Urban wastewater as a source of reclaimed water for irrigation: barriers and future possibilities

Water resources are under pressure worldwide, resulting in scarcity and deterioration of freshwater quality. According to European directives, we could reduce the pressure on water resources in urban areas by increasing the reuse of treated wastewater, reducing the impact on water bodies, and promoting water recycling through multiple uses of urban wastewater. Besides the need to address water supply challenges, wastewater treatment systems show environmental stewardship and innovative practices. Using reclaimed water for agricultural irrigation is gaining interest because of the drought conditions experienced in Europe over the past few years. Furthermore, using treated wastewater for agricultural irrigation may help to restore nutrients (N and P) to natural biogeochemical cycles. This review highlights the importance of water reuse, current legislation, and existing technologies to implement in wastewater treatment systems to meet the minimum requirements to produce reclaimed water to reuse in agricultural irrigation.info:eu-repo/semantics/publishedVersio

Rapid sintering of weathered municipal solid waste incinerator bottom ash and rice husk for lightweight aggregate manufacturing and product properties

This study assessed the technical feasibility of formulating lightweight aggregates (LWA) from municipal solid waste incinerator bottom ash (IBA) and residual biomass. Weathered IBA (WIBA) particles larger than 8 mm contain a mixture of calcium-rich compounds and other silicates mainly composed of glass and synthetic and natural ceramics, with low contents of heavy metals and soluble salts. Unfired LWA were formulated with the particle size fraction of WIBA larger than 8mm and rice husk (RH) used as the bloating agent. Rapid sintering of the unfired spherical pellets at 1,100°C for 5min produced some cohesive sintered LWA, whose porosity, apparent particle density, water absorption, and compressive strength directly correlated with the percentage of RH added. The fired LWA formulated with 5wt% of RH showed the highest bloating index (115%) and porosity (53%) and the lowest apparent particle density (0.61Mgm−3) and compressive strength (1.4MPa). The addition of more than 5wt% of RH increased the internal temperature of the sintered aggregates and decreased the viscosity of the molten glassy materials, resulting in the collapse of the inner structure. Consequently the porosity decreased and the apparent density of the particles increased, thereby shrinking the volume of the fired LWA. According to the standard leaching test (EN 12457-4), both the unfired precursor and the sintered aggregates showed concentrations of heavy metals and metalloids in the leachates that were well below the safety limits established for their reuse as secondary material

Electrochemical reduction of hematite-based ceramics in alkaline medium: challenges in electrode design

Electrochemical reduction of low-conductive hematite-based ceramics represents a novel approach for iron recovery and waste valorisation. The process itself allows a flexible switching between hydrogen generation and iron reduction, important for the intermittent renewable-energy-powered electrolytic process. The present study focuses on the direct electrochemical reduction of aluminium-containing hematite in strong alkaline media. Within this scope, the reduction mechanisms of porous and dense cathodes, with 60%, 37% and 3% of open porosity, were investigated using different types of electrodes configuration: nickel-foil and Ag-modified nickel-foil supported configuration (cathodes facing or against the counter electrode), and nickel-mesh supported configuration. The efficiency of the iron reduction was compared for different electrode concepts. The results highlight the importance of electrolyte access to the interface between the metallic current collector and ceramic cathode for attaining reasonable electroreduction currents. Both excessively porous and dense ceramic cathodes are hardly suitable for such reduction process, showing a necessity to find a compromise between mechanical strength of the electrode and its open porosity, essential for the electrolyte access.publishe

Direct processing of cellular ceramics from a single red mud precursor

The feasibility of recycling red mud waste by its direct transformation into highly-porous cellular ceramics was successfully demonstrated. Ceramic materials with designed cellular porosity were processed by emulsification of red mud suspensions with liquid paraffin. Taguchi method was used to study the effects provided by varying the red mud load in the suspension, gelatine content and emulsion stirring time on the micro structural features of the cellular ceramics. Additional experiments analysed the effects of the organic to suspension ratio and firing temperature. Emulsification of paraffin followed by gelatine consolidation, drying, elimination of the droplets of the discontinuous organic phase and firing, allowed one to design cellular ceramic pieces with open porosity up to 75%, consisting in interconnected cells with adjustable cell size and low resistance to percolation. These results allow one to consider prospective applications of red mud-based cellular ceramics with designed microstructures as highly-porous membranes for the capture of pollutants.publishe

Alkaline electrochemical reduction of a magnesium ferrospinel into metallic iron for the valorisation of magnetite-based metallurgical waste

The electrochemical reduction of iron oxides in alkaline media arises as a novel approach for ironmaking and iron-rich waste valorisation. Strong advantages and attractive aspects of alkaline electroreduction include lower electric energy consumption, absence of CO2 emissions, and non-polluting valuable by-products such as H2 and O2. Another potential advantage originates from the compatibility of this concept with intermittent renewable energies. However, to bring this technology to a competitive level, especially compared to the traditional steelmaking, innovative approaches and developments in materials processing and their appropriate integration into the electrolysis process are required. This research work explores the prospects for electrochemical reduction of a magnesium-containing ferrospinel, as a potential component in iron-containing wastes. The experimental approach considers bulk cathode- and suspension-based electrolysis concepts, which allow reaching 55% and 20% Faradaic efficiencies of the reduction to metallic iron, respectively. The effects imposed by the magnesium presence on the electroreduction kinetics, phase composition and morphology of the electroreduction products are evaluated and discussed. The obtained results open new perspectives for the recovery of metallurgical residues with low magnesium impurities content.publishe

