Enhanced methane production from pig slurry with pulsed electric field pre-treatment

Influence of zero-valent iron nanoparticles on anaerobic digestion of swine manure: effects on methane yield

This study evaluated the effect of zero-valent iron nanoparticles (NZVI) on the anaerobic digestion of swine manure. A wide range of doses of NZVI was evaluated (5, 10, 15, 20, 25, 50, and 100 mgFe°/gVS). The maximum methane yield of 0.4506 L/gVSremoved was obtained with the concentration of 10 mgFe°/gVS representing an increase of 58.99% than the control system with 0.2834 L/gVSremoved, indicating that Fe° improves the methanogenic activity. However, when using doses greater than 20 mgFe°/gVS, there were decreases in the methane yield of 34.4-47.98%. Also, to observe the effect of NZVI in anaerobes was evaluated the activity in the electron transport system (ETS), where the control reactor showed an activity of 31.91 μg INTred/gVS•h, while in reactors with NZVI showed values of 39.48 μg INTred/gVS•h (10 Fe°mg/gVS), observing a stimulation of Fe° in microbial activity. However, the dose of 100 mgFe°/gVS showed the greatest decrease in methane yield (0.1474 L/gVSremoved) and a reduction in ETS was observed by 8.5% compared to the control. The effect on the composition of the volatile fatty acids was observed, where the control system obtained a maximum production of acetic acid of 639 mg/L, which was exceeded with the dose of 10 mg Fe°/gVS by 215% and a decrease of 41.15% with the inhibitory concentration of 100 mg Fe°/gVS. As a result, higher doses of NZVI affect the metabolic activity of anaerobes as well as the acetoclastic pathway causing a decrease in the methane production.

Efficient utilization of photoelectron-hole at semiconductor-microbe interface for pyridine degradation with assistance of external electric field

In this study, enhanced pyridine bio-photodegradation with assistance of electricity was achieved. Meanwhile, photoelectron-hole played a vital role in accelerating pyridine biomineralization. The significant separation of photoelectron-hole was achieved with an external electric field, which provided sufficient electron donors and acceptors for pyridine biodegradation. The enhanced electron transport system activity also revealed the full utilization of photoelectron-hole by microbes at semiconductor-microbe interface with assistance of electricity. Microbial community analysis confirmed the enrichment of functional species related to pyridine biodegradation and electron transfer. Microbial function analysis and microbial co-occurrence networks analysis indicated that upregulated functional genes and positive interactions of different species were the important reasons for enhanced pyridine bio-photodegradation with external electric field. A possible mechanism of enhanced pyridine biodegradation was proposed, i.e., more photoelectrons and holes of semiconductors were utilized by microbes to accelerate reduction and oxidation of pyridine with the assistance of electrical stimulation. The excellent performance of the photoelectrical biodegradation system showed a potential alternative for recalcitrant organic wastewater treatment.

Natural Ecuadorian zeolite: An effective ammonia adsorbent to enhance methane production from swine waste

Anaerobic digestion (AD) of swine waste allows obtaining renewable energy, biofertilizer and the reduction of environmental impacts. However, the low C:N ratio of pig manure generates high concentrations of ammonia nitrogen in the digestion process, reducing methane production. Zeolite is an effective ammonia adsorbent; thus, in this research the ammonia adsorption capacity of natural Ecuadorian zeolite was studied under different operating conditions. Subsequently, its effect on methane production from swine waste was evaluated using three doses of zeolite, 1.0, 4.0 and 8.0 g, in 1 L batch bioreactors. The results showed that the Ecuadorian natural zeolite has an adsorption capacity of around 19 mgNH₃-N gZ^-1 when using ammonium chloride solution and, an adsorption capacity between 37 and 65 mgNH₃-N gZ^-1 using swine waste. On the other hand, the addition of zeolite had a significant effect on methane production (p < 0.01). The zeolite doses that provided the highest methane production were 4.0 and 8.0 g L^-1, which led to values of 0.375 and 0.365 Nm³CH₄ kgVS^-1, compared to the values of 0.350 and 0.343 Nm³CH₄ kgVS^-1 that were obtained for the treatments without addition of zeolite and using a dose of 1.0 g L^-1, respectively. Addition of natural Ecuadorian zeolite meant not only a significant increase on methane production in the AD of swine waste, but also a better quality of the biogas with higher percentages of methane and lower concentrations of H₂S.

