Reduced hydraulic retention times in low-cost tubular digesters: Two issues

Low-cost tubular digesters have been implemented in several developing countries. One of the problems reported from field surveys is that biogas generation that does not meet the user’s expectations. This report provides two reasons for the discrepancy between the biogas generation rate estimated in the design phase and the actual rate measured after construction, due to a lower final hydraulic retention time (HRT). The hydraulic retention time is normally determined from the liquid volume calculated from the cylindrical shape of the bag and not from the trench dimensions. The result is a reduction in HRT of 6%–51%, depending on the dimensions of the trench recommended by various authors. Another factor that is not normally considered is the influence of the biogas pressure on the liquid level inside the digester which negatively affects the liquid volume of the digester, reducing HRT by as much as 15%

Dynamic thermal simulation of a solar chimney with PV modules

The issue of this paper is to present theoretical results for a solar chimney with thermal mass, where the glass surface is replaced by photo-voltaic (PV) modules. A portion of the heat ab-sorbed by the PV modules is dissipated to the air channel in convective form, and it exchanges radiation heat with the concrete wall. These cooling phenomena for the PV modules im-prove their efficiency with a lower working temperature. Both phenomena are heating proc-ess to the air and the concrete wall, that produce natural ventilation. The solar chimney is sup-posed to be isolated from any building. The re-sults obtained are an average air mass flow rate around 0.02 kg/s along the day and night, and a maximum PV temperature of 321 K

Dynamic physical model for a solar chimney

The aim of this research is to investigate the theoretical usefulness of a solar chimney with thermal inertia applied to the Mediterranean climates, offering nocturnal ventilation benefits. A mathematical dynamical model is proposed to evaluate the energy performance of a solar chimney with 24 cm concrete wall as storage surface for solar radiation. The results obtained with the proposed model are coherent with several models response and experiments reported on solar chimneys. As well, the difference of the proposed model to others is the incorporation of an unsteady state and the inclusion of thermal inertia. The results show that for a 2 m height and width of air channel of 14.5 cm, 0.011 kg/s air mass flow rate is obtained for 450 W/m2. The 24 cm thickness concrete wall, reaches its greater temperature 2 h later with respect to the maximum ambient temperature, maintaining its temperature over the beginning of the night, so nocturnal ventilation is achieved. The model shows the interest in continuing investigating on this cooling techniques and to built a solar chimney with thermal inertia for future experimental research

Household anaerobic digesters for biogas production in Latin America: a review

This review aims to provide an overview of household biogas digester implementation in rural areas of Latin America. It considers the history of household digesters in Latin America, including technical, environmental, social and economic aspects. Several successful experiences have been promoted during the last decade, including the creation of the Network for Biodigesters in Latin America and the Caribbean (RedBioLAC) that provides a forum to coordinate implementation and research programmes throughout the continent. Although the potential of this technology is well demonstrated, some barriers are identified, such as the need for technical improvements, lack of social acceptance and high investment costs. Thus, further efforts should be undertaken to overcome these barriers and improve the technical performance, social acceptance, economic benefits and environmental impact in order to enhance its wide-spread dissemination in energy poor communities.Peer ReviewedPostprint (author's final draft

Fast simultaneous determination of prominent polyphenols in vegetables and fruits by reversed phase liquid chromatography using a fused-core column

A reversed-phase high-performance liquid chromatography method with photodiode array detection has been developed enabling the joint determination of 17 prominent flavonoids and phenolic acids in vegetables and fruits. A multi-segmented gradient program using a fused-core column for the separation of several phenolic classes (phenolic acids and flavonoids) has been optimised. The influence of extraction conditions (sample freeze-drying, ultrasound extraction, solvent composition and extraction time) has been also optimised using response surface methodology with tomato samples as a model. Complete recoveries (76–108%) were obtained for the phenolic compounds present in tomato. The developed method provided satisfactory repeatability in terms of peak area (RSD < 2.9%) and retention time (RSD < 0.2%) both for standards and real samples. Detection limits ranged between 3 and 44 μg kg−1 for the detected polyphenols. This method is recommended for routine analysis of large number of samples typical of production quality systems or plant breeding programs

Performance Analysis of a Small-Scale Biogas-Based Trigeneration Plant: An Absorption Refrigeration System Integrated to an Externally Fired Microturbine

Trigeneration or combined cooling, heat and power (CCHP) systems fueled by raw biogas can be an interesting alternative for supplying electricity and thermal services in remote rural areas where biogas can be produced without requiring sophisticated equipment. In this sense, this study considers a performance analysis of a novel small-scale CCHP system where a biogas-fired, 5 kWel externally fired microturbine (EFMT), an absorption refrigeration system (ARS) and heat exchangers are integrated for supplying electricity, refrigeration and hot water demanded by Bolivian small dairy farms. The CCHP solution presents two cases, current and nominal states, in which experimental and design data of the EFMT performance were considered, respectively. The primary energy/exergy rate was used as a performance indicator. The proposed cases show better energy performances than those of reference fossil fuel-based energy solutions (where energy services are produced separately) allowing savings in primary energy utilization of up to 31%. Furthermore, improvements in electric efficiency of the EFMT and coefficient of performance (COP) of the ARS, identified as key variables of the system, allow primary energy savings of up to 37%. However, to achieve these values in real conditions, more research and development of the technologies involved is required, especially for the EFM

