Net Energy Benefit Research Articles

Integration of biogas and liquid recirculation enhance methane production in high-solid anaerobic digestion of pig manure and rice husks

High-solid anaerobic digestion (HSAD) is a promising technology for treating livestock manure and agricultural waste; however, the wide application has been limited due to homogenization problems. This study established a novel HSAD system by integrating liquid and biogas recirculation (RBL), aiming to enhance the biogas conversion efficiency of high-solid substrates at low costs. Results showed that the highest methane yield was 357 mL/gVSadded in the novel HSAD system (RBL), 30.7 % and 251.7 % higher than those with only liquid recirculation (RL) or with no recirculation (RNo). Biogas recirculation helped enhance dissolution and degradation of organic matter, and prevented the VFAs accumulation, contributing to the enhanced methane production in the novel HSAD system. The net electric energy benefit of RBL was 301.2 kWh for treating 1-ton raw materials, suggesting the high economic feasibility of the novel HSAD system for the sustainable treatment of high-solid organic wastes.

New insight into Na+-promoted microbial electrolysis cell towards hydrogen energy recovery: Feasibility and dual mechanism in salt-containing wastewater treatment

The salt-containing wastewater treatment has become serious challenge, while conductivity and micro-ecosystem disorder severely limited microbial electrolysis cell (MEC) efficiency. In order to synchronously overcome the above bottlenecks, this study proposed an innovative Na+-promoted MEC system for efficient salt-containing wastewater treatment. The Na+ presence greatly improved conductivity to impair electric resistance, resulting in rapid electron transfer pattern towards organic degradation in anode and hydrogen synthesis in cathode. Furthermore, the selective Na+ stress triggered microbial community evolution and improved electroactive bacteria activity after salinity cultivation in MEC (0.09–0.17 mol Na+/L), which played “bacteria screening” role for salt-tolerant “electrochemical hydrogen-producing” bacteria community formation. The organic-degrading and hydrogen-producing bacteria with their assistors were tolerant to Na+ stress, which were considerably enriched into dominant microorganisms, while the unfavorable bacteria responsible for hydrogen consumption and competition were inhibited due to salinity-sensitivity. Correspondingly, the metabolic pathways for metabolism, genetic information processing and environmental information processing were improved, positively associating with organic degradation and hydrogen production. Such dual driving contributions of Na+-improved electron transfer-utilization pattern and Na+-modified microbial metabolisms boosted the organic pollutant degradation at anode to 91.34 % while improving the performance and speeds of hydrogen production by 1.57–1.70 times. The hydrogen abundance was also increased to 71.57 % in biogas. The energy efficiencies relative to external electricity and substrates were elevated by 8.80–28.44 %, the coulombic efficiency raised by 14.05 % and reached 109.72 %, suggesting the positive net energy benefits. The findings provided inspirations to the feasible application of MEC in salt-containing wastewater treatment with efficiency benefits.

Combined hydrothermal pretreatment of agricultural and forestry wastes to enhance anaerobic digestion for methane production

The dense structure and significant differences in the properties of agricultural and forestry wastes make it difficult to achieve anaerobic conversion. This study employed hydrothermal pretreatment (HTP) and combined hydrothermal pretreatment (CHTP) to enhance the anaerobic digestion (AD) performance of agricultural and forestry organic wastes. At a specific hydrothermal condition of 140℃ for 30 mins, the cumulative methane production of garden waste (GW), chicken manure (CM), duck manure (DM), and pig manure (PM) increased by 14.70%, 14.18%, 27.48%, and 21.81%, respectively. Under the same conditions, CHTP of garden waste with livestock and poultry manures showed noticeable synergistic effects, resulting in the methane production potential of garden waste mixed with chicken manure, duck manure, and pig manure increased by 28.82%, 36.59%, and 37.56%, respectively, compared with the untreated group. Metabolomic analysis showed that CHTP could significantly promote the decomposition of biomass carbohydrates, proteins, and lipids, leading to increased levels of small molecular metabolites. Analysis of microbial community diversity showed that HTP and CHTP increase the abundance of specific functional microbial communities, such as hydrolysis bacteria and methanogens, thereby promoting the anaerobic production of methane from biomass waste. Energy balance analysis shows that HTP-AD and CHTP-AD have a positive net energy benefit. This study provides an efficient CHTP technology and theoretical support for the resource utilization and energy conversion of agricultural and forestry wastes.

