Analysis of products from the pyrolysis and liquefaction of single plastics and waste plastic mixtures

Waste plastics in the form of two examples of real world municipal solid waste plastics and a simulated mixture of municipal waste plastics were pyrolysed and liquefied under moderate temperature and pressure in a batch autoclave reactor. In addition, the five main polymers which constitute the majority of plastics occurring in European municipal solid waste comprising, polyethylene, polypropylene, polystyrene, polyethylene terephthalate and polyvinyl chloride were also reacted. The plastics were reacted under both a nitrogen (pyrolysis) and hydrogen pressure (liquefaction) and the yield and composition of products are reported. The hydrocarbon gases produced were mainly methane, ethane, propane and lower concentrations of alkene gases. A mainly oil product was produced with the mixed plastic waste with significant concentrations of aromatic compounds, including single ring aromatic compounds. The composition of the oils and gases suggested that there was significant interaction of the plastics when they were pyrolysed and liquefied as a mixture compared to the results expected from reactions of the single plastics.     

European Union waste management strategy and the importance of biogenic waste

In the European Union (EU), waste management is almost totally regulated by EU directives, which supply a framework for national regulations. The main target in view of sustainability is the prevention of direct disposal of reactive waste in landfills. The tools to comply with these principles are recycling and material recovery as well as waste incineration with energy recovery for final inertization. The adaptation of the principles laid down in EU directives is an ongoing process. A number of countries have already enacted respective national regulations and their realization shows that recycling and incineration are not in competition but are both essential parts of integrated waste management systems. In the EU, the amount of residual waste available for energy recovery can supply approximately 1% of the primary energy demand. About 50% of the energy inventory of municipal solid waste (MSW) in most EU countries is of biogenic origin, and MSW is to the same extent to be looked upon as regenerative fuel. Hence part of the CO₂ released from waste incineration is climate neutral. In the EU, this share could produce savings of the order of 1% of annual CO₂ emissions if energy from MSW replaced that derived from fossil fuel.     

Reductive decomposition of waste gypsum with SiO<Subscript>2</Subscript>, Al<Subscript>2</Subscript>O<Subscript>3</Subscript>, and Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> additives

From the point of view of a sustainable and environment-friendly society based on the recycling of material resources, it is preferable to utilize waste gypsum as a substitute for lime, which is currently produced by the calcination of limestone. In the present work, the reductive decomposition of CaSO₄ was investigated under an atmosphere of CO: 2 vol%, CO₂: 30 vol%, with N₂ as a carrier gas without and with the addition of SiO₂, Al₂O₃, or Fe₂O₃. It was found that the decomposition temperature of CaSO₄ was significantly reduced from 1673 K to 1223 K when only 5 wt% Fe₂O₃ was added to CaSO₄. In the case of the addition of SiO₂ or Al₂O₃ to CaSO₄, the decomposition temperature was reduced from 1673 K to 1623 K. This was due to the formation of composite oxides (calcium ferrite, calcium silicate, or calcium aluminate) during the reaction of CaSO₄ with the additives at a lower temperature. In addition, the formation of unfavorable product CaS was inhibited in the presence of 5 wt% Fe₂O₃, and this inhibition effect further increased as the addition of Fe₂O₃ was increased. In contrast, no significant effect on the inhibition of CaS formation was observed on the addition of SiO₂ or Al₂O₃.     

Resource recovery treatment of waste sludge using a solubilizing reagent

The dewatering of waste sludge continues to be a major problem in wastewater treatment. In this study, the solubilization treatment of waste sludge and extracellular polymeric substances using a solubilizing reagent was examined experimentally. For this purpose, a compression test of thickened waste sludge obtained after solubilization treatment was carried out. The total solid content of the dewatered cake was over 30% when using hydrochloric acid or acetic acid as the solubilizing reagent; however, it was about 20% when using sodium hydroxide. The thickened waste sludge was effectively solubilized when the concentration of acetic acid in the sludge, assuming that it was diluted by free water and not bound water in the sludge, was greater than 0.3 kmol/m³. A flocculated sedimentation test using the supernatant water after solubilization treatment was also carried out, revealing that it functions in a similar manner to commercial flocculant in aggregating solid particles under gravity. This result indicates that the supernatant water can act as a bioflocculant. Methane fermentation of the supernatant water was subsequently carried out. The findings showed that by using acetic acid as a solubilizing reagent, solubilized organic substances in the supernatant water could be recovered as a bioenergy resource.     

