Pyrolysis of mixtures of sewage sludge and manure: a comparison of the results obtained in the laboratory (semi-pilot) and in a pilot plant

A pilot-scale pyrolysis process was carried out for the treatment of a mixture of two types of waste, sewage sludge and cattle manure, comparing the results with others obtained under laboratory conditions (semi-pilot scale). The aim of this study was to obtain the energetic valorization of the products. Owing to the specific characteristics of the plant, two products were obtained from the process: gas and carbonized solid. As no liquid fraction was obtained, the gas fraction is a greater percentage made up of both condensable and non-condensable compounds, which were obtained separately at the laboratory scale. The pilot plant was designed so that the gases produced by thermolysis were burnt continuously in a combustion chamber, while the carbonized fraction was fed in batches for co-combustion. To determine composition and combustion ability, the gas and solid products from the pilot process were characterized by chromatographic analysis of the gaseous fraction and chemical analysis and programmed-temperature combustion of the carbonized solid. The composition of the combustion gases, rich in light hydrocarbons, and the carbon present in the carbonized fraction enable the energetic valorization of these products. The combustion gases were subjected to a cleaning process and their composition analysed twice: before and after the gas cleaning treatment. The study led to a positive assessment of the possible use of the process products as fuel, provided that the combustion gases are treated. As most of the sulphur and chlorine from the original waste are mainly concentrated in the solid fraction, the use of char as a fuel will depend on the effectiveness of clean-up techniques for combustion gases. During gas cleansing, neutralizing with sodium bicarbonate proved effective, especially for the acidic compounds HCl, HF and SO(2).     

Use of inert C&D materials for seawall foundation: quality control measures

The technical viability of using inert construction and demolition (C&D) materials for the construction of seawall and breakwater foundations has been established by laboratory testing of the materials, numerical analysis of foundation stability, and a pilot field-scale engineering performance evaluation. However, quality control measures are still required so that only suitable materials are used for seawall and breakwater foundation construction. The development of different quality control measures for different site conditions is presented in this paper. The rationale, practicality, and implementation of these quality control measures are also discussed.     

Determining biodegradability of plastic materials under controlled and natural composting environments

With the advent of recently promulgated Government regulations on plastics in Mauritius, a study was initiated to examine the biodegradability of two different types of plastic, namely Willow Ridge Plastics - PDQ-H additive (Plastic A) and Ecosafe Plastic - TDPA additive (Plastic B) under controlled and natural composting environments. The results obtained from the controlled composting environment showed that the cumulative carbon dioxide evolution for Plastic A was much higher than that for Plastic B. Plastic A therefore showed a higher level of biodegradation in terms of CO2 evolution than Plastic B. However, from the regression analysis, it was found that the level of CO2 varying with time fitted the sigmoid type curves with very high correlation coefficients (R2 values: 0.9928, 0.9921 and 0.9816, for reference material, inoculum and Plastic A, respectively). The corresponding F-values obtained from the ANOVA analysis together with significance levels of p<0.05 indicated that the three treatments analysed in the biodegradability experiment were significant. The other experiment was undertaken to observe any physical change of Plastics A and B as compared to a reference plastic, namely, compostable plastic bag (Mater-Bi product-Plastic C), when exposed to a natural composting environment. Thermophilic temperatures were obtained for about 3-5 days of composting and the moisture content was in the range of 60-80% throughout the degradation process. It was observed that after 55 days of composting, Plastic C degraded completely while Plastic A and Plastic B did not undergo any significant degradation. It can be concluded that naturally based plastic made of starch would degrade completely in a time frame of 60 days, whereas plastics with biodegradable additive would require a longer time.     

Flexible and robust strategies for waste management in Sweden

Treatment of solid waste continues to be on the political agenda. Waste disposal issues are often viewed from an environmental perspective, but economic and social aspects also need to be considered when deciding on waste strategies and policy instruments. The aim of this paper is to suggest flexible and robust strategies for waste management in Sweden, and to discuss different policy instruments. Emphasis is on environmental aspects, but social and economic aspects are also considered. The results show that most waste treatment methods have a role to play in a robust and flexible integrated waste management system, and that the waste hierarchy is valid as a rule of thumb from an environmental perspective. A review of social aspects shows that there is a general willingness among people to source separate wastes. A package of policy instruments can include landfill tax, an incineration tax which is differentiated with respect to the content of fossil fuels and a weight based incineration tax, as well as support to the use of biogas and recycled materials.     

Life cycle assessment of a national policy proposal - the case of a Swedish waste incineration tax

At the core of EU and Swedish waste policy is the so-called waste hierarchy, according to which waste should first be prevented, but should otherwise be treated in the following order of prioritisation: reuse, recycling when environmentally motivated, energy recovery, and last landfilling. Some recent policy decisions in Sweden aim to influence waste management in the direction of the waste hierarchy. In 2001 a governmental commission assessed the economic and environmental impacts of introducing a weight-based tax on waste incineration, the purpose of which would be to encourage waste reduction and increase materials recycling and biological treatment. This paper presents the results of a life cycle assessment (LCA) of the waste incineration tax proposal. It was done in the context of a larger research project concerning the development and testing of a framework for Strategic Environmental Assessment (SEA). The aim of this paper is to assess the life cycle environmental impacts of the waste incineration tax proposal, and to investigate whether there are any possibilities of more optimal design of such a tax. The proposed design of the waste incineration tax results in increased recycling, but only in small environmental improvements. A more elaborate tax design is suggested, in which the tax level would partly be related to the fossil carbon content of the waste.     