Mechanism of ball milling pretreatment to improve the anaerobic digestion performance and energy conversion efficiency of corn straw

In this study, the effects of ball-milling (BM) pretreatment on the anaerobic digestion (AD) performance and energy conversion efficiency of corn straw (CS) were explored. The AD testing was conducted by varying BM times (0–120 min) and TS (4–10 %). The results showed that BM pretreatment increased microbial and enzyme accessibility to the CS and facilitated the hydrolytic acidification process of AD. The peak concentration of volatile fatty acids (VFAs) (5325.69 mg/L) and chemical oxygen demand (COD) (14524 mg/L) were increased, resulting in more substrates available for methanogenic bacteria. The lag phase time was shortened (37.41–56.12 %) and the cumulative methane production was increased (45.63–104.11 %). Accelerated rate of total ammonia nitrogen (TAN) release resulted in increased buffering capacity of the digestion system. Reduced the initial density of the digestive slurry (6.91–9.58 %) and altered the water distribution (maximum increase in free water content to 70.4 %), which facilitated the agitation of the AD process. Excessive BM times (>60 min) and TS (>8%) are not recommended. The BM60-6 presented the highest volatile solids (VS) removal (78.79 %), cellulose degradation (92.07 %) and biochemical methane potential (BMP) (309.69 mL/g VS). The BM pretreatment also improved the rheological characteristics of digestive slurry and reduced the stirring power consumption of the AD process. The BM60-6 showed the largest net energy benefit (28.2101 KJ/g VS) and net residual value (0.5000), and the high energy input of the pretreatment was balanced. This discovery breaks the conventional wisdom that mechanical pretreatment is meaningless because of higher power consumption.

The Planter performance under varied seed rate and nutrient management in chickpea (<i>Cicer arietinum</i>)

A field study was carried out during winter (rabi) seasons of 2020–21 and 2021–22 at Agricultural Research Institute, Professor Jayashankar Telangana State Agricultural University, Hyderabad, Telangana to evaluate planter performance in chickpea (Cicer arietinum L.). Experiment was laid in split plot design with 4 seed rates (52, 70, 77 and 105 kg/ha) with corresponding two inter and intra row spacings (30, 40 and 7.5, 10 cm) in main plots and 7 nutrient management treatments in sub plots, viz. Absolute control, 75, 100, 125% RDF, 75% RDF + Microbial consortia (MC) – Azotobacter + Phosphorus solubilizing bacteria + Potassium releasing bacteria + Zinc solubilizing bacteria (5 kg/ha), 100% RDF + MC and 125% RDF+MC. Results revealed that miss and multiple indices were 11.31 and 10.25 and 4.89 and 4.51% for 10 cm spacing and 7.21 and 6.00 and 5.12 and 5.19% for 7.5 cm spacing during 2020–21 and 2021–22. Higher energy use efficiency (4.64), energy intensiveness (1.61 MJ/₹), net energy benefit (58106.4 MJ/ha) and energy efficiency ratio (2.37) were with 105 kg/ha seed rate and higher specific energy (8.91 MJ/ha) was with 52 kg /ha. Among nutrient management, highest energy use efficiency (4.98) and energy efficiency ratio were with absolute control while, 125% RDF + MC resulted in higher energy intensiveness (1.61 MJ/₹) and net energy benefit (54365.1 MJ/ha). Higher specific energy and agro-chemical energy ratio was with 75% RDF (7.94 MJ/ha) and 125% RDF (0.48). Among seed rate, yield (seed and haulm) and energy indices were highest with 105 kg/ ha and among nutrient management, highest yield and energy indices were with 125% RDF + MC but, on par with 100% RDF + MC and 125% RDF treatments.

