Biodrying Process Research Articles

Comparative Biodrying Performance of Municipal Solid Waste in the Reactor under Greenhouse and Non-greenhouse Conditions

The high moisture content of municipal solid waste yields a lower energy content of solid fuel that affects the thermal conversion efficiency. Biodrying is an alternative drying method using bio-heat generated by microbial metabolism to reduce the moisture content of municipal solid waste. This research was conducted in three pilot-scale biodrying reactors, two under greenhouse conditions compared with one conventional non-greenhouse condition. Two bunkers with greenhouse cladding were connected with aerators, and airflow rates were set at 0.4 and 0.6 m3/(kgwaste·day), respectively. Meanwhile, a passive aeration method was applied to the non-greenhouse bunker. This study aims to investigate the effect of the greenhouse condition on the biodrying process and assess the performance of the drying process through different operating conditions. The result shows that the greenhouse mainly affects the air temperature rise in the reactor. The aeration rate is positively correlated with weight reduction (r = 0.93). At 0.6 m3/(kgwaste·day) airflow rate, the treatment can reach a moisture content less than 30% on average within ten days, while at 0.4 m3/(kgwaste·day) airflow rate, it takes 15 days to reduce the moisture content to less than 30%. Biodrying under the greenhouse condition with active aeration potentially achieves desirable moisture content reduction and heating value increase more efficiently than the common biodrying. However, the airflow rate is a crucial factor in determining the suitable drying time in biodrying under the greenhouse condition.

Effect of Intermittent Negative Ventilation in Biodrying Process for Treating Pre-Shredded Waste

A pre-shredded waste with 49.4% of moisture content from a municipality in Thailand was treated in biodrying lysimeters with intermittent negative ventilation at the rate of 0.5 m3/kgwaste/day. Two air patterns were set with an interval of 30 min run/30 min stop (T1) and 30 min run/60 min stop (T2) and ran for seven days. The highest temperature was found in T2 at about 68.3 °C. The degradation of degradable materials was at 3.49% and 2.9% in T2 and T1, respectively. In T2, the weight could be reduced from 90 kg to 79.9 kg, corresponding to 11.2% of weight reduction. After seven days, moisture content and the heating value was in acceptable requirement of Refuse Derived Fuel (RDF) for local cement plants. The highest moisture removal was presented in T2 which can reduce the moisture content of 58.24% and the heating value was increased of 42.75% from initial heating value. Based on the local RDF requirement, it could be concluded that T2 is the best performance in this study with 20.63% of final moisture content and 17,719 kJ/kg of heating value.

Municipal solid waste (MSW) - competitive raw materials for combustible materials obtaining

Waste-to-energy projects can be classified as a complementary technology for energy recovery from nonrecyclable municipal waste fractions and should therefore not compete with measures to reduce, reuse, and recycle materials. The article presents the characterization of some treated municipal solid wastes as competitive raw materials for combustible materials obtaining. Samples with lignocellulosic and polymeric composition were analyzed, namely 3 samples of SRFs (solid recovered fuels) used as secondary raw material in cement plants, SRF1, SRF2, SRF3; a sample of RDF, consisting of household waste; a sample of fluff (a homogeneous mixture of non-hazardous waste - selected, mechanically treated and dried) used as a secondary raw material in cement plants; 4 samples of municipal solid waste, fractions smaller than 100 mm, after a bio-drying process, with composition: paper and cardboard (70-80%), wood (6-15%), plastic (6-10%), glass and metal (3-14%), MBU1, MBU2, MBU3, MBU4. The waste samples were characterized in terms of technical and elementary characteristics and the ash (obtained by the sample incineration) behavior in the combustion process. The mineral matter was investigated by the X-ray fluorescence analytical technique using the Rigaku CG X-ray Spectrofluorimeter. The analysis of the indices used for the slagging and deposit formation risks evaluation shows that the analyzed samples present an obvious risk of melt formation and deposits, due to a high content of base oxides and silicon oxide.

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.