Towards thermal design optimization of tubular digesters in cold climates: A heat transfer model

A cold climate, low cost, tubular digester is monitored and temperatures from different parts of the slurry, greenhouse, and adobe walls are presented, discussing the thermal performance of the digester. The slurry exhibits a vertical gradient of 6&nbsp;&deg;C, with a mean value of 24.5&nbsp;&deg;C, while the ambient temperature varies from 10&nbsp;&deg;C to 30&nbsp;&deg;C, showing the efficiency of the system as a solar heat collector with thermal inertia. A simple time-dependent thermal model is developed using inputs of solar radiation, wind velocity, ambient temperature, and digester geometry. The model outputs include temperatures of the slurry, the biogas, its holding membrane and the greenhouse air, wall and cover. Radiative, convective and conductive heat transfer phenomena are considered between all system elements. The model has 0.47&nbsp;&deg;C (2%) standard error for the average slurry temperature. This model can be used to predict the influence of geometry and materials on the performance of the digester

Simultaneous determination of main phenolic acids and flavonoids in tomato by micellar electrokinetic capillary electrophoresis

[EN] A methodology for the determination of tomato phenolic acids and flavonoids has been developed combining MEKC and DAD detection. The influence on polyphenol separation of pH and background electrolyte, BGE (borax, acetonitrile, methanol and SDS concentrations), was studied and optimized using response surface methodology and weighted desirability function. Separation of polyphenols was achieved within 20 min at 15 degrees C using 11.3 mM borax and 11.2 mM SDS adjusted to pH 8.5 as BGE. Validation was performed using standards and tomato extracts. Recoveries ranged from 77 to 106%. Acceptable repeatabilities were obtained for peak area (% RSD <3.1% and <3.7%) and migration times (% RSD <0.2% and <1.4%) for intra-and inter-day respectively. Detection limits ranged between 0.8 and 3.8 mg kg (1). Five and seven of these polyphenols were determined in samples of tomato and related species. This methodology will be valuable tool in breeding programs, analyzing a large number of samples. (C) 2016 Elsevier Ltd. All rights reserved.This study was partially supported by Project RTA2011-00062C04 funded by Instituto Nacional de Investigacion y Tecnologia Agraria y Alimentaria. J.M. H-M expreses his thanks to the project CTQ2014-52765-R (MINECO of Spain and FEDER).Martí-Renau, R.; Valcárcel Germes, M.; Herrero-Martínez, JM.; Cebolla Cornejo, J.; Rosello Ripolles, S. (2017). Simultaneous determination of main phenolic acids and flavonoids in tomato by micellar electrokinetic capillary electrophoresis. Food Chemistry. 221:439-446. https://doi.org/10.1016/j.foodchem.2016.10.105S43944622

Influencing factors in energy use of housing blocks: a new methodology, based on clustering and energy simulations, for decision making in energy refurbishment projects

In recent years, big efforts have been dedicated to identify which are the factors with highest influence in the energy consumption of residential buildings. These factors include aspects such as weather dependence, user behaviour, socio-economic situation, type of the energy installations and typology of buildings. The high number of factors increases the complexity of analysis and leads to a lack of confidence in the results of the energy simulation analysis. This fact grows when we move one step up and perform global analysis of blocks of buildings. The aim of this study is to report a new methodology for the assessment of the energy performance of large groups of buildings when considering the real use of energy. We combine two clustering methods, Generative Topographic Mapping and k-means, to obtain reference dwellings that can be considered as representative of the different energy patterns and energy systems of the neighbourhood. Then, simulation of energy demand and indoor temperature against the monitored comfort conditions in a short period is performed to obtain end use load disaggregation. This methodology was applied in a district at Terrassa City (Spain), and six reference dwellings were selected. Results showed that the method was able to identify the main patterns and provide occupants with feasible recommendations so that they can make required decisions at neighbourhood level. Moreover, given that the proposed method is based on the comparison with similar buildings, it could motivate building occupants to implement community improvement actions, as well as to modify their behaviour.Peer ReviewedPostprint (author's final draft

Transfer of low-cost plastic biodigester technology at household level in Bolivia

The familiar low cost biodigestores are an important tool for urban and rural development. These natural systems fulfill the criteria of appropriate technology, producing biog&aacute;s and improved natural fertilizer, through the anaerobic digestion of organic remainders. Also the health and hygiene of the families, as well as of the cattle, affect positively, being a sustainable handling environmentally of remainders that otherwise are polluting. The potential of this technology in Bolivia is very high, and once it has already been developed to cover the three different regions (Altiplane, valley and jungle), validated like development tool and accepted by the families, it is precise `to popularize the technology&#39;, so to make it accessible to the greater number of people. In this article a review to the development of the biodigestores in Bolivia, its adaptation to high altitudes, as well as the learned lessons is made, to in the end comment the first steps that already are occurring to popularize this technology