Composition of a Spanish sewage sludge and effects on treated soil and olive trees

The effects of sewage sludge (SL) application on the soil and olive trees (Olea europaea L., cultivar: cornicabra) were studied. The plants were grown in 8.5L pots and subjected to the following treatments: 0, 3.66, 7.32, 14.65, 29.3, 58.6, and 117.2 g SL kg(-1) soil that corresponded, respectively, to 0, 4, 8, 16, 32, 64 and 128 M g ha(-1) dry weight of sewage sludge. The application of SL at the rates 64 and 128 M g ha(-1) produced leaf tip burning and leaf drop after 120 days, although cumulative metal pollutant loading rates was below USEPA and European regulations. This toxicity symptom could be caused by the high sodium levels in the leaves (over 0.19%), which can damage olive tree development. The Na contents of leaves were well correlated with soil Na content (r2: 0.91). In general, SL rates significantly increased the level of Cr, Ni, Cu, Zn, Cd and Pb in soil and plants, but these concentrations were in the normal ranges, except for the Zn concentration, which was over the critical soil content for the rates of 32, 64, 128 Mg ha(-1) but not in the leaves. Results suggested that regulations about the utilization of sewage sludge on agricultural land should consider the limit values for salt, and not only metals, that may be added to soil, in order to minimize the risk of negative effects to plant health.     

Managing scuba divers to meet ecological goals for coral reef conservation

Marine protected areas increasingly are challenged to maintain or increase tourism benefits while adequately protecting resources. Although carrying capacity strategies can be used to cope with use-related impacts, there is little understanding of divers themselves, their management preferences, and how preferences relate to conservation goals. By using a stated preference choice modeling approach, we investigated the choices divers make in selecting diving trips to marine protected areas as defined by use level, access, level of supervision, fees, conservation education, and diving expectations. Logit models showed that divers preferred a more restrictive management scenario over the status quo. Divers favored reductions in the level of site use and increased levels of conservation education. Divers did not favor fees to access protected areas, having less access to the resource, or extensive supervision. Finally, divers were much more willing to accept increasingly restrictive management scenarios when they could expect to see increased marine life.     

International trade in meat: the tip of the pork chop

This paper provides an original account of global land, water, and nitrogen use in support of industrialized livestock production and trade, with emphasis on two of the fastest-growing sectors, pork and poultry. Our analysis focuses on trade in feed and animal products, using a new model that calculates the amount of "virtual" nitrogen, water, and land used in production but not embedded in the product. We show how key meat-importing countries, such as Japan, benefit from "virtual" trade in land, water, and nitrogen, and how key meat-exporting countries, such as Brazil, provide these resources without accounting for their true environmental cost. Results show that Japan's pig and chicken meat imports embody the virtual equivalent of 50% of Japan's total arable land, and half of Japan's virtual nitrogen total is lost in the US. Trade links with China are responsible for 15% of the virtual nitrogen left behind in Brazil due to feed and meat exports, and 20% of Brazil's area is used to grow soybean exports. The complexity of trade in meat, feed, water, and nitrogen is illustrated by the dual roles of the US and The Netherlands as both importers and exporters of meat. Mitigation of environmental damage from industrialized livestock production and trade depends on a combination of direct-pricing strategies, regulatory approaches, and use of best management practices. Our analysis indicates that increased water- and nitrogen-use efficiency and land conservation resulting from these measures could significantly reduce resource costs.     

Leachate recirculation effects on waste degradation: study on columns

The purpose of this study is to determine the impact of leachate recirculation on the degradation of municipal solid wastes (bioreactor concept). The study was carried out using columns containing approximately 50 kg of waste, in order to follow waste degradation over a limited time. Three types of waste were studied: fresh waste of standard composition, fresh waste of fermentable composition and some 8-yr-old waste extracted from a site in France. Measurement of the global parameters, such as chemical oxygen demand (COD), volatile acidity, alkalinity, leachate conductivity, methane potential of the wastes and biogas production monitoring (volume of CO2 and CH4 produced), were carried out. The quantity of oxydizable matter and biogas production was increased by the leachate recirculation, and the duration of the first degradation phases was reduced in all cases. Chloride, ammonium and organic pollution accumulation was observed according to the duration of recirculation. After 400 days of degradation, waste stabilization seemed to be reached for all of the recirculated columns (COD<300 mg/L O2, and methane potential reached).     

Integrated biomonitoring of air quality with plants and lichens: a case study on ambient ozone from central Italy

A biennial integrated survey, based on the use of vascular plants for the bioindication of the effects of tropospheric ozone together with the use of automatic analysers of ozone, as well as the mapping of lichen biodiversity was performed in the area of Castelfiorentino (Tuscany, central Italy). Photochemically produced ozone proved to be a fundamental presence during the warm season, with maximum hourly means reaching 114 ppb, exceeding the information threshold as fixed by EU: the use of supersensitive tobacco Bel-W3 confirmed the opportunity of carrying out detailed cost-effective monitoring surveys. The potential for didactical and educational implications of this methodology are appealing. Critical levels set up for the protection of vegetation have exceeded considerably. The comparison of biomass productivity in sensitive and resistant individuals (NC-S and NC-R white clover clones, in the framework of an European network) provided evidence that ambient ozone levels are associated with relevant reduction (up to 30%) in the performance of sensitive material; effects on flowering were also pronounced. The economic assessment of such an impact deserves attention. Mapping of epiphytic lichen biodiversity – which has been used to monitor air quality worldwide – was not related to ozone geographical distribution as depicted by tobacco response.