Drying municipal sewage sludge with v-groove triple-pass and quadruple-pass solar air heaters along with testing of a solar absorber drying chamber

Performance analysis of single‐pass solar air heater thermal collector with adding porous media and finned plate

The recent study encompasses a practical inspect on adding porous material above absorber flat plate having fins to improve the effectiveness of solar air heater (SAH) collector along with forced air circulation process. The efficiency of the altered model and conventional SAH system is compared at the same time to display the impacts of adding porous material. The model that used porous material is called Model‐2, whereas the conventional SAH is called Model‐1. The measuring data is collected in January 2021 in Iraq (Mosul city). Outcomes emphasize that the effectiveness of altered model is better than traditional model by 7% for all air mass flow rates values. The highest efficiency is obtained equal 67% for Model‐2 and 60% for Model‐1 for mass flow rate 0.02 kg/s. For all mass flow rate values, a substantially change in temperature is observed in altered system as compared to traditional system, where the exhaust temperature of Model‐2 is higher than Model‐1. The improvement in the effectiveness of Model‐2 demonstrates that the employ of porous material has an extreme action on the heat exchange and subsequently heat transfer rate.

Characteristics of Solidified Carbon Dioxide and Perspectives for Its Sustainable Application in Sewage Sludge Management

Appropriate management is necessary to mitigate the environmental impacts of wastewater sludge. One lesser-known technology concerns the use of solidified CO₂ for dewatering, sanitization, and digestion improvement. Solidified CO₂ is a normal byproduct of natural gas treatment processes and can also be produced by dedicated biogas upgrading technologies. The way solidified CO₂ is sourced is fully in line with the principles of the circular economy and carbon dioxide mitigation. The aim of this review is to summarize the current state of knowledge on the production and application of solid CO₂ in the pretreatment and management of sewage sludge. Using solidified CO₂ for sludge conditioning causes effective lysis of microbial cells, which destroys activated sludge flocs, promotes biomass fragmentation, facilitates efficient dispersion of molecular associations, modifies cell morphology, and denatures macromolecules. Solidified CO₂ can be used as an attractive tool to sanitize and dewater sludge and as a pretreatment technology to improve methane digestion and fermentative hydrogen production. Furthermore, it can also be incorporated into a closed CO₂ cycle of biogas production-biogas upgrading-solidified CO₂ production-sludge disintegration-digestion-biogas production. This feature not only bolsters the technology's capacity to improve the performance and cost-effectiveness of digestion processes, but can also help reduce atmospheric CO₂ emissions, a crucial advantage in terms of environment protection. This new approach to solidified CO₂ generation and application largely counteracts previous limitations, which are mainly related to the low cost-effectiveness of the production process.

Assessing the suitability of solar dryers applied to wastewater plants: A review

Sludge dewatering and drying are the main processes related to sludge management in wastewater treatment plants (WWTPs). Sludge disposal is a high-cost activity, and drying the sludge reduces its mass and volume, resulting in savings in storage, handling and transportation. The discoveries regarding the use of solar energy in agricultural studies provided valuable information for using in sewage sludge drying. Some studies have reported that dry sludge has met the EPA Class A requirement for biosolids using only solar energy as an energy source. The proper sludge mixture, manual or mechanical, and the dewatering process can significantly increase the drying rate, reducing drying time and the surface area needed. The environmental conditions and the sludge's type greatly influence the drying system. A solar dryer system may be suitable to dry different types of wastewater sludge. Modeling techniques can predict the behavior of the solar drying system and, thus, save time and money in experimental steps. CFD modeling of the sludge drying system is usually done by adopting specific boundary conditions and solving the Navier Stokes equations for air and sludge. There is no standard methodology for comparing solar dryers and common methodologies, such as system efficiency and thermal efficiency, disregards different dryers in different operational conditions. A SWOT (strengths, weaknesses, opportunities, and threats) analysis indicated that, in general, the chapel-type greenhouse with mixed-mode drying has higher drying rates, resulting in reduced drying time and can be scaled to any size. Thus, this type of dryer emerges as a more economical alternative to commercial solar dryers. Based on a systematic review, this work points the SWOT analysis as a useful tool for selecting solar dryers.

Effects of the sludge physical-chemical properties on its microwave drying performance

Thermal drying is an effective sludge treatment method for dealing with large volumes of sludge. Microwave (MW) technology has been proposed as an effective and efficient technology for sludge drying. The physical-chemical properties of the sludge depend both on the origin of the sludge, as well as on the treatment process at which the sludge has been exposed. The physical-chemical properties of the sludge affect the performance and the subsequent valorisation and management of the sludge. This study evaluated the effect of certain physical-chemical properties of the sludge (moisture content, organic content, calorific value, porosity, hydrophobicity, and water-sludge molecular interaction, among others) on the MW sludge drying and energy performance. Four different types of sludge were evaluated collected from municipal wastewater treatment plants and septic tanks. The performance of the MW system was assessed by evaluating the sludge drying rates, exposure times, energy efficiencies and power input consumed by the MW system and linking the MW drying performance to the sludge physical-chemical properties. The results confirmed that MW drying substantially extends the constant drying period associated with unbound water evaporation, irrespective of the sludge sample evaluated. However, the duration and intensity were determined to depend on the dielectric properties of the sludge, particularly on the distribution of bound and free water. Sludge samples with a higher amount of free and loosely bound water absorbed and converted MW energy into heat more efficiently than sludge samples with a lower amount of free water. As a result, the sludge drying rates increased and the constant drying rate period prolonged; hence, leading to an increase in MW drying energy efficiency. The availability of free and loosely bound water molecules was favoured when hydrophobic compounds, e.g., oils and fats, were present in the sludge.

