Biodrying Of Waste Research Articles

Integrated Waste Management in the Circular Economy Era: Insights from Research and Practice

This Special Issue on integrated waste management explores innovative approaches and multifaceted strategies aimed at addressing the critical challenges facing modern waste management systems. The featured eight original research articles cover diverse topics, including sewage sludge valorization, municipal waste biodrying, recyclables collection optimization, biomass-to-energy policies, and the management of compostable packaging waste. Technological advancements, such as AI-driven waste sorting and route optimization algorithms, are highlighted alongside policy frameworks supporting circular economy principles. The studies also address barriers to implementation, including public awareness gaps, technological disparities, and financial constraints, while emphasizing the importance of stakeholder collaboration across governments, industries, and communities. Additionally, environmental risks associated with waste management practices, such as nanoparticle contamination and leachate emissions from ashes, are critically analyzed. This Special Issue provides a holistic perspective on waste management, combining technical innovations, environmental stewardship, and policy integration. The insights of the works published in this Special Issue aim to guide researchers, policy-makers, and practitioners toward building resilient, sustainable, and resource-efficient waste management systems in alignment with global sustainability goals.

Characteristics of Wastewater from Municipal Waste Bio-Drying and Its Impact on Aquatic Environment—Long-Term Research on a Technical Scale

The implementation of appropriate solutions for municipal waste management is still a significant challenge for the operators of technological facilities. Although there are many separate collection procedures and waste neutralisation systems available, it is still necessary to search for new economically and technologically justified solutions. The priority is environmental care and circular economy compliance. An important aspect is recycling and energy recovery from waste as an alternative fuel. Preparation of municipal waste for energy production requires many preliminary unit processes, and one of the most important factors is drying. It should be emphasised that environmental impact assessment is an indispensable aspect of waste management. The aim of long-term research was to determine the effect of bio-drying of municipal waste on the characteristics of technological and precipitation wastewater and its impact on the quality of the aquatic environment. An investigation was carried out between 2015–2021 on a large-scale installation for 200,000 residents. It was proven that during the wastewater treatment plant operation, the concentration of N-NH4 was exceeded. The concentrations of other pollution indicators corresponded to the normative values. The quality of groundwater also deteriorated. A comparative analysis of municipal waste drying methods showed that the bio-drying process has a significantly lower impact on the natural environment than the methods that are lower in the municipal waste management hierarchy.

Vegetable Waste Biodrying Treatment for Energy Recovery as Refuse Derived Fuel Potential

Vegetable waste is a type of biodegradable organic waste found in every location in Indonesia. In addition, vegetable waste also dominates food waste. One of the ways to use vegetable waste is to use energy recovery. Energy recovery of vegetable waste can be done by time-dependent biodrying and bioactivator. This study aimed to determine the effect of time and activator application on the vegetable waste biodrying process. In this study, 0.5 kg of waste is used with an airflow rate of 15 liters/minute, the temperature in the process is in the range of 28.4-34.1°C. The bioactivators used in this study were baker's yeast, tempeh, and tape. The maximum decrease in mass occurs in the biodrying process with the addition of a bioactivator. The multivariate effect test results showed an effect of time and bioactivator on changes in water content and caloric value. However, the interaction between time and bioactivator only affects the water content. This is because the degradation process occurs utilizing microorganisms stored in the bioactivator liquid and water in vegetable waste. Further research is needed to know the effect of other variables in the biodrying process, especially the right detention time and bioactivators that accelerate the rate of degradation.

