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Abstract The foam-mat drying technique is used to dry fruit syrups into powder. Literature has indicated that solar energy has not yet been used in this field. Thus, it is the object of the present work to dry the foamed syrups of different fruits in a solar energy augmented drying unit. This leads to a saving in both energy and environmental pollution. An auxiliary heater, along with a control unit, is used to ensure drying at constant temperature. Foaming is effected by suitable edible additives and in some cases a stabilizer is needed as well. New techniques concerning the concentration and neutralization of fruit syrup were reached. The drying experiments were run on orange, lemon, grapefruit, tomatoes, strawberry, guava and apple. The results showed that foaming decreased the time of drying by 30.8–41.5% in the case of direct sun drying and by 47.1–73.2% in the case of solar drying compared to the drying time of unfoamed syrup. The present study showed that the solar-augmented foam-mat drying technique proves to be of sufficient efficiency and acceptability to replace spray drying which is known to be a highly complicated and energy-consuming technique.

Abstract In rural Egypt, communities face multiple challenges such as insufficient infrastructures for waste treatment, limited access to cheap energy and poor soils fertility. A decentralized, low-tech biogas technology for combined waste treatment and energy production, anaerobic digestion can achieve many sustainable development goals and resolve many issues faced by rural communities, treating and stabilizing organic waste into high-quality biofertilizer. Household biogas units for rural communities, however, should be subjected to techno-economic assessment to confirm their feasibility and technical efficiency. Therefore, this paper conducted: (1) survey of household biogas units and agricultural crop residues in rural communities in Egypt, (2) technical study of household biogas units, and (3) financial economic study. The results can be summarized as follows: (1) complete set of technical data on biogas units were documented, (2) crop residues were mapped using GIS software, (3) financial feasibility results were discussed. The total revenues were 1716.01, 2574.02, 3432.02, and 5148.04 EUR for the household biogas unit with the capacity of 2, 3, 4, and 6 m3, respectively. It was concluded that the units available in rural Egypt are considered as profitable projects from the profitability perspectives, and the values of the profitability indicators increased as the unit size increased.

Abstract Microwave (MW) sludge pretreatment enhances anaerobic digestion in terms of organics solubilization, sludge de-waterability and biogas production. The aim here is to optimize different biogas models under MW pretreatment conditions. Biogas generated from MW pretreatment of waste activated sludge under seven different MW intensities and temperatures is measured. Four biogas mathematical models, namely Modified-Gompertz (MG), Logistic-function, Reaction-Curve (RC) and exponential-rise (ER) are optimized under the seven different cases. The tunable model parameters are estimated using the gradient-based optimization technique. The performance measure of each model for the multiple experimental cases is consistent. Results reveal that the LF and MG are better fitted with experimental data than the RC and ER models. MG proves to be the best among the tested models based on percentage error (4.5%) while the RC results in the highest errors of 16.77%. However, the MG requires high computational efforts due to number of parameters. The ER, being simple and requires less computational time and at reasonable relatively errors of 10.5% is considered the best. These findings of optimal fitted model, model parameters, and its kinetics can set the stage for large scale predictive model development for biogas generation similar to those utilized for LandGEM-USEPA.

Abstract Nowadays, microalgae are widely discussed as a promising feedstock for biodiesel production due to the legitimate concerns about the consequences of using edible oils. Selection of the most suitable microalgal species relies on several key parameters such as growth rate, lipid productivity and fatty acid profile. In the present study, different species of Scenedesmus were isolated and compared for their efficiency as biodiesel feedstocks. S. obliquus showed the highest biomass productivity of 0.102 g CDW L−1 d−1 at stationary phase. However, S. intermedius showed the highest significant lipid content of 400.9 mg g−1 CDW. Regarding lipid productivity, S. obliquus was the most lipid productive strain at stationary phase with up to 24.94 mg L−1 d−1, representing 23.9% significant increase over that of S. intermedius. In addition, cetane number and iodine value of S. obliquus FAMEs were 54.12 and 110.37 g I2/100 g, respectively. Moreover, FAMEs of S. obliquus showed kinematic viscosity and specific gravity of 1.9–6.0 mm2 s−1 and 0.88 g cm−3, respectively, which are in accordance with the international standards. Among the different studied species of Scenedesmus, the present study nominated S. obliquus as a promising renewable feedstock for biodiesel production.

In the case of a supply system based on solar energy, there are problems in determining in advance the amount of generated power. A real-time control is necessary to track the maximum power generated and to perform the load balance in order not to overload the system. In this paper, a photovoltaic generation system in a newly developed remote area is presented. The electric energy generated covers the water pumping energy for irrigation and household purposes and the energy needs of the population. The control of the whole system is carried out by a special-purpose computer, the programmable logic controller.

