Sewage Sludge Processing Research Articles

Non-Energetic Chemical Products by Fermentation of Hydrolyzed Sewage Sludge

Hydrolysis and the solubilization of sewage sludge processes are important tools to obtain small and medium molecules with different application perspectives. Although the production of biomethane and other products such as biohydrogen from sludge as biofuel alternatives has been profusely studied, the current perspectives are mainly focused on the use of the sludge hydrolysate to produce non-energy bioproducts and biomaterials. In this review, the most recent bibliography dealing with the use of sludge hydrolysates as fermentation media for the bioproduction of new non-energetic products with industrial interest is here revised and discussed. In this regard, the main research effort has been focused on the bioproduction of short-chain fatty acids due to their direct use in industrial applications or as a carbon source for polyhydroxyalkanoates-producing microorganisms. The use of sludge hydrolysates as fermentation media using pure cultures to produce more complex biomolecules, such as enzymes or lipids, is gaining interest, but it remains an undervalued topic. The literature has been divided into processes where hydrolysis and fermentation stages took place simultaneously or separately, centering them on the effect of the main operational conditions on the yields and properties of the corresponding metabolites produced. In general, the main limiting step of these kinds of processes is the proper solubilization and hydrolysis of the sludge, which can improve the bioassimilation of nutrients and, subsequently, the productivities and compositions of the metabolites obtained. Biological and/or thermal pretreaments are the options more profusely employed, which are frequently assisted by different promoters such as oxidants, surfactants, or cation exchange resins.

Application of Data Validation and Reconciliation to Improve Measurement Results in the Determination Process of Emission Characteristics in Co-Combustion of Sewage Sludge with Coal

One of the actions popularized worldwide to reduce the consumption of fossil fuels is the combustion of renewable fuels and the co-combustion of both of these fuels. To properly implement combustion and co-combustion processes in power-generation installations, operational characteristics, including emission characteristics are required. To determine these characteristics, tests must be conducted, within the scope of which, for individual operating stages of the installation’s work, the readings collected from a relatively large number of control and measurement instruments should be taken into account. All these instruments have different levels of accuracy, which, among other factors, bring about lower adequacy of the characteristics determined on the basis of these measurements. The objective of this study is to present possible adaptations of data validation and reconciliation methods to increase the adequacy of emission characteristics for the process of co-combustion of fuels. The methodology is discussed based on the example of studies on the co-combustion process of sewage sludge with coal in a grate furnace. The aforementioned characteristics were determined based on measurement tests of gaseous emissions of flue gas components. The tests were carried out for various preset operational conditions of the process, such as the thickness of fuel layer on the grate, the share of sludge in the fuel, the humidity of the sludge, the theoretical ratio of excess air to combustion, and the distribution of air stream during the process. The research object is described and detailed research results concerning two exemplary measurement tests are given, as well as the most important results referring to the whole research. The performed calculations indicate the necessity to take into account often significant corrections, which can amount to about 10% of the measured value.

Dehumidification of sewage sludge using quonset solar tunnel dryer: An experimental and numerical approach

In this study, it is aimed to design an efficient and sustainable solar tunnel dryer to be used in drying process of sewage sludge. In the first step of this study, heat and flow structure of three tunnel dryers including rectangular tunnel (RSTD), quonset tunnel (QSTD) and quonset tunnel with fins (QSTD/F) have been numerically surveyed to determine the effective design. Based on CFD results, quonset-type tunnel designs have been fabricated, experimentally analyzed and compared with numerical findings. In this work, different from previous studies on quonset-type solar-thermal systems, top surface of quonset geometry was made from sheet metal as an absorber to enhance heat transfer area. The drying tests have been performed in different months of the year (June and January) by applying two different air velocities to evaluate the performance of tunnel dryers at various climatic conditions. Integrating fins to the quonset tunnel had considerable positive effects on both thermal and drying performances. According to the experimental findings, specific moisture extraction rate (SMER) value was attained on June and January in the range of 0.50–0.89 and 0.39–0.65 kg/kWh, respectively. The results indicated the successfulness of quonset solar tunnel dryer design in the dehumidification process of sewage sludge.

Investigation of sewage sludge for the purpose of their secondary use as agricultural fertilizer

Substantiated the possibility of using an optimized technology for processing sewage sludge in the production of agricultural fertilizers. The researches have been experimentally tested on a pyrolysis plant -a physical model assembled under laboratory conditions. Selected, calculated and experimentally confirmed the optimal composition of agricultural fertilizer based on sewage sludge. The suggestions allow to increase the production of mineral fertilizers and reduce the accumulation of sewage sludge in the sludge fields of treatment facilities of industrial enterprises.

