Performance of a new household composter during in-home testing

This article presents the methodology and the results of the performance testing of a prototype system for the production of high quality compost from biodegradable household waste separated at the source. Selected households in three municipalities of the Attica Region in Greece constituted the users of the home composter. The results indicated the effective operational performance of the prototype household composter in practice (use of the system by the householders on a daily basis), as well as the high level of response of the householders in adopting the composting practice in their daily activities as common practice. The compost that was produced in the households was characterized by high quality, which is in accordance with the quality standards that are set for its use. In only a few cases (in the first cycle of the pilot implementation) the quality of the compost was not high due to the fact that some householders were not yet familiar with the use of the composter, but these operational problems were solved and the compost that was later produced was considered high quality.     

Fate Of An Absorbent Gelling Material For Hygiene Paper Products In Landfill And Composting

A cross-linked polyacrylate polymer, referred to as absorbent gelling material (AGM), has been developed for use in hygiene paper products, such as infant diapers (nappies). The fate and effects of this polymer were studied in laboratory models of landfill and aerobic composting. Radiolabelled (¹⁴C) AGM was used to facilitate determination of fate and mass balance. Tests were conducted in 1201 reactors containing a mixture of solid waste and compost or solid waste only, and panty diaper pads. Controlled temperature and leachate recycle were used to accelerate the biological processes. AGM caused no adverse effects and most of the material remained associated with the diaper pad and surrounding waste. Very little AGM (less than 1%) biodegraded to CO₂/CH₄ under landfill conditions, while 2-4% appeared in leachate. The leachate was highly biodegradable aerobically. More of the AGM (6.4%) biodegraded to CO₂/CH₄ under aerobic composting conditions, while less than 1% appeared in leachate.     

Effect of C/N ratio on the in-vessel composting under air pressure of organic fraction of municipal solid waste in Morocco

The goal of this research was to investigate the effect of the C/N ratio on the in-vessel composting, under air pressure, of organic fraction of municipal solid waste in Morocco. Firstly, an in-vessel bioreactor was designed and used to evaluate the appropriate initial pressure for the composting process. Secondly, five bioreactors were run with C/N ratios of 26 (control; no C supplement), 32.2, 38.4, 44.6, and 50.8. Parameters monitored included internal air pressure, C/N ratio, temperature, volatile solids reduction, and maturity of the obtained composts. The relative microbial activity was observed indirectly using volatile solids removal and the relative heat generation data. The experimental results showed that organic waste could be composted within 10?days and the operating initial parameters that converted the most volatile solids and carbons in the feedstock were as follows: 0.6?×?10⁵ Pa for the initial air pressure and 26 for the C/N ratio. Maturity tests, in optimal conditions, showed that the final compost has characteristics of stable compost and can be used as a soil conditioner. In addition, compost obtained from the experiment that considered a C/N ratio of 32.2 showed good maturity levels and may also be used for agricultural applications.     

Degradable polymers: The role of the degradation environment

The degradability of several degradable polymers was examined using three types of degradation environments. These include exposure in a laboratory-scale composting test system containing material representative of the organic fraction of municipal solid waste (MSW), exposure in a thermal hydrolytic environment consisting of water at 60‡C, and exposure in a thermal-oxidative, dry oven environment of 60‡C. The results of the investigation clearly indicate that, in addition to chemical and biological activity which can lead to polymer degradation, physical restructuring and reorganization of the macromolecular structure may also occur at temperatures typically found in a compost environment, resulting in changes in the mechanical properties of the polymer films. In the case of the polyethylene-modified polymers evaluated in this study, all behaved similarly, but differently from the other polymer types. The polyethylene-based films appeared to be susceptible to oxidative degradation and should degrade in a composting environment providing that there is sufficient air in contact with the film for a sufficient period of time. However, when exposed in a laboratory composter, it appears that although ideal temperature-time curves may be obtained, the test time period was insufficient in comparison to the induction period required to achieve the desired thermal oxidative degradation. Issued as NRCC No. 37620.     

