Joan Colón

Evaluation of the ecotoxicity of model nanoparticles

Since society at large became aware of the use of nanomaterials in ever growing quantities in consumer products and their presence in the environment, critical interest in the impact of this emerging technology has grown. The main concern is whether the unknown risks of engineered nanoparticles (NPs), in particular their impact on health and environment, outweighs their established benefits for society. Therefore, a key issue in this field is to evaluate their potential toxicity. In this context we evaluated the effects on plants and microorganisms of model nanoparticles, in particular of a stable metal (Au, 10nm mean diameter), a well-known bactericide (Ag, 2 nm mean diameter) and the broadly used Fe(3)O(4) (7 nm mean diameter). The toxicity of these nanoparticles was assayed using standard toxicity tests. Specifically, germination (cucumber and lettuce), bioluminescent (Photobacterium phosphoreum) and anaerobic toxicity tests were performed. Germination tests were conducted at a NP dose of 62, 100 and 116 microg mL(-1) for Au, Ag, and Fe(3)O(4), respectively. The bioluminscent testing (P. phosphoreum) was conducted at a dose of 28, 45 and 52 microg mL(-1) for Au, Ag, and Fe(3)O(4), respectively. Finally, anaerobic tests were conducted at a NP dose of 10, 16 and 18 microg mL(-1) for Au, Ag, and Fe(3)O(4), respectively. In all cases low or zero toxicity was observed. However, some perturbation of the normal functions with respect to controls in germinating tests was observed, suggesting the necessity for further research in this field. At the same time, the effect of NP-solvents was sometimes more significant than that of the NPs themselves, a point that is of special interest for future nanotoxicological studies.

The use of life cycle assessment for the comparison of biowaste composting at home and full scale.

Environmental impacts and gaseous emissions associated to home and industrial composting of the source-separated organic fraction of municipal solid waste have been evaluated using the environmental tool of life cycle assessment (LCA). Experimental data of both scenarios were experimentally collected. The functional unit used was one ton of organic waste. Ammonia, methane and nitrous oxide released from home composting (HC) were more than five times higher than those of industrial composting (IC) but the latter involved within 2 and 53 times more consumption or generation of transport, energy, water, infrastructures, waste and Volatile Organic Compounds (VOCs) emissions than HC. Therefore, results indicated that IC was more impacting than HC for four of the impact categories considered (abiotic depletion, ozone layer depletion, photochemical oxidation and cumulative energy demand) and less impacting for the other three (acidification, eutrophication and global warming). Production of composting bin and gaseous emissions are the main responsible for the HC impacts, whereas for IC the main contributions come from collection and transportation of organic waste, electricity consumption, dumped waste and VOCs emission. These results suggest that HC may be an interesting alternative or complement to IC in low density areas of population.

Chromium VI adsorption on cerium oxide nanoparticles and morphology changes during the process.

In this study, suspended cerium oxide nanoparticles stabilized with hexamethylenetetramine were used for the removal of dissolved chromium VI in pure water. Several concentrations of adsorbent and adsorbate were tested, trying to cover a large range of possible real conditions. Results showed that the Freundlich isotherm represented well the adsorption equilibrium reached between nanoparticles and chromium, whereas adsorption kinetics could be modeled by a pseudo-second-order expression. The separation of chromium-cerium nanoparticles from the medium and the desorption of chromium using sodium hydroxide without cerium losses was obtained. Nanoparticles agglomeration and morphological changes during the adsorption-desorption process were observed by TEM. Another remarkable result obtained in this study is the low toxicity in the water treated by nanoparticles measured by the Microtox(®) commercial method. These results can be used to propose this treatment sequence for a clean and simple removal of drinking water or wastewater re-use when a high toxicity heavy metal such as chromium VI is the responsible for water pollution.

Determination of the energy and environmental burdens associated with the biological treatment of source-separated Municipal Solid Wastes

Environmental burdens of four different full-scale facilities treating source-separated organic fraction of Municipal Solid Wastes (OFMSW) have been experimentally evaluated. The studied facilities include different composting technologies and also anaerobic digestion plus composting. Home composting, as an alternative to OFMSW management, was also included in the study. Energy (electricity and diesel), water consumption and emissions of volatile organic compounds (VOC), ammonia, methane and nitrous oxide have been measured for each process. Energy consumption ranged between 235 and 870 MJ Mg OFMSW−1 while the emissions of the different contaminants considered per Mg OFMSW were in the range of 0.36–8.9 kg VOC, 0.23–8.63 kg NH3, 0.34–4.37 kg CH4 and 0.035–0.251 kg N2O, respectively. Environmental burdens of each facility are also analyzed from the point of view of process efficiency (i.e. organic matter stabilization degree achieved, calculated as the reduction of the Dynamic Respiration Index (DRI) of the waste treated). This study is performed through two new indices: Respiration Index Efficiency (RIE), which includes the reduction in the DRI achieved by the treatment process and Quality and Respiration Index Efficiency (QRIE), which also includes the quality of the end product. Finally, a Life Cycle Assessment is performed using the Respiration Index Efficiency (RIE) as the novel functional unit instead of the classical LCA approach based on the total mass treated.

