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Abstract Bioproducts from biomass feedstocks and organic wastes have shown great potential to address challenges across food-energy-water systems. However, bioproducts production is at an early, nascent stage that requires new inventions and cost-reducing approaches to meet market needs. Biochar, a byproduct of the pyrolysis process, derived from nutrient-rich biomass feedstocks (e.g., cattle manure and poultry litter) is one of these bioproducts that has numerous applications, such as improving soil fertility and crop productivity. This study investigates the market opportunity and sustainability benefits of converting manure to biochar on-site, using a portable refinery unit. Techno-economic and environmental impact assessments are conducted on a real case study in Twin Falls, Idaho, USA. The techno-economic analysis includes a stochastic optimization model to calculate the total cost of biochar production and distribution. The environmental study employs a life cycle assessment method to evaluate the global warming potential of manure-to-biochar production and distribution network. The total cost of biochar production from cattle manure near the feedlots is approximately $237 per metric ton, and total emission is 951 kg CO2 eq. per metric ton. The on-site operation and manure moisture content are two key parameters that can reduce biochar unit price and carbon footprint of manure management. It is concluded that converting cattle manure, using the presented strategy and process near the collection sites can address upstream and midstream sustainability challenges and stimulate the biochar industry.

Abstract This paper describes an analysis approach to assess water consumption attributed to electricity generation required to meet the demand for the entire Saudi residential building stock. In addition, the analysis aims at estimating the water consumption reduction due to cost-effective energy retrofit measures for the Saudi housing stock. The analysis estimated that the water consumed annually to generate electricity for the Saudi entire housing stock is 135 MCM representing almost 10% and 4% of the water used by the industrial sector. Moreover, it is found that both electricity generation need and associated water consumption can be reduced by 15.7% when lighting is retrofitted with low-energy fixtures and by 25.8% when high efficiency air conditioning systems are installed for all the existing Saudi housing stocks. For the housing stock located in the Central region with prevalent dry climates, replacing existing air conditioning by evaporative coolers can save 11.1 TWh/a (25.5%) in electricity consumption but increase the water consumption by 36.2 MCM/a (80.6%). A cost-benefit analysis of lighting retrofit is found to be highly cost-effective for both households and the government with payback periods of less than 1 year.

Abstract Desalination powered by renewable energy sources is an attractive solution to address the worldwide water-shortage problem without contributing significant to greenhouse gas emissions. A promising system for renewable energy desalination is the utilization of low-temperature direct contact membrane distillation (DCMD) driven by a thermal solar energy system, such as a salt-gradient solar pond (SGSP). This investigation presents the first experimental study of fresh water production in a coupled DCMD/SGSP system. The objectives of this work are to determine the experimental fresh water production rates and the energetic requirements of the different components of the system. From the laboratory results, it was found that the coupled DCMD/SGSP system treats approximately six times the water flow treated by a similar system that consisted of an air–gap membrane distillation unit driven by an SGSP. In terms of the energetic requirements, approximately 70% of the heat extracted from the SGSP was utilized to drive thermal desalination and the rest was lost in different locations of the system. In the membrane module, only half of the useful heat was actually used to transport water across the membrane and the remainder was lost by conduction in the membrane. It was also found that by reducing heat losses throughout the system would yield higher water fluxes, pointing out the need to improve the efficiency throughout the DCMD/SGSP coupled system. Therefore, further investigation of membrane properties, insulation of the system, or optimal design of the solar pond must be addressed in the future.

Abstract While the use of energy efficient absorption heat pumps has been typically limited to the high capacity commercial and industrial applications, the use of a semi-open absorption heat pump for water heating has been demonstrated to be an energy efficient alternative for residential scale applications. A semi-open absorption system uses ambient water vapor as the refrigerant in the absorber where its heat of phase change is transferred to the process water, cooling the solution in the absorber. The solution is pumped to the desorber, where by adding heat, the water vapor is released from the solution and condensed in the condenser. The heat of phase change of water vapor is transferred to process water again in the condenser. This cycle when implemented with a membrane-based absorber in a plate and frame form of heat exchanger using ionic liquids can overcome the challenges related to the system architecture of conventional absorption heat pumps like the lower efficiency at small scale, crystallization/corrosion issues with the desiccants and the high cost of hermetically sealed components. The cycle COP for such a system was previously demonstrated by Chugh et al. for high humidity conditions. In this experimental study, design improvements were made that expand the system’s applicability to more practical and standardized test conditions. With these improvements, the performance of the system was evaluated. The results presented in this study demonstrate the improved system’s viability as a heat pump water heater conforming to standard water heater test conditions. Performance was measured at a cycle thermal COP of 1.2 with a hot water delivery water temperature of 56 °C and ambient air at 19 °C and 49% RH.

