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In this paper, a recurrent high order neural observer (RHONO) for anaerobic processes is proposed. The main objective is to estimate variables of methanogenesis: biomass, substrate and inorganic carbon in a completely stirred tank reactor (CSTR). The recurrent high order neural network (RHONN) structure is based on the hyperbolic tangent as activation function. The learning algorithm is based on an extended Kalman filter (EKF). The applicability of the proposed scheme is illustrated via simulation. A validation using real data from a lab scale process is included. Thus, this observer can be successfully implemented for control purposes.

Controlling large-scale biogas fermenters needs a deep understanding of the interaction between process parameters and microbiology. Therefore, monitoring of not only critical metabolic states of the microbial community, but also relationships between sub-processes is required. Once the process is understood, manipulation, for instance, by application of a brief, intense electric field in a controlled way can increase the methane yield. The electric treatment protocols depend not only on the location within the process, but also on the composition of the raw substrate and the process temperature. Besides the direct action of the electric field, side effects like shockwaves, Joule heating, electrowetting or the generation of reactive electrode byproducts can influence the effectiveness of the treatment.

Urgent efforts and appropriate measures to utilise food waste (FW) for holistic exploitation of resources are needed. This chapter briefly reviews the global FW generation scenario among several selected high economic and low developing countries. It further highlights the common globally adopted treatment techniques, such as landfilling, composting, heat–moisture reaction, and anaerobic digestion, their challenges, and associated merits for FW treatment. This review discusses considerations for optimal resource generation from FW and highlights the selection of three conceptual routes. The first route proposes anaerobic digestion and pyrolysis, where valuable products such as biochar can serve as additives in anaerobic digestion for optimal biogas production and stabilised digestates. In addition, in the upstream coupling section, pyro-oil and syngas can be used in anaerobic digestion for biomethanation enhancement. The performance of the syngas biomethanation in anaerobic digestion reflects on hydrogen and carbon monoxide concentrations. A higher concentration of hydrogen could accelerate the carbon monoxide degradation rate and vice versa. The second route offers a direction for high water content FW valorisation via hydrothermal carbonation (HTC) combined with anaerobic digestion and vice versa to obtain hydrochar and valuable products, such as hydro-oil, high biogas, and enriched digestates. Previous studies showed that hydrochar could mitigate ammonia in anaerobic digestion and enhance methane generation compared with pyrochar. For high hydrogen syngas generation, the gasification technique coupled with anaerobic digestion was proposed for FW and associated residues in the third route, thus offering sustainability towards increased bioenergy production. This review stimulates the possibility for the development of the baseline approach on FW and associated residues in different technology (anaerobic digestion, pyrolysis, HTC, and gasification) combinations for optimal resource recovery.

Food waste (FW) management is a big challenge in China due to its huge production and the environmental problems associated with its treatment. The rapidly growing FW generation requires efficient and eco-friendly management strategies. In this chapter, the main FW treatment technologies and their application in China have been summarised. The food waste management in Shenzhen, one of the fastest-growing cities in China, has been analysed. Three industrial-scale projects of FW treatment have been discussed as examples for different technologies, including anaerobic digestion (AD), aerobic composting, and insect-based conversion. The operations of these projects, including their technologies, investment, treatment process, and challenges, have been analysed. Assessment of recovery rate and greenhouse gas emission have also been provided based on the capacity of the three FW treatment plants. AD is suitable for large-scale treatment because of its high energy recovery and low greenhouse gas emissions. FW can also be treated using aerobic composting, and its products can be used as fertilisers or for soil amendment. Insect-based conversion is a new and promising technology. Future research is needed to address some potential environmental issues, such as odour emission and digestate treatment. This review can provide practical information for the selection of FW treatment technologies.

Pretreatment equipment for food waste preparation is described at a laboratory and industrial scale. Small-scale methods include sonication, ultrasound, and microwave. The majority of industrial-scale installations rely on mechanical particle size reduction and heat treatment. Pretreatment equipment may be used not only to prepare food waste for anaerobic digestion (AD) but also to remove contaminants harmful to the AD process, enhance AD process performance, and achieve regulatory compliance: particularly in achieving product and process hygiene standards. The need for whole-life assessment of pretreatment technology is discussed, particularly in terms of energy consumption and environmental risks associated with the dispersal of plastic residues and microplastics.

In the processes of high microbiological complexity and operating extreme conditions, as thermophilic-dry anaerobic digestion, the application of specific microbiological techniques is the principal tool to accomplish the start-up and control of the equipments. The estimate of microorganisms number in mixed cultivations is very complex, since the diversity of these populations is extreme. Therefore, it is convenient to use several procedures of quantification. DAPI technique is representative of main microbial groups contained in the digester in each organic loading rate studied. While than autofluorescence microscopy technique was not representative of the total methanogenic population or specific. Therefore, the utilisation of a specific technique to determine the methanogens was necessary. FISH technique has allowed to quantify total methanogenic population or specific (H₂-utilising methanogens and acetate-utilising methanogens) by ARC915, MB1174 and MX825 probes, respectively.