Life cycle inventory for an organic swine waste treatment system

The aim of this study was to analyze the efficiency of a system of treatment of organic swine waste as a management tool in the transformation of organic waste into products of value in the swine industry. The residues from the pig farm and the products obtained (compost, biol and biogas) were quantified and characterized, as were the energy used within the process and the distribution of the products. The negative impacts on the soil and adjacent river, as well as the efficiency of the compost as fertilizers and biol in grass and corn crops, were evaluated. The subsystems were: S1-slurry separation, S2-anaerobic digestion, S3-composting solid fraction of slurry, and S4-composting of dead tissues. S2 was not efficient in obtaining biol, with COD and TSS required. The process requires 31.1 kW/d of electrical energy and 3.22 L/d of diesel. The biogas (35,486.0 m³/d) is used for cooking food and heating houses, whilst the compost (82 kg/d) and biol (7.72 m³/d) replace inorganic fertilizers in crops. The system was adequate for the transformation of 38,109.0 kg/d of waste into valuable products. The biol needs further treatment time or to couple biodigesters-another treatment. The pig farm can be considered eco-efficient.

Mathematical Modeling and Experiments on Pyrolysis of Walnut Shells Using a Fixed-Bed Reactor

Pyrolysis is a low-emission and sustainable thermochemical technique used in the production of biofuels, which can be used as an alternative to fossil fuels. Understanding the kinetic characterization of biomass pyrolysis is essential for process upscaling and optimization. There is no accepted model that can predict pyrolysis kinetics over a wide range of pyrolysis conditions and biomass types. This study investigates whether or not the classical lumped kinetic model with a three-competitive reaction scheme can accurately predict the walnut shell pyrolysis product yields. The experimental data were obtained from walnut shell pyrolysis experiments at different temperatures (300–600 °C) using a fixed-bed reactor. The chosen reaction scheme was in good agreement with our experimental data for low temperatures, where the primary degradation of biomass occurred (300 and 400 °C). However, at higher temperatures, there was less agreement with the model, indicating that some other reactions may occur at such temperatures. Hence, further studies are needed to investigate the use of detailed reaction schemes to accurately predict the char, tar, and gas yields for all types of biomass pyrolysis.

Increasing the Biogas Potential of Rapeseed Straw Using Pulsed Electric Field Pre-Treatment

Due to the high availability of lignocellulosic biomass, which can be obtained from terrestrial plants, agricultural waste biomass, and the agro-food, paper or wood industries, its use for energy production by methane fermentation is economically and environmentally justified. However, due to their complex structures, lignocellulosic substrates have a low conversion factor to biogas. Therefore, scientists are still working on the development of new methods of the pre-treatment of lignocellulosic materials that will increase the biogas productivity from lignocellulosic biomass. The presented research focuses on the use of a pulsed electric field (PEF) to disintegrate rapeseed straw prior to the methane fermentation process. Scanning electron microscopy observation showed that, in the disintegrated sample, the extent of damage to the plant tissue was more severe than in the control sample. In the sample disintegrated for 7 min, the chemical oxygen demand increased from 4146 ± 75 mg/L to 4920 ± 60 mg/L. The best result was achieved with a 5-min PEF pre-treatment. The methane production reached 290.8 ± 12.1 NmL CH4/g VS, and the biogas production was 478.0 ± 27.5 NmL/g VS; it was 14% and 15% higher, respectively, compared to the control sample.

Pulsed electric field: An emerging pretreatment technology in a biogas production

This review focuses on current status of pulsed electric field (PEF) technology and its implementation in biogas production. First, basic principles of PEF and a schematic overview of typical PEF processing system were provided. Thereafter, lab- and pilot-scale PEF pretreatments of sludge with subsequent anaerobic digestion (AD) were provided. Furthermore, PEF technology, as an emerging technology for the lignocellulose (LC) pretreatment in biogas production which is still predominantly used at lab-scale, was outlined. Eventually, conclusion together with future perspectives and challenges were outlined.

Microbial fuel cell driven mineral rich wastewater treatment process for circular economy by creating virtuous cycles

The aim of this work is to study for concurrent harvesting bioelectricity and struvite mineral from mineral rich wastewater containing with nitrogen (N) and phosphorous (P) contents using MFCs and a chemical precipitation system. Whole reaction was constructed to sequentially run hybrid reactor (consisting of MFCs and struvite precipitation), gravitational sedimentation, nitrogen purging and MFCs. The MFCs generated around 6.439 ± 0.481 mA and 2.084 ± 0.310 mW as I_max and P_max, respectively under 2g/l of COD. More than 70% of C source, and around 95% of P and N sources have been removed. Struvite mineral was precipitated in the hybrid reactor after the injection of Mg²⁺ and collected in sedimentation tank. Economic feasibility and beneficial concerns were carefully investigated, and it is proposed for applications in the "decentralised treatment process" of agriculture and livestock wastewater in order to realise circular and strong economy in agriculture by creating virtuous cycles.

