Adriana Artola

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.

In search of a reliable technique for the determination of the biological stability of the organic matter in the mechanical-biological treated waste

The biological stability determines the extent to which readily biodegradable organic matter has decomposed. In this work, a massive estimation of indices suitable for the measurement of biological stability of the organic matter content in solid waste samples has been carried out. Samples from different stages in a mechanical-biological treatment (MBT) plant treating municipal solid wastes (MSW) were selected as examples of different stages of organic matter stability in waste biological treatment. Aerobic indices based on respiration techniques properly reflected the process of organic matter biodegradation. Static and dynamic respirometry showed similar values in terms of aerobic biological activity (expressed as oxygen uptake rate, OUR), whereas cumulative oxygen consumption was a reliable method to express the biological stability of organic matter in solid samples. Methods based on OUR and cumulative oxygen consumption were positively correlated. Anaerobic methods based on biogas production (BP) tests also reflected well the degree of biological stability, although significant differences were found in solid and liquid BP assays. A significant correlation was found between cumulative oxygen consumption and ultimate biogas production. The results obtained in this study can be a basis for the quantitative measurement of the efficiency in the stabilization of organic matter in waste treatment plants, including MBT plants, anaerobic digestion of MSW and composting plants.

Odours and volatile organic compounds emitted from municipal solid waste at different stage of decomposition and relationship with biological stability

Odours (OU(E)) and volatile organic compounds (VOC) emission during biological process used to treat MSW were studied under standardized conditions in order to detect potential risk for workers and population. Results obtained indicated that odours and VOCs emitted depend on the biological stability of waste measured by the dynamic respiration index (DRI) and a very good correlation were found between these parameters (OU(E) vs. DRI, r=0.96, p<0.001, n=6; VOC vs. DRI, r=0.97, p<0.001, n=6). GC-MS study of the VOCs indicated the presence of a group of molecules that were degraded during the process. On the other hand, a second group of molecules, i.e. aromatic and halogenated compounds, and furan persisted in the waste sample, although molecule concentrations were always lower than Threshold Limit Value-Time Weighted Average (TLV-TWA).

Air filled porosity measurements by air pycnometry in the composting process: a review and a correlation analysis.

Air filled porosity (AFP) appears as the best measure to determine the available porosity in a composting material or, in general, in an organic matrix. Several methodologies, including theoretical and empirical approaches have been developed to estimate AFP. Among them, air pycnometry has been considered the most suitable and accurate technique to obtain reliable measures of AFP. In this review, the published methodologies to determine AFP by air pycnometry are explained in detail, and the main advantages and disadvantages of such methodologies are discussed. Also, a massive sampling of several organic wastes and mixtures intended for composting has been characterized by air pycnometry, and the theoretical and empirical correlations proposed in literature are compared in terms of accuracy in AFP measurement. Results obtained show that some theoretical correlations are suitable for estimating AFP in the majority of organic wastes studied. However, some waste samples need an experimental determination to obtain a realistic value of AFP.

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.

Heavy metal binding to anaerobic sludge

Heavy metal interaction with anaerobically digested sludge was investigated using copper, cadmium and nickel chloride salt solutions. The behaviour of the well-known glycine-metal aqueous system was compared with the behaviour of the sludge-metal system. When equilibrium pH values are presented against the initial metal concentration for the glycine-copper system the profile obtained shows a sharp peak. This behaviour is similar to the behaviour of the experimental sludge-copper system. The peak also appears for cadmium and nickel-glycine systems. However, it is not as pronounced as in the glycine-copper system and cannot be observed in the sludge-metal systems. The similar behaviour of both copper systems suggests that the metal binding mechanism of the sludge involves amino acid functional groups which are present in the cell wall. Due to this similarity, an apparent molarity of the sludge can be evaluated by sludge titration with copper (II). The value obtained can be expressed as mmols of equivalent glycine per gram of sludge.

A systematic study of the gaseous emissions from biosolids composting: Raw sludge versus anaerobically digested sludge

Volatile organic compound (VOC) and ammonia, that contribute to odor pollution, and methane and nitrous oxide, with an important greenhouse effect, are compounds present in gaseous emission from waste treatment installations, including composting plants. In this work, gaseous emissions from the composting of raw (RS) and anaerobically digested sludge (ADS) have been investigated and compared at pilot scale aiming to provide emission factors and to identify the different VOC families present. CH4 and N2O emissions were higher in ADS composting (0.73 and 0.55 kg Mg(-1) sludge, respectively) than in RS composting (0.01 kg Mg(-1) sludge for both CH4 and N2O). NH3 and VOCs emitted were higher during the RS composting process (19.37 and 0.21 kg Mg(-1) sludge, respectively) than in ADS composting (0.16 and 0.04 kg Mg(-1) sludge). Significant differences were found in the VOC compositions emitted in ADS and RS composting, being more diverse in RS than ADS composting.

Detection, Composition and Treatment of Volatile Organic Compounds from Waste Treatment Plants

Environmental policies at the European and global level support the diversion of wastes from landfills for their treatment in different facilities. Organic waste is mainly treated or valorized through composting, anaerobic digestion or a combination of both treatments. Thus, there are an increasing number of waste treatment plants using this type of biological treatment. During waste handling and biological decomposition steps a number of gaseous compounds are generated or removed from the organic matrix and emitted. Different families of Volatile Organic Compounds (VOC) can be found in these emissions. Many of these compounds are also sources of odor nuisance. In fact, odors are the main source of complaints and social impacts of any waste treatment plant. This work presents a summary of the main types of VOC emitted in organic waste treatment facilities and the methods used to detect and quantify these compounds, together with the treatment methods applied to gaseous emissions commonly used in composting and anaerobic digestion facilities.

Gaseous emissions in municipal wastes composting: Effect of the bulking agent

In this study, the emissions of volatile organic compounds (VOC), CH4, N2O and NH3 during composting non-source selected MSW, source selected organic fraction of municipal solid wastes (OFMSW) with wood chips as bulking agent (OF_wood) and source selected OFMSW with polyethylene (PE) tube as bulking agent (OF_tube) and the effect of bulking agent on these emissions have been systematically studied. Emission factors are provided (in kg compound Mg(-1) dry matter): OF_tube (CH4: 0.0185±0.004; N2O: 0.0211±0.005; NH3: 0.612±0.269; VOC: 0.688±0.082) and MSW (CH4: 0.0549±0.0171; N2O: 0.032±0.015; NH3: 1.00±0.20; VOC: 1.05±0.18) present lower values than OF_wood (CH4: 1.27±0.09; N2O: 0.021±0.006; NH3: 4.34±2.79; VOC: 0.989±0.249). A detailed composition of VOC is also presented. Terpenes were the main emitted VOC family in all the wastes studied. Higher emissions of alpha and beta pinene were found during OF_wood composting processes.