Mechanical-biological Waste Treatment Plants Research Articles

Hydrothermal Carbonization of the Wet Fraction from Mixed Municipal Solid Waste: A Fuel and Structural Analysis of Hydrochars

One of the by-products of a mechanical-biological waste treatment plant is the under-sieve fraction, which requires separation prior to further processing of municipal mixed waste. This stream usually follows the fate of landfilling. Instead, it could be introduced to the hydrothermal carbonization (HTC) process to improve its fuel properties and become solid recovered fuel. The organic fraction and high moisture content (approximately 26%) of under-sieve fraction are favorable properties for the HTC process. In this study, hydrochars, the solid product of HTC, were produced at 200 and 220 °C with residence times of 1, 4, and 8 h. The main aim of this investigation was to establish the influence of different process parameters on hydrochars’ fuel properties. Thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) were employed in the analyses. The results confirmed the positive effects of hydrothermal carbonization on the under-sieve fraction of municipal mixed waste properties. The ignition temperature increased from 247 °C to 288 °C and burnout temperature decreased to 443 °C from 489 °C after hydrothermal carbonization, causing a shorter combustion process. The determined key combustion parameters were: S = 12.4 × 10−8%·min−2·°C−3, Hf = 1174.9 °C and Di = 0.0075%·min−3, which in comparison to USF decreased by 44%, increased by 33%, and decreased by 29%, respectively, and became closer to those of coal. Furthermore, the identified structural changes indicate that hydrochars could be successfully used in energy production. The most promising results were found for hydrochar produced at 220 °C for 1 h, leading to a better combustion performance and providing a more stable and a less violent flame.

The Air and Sewage Pollutants from Biological Waste Treatment

The mechanical-biological waste treatment plants (MBTP), which include the municipal waste biogas plants, have an important role in sustainable urban development. Some plants are equipped with a sewage pre-treatment plant, which is then directed to the sewerage system and the treatment plant. Others, on the other hand, have only a non-drainage tank. The parameters of technological sewage (TS) or processing technology could reduce sewage contamination rates. In addition to the quality of sewage from waste treatment plants, the emission of odours is also an important problem, as evidenced by the results obtained over the sewage pumping station tank. The conducted statistical analysis shows a significant positive correlation between odour concentration (cod) and volatile organic compounds (VOCs). Analysing the individual compounds, a high positive correlation was also found—the strongest being between H2S, NH3 and VOCs. In the case of sewage compounds, the insignificant correlation between P total and other parameters was found. For the rest of the compounds, the highest positive correlation was found between COD and BOD and N-NO2 and N-NH3 as well as COD and N-NO2. The dilution of sewage is only an ad hoc solution to the problem. Further work should be aimed at reducing sewage pollution rates. The obtained results indicate large pollution of technological sewage and a high level of odour and odorants concentration. The novelty and scientific contribution presented in the paper are related to analyses of various factors on technological sewage parameters and odour and odorant emission from TS tank at biogas plant processing municipal waste, which may be an important source of knowledge on the management of TS, its disposal and minimisation of emitted compound emissions.

Prospects for environmentally safe mechanical biological treatment of municipal solid waste in Ukraine

Improving waste management is currently one of the priorities for Ukraine in the environmental safety. EU experience in the use of mechanical biological waste treatment technologies should be applied now in connection with the development and implementation of Regional Waste Management Plans in Ukrainian regions. The aim of the paper is to analyse the benefits and the preconditions of using mechanical biological waste treatment technologies in Ukraine, as well as barriers that may hinder the construction of mechanical biological waste treatment plants. The analysis of the eight drafts of the Regional Waste Management Plans showed that the mechanical biological waste treatment technologies market is free in Ukraine and the best option for the regions where there are cement plants operating is production of solid recovered fuel. Such types of projects could be affordable for Ukrainians with the cost recovery period more than 8 years. On the other hand there are significant obstacles of economic, organizational and technological nature to their immediate implementation i.e. low rates on waste disposal tax, partly compliance on air emissions monitoring system, absence of necessary standards etc. The priority actions to speed up mechanical biological waste treatment technologies implementation have been defined.

The correlations of the particle size, calorific value, moisture- and ash content of waste derived fuel, and examination of its heavy metal content

Significant development has taken place in the field of waste management recently in the preparation of the energetic exploitation of recyclable, non-hazardous municipal solid waste. With mechanical-biological waste treatment, 35-40% of the weight of this waste can be made appropriate for energetic exploitation, mainly for co-incineration in cement factories and power plants.
 The recoverability of waste derived fuel produced in mechanical-biological waste treatment plants highly depends on the burning and combustion technological properties of the mixture, and on its compounds influencing burning and different emissions. Waste recovery facilities do not take over fuel below a specific calorific value and over a given heavy metal, halogen and pollutant content.
 In our research we were looking for correlations in the particle size, calorific value, moisture-, ash- and heavy metal content of waste derived fuel. On the basis of the measurement results, the connection between the particle size fractions and the fuel properties can clearly be stated. The fractions of smaller particle size have higher moisture-, ash- and heavy metal content, while the fractions of bigger particle size have higher calorific value.

