Biodrying for municipal solid waste: volume and weight reduction

Biodrying of municipal solid waste-correlations between moisture content, organic content, and end of the biodrying process time

Biodrying refers to the decomposition of organic municipal solid waste (MSW) under aerobic conditions. This process usually lasts 14 days and requires large amounts of air to be injected into the waste matrix. The efficiency of the biodrying process depends on several geotechnical parameters, including initial moisture content, initial organic content, bulk density, dry density, solid particle density, and porosity. To examine the potential influence of these parameters on the biodrying process, we analyzed 13 biodried MSW samples. The results revealed a strong positive linear relationship between the initial moisture content and the mass loss percentage. In the first three days of the biodrying process, the waste mass rapidly decreased; afterwards, the daily mass loss occurred at a less rapid, more constant rate. The established average mass removal ratio between the volatile solids and water was 1:6.38 with a standard deviation of 1.06. Dry and solid particle densities were preserved in all 13 experiments; thus, the corresponding void ratio remained unchanged. This finding suggests that the settlement and degradation of MSW that occur during the biodrying process did not significantly influence the airflow rate.

Conversion of solid wastes and natural biomass for deciphering the valorization of biochar in pollution abatement: A review on the thermo-chemical processes

This overview addresses the formation of solid trash and the various forms of waste from a variety of industries, which environmentalists have embraced. The paper investigates the negative effects on the environment caused by unsustainable management of municipal solid trash as well as the opportunities presented by the formal system. This examination looks at the origins of solid waste as well as the typical treatment methods. Pyrolysis methods, feedstock pyrolysis, and lignocellulosic biomass pyrolysis were highlighted. Explain in detail the various thermochemical processes that take place during the pyrolysis of biomass. Due to its carbon content, low cost, accessibility, ubiquitousness, renewable nature, and environmental friendliness, biomass waste is a unique biochar precursor. This study looks at the different types of biomass waste that are available for treating wastewater. This study discussed a wide variety of reactors. Adsorption is the standard method that is used the most frequently to remove hazardous organic, dye, and inorganic pollutants from wastewater. These pollutants cause damage to the environment and water supplies, thus it is important to remove them. Adsorption is both simple and inexpensive to utilize. Temperature-dependent conversions explain the kinetic theories of biomaterial biochemical degradation. This article presents a review that explains how pyrolytic breakdown char materials can be used to reduce pollution and improve environmental management.

Methods, mechanisms, models and tail gas emissions of convective drying in sludge: A review

In tandem with the population and economic growth worldwide, the scale of wastewater treatment has been increasing each year. Thus, a large amount of sludge is being produced. If the problem of sludge treatment and disposal cannot be effectively solved, it will cause serious environmental pollution. The premise of sludge drying is that sludge is "harmless" and can be "recycled." Currently, the studies on convective drying focus on the direction of thin-layer drying, fluidized bed drying, spray drying and pneumatic drying. This paper systematically reviews the convective drying technology of sludge. First, the effects of air velocity temperature, relative humidity and particle size on the drying effect are precisely described, as well as the four different drying stages in the drying process, including preheating, constant rate drying, first falling rate drying, and second falling rate drying stages. Second, the research progress of different convective drying treatment technologies and the application of eight mathematical models of thin-layer drying in this field are elaborated. The effects of sludge shrinkage formation mechanisms and sludge viscous resistance generation during the drying process are also discussed in detail. The formation mechanism of sludge shrinkage and the effect of sludge viscosity resistance during drying are also elaborated. Finally, the main dry tail gases and restraining methods are elaborated during the drying process. This paper will provide a structured reference for the related research of sludge convective drying in the future.

Biodrying with the hot-air aeration system for kitchen food waste

Biodrying is a promising method that produces bio-stabilized output with minimum pretreatment requirements. In this study, a hot-air supply system was added to the traditional biodrying process for kitchen waste, which showed significant reduction in moisture content in 5 days (maximum reduction of 37.45%). A series of experiments was conducted to optimize the hot-air biodrying system utilizing different aeration rates, temperatures, and mixing ratios of feedstock to bulking agents. The results showed that a 65 °C aeration temperature led to the highest water removal rate and low volatile solids consumption rate, with the biodrying index reaching 4.9 g water per gram of volatile solids. On the other hand, evaluation of the overall biodrying efficiency based on the weight loss and bio-stabilization showed that intermittent aeration temperature at 55 °C performed best, offering suitable conditions for water evaporation and bio-degradation. In combination with a flow rate of 0.8 L/kg*min and 1:1 mixing ratio, these conditions resulted in the maximum volatile solids consumption of 26.26% in 5 days. The volatile solids consumption and 34.47% water removal rate of the trial had contributed to a total of 64.13% weight loss. The weight loss was even higher than that of a conventional biodrying system which was conducted for more than 14 days.

