Anaerobic digestion of food waste with aerobic post-treatment: Effect of fruit and vegetable content

Localized mixing of anaerobic plug flow reactors

An innovative localized-mixing concept was tested in an Anaerobic Plug Flow Reactor (AnPFR) treating Food Waste (FW) mixed with municipal Wastewater (WW). The proposed concept consists of placing propellers along the shaft of the AnPFR at key points that represent the mid-region of each of the anaerobic digestion stages: hydrolysis, acidogenesis, and methanogenesis. First, the need for and efficiency of localized mixing (the new concept suggested by the authors) were investigated. While the main benefit of localized mixing is the reduction of energy demand associated with (conventional) uniform mixing (i.e., throughout the longitudinal axis), the system can also benefit from synergetic reactions in non-mixed zones. In fact, at a Total Solid (TS) content of 15% (Organic Loading Rate (OLR) of 4.2 g VS.L ^- 1.d ^- 1) and a Hydraulic Retention Time (HRT) of 28 days, the mixing pattern was sufficient to maintain stable operation, with high removal rates (up to 96% of solids) and high biogas generation (1128 ± 55 ml.g VS_fed^-1, of which 68.9% consisted of CH₄); but when mixing was halted, the system's performance deteriorated. Second, the loading capacity of the locally-mixed AnPFR was investigated by subjecting it to different TS content (10%, 15%, 20%, and 22.5%, corresponding to OLRs of 2.8, 4.2, 6.3, and 7.9 g VS.L ^- 1.d ^- 1, respectively) while operating under the same HRT. It was found that the system can adequately sustain a feed with a maximum TS of 20% while achieving removal rates up to 92% for solids and a CH₄ yield of 613 ml.g VS_fed^-1. The digester was simulated using computational fluid dynamics. The outputs revealed: (1) highest radial mixing at the center of the methanogenesis zone where the propeller is located and (2) low longitudinal mixing before and after the propeller of the methanogenesis stage, implying the presence of sedimentation zones that was visually verified. The former is assumed to favor better dispersion of inhibitors and improved stability, while the latter is expected to provide stagnant areas for enhanced biochemical synergies.

Elevated biogas production from the anaerobic co-digestion of farmhouse waste: Insight into the process performance and kinetics

The biodegradable portion of solid waste generated in farmhouses can be treated for energy recovery with small portable biogas plants. This action can be done across the Netherlands and all around the planet. This study aims to appraise the performance of anaerobic digestion of different wastes (cow manure, food waste and garden waste) obtained from a regional farmhouse. Batch reactors were established under mesophilic conditions in order to investigate the impact of ternary mixtures on the anaerobic digestion process performance. Different mixing ratios were set in the batch tests. The upshots from the experiments connoted that ternary digestion with cow manure:food waste:garden waste mixing ratio of 40:50:10 yielded higher biogas amount. The kinetics' results showed quite good congruence with the experimental study. The results from the kinetic analysis appeared to be in line with the experimental one.

A PESTLE Analysis of Biofuels Energy Industry in Europe

Biofuels production is expected to be an intrinsic confluence to the renewable energy sector in the coming years under the European regulations for renewable energy. Key standpoints of the biofuels promotions are the reduction of national carbon emissions and rural deployment. Despite jubilant outlook of biofuels for sustainable development, research efforts still tend to link the biofuel industry and regional growth. The aim of this study is to explore and review the biofuels industry through a socio-political, techno-economic, legal and environmental (PESTLE) analysis approach, and discuss the interrelation between technological facets and sustainable deployment.

Preliminary Assessment of a Biogas-based Power Plant from Organic Waste in the North Netherlands

Biogas is expected to play a crucial role in achieving the energy targets set by the European Union. Biogas, which mainly comprises methane and carbon dioxide, is produced in an anaerobic reactor, which transforms biomass into biogas. A consortium of anaerobic bacteria and archaea produces biogas during the anaerobic digestion (AD) of various types of feedstocks, such as animal slurries, energy crops, and agricultural residues. A biogas-fed gas turbine-generator and steam generator produce heat and power. In this study, a combined heat and power installation is studied. The biogas-based power plant treating cow manure, grass straw, and sugar beet pulp was examined using the software SuperPro Designer, and the obtained economic reports are evaluated. From the results, subsidy for electricity does not change the feasibility of the plants in case that cow manure or sugar beet pulp are used as feedstocks. The net present value (NPV) of biogas plants treating cow manure and sugar beet pulp was negative and the subsidy is not sufficient to make profitable these cases. The biogas power plant treating straw showed a positive net present value even without subsidy, which means that it is more desirable to invest in a plant that produces electricity and digestate from grass straw.

A Review of the Chemistry of Anaerobic Digestion: Methods of Accelerating and Optimizing Process Efficiency

The anaerobic digestion technology has been in existence for centuries and its underlying theory established for decades. It is considered a useful technology for the generation of renewable energy, and provides means to alleviate problems associated with low access to energy. However, a great deal of current research is targeted towards the optimization of this technology under diverse digestion process conditions. This review presents an in-depth analysis of the chemistry of anaerobic digestion and discusses how process chemistry can be used to optimize system performance through identification of methods that can accelerate syntrophic interactions of different microorganisms for improved methanogenic reactions. Recent advances in addition to old research are discussed in order to offer a general but comprehensive synopsis of accumulated knowledge in the theory of anaerobic digestion, as well as an overview of previous research and future directions and opportunities of the AD technology. Achieving a sustainable energy system requires comprehensive reforms in not just economic, social and policy aspects, but also in all technical aspects, which represents one of the most crucial future investments for anaerobic digestion systems.

Efficient resource valorization by co-digestion of food and vegetable waste using three stage integrated bioprocess

During two-stage (Acidogenesis-Methanogenesis) process, solid organics and gaseous by-products are usually left unused. To increase resource recovery efficiency, a three stage process (Hydrolysis/Acidogenesis-Methanogenesis-Composting) was designed. Initially, co-digestion of food waste (FW) and vegetable waste (VW) was carried out in Leach Bed Reactor (LBR) for hydrolysis and acidogenesis, followed by airlift reactor (ALR) for methanogenesis for 21 days using two different feed stocks [2:3 FW:VW~FVW; FW alone]. Off gas from LBR was diverted to ALR to enhance methane recovery. Results depicted that volatile fatty acids (VFA) and biohydrogen production was more for FW fed system, while methane production was higher in FVW fed system. Three different functional zones in three separate chambers significantly accelerated organic removal rate while gas diversion increased overall methane recovery. In third stage, residual solid organic matter from LBR was subjected to aerobic composting and compost with N (%): 2.90 & 2.76; C/N ratio: 18.2 & 20.8 for FVW and FW was recovered. The three-stage process has advantages of zero waste generation and overall process stability, accounting for resource efficient circular loop.