesophilic digestate additions. This effect was transient and was no longer measurable at harvest. In summary, food waste digestates, especially those that were thermophilically produced, had nematode suppressive and plant growth-improving properties. These effects were not long lasting and probably need additional mitigation for practical utility. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

Renewable energy adoption and rural livelihoods in Ethiopia

AbstractThe introduction of new policies promoting decentralized energy technologies is likely to have profound effects across all the nexus activities, including agricultural production, input use, and labor allocations. Thus, this paper analyzes the potential synergies and trade‐offs created by the adoption of renewable energy technologies along the water–energy–food security nexus in Ethiopia. We use a mathematical programming‐based household model to compare the impacts of fossil‐based and renewable energy use on rural households’ livelihoods. Our findings show that only a 10% subsidy to the price of biogas digester considerably changes the energy mix of all types of households and increases the use of decentralized modern energy sources. Household crop production patterns are not changed substantially as a consequence of the biogas subsidy, despite the competition over resources between crop and energy production. Nonetheless, the subsidy policy can lead to family labor reallocation from collecting fuelwood to agricultural activities. Moreover, the biogas subsidy can improve household incomes. Specifically, the findings indicate that 10% biogas subsidy can lead to 0.93% and 3.44% increases in the net incomes of wealthier and poorer households, respectively, compared to the business‐as‐usual scenario, that is, also has a pro‐poor dimension. Sensitivity analyses are carried out and it appears among others that more subsidy of the price of biogas digester leads to an increase in the net income of the two household types. Overall, the benefits generated by the biogas subsidy in terms of increases in net household incomes outweigh the total costs of the subsidy program. The findings indicate the importance of the subsidy policy to improve rural households’ welfare.

Comparison of prediction of biogas yield in a batch mode underground fixed dome digester with cow dung

The study aimed to compare the development of an artificial neural network (ANN) and multilinear regression (MLR) model used to predict the performance of biogas in a batch-mode underground fixed dome biogas digester. In this study, 50 experimental datasets were used to assess the rate of biogas production with developed ANN and MLR models. The six variables, including solar irradiance, relative humidity, slurry temperature, biogas temperature, pH, and ambient temperature, were selected as the input parameters or predictors of the model. Therefore, the developed ANN and MLR models were used to describe the rate of biogas yield. The study found that the determination coefficient (R2) and root mean square error (RMSE) for ANN and MLR were 0.999/0.968 and 8.33 × 10−6/1.84 × 10−4, respectively. Both models were significant because of their high correlation between measured and predicted values of the biogas yield. However, the ANN performs better because of the smaller RMSE and higher R2 derived compared to the corresponding values of the MLR. The study proved that both the ANN and MLR can accurately predict the rate of biogas production but with better predictions obtained from ANN.

Characterisation and analysis on the agitation of downward pitched blade turbine in the Stirred Tank Reactor

In anaerobic digestion biogas plant industry, high-efficiency agitation system in the Continuously Stirred Tank Reactor (CSTR) is vital for encouraging mixing between substrates and bioliquids with low energy consumption. This study numerically investigated the downward pumping agitation system in an industrial CSTR test site to explore the dynamic characteristics of flow patterns with varied pitched blade turbine (PBT) design. A novel approach was developed to visually distinguish the agitation zone in the CSTR tank, which could be utilised to quantitatively assess the agitation performance and to assist the design of impeller spacing. The numerical approach would vastly improve the cost-efficiency to investigate the close connections among impeller spacing, pitched angle, and agitation intensity The pitched angle was found having more prominent effects on the shape and size of formed circulation loops in the tank. The 45-degree would be the critical pitched angle for PBT since the agitation zone would be rapidly shrunk once the configuration goes beyond this value.

Effect of Reactive and Non-Reactive Additive Treatment on the Recovery of Phosphorus from Biogas Digestate

The annual phosphate (PO43−) utilization has increased, leading to a depletion of existing sources of phosphorus (P). To overcome this, digestate as a source to recover P is being investigated. Due to the abundance of nutrients, the digestate from an agricultural biogas plant is used as fertilizer for crops. The separation of solids and liquids from the digestate by a screw press is the simplest form of concentrating, therefore, recovering PO43−. This is the most commonly employed method in existing biogas plants. However, the separation is not very efficient as only 20–30% of P is recovered in the solid phase. The goal of this study is to increase the separation efficiency and recover more P into the solid phase, in order to improve the transportability. For this, separation trials at a laboratory scale were performed for five experimental groups, with biochar and straw flour as non-reactive additives and kieserite as a reactive additive. In addition, untreated digestate was studied as a control. The control and the treatment with biochar and straw flour were carried out at 25 °C, while the treatment with kieserite was performed at 25 °C and 50 °C. The separation trails were performed at treatment times of 0 h, 1 h, 2 h, 8 h, and 20 h. The results showed that the treatment with additives had a beneficial effect on the recovery of P. It was noted that kieserite treatment at 25 °C and 50 °C bound about 61% of the total P present in the digestate to the solid phase. A sequential extraction was performed to study the effect of additives on the recovery of different P species. The results concluded that, compared to biochar and straw flour, kieserite was efficient in recovering the non-labile fractions (NaOH-P and HCl-P) of P, which act as slow-release fertilizers. This study shows that the use of additives, especially kieserite, has a positive influence on recovering P from digestate, and further research to optimize the recovery process would be beneficial.