The redistribution and migration mechanism of nitrogen in the hydrothermal co‑carbonization process of sewage sludge and lignocellulosic wastes

Blending lignocellulosic wastes (such as cornstalk, CS) into sewage sludge (SS) for hydrothermal carbonization (HTC) could contribute to the importance of the hydrothermal solid product (hydrochar) as a substitute for fossil fuel. However, the interactions between SS and CS changed the fate of Nitrogen (N), affecting the clean combustion utilization of hydrochar. This study focused on the influence of SS–CS interactions on the redistribution and migration behavior of N during the co-HTC process by tuning the mass ratio of SS to CS (SS:CS), reaction temperature, and residence time. Under the hydrothermal condition of 220 °C, 2 h, and SS:CS = 1:1, the high heating value of hydrochar and the energy recovery efficiency (ERE) respectively reached 15.89 MJ/kg and 71.19%. Further raising the temperature to 250 °C, the hydrochar was enhanced in the coalification degree, whereas ERE decreased to 61.86%. Part of the amino-N in sludge organics was fractured during the co-HTC process and reacted with carbohydrate and intermediate products, such as 5-hydroxymethylfurfural, which degraded from CS, to generate heterocyclic-N compounds (including pyridine, pyrrole, and pyrazine). The remaining amino-N formed pyridine-N, pyrrole-N, and quaternary-N through various solid–solid conversions. The heterocyclic-N polymerized and formed melanoidins, which thereafter polymerized with aromatic clusters to form the N-containing polyaromatic char. Therefore, the N retention rate (NRR) was enhanced and showed a synergistic effect. NRR was increased by raising the proportion of CS or extending time, reaching 57.02% at SS:CS = 1:1 and 8 h. Conversely, rising temperatures resulted in a downward trend of NRR with a phased increase at 220 °C–250 °C.

P-01 水素製造効率向上のための下水汚泥・木炭の共ガス化プロセスの設計と評価

P-01 水素製造効率向上のための下水汚泥・木炭の共ガス化プロセスの設計と評価

Degradation and effect of 6:2 fluorotelomer alcohol in aerobic composting of sludge.

Perfluoroalkyl carboxylates (PFCAs) is toxic to the environment and human health. However, the degradation characteristics of fluorotelomer alcohols (FTOHs), precursors of PFACAs biodegradation, in the sludge during aerobic composting remain unclear. In this study, the degradation characteristics of 6:2 FTOH in sewage sludge by composting were researched and the influences of 6:2 FTOH on the composting process and microbial communities of the sludge were evaluated. After 52days of composting, 6:2 FTOH retained only 0.73% of its original concentration, and its half-life was less than 1 d; 6:2 FTOH was degraded finally to perfluorohex unsaturated acid, perfluoropentanoic acid, 5:3 polyfluorinated acid (FTCA), 4:3 FTCA, and perfluorobutanoic acid through two pathways; and 6:2 FTCA and 6:2 fluorotel unsaturated acid were the intermediate products. Notably, dosing with 6:2 FTOH affected the composting process of sewage sludge. Additionally, 50mg/kg 6:2 FTOH resulted in a decrease in the microbial richness and diversity of sludge compost. When compared with the compost without 6:2 FTOH, the proportion of Proteobacteria had increased, and the proportion of Firmicutes had decreased as the concentration of 6:2 FTOH increased. The negative effect of a dosage of 50mg/kg 6:2 FTOH was more obvious than the effect of other treatments. This study expanded our understanding of the risk of sludge contaminated by 6:2 FTOH being used as a fertilizer after composting.