Metagenomic analysis reveals the microbial degradation mechanism during kitchen waste biodrying

Biodrying is a treatment to remove moisture using bio-heat generated during organic degradation. Organic matter degradation and microbial metabolism were studied during the whole kitchen waste biodrying, using metagenomic analysis. After the 25-day biodrying process, carbohydrate, protein and lipid contents decreased by 83.7%, 27.8% and 79.3%, respectively, and their degradation efficiencies increased after the thermophilic phase. Lipase activity exceeded 10 mmol d−1 g−1 throughout biodrying. Cellulase and lipase activities recovered by 2.21% and 5.77%, respectively, after the thermophilic phase, while the protease activity had a maximum increment of 347%. Metabolic analysis revealed that carbohydrate, amino acid and lipid metabolism was possibly inhibited by the high temperature, but the relative abundances of related predicted functions recovered by more than 0.9%, 7% and 11%, respectively, by the end of biodrying. Protein function prediction suggests that β-oxidation, fatty acid biosynthesis, and the degradation of cellulose and chitin were possibly enhanced during the thermophilic phase. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed that leucine, isoleucine and lysine could ultimately degraded to acetyl-CoA. Weissella, Aeribacillus and Bacillus were the genera with the most enriched functional genes during the whole biodrying process. These findings help elucidate the microbial degradation processes during biodrying, which provides further scientific support for improving the application of biodrying products.

Optimization of Aeration for Accelerating Municipal Solid Waste Biodrying

Biodrying technology is commonly used in Thailand to produce refuse-derived fuel (RDF), however, this technology remains ineffective on high-moisture waste. Air supply is key to ensuring homogenous temperature development within the waste matrix during biodrying, increasing RDF quality. This study investigated negative aeration during local municipal solid waste biodrying to meet RDF standards in reduced time. Lysimeter experiments were performed on pre-shredded waste (300 kg/m3) using different aeration patterns. The temperature, vent gas oxygen level, weight loss, and leachate volume during the biodrying process were monitored. In addition, the treated waste’s temperature, moisture, and heating values were evaluated to determine the biodrying process efficiency. The results indicate that shorter heating phases can be achieved during continuous aeration. No significant temperature variation was observed in the waste layers, with a low standard deviation of 1.96% during constant air supply, indicating homogeneous temperature development during the biodrying process. The vent gas contained 15–20% oxygen and non-detectable methane, evidencing sufficient air supply. The total heat development was independent of aeration pattern; therefore, biodrying was unaffected by excess air supply at a 95% confidence level. The highest weight loss and moisture content reduction were 25% and 66%, respectively. The optimal aeration was continuous mode with non-excessive aeration, increasing the lower heating value from 2,884.0 to 4,938.0 kCal/kg, and reducing the moisture content from 48.5% to 22.2%. RDF quality can be improved 1.7 times to meet Thailand’s standards within a short biodrying period of 7 days using homogeneous temperature distribution operated under continuous aeration

Migration and transformation of main components during perishable waste bio-drying process

Bio-drying can significantly reduce the moisture content of waste. The factors, functional microorganisms, and the transformation of main components were investigated during bio-drying of perishable waste. This study provides a scientific basis for the improvement of the bio-drying process and the necessity for secondary pollutant control. Reaction temperature and microbial biomass were main factors during the bio-drying process. The ideal bio-drying conditions included an initial temperature above 20 °C, intermittent ventilation, and appropriate microbial inoculation. The main microorganisms included Alcaligenes, Aquamicrobium, and Brevundimonas. From each gram of the carbonaceous, nitrogenous, sulfur-containing compounds, and phosphorus-containing substances in the perishable waste, approximately 0.74 g, 0.66 g, 0.40 g, and 0.94 g, respectively, were transferred as gas-phase products; consisting mainly of ammonia and volatile organic compounds: 2-heptanone, dimethyl heptanone, and benzene. In the leachate, the respective amounts of the carbonaceous, nitrogenous, sulfur-containing compounds, and phosphorus-containing substances were 3.20 × 10−3 g, 4.08 × 10−3 g, 0.33 g, and 9.52 × 10−3 g, while those of the residual substances remaining in solid were 0.26 g, 0.33 g, 0.28 g, and 0.05 g.

