Design and implementation study of a Permanent Selective Collection Program (PSCP) on a University campus in Brazil

The selective collection and recycling of municipal solid waste are presented as stages of an integrated program of solid waste management to minimize the environmental impact of the treatment and final disposal of solid waste. Therefore, this program aims to save natural resources, such as energy and raw materials, in the manufacture of new products and to conserve areas for sites, such as to minimize the use of existing landfill sites, and to minimize the need for new waste treatment sites. A university is composed of educational professionals aware of their societal responsibilities, and, therefore, they play a fundamental role in the management of the university's solid waste. This study presents the design and implementation of a Permanent Selective Collection Program (PSCP) at the Federal University of Itajubá (Universidade Federal de Itajubá, UNIFEI), Itajubá-MG, Brazil. The material requirements for initiating the PSCP have been identified, and an action plan for continuous program improvement, which is initially based on the collection of performance indicator data for the PSCP campus, has been developed. Finally, the data from the PSCP performance indicators and software from the United States Environmental Protection Agency, the Landfill Gas Generation Model (LandGEM) and the Waste Reduction Model (WARM), were used to evaluate the impact of implementing PSCP in terms of energy and the generation of greenhouse gases (GHG). The results were promising, showing that there has been an improvement, since the inception of PSCP in 2006, in separating materials for selective collection, even though paper (41.00 wt%), plastic (6.00 wt%) and organic matter (26.00 wt%) are still highly generated wastes. The WARM simulations for a scenario in which 90% of the waste is sent for recycling resulted in an economy of −7 tCO₂ or −74.91 GJ (on an energy basis). The LandGEM (USEPA) simulations estimated 1424.60 kWh of energy in the peak production year.     

CO2 capture from hot stove gas in steel making process

The capture of CO₂ from a hot stove gas in steel making process containing 30 vol% CO₂ by chemical absorption in a rotating packed bed (RPB) was studied. The RPB had an inner diameter of 7.6 cm, an outer diameter of 16 cm, and a height of 2 cm. The aqueous solutions containing 30 wt% of single and mixed monoethanolamine (MEA), 2-(2-aminoethylamino)ethanol (AEEA), and piperazine (PZ) were used. The CO₂ capture efficiency was found to increase with increasing temperature in a range of 303–333 K. It was also found to be more dependent on gas and liquid flow rates but less dependent on rotating speed when the speed was higher than 700 rpm. The obtained results indicated that the mixed alkanolamine solutions containing PZ were more effective than the single alkanolamine solutions. This was attributed to the highest reaction rate of PZ with CO₂. A higher portion of PZ in the mixture was more favorable to CO₂ capture. The highest gas flow rates allowed to achieve a desired CO₂ capture efficiency and the correspondent height of transfer unit (HTU) were determined at different aqueous solution flow rates. Because all the 30 wt% single and mixed alkanolamine solutions could result in a HTU less than 5.0 cm at a liquid flow rate of 100 mL/min, chemical absorption in a RPB instead of a packed bed adsorber is therefore suggested to capture CO₂ from the flue gases in steel making processes.     

Survey of household waste composition and quantities in Abuja,Nigeria

Inadequate management of household solid waste is a serious problem in many developing cities. The study aimed to evaluate the quantities and composition of household solid waste generation in Abuja within different socioeconomic groups. The wastes from 74 households across different socioeconomic levels in Abuja were collected, weighted and classified on a daily basis for seven days in February 2012. The result showed that the average daily per capita household waste generation is 0.634 kg/capita/day. The characteristic of solid waste in Abuja are typical for the developing cities and dominated by organic waste. Households waste consisted of 63.6% organic waste, 9.7% paper, 8.7% plastics, 3.2% metal, 2.6% glass, 1.6% textile and 10.6% others (unclassified) and the bulk density was 240 kg/m³. The evaluation of relationship between income and daily per capita household waste generation showed a positive relationship. The study revealed a statistically significant difference between household size and daily per capita household waste generation in high-income group; a slight significant difference between household size and daily per capita household waste generation in medium income group and no statistically significant difference between household size and daily per capita household waste generation in low-income group.     