The Biological Drying of Municipal Waste in an Industrial Reactor—A Case Study

One of the methods of municipal solid waste (MSW) treatment is biodrying. The literature describes mainly the results obtained in a laboratory- and a pilot-scale reactor. The manuscript presents the results of MSW treatment in a full-scale bio-drying reactor (150 m3). The reactor is operated in one of the Polish installations specializing in mechanical-biological treatment (MBT). During the 14 day period of biodrying in the reactor, the parameters of MSW such as the moisture, temperature, loss on ignition (LOI), and net heating value (NHV) were examined. The temperature of the air in the reactor was also examined. The research also included changes in the above-mentioned parameters of MSW located in three parts of the reactor: the front, middle, and back. The test results showed that the moisture content of the waste decreased from the initial level of 55% to the level of 30%. This was accompanied by an increase in the NHV from 6.3 MJ kg−1 to 9.6 MJ kg−1. At the same time, the LOI decreased from 68% d.m. to 45% d.m. The LOI decrease is not favorable from the point of view of using MSW as refuse-derived fuel (RDF), as was expected in the final usage stage. The results have application value as the plant operator, having at their disposal the controlling of the reactor’s ventilation and the temperature inside the reactor, should select the speed of the moisture removal from MSW at such a level as to minimize the LOI decrease.

Solar composting greenhouse for organic waste treatment in fed-batch mode: Physicochemical and microbiological dynamics

Composting is a sustainable means of managing organic waste, and solar composters offer a viable solution in rural areas lacking connection to municipal power supplies. This study tracked the physicochemical and microbiological changes that occur in a solar composting greenhouse during the treatment of food and green cellulosic waste in fed-batch mode, which remain poorly understood. Solar composting greenhouse performed well on waste reduction and nutrient retention, resulting in a 45.0-58.8% decrease in feedstock volume over 12-day composting cycles, a 41% removal in dry matter after three batches of composting, and 29.5%, 252.9% and 96.6% increase in the nitrogen, phosphorus and potassium content respectively after 42 days of composting. Batch feeding and composting jointly influenced microbiological succession by altering the physicochemical properties of compost. The contents of nitrogen and phosphorus, pH, and electrical conductivity significantly accounts for variations in culturable microbial populations. The succession of dominant bacterial genera such as Lactobacillus, Pseudoxanthomonas, Bacillus, and Pseudomonas were closely related to pH, cellulose, NH₄⁺-N, carbon content, and temperature. In addition, Pichia kudriavzevii, Thermomyces lanuginosus, and Scopulariopsis brevicaulis successively became the dominant fungal species during composting. Preliminary compost quality assessments showed that solar composting greenhouse has a high potentiality to transform organic waste into organic fertilizer. Additionally, corresponding purposeful suggestions were proposed for future optimization in this system, mainly from a microbiological aspect.

Seasonal characterisation of municipal solid waste from Astana city, Kazakhstan: Composition and thermal properties of combustible fraction

This study presents the results of a seasonal municipal solid waste composition campaign, that took place over the period of September 2017 to June 2018 in the capital city of Kazakhstan, Astana. Four sampling campaigns were conducted in order to identify the seasonal variation of municipal solid waste composition, recyclables and energy potential materials, such as combustible fraction, useful for the evaluation of waste-to-energy potential. The combustible fraction was analysed for thermal fuel properties, such as proximate and elemental analyses and gross calorific value. The results over the four different seasons showed that the average recyclable fraction of municipal solid waste on a wet basis of 33.3 wt.% and combustibles fraction was 8.3 wt.%. The largest fraction was the organics (47.2 wt.%), followed by plastic (15.4 wt.%) and paper (12.5 wt.%). Small seasonal variations were observed for organics, paper, plastic and glass fractions. The highest values were found in summer for the organic waste, in spring for paper and plastic and autumn for glass. The recyclables fraction showed an absolute seasonal variation of 5.7% with a peak in the winter season (35.4%) and the combustibles fraction showed a seasonal variation between 8.3 wt.% to 9.4 wt.%. Finally, the average calorific value of the combustible fraction was estimated to be 21.6 MJ kg^-1 on a dry basis.