Practical Simulation Of Composting In The Laboratory

A closed incubation system was developed for laboratory simulation of composting conditions at the interior of a large compost pile. A conductive heat flux control system (CHFC) was used to adjust the temperature of the internal wall to that of the compost center and compensate for heat loss. Insulated small vessels (400 cm³) controlled by the CHFC system were compared with similar vessels maintained at 30°C (mesophilic) and 55°C (thermophilic), and with large vessels (10 000 cm³) with and without the CHFC. Compost temperature rose rapidly to a maximum within 2-4 days, then gradually decreased. In mesophilic treatments (no CHFC), temperature at the matrix center increased to a maximum of 36°C in the small vessel and 50°C in the large vessel, while temperature in both vessels reached 50°C with the CHFC. Microbial activity was maintained by allowing compost to self-heat and controlling temperature externally with the CHFC. Higher temperatures were sustained for longer periods in CHFC vessels than in vessels without the CHFC. Periodic mixing of the compost matrix increased temperature and CO₂ evolution. Small vessels were successfully used in laboratory simulation of field-scale composting of a soil/organic matrix containing TNT and RDX munitions. The small vessel system reduced subsample error in compost monitoring from that of the large vessels. The CHFC has particular utility in research requiring expensive chemicals or hazardous substances.     

Optimising energy recovery and use of chemicals,resources and materials in modern waste-to-energy plants

Due to ongoing developments in the EU waste policy, Waste-to-Energy (WtE) plants are to be optimized beyond current acceptance levels. In this paper, a non-exhaustive overview of advanced technical improvements is presented and illustrated with facts and figures from state-of-the-art combustion plants for municipal solid waste (MSW). Some of the data included originate from regular WtE plant operation – before and after optimisation – as well as from defined plant-scale research. Aspects of energy efficiency and (re-)use of chemicals, resources and materials are discussed and support, in light of best available techniques (BAT), the idea that WtE plant performance still can be improved significantly, without direct need for expensive techniques, tools or re-design. In first instance, diagnostic skills and a thorough understanding of processes and operations allow for reclaiming the silent optimisation potential.     

Low energy comsumption management of agricultural residues

In this paper, a mechanical filtering system to treat pig slurry is proposed. The filter was made from the aerobic decomposition product of the organic fraction of municipal wastes and wheat straw was used as the support.Using a pilot plant to treat 2100 liters of swine slurry, an adequate reduction in BOD₅; COD, and other parameters was obtained. The organic matter content of the material trapped in the filter was similar to that of compost and farmyard manure, but the nitrogen and phosphorous levels and the C/N ratio were more similar to farmyard manure. After passing through a filtering system, the treated liquid can be used for fertirrigation and as a feed for algae ponds. After a period of stabilization, the solid material can be mixed to produce manure. Although wheat straw was used as the support in this experiment, other agricultural wastes such as rice straw, corn stalks, millet stems, banana, cotton, and coconut trash can be used. Rather than municipal solid waste compost, other kinds of compost obtained from agricultural wastes such as leaves, bark, husks, etc., can be used as the filter.     

Digesting The Organic Fraction Of Municipal Solid Waste: Moving From Mesophilic (37°C) To Thermophilic (55°C) Conditions

This paper shows the possibility of moving in a matter of weeks from mesophilic (37°C) to thermophilic (55°C) conditions in the anaerobic digestion of the organic fraction of municipal solid waste (MSW) at high levels of solids (20%). After the temperature increases, a first pseudo steady-state condition can be reached after a month and a final steady-state condition after 2 months. No particular evidence of digester instability was observed using this approach in changing temperature range. The higher yields obtained in the latter condition (110% larger in terms of specific production) are shown.     