Waste-to-energy nexus: A sustainable development

An upsurge in global population due to speedy urbanization and industrialization is facing significant challenges such as rising energy-demand, enormous waste-generation and environmental deterioration. The waste-to-energy nexus based on the 5R principle (Reduce, Reuse, Recycle, Recovery, and Restore) is of paramount importance in solving these Gordian knots. This review essentially concentrates on latest advancements in the field of 'simultaneous waste reduction and energy production' technologies. The waste-to-energy approaches (thermal and biochemical) for energy production from the agricultural residues are comprehensively discussed in terms environmental, techno-economic, and policy analysis. The review will assess the loopholes in order to come up with more sophisticated technologies that are not only eco-friendly and cost-effective, but also socially viable. The waste-to-energy nexus as a paradigm for sustainable development of restoring waste is critically discussed considering future advancement plans and agendas of the policy-makers.

Effects of Ammonia Stripping and Other Physico-Chemical Pretreatments on Anaerobic Digestion of Swine Wastewater

In order to overcome anaerobic digestion (AD) inhibition due to the large nitrogen content of swine wastewater (SW), air stripping (AS) and other chemical and physical pretreatments were applied on raw SW before AD. The efficiency of these pretreatments on both ammonia removal—recovering ammonia salts to be used as fertilizers in agriculture—and the increase of methane production were assessed in batch tests. Since the pH, temperature, and air flow rate heavily influence AS efficiency and the composition of treated SW, these parameters were set individually or in combination. In more detail, the pH was increased from the natural value of SW to 8 or 10, temperature was increased from the room value to 40 °C, and the air flow rate was increased from zero to 5 Lair LSW−1 min−1. AS was generally more efficient at removing ammonia (up to 97%) from raw (non-treated) SW compared to the other treatments. However, the tested pretreatments were not as efficient as expected in increasing the biogas production, because the methane yields of all pretreated substrates were lower (by about 10–50%) to compared raw SW. The inhibitory effect on AD could have been due to the lack of nutrients and organic matter in the substrate (due to the excessive removal of the pretreatments), the concentration of toxic compounds (such as metal ions or furfural due to water evaporation), and an excess of alkali ions (used to increase the pH in AS). Overall, AS can be considered a sustainable process for the recovery of ammonium sulphate and the removal of other polluting compounds (e.g., organic matter) from SW. Conversely, the use of AS and other chemical and/or thermal processes tested in this study as pretreatments of SW before AD is not advised because these processes appear to reduce methane yields.

Environmental and Economic Sustainability of Swine Wastewater Treatments Using Ammonia Stripping and Anaerobic Digestion: A Short Review

One of the most promising systems to treat swine wastewater is air stripping. This system simultaneously recovers nitrogen salts, to be used as fertiliser, and reduces the organic pollutant load in the effluents of swine breeding farms. Several reviews have discussed the air stripping as a treatment for many types of industrial wastewater or nitrogen-rich digestate (the liquid effluent derived from the anaerobic digestion plants) for the stripping/recovery of nutrients. However, reviews about the use of air stripping as treatment for raw or anaerobically digested swine wastewater are not available in literature. To fill this gap, this study: (i) Summarises the experiences of air stripping for recovery of ammonium salts from both raw and digested swine wastewater; and (ii) compares air stripping efficiency under different operational conditions. Moreover, combined systems including air stripping (such as struvite crystallisation, chemical precipitation, microwave radiation) have been compared. These comparisons have shown that air stripping of raw and digested swine wastewater fits well the concept of bio-refinery, because this system allows the sustainable management of the piggery effluent by extracting value-added compounds, by-products, and/or energy from wastewater. On the other hand, air stripping of raw and digested swine wastewater has not been extensively studied and more investigations should be carried out.

Electroporation of harvest residues for enhanced biogas production in anaerobic co-digestion with dairy cow manure

The aim of this research was to develop a method for pretreatment of lignocellulose (LC) substrates (harvest residues (HR)) via electroporation (EP) for the purpose of improving the biogas production process. In addition, pretreated LC substrates were analyzed by scanning electron microscopy (SEM) and the energy balance of the total process was calculated. After the conducted pretreatment and anaerobic co-digestion with dairy cow manure (DCM), the statistical data analysis showed statistically significant differences in biogas and/or methane yield for all three LC substrates and their fractions. It was concluded that, after the pretreatment of LC substrates via EP, it is possible to improve the anaerobic co-digestion process and to achieve positive energy balance of the total process.