Formation Characteristics of PCDD/Fs in the Co-combustion and Pyrolysis Process of Coal and Sewage Sludge

ABSTRACT Co-combustion technology of coal and sewage sludge (SS) was encouraged and recommended in China. Previous studies most focused on its influence on combustion characteristics, migration characteristics of heavy metals in fly ash, and emission of conventional pollutants, etc., but less reported the formation characteristics of polychlorinated-ρ-dibenzodioxins and dibenzofurans (PCDD/Fs). To well reveal it, this study carried out five parallel experiments, including the pyrolysis of SS, the combustion of SS, the co-combustion of coal and SS with the proportion of 0%, 2.5% and 5%, respectively. The emission concentration of PCDD/Fs respectively increased from 0.42 ng g–1 (0.0022 ng I-TEQ g–1) to 0.54 ng g–1 (0.0030 ng I-TEQ g–1) and 1.70 ng g–1 (0.0305 ng I-TEQ g–1) with increasing blending proportion of SS. The dominant part was also changed from PCDF (0.32 ng g–1 in M-0%, 0.38 ng g–1 in M-2.5%) to PCDD (1.11 ng g–1 in M-5%). The formation concentration of PCDD/Fs in the combustion process of SS was about 0.34 ng g–1 (0.0019 ng I-TEQ g–1). In the pyrolysis process of SS, the concentration of PCDD/Fs was 0.59 ng g–1 (0.0037 ng I-TEQ g–1). The de novo synthesis should be the major formation pathway of PCDD/Fs in the co-combustion process of coal and SS. On the basis of sufficient carbon sources, the PCA analysis revealed the chlorine source (Cl) and metal catalyst (Fe) should contribute a lot on the formation of PCDD/Fs. The results paved the way for further optimization on the operation of co-combustion of coal and SS and assist in controlling the PCDD/F emission from co-combustion process.

Standards, rules, and analytical techniques for sewage sludge management

This article discusses the most common sewage sludge management techniques, as well as the unit activities and procedures that relate to them. Reclamation and adaptation of lands to specific needs; plant cultivation not intended for human consumption or food production; use in agriculture; use in construction; recovery of phosphorus, rare earth metals, or fats and use in industry; production of combustible pellets, granulates, or other usable materials such as absorbents; and storage on treatment territory Stabilization processing results in the creation of materials that may be contaminated with a range of organic chemicals. Because this method of management often involves dumping processed sludge on the ground, it has the potential to contaminate soil with unknown organic substances. Thermal processing of raw sewage sludge, on the other hand, virtually eliminates this possibility. The vast majority of organic stuff is converted to a simple, mineralized state. In this instance, the most serious concern is heavy metal poisoning of sewage sludge ash. The identification of heavy metals in ashes is, however, considerably easier than that of organic molecules. Chemical analysis may be extremely helpful in determining the environmental safety of sewage sludge that has been treated and handled. As a result, there are many analytical approaches in use that are likely to aid in the process of developing and implementing innovative economically and ecologically sound methods of sewage sludge reuse. The method of technical sewage sludge use at Gdansk's Wastewater Treatment Plant "Wschod" is also explained. The technical line has just been updated.

Evaluation of Bio-drying Process of Sewage Sludge using Mathematical Model of Heat and Mass Balance: Effects of Temperatures of Supplied Air and Exhaust Gas

Objectives : The effects of temperatures of supplied air and exhaust gas on moisture removal in the bio-drying process of sewage sludge were assessed by simulating the process. We also suggested performance and efficiency indicators for moisture removal in this process and identified their effectivity.Methods : The bio-drying process of sewage sludge was simulated by mathematical modeling of heat and mass balance under different combinations of supplied-air temperatures and control ranges of exhaust gas temperatures. The simulation results were analyzed by using some indicators for assessing the performance and efficiency of moisture removal.Results and Discussion : While BVS (biodegradable volatile solid) degradation was inhibited at a higher supplied-air temperature and a lower control range of exhaust gas temperature, moisture reduction was enhanced at the supplied-air temperature nearer to ambient and the controlled exhaust gas temperature for 45 to 50℃. The drying performance could be improved by the utilization of both metabolic heat and convective heat from hot supplied-air for the source of heat necessary for moisture removal. We suggested the moisture removal rate as a performance indicator, and both the moisture removing capacity of supplied-air and the mass ratio of moisture removal to BVS degradation as an efficiency indicator. We identified that this mass ratio could be an alternative for thermal efficiency of drying.Conclusions : It is effective to control the air-flow rate to keep the exhaust gas temperature within 45~50℃ during bio-drying of sewage sludge in terms of drying performance and efficiency. It is expected that a specified range or minimum required value for the performance and efficiency indicators in the bio-drying process which suggested in this study needs to be established.