Experimental performance of a full-scale solar thermal system designed to meet residential heating demands with passive solar energy

This article presents the results of a 250 day study into a novel mechanical system (called PiSCES) that increases the proportion of residential heating demands that can be met with passive solar energy. PiSCES uses hydronic floor cooling to capture excess solar gains to avoid overheating in highly glazed spaces and this extracted energy is transferred to thermal energy storage (TES) systems via a heat pump. The stored energy can then be used to supply active space heating (SH) and domestic hot water (DHW) heating demands as needed. In the current experiment, active cooling removed 54% of the passive solar gains entering the test house and, of the gains left in the conditioned spaces, 93% were able to offset active heating demands without causing overheating. The excess daytime solar gains collected by PiSCES were used towards active heating demands and resulted in modest solar fractions between 51%–54% for SH and between 30%–39% for DHW demands. The utilization of passive solar gains towards heating demands was increased from 49% to around 70% with the addition of PiSCES to manage and distribute the incoming gains. Although PiSCES, as it is currently configured, was not seen to be a net energy benefit for the test house (the system consumed more electrical energy to operate than the solar energy it was able to resupply), it is suspected that improved TES efficiency, increased TES capacity, and a modified heat pump design could significantly improve performance in future studies.

Net daily energy benefit as a criterion for enhancing the performance of an existing anaerobic digestion facility using co-digestion of available municipal waste resources

Net daily energy benefit as a criterion for enhancing the performance of an existing anaerobic digestion facility using co-digestion of available municipal waste resources

Intermittent energization improves microbial electrolysis cell-assisted thermophilic anaerobic co-digestion of food waste and spent mushroom substance

Microbial electrolysis cell-assisted thermophilic anaerobic digestion (MEC-TAD) is a promising method to improve anaerobic co-digestion efficiency; however, its application is restricted by high energy consumption. To improve the energy use efficiency of MEC-TAD, this study investigated the effect of different intermittent energization strategies on thermophilic co-digestion performance. Results revealed that an 18 h-ON/6h-OFF energization schedule resulted in the fastest electron transfer rate and the highest methane yield (364.3 mL/g VS). Mechanistic analysis revealed that 18 h-ON/6h-OFF resulted in the enrichment of electroactive microorganisms and increased abundance of enzyme-coding genes associated with energy metabolism (ntp, nuo, atp), electron transfer (pilA, nfrA2, ssuE), and the hydrogenotrophic methanogenic pathway. Finally, energy balance analysis revealed that 18 h-ON/6h-OFF had the highest net energy benefit (2.52 kJ) and energy conversion efficiency (110.76 %). Therefore, intermittent energization of MEC-TAD using an 18 h-ON/6h-OFF schedule can provide improved performance and more energy savings.

Net energy and cost benefit of phthalocyanine and heptamethine transparent photovoltaics in commercial buildings

There is a growing interest in using transparent organic photovoltaics (TOPVs) to generate on-site electricity and reduce building energy demand. This study evaluates the use of chloroaluminium phthalocyanine and heptamethine-based TOPVs in five types of commercial buildings and four climates in the U.S. The building energy demand is modeled with and without TOPVs, along with the electricity generation from the TOPVs, and the cradle to gate life-cycle cumulative energy demand to manufacture the TOPV modules on glass. The net energy benefit is positive for all five commercial buildings in all four locations meaning that more energy is produced or saved than used in manufacturing TOPVs. The energy payback times for TOPVs are less than other building integrated PV technologies. All commercial buildings save energy, cost, and greenhouse gas emissions with TOPVs, and the best applications depend on the building’s window-wall ratio, occupancy, and usage. In the future, the spectral properties of TOPVs could be tailored to save more cooling and heating energy based on the building’s structure, climate, and energy demand.