The value of post-combustion carbon dioxide capture and storage technologies in a world with uncertain greenhouse gas emissions constraints

By analyzing how the largest CO₂ emitting electricity-generating region in the United States, the East Central Area Reliability Coordination Agreement (ECAR), responds to hypothetical constraints on greenhouse gas emissions, the authors demonstrate that there is an enduring role for post-combustion CO₂ capture technologies. The utilization of pulverized coal generation with carbon dioxide capture and storage (PC + CCS) technologies is particularly significant in a world where there is uncertainty about the future evolution of climate policy and in particular uncertainty about the rate at which the climate policy will become more stringent. The paper's analysis shows that within this one large, heavily coal-dominated electricity-generating region, as much as 20–40 GW of PC + CCS could be operating before the middle of this century. Depending upon the state of PC + CCS technology development and the evolution of future climate policy, the analysis shows that these CCS systems could be mated to either pre-existing PC units or PC units that are currently under construction, announced and planned units, as well as PC units that could continue to be built for a number of decades even in the face of a climate policy. In nearly all the cases analyzed here, these PC + CCS generation units are in addition to a much larger deployment of CCS-enabled coal-fueled integrated gasification combined cycle (IGCC) power plants. The analysis presented here shows that the combined deployment of PC + CCS and IGCC + CCS units within this one region of the U.S. could result in the potential capture and storage of between 3.2 and 4.9 Gt of CO₂ before the middle of this century in the region's deep geologic storage formations.     

In-depth analysis of aluminum flows in Austria as a basis to increase resource efficiency

Based on the method of material flow analysis (MFA), a static model of Austrian aluminum (Al) flows in 2010 was developed. Extensive data research on Al production, consumption, trade and waste management was conducted and resulted in a detailed model of national Al resources. Data uncertainty was considered in the model based on the application of a rigorous concept for data quality assessment. The model results indicated that the growth of the Austrian “in-use” Al stock amounts to 11 ± 3.1 kg yr⁻¹ cap⁻¹. The total “in-use” Al stock was determined using a bottom-up approach, which produced an estimate of 260 kg Al cap⁻¹. Approximately 7 ± 1 kg of Al yr⁻¹ cap⁻¹ of old scrap was generated in 2010, of which 20% was not recovered because of losses in waste management processes. Quantitatively, approximately 40% of the total scrap input to secondary Al production originated from net imports, highlighting the import dependency of Austrian Al refiners and remelters. Uncertainties in the calculation of recycling indicators for the Austrian Al system with high shares of foreign scrap trade were exemplarily illustrated for the old scrap ratio (OSR) in secondary Al production, resulting in a possible range of OSRs between 0 and 66%. Overall, the detailed MFA in this study provides a basis to identify resource potentials as well as resource losses in the national Al system, and it will serve as a starting point for a dynamic Al model to be developed in the future.     

Environmental benefits from the use of the residual biomass in nurseries

Every year, nurseries waste about 40 t of residual biomass for each ha of potted plants cultivation. The European nursery sector deals with about 90,000 ha of cultivated land and 120,000 ha of nurseries, with a turnover of 19.8 billion Euros in 2011. In recent years, a number of Italian projects highlighted that GHG (greenhouse gas) emissions for the nursery sector range between 37 tCO₂eq/ha/year and 45 tCO₂eq/ha/year for potted plants, mainly due to the consumption of electric energy, plastics and peat. Moreover, other studies analyse the impacts associated to nurseries, recommending best practices for energy reductions and waste recycle or reuse. Therefore, the present work focused its attention to the possible environmental benefits associated to the reuse of residues (wood and substrate) of potted plants that are discarded from the nursery production chain. GHG emissions and fossil energy requirement were quantified by considering the CO₂eq (CO₂ equivalent) and the CER (cumulative energy requirement) respectively, in order to assess the environmental impacts of two different scenarios proposed for the materials recovery. Final results highlighted that the solutions which are able to recover the substrate and the wood allow impact reductions compared to landfill disposal. In particular, the scenario consisting in the immediate separation of the substrate from the root-plant system and the successive chipping of wood for energetic reuse, allows higher savings than those obtainable through shredding and subsequent wind separation. Moreover, for what concerns the CO₂eq, an adequate use of the residual biomass make it possible to compensate the GHG emissions of the nurseries up to 15%.     