High-solid anaerobic digestion of sewage sludge: achievements and perspectives

High-solid anaerobic digestion (HS-AD) has been applied extensively during the last few decades for treating various organic wastes, such as agricultural wastes, organic fractions of municipal solid wastes, and kitchen wastes. However, the application of HS-AD to the processing of sewage sludge (SS) remains limited, which is largely attributable to its poor process stability and performance. Extensive research has been conducted to attempt to surmount these limitations. In this review, the main factors affecting process stability and performance in the HS-AD of SS are comprehensively reviewed, and the improved methods in current use, such as HS sludge pre-treatment and anaerobic co-digestion with other organic wastes, are summarised. Besides, this paper also discusses the characteristics of substance transformation in the HS-AD of SS with and without thermal pre-treatment. Research has shown that the HS effect is due to the presence of high concentrations of substances that may inhibit the function of anaerobic microorganisms, and that it also results in poor mass transfer, a low diffusion coefficient, and high viscosity. Finally, knowledge gaps in the current research on HS-AD of SS are identified. Based on these, it proposes that future efforts should be devoted to standardising the definition of HS sludge, revealing the law of migration and transformation of pollutants, describing the metabolic pathways by which specific substances are degraded, and establishing accurate mathematical models. Moreover, developing green sludge dewatering agents, obtaining high value-added products, and revealing effects of the above two on HS-AD of SS can also be considered in future.

Enzymatic Potential of Bacteria and Fungi Isolates from the Sewage Sludge Composting Process

The aim of this study was the isolation and characterisation of the fungi and bacteria during the composting process of sewage sludge under a semipermeable membrane system at full scale, in order to find isolates with enzymatic activities of biotechnological interest. A total of 40 fungi were isolated and enzymatically analysed. Fungal culture showed a predominance of members of Ascomycota and Basidiomycota division and some representatives of Mucoromycotina subdivision. Some noticeable fungi isolated during the mesophilic and thermophilic phase were Aspergillus, Circinella, and Talaromyces. During the maturation phase, some lignin modifying enzyme producers, like Purpureocillium, Thielavia, Bjerkandera, or Dichotomyces, were found. Within this group, Thielavia and Bjerkandera showed high activity with production of laccases and peroxidases. In the bacterial culturome, a total of 128 strains were selected and enzymatically analysed. Bacillales, Actinomycetales, Pseudomonadales, and Lactobacillales were the orders most represented in culture-bacteria. Bacillus pumilus, B. stratosphericus, B. safensis, and Pseudomonas formosensis were the species most efficient in enzyme production, particularly peroxidases, polyphenol oxidases ammonifying activity, and amylases. These results showed that sewage sludge composting piles could represent a source of microorganisms which have adapted to adverse conditions.

Assessment of co-composting of sewage sludge, woodchips, and sawdust: feedstock quality and design and compilation of computational model.

Composting process of sewage sludge requires a preprocessing step in order to prepare the appropriate mixture of dewatered sludge (Xs) with amendment (Xa), bulking agent (Xb), and/or recycled materials (Xr). This research aimed to develop a novel mathematical model for finding an optimal mixture ratio of dewatered sludge with the aforementioned influencing elements on co-composting process. Seven feasible scenarios were presented and the best one was selected in viewpoint of technical and economic perspectives. The optimum mixture was prepared and its quality was evaluated in the terms of physical, chemical, and microbial characteristics. The optimum mixture was loaded in an aerated static pile composting reactor in order to evaluate the quality of the final compost product. If the test results were not in compliance with the USEPA standards, the model was iteratively modified to fulfill the desired objective. The model was validated using the experimental results. The mixture of Xs:Xa:Xb:Xr with a weight ratio 7.4:1.0:1.4:2.3 allowed optimal moisture content (59.8 ± 0.5%), organic matter (80.0 ± 2.6%), dry matter (40.2 ± 0.6%), C/N ratio (28.0 ± 1.6), and free air space (> 30%) across the composting pile. The final product of compost met the heavy metal and microbial requirements for land application. It can be concluded this mathematical model is a promising method for selecting the optimal amount and type of materials for preparing the initial mixture of co-composting process.