Modelling and simulation of food waste bio-drying

Bio-drying of food waste is an attractive aerobic treatment method for moisture removal and producing refuse-derived fuel (RDF) beneficial for waste utilization as an energy source. Understanding the mechanism of process and interaction of key variables is necessary for optimizing the parameters to improve the water removal rate. In the present study, an attempt was made to develop mass and energy balances using the first principles to predict the variation of key variables namely concentration of degradable matter, moisture, oxygen concentration, and temperature based on process kinetics. The simulation of the developed first-order ordinary differential equations combined for three horizontal layers of the waste pile was carried out using Simulink software in MATLAB R2020b interface. The predicted output was compared with experimental data of the pilot-scale plant for food waste with different municipal solid waste components including paper and plastic and with literature data for food waste with a bulking agent (BA). A good prediction of bio-drying performance was achieved using the proposed model and the experimental data.

Carbohydrate degradation contributes to the main bioheat generation during kitchen waste biodrying process: A pilot study.

Biodrying is a promising method for processing kitchen waste (KW) with high moisture content into reusable solid recovered fuels (SRFs). During biodrying, a large amount of bioheat generated from biodegradation of biochemical components results in KW dehydration. However, the degradation rules of these components and their contribution to the bioheat in KW biodrying have not been systematically clarified. Here, a pilot experiment was performed to investigate the variations in biochemical components, hydrolase activities, and bioheat generation during three successive cycles of biodrying processes. Results showed that KW could be rapidly converted into SRFs with low calorific values of 6705-7062kJ/kg and moisture content of 31.26%-35.21%. Analyses of hydrolase activities and mean fluorescence intensity suggested that the biodrying process pioneered the degradation of lipids and proteins in the warming stages, while carbohydrates (i.e. amylum, celluloses, etc.) underwent rapid decomposition in a large extent in the high-temperature and cooling stages. Carbohydrates with minimal difficulty in degradation, contributed 73.37%-89.92% to the total degradation mass and 59.23%-60.80% to the bioheat source during the three-cycle biodrying process. The generated bioheat was 4.32-4.56 times the amount of the theoretical heat used for water removal, indicating that internal bioheat could significantly enhance water evaporation and was sufficient for the expected water removal mass. Therefore, the evaluation of the main components to bioheat generation and its utilization efficiency makes a prominent contribution that can greatly clarify the conversion of KW biodrying into SRFs in order to efficiently promote renewable bioenergy and support the bioeconomy.

Analysis of the Long-Term Mass Balance and Efficiency of Waste Recovery in a Municipal Waste Biodrying Plant

The aim of this study was to determine the role of an installation based on biodrying of municipal waste in a Circular Economy by taking into account the quantitative and qualitative changes in its selectively collected waste stream. As a case study, the Mechanical-Biological municipal waste treatment installation in Olsztyn, Poland, was selected, which is equipped with a separate section for valorizing the selectively collected waste stream. The scope of the work included a complete mass balance of the waste treatment plant, an assessment of the technological efficiency of the municipal waste biodrying installation, and determination of the changes in the main waste from 2016 to 2020. This paper proposes an empirical method for estimating process loss during biodrying and provides many technological results. The average process loss was 23.47%, and on average, 88.9% of the waste produced by biodrying consisted of the Refuse-Derived Fuel fraction. The recovery of commercial assortments from selectively collected waste increased from 84.82% in 2016 to 89.26% in 2020. Considering the current morphology of municipal waste in this region, the maximum share of waste subjected to material and organic recycling processes in the analyzed region could be increased to around 60%, which indicates that Circular Economy targets can be achieved. This work should provide a compendium of information for countries implementing a Circular Economy.

Microbial succession and degradation during kitchen waste biodrying, highlighting the thermophilic phase

Biodrying in conjunction with compound stone amendment was used to treat kitchen waste, which improved biodrying. After 16 days, the pile moisture content decreased from 68.8% to 23.0%. Lignin, cellulose and hemicellulose concentrations decreased from 104.6 mg g−1 d.b., 322.9 mg g−1 d.b. and 155.9 mg g−1 d.b., respectively, to 74.0 mg g−1 d.b., 224.8 mg g−1 d.b. and 134.5 mg g−1 d.b., respectively. The Shannon index for bacteria increased from 2.5 to 3.1, while for fungi, it decreased from 4.6 to 0.6. The relative abundances of Amino Acid Metabolism and Carbohydrate Metabolism exceeded 7%. The thermophilic phase during the process inactivated the pathogenic microorganisms, increased the bacterial diversity, decreased the fungal diversity, and potentially improved the metabolism of nutrients, including amino acids, carbohydrates, lipids and vitamins. The biomarker analysis and predicated protein sequences provide genetic evidence to elucidate why the thermophilic phase is the peak time for nutrient metabolism.