Seasonal effects on anaerobic digestion of the source sorted organic fraction of municipal solid waste

The effects of seasonal temperature change on the quality of easily degradable organic matter in municipal solid waste was monitored and the related influence on the anaerobic digester performance examined. It was verified that increased external temperature caused the transformation of the ethanol contained in the source—sorted organic fraction of municipal solid waste fed to the digester, into acetate. This transformation has been associated with a remarkable effect on the process kinetics of substrate utilization. Thus, the kinetic constant for the first order substrate utilization model in the summer (external temperature greater than 18–20 °C) doubled with respect to the winter, although the digester was held at 35 ± 2 °C throughout.     

Treatment of discarded oil in supercritical carbon dioxide for preparation of carbon microspheres

Carbon microspheres with diameter of 1–10 μm were prepared by treatment of waste oil in a supercritical carbon dioxide (scCO₂) system. The structure and morphology of the products were characterized by X-ray diffraction, field-emission scanning electron microscopy, and Raman spectrometry. It is shown that the products consist of graphite microspheres with relatively low graphitization. The yield of solid products increased from 26.8 wt% to 42.2 wt% as the reaction temperature was raised from 530°C to 600°C. Spheres with multilayer structure could be obtained by means of subsequent vacuum annealing of the carbon microspheres at 1500°C. The formation mechanisms of carbon microspheres in the scCO₂ system and the influence of vacuum annealing on the structure are discussed in detail.     

Sources and levels of potentially toxic elements in the biodegradable fraction of autoclaved non-segregated household waste and its compost/digestate

Waste that reflected the average UK composition of household waste was treated by autoclaving at the three set pressure/temperature levels of 2.7 bar/130 degrees C, 6.2 bar/160 degrees C and 15.5 bar/200 degrees C. The biodegradable fraction of the autoclaved household waste (;floc') was manually separated by screening and underwent characterization for its Cd, Cr, Cu, Pb, Hg, Ni, and Zn content. Autoclaving did not guarantee the production of compost/digestate that met the UK specification for compost, BSi PAS100, without restrictions being made on the composition of the waste feedstock. Results indicate that the levels of Zn and Cd associated with floc materials alone could lead to compost limit values being exceeded. For all other potentially toxic elements (PTEs), the estimated excessive (i.e. above levels of compliance) PTEs levels for compost/digestate were mainly due to external (i.e. non-floc) materials, primarily electronic/electrical waste. Batteries may have also contributed to the high levels of Zn and Hg. In this study, for all PTEs examined, with the exception of Cd and Zn, autoclaving had a performance comparable to that of the most effective mechanical biological treatment systems.     

Evaluation of thermally treated asbestos based on fiber number concentration determined by transmission electron microscopy

Appropriate treatment of asbestos waste is a significant problem. In Japan, inertization of asbestos-containing waste by novel techniques approved by the Ministry of the Environment is now promoted. A quantitative method of testing with high sensitivity to the asbestos levels present in the inertization products is required for the approval process, but many testing methods are only qualitative. Thus, we have developed an evaluation method for asbestos in inertized products, consisting of the extraction of fibers from inertized products and determination of fiber number concentration by transmission electron microscopy. We adopted this testing method to evaluate thermally treated asbestos. It was found that fiber number concentrations of thermally treated asbestos decreased with increased treatment temperature, and were below the environmental level (10² Mf/g) at more than 1000 °C for chrysotile and crocidolite and more than 1400 °C for amosite and other amphibole forms of asbestos.     

Studies on the pyrolysis behavior of gasification and melting systems for municipal solid waste

 It is important to investigate the pyrolysis processes of municipal solid waste (MSW) in the same way as for any mixture comprised of multiple substances. In this article, a two-reaction model for a variety of MSW mixtures is proposed to predict mass changes due to pyrolysis. In order to formulate the model based on pyrolysis kinetics, we conducted experiments to determine the kinetic model parameters. By thermal analysis of the typical components of MSW, mass changes attributable to the pyrolysis reaction were found at about 350°C for paper, 400°–500°C for plastics, and 200°–400°C for garbage (dry condition). Activation energies were obtained by the Ozawa method based on the mass changes in pyrolysis. Thus, the pyrolysis behavior is formulated as a function of temperature. Then the pyrolysis mass change of the mixture can be predicted by using a weighted sum of the individual components. The model proved useful in experiments with real waste (refuse-derived fuels). Furthermore, the weight yields (pyrolysis gas, tars, solid residues) of the mixture can be calculated by their additive property after measuring the mass balance of each component. Received: May 11, 2001 / Accepted: November 16, 2001     