A methodology to determine gaseous emissions in a composting plant

Environmental impacts associated to different waste treatments are of interest in the decision-making process at local, regional and international level. However, all the environmental burdens of an organic waste biological treatment are not always considered. Real data on gaseous emissions released from full-scale composting plants are difficult to obtain. These emissions are related to the composting technology and waste characteristics and therefore, an exhaustive sampling campaign is necessary to obtain representative and reliable data of a single plant. This work proposes a methodology to systematically determine gaseous emissions of a composting plant and presents the results obtained in the application of this methodology to a plant treating source-separated organic fraction of municipal solid waste (OFMSW) for the determination of ammonia and total volatile organic compounds (VOC). Emission factors from the biological treatment process obtained for ammonia and VOC were 3.9 kg Mg OFMSW(-1) and 0.206 kg Mg OFMSW(-1) respectively. Emissions associated to energy use and production were also quantified (60.5 kg CO2 Mg OFMSW(-1) and 0.66 kg VOC Mg OFMSW(-1)). Other relevant parameters such as energy and water consumption and amount of rejected waste were also determined. A new functional unit is presented to relate emission factors to the biodegradation efficiency of the composting process and consists in the reduction of the Respiration Index of the treated material. Using this new functional unit, the atmospheric emissions released from a composting plant are directly related to the plant specific efficiency.

Possibilities of composting disposable diapers with municipal solid wastes

The possibilities for the management of disposable diapers in municipal solid waste have been studied. An in-depth revision of literature about generation, composition and current treatment options for disposable diapers showed that the situation for these wastes is not clearly defined in developed recycling societies. As a promising technology, composting of diapers with source-separated organic fraction of municipal solid waste (OFMSW) was studied at full scale to understand the process performance and the characteristics of the compost obtained when compared with that of composting OFMSW without diapers. The experiments demonstrated that the composting process presented similar trends in terms of evolution of routine parameters (temperature, oxygen content, moisture and organic matter content) and biological activity (measured as respiration index). In relation to the quality of both composts, it can be concluded that both materials were identical in terms of stability, maturity and phytotoxicity and showed no presence of pathogenic micro-organisms. However, compost coming from OFMSW with a 3% of disposable diapers presented a slightly higher level of zinc, which can prevent the use of large amounts of diapers mixed with OFMSW.

Performance of compostable baby used diapers in the composting process with the organic fraction of municipal solid waste.

In modern societies, disposable diapers constitute a significant percentage of municipal solid wastes. They have been traditionally landfilled or incinerated as only limited recycling processes are being implemented in some parts of Europe. With the implementation of separated collection systems for the organic fraction of municipal solid wastes (OFMSWs) and the need to preserve the environment, compostable diapers have appeared in the market to avoid the main environmental impacts associated to non-biodegradable disposable diapers. In this study, a full-scale composting of door-to-door collected OFMSW with a 3% (w/w) of compostable diapers has also been carried out. Previously, lab-scale experiments confirmed that almost 50% of carbon of compostable diapers is emitted as CO2 under aerobic controlled conditions. The results obtained at full-scale demonstrate that both the composting process and the final end product (compost) are not altered by the presence of compostable diapers in crucial aspects such as pathogenic content, stability and elemental composition (including nutrients and heavy metals). The main conclusion of this study is that the collection of the OFMSW with compostable diapers can be a new way to transform this waste into high-quality compost.

Environmental impact of rejected materials generated in organic fraction of municipal solid waste anaerobic digestion plants : comparison of wet and dry process layout

Anaerobic digestion of source separated organic fraction of municipal solid waste is an increasing waste valorization alternative instead of incineration or landfilling of untreated biodegradable wastes. Nevertheless, a significant portion of biodegradable wastes entering the plant is lost in pre-treatments and post-treatments of anaerobic digestion facilities together with other improper materials such as plastics, paper, textile materials and metals. The rejected materials lost in these stages have two main implications: (i) less organic material enters to digesters and, as a consequence, there is a loss of biogas production and (ii) the rejected materials end up in landfills or incinerators contributing to environmental impacts such as global warming or eutrophication. The main goals of this study are (i) to estimate potential losses of biogas in the rejected solid materials generated during the pre- and post-treatments of two full-scale anaerobic digestion facilities and (ii) to evaluate the environmental burdens associated to the final disposal (landfill or incineration) of these rejected materials by means of Life Cycle Assessment. This study shows that there is a lost of potential biogas production, ranging from 8% to 15%, due to the loss of organic matter during pre-treatment stages in anaerobic digestion facilities. From an environmental point of view, the Life Cycle Assessment shows that the incineration scenario is the most favorable alternative for eight out of nine impact categories compared with the landfill scenario. The studied impact categories are Climate Change, Fossil depletion, Freshwater eutrophication, Marine eutrophication, Ozone depletion, Particulate matter formation, Photochemical oxidant formation, Terrestrial acidification and Water depletion.

Environmental burdens of source-selected biowaste treatments: comparing scenarios to fulfil the European Union landfill directive. The case of Catalonia

The Organic Fraction of Municipal Solid Waste (OFMSW), or biowaste, can be valorized using different treatment technologies, such as anaerobic digestion and composting or the combination of them. The use of the end products (biogas and/or compost) generates benefits over the alternative of sending waste to landfill. The European Union regulations (i.e. Landfill Directive) encourage the diversion of untreated biodegradable waste from landfilling. However, OFMSW treatment installations also produce environmental impacts that must be assessed. This paper presents different future scenarios at regional scale proposed to accomplish the Landfill Directive and their environmental assessment in terms of environmental impact categories. The geographical area under study is Catalonia (Spain). Field data obtained in previous studies undertaken in the same geographical area are used to determine the environmental burdens of the present situation in order to compare them with different future scenarios. A combined scenario to treat 921 Gg of OFMSW source selected including the increase of the quantity of biowaste treated by anaerobic digestion (61.2% of the total biowaste), the modification of composting plants to ensure the treatment of all the gaseous emissions (25.3% and 8.1% of the total biowaste treated in in-vessel composting plants and in enclosed windrows composting plants respectively) and the incorporation of home composting as a waste treatment alternative (5.4% of total biowaste) results in the lowest impact scenario considered in the present study. Energy recovery through anaerobic digestion and benefits of gaseous emissions reduction are the key factors in the impact reduction of biowaste treatment.