Performance of Biodrying Process based on Temperature Profile and Cumulation

The biodrying process of solid waste is an approach to the use of biomass energy, where solid waste is dried using the heat generated from aerobic degradation of organic matter. Temperature profile and cumulation of the solid waste biodrying process are the success factors in drying solid waste. The reactor used is made of plywood with dimensions of (30 × 30 × 100) cm equipped with a heat sink using Thermoshield Universal to minimize heat loss. Aeration discharge at the biodrying process reactor is 0.023 m3/kg/h. The results showed a maximum temperature of 61°C produced from the bottom layer of the biodrying reactor (addition of 6 l / min air flow) on the first day at 10:00 pm. Cumulation temperature in the bottom layer of the biodrying reactor for 21 days of research reached 186.9°C. This value is a source of heat generated from the decomposition of waste under aerobic conditions. Based on the three layers, it can be concluded that the bottom layer produces higher temperature cumulation than the top or middle layer. This research can be a reference for determining temperature monitoring points and knowing Temperature cumulation generated from the waste decomposition process using biodrying technology.

Biological drying of municipal solid waste from landfill

The aim of this work was to investigate the process of biodrying of municipal solid waste from the old landfill to preparing it for pyrolysis or gasification. New aspect of this research is biodrying of waste from old landfill. Biodrying of wastes was carried out at different aeration rates (7, 35, and 175 dm3/kg dry matter/d) at two temperatures (23 and 50 °C). The research was carried out in the laboratory bioreactors of special design (lysimeters), which simulated the conditions prevailing in the landfill. The optimal conditions for reduction of moisture in waste (63.2%) has been attained for the highest aeration rate (175 dm3/kg dry matter/d) and temperature equal to 50 °C. The final moisture content of the obtained biodried product was 23% w/w. In the bioreactor, in which the greatest reduction of moisture was obtained, the total amount of produced CO2 was 44.9 gC/kg dry matter, and the biodrying efficiency was equal to 0.89. During biodrying of wastes in optimal conditions, higher heating value of waste increased from 4.3 to 11.0 MJ/kg. As a result of the performed pyrolysis of biodried waste at 900 °C, char, oil, and gas were obtained the respective yields of 47, 32, and 21% w/w. The gas emerging in the gasification process was characterized by higher heating value equal to 11.3 MJ/m3.

Biodrying performance and combustion characteristics related to bulking agent amendments during kitchen waste biodrying

Biodrying of kitchen waste amended with different bulking agents was carried out to evaluate performance, heat values and combustion characteristics. Results showed that adding bulking agents produced higher water removal rates of 55.6%−65.4%. Addition of bulking agents also yielded higher volatile solid contents related to slower degradation. Lower heat values of bulking agent treatments increased from 2000–3218 kJ·kg−1 to 8544–9849 kJ·kg−1. Organic degradation did not influence ignition or combustion temperatures during the second combustion stage, but did influence combustion rate. Maximum combustion rate and temperature of the third combustion stage remained stable. Bulking agents produced higher apparent activation energies compared with the control, although biodrying made combustion of kitchen waste easier, because of an overall decrease in apparent activation energy.