Food waste treatment in a community center

For urban community composting centers, the proper selection and use of bulking agent is a key element in not only the cost but also the quality of the finished compost. Besides wood chips (WC) widely used as BA, readily usable cereal residue pellets (CRP) can provide biodegradable carbon and sufficient free air space (FAS) to produce stabilizing temperatures. The objective of the present project was to test at a community center, the effectiveness of CRP in composting food waste (FW). Two recipes were used (CRP with and without WC) to measure: FAS; temperature regimes, and; losses in mass, water, carbon and nitrogen. Both recipes were composted during three consecutive years using a 2 m³ commercial in-vessel composter operated in downtown Montreal (Canada). For all recipes, FAS exceeded 30% for moisture content below 60%, despite yearly variations in FW and BA physical properties. When properly managed by the center operator, both FW and CRP compost mixtures with and without WC developed within 3 days thermophilic temperatures exceeding 50 °C. The loss of total mass, water, carbon and nitrogen was quite variable for both recipes, ranging from 36% to 54%, 42% to 55%, 48% to 65%, and 4% to 55%, respectively. The highest loss in dry mass, water and C was obtained with FW and CRP without WC aerated to maintain mesophilic rather than thermophilic conditions. Although variable, lower nitrogen losses were obtained with CRP and WC as BA, compared to CRP alone, as also observed during previous laboratory trials. Therefore and as BA, CRP can be used alone but nitrogen losses will be minimized by adding WC. Compost stabilization depends on operator vigilance in terms of aeration. The measured fresh compost density of 530-600 kg/m³ indicates that the 2 m³ in-vessel composter can treat 6.5 tons of FW/year if operated during 7 months.     

Municipal solid waste management in Tehran: current practices, opportunities and challenges

Tehran, the capital city of Iran and a metropolis with a population of 8.2 million and containing 2.4 million households, generated 2,626,519 tons of solid waste in 2005. The present study is aimed at evaluating the generation, characteristics and management of solid waste in Tehran. Municipal solid waste comprises more than 97% of Tehran's solid waste, while three other types of solid waste comprise less than 3% of it, namely hospital waste (1.0%), industrial waste (0.6%) and construction and demolition waste (0.5%). The contribution of household solid waste to total municipal solid waste is about 62.5%. The municipality of Tehran is responsible for the solid waste management of the city; the waste is mainly landfilled in three centers in Tehran, with a small part of it usually recycled or processed as compost. However, an informal sector is also active in collecting recyclable materials from solid waste. The municipality has recently initiated some activities to mechanize solid waste management and reduce waste generation. There remain important challenges in solid waste management in Tehran which include: the proper collection and management of hospital waste; public education aimed at reducing and separating household waste and educating municipal workers in order to optimize the waste collection system; and the participation of other related organizations and the private sector in solid waste management.     

Fungal Degradation of Poly(Butylene Adipate-Co-Terephthalate) in Soil and in Compost

The present work mainly dedicated to fungal degradation of poly(butylene adipate-co-terephthalate) [PBAT], to enclose the role of fungi in a real process of biodegradation, the degree of degradation, and to understand the kinetics of PBAT biodegradation. Respirometer tests were realized in soil at 30 °C, and in compost at 30 and 58 °C. Results have shown that temperature is one of the essential parameters governing the fungal degradation of PBAT. Moreover, the final rates of PBAT biodegradation in an inoculated compost with fungi and in a real compost were found comparable, which means that the selected fungi were efficient as much as a mixture of bacteria and fungi. The curves of PBAT biodegradation were modeled by Hill sigmoid. Fungal degradation was completed by investigating the physical and the chemical properties of the polymer during the process of degradation using several analytical methods such as matrix assisted laser desorption ionization-time of fly spectroscopy, size exclusion chromatography, and differential scanning calorimetry. These experiments led to a better understanding of the various stages of fungal degradation of PBAT: hydrolysis as well as mineralization. Furthermore, the analysis of metabolizing products was investigated also.     