The Use of Biodrying to Prevent Self-Heating of Alternative Fuel

Alternative fuels (refuse-derived fuels—RDF) have been a substitute for fossil fuels in cement production for many years. RDF are produced from various materials characterized by high calorific value. Due to the possibility of self-ignition in the pile of stored alternative fuel, treatments are carried out to help protect entrepreneurs against material losses and employees against loss of health or life. The objective of the research was to assess the impact of alternative fuel biodrying on the ability to self-heat this material. Three variants of materials (alternative fuel produced on the basis of mixed municipal solid waste (MSW) and on the basis of bulky waste (mainly varnished wood and textiles) and residues from selective collection waste (mainly plastics and tires) were adopted for the analysis. The novelty of the proposed solution consists in processing the analyzed materials inside the innovative ecological waste apparatus bioreactor (EWA), which results in increased process efficiency and shortening its duration. The passive thermography technique was used to assess the impact of alternative fuel biodrying on the decrease in the self-heating ability of RDF. As a result of the conducted analyses, it was clear that the biodrying process inhibited the self-heating of alternative fuel. The temperature of the stored fuel reached over 60 °C before the biodrying process. However, after the biodrying process, the maximum temperatures in each of the variants were about 30 °C, which indicates a decrease in the activity of microorganisms and the lack of self-ignition risk. The maximum temperatures obtained (>71 °C), the time to reach them (≈4 h), and the duration of the thermophilic phase (≈65 h) are much shorter than in the studies of other authors, where the duration of the thermophilic phase was over 80 h.

Effects of inoculation amount and application method on the biodrying performance of municipal solid waste and the odor emissions produced

The effects of inoculation amount and application method on the biodrying of municipal solid waste (MSW) was investigated in this study. Results showed that a low level (5%) of inoculation with mature compost significantly improved the biodrying index (4.96), while adding greater amounts decreased the biodrying performance by increasing the volatile solid degradation rate. Covering the pile with inoculation material resulted in the highest water removal (72.7%) and greatest water content reduction (from 60.2% to 17.7%). Meanwhile, first covering and then incorporating the inoculation material into the biodrying pile did not improve biodrying performance. Clearly, addition of varying amounts of inoculation material via different application methods enhanced cellulose degradation rates by 2.3-14.2%. Using 10% inoculation material reduced the NH₃ emissions by 39.1-54.3% regardless of inoculation method, inoculation amount had a greater effect on NH₃ emissions than that of inoculation method. The covering inoculation material could reduce 65.08% H₂S emission, the inoculation method had a greater effect on H₂S emissions than that of inoculation amount. Given the comprehensive considerations of emission reduction and biodrying performance, a covering of 10% inoculating material is a suitable approach to improve biodrying performance and mitigate odorous gases emissions.

Co-biodrying of sewage sludge and organic fraction of municipal solid waste: Role of mixing proportions

This study investigated the performance of co-biodrying sewage sludge and organic fraction of municipal solid waste (OFMSW) at different proportions. Cornstalk was added at 15% (of total wet weight) as the bulking agent. Results show that increasing OFMSW percentage promoted the biodegradation of organic matter, thus enhancing the temperature integration value and water removal to above 75% during sludge and OFMSW co-biodrying. In particular, adding more OFMSW accelerated the biodegradation of soluble carbohydrates, lignins, lipids, and amylums, resulting in more organic loss and thus lower biodrying index (3.3-3.7 for 55-85% OFMSW). Water balance calculation indicated that evaporation was the main mechanism for water removal. Heat used for water evaporation was 37.7-48.6% of total heat consumption during co-biodrying. Our results suggest that sludge and OFMSW should be mixed equally for their efficient co-biodrying.