Thin layer drying kinetics and quality dynamics of persimmon (Diospyros kaki) treated with preservatives and solar dried under different temperatures

Poor postharvest handling, microbial infestation, and high respiration rate are some the factors are responsible for poor storage life of perishable commodities. Therefore, effective preservation of these commodities is needed to lower the damages and extend shelf life. Preservation is regarded as the action taken to maintain desired properties of a perishable commodity as long as possible. Persimmon (Diospyros kaki) is perishable fruit with high nutritive value; however, has very short shelf-life. Therefore, effective preservation and drying is needed to extend its storage life. Drying temperature and preservatives significantly influence the quality of perishable vegetables and fruits during drying. The current study investigated the effect of different temperatures and preservatives on drying kinetics and organoleptic quality attributes of persimmon. Persimmon fruits were treated with preservatives (25% honey, 25% aloe vera, 2% sodium benzoate, 1% potassium metabisulfite, and 2% citric acid solutions) under different drying temperatures (40, 45, and 50°C). All observed parameters were significantly affected by individual effects of temperatures and preservatives, except ash contents. Similarly, interactive effects were significant for all parameters except total soluble sugars, ash contents, and vitamin C. Generally, fruits treated with citric acid and dried under 50°C had 8.2% moisture loss hour^-1, 14.9 drying hours, 0.030 g H₂O g^-1 hr^-1, 1.23° Brix of total soluble solids, 6.71 pH, 1.35% acidity, and 6.3 mg vitamin C. These values were better than the rest of the preservatives and drying temperatures used in the study. Therefore, treating fruits with citric acid and drying at 50°C was found a promising technique to extend storage life of persimmon fruits. It is recommended that persimmon fruits dried at 50°C and preserved in citric acid can be used for longer storage period.

Water-heat balance characteristics of the sewage sludge bio-drying process in a full-scale bio-drying plant with circulated air

Sewage sludge bio-drying technology has attracted considerable attention in recent years. In this study, we explored the water-heat balance under two ventilation strategies for the first time in bio-drying plants with circulated air, and examined the influence of air circulation on water removal and heat recovery. We want to obtain the relationships of pile temperature, ventilation, and water removal. Then, it provides support for optimizing the bio-drying process conditions and improving the efficiency through analysis of the water-heat relationship. In the low-ventilation and high-ventilation trials, water removed was mainly on Days 9-12 and 1-4, respectively. Ventilation and pile temperature jointly determine the water removed during the bio-drying process. Water balance indicated that more than 30% of the water was removed under the nonventilated process. More organic matter was degraded to maintain a higher pile temperature under low-ventilation than under high-ventilation, which also led to more radiation heat being lost. High-ventilation trial input less energy (3.36 MJ/kg water removed) but obtained a higher bio-drying index I (7.04) and heat utilization efficiency Qeffic (94.1%). Heat balance showed that lower energy consumption by dry air (Qdryair) was obtained due to circulation air with high temperature. Circulation air also has a higher carried capacity of water vapor but carries more water into the pile due to higher humidity.

A Time Series Forecasting of Global Horizontal Irradiance on Geographical Data of Najran Saudi Arabia

Environment-friendly and renewable energy resources are the need of each developed and undeveloped country. Solar energy is one of them, thus accurate forecasting of it can be useful for electricity supply companies. This research focuses on analyzing the daily global solar radiation (GSR) data of Najran province located in Saudi Arabia and proposed a model for the prediction of global horizontal irradiance (GHI). The weather data is collected from Najran University. After inspecting the data, I we found the dependent and independent variables for calculating the GHI. A dataset model has been trained by creating tensor of variables belonging to air, wind, peak wind, relative humidity, and barometric pressure. Furthermore, six machine learning algorithms convolutional neural networks (CNN), K-nearest neighbors (KNN), support vector machines (SVM), logistic regression (LR), random forest classifier (RFC), and support vector classifier (SVC) techniques are used on dataset model to predict the GHI. The evaluation metrics determination coefficients (R2), root mean square error (RMSE), relative root mean square error (rRMSE), mean bias error (MBE), mean absolute bias error (MABE), mean absolute percentage error (MAPE), and T-statistic (t-stat) are used for the result verification of proposed models. Finally, the current work reports that all methods examined in this work may be utilized to accurately predict GHI; however, the SVC technique is the most suitable method amongst all techniques by claiming the precise results using the evaluation metrics.