Waste electric and electronic toys: Management practices and characterisation

The main objective of this paper is to characterise, both physically and chemically, waste electric and electronic toys, belonging to the category 7 of the Directive, 2012/19/UE, in order to obtain information about the generation and composition of this waste which is not widely found in the literature. For this, a campaign was designed with the aim of collecting a representative sample of waste toys in different schools in a Spanish town. Altogether 1014.25 kg of waste toys were collected, of which 31.83% corresponded to the electric and electronic fraction, which is the object of study. The collected wastes were divided into subcategories and a representative sample of each was one used to characterise them physically and chemically. Physical characterisation provided information about the materials they were made of, the electrical and electronic parts, fixing and assembly systems, and so forth. The results showed that the weight of a toy is comprised of 72.30% of plastics, 12.07% of electrical and electronic components, 4.47% of metals, and 11.15% other materials. In general, the most common types of polymers were PS, PP and ABS. Chemical characterisation made it possible to analyse the composition of the plastic components, which is information that is essential to be able to determine the feasibility of recovering the resulting fractions. The results showed that the content of hazardous substances in these plastics is far below the limits stipulated in Directive 2002/95/EC (RoSH Directive). The findings of this study show a need for a specific management system for this fraction of domestic wastes and a wide range of potential reusability of the discarded toys since 65% of the toys from the collected sample worked in perfect condition. We also found that the end-of-life is one of the aspects that have not been considered during their design as both materials and disassembly sequence do not facilitate the end-of-life of this type of wastes. This information could be used to improve the ecodesign of electrical and electronic equipment toys regarding their end-of-life.     

Resource consumption of pharmaceutical waste solvent valorization alternatives

In this article, for the treatment of two specific pharmaceutical waste solvents the resource consumption of an on-site distillation process is evaluated and compared with an off-site incineration process. Both techniques are evaluated based on a thermodynamic quantitative method. The exergy approach and the cumulative exergy extracted from the natural environment (CEENE) are envisaged in order to evaluate the overall resource intake at different levels. Scenarios are constructed to make a fair comparison of both techniques. Two waste solvents, toluene (TOL) and dichloromethane (DCM), from the pharmaceutical industry which are frequently sent to distillation were evaluated. The functional unit for the comparison of both treatment alternatives is the treatment of 1 kg waste solvent + the incineration of W kg low calorific hazardous waste + the delivery of X kg “recovered” solvent + the production of Y MJ heat and Z MJ electricity. W, X, Y and Z depend on the waste solvent properties. In terms of resource requirements, distillation requires 17% (TOL) and 66% (DCM) less resources than incineration. It can be concluded that the waste solvent properties, the efficiency of the distillation process and the efficiency of the fresh solvent production process are of major importance on the resource consumption and the final choice between incineration and distillation. For a full environmental impact analysis of both treatment options, also the emissions should be taken into account. It also has to be stressed that in practice, only solvents go to incineration which cannot be distilled due to the type and degree of pollution/composition of the solvent. If distillation is not feasible, then such solvents are sent to incineration with energy recovery, according to the EU directive 2006/12/EG.     