Effects of adding bulking agents on the biodrying of kitchen waste and the odor emissions produced

The effects of adding a bulking agent on the performance and odor emissions (ammonia and eight sulfur-containing odorous compounds) when biodrying kitchen waste were investigated. Three treatments were considered: the addition of either cornstalks (CS) or wood peat (WP) to kitchen waste as a bulking agent before biodrying, and a control treatment (CK). The water-removal rates for CK, CS, and WP treatments were 0.35, 0.56, and 0.43kg/kg, respectively. Addition of bulking agents to kitchen waste produced less leachate, higher moisture-removal rates, and lower consumption of volatile solids. The CS treatment had the highest biodrying index (4.07), and those for the WP and CK treatments were 3.67 and 1.97, respectively. Adding cornstalks or wood peat decreased NH₃ emissions by 55.8% and 71.7%, respectively. Total sulfur losses were 3.6%-21.6% after 21days biodrying, and H₂S and Me₂SS were the main (>95%) sulfur compounds released. The smallest amounts of sulfur-containing odorous compounds were emitted when cornstalks were added, and adding cornstalks and wood peat decreased total sulfur losses by 50.6%-64.8%.

Effects of adding bulking agents on biostabilization and drying of municipal solid waste

The influence of adding a bulking agent on the bio-stabilization and drying of municipal solid waste (MSW) was investigated. Three treatments were considered: the addition of either cornstalks or wood peat to MSW as a bulking agent before bio-drying and a control treatment that contained no bulking agent. Addition of bulking agents to MSW produced less leachate, higher moisture-removal rates, and consumed less volatile solids. Bulking with cornstalks achieved the highest water-removal rate (0.58-0.65kgkg^-1). The extent of organic degradation was related to temperature integration during bio-drying. Lipids and cellulose were the main components of organic losses in all treatments and adding a bulking agent changed the sequence and extent of degradation of biochemical components. The bio-drying index values were 1.75, 3.18, and 2.64 for MSW alone, MSW with cornstalks, and MSW with wood peat, respectively. Evaporation heat was the main component of heat consumption, accounting for 58.1-60.7% of the total energy consumption.

Monitoring the performances of a real scale municipal solid waste composting and a biodrying facility using respiration activity indices

Objective of the work was to monitor two full-scale commingled municipal solid waste (MSW) mechanical and biological pretreatment (MBT) facilities in Greece, namely a biodrying and a composting facility. Monitoring data from a 1.5-year sampling period is presented, whilst microbial respiration indices were used to monitor the decomposition process and the stability status of the wastes in both facilities during the process. Results showed that in the composting facility, the organic matter reduced by 35 % after 8 weeks of combined composting/curing. Material exiting the biocells had a moisture content of less than 30 % (wb) indicating a moisture limitation during the active composting process. The static respiration indexes indicated that some stabilization occurred during the process, but the final material could not be characterized as stable compost. In the biodrying facility, the initial and final moisture contents were 50 % and less than 20 % wb, respectively, and the biodrying index was equal to 4.1 indicating effective biodrying. Lower heating values at the inlet and outlet were approximately 5.5 and 10 MJ/wet kg, respectively. The organic matter was reduced by 20 % during the process and specifically from a range of 63-77 % dw (inlet) to a range of 61-70 % dw. A significant respiration activity reduction was observed for some of the biodrying samples. A statistically significant correlation among all three respiration activity indices was recorded, with the two oxygen related activity indices (CRI7 and SRI24) observing the highest correlation.

Research on the drying kinetics of household food waste for the development and optimization of domestic waste drying technique

Domestic food waste drying foresees the significant reduction of household food waste mass through the hygienic removal of its moisture content at source. In this manuscript, a new approach for the development and optimization of an innovative household waste dryer for the effective dehydration of food waste at source is presented. Food waste samples were dehydrated with the use of the heated air-drying technique under different air-drying conditions, namely air temperature and air velocity, in order to investigate their drying kinetics. Different thin-layer drying models have been applied, in which the drying constant is a function of the process variables. The Midilli model demonstrated the best performance in fitting the experimental data in all tested samples, whereas it was found that food waste drying is greatly affected by temperature and to a smaller scale by air velocity. Due to the increased moisture content of food waste, an appropriate configuration of the drying process variables can lead to a total reduction of its mass by 87% w/w, thus achieving a sustainable residence time and energy consumption level. Thus, the development of a domestic waste dryer can be proved to be economically and environmentally viable in the future.