Effects of the aeration pattern, aeration rate, and turning frequency on municipal solid waste biodrying performance

Interactive influences of the aeration pattern, aeration rate, and turning frequency on municipal solid waste biodrying performance were investigated. Energy and water mass balances were used to identify the main water-removal routes and determine the amount of energy used and efficiency. Changing the aeration pattern and turning frequency did not significantly affect biodrying performance when the other conditions and total aeration volume were constant. The total aeration volume controlled the pile temperature and evaporation, making it the main factor affecting water loss during biodrying. A continuous aeration rate of 0.5 L kg−1 dry matter·min−1 gave the best biodrying performance (the highest water-removal rate, biodrying index, and sorting efficiency, 0.5 kg kg−1, 4.12, and 86.87%, respectively, and the highest lower heat value (LHV) and heat utilization rate, 9440 kJ kg−1 and 68.3%, respectively). There was an optimum aeration rate, water loss reaching a maximum at an aeration rate of 0.5 L kg−1 DM·min−1 and not increasing further as the aeration rate increased further. Lower aeration rates gave higher volatile solid degradation rates. The effects of turning could be achieved by increasing the aeration rate. The recommended biodrying parameters are continuous aeration at an aeration rate of 0.5 L kg−1 dry matter min−1 and one turn every 3 d.

Full-scale biodrying process of municipal solid waste

The paper presents the results obtained in the full-scale waste biodrying reactor. The studied facility includes in the biological stage a rectangular-shaped, galvanized steel reactor equipped with a module for active aeration connected with a stove and a bio-filter for removing odours. The undersize fraction (O days in the 150 m3 capasity reactor. Initial moisture content of the untreated waste was 54.65%. Moisture content was declined gradually during biodrying process. Temperature changes during 14th days of biodrying process were monitored with the maximum temperature 70°C. To assess the degree of stabilization of the biodried waste, the determination of the O2 uptake was measured. The oxygen demand of untreated waste was 53.16 mg O2 /g d.m. and after 14th days for biodried waste oxygen consumption was 19.78 mg O2 /g d.m. The results obtained in studies by respirometric dynamic method of oxygen uptake (expressed as O2 /96h parameter) had been compared to the results performed using the static method, where AT4 is the applied indicator.

Comparison between conventional biofilters and biotrickling filters applied to waste bio-drying in terms of atmospheric dispersion and air quality

ABSTRACTBiofiltration has been widely applied to remove odours and volatile organic compounds (VOCs) from industrial off-gas and mechanical-biological waste treatments. However, conventional open biofilters cannot guarantee an efficient dispersion of air pollutants emitted into the atmosphere. The aim of this paper is to compare conventional open biofilters with biotrickling filters (BTFs) in terms of VOC dispersion in the atmosphere and air quality in the vicinity of a hypothetical municipal solid waste bio-drying plant. Simulations of dispersion were carried out regarding two VOCs of interest due to their impact in terms of odours and cancer risk: dimethyl disulphide and benzene, respectively. The use of BTFs, instead of conventional biofilters, led to significant improvements in the odour impact and the cancer risk: when adopting BTFs instead of an open biofilter, the area with an odour concentration > 1 OU m−3 and a cancer risk > 10−6 was reduced by 91.6% and 95.2%, respectively. When replacing the biofilter with BTFs, the annual mean concentrations of odorants and benzene decreased by more than 90% in the vicinity of the plant. These improvements are achieved above all because of the higher release height of BTFs and the higher velocity of the outgoing air flow.

Biodrying of municipal solid waste under different ventilation modes: drying efficiency and aqueous pollution

Ventilation is very important during the biodrying process because it affects the biodrying efficiency and secondary pollution. In this study, three ventilation modes-intermittent negative ventilation (IN), continuous negative ventilation (CN) and intermittent positive ventilation (IP)-were used to provide the same amount of total air during biodrying of municipal solid waste (MSW). During the entire 16-day experiment, 68.4%, 68.7% and 67.2% of water contained in the initial waste was removed under IN, CN and IP trials respectively. The ratio of water loss to volatile solid loss was used to evaluate the biodrying efficiency, with values of 5.35, 5.93 and 4.82 being observed for IN, CN and IP trials respectively. The total organic carbon concentrations of the leachate generated from the biodrying of waste were as high as 25,000 mg/l, while those of the condensate were not higher than 3500 mg/l. During the entire process, the average ammonia concentrations of leachate and condensate were 1350 mg/l and 2140 mg/l respectively. From the aspect of biodrying efficiency, continuous negative ventilation was the most preferable ventilation mode for biodrying of MSW, while special care should be taken to prevent aqueous pollution if it is used in a MSW treatment plant.