Study of inexpensive oxygen carriers for chemical looping combustion

Norwegian industrial tailings and by-products, as well as naturally occurring minerals and ores have been surveyed with the purpose of identifying candidate oxygen carrier materials for use in a chemical looping combustion process. Nine materials, based on manganese and/or iron oxide, were selected for an initial screening test; six were deemed promising and were hence investigated further. Thermogravimetric experiments were performed to investigate the oxygen capacity, the reaction kinetics and reversibility of the oxygen absorption reaction. A manganese ore with a reversible capacity of 4.9 wt% oxygen at 1000 °C was selected as the most promising for chemical looping combustion applications. This material was modified by addition of calcia to explore the possibility of enhancing the kinetic, catalytic and mechanical properties. The addition of excess calcium relative to manganese resulted in formation of calcium manganite and related phases. The oxygen capacity of the modified material was 4.5 wt% at 1000 °C, but it has potential advantages in terms of kinetics and chemical and mechanical stability relative to the pure ore.     

Environmental impacts of different food waste resource technologies and the effects of energy mix

The environmental impacts of food waste management strategies and the effects of energy mix were evaluated using a life cycle assessment model, EASEWASTE. Three different strategies involving landfill, composting and combined digestion and composting as core technologies were investigated. The results indicate that the landfilling of food waste has an obvious impact on global warming, although the power recovery from landfill gas counteracts some of this. Food waste composting causes serious acidification (68.0 PE) and nutrient enrichment (76.9 PE) because of NH₃ and SO₂ emissions during decomposition. Using compost on farmland, which can marginally reduce global warming (−1.7 PE), acidification (−0.8 PE), and ecotoxicity and human toxicity through fertilizer substitution, also leads to nutrient enrichment as neutralization of emissions from N loss (27.6 PE) and substitution (−12.8 PE). A combined digestion and composting technology lessens the effects of acidification (−12.2 PE), nutrient enrichment (−5.7 PE), and global warming (−7.9 PE) mainly because energy is recovered efficiently, which decreases emissions including SO₂, Hg, NO_x, and fossil CO₂ during normal energy production. The change of energy mix by introducing more clean energy, which has marginal effects on the performance of composting strategy, results in apparently more loading to acidification and nutrient enrichment in the other two strategies. These are mainly because the recovered energy can avoid fewer emissions than before due to the lower background values in power generation. These results provide quantitative evidence for technical selection and pollution control in food waste management.     

Heat of absorption of CO2 in aqueous ammonia and ammonium carbonate/carbamate solutions

A reaction calorimeter was used to determine the enthalpies of absorption of CO₂ in aqueous ammonia and in aqueous solutions of ammonium carbonate at temperatures of 35–80 °C. The heat of absorption of CO₂ with 2.5 wt% aqueous ammonia solution was found to be about 70 kJ/mol CO₂, which is lower than that with MEA (around 85 kJ/mol) at 35 and 40 °C. The value decreases with increased loading, but not to as low a value as expected by the carbonate–bicarbonate reaction (26.88 kJ/mol). The enthalpy of absorption of CO₂ in aqueous ammonia at 60 and 80 °C decreases with loadings at first, then increases between 0.2 mol CO₂/mol NH₃ and 0.6 mol CO₂/mol NH₃, and then decreases again. The behavior of the heat of absorption of CO₂ in 10 wt% ammonium carbonate solution was found to be the same as that of aqueous ammonia at loadings above 0.6 mol CO₂/mol NH₃. The heat of absorption increases with increasing temperature. The heats of absorption are directly related to the extent of the various reactions with CO₂ and can be assessed from the species variation in the liquid phase.     

Effect of feeding strategy and COD/sulfate ratio on the removal of sulfate in an AnSBBR with recirculation of the liquid phase