Hybrid planktonic-biofilm cultivation of a Nordic mixed-species photosynthetic consortium: A pilot study on carbon capture and nutrient removal

Mixed-species photosynthetic consortia have several advantages over conventional microalgal monocultures, including better carbon capture, more efficient wastewater treatment, and resilience to environmental stressors. In this study, a constructed photosynthetic consortium was investigated using a hybrid cultivation approach (combined planktonic and biofilm growth) in a pilot-scale raceway pond. A blend of locally-sourced waste streams was used as growth medium; biogas digestate and aquaculture effluent. The consortium performed well in terms of carbon capture, with 80.1% and 78.6% removal of inorganic and organic carbon species, respectively, over a 42-day cultivation period. Removal of phosphate and nitrogen species was suboptimal; 46.8% of phosphate had been consumed by the end of cultivation, but just 27.9% of total nitrogen had been removed. Despite inefficient total nitrogen removal, nitrite and ammonia were almost completely depleted after 15 days. Light microscopy was employed to monitor biofilm formation and changes in biodiversity over time, which helped to elucidate the processes responsible for nutrient and carbon flux, as well as biofilm formation and interspecies associations. Understanding how different mechanisms and biological functions can be encouraged or inhibited in mixed-species consortia is imperative for tailoring consortia to industrially-relevant applications, such as carbon capture, nutrient removal, or production of biomass or specific metabolites. The present study demonstrates not only the importance of cultivating dynamic, biodiverse, and adaptable consortia instead of fragile monocultures, but also the utility in real-time monitoring of such systems, so that environmental parameters can be adjusted for optimal performance.

Evaluating the ability of green roof plants in capturing air pollutants using biogas-digestate: Exploring physiological, biochemical, and anatomical characteristics

The undeniable impact of plants in reducing air pollution and the crucial role of nutrition in improving stress tolerance in plants has brought attention to the use of eco-friendly fertilizers. The objective of the study was to investigate how Biogas-digestate (BD) can enhance the tolerance of green roof plants in capturing air pollutants. Four plant species, namely reflexed stonecrop (Sedum reflexum), blue fescue (Festuca glauca), garden mum (Chrysanthemum morifolium), and Peppermint (Mentha piperita) were planted in three urban sites in Mashhad, Iran, with different levels of air pollution. The physiological, biochemical, and morphological characteristics of the treated plants were compared to assess their ability to trap air pollutants. The results showed that the treated M. piperita at Razavi with BD, exhibited the highest level of APTI. Although it was influenced by the site conditions, the determination of the optimum API yielded same results. The F. glauca treated in Khayyam had the highest proline content, while S. reflexum at the Honarestan site had the lowest H2O2 level, without significantly affecting BD. F. glauca, S. reflexum, and M. piperita exhibited the highest levels of SOD, PPO, and GPX activity, respectively, which were significantly increased by the BD treatment. Most of the heavy elements showed increased levels with BD treatment, and M. piperita had the highest concentrations of heavy elements. The leaf surfaces of S. reflexum and M. piperita, had the highest and lowest deposition of particulate matter (PMs), respectively. Carbon and oxygen constituted the majority of PMs on the surface of leaves at all three study locations. The following ranks included the elements Si, Ca, Mg, and Al. BD, particularly in the case of S. reflexum and M. piperita, enhanced the plants' tolerance to air pollution. It is recommended to cultivate S. reflexum using BD on the green roof in polluted areas due to its superior capacity to absorb PMs and the fact that it is not edible.

Hydrothermal pretreatment of sugarcane bagasse pith for biogas production and digestate valorization to biochar

Sugarcane bagasse pith is generated as waste from bagasse-based paper industries which is still underutilized and mostly burnt as fuel in boilers. Therefore, an integrated pathway for the value-addition of the pith is explored. In the present study, hydrothermal pre-treatment of pith through response surface methodology and C/N was optimized for enhanced biogas production. At optimized conditions, a maximum biogas yield of 474.3 mL/gVS with ∼55% methane was attained with cellulose and reducing sugar of 59.2% and 3.68 g/L respectively. A severity factor of 3.8–4 was found suitable for cellulose enrichment, reducing sugar and biogas production, and at higher severity, a reduction in the above parameters was observed. Moreover, the digestate-based biochar delivered the highest biochar yield and surface area of 75.8 wt% and 254.47 m2/g respectively. This study is the first of its kind where the bagasse pith has been explored in a biorefinery approach to achieve circularity.