Recovery of biomass cellulose from waste sewage sludge

In our previous work, the primary sludge from wastewater treatment plants was shown to contain a considerable amount of cellulose (about 20%, based on suspended solids) owing to the discharge of toilet paper. For the purpose of using the cellulose as a biomass resource, this study examined a simple method for its recovery. When fibrous cellulose was suspended in 0.3% sulfuric acid and autoclaved at 130°C for 60 min, 85%–88% of the initial solids remained without dissolving. Under these conditions, an activated sludge sample not containing cellulose was strongly hydrolyzed and only 7% of the initial solids remained. The prescribed amounts of cellulose added to the activated sludge sample were quantitatively recovered by the autoclaving treatment. In the treatment of primary sludge containing >20% cellulose, residual solids with relatively high levels of cellulose (>69%) could be obtained. The results indicate that the method proposed here could recover cellulose practically from waste sewage sludge for biomass utilization. Received: July 17, 2000 / Accepted: July 4, 2001     

Open windrow composting of polymers: an investigation into the rate of degradation of polyethylene

The compostability of degradable polymers under open windrow composting conditions is explored within this paper. Areas for consideration were the use of, and impacts of, degradable polyethylene (PE) sacks on the composting process and the quality of the finished compost product. These factors were investigated through polymer weight loss over the composting process, the amount of polymer residue and chemical contaminants in the finished compost product, the windrow temperature profiles and a bioassay to establish plant growth and germination levels using the final compost product. This trial also included a comparative study of the weight loss under composting conditions of two different types of ‘degradable’ polymer sacks currently on the European market: PE and a starch based product. Statistical analysis of the windrow temperature profiles has led to the development of a model, which can help to predict the expected trends in the temperature profiles of open compost windrows where the organic waste is kerbside collected using a degradable PE sack.     

An overview of waste materials recycling in the Sultanate of Oman

Various wastes and by-product materials are generated in the Sultanate of Oman including reclaimed asphalt pavement (RAP) aggregate, demolition concrete, cement by-pass dust (CBPD), copper slag, petroleum-contaminated soils (PCS), discarded tires, incinerator ash, and others. Recycling of such materials in construction is not practiced. Research data are also minimal into the potential use of selected materials in construction applications. This paper will present the results of several laboratory studies conducted into the use of PCS in asphalt concrete mixtures; on the use of CBPD in soil stabilization and flowable fill mixtures; on the utilization of copper slag and CBPD as cementitious materials; on the use of incinerator ash in cement mortars; and on the use of RAP aggregate in road bases and sub-bases. Laboratory data generally indicate that it is feasible to partially reuse some of these materials in construction provided that economic incentives and environmental concerns are taken into consideration.     

Mechanical performance of woodfibre–waste plastic composite materials

Plastic products used for packaging are often discarded after a single use resulting in an inexhaustible supply of waste polymeric materials. The stiffness and strength of polymeric materials have been known to improve with the addition of lignocellulosic fibres available in abundance in nature. Hence, composite materials containing natural fibres and waste plastics would result in the reduction of solid wastes and the use of cheap, renewable resources. Composite specimens, consisting of waste plastics obtained from a Kerbside collection (high density polyethylene (HDPE) waste, Janitorial waste, Kerbside waste I and Kerbside waste II) and Pinus radiata woodfibres (medium density fibres (MDF)), have been produced through melt blending and injection moulding. The effects of fibre content, matrix type and interfacial bonding on the tensile and flexural properties of these composite materials have been determined through extensive testing at various conditions. The mechanical properties of these composites at room temperature and humidity depend on the amount of woodfibres, the mechanical properties of the waste plastics used and the presence of a suitable coupling agent. The tensile strengths of MDF/waste plastic composites do not generally change with fibre content except for 40% MDF/HDPE waste and 40% MDF/Kerbside waste II (plus 1% Epolene™) composites, where the tensile strengths increase by about 25% compared to those of the corresponding waste plastics. Flexural strengths of MDF/waste plastic composites increase with the addition of medium density fibres with the exception of MDF/Kerbside waste I composites. The tensile and flexural moduli of MDF/waste plastic composites mostly increase with increasing fibre content.     

Formal and informal recovery of recyclables in Mexicali, Mexico: handling alternatives

The purpose of this paper is to review the case of a Mexican municipality in this field and highlight and identify critical gaps to be addressed. The paper seeks to explore intersectorial partnerships as a means to achieve sustainable solid waste management systems. Its point of departure is that, the highest level of service and maximum benefit is gained when a municipality sees its solid waste management mandates and handicaps clearly, uses the strengths of the other actors. The four main types of actors considered in this paper are: the municipal government, the formal private (commercial) sector, and the informal sector, which, includes individuals, small entrepreneurs, and micro-enterprises already working with discarded materials or having the potential to do so. Community based organizations (CBOs), either idealistically motivated or working for their own welfare, and non-governmental organizations (NGOs), usually in pursuit of their own idealistic goals are also a part of the informal sector.     

Households’ recycling efforts

Households’ recycling effort is often argued to be of an insignificant size. It is also frequently argued that this contribution, if significant, is not a cost to households, since it is voluntary. Thus households’ use of time and energy are frequently disregarded in cost-benefit analyses of stricter recycling targets. In this survey, based on 1162 interviews, we find that sorting at source involves significant extra use of time and energy in the households. On average, each of those asked reported that they use close to half an hour a week for cleaning, sorting and transporting recyclable waste. On average, 185 h is used per tonne of waste. Four out of ten reported that they use warm or hot water to clean the materials. When investigating the motives for sorting waste, we find that many perceive sorting as mandatory, while some in fact find it a pleasant activity in itself. Moral motives for sorting at source are also widespread. A majority would prefer that a company took over the sorting if this were possible, and on average, the respondents are willing to pay US$ 20/year for this service.