The objective of this work was to analyze the effect of the interaction between feeding strategy and COD/sulfate ratio on the removal efficiency of sulfate and organic matter from a synthetic wastewater. An anaerobic sequencing batch reactor with recirculation of the liquid phase and containing immobilized biomass on polyurethane foam (AnSBBR) was used. The AnSBBR with a total volume of 3.7 L, treated 2.0 L synthetic wastewater in 8-h cycles at 30 ± 1 °C and was inoculated with anaerobic biomass from a UASB. Two feeding strategies were assessed: (a) batch and (b) batch followed by fed-batch. In strategy (a) the reactor was fed in 10 min with 2 L wastewater containing sulfate and carbon sources. In strategy (b) 1.2 L wastewater (containing only the sulfate source) was fed during the first 10 min of the cycle and the remaining 0.8 L (containing only the carbon source) in 240 min. The COD/sulfate ratios assessed were 1 and 3. Based on these values and on the concentrations of organic matter (0.5–11.25 gCOD/L) and sulfate (0.5 and 2.5 gSO₄^2?/L), the sulfate and organic matter loading rates applied equaled 1.5 and 4.5 gSO₄^2?/L d for sulfate and 1.5, 4.5 and 13.5 gCOD/L d for organic matter. After stabilization of the system time profiles were run of monitored parameters (COD, sulfate, sulfide and sulfite). In general, the reactor showed to be robust for use in the anaerobic treatment of wastewaters containing sulfate. Gradual feeding (strategy b) of the carbon source favored sulfate reduction, resulting in sulfate removal efficiencies of 84–98% and organic matter removal efficiencies of 48–95%. The best results were observed under COD/sulfate ratio equal to 1 (loading rates of 1.5 and 4.5 gSO₄^2?/L d for sulfate, and 1.5 and 4.5 gCOD/L d for organic matter). When COD/sulfate ratio was 3 (loading rates of 1.5 and 4.5 gSO₄^2?/L d for sulfate, and 4.5 and 13.5 gCOD/L d for organic matter) the effect of feed mode became less significant. These results show that the strategy batch followed by fed-batch is more advantageous for COD/sulfate ratios near the stoichiometric value (0.67) and higher organic matter and sulfate concentrations.     

Storage and characterization of cotton gin waste for ethanol production

In 2002, about 17.1 million bales of cotton were ginned in the United States and the estimated cotton gin waste was 2.25 × 10⁹ kg. The disposal of cotton gin waste (CGW) is a significant problem in the cotton ginning industry, but CGW could be potentially used as feedstock for bioethanol. Freshly discharged CGW and stored CGW were characterized for storage stability and potential for ethanol production by determining their summative compositions. The bulk densities of the fresh wet and dry CGW were 210.2 ± 59.9 kg m⁻³ and 183.3 ± 52.2 kg m⁻³, respectively. After six months of storage the volume of piles A, B, and C decreased by 38.7%, 41.5%, and 33.3%, respectively, relative to the volume of the pile at the start of the storage. The ash content of the CGW was very high ranging from 10% to 21% and the acid-insoluble fraction was high (21–24%). The total carbohydrate content was very low and ranged from 34% to 49%. After three months storage, chemical compositional analysis showed the loss of total carbohydrates was minimal but after six months, the losses were as high as 25%. This loss of carbohydrates suggests that under open storage conditions, the feedstock must be processed within three months to reduce ethanol yield losses.     

Effect of impeller type and agitation on the performance of pilot scale ASBR and AnSBBR applied to sanitary wastewater treatment

The objective of this work was to assess the effect of agitation rate and impeller type in two mechanically stirred sequencing batch reactors: one containing granulated biomass (denominated ASBR) and the other immobilized biomass on polyurethane foam (denominated AnSBBR). Each configuration, with total volume of 1 m³, treated 0.65 m³ sanitary wastewater at ambient temperature in 8-h cycles. Three impeller types were assessed for each reactor configuration: flat-blade turbine impeller, 45°-inclined-blade turbine impeller and helix impeller, as well as two agitation rates: 40 and 80 rpm, resulting in a combination of six experimental conditions. In addition, the ASBR was also operated at 20 rpm with a flat-blade turbine impeller and the AnSBBR was operated with a draft tube and helix impeller at 80 and 120 rpm. To quantify how impeller type and agitation rate relate to substrate consumption rate, results obtained during monitoring at the end of the cycle, as well as the time profiles during a cycle were analyzed. Increasing agitation rate from 40 rpm to 80 rpm in the AnSBBR improved substrate consumption rate whereas in the ASBR this increase destabilized the system, likely due to granule rupture caused by the higher agitation. The AnSBBR showed highest solids and substrate removal, highest kinetic constant and highest alkalinity production when using a helix impeller, 80 rpm, and no draft tube. The best condition for the ASBR was achieved with a flat-blade turbine impeller at 20 rpm. The presence of the draft tube in the AnSBBR did not show significant improvement in reactor efficiency. Furthermore, power consumption studies in these pilot scale reactors showed that power transfer required to improve mass transfer might be technically and economically feasible.     