Inter-kingdom interactions and stability of methanogens revealed by machine-learning guided multi-omics analysis of industrial-scale biogas plants

Multi-omics analysis is a powerful tool for the detection and study of inter-kingdom interactions, such as those between bacterial and archaeal members of complex biogas-producing microbial communities. In the present study, the microbiomes of three industrial-scale biogas digesters, each fed with different substrates, were analysed using a machine-learning guided genome-centric metagenomics framework complemented with metatranscriptome data. This data permitted us to elucidate the relationship between abundant core methanogenic communities and their syntrophic bacterial partners. In total, we detected 297 high-quality, non-redundant metagenome-assembled genomes (nrMAGs). Moreover, the assembled 16 S rRNA gene profiles of these nrMAGs showed that the phylum Firmicutes possessed the highest copy number, while the representatives of the archaeal domain had the lowest. Further investigation of the three anaerobic microbial communities showed characteristic alterations over time but remained specific to each industrial-scale biogas plant. The relative abundance of various microorganisms as revealed by metagenome data was independent from corresponding metatranscriptome activity data. Archaea showed considerably higher activity than was expected from their abundance. We detected 51 nrMAGs that were present in all three biogas plant microbiomes with different abundances. The core microbiome correlated with the main chemical fermentation parameters, and no individual parameter emerged as a predominant shaper of community composition. Various interspecies H2/electron transfer mechanisms were assigned to hydrogenotrophic methanogens in the biogas plants that ran on agricultural biomass and wastewater. Analysis of metatranscriptome data revealed that methanogenesis pathways were the most active of all main metabolic pathways.

Carbon Emission Reduction Potential and Economic Valuation of Biogas at Cengkir Gading Edufarm in Boyolali

Cengkir Gading Edufarm is a cattle breeding center for livestock education and manure management purposes that focuses on creating green renewable energy. The program is supported by CSR schemes carried out by PT Pertamina Patra Niaga DPPU Adi Sumarmo. The study objective is to assess the effectiveness of biogas digester construction in Cengkir Gading in reducing carbon emissions and evaluate the reduction cost in energy used. The result showed that the digester unit could help convert cattle dung waste by installing a 30 cubic sized WWTP into biogas, the amount of cow manure being accommodated as much as ± 20 kg/day (10 kg for 2 cattle). Reduction of GHG from livestock activities by 0.0162 CO2-eq Gg/year and LPG fuel by 45.377 CO2-eq Kg/year. The potential of electrical energy converted from biogas is 6.16 kWh/day, which produces a power of 0.65 kW. This digester produces 0.8 m3 biogas/day that can be converted into heat energy of 8658 kcal/day, so it potentially saved 0.19 kg/day of LPG consumption, reduced costs for purchasing LPG gas of 1,140 IDR/day or 34,200 IDR/month, it also saves the cost of paying for electricity 249,849 IDR/ month for a 900 VA.

Plasma Treated Cattle Slurry Moderately Increases Cereal Yields

Plasma treatment offers an approach to enhance the nitrogen (N) content of livestock slurry and biogas digestate, thereby increasing the efficacy of organic fertilizers. This innovative method is used to produce nitrogen-enriched organic fertilizer (NEO) containing a double concentration of plant-available N. Over three years, we conducted a comprehensive study in 14 spring wheat and barley field trials in Norway. The primary objective was to assess and compare the cereal grain yield achieved by applying NEO to other conventional fertilizers. The NEO utilized in our research was derived from the unit developed by the Norwegian company N2 Applied. The results indicated that 120 kg N ha−1 in NEO yielded in the same range of cereal grains as 95 kg N ha−1 in mineral fertilizer. Moreover, the combination of untreated slurry and 55 kg N ha−1 in mineral fertilizer Opti-NS yielded the same as 120 kg N ha−1 in NEO. Surprisingly a combination of 12 kg N ha−1 in mineral fertilizer at sowing day and 108 kg N ha−1 in NEO at the three-leaf stage led to a higher yield in spring wheat than 120 kg N ha−1 NEO spread at sowing day in two out of three experimental years. Moreover, applying NEO directly to plants has shown no visible signs of harm. Lastly, filtering the slurry resulted in higher cereal grain yields than the untreated slurry. In conclusion, despite possessing the same N content, utilizing NEO yielded a 15–20% lower cereal grain yield than mineral fertilizer. Nonetheless, 20–30% more yield than the native amount of cattle slurry it derived. However, we have observed an unexplained loss of approximately 17% of the nitrogen in NEO, which does not translate into increased grain yield or nitrogen productivity.