Low-temperature (<20°C) anaerobic digestion is an emerging, cost-efficient technology, which has been successfully applied to a variety of high-strength hazardous and non-hazardous waste-streams. Operated at low-temperature, expanded granular sludge bed (EGSB) reactors favour the development of a methanogenic consortium adapted to high biodegradation rates. Reactor operating parameters, such as wastewater characteristics and organic loading rate, affect microbial consortium physiology and therefore could shift bacterial 16S rRNA ratios, for example by changing growth rates and/or physiological activity. Thus, as a screening tool, temporal DGGE-profiling, comparing DNA and cDNA, was employed to highlight the potentially key organisms directly involved in psychrophilic (12°C) toluene methanogenesis in a laboratory-scale EGSB bioreactor. Biomass samples were taken and analysed over a 5-day period, immediately following an imposed increase in toluene loading rate. Functionally active potential toluene-degraders were successfully characterized. The results suggested that a putatively psychrophilic Geobacter-like organism was involved in the process along with hydrogenotrophic Methanospirillum-like and acetotrophic Methanosaeta-like Archaea. The presence of additional mesophilic and thermophilic putative toluene-degraders suggested, however, that reactor operating temperature may not have been the main factor for the development of this well-established and active microbial methanogenic consortium.

This paper studies the characteristics of the emission of odor pollutants during the process of anaerobic digestion in kitchen garbage. Cold trap enrichment-gas chromatography/mass spectrometry (GC/MS) technology was used to determine the composition, material contents and source profile of typical kitchen garbage from treatment facilities in Jinan. Alkanes, olefins, aromatics, halogenated hydrocarbons, oxygen-containing organic compounds, sulfide and ammonia etc. were found in the air of the kitchen garbage treatment facilities, with oxygenated organic compounds being the main components. The main processing units, when ranked in decreasing order of odorants concentration, were as follows: temperature sterilization device, oil-water separator, anaerobic fermenter, separation equipment, unloading area. From the data, the five characteristic pollutants in the facilities were preliminarily identified as ethanol, hydrogen sulfide, dimethyl disulfide, ammonia, limonene in the unloading areas and separation equipment, ethanol, methyl mercaptan, hydrogen sulfide, dimethyl disulfide, limonene in the temperature sterilization device and oil-water separator, and ethanol, hydrogen sulfide, dimethyl disulfide, p-diethylbenzene, limonene in the anaerobic fermenter.

At present, we are facing many serious problems, such as the unreasonable primary energy structure, shortage of fossil energy, excessive energy consumption and deterioration of ecological environment in our country. In the process of seeking renewable clean alternative energy sources, Miscanthus emerges victoriously as it is a kind of ideal energy resource to solve the above problems. This paper analyses the feasibility of the anaerobic digestion mode of Miscanthus and its benefit assessment, comparing with the mode of direct combustion and gasification. For environment benefit analysis, we made a life cycle assessment (LCA) with an example of daily production of 1400 m³ biological gas of the anaerobic digestion engineering. It takes 1 MJ heat for the final product. Compared with the direct combustion mode, the CO₂ emission reduction rate is 81.1%. According to the emissions weighted calculation for environment impact potential, the environment impact load for anaerobic digestion is annual -211.3 people equivalent. In comparison, that of direct combustion is annual 144.21 people equivalent. Moreover, the investment recovery period of this system is 5.88 years; it shows the economy that it is good. In conclusion, the energy utilization mode of Miscanthus anaerobic digestion is environmentally friendly. It has great resource value, economic, environmental and social benefits, so its development and utilization has broad prospects.

In this study, an applicability of thermal pre-treatment for waste activated sludge in various total solid concentration, which are generated in a sewage treatment plant, was evaluated. The efficiency and characteristic was investigated with each sludge in various concentration after pre-treatment under the condition of 80~200℃ for 30 minutes. As the result, it was found that SCOD, NH₄⁺, VFA concentrations increased as the pre-treatment temperature increased. For COD solubilization, it was also higher dependent on increase of temperature resulting in acceleration on hydrolysis and acid fermentation. In the BMP (Biochemical Methane Potential) experiment, it showed the highest biogas production in the range of 160~180℃. In addition, the methane yield was increased around 62~85% in all concentration of sludge, and this means that thermal solubilization process applicability was appeared to be outstanding regardless of sludge concentration.

In this study, the experiment was carried out to produce methane by applying liquid recirculation system for anaerobic digestion with source sorted food waste. There were two systems and each system consisted of a bioreactor and leachate tank. Each bioreactor had a screen near the bottom of the reactor. 2.5L of separated liquid was transferred to the leachate tank for 30min each day and the liquid from the leachate tank was pumped to the bioreactor as soon as the transfer was ended. At the beginning of the experiment, food waste/inoculum anaerobic sludge volume ratio was 2:8. Feeding was conducted every two weeks. Two different food waste loading were studied. Experimental results showed that the average organic loading rates were 3.51g VS/d for System A and 3.86g VS/d for System B, respectively. The average produced methane based on food waste fed to bioreactor were observed as 6.30m3CH4/kgVS·d for system A and 4.94m3CH4/kgVS·d for System B, respectively.

The object of this research was to evaluate biodegradability of various organic waste in anaerobic digestion(AD). Slaughterhouse by-production and sludge, sewage sludge, animal manure and food waste has been used in this study. C/N ratio was used to estimate and to enhance the efficiency of AD. The highest biodegradability was appeared from food waste as 92.14%, and the lowest was shown from animal manure as 15.34%. Cattle rumen content showed highest C/N ratio (19.2), however, biodegradability was low as 34.02%.