The contemporary European silver cycle

This paper examines the 1-year anthropogenic stocks and flows of silver as it progresses from extraction to final disposal on the European continent. The primary flows of silver include production, fabrication and manufacturing, use, and waste management. A substance flow analysis (SFA) was used to trace the flows and inventory data, and mass balance equations were used to determine the quantity of flows. The results reveal that Europe has a low level of silver mine production (1580 Mg Ag/year) and instead relies on silver imports and the recycling of scrap in production and fabrication. In the year 1997, Europe imported 1160 Mg Ag of ore concentrate and 2010 Mg Ag of refined silver, and recycled 2750 Mg Ag of new and old scrap. There is a net addition of 3320 Mg Ag/year into silver reservoirs at the use stage. This is the result of a greater amount of silver entering the system from manufacturing than is leaving the system into waste management. The waste flow with the highest content of silver is municipal solid waste, which contains 1180 Mg Ag/year. In total, 62% of all discarded silver is recycled and 38% is sent to landfills. The results of this study and other element and material flow analyses can help guide resource managers, environmental policy makers, and environmental scientists in their efforts to increase material recovery and recycling, address resource sustainability, and ameliorate environmental problems.     

Household income,living and working conditions of dumpsite waste pickers in Bantar Gebang: Toward integrated waste management in Indonesia

This paper clarifies household income, living and working conditions of dumpsite waste pickers at Bantar Gebang final disposal site for municipal solid waste generated in Jakarta, and investigates the feasibility of integrating the informal sector into formal waste management in Indonesia. The first author did fieldwork for totally 16 months at the site and quantitative field surveys were conducted twice during the period. All respondents in the first round quantitative survey (n = 1390) were categorized as follows: waste pickers, family workers, wage labors, bosses, family of the bosses, housewives, pupils/students, preschoolers, the unemployed, and others. Based on the results of the second round quantitative survey (n = 69 households), their average household income was estimated to be approximately US 216 dollars per month (n = 59 households), which was virtually equivalent to the minimum wage in Jakarta in 2013. Living conditions of scavengers at the site were horrible, and their working conditions were dangerous due to medical waste and other sharp waste. Polluted groundwater was one of the serious environmental problems at the site. Despite the social, health and environmental problems, they were attracted to the freedom of entering the informal recycling system in Bantar Gebang and withdrawing from the system, in which a lot of opportunities were provided for the people having few marketable skills to obtain cash earnings. The freedom of their choice should be guaranteed as a prerequisite before integrating the informal sector into formal waste management. Furthermore, special attentions are required when incomes of scavengers are the same level as minimum wages and the national economy is rapidly growing, because scavengers cannot easily change their jobs due to few marketable skills. Indonesian national waste laws and regulations should be properly applied to facilitate a socialization process at final disposal sites. Measures need to be taken to prevent children from working as informal recycling actors, especially for waste pickers aged 15 or younger.     