Refuse Derived Fuel Production through Biodrying Process (Case study: Solid Waste from Canteens)

Due to its calorific value, wastes could be treated into Refuse Derived Fuel (RDF) through several processes. In order to get higher calorific value, moisture content in the wastes could be removed by utilizing the heat generated from decomposition of organic fraction by microorganism (biodrying process). The study aims to treat solid wastes generated from canteens in Ganesha Campus of Institut Teknologi Bandung into RDF through biodrying process. Through standard sampling procedure, total waste generated from 59 canteens was 228 kg/day and organic fraction became the dominant (74%). There were 3 biodrying piles prepared, namely aeration, windrow, and control pile. Temperature in all piles increased in first and second weeks, then it gradually decreased and the average temperature were between 23-48 oC. The heat generated during the process could be remove water content and the optimum time 17-22 days could reach 20-30% of moisture content. The highest calorific value could be obtained from aerated pile (14.98 MJ/kg). By considering several parameters, the best RDF were produced from aerated pile. The parameters which still did not comply with the international standard of RDF were ash content, fixed carbon, and organic carbon. The quality of RDF was affected significantly by the composition of the feed. Though it could not meet with all parameters as an international standard of RDF, the product could be used as co-fuel to substitute coal or other fossil fuels for industrial activities. By knowing that the wastes could be converted into valuable product, the local municipality may shift the conventional paradigm of the waste management which is only collect-haul-dispose into a new paradigm by prioritizing waste recycle.

English

English

Refuse Derived Fuel (RDF) dari Sampah Perkotaan dengan Proses Biodrying: Review

The utilization of waste into fuel (Refuse Derived Fuel, RDF) is an alternative to overcome the problem of municipal solid waste (MSW). Many processes can be applied to produce RDF including through biodrying process. Biodrying is a part of Mechanical-Biological Treatment (MBT) aiming to reduce water content in the waste by utilizing heat generated from microorganism activities while degrading organic matter in the waste, thus the calorific value will increase. The paper aims to make a review from various research papers on biodrying process published in scientific journals, so it becomes one of reference on further research on biodrying process by considering the characteristics of waste in Indonesia. The review has been conducted by focusing on several important aspects on the research such as operation principle, reactor design configuration, parameters to be examined, and the characteristics of feed and product.

Addition of Solid Recovered Fuel (SRF) to the Bio-drying Process and the Effects of Variation in Air Discharge on Temperature Parameters and Urban Waste Water Content

Bio-drying is a technology used to reduce water content in waste using microorganisms that naturally increase the temperature in the decomposition process. With this process, the water content can drop more within a month. Bio-drying produces a product in the form of Solid Recovered Fuel (SRF) which is produced from partially degraded waste. To obtain a waste that is not fully stabilized and maintains a high biomass content, degradation of organic compounds is carried out partially. During the bio drying process, temperature affects the degradation process. Temperature affects the bio drying, which will also affect the bio drying product that is indicated by the value of water content. Therefore, in this study, the change of process parameters will be explained, which is in the form of temperature and water content, that is caused by the difference in the air discharge entering the reactor (0, 2, 4, and 6 l/m) with the initial water content of 60%-65%. After 30 days, the optimum airflow is 4 l/m with a decrease in water content of 58.29%; on the last day of the bio drying process (30th day).

Simultaneous effects of airflow and temperature increase on water removal in bio-drying

Bio-drying MBT is a type of mechanical biological treatment (MBT) system, whereby the aerobic biological process is first used to remove moisture, which is followed by the mechanical separation to recover material and energy as a solid recovered fuel (SRF). Among various parameters of this process, the simultaneous effects of airflow rate and organic contents were examined in this study. A 25 L acrylic column reactor was filled with simulated waste. Temperature and humidity of the air inlet and outlet were continuously monitored, and CO2 concentrations in outlet air were periodically analyzed to observe aerobic biodegradation as well as metabolic water generation. Based on the data, the different water removal contributions by airflow and biodegradation were compared, and finally, evaluation of the inter-dependence of parameters and feedback effect in the bio-drying process was carried out. While the biodegradation of organics induced a significant amount of water removal due to increased temperature, high organic content has a negative effect on water removal by generating metabolic water. Water removal by air replacement is greater than that associated with temperature increases caused by biodegradation. However, excessive airflow rate can terminate biodegradation by drastically lowered moisture content, even though organics remained.

Reduction of sludge by a biodrying process: Parameter optimization and mechanism

Sewage sludge generated from chemical fiber plants is a hazardous waste with high disposal costs, and it is important to reduce the amount of sludge produced. In this study, a biodrying technology was controlled by thermophilic microorganisms to reduce and detoxify hazardous waste sludge. Ten batches of experiments were conducted under optimal parameters (i.e., under the conditions of a one-time feeding with the equipment temperature controlled at 60 °C, where the dosage of the microbial agent accounted for 4% of the dry weight of sludge) to evaluate the performance of the biodrying system reducing and detoxifying hazardous waste sludge under a continuous reaction. The results showed that the degree and rate of dehydration during the continuous reaction were 65.97% and 2.51%, respectively. The degrees of reduction for dry matter and toxic substances were 22% and 9%, respectively. The calorific value of sludge after treatment increased from 1678.53 J (later abbreviated as J) to 12256.17 J. The reduction effect in the pilot-scale experiment was 65%. Spectral analysis and microbial sequencing of the freeze-dried sludge advance our understanding of biodrying mechanisms and provide a foundation for the application of key technologies for the reduction and detoxification of hazardous waste sludge.