To optimize methane production from bituminous coal through use of a well-studied microbial community derived from the same Illinois basin in USA, a total of 12 parameters were first evaluated by setting up 64 reactors following a 2-level factorial design. Among the 12 parameters, temperature, coal loading, particle size and ethanol were found to have statistically significant effects on methane content and yield from coal. Following screening, to identify optimal value for each significant factor, a Box-Behnken design necessitating 29 reactors was adopted. Optimal conditions provided by the Design of Expert software for the highest methane yield were: temperature, 32 °C; coal loading, 201.98 g/L; coal particle size, <73.99 μm; and ethanol at 300 mM. Under these optimum conditions, the predicted methane yield and content was 2957.4 ft3/ton (83.7 mm3/ton) and 74.2%, respectively. To confirm the predicted results, a verification experiment was conducted, where a methane yield of 2900 ft3/ton (82.1 mm3/ton) with a methane content of 70% was observed. Thus, models developed from this study can be used to predict methane content and yield from bituminous coal through biogasification ex situ.

Abstract The paper focused on the start-up and performance characterisation of a new type of microbial fuel cell (MFC), in which an algae culture was seeded in the cathodic chamber to produce the oxygen required to complete the electrochemical reactions of the MFC, thus circumventing the need for a mechanical aerator. The system did not use mediators or high cost catalysts and it can be started-up easily using a straightforward three-stage procedure. The start-up consists of the separate production of the electricity-producing microorganisms and the algae cultures (stage I), replacement of the mechanical aeration system by the algae culture (stage II) and a change in the light dosage from a continuous input to a dynamic day/night profile. The MFC was operated under a regime of 12 h light and 12 h dark and was also operated in batch and continuous substrate-feeding modes. The same cell voltage was achieved when the cathode compartment was operated with air supplied by aerators, which means that this configuration can perform as well as the traditional one. The results also show the influence of both the organic load and light irradiation on electricity production and demonstrate that this type MFC is a robust and promising technology that can be considered as a first approach to perform a lagooning wastewater treatment with microbial fuel cells.

Thermophilic co-digestion of sewage sludge with three different doses of trapped grease waste (GW) from the pre-treatment of a WWTP has been assessed in a CSTR bench-scale reactor. After adding 12% and 27% of grease waste (on COD basis), the organic loading rate increased from 2.2 to 2.3 and 2.8 kgCOD m-3 d-1 respectively, and the methane yield increased 1.2 and 2.2 times. Further GW increase (37% on COD basis) resulted in an unstable methane yield and in long chain fatty acids (LCFA) accumulation. Although this inestability, the presence of volatile fatty acids in the effluent was negligible, showing good adaptation to fats of the thermophilic biomass. Nevertheless, the presence of LCFA in the effluent worsens its dewatering properties. Specific methanogenic activity tests showed that the addition of grease waste ameliorates the acetoclastic activity in detriment of the hydrogenotrophic activity, and suggests that the tolerance to LCFA can be further enhanced by slowly increasing the addition of lipidrich materials.

Abstract The question of increasing biofuels production and the development of different biofuels production technologies has become controversial. On the one hand, production of corn-based biofuels creates a ‘food/feed vs. fuel’ tradeoff condition, along with subsequent uncertainties for both consumers and producers (farmers). On the other, advanced biofuels (from, e.g., switchgrass, miscanthus, algae), although acknowledged as environmentally friendly, are not available on a large commercial scale yet. In addition, the limited resource availability for the production of biofuels feedstocks and the question of a sustainable biofuels production are major issues impacting decision making. Most recently, climatic conditions and the 2011–2012 drought in the US have imposed new uncertainties that need to be considered in policy- making processes. By using a multi-objective optimization model, the paper presents an approach of modeling sustainable biofuels production from conventional and advanced biofuels feedstocks, under the condition of limited resources and uncertainty resulting from incomplete information or missing knowledge about the consequences of possible policy actions.