Current results and future perspectives for Japanese recycling of home electrical appliances

The Japanese system of recycling home electrical appliances has several unique aspects, including (1) a limited number of target appliances, (2) a recycling fee system that requires consumers to pay a recycling fee at the time of disposal, and (3) a direct recycling obligation for manufacturers, who have a physical, rather than a financial, responsibility for their end-of-life products. We studied data from 2001 to 2007 and found that the amount of four specified home electrical appliances and their materials that was recycled increased from about 319,249 tonnes in 2001 to about 447,262 tonnes—or 3.5 kg per inhabitant—in 2006. Recycling yield and development of recycling technologies have also improved. New recycling technologies have enabled a higher rate of material recycling of plastics (i.e., a closed-loop recycling). Improved eco-design, such as design for easier disassembly, has been promoted, and the higher quality of discarded appliances has enhanced the reuse market. Hazardous substances and fluorocarbons are being well managed. Problems with the recycling system include inelastic recycling fees, illegal dumping, illegal transfer by retailers, and the limited number of target appliances. Recycling fees could be reduced; this move might reduce the incidence of illegal dumping, as would engage stakeholders in collaborative efforts against illegal dumping. Illegal transfers could be reduced by improved traceability for retailers. Products such as liquid crystal displays, plasma display panels and clothes dryers have become increasingly common and should be also be targeted for recycling.     

The Austrian P budget as a basis for resource optimization

Phosphorus (P) is a finite and non-substitutable resource that is essential to sustaining high levels of agricultural productivity but is also responsible for environmental problems, e.g., eutrophication. Based on the methodology of Material Flow Analysis, this study attempts to quantify all relevant flows and stocks of phosphorus (P) in Austria, with a special focus on waste and wastewater management. The system is modeled with the software STAN, which considers data uncertainty and applies data reconciliation and error propagation. The main novelty of this work lies in the high level of detail at which flows and stocks have been quantified to achieve a deeper understanding of the system and to provide a sound basis for the evaluation of various management options. The budget confirms on the one hand the dependence of mineral P fertilizer application (2 kg cap⁻¹ yr⁻¹), but it highlights on the other hand considerable unexploited potential for improvement. For example, municipal sewage sludge (0.75 kg cap⁻¹ yr⁻¹) and meat and bone meal (0.65 kg cap⁻¹ yr⁻¹) could potentially substitute 70% of the total applied mineral P fertilizers. However, recycling rates are low for several P flows (e.g., 27% of municipal sewage sludge; 3% of meat and bone meal). Therefore, Austria is building up a remarkable P stock (2.1 kg P cap⁻¹ yr⁻¹), mainly due to accumulation in landfills (1.1 kg P cap⁻¹ yr⁻¹) and agricultural soils (0.48 kg P cap⁻¹ yr⁻¹).     

1D and 2D absorption-rate/kinetic modeling and simulation of carbon dioxide absorption into mixed aqueous solutions of MDEA and PZ in a laminar jet apparatus

The kinetics of the reaction between carbon dioxide (CO₂) and mixed solutions of methyldiethanolamine (MDEA) and piperazine (PZ) was investigated experimentally in a laminar jet apparatus. The experimental kinetic data were obtained under no interfacial turbulence and over a temperature range from 313 to 333 K, MDEA/PZ wt% concentration ratios of 27/3, 24/6 and 21/9, and CO₂ loadings from 0.0095 to 0.33 mol CO₂/mol amine. In addition, a new absorption-rate/kinetics model for the kinetics of the mixed of solvents was developed, which takes into account the coupling between chemical equilibrium, mass transfer, and all possible chemical reactions involved in the CO₂ reaction with MDEA/PZ solvent. The partial differential equations of this model were solved by the finite element numerical method (FEM) based on COMSOL software. The obtained experimental kinetics data were used to obtain the kinetic parameters of CO₂ absorption into MDEA/PZ solutions. The reaction-rate constant obtained for PZ blended with MDEA was kPZ = 2.572 × 10¹² exp(?5211/T). The 2D model for the blended amines MDEA/PZ has revealed the concentration profiles of all the species in both the radial and axial directions of the laminar jet which has enabled a better understanding of the correct sequence in which the reaction steps involved in the reactive absorption of CO₂ in aqueous mixed MDEA/PZ solution occur. It also revealed that PZ may be depleted by the time the solvent blend of MDEA/PZ with a loading greater than 0.015 mol/mol amine is exposed to CO₂ from the top of the laminar jet absorber.