On the feasibility of precompression for direct atmospheric cryogenic carbon capture

Carbon dioxide (CO2) capture is a crucial approach to reducing greenhouse gases in the atmosphere to directly combat climate change. Major components of the technology to desublimate CO2 at cryogenic temperatures are mature and have the potential to be applied to build large Artic/Antarctic direct-air CO2 capture plants. The discussion of precompression of atmospheric air for a direct-air capture CO2 system using an attached “waste-cool” precooler is examined in this study. In this novel approach, a thermodynamic model based on psychrometric theories is evaluated to determine the required work input of the system at various inlet compression ratios and various inlet temperatures. Turbine recovery is also considered for the potential to capture waste energy. The results show that precompression integrated with a turbine recovery system does not provide a net energy benefit compared to a system with no precompression.

Life Cycle Energy and Environmental Assessment of the Thermal Insulation Improvement in Residential Buildings

The refurbishment of the building stock is a key strategy towards the achievement of the climate and energy goals of the European Union. This study aims at evaluating the energy and environmental impacts associated with retrofitting a residential apartment to improve its vertical envelope thermal insulation. Two insulation materials, stone wool and cellulose fibers, are compared. The life cycle assessment methodology is applied assuming 1 m2 of retrofitted vertical envelope as functional unit. Moreover, to estimate the net energy and environmental benefits achievable in the retrofitted scenario compared with the non-retrofitted one, a second analysis is performed in which the system boundaries are expanded to include the building operational phase, and 1 m2 of walkable floor per year is assumed as reference. The results show that the use of cellulose fibers involve lower impacts in most of the assessed categories compared to stone wool, except for abiotic resource depletion. In detail, the use of cellulose fibers allows to reduce the impact on climate change up to 20% and the consumption of primary energy up to 10%. The evaluation of the net energy and environmental benefits shows the effectiveness of the retrofit energy policies.

Life cycle energy and greenhouse gas emissions implications of using carbon fiber reinforced polymers in automotive components: Front subframe case study

Vehicle lightweighting benefits consumers through fuel savings, manufacturers through a more fuel-efficient vehicle portfolio, and the environment through reduced fossil fuel use and lower emissions. Vehicle components can be lightweighted by replacing conventional materials with alternatives such as aluminum or composites. However, lightweight materials come with their own set of environmental and economic challenges. Often, manufacturing of lightweight materials requires more energy than for conventional materials such as steel. Understanding the net energy and environmental benefits of lightweighting requires life cycle assessment with a large enough system boundary to prevent shifting of impacts and to ensure a fair comparison between different material options. Life cycle assessments of carbon fiber composite parts are hampered by substantial uncertainties in the energy needed for their production and recycling and the vehicle fuel consumption benefits. The present study addresses these deficiencies using a detailed vehicle fuel consumption model and industrially relevant carbon fiber production data and component design. The front subframe case study considered illustrates the challenges associated with achieving life cycle energy and greenhouse gas savings using carbon fiber. The base case with no powertrain resizing, secondary weight savings, or recycled carbon fiber and with 160,000 miles vehicle lifetime has no energy or emission benefits. When powertrain resizing, secondary weight savings, carbon fiber recycling, and increased vehicle lifetime travel were considered, energy and greenhouse gas benefits were found.

Bridging the Energy Benefit and POPs Emission Risk from Waste Incineration

SummaryIncineration has been the globally controversial and concerned method of solid waste disposal. Energy recovery and volume reduction are the benefits from waste incineration, but risk due to release of persistent organic pollutants is the major public concern in the world. In this study, the emission of organic pollutants including dioxins and polychlorinated naphthalenes from solid waste incineration in China was comprehensively evaluated, and a relationship between energy benefit and pollutant emission was firstly established. The results show that production of medical and industrial waste was smaller than that of municipal waste but yielded comparable or even higher emission of dioxins. The energy benefit-to-emission index for organic pollutants (EBEIOP) for evaluation of solid waste management on a local or regional scale was proposed. Significant correlations between net energy benefit and pollutant emission for provinces with higher EBEIOP values were found. Furthermore, higher EBEIOP values were associated with economic factors while lower values were influenced by emission from incineration of medical and industrial waste. We suggest that an EBEIOP value of ≥60 can serve as a reference for “profitable” solid waste management, assisting decision making during energy benefit and environmental risk assessment.