Assessment of the Efficiency of Biological Treatment of Gases from Municipal Waste Processing

Abstract The objective of the study is research on a biofilter existing at a mechanical-biological waste treatment plant in Radom. The paper presents results of research on the filling of the analysed biofilter (moisture, organic matter content, nutrient content, pH, grain size composition, and equivalent diameter), process gases (temperature, humidity and pH, concentrations of the main pollutants - ammonia, hydrogen sulphide, volatile organic compounds, acetic acid, ethanol) and operational parameters (flow rate, height of the biofilter layer, surface load, gas residence time in the filter bed). Irregularities were observed related to biofiltration efficiency, particularly resulting from improperly selected filling material and improper biofilter operation. The technological research permitted the identification of problems and determination of the requirement of performing necessary operational changes. Further works will involve the design, manufacture, and installation of an integrated biofilter with two-stage gas purification process (a classic biofilter and a semi-permeable membrane).

Efficiency of waste processing in the MBT system

In the professional literature there is no information on the efficiency of waste treatment in MBT (mechanical-biological waste treatment) systems in Poland. This knowledge is currently particularly important as it will decide on the role of the MBT system in the new reality of the circular economy, and consequently on the direction and necessary scope of modernization of these systems. The article presents a series of technical and technological indicators designated for one of the recently commissioned MBT plants against the background of minimum, maximum and average values of these parameters set for 20 systems with various MBTs covered by the research as part of the review of technological solutions used in Poland, made in 2015. For the system in Marszów, respectively in 2017 and 2018, the average value of the ratio of underscreen to overscreen fraction was 1.4; the losses of mass in the biological treatment process amounted to 28.7 and 29.4%; energy demand – 46.6 and 44.3 kWh/Mg; the aeration index – 16.7 m3/(Mg h); the average waste recycling rate – 15.2 and 17.3%; the share of fuel fraction recovery – 11.6 and 16,6% and the share of waste sent to landfill – 33.2 and 32.3%.

Life cycle assessment of refuse-derived fuel production from mixed municipal waste

ABSTRACTThe aim of this study is to identify and assess the potential environmental impacts caused by refuse-derived fuel (RDF) production from mixed municipal waste, in a mechanical–biological waste treatment plant in Krakow, Poland. The study is based on life cycle assessment methodology, employing EASETECH model. The system boundaries include only those operations which lead to the production of RDF. The adopted functional unit is 1 Mg of mixed municipal waste generated in Krakow, which enters the mechanical–biological waste treatment plant.

Reducing the Indoor Odorous Charge in Waste Treatment Facilities

Characterising and determining the odorous charge of indoor air through Odour Units (OU) is an advantageous approach to evaluate indoor air quality and discomfort inside municipal solid waste facilities. The assessment of the OU can be done through the determination of Volatile Organic Compounds (VOC) concentrations and their odour thresholds. The aim of the study was to evaluate the differences in the odorous charge in the organic matter pit of a mechanical-biological waste treatment plant with a processing capacity of 287,500 tons year-1. The sampling was carried out during the months of September 2012 (original situation) and October 2012 (after emptying the organic matter pit drain pipe). 150 chemical compounds were determined qualitatively in the studied location, from which 102 were quantified due to their odorous characteristics as well as their potentiality of having negative health effects. The results obtained demonstrated that after a maintenance cleaning operation such as draining the organic matter pit pipe, the odorous charge inside the facility can be diminished in a great way, up to a 95%.

Implementing an advanced waste separation step in an MBT plant: assessment of technical, economic and environmental impacts

Heavy fractions resulting from mechanical treatment stages of mechanical-biological waste treatment plants are posing very specific demands with regard to further treatment (large portions of inert and high-caloric components). Based on the current Austrian legal situation such a waste stream cannot be landfilled and must be thermally treated. The aim of this research was to evaluate if an inert fraction generated from this waste stream with advanced separation technologies, two sensor-based [near-infrared spectroscopy (NIR), X-ray transmission (XRT)] and two mechanical systems (wet and dry) is able to be disposed of. The performance of the treatment options for separation was evaluated by characterizing the resulting product streams with respect to purity and yield. Complementing the technical evaluation of the processing options, an assessment of the economic and global warming effects of the change in waste stream routing was conducted. The separated inert fraction was evaluated with regard to landfilling. The remaining high-caloric product stream was evaluated with regard to thermal utilization. The results show that, in principal, the selected treatment technologies can be used to separate high-caloric from inert components. Limitations were identified with regard to the product qualities achieved, as well as to the economic expedience of the treatment options. One of the sensor-based sorting systems (X-ray) was able to produce the highest amount of disposeable heavy fraction (44.1%), while having the lowest content of organic (2.0% C biogenic per kg waste input) components. None of the high-caloric product streams complied with the requirements for solid recovered fuels as defined in the Austrian Ordinance on Waste Incineration. The economic evaluation illustrates the highest specific treatment costs for the XRT (€ 23.15 per t), followed by the NIR-based sorting system (€ 15.67 per t), and the lowest costs for the air separation system (€ 10.79 per t). Within the ecological evaluation it can be shown that the results depend strongly on the higher heating value of the high caloric light fraction and on the content of C biogenic of the heavy fraction. Therefore, the XRT system had the best results for the overall GWP [-14 kg carbon dioxide equivalents (CO2 eq) per t of input waste] and the NIR-based the worst (193 kg CO2 eq per t of input waste). It is concluded that three of the treatment options would be suitable under the specific conditions considered here. Of these, sensor-based sorting is preferable owing to its flexibility.