Evaluation of the number of first-order reactions required to accurately model biomass pyrolysis

Thermogravimetric analysis (TGA) experimental measurements, combined with modeling techniques, are widely employed for the characterization of the pyrolysis process of all kinds of biomass. The present work evaluates the number of reactions required to accurately model the pyrolysis process of lignocellulosic biomass, microalgae, and sewage sludge. A model with different number of parallel first-order reactions, from a single reaction up to ten reactions, is tested to fit the experimental TGA pyrolysis results, obtained for constant heating rates, and to determine the required optimal number of reactions for each type of biomass. The results show that the optimal number of reactions to precisely model the kinetics of lignocellulosic biomass is 5, whereas a model of 6 reactions is optimal for the characterization of microalgae and 8 reactions are required to accurately model the pyrolysis of sewage sludge. The outcome of the model, expressed in terms of the pyrolysis kinetics parameters and the relative contribution of each of the parallel reactions on the overall process, can be successfully extrapolated to the use of inverse exponential temperature increases, which are characteristic of pyrolysis processes occurring in isothermal reactors. Under these circumstances, the model is also capable of accurately reproducing the experimental results for all the different maximum temperatures and exponential temperature increases tested, demonstrating its robustness and applicability to pyrolysis processes occurring under non-linear temperature increases.

Synthesis of an easily recyclable and safe adsorbent from sludge pyrochar for ciprofloxacin adsorption

Utilization of sludge pyrochar (SP) is the terminal step to loop the entire harmless disposal process of sewage sludge with pyrolysis. A new, easily recyclable, and safe adsorbent with well-immobilized heavy metals (HMs) was prepared from SP for ciprofloxacin (CIP) adsorption. The operational conditions for the adsorbent preparation were systematically optimized based on recycling rate and adsorption performance. Additionally, the adsorption conditions, adsorption kinetics, isotherms, and regeneration of adsorbents were further investigated in the present study. The results showed that easily recyclable and safe adsorbents were successfully prepared at 1100 °C under N2 atmospheric conditions (SPA-N-1100) with a maximum CIP adsorption capacity of 10.42 mg/g. SPA-N-1100 exhibited good CIP adsorption performance at an adsorption temperature of 45 °C and pH between 8.0 and 9.0. The adsorbents were regenerated by thermal desorption at 450 °C with a thorough decomposition of CIP. The adsorption mechanism was mainly dominated by its special porous microspheres-accumulation structure and surface species (e.g., FeP and graphite). Moreover, HMs in the adsorbents were well immobilized in SPA-N-1100 by the generation of new metal mineral phases and encapsulation of melting minerals, which had an ultralow potential for ecological risk during application.

Development of a continuous‐flow anaerobic co‐digestion process of olive mill wastewater and municipal sewage sludge

AbstractBACKGROUNDOlive mill wastewater (OMW) represents an environmental problem due to its high organic load and relevant concentration of phenolic compounds (PCs). OMW treatment and disposal represents a relevant challenge and cost for olive mills and multi‐utilities in charge of waste management in Mediterranean countries. The goal of this study was to develop an anaerobic co‐digestion (co‐AD) process of OMW and sewage sludge (SwS) from municipal wastewater treatment.RESULTSDifferent volumetric OMW:SwS ratios up to 100% OMW were fed in continuous 1.7‐L bioreactors. The reactors fed with raw OMW (rOMW) performed better than those fed with OMW dephenolized by adsorption (dOMW). At a 23‐day hydraulic retention time, the best performances were obtained in the reactor fed with 25% rOMW, with a 105% increase in methane yield in comparison to the 100% SwS test. At a 40‐day hydraulic retention time, the reactor fed with 40% rOMW attained a 268 NLCH4/kgvolatile solids methane yield. The conversion of phenolic compoundsreached 70% when the hydraulic retention time was increased from 23 to 40 days. A cost–benefit analysis indicated that both rOMW co‐AD in existing digesters and phenolic compounds recovery from OMW followed by co‐AD of dOMW can lead to relevant additional revenues for the multi‐utilities in charge of wastewater management.CONCLUSIONThis work proves that, using the existing network of SwS anaerobic digesters, it is feasible to co‐digest the entire OMW production in regions characterized by intense olive oil production, thus attaining a relevant increase in methane production yield (a 144% increase in comparison to 100% SwS). © 2020 Society of Chemical Industry (SCI)

Pharmaceuticals effect and removal, at environmentally relevant concentrations, from sewage sludge during anaerobic digestion

This paper investigates the performance of AD in the presence of high-risk pharmaceuticals found in sewage sludge and its removal capacity. The digestion process of synthetic sewage sludge was observed in two 7L glass reactors (D1 and D2) at 38 °C (OLR 1.3 gVS L-1 d-1 and HRT 43 d). Environmentally relevant pharmaceuticals (clarithromycin, clotrimazole, erythromycin, fluoxetine, ibuprofen, sertraline, simvastatin and tamoxifen) were added in D2 at predicted environmental (sludge) conditions.The results demonstrated that long-term presence of pharmaceuticals can affect AD and induce instability resulting in an accumulation of VFAs. This study showed a concurrent effect on AD microbial composition, increasing the percentage of Firmicutes (>70%) and decreasing the percentages of Bacteroidetes and Euryarchaeota (<5%), which seems to be the cause of VFA accumulation and resultant the decrease in the biogas production.However, it seems that anaerobic microorganisms offer enhanced removal of the antibiotics clarithromycin and erythromycin over aerobic techniques.