Wetting- and fouling-resistant hollow fiber membranes for dissolved methane recovery from anaerobic wastewater treatment effluents

Anaerobic wastewater treatment processes are becoming increasingly widespread due to their advantages in sludge management and net energy consumption. One major reason behind the energy benefit of the mainstream anaerobic processes is methane (CH4) production. Nevertheless, over one-third of the produced CH4 typically remains in effluent streams in dissolved form. To recover the dissolved CH4 (dCH4) from anaerobic effluents, the membrane contactor (MC) process enabled by porous membranes offers a promising way. However, membrane wetting and fouling issues hinder the practical implementation of the concept. Here we report a wetting- and fouling-resistant hollow fiber membrane that can operate with realistic anaerobic effluents. Coating of a highly porous (~85%) hollow fiber support with a conformal layer of polydimethylsiloxane (PDMS) provides resistance to wetting, but fouling persists. To tackle the fouling issue, we post-treated the uncured PDMS-coatings with PDMS-based amphiphilic copolymers with short (147 Da) or long (~1570 Da) side chains. Both types of post-treated membranes exhibited an improved performance when tested against effluent samples taken not only from an anaerobic membrane bioreactor but also from an upflow anaerobic sludge blanket (UASB) reactor. The membrane treated with the short-side-chain copolymer could sustain 7 days of continuous operation with UASB effluent with a performance loss of only ~10%. We observed that the fouling layers were much richer in proteins rather than subtances similar to humic and fulvic acids and microbial byproducts. Besides, we calculated that our wetting/fouling-resistant membranes provide a net energy benefit for the MC process (when the recovered CH4 is retrofitted to the process as fuel). Thus, our results suggest that the MC-based dCH4 recovery process is a viable alternative for industrial practices in case the demonstrated custom-designed membranes are employed.

Regional integrative benefits of converting livestock excrements to energy in China: An elaborative assessment from life cycle perspective

Livestock excrements (LEs) are important biomass, whose utilization for energy conversion can potentially ameliorate environmental problems and create economic profits. The integrative benefits contributed by LEs utilization have not been adequately explored especially from life cycle perspective. Due to different levels of husbandry development, LEs utilization in China’s provincial regions may present spatial disparity. We construct an integrated assessment model that is capable of elaborating the life cycle energy, environmental and socioeconomic benefits of utilizing LEs from commercial scale husbandry feedlots. The model is applied to 30 provincial regions in China to reveal the spatial features of the benefits. On the national level, the theoretical reserve of LEs shows an increasing trend during 2008–2017, reaching 200.36 Mt in 2017. 11.30 Mt coal-eq net energy benefits can be generated. The eutrophication potential is most significant as −9.08E+08 kg PO4-eq, accounting for 96.77% in total potential followed by the potentials of climate change, photochemical oxidation and acidification. Sichuan has the largest mitigated potentials of climate change and photochemical oxidation, and Henan has the largest mitigated potentials of eutrophication and acidification. In total 1.88 billion USD net profit and 73.06 thousand employments could be created. There overall forms a consistency among the three types of benefits spatially, with Sichuan, Yunnan, Shandong, Henan, Heilongjiang, Inner Mongolia, Hunan and Hebei more advantageous. These regions should be prioritized when deploying LEs utilization. The comprehensive benefits and their spatial features presented by this study are expected to offer better support in formulating region-specific planning regarding LEs utilization and development.

Environmental impact of cool roof paint: case-study of house retrofit in two hot islands

Cool roofs save energy and are particularly suited for low rise buildings in hot climates. This paper presents results of potential energy savings for existing houses in two islands (Sicily and Jamaica) based on validated thermal models. It also presents the lifecycle environmental impact of the cool paint focussing on both the midpoint and endpoint impact categories and compares these with thermal insulation impact. It was found that significant net energy benefits are possible in both locations by a cool roof, more pronounced in Jamaica, which has no heating demand; savings are comparable with thermal insulation reductions. The environmental impact of cool paint is lower than a variety of thermal insulation materials with the exception of water depletion potential. The main hotspots of the cool paint are the production of the polymer followed by the production of the pigment.

