Environmental evaluation of plastic waste management scenarios

The management of the plastic fraction is one of the most debated issues in the discussion on integrated municipal solid waste systems. Both material and energy recovery can be performed on such a waste stream, and different separate collection schemes can be implemented. The aim of the paper is to contribute to the debate, based on the analysis of different plastic waste recovery routes. Five scenarios were defined and modelled with a life cycle assessment approach using the EASEWASTE model. In the baseline scenario (P0) the plastic is treated as residual waste and routed partly to incineration with energy recovery and partly to mechanical biological treatment. A range of potential improvements in plastic management is introduced in the other four scenarios (P1–P4). P1 includes a source separation of clean plastic fractions for material recycling, whereas P2 a source separation of mixed plastic fraction for mechanical upgrading and separation into specific polymer types, with the residual plastic fraction being down-cycled and used for “wood items”. In P3 a mixed plastic fraction is source separated together with metals in a “dry bin”. In P4 plastic is mechanically separated from residual waste prior to incineration.A sensitivity analysis on the marginal energy was carried out. Scenarios were modelled as a first step assuming that marginal electricity and heat were based on coal and on a mix of fuels and then, in the sensitivity analysis, the marginal energy was based on natural gas.The study confirmed the difficulty to clearly identify an optimal strategy for plastic waste management. In fact none of the examined scenarios emerged univocally as the best option for all impact categories. When moving from the P0 treatment strategy to the other scenarios, substantial improvements can be obtained for “Global Warming”. For the other impact categories, results are affected by the assumption about the substituted marginal energy. Nevertheless, irrespective of the assumptions on marginal energy, scenario P4, which implies the highest quantities of specific polymer types sent to recycling, resulted the best option in most impact categories.     

Control of environmental impact with modern chemical technology

Here are assembled representative excerpts from a new text in applied chemistry. They illustrate the well-referenced treatment of industrial processes that are here considered with their related emission control problems and solutions. A brief account of general aspects of the industry is followed by surveys of the significance and technical aspects of air and water pollution chemistry. Consideration is given to emission avoidance or containment, waste treatment, and waste disposal options as they relate to both of these environmental areas. Details of salt recovery and the products of brine electrolysis plus environmental aspects of these operations are treated as examples of some of the processes discussed. Also covered are fertilizer constituent preparation, formulation, and use with consideration of the large-scale effects of each of these activities. Detailed reference is made to the chemical technology and emission control aspects of the pulp and paper industry and refinery operations. Throughout, integral process changes and waste recycling practices are directly related to emission control aspects of each process in a way to be useful to the student and professional alike. These excerpts are extracted from one of the first, single volume accounts to take this unified approach to the subject.Extract from the bookModern Chemical Technology and Emission Control by M. B. Hocking, published by Springer-Verlag, Berlin, Heidelberg, New York, Tokyo (1985).     

Environmental impact minimization of a total wastewater treatment network system from a life cycle perspective

Synthesis of distributed wastewater treatment plants (WTPs) has focused on cost reduction, but never on the reduction of environmental impacts. A mathematical optimization model was developed in this study to synthesize existing distributed and terminal WTPs into an environmentally friendly total wastewater treatment network system (TWTNS) from a life cycle perspective. Life cycle assessment (LCA) was performed to evaluate the environmental impacts of principal contributors in a TWTNS. The LCA results were integrated into the objective function of the model. The mass balances were formulated from the superstructure model, and the constraints were formulated to reflect real wastewater treatment situations in industrial plants. A case study validated the model and demonstrated the effect of the objective function on the configuration and environmental performance of a TWTNS. This model can be used to minimize environmental impacts of a TWTNS in retrofitting existing WTPs in line with cleaner production and sustainable development.     

Environmental assessment of different management options for individual waste fractions by means of life-cycle assessment modelling

Several alternatives exist for handling of individual waste fractions, including recycling, incineration and landfilling. From an environmental point of view, the latter is commonly considered as the least desirable option. Many studies based on life-cycle assessment (LCA) highlight the environmental benefits offered by incineration and especially by recycling. However, the landfilling option is often approached unjustly in these studies, maybe disregarding the remarkable technological improvements that landfills have undergone in the last decades in many parts of the world.This study, by means of LCA-modelling, aims at comparing the environmental performance of three major management options (landfilling, recycling and incineration or composting) for a number of individual waste fractions. The landfilling option is here approached comprehensively, accounting for all technical and environmental factors involved, including energy generation from landfill gas and storage of biogenic carbon. Leachate and gas emissions associated to each individual waste fraction have been estimated by means of a mathematical modelling. This approach towards landfilling emissions allows for a more precise quantification of the landfill impacts when comparing management options for selected waste fractions.Results from the life-cycle impact assessment (LCIA) show that the environmental performance estimated for landfilling with energy recovery of the fractions “organics” and “recyclable paper” is comparable with composting (for “organics”) and incineration (for “recyclable paper”). This however requires high degree of control over gas and leachate emissions, high gas collection efficiency and extensive gas utilization at the landfill. For the other waste fractions, recycling and incineration are favourable, although specific emissions of a variety of toxic compounds (VOCs, PAHs, NO_x, heavy metals, etc.) may significantly worsen their environmental performance.