Characterization and determination of the odorous charge in the indoor air of a waste treatment facility through the evaluation of volatile organic compounds (VOCs) using TD–GC/MS

Municipal solid waste treatment facilities are generally faced with odorous nuisance problems. Characterizing and determining the odorous charge of indoor air through odour units (OU) is an advantageous approach to evaluate indoor air quality and discomfort. The assessment of the OU can be done through the determination of volatile organic compounds (VOCs) concentrations and the knowledge of their odour thresholds. The evaluation of the presented methodology was done in a mechanical–biological waste treatment plant with a processing capacity of 245.000tonsyear−1 of municipal residues. The sampling was carried out in five indoor selected locations of the plant (Platform of Rotating Biostabilizers, Shipping warehouse, Composting tunnels, Digest centrifugals, and Humid pre-treatment) during the month of July 2011. VOC and volatile sulphur compounds (VSCs) were sampled using multi-sorbent bed (Carbotrap, Carbopack X, Carboxen 569) and Tenax TA tubes, respectively, with SKC AirCheck 2000 pumps. The analysis was performed by automatic thermal desorption (ATD) coupled with a capillary gas chromatography (GC)/mass spectrometry detector (MSD). One hundred and thirty chemical compounds were determined qualitatively in all the studied points (mainly alkanes, aromatic hydrocarbons, alcohols, aldehydes, esters, and terpenes), from which 86 were quantified due to their odorous characteristics as well as their potentiality of having negative health effects. The application of the present methodology in a municipal solid waste treatment facility has proven to be useful in order to determine which type of VOC contribute substantially to the indoor air odorous charge, and thus it can be a helpful method to prevent the generation of these compounds during the treatment process, as well as to find a solution in order to suppress them.

The effect of storage and mechanical pretreatment on the biological stability of municipal solid wastes

Modern mechanical–biological waste treatment plants for the stabilization of both the source-separated organic fraction of municipal solid wastes (OFMSW) and the mixed stream of municipal solid wastes (MSW) include a mechanical pretreatment step to separate recyclable materials such as plastics, glass or metals, before biological treatment of the resulting organic material. In this work, the role of storage and mechanical pretreatment steps in the stabilization of organic matter has been studied by means of respiration techniques. Results have shown that a progressive stabilization of organic matter occurs during the pretreatment of the source-separated OFMSW, which is approximately 30% measured by the dynamic respiration index. In the case of mixed MSW, the stabilization occurring during the reception and storage of MSW is compensated by the effect of concentration of organic matter that the pretreatment step provokes on this material. Both results are crucial for the operation of the succeeding biological process. Finally, respiration indices have been shown to be suitable for the monitoring of the pretreatment steps in mechanical–biological waste treatment plants, with a strong positive correlation between the dynamic respiration index and the cumulative respiration index across all samples tested.

Intended process water management concept for the mechanical biological treatment of municipal solid waste

Accumulating operational experience in both aerobic and anaerobic mechanical biological waste treatment (MBT) makes it increasingly obvious that controlled water management would substantially reduce the cost of MBT and also enhance resource recovery of the organic and inorganic fraction. The MBT plant at Gescher, Germany, is used as an example in order to determine the quantity and composition of process water and leachates from intensive and subsequent rotting, pressing water from anaerobic digestion and scrubber water from acid exhaust air treatment, and hence prepare an MBT water balance. The potential of, requirements for and limits to internal process water reuse as well as the possibilities of resource recovery from scrubber water are also examined. Finally, an assimilated process water management concept with the purpose of an extensive reduction of wastewater quantity and freshwater demand is presented.

Comparison of aerobic and anaerobic stability indices through a MSW biological treatment process

A complex mechanical-biological waste treatment plant designed for the processing of mixed municipal solid wastes (MSW) and source-selected organic fraction of municipal solid wastes (OFMSW) has been studied by using stability indices related to aerobic (respiration index, RI) and anaerobic conditions (biochemical methane potential, BMP). Several selected stages of the plant have been characterized: waste inputs, mechanically treated wastes, anaerobically digested materials and composted wastes, according to the treatment sequence used in the plant. Results obtained showed that the main stages responsible for waste stabilization were the two first stages: mechanical separation and anaerobic digestion with a diminution of both RI and BMP around 40% and 60%, respectively, whereas the third stage, composting of digested materials, produced lesser biological degradation (20-30%). The results related to waste stabilization were similar in both lines (MSW and OFMSW), although the indices obtained for MSW were significantly lower than those obtained for OFMSW, which demonstrated a high biodegradability of OFMSW. The methodology proposed can be used for the characterization of organic wastes and the determination of the efficiency of operation units used in mechanical-biological waste treatment plants.