Water scarcity is a big challenge in many countries including Saudi Arabia, for which solar water desalination is a strategic goal due to the high solar intensities and the long sunshine duration. The main objective of this study is to develop a low cost and high efficiency solar water desalination device for small communities and remote areas in Saudi Arabia. The study is conducted in December 7th, 2020 (winter season) under the climatic conditions of Ha'il city (27.66 oN, 41.72 oE), Saudi Arabia. An inclined solar still was designed with a black cotton wick and a continuous saline water circulation flow via a small pump. Results showed high device performance with low freshwater production cost. The device is able to produce 3.21 L/m2day with 50.55% thermal efficiency and $0.0118/L cost of freshwater yield. Also, the device productivity is expected to be higher in the summer season. The proposed device has a significant low cost of $76.5/m2 which can be very attractive in the solar desalination market. The developed device increases the efficiency and productivity by 139.12% and 21.13%, respectively, and lowered the freshwater production cost by 57.86% compared with the device without the wick.

Abstract An experimental work is presented on comparing the performance of passive and active single slope (SS) and double slope (DS) solar stills without and coupled with parabolic trough collector (PTC). The comparison is based on still freshwater productivity, and energy and exergy efficiencies. This work is performed at hot (summer) and cold (winter) climate conditions under meteorological conditions of upper Egypt. Results illustrate that the freshwater productivity and efficiency of the solar stills with or without PTC in summer is greater than winter. Moreover, DS still has greater freshwater productivity, energy and exergy efficiencies than SS. The maximum freshwater productivity increases by about 6% in case of using DS still with PTC (DS + PTC) instead of SS with PTC (SS + PTC). Coupling PTC with SS still rises its daily yield by 115% and 85% and its average daily energy efficiency by 38.3% and 49.1% in summer and winter, respectively. The maximum average daily energy efficiency of the DS + PTC system is 49.09% and its total efficiency is 22.96% with an increase of 16.5% and 5%, respectively compared to SS + PTC. The average daily exergy efficiency of the DS only and DS + PTC in summer increases by 3.3% and 2.6%, respectively compared to the corresponding SS.

Abstract In this paper, experimental and theoretical study of a portable apparatus for extracting water from atmospheric air is presented. The experimental water-extraction unit is designed, manufactured, and tested at the Faculty of Engineering, Mansoura University, Egypt (latitude 31.0409 N and longitude 31.3785 E). The unit extracts water from atmospheric air by using solar energy as the heating source and Calcium Chloride (CaCl2) solution as desiccant material. The unit consists of double-faced conical-finned absorber (64 cm diameter and 64 cm height), double-faced conical transparent surface (68 cm diameter and 68 cm height). The unit is provided with a telescopic stick (carrier), and base. At night, the conical absorber which is made from cloth layer impregnated with desiccant solution is exposed to atmospheric air to allow Calcium Chloride solution to absorb moisture. During daytime, the absorber is covered with the tightly-closed double-faced conical transparent surface which is exposed to solar radiation. As solar energy increases the absorber temperature, the absorbed vapor evaporates from the solution and condenses on the surface. The condensate is collected in a bottle through a hose. Radiation intensity, temperature, cover temperature, ambient temperature, and productivity are recorded at a number of different operating days year-round. The measured accumulated productivity is found to range from 0.3295 to 0.6310 kg/m2/day.

Abstract There is a growing demand for exploiting cost-effective carbon sources for mixotrophic cultivation of microalgae. Fucoidan and alginate were extracted from the brown seaweed Cystoseira trinodis and were subjected to hydrolysis using H2O, HCl, or NaOH for the mixotrophic cultivation of Dunaliella salina. The algal biomass was enhanced to 0.46 g L−1 and biomass productivity reached 41.83 mg L−1 day−1 using alkali hydrolyzed alginate, which was ∼1.6-fold higher than the values under the photoautotrophic conditions. Lipid content was increased to 21.81% w/w using alkali hydrolyzed fucoidan which was 1.78-times higher than the control. Several biodiesel quality parameters were calculated and indicated that mixotrophic cultivation enhanced the biodiesel properties. The biochemical composition showed that amino acid and insoluble and soluble protein productivities were promoted 2-3-folds in relation to the control. Similarly, glycerol and soluble carbohydrate (starch) productivities were increased ∼ 1.4-times, while insoluble carbohydrate productivity was 3.3-times higher than the control. Principal component analysis demonstrated that the starch content of D. salina was reduced in compensatory of lipid accumulation. In addition, the algal growth behavior was statistically fitted using modified logistic model which indicated that lag-phase and maximum growth rate were 0.75–3.89 day and 0.019–0.066 day−1, respectively.