Bioconversion of industrial wastes: paint sludge from automotive manufacturing

The compostability of water-based paint sludge originating from the automotive industry was investigated. Six reactors were operated. Wastewater treatment sludge from the same industry was used as additional substrate, and corncob was used as a bulking agent. The level of paint sludge within the compost mixtures varied between 55 and 85%. All reactors yielded a temperature increase up to thermophilic phase levels (>?40 °C) for a minimum of 5 days, and organic matter and C/N losses were observed. BTEX concentrations decreased during composting. Nickel and tin levels in the final product exceeded the legal compost limits. The calorific value of the compost mixtures increased from 9532 to 18774 kJ/kg at the end of the composting process. It was seen that the process applied in this study can be utilized as a biodrying step before the usage of paint sludge at cement kilns as additional fuel.     

The applicability of Fourier transform infrared (FT-IR) spectroscopy in waste management

State and stability or reactivity of waste materials are important properties that must be determined to obtain information about the future behavior and the emission potential of the materials. Different chemical and biological parameters are used to describe the stage of organic matter in waste materials. Fourier transform infrared spectroscopy provides information about the chemistry of waste materials in a general way. Several indicator bands that are referred to functional groups represent components or metabolic products. Their presence and intensity or their absence shed light on the phase of degradation or stabilization. The rapid assessment of the stage of organic matter decomposition is a very important field of application. Therefore, infrared spectroscopy is an appropriate tool for process and quality control, for the assessment of abandoned landfills and for checking of the successful landfill remediation. A wide range of applications are presented in this study for different waste materials. Progressing stages of a typical yard/kitchen waste composting process are shown. The fate of anaerobically "stabilized" leftovers in a subsequent liquid aerobic process is revealed by spectroscopic characteristics. A compost that underwent the biological stabilization process is distinguished from a "substrate" that comprises immature biogenic waste mixed with mineral compounds. Infrared spectra of freeze-dried leachate from untreated and aerated landfill material prove the effect of the aerobic treatment during 10 weeks in laboratory-scale experiments.     

The Origins Of Municipal Solid Waste: II. Policy Options For Plastics Waste Management

Plastic items in some portions of municipal solid waste (MSW), particularly from households and restaurants, have long been viewed as a disposal problem and a symbol of a "throwaway society". There is no question that the amount of plastics in solid waste is growing. However, this observation alone should not cause an hysteria of public policies for the separate management of the plastics or any other portion of the waste. The amount of plastics, and the contribution of the items discarded, must be viewed holistically in setting a solid waste management policy. This paper questions the basis for some U.S. plastics waste policy proposals by reviewing recent U.S. data on the effect of plastics on waste reduction, and the fate of discarded plastics products. Some alternative future policy directions are also discussed.     

The leaching behavior of borate waste glass SL-1

Vitrification is an attractive approach for treatment of the borate waste from nuclear power plants. SL-1 glass is a suitable borosilicate glass form to solidify the borate waste containing relatively high quantities of B and Na. The leaching behavior of SL-1 glass in deionized water has been investigated. Compared to the HLW-glass, the network structure of SL-1 glass is weak. It was found that the ion-exchange reactions dominated the glass corrosion process with water in low temperature leaching conditions (⩽70°C). The ion-exchange and network hydrolysis reactions together controlled the glass dissolution in high temperature leaching conditions (>70°C). There was a peak in leach rate at about 70°C and a valley at about 110°C. The surface layer thickness was about 25 μm (MCC-1, 90°C for 28 days in deionized water). Na was almost totally depleted in the surface layer. At low temperature, the glass corrosion increases with leaching time. The glass corrosion remains about constant with leaching time at 90°C. The surface layer formed at 90°C is protective, which is less porous than the surface layer formed at 40 and 70°C.