Energy and exergy assessment of new designed solar air heater of V-shaped transverse finned absorber at single- and double-pass flow conditions

Flat plate solar collector is one of the main solar collectors that has a simple structure, reliable operation, large heat preoccupation area, and low cost. Its drawback is the low heat transfer between the working air and the absorber plate. A solar air heater of V-shaped transverse finned absorber having new designed absorber plate of lateral gaps and central holes to enhance its performance is investigated experimentally at single-pass and double-pass airflow conditions. Moreover, the energy and exergy assessment of its performance was studied and compared with traditional longitudinal finned heater having the same fin surface area and construction except for the absorber plate design. The study is investigated at air mass flow rates of 0.025, 0.05, and 0.075 kg/s. Findings show that the new heater achieves maximum outlet temperature rising of 28.2 °C at 0.025 kg/s and double-pass flow. Moreover, it has an average daily energy efficiency of 88.5%, 81.88%, and 61.3% at mass flow rates of 0.075, 0.05, and 0.025 kg/s with increments of 9.4%, 13.3%, and 9.66%, respectively, compared to the longitudinal finned heater. Additionally, it achieves exergy efficiencies of 2.5%, 2.1%, and 1.7% at mass flow rates of 0.025, 0.05, and 0.075 kg/s with increments 18%, 25.7%, and 18.2%, respectively, relative to longitudinal finned heater. Furthermore, the new heater design possesses greater energy efficiency comparing to former studied SAH designs.

Thermohydraulic Performance and Entropy Generation of a Triple-Pass Solar Air Heater with Three Inlets

In this paper, a triple-pass solar air heater with three inlets is analytically investigated. The effects of airflow ratios of the second and third passes (ranging from 0 to 0.4), and the Reynolds number of the third pass (ranging from 8000 to 18,000) on the thermohydraulic efficiency and entropy generation are assessed. An absorber plate equipped with rectangular fins on both sides is used to enhance heat transfer. The air temperature change in the passes is represented by ordinary differential equations and solved by numerical integration. The results demonstrate that the effect of the third pass airflow ratio on the thermohydraulic efficiency and entropy generation is more significant than that of the second pass airflow ratio. The difference in air temperature through the collector shows an insignificant reduction, but the air pressure loss is only 50% compared with that of a traditional triple-pass solar air heater. Increasing the air flow ratios dramatically reduces entropy generation. Multi-objective optimization found a Reynolds number of 11,156 for both the airflow ratio of the second pass of 0.258 and airflow ratio of the third pass of 0.036 to be the an optimal value to achieve maximum thermohydraulic efficiency and minimum entropy generation.

Providing an accurate global model for monthly solar radiation forecasting using artificial intelligence based on air quality index and meteorological data of different cities worldwide

This study aims to present an exact model for predicting solar radiation worldwide through a general model. In this study, mean monthly global solar radiation would have been predicted by applying artificial intelligence methods including artificial neural network, adaptive neuro-fuzzy inference system and hybrid genetic algorithm for different cities worldwide. Investigating different models under various situations showed that the adaptive neuro-fuzzy inference system created the most accurate and precise model for predicting solar radiation. Statistics indexes, such as the determination coefficient, mean absolute percentage error, root mean square error and mean bias error, for the best model selected are 0.999, 5.50E-04, 5.90E-05 and 0.425, respectively. It can be claimed that according to the amount of the statistical indexes, which was mentioned above, the provided model has approximately more formidable accuracy and credibility in comparison with other models, which other researchers did.

Assessment of double-pass pin finned solar air heater at different air mass ratios via energy, exergy, economic, and environmental (4E) approaches

In this study, an assessment based on energy, exergy, economic, and environmental approaches on a double-pass (DP) solar air heater (SAH) having pin finned absorber at different air mass ratios up and down the absorber is investigated experimentally. Four air mass ratios are considered: (i) all the air mass flow passes up the absorber and returns to pass down the absorber (DP), (ii) 2/3 of the airflow passes up the absorber and returns to mix with the remainder of air to pass down the absorber (2/3 DP), (iii) the same as (ii) but 1/3 of the air passes up the absorber (1/3 DP), and (iv) all the air mass passes only down the absorber (single pass, SP). For all mass ratios, the performance of pin finned SAH (P_SAH) is compared with that of flat SAH (F_SAH). The results indicated that the air temperature rise and energy and exergy efficiencies of P_SAH are highly greater than those of F_SAH. The highest average thermal efficiency of F_SAH is 56.7% obtained at DP flow condition, whereas the highest value of P_SAH is 65.21% obtained at 2/3 DP with an increase of 17.6% compared with F_SAH. Also, P_SAH has higher average exergy efficiency of about 34.7% compared to F_SAH. Furthermore, P_SAH achieves energy payback time (EPBT) lower than that of F_SAH, while P_SAH has higher embodied energy. The findings indicated that F_SAH at SP airflow pattern has the maximum energy cost (0.0427 $/kWh), whereas P_SAH at 2/3 DP airflow pattern achieves the minimum energy cost (0.037 $/kWh). Finally, the proposed P_SAH system appears to be more viable from exergoeconomic and enviroeconomic approaches compared to F_SAH.