Investigation of the application of an enzyme-based biodegradability test method to a municipal solid waste biodrying process

This paper presents a study to evaluate the recently developed enzymatic hydrolysis test (EHT) through its repeated application to a waste treatment process. A single waste treatment facility, involving a biodrying process, has been monitored using three different methods to assess the biodegradable content of the organic waste fractions. These test methods were the anaerobic BMc, aerobic DR4 and the EHT, which is a method based on the enzymatic hydrolysis of the cellulosic content of waste materials. The input municipal solid waste (MSW) and the output solid recovered fuel (SRF) and organic fines streams were sampled over a period of nine months from a single mechanical biological treatment (MBT) facility. The EHT was applied to each stream following grinding to <10 mm and <2 mm, in order to investigate the effect of particle size on the release of dissolved organic carbon (DOC) from enzyme hydrolysis. The output organic fines were found to more biodegradable than the MSW input and SRF output samples in each of the test methods, significantly ( p < 0.05) for the EHT and DR4 methods, on the basis of DOC released and oxygen consumed, respectively. The variation between sample replicates for the EHT was higher where sample sizes of <2 mm were analysed compared to sizes of <10 mm, and the DOC release at each phase of the EHT was observed to be higher when using particle sizes of <2 mm. Despite this, additional sample grinding from the <10 mm to a smaller particle size of <2 mm is not sufficiently beneficial to the analysis of organic waste fractions in the EHT method. Finally, it was concluded that as similar trends were observed for each test method, this trial confirms that EHT has the potential to be deployed as a practical operational biodegradability monitoring tool.

Lower Heating Value Dynamics during Municipal Solid Waste Bio-Drying

In agreement with the new European Union directives concerning the valorization of materials and energy recovery, Municipal Solid Waste (MSW) management is, in general based on an integrated approach characterized by a combination of different treatment processes. The bio-mechanical treatment (BMT) of MSW is an increasing option in Europe either as a pre-treatment before landfilling or as a pre-treatment before combustion. In this context the research on the bio-drying process is not fully developed. In the present paper the Lower Heating Value (LHV) dynamics during MSW bio-drying has been assessed. Measurements were made using a pilot scale bio-dryer that allows the recording of data as air flow, temperature (at the entrance, at the exit and inside the waste), and weight loss. An initial characterization of the MSW completes the input data. Results give information on the dynamics of the main process parameters (humidity, volatile solids, ammonia, Lower Heating Value) and also of additional parameters.

Biostabilization–biodrying of municipal solid waste by inverting air-flow

The process of biodrying could be a good solution for municipal solid waste management, allowing the production of fuel with an interesting energy content. Previous work (Adani, F., Baido, D., Calcaterra, E., Genevini, P.L., 2002. The influence of biomass temperature on biostabilization–biodrying of municipal solid waste. Bioresource Technology 83 (3), 173–179) has indicated that appropriate management of the processing parameters (air-flow rate and biomass temperatures) could achieve biomass drying in very short times (8–9 days). However, the data of that work also evidenced that if the conditions do not consider pile turning, and the air-flow is always from one direction, temperature gradients arise within the biomass, resulting in a lack of homogeneity in the moisture and energy content of the final product. Therefore, a new laboratory study was conducted on municipal solid waste biodrying–biostabilization in an effort to obtain homogeneous final products. Our proposal to solve this lack of homogeneity is to periodically invert the air-flow direction. Thus, in line with a previous study, two trials, A and B, were carried out, dividing the biomass into three layers to study temperature and moisture gradients throughout the process, and a third trial (C) simulating air-flow inversion at regular intervals was introduced. The results suggest that the daily inversion of air-flow eliminates marked temperature differences and leads to a homogeneous final product.