Biogas from goat waste as a green energy source

Energy is one of the essential needs in the household sector. Sukasari Village in Rumpin District is one of the areas in Bogor, West Java, where some residents still use kerosene or firewood for their daily household needs. Burning kerosene or firewood will produce carbon emissions and can damage the environment. There needs to be an alternative source of clean energy that is both environmentally friendly and economical. Many goat farming operations in the Rumpin area generate waste, which has the potential to be converted into biogas and used as a source of clean energy. Based on the survey, the goats' waste is only processed into fertilizer. A solution for providing clean energy sources while utilizing goat waste is to create useful products for everyday live through training and socialization in the construction of biogas digester. Based on the activities, residents can understand the solution to providing clean energy sources through using goat manure waste and are interested in using biogas from goat manure waste for their daily household needs.

Novel Intelligent System Based on Automated Machine Learning for Multiobjective Prediction and Early Warning Guidance of Biogas Performance in Industrial-Scale Garage Dry Fermentation

Industrial-scale garage dry fermentation systems are extremely nonlinear, and traditional machine learning algorithms have low prediction accuracy. Therefore, this study presents a novel intelligent system that employs two automated machine learning (AutoML) algorithms (AutoGluon and H2O) for biogas performance prediction and Shapley additive explanation (SHAP) for interpretable analysis, along with multiobjective particle swarm optimization (MOPSO) for early warning guidance of industrial-scale garage dry fermentation. The stacked ensemble models generated by AutoGluon have the highest prediction accuracy for digester and percolate tank biogas performances. Based on the interpretable analysis, the optimal parameter combinations for the digester and percolate tank were determined in order to maximize biogas production and CH4 content. The optimal conditions for the digester involve maintaining a temperature range of 35–38 °C, implementing a daily spray time of approximately 10 min and a pressure of 1000 Pa, and utilizing a feedstock with high total solids content. Additionally, the percolate tank should be maintained at a temperature range of 35–38 °C, with a liquid level of 1500 mm, a pH range of 8.0–8.1, and a total inorganic carbon concentration greater than 13.8 g/L. The software developed based on the intelligent system was successfully validated in production for prediction and early warning, and MOPSO-recommended guidance was provided. In conclusion, the novel intelligent system described in this study could accurately predict biogas performance in industrial-scale garage dry fermentation and guide operating condition optimization, paving the way for the next generation of intelligent industrial systems.

Bioponics—An Organic Closed-Loop Soilless Cultivation System: Yields and Characteristics Compared to Hydroponics and Soil Cultivation

Sustainable food production has become increasingly important. Soilless cultivation systems offer several advantages, such as water and nutrient use efficiency, and can be implemented where traditional agriculture is impossible. Bioponic systems use locally or regionally available nutrient sources from organic waste streams (either fluid or solid) and can thus contribute to closing nutrient cycles locally. Bioponics harnesses the metabolic processes of microorganisms which release nutrients from organic matter. This study aimed to set up a bioponic system, by using biogas digestate concentrate and biochar as nutrient sources, and promoting nutrient release from the organic sources by including a biofilter in the system. The development of water quality, plant growth, and quality was monitored extensively. In addition, the influence of either the fungal biocontrol agent Trichoderma atrobrunneum or UV-C treatment of the nutrient solution on plant health and growth was investigated. Three cultivation cycles with Lactuca sativa (“HAWKING” Salanova®) in bioponic (BP), hydroponic (HP), and soil (SO) cultivation were performed. The study showed that healthy lettuces could be produced in BP systems, using a biogas digestate concentrate and biochar as nutrient sources, despite salt accumulation in the nutrient solution. In plant sap analyses, lettuces cultivated in BP systems contained less nitrate but more ammonium and chloride. The yield of the lettuces grown in the BP systems was intermediate, compared to the HP and the SO. The fungus, T. atrobrunneum, strain, T720, survived in soil and soilless cultivation systems. Compared to the HP and the SO systems, the shoot height of lettuces grown in the BP system, with the application of Trichoderma, was significantly increased. In SO systems with Trichoderma application, a significantly higher chlorophyll and flavonoid content, but significantly lower shoot height was observed. The fresh weight of lettuce roots was significantly higher in HP systems with Trichoderma treatment. Cultivating plants by using organic waste streams requires commitment and experience from producers. In BP systems, a biofilter (either within the system or externally, to increase nutrient levels) can help to rapidly convert the ammonium-rich fertilizer to plant-available nutrients. Unlike conventional HP systems, in BP systems, nutrients are released slowly over time, requiring close monitoring and adjustments. In conclusion, healthy lettuces for human consumption can be produced in BP systems, and the application of the biocontrol agent used has some beneficial influence on plant growth.