Potential Utilization of RDF as an Alternative Fuel to be Used in Cement Industry in Jordan

This experimental research aimed to examine potential production and utilization of RDF derived from mixed municipal solid waste using bio-drying technology to be used as a substitute fuel for the traditional fuel currently used in cement plants in Jordan. The characteristics of RDF produced were identified and compared with limits and criteria set by some European countries. An economic model for RDF utilization in cement industry was created. The model proposes six different options resulting from adding RDF as a substitute fuel for the petcoke fuel currently used. A cost analysis for each option proposed was performed to estimate the economic and environmental savings of RDF utilization in cement industry. At the end of the bio-drying process, the mass of dried waste directed to the landfill was reduced by about 35%. In the case of the recovery of RDF materials from dried waste, the mass of waste to be landfilled was reduced by 69%. The bio-drying process allowed an increase in the heating value of waste (LHV) by 58% to reach 15.58 MJ/kg, as a result of the reduction of waste moisture. RDF produced had high calorific value, low water content, and satisfactory chlorine content. With regard to the concentration of the heavy metals, all of the RDF samples tested had lower concentrations than those values set by some European countries. The findings showed that adding 15% RDF as a substitute fuel, equaling 4.92 tons/h, to the fuel used in cement kilns will save 486 USD/h in petcoke costs, with 2.27 tons/h of CO2 being emitted into the atmosphere at a net saving of 389 USD/h.

Effect of temperature and bulking agents on deep bio-drying of high-solid anaerobically digested sludge

The effect of temperature and bulking agents, namely sawdust (SD), wheat bran (WB), and wheat straw (WS), on bio-drying of high-solid anaerobically digested sludge (ADS) was evaluated. A mixture of dewatered ADS with municipal sludge compost product (CP) and different bulking agents was loaded into a 180-L pilot-scale reactor. Intermittent aeration of 12 L min−1 with 20 min run/40 min stop was adopted during the whole bio-drying process. After 18 to 21 days of bio-drying, volatile solids (VS) in the trials with SD, WB, and WS degraded at a rate of 86.6, 284.3, and 344.2 g kg−1 initial VS, respectively. The matrix with easier biodegradable WB and WS achieved faster and higher water removal at a rate of 692.7 to 764.2 g kg−1 initial water, and a higher temperature cumulation of 373 to 427 °C·d. Approximately 70% of the bio-generated heat consumed for water evaporation. In the trials with WB and WS, the matrix moisture content decreased to below 39%, and the weight declined by above 48%. Water removal and VS degradation contributed to 85.2 ± 3.4% and 14.8 ± 3.4% of the total weight loss, respectively. The residual WB in bio-dried products (BP) caused low germination index (GI), indicating possible phytotoxic effects in soils. WS was determined to be the best agent with significantly higher GI and lower cost compared to WB, implying promising land utilization potential of BP.

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.

Exploration of Biodrying Process for Mixed Municipal Solid Waste Management

The exploitation of self-heating nature of municipal solid waste for moisture reduction, through convective evaporation reaction called 'Biodrying Process' is promising for converting municipal solid waste with high moisture content in to a renewable energy substrate. The simultaneous regulation of air flow rate and reactor feed volume in the pilot scale reactor system has brought about a significant change in the spatial and temporal distribution of self heating reaction. The constant volumetric air flow rate of 40 L/m and initial filled height of reactor matrix was 1.65 m have been maintained in the first experiment, while the air flow rate has been doubled to of 80 L/m and the filled height of reactor matrix was raised to 2.0 m in the second experiment. Weight reduction of 29.6 % and moisture loss of 24.6 % has been achieved at the end of 11 days of reaction in the first study. A considerable improvement in biodrying process has been observed in the second experiment with a weight reduction of 40.7 % and moisture loss of 38.8 % achieved after 11 days of reaction. The accelerated evaporative cooling mechanism observed in the second experiment has found to improve the biodrying process efficiency.

