Thermal Analysis of Tilapia Fish Drying by Hybrid Solar Thermal Drying System

The present work presents a hybrid solar thermal drying of Tilapia fish to improve the product quality and satisfy the importers. The developed hybrid dryer utilized direct solar drying, a solar air heater and a thermal backup unit which sustains the drying process during the night, cloudy and rainy weather conditions. Besides, a new feature of the developed dryer utilizes the flue gas exhausted from the thermal unit to enhance the updraft in the drying chamber by re-injection of the flue gases in the chimney. The initial moisture content of the Tilapia fish used in the investigation was 246.6% on a dry basis, equivalent to 74% on a wet basis. The investigations were repeated three times on different days. Experimental results showed that the moisture content was reduced to an average final of 17.0% db (5.0% wb) within 17.5 hours, while in the open sun drying, it required around 48-72 hours. Hybrid solar drying required around 72% shorter time than open sun drying. The average overall drying efficiency of the developed system for drying Tilapia fish was 13.0%. The Re-injection technique used in the present hybrid solar-thermal system has excluded the need for an electric source for air extraction from the drying chamber, which is highly desired in the rural and fishery regions.

EFFECT OF THE CURING CONDITIONS ON THE CHARACTERISTICS OF CITROGYPSUM-CONTAINING ALKALI-ACTIVATED BINDERS

when hardening the binder system and it transforms into a consolidated conglomerate, the efficiency of the for-mation of the structural framework and the main operational characteristics of the final product dramatically de-pend on the thermal and humidity conditions of the environment medium, where the binder or raw material is con-solidated. In this study, various conditions of hardening of binders with alkaline activation of various composi-tions were studied. Based on the literature analysis, the following were chosen as the hardening conditions for the experimental alkali-activated systems: 1) - thermal drying, which was carried out in an oven at a temperature of 60°C for 24 hours; 2) hardening in ambient laboratory conditions, at a temperature of 23 ± 2°C, relative humidity - 33 ± 2%. An aqueous solution of alkali NaOH and salt Na2SiO3 were used as alkaline activators. The resulted data of the change in the average density showed that when using an alkaline activator, heat drying promotes the compaction of the hardened composite (typical for both types of the alkaline component) by 5 and 7 % for NaOH and Na2SiO3, respectively. The absence of alkaline activators in the experimental samples leads to decompaction of the structure after exposure to thermal drying and a decrease in the average density to 18%. The experimental results showed that thermal drying contributes to an increase in the strength parameters of experimental samples of an alkali-activated binder using Na2SiO3 to 110% (from 1.9 to 4 MPa). For the rest of the samples, a significant decrease in strength is observed (more than 2 times). A visual analysis of experimental samples of alkali-activated binders showed that the binders containing the addition of citrogypsum showed clear signs of efflorescence in the case of their hardening in ambient laboratory conditions. At the same time, for similar compositions from a series of samples hardened under thermal drying conditions, there is a complete absence of this phenomenon

Mass Treatment of Flooded Archival Materials by Gamma Radiation

This work describes mass recovery processes of flooded archival materials at industrial scale. The presence of fungi on paper represents a threat to the integrity of the document because they degrade cellulose, one of the main components of paper. Gamma radiation treatments are investigated as mass disinfection agents for their high penetrating power, speed of treatment, and absence of risk due to chemical residuals. We compared two different recovery processes: thermal drying followed by gamma irradiation and gamma irradiation followed by thermal drying. Both these processes were conducted simultaneously on naturally contaminated archival items and on paper specimens artificially contaminated with species test. Efficacy was assessed by culture method and ATP assay, right after the treatments and after four years of storage at room temperature. Coupling gamma irradiation with a drying step with dry heat at 55–60 °C reduces the fungal loads on natural items up to levels close to the detection limits, and the reduction is maintained after four years. On artificial specimens, spore germination is completely inhibited, mycelia growth is also highly affected, but the melanised test species appear to be more resistant. A synergistic effect between gamma irradiation, water content, and thermal drying is highlighted in this paper.

Freeze-Drying versus Heat-Drying: Effect on Protein-Based Superabsorbent Material

Porcine plasma protein is a by-product of the meat industry, which has already been applied in the manufacture of superabsorbent materials. The effects of plasticizer content (0%, 25%, 50%), together with those of the drying method (freeze-drying, thermal drying at 50 °C), during the processing of superabsorbent porcine plasma matrices were studied in this manuscript. Although the presence of glycerol accelerated the water absorption kinetics, the highest water absorption (~550%) was achieved by samples not containing any plasticizer. Viscoelasticity decreased at higher glycerol contents and especially after water absorption. When swollen samples were dried through freeze-drying, porous structures with a sponge-like appearance were obtained. Oppositely, thermally dried samples suffered an evident shrinkage that reduced porosity, displaying a more uniform surface. The effect of the drying method was observed since only freeze-dried samples can be rehydrated, displaying a superabsorbent ability (absorption higher than 1000%), which could be used in several applications (food, agriculture, personal care).

Comparison of Alum and Sulfuric Acid to Retain and Increase the Ammonium Content of Digestate Solids during Thermal Drying

Aluminum sulphate (alum, Al2(SO4)3·nH2O) has successfully been used to reduce ammonia loss from poultry litter, cattle feedlots and manure composting, but has not yet been utilized in the thermal drying process of digestate solids. The objectives of the present study were to evaluate the effects of alum addition on ammonium nitrogen (NH4+-N) content and phosphorus (P) solubility in dried digestate solids in comparison to the addition of concentrated sulfuric acid (H2SO4). Manure-based (MDS) and sewage sludge-based (SDS) digestate solids were chosen to conduct a drying experiment at four pH levels (original pH, 8.0, 7.5 and 6.5) and using two acidifying agents (alum, concentrated H2SO4). Alum addition increased the final NH4+-N content significantly from 1.4 mg g−1 in the non-acidified control up to 18 mg g−1 and 10.8 mg g−1 in dried MDS and SDS, respectively, which were higher levels than obtained with the addition of concentrated H2SO4. Moreover, alum considerably lowered the water extractable phosphorus (WEP) in raw and dried SDS by 37–83% and 48–72%, respectively, compared with the non-treated control. In contrast, concentrated H2SO4 notably increased WEP in raw and dried MDS by 18–103% and 29–225%, respectively. The comparison between the two acidifying agents indicated that alum had the potential to be an efficient and easy-handling alternative to concentrated sulfuric acid, resulting in higher NH4+-N content and lower P solubility.