Energetic, environmental and economic analysis of drying municipal sewage sludge with a modified sustainable solar drying system

Disposal of sewage sludge is an important problem for the sustainability of cities. In recycling process of sewage sludge, a big part of energy demand is consumed in the drying process. Therefore, utilizing clean and sustainable energies in recycling process of sewage sludge can be a good solution. In this work, a drying chamber with transparent cover has been designed and analyzed in the process of drying sewage sludge experimentally and numerically. Also, a conventional drying chamber has been tested and its performance compared with modified drying chamber’s performance. The main purpose of modifying the drying chamber using transparent cover is to harvest more solar energy in the system and consequently reduction in the drying time. Moreover, in the drying tests a single-pass conventional unglazed solar air collector has been combined with the drying chamber. The performance tests of drying systems have been conducted in two various flow rates including 0.010 and 0.014 kg/s. Experimental and numerical findings demonstrated that using drying chamber with transparent cover reduced the drying time significantly. The obtained average specific energy consumption and specific moisture extraction rate values are in the range of 1.77–2.86 kWh/kg and 0.77–1.34 kg/kWh, respectively. Moreover, levelized cost of heating values were found between 1.7 and 2.0 $-ct/kWh for the system which uses drying chamber with transparent cover.

Enhancing the energetic potential of Mediterranean food waste by anaerobic co‐digestion with sewage sludge

AbstractMediterranean Food Waste (FW) with high Carbon/Nitrogen (C/N) ratio (≈31) and a biodegradability (BD) above 75%, were anaerobically co‐digested with Sewage Sludge (SS), in both batch and semicontinuous processing systems. Biochemical Methane Potential (BMP) tests were carried out for five mixture ratios (VS basis). The highest methane yield was obtained for the Food Waste to Sewage Sludge (FW/SS) ratio of 3:1, reaching a Specific Methane Production (SMP) of of 452 ml CH4/g VSadded. Moreover, this ratio has shown a BD of 40%, twofold lower than the one obtained for digestion of FW alone. Applying the semi‐continuous process, a methane yield of 200 ml CH4/g VS was obtained at the high Organic Loading Rate (OLR) of 8 g VS/L·day, indicating a good performance of the system facing a high daily feeding. A predictive study of the energy efficiency of this system provided an estimated daily production of 1.4 kilowatt‐hour electricity load (KWhel)/kg VSadded and 2.2 kilowatt‐hour thermal load (KWhth)/kg VSadded.

Testing of a novel convex-type solar absorber drying chamber in dehumidification process of municipal sewage sludge

Each day high portion of municipal wastewater sludge is generated in cities and developing a suitable and environmentally friendly treatment technique for municipal wastewater is required. Providing a cost-effective and suitable way for sewage sludge refinement with the purpose of reducing environmental impacts or reutilization of sewage sludge can be an important issue for researchers. In the present study, a novel convex-type solar absorber assisted dryer has been designed for drying municipal sewage sludge. In the experimental setup, an unglazed single-pass solar air collector has been used as main air heater and integrated to the drying conventional and modified drying chambers. Experimental and CFD simulation have been used to investigate the performance of fabricated solar energy assisted dryers. Also, the effectiveness of the developed system has been analyzed in various conditions to clarify the potential of fabricated dryers. According to the results utilizing convex solar absorber led to provide high air flow rate with high temperature inside the drying chamber and consequently shortened the drying time. Experimentally obtained average energy efficiency of the modified and conventional indirect solar drying system were in the range of 32.85–47.09% and 21.32–30.45%, respectively. Moreover, the experimental results collected from CSD (conventional solar dryer) and CSASD (solar dryer with convex solar absorber) are also discussed in terms of R2, RMSE, RRMSE, MBE, and MAPE, and a very satisfying correlation between the systems CSD and CSASD is noticed with the statistical metrics. The findings of the present study demonstrate the potential of utilizing the designed dryers in drying municipal wastewater sludge.