System Size Dependence of Hydration-Shell Occupancy and Its Implications for Assessing the Hydrophobic and Hydrophilic Contributions to Hydration.

The occupancy distribution of water molecules in the first hydration shell around a solute is intimately connected with solvent density fluctuations and is of fundamental interest in understanding hydration. The free energies to evacuate the first hydration shell around a solute and a cavity defined by the first hydration shell depend on the system size, emphasizing that the solvent density fluctuations are themselves dependent on the system size. This observation interpreted within the quasichemical theory shows that both the hydrophilic and the hydrophobic contributions to hydration depend on the system size, decreasing with increasing system size. The net hydration free energy benefits somewhat from the compensation of hydrophilic and hydrophobic contributions; nevertheless a large system appears necessary to describe correctly the balance of these contributions in the hydration of the macromolecule.

Bio-coal: A renewable and massively producible fuel from lignocellulosic biomass.

Development of renewable energy is essential to mitigating the fossil fuel shortage and climate change issues. Here, we propose to produce a new type of energy, bio-coal, via a fast pyrolysis coupled with atmospheric distillation process. The high heating values of the as-prepared bio-coals from the representative biomass are within 25.4 to 28.2 MJ kg-1, which are comparable to that of the commercial coals. Life cycle assessment further shows that the bio-coal production process could achieve net positive energy, financial, and environmental benefits. By using available biomass wastes as feedstock, China is expected to have a total bio-coal production of 402 million tons of standard coal equivalent, which is equal to 13% of national coal consumption. It would grant China an opportunity to additionally cut 738 million tons of CO2 emission by substituting an equal amount of coal with bio-coal in 2030.

Net energy and cost benefit of transparent organic solar cells in building-integrated applications

Transparent photovoltaics is a new technology that can be used in buildings applications to simultaneously save energy and produce electricity. This study evaluates the potential of transparent photovoltaic (TPV) in window and skylight applications for four cities in the United States: Detroit, Los Angeles, Phoenix and Honolulu. Building energy demand simulation, photovoltaic generation, and life cycle assessment (LCA) are combined to evaluate the net energy benefit (NEB). The use of TPV on windows is evaluated for both new windows, for which the solar cell is deposited in the interior surface of the glass pane, and for the refurbishment of existing windows, for which plastic encapsulated solar cells are placed on the interior surface of existing windows. The NEB was found to be positive for all scenarios considered, and the cradle to gate energy to manufacture a transparent organic photovoltaic module was found to be negligible. The NEB was used to calculate the energy return on investment (EROI) and the energy payback time (EPBT). Both were found to be either better or comparable to other photovoltaic technologies. For glass modules, the best EROI was 102 in Phoenix for window and 208 in Honolulu for skylights. The EPBT varied from 51 days to 1.1 years, depending on the location and type of module. The use of transparent photovoltaics in the US was found to have both environmental and cost benefits due to the combined reduction in building energy consumption and electricity production.

Elucidation of hydrodynamics and heat transfer characteristic of converging and equivalent uniform riser for dilute phase gas–solid flow

An investigation on the influence of a riser geometry on gas–solid hydrodynamics and heat transfer in dilute phase vertical pneumatic conveying system was studied using a simplified one-dimensional simulation program. Risers of equivalent uniform and converging diameters were considered for the comparative studies. The effects of riser shape on gas velocity, relative velocity, Reynolds number, pressure drop, and heat transfer coefficient is also investigated. The effect of convergence angle on total pressure drop and gas–particle heat transfer has been also studied. The significant findings of the present study shows that the converging shape of the riser enhances the gas–particle heat transfer due to higher gas–particle Reynolds number. The heat transfer coefficient and pressure drop is 0.6146W/m2 K and 415N/m2 for converging riser and 0.3938W/m2 K and 364N/m2 for uniform diameter riser. A cost estimation on the net energy benefit has been also done and found 20.67% improvement of heat recovery by solids at the expense of additional 14.02% of pumping energy by using converging riser in place of uniform diameter riser. Thus it can be revealed that the converging riser can enhance the gas–solid heat transfer and hydrodynamics parameter.