Filling in sewage sludge biodrying gaps: Greenhouse gases, volatile organic compounds and odour emissions

In the present work, a complete study of the sewage sludge (SS) biodrying technology was conducted at bench-scale, aiming at assessing its performance and providing a valuable insight into the different gaseous emission patterns found for greenhouse gases (GHG) and odorant pollutants. As process key parameters, temperature, specific airflow, dynamic respiration index, final moisture content and Lower Calorific Value (LCV) were evaluated. At the end of the biodrying, a product with a 35.9% moisture content and a LCV of 7.1 MJ·kg−1product was obtained. GHGs emission factor was 28.22 kgCO2eq per Mg of initial mass of dry matter in the SS (DM0-SS). During the biodrying process, maximum odour concentration measured was 3043 ou·m−3 and the estimated odour emission factor of the biological treatment was 3.10E + 07 ou per Mg DM0-SS. Finally, VOCs were completely identified and quantified. The most abundant VOCs found in the biodrying gaseous emissions were terpenes, sulphur-compounds and ketones.

The biodrying process of sewage sludge – a review

Sewage treatment can be classified into three phases: liquid, gaseous, and solid. Treatment of solids is performed in several steps, and the greatest difficulty in removing water from sewage sludge is due to the bound water present in the sludge. Thus, biodrying, a drying method that can be classified as biological, has been recently applied to treat this type of waste. This review paper aims to report and compile data from 49 biodrying assays of sewage sludge found in the literature (through the present, 2019) into one synthesis table, to discuss and compare the numerous variables found in these papers and their implications for biodrying, and to suggest possibilities for future research. This paper additionally intends to improve knowledge of biodrying and to consequently contribute to the monitoring and understanding of the process.

Co-biodrying of sewage sludge and organic fraction of municipal solid waste: A thermogravimetric assessment of the blends

This study investigated the thermogravimetric properties of sewage sludge and organic fraction of municipal solid waste (OFMSW) during their co-biodrying at different fractions. Sewage sludge and OFMSW were co-biodried at the mass proportion of 0%, 42.5% and 85% (of the total wet weight), respectively, with 15% cornstalk as the bulking agent. Results show that of these three raw materials, OFMSW exhibited the lowest ignition temperature and the highest burnout temperature. Moreover, OFMSW had a better comprehensive combustion performance (S) than sewage sludge. Blending OFMSW, sewage sludge and cornstalk showed the highest S value (4.0 × 10−7%2 min−2 °C−3). In addition, there existed certain interactions between the co-combustion process, especially at high temperature stage. The burning characteristics, including ignition performance, burnout efficiency, DTGmax and S increased with fluctuations in the first 6–9 days of co-biodrying process, and then declined in all treatments. Hence, 15-day of biodrying made the product with poor burning behavior (S value of 1.0 × 10−7–1.4 × 10−7%2 min−2 °C−3). More importantly, the optimal combustion performance was observed when co-biodrying the same amount (42.5%) of sewage sludge and OFMSW with the peak of 8.3 × 10−7%2 min−2 °C−3 achieved on day 9. In addition, the blends were easier to burn after the biodrying process.

Anaerobic mono-digestion of pig manure in a leach bed coupled with a methanogenic reactor: Effects of the filter media

This work pioneered the efficient coupling of a leach bed reactor (using a filter medium and no anaerobic sludge) and a continuous stirred-tank reactor (LBR-CSTR) to perform the anaerobic mono-digestion of pig manure. The leachate residue of the pig manure (LR-PM) was dried by a biodrying process. The results revealed that the LBR-CSTR (with ceramsite (C) as the filter medium) showed the best performance (the biogas production was 241.68 ml/g volatile solids (VS), which was 1.24 times higher than that of the control CSTR (CK)), the weight loss of pig manure was the highest (the reduction was 95.83%), and the organic degradation was 86.82% (which was 19.49% higher than that of the CK). The seed germination index (GI) was higher than 50%, and the clogging of the leach bed was overcome. The energy and resource utilizations of pig manure were readily achieved.

Sludge bio-drying followed by land application could control the spread of antibiotic resistance genes

The process of sludge bio-drying has been adopted in response to the increasing amount of residual sewage sludge. It has been demonstrated that sludge bio-drying effectively reduces both antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs), whereas ermF, tetX, and sulII become enriched in response to the dynamic development of the microbial community. The present study further demonstrated that the land application of sludge bio-drying products under current application rate did not cause an increase in the abundance of quantified ARGs in the soil but the persistence of ARB should be paid attention. Although land application introduced ermF, tetX, and tetG into the soil, these soon decreased to control levels. Furthermore, the decay rate varied between soil types, with red soil being the most persistent based on kinetics modeling. The fate of ARGs could also be attributed to the dynamics of the microbial community during land application, and the genus Parasegetibacter, which can degrade extracellular DNA, might play a key role in the control of ARGs. In summary, sludge bio-drying following land application could constitute an effective means of controlling the spread of ARGs, and microbial community changes contributed the most to the fate of the ARGs during the entire treatment chain (residual sewage sludge → bio-drying process → land application).

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.