Legal situation and current practice of waste incineration bottom ash utilisation in Europe

Almost 500 municipal solid waste incineration plants in the EU, Norway, and Switzerland generate about 17.6 Mt/a of incinerator bottom ash (IBA). IBA contains minerals and metals. Metals are mostly separated and sold to the scrap market and minerals are either disposed of in landfills or utilised in the construction sector. Since there is no uniform regulation for IBA utilisation at EU level, countries developed own rules with varying requirements for utilisation. As a result from a cooperation network between European experts an up-to-date overview of documents regulating IBA utilisation is presented. Furthermore, this work highlights the different requirements that have to be considered. Overall, 51 different parameters for the total content and 36 different parameters for the emission by leaching are defined. An analysis of the defined parameter reveals that leaching parameters are significantly more to be considered compared to total content parameters. In order to assess the leaching behaviour nine different leaching tests, including batch tests, up-flow percolation tests and one diffusion test (monolithic materials) are in place. A further discussion of leaching parameters showed that certain countries took over limit values initially defined for landfills for inert waste and adopted them for IBA utilisation. The overall utilisation rate of IBA in construction works is approximately 54 wt.%. It is revealed that the rate of utilisation does not necessarily depend on how well regulated IBA utilisation is, but rather seems to be a result of political commitment for IBA recycling and economically interesting circumstances

Thermal Runaway Conditions of a Partially Diluted Catalytic Reactor

The generalized parametric sensitivity criterion was used to obtain runaway diagrams for one- and two-dimensional heterogeneous models and a one-dimensional pseudo-homogeneous model. The simulation work was based on the partial methanol oxidation to formaldehyde, which occurs in a fixed-bed reactor, with two distinct catalytic zones. At the inlet of the reactor, the catalyst was diluted with inert packing followed by a region with pure catalyst. This activity profile induces a reduction in the parametric sensitivity of the process to temperature runaway, when compared to a uniform activity bed, and the sensitivity functions reach a minimum when the inlet temperature is in the range of 530−540 K. The dilution of the catalytic bed leads to an enlargement of the stable region of operation, which allows a gain in the critical methanol concentration of 20% for a feed temperature of 530 K (industrial operating temperature), higher gains being possible (40%) for higher inlet temperatures. Moreover, depending on the particular set of the operating conditions, one or two hot spots can be developed, one in each zone of the bed, it being important to follow both because one or the other can determine the critical conditions of the system. The additional mass flux by intraparticle convection leads to an increase in the parametric sensitivity when compared with the case where diffusion is the only mechanism taken into account

Model comparison and sensitivity analysis for a fixed bed reactor with two catalytic zones

In this work, comparisons between the behaviour predicted by different types of mathematical models are presented. The system studied was the partial oxidation of methanol to formaldehyde, which occurs in a fixed bed reactor with two distinct zones: at the entrance the catalyst is diluted with inert, followed by a region with pure catalyst. This type of distribution of the catalyst activity leads to different temperature and concentration profiles, when compared with those obtained by a uniform activity bed. Parametric sensitivity is examined for all the dimensionless parameters associated to the different mathematical models of the reactor. The parametric sensitivity analysis shows that the system is particularly sensitive to the wall temperature and almost insensitive to the side reaction and mass transfer parameters.http://www.sciencedirect.com/science/article/B6TFJ-3XSJSXX-1/1/1a6fd7c52948bc7974a8d9dae20ad9b

Treatment and use of air pollution control residues from MSW incineration: An overview

This work reviews strategies for the management of municipal solid waste incineration (MSWI) residues, particularly solid particles collected from flue gases. These tiny particles may be retained by different equipment, with or without additives (lime, activated carbon, etc.), and depending on the different possible combinations, their properties may vary. In industrial plants, the most commonly used equipment for heat recovery and the cleaning of gas emissions are: heat recovery devices (boiler, superheater and economiser); dry, semidry or wet scrubbers; electrostatic precipitators; bag filters; fabric filters, and cyclones. In accordance with the stringent regulations in force in developed countries, these residues are considered hazardous, and therefore must be treated before being disposed of in landfills. Nowadays, research is being conducted into specific applications for these residues in order to prevent landfill practices. There are basically two possible ways of handling these residues: landfill after adequate treatment or recycling as a secondary material. The different types of treatment may be grouped into three categories: separation processes, solidification/stabilization, and thermal methods. These residues generally have limited applications, mainly due to the fact that they tend to contain large quantities of soluble salts (NaCl, KCl, calcium compounds), significant amounts of toxic heavy metals (Pb, Zn, Cr, Cu, Ni, Cd) in forms that may easily leach out, and trace quantities of very toxic organic compounds (dioxin, furans). The most promising materials for recycling this residue are ceramics and glass-ceramic materials.http://www.sciencedirect.com/science/article/B6VFR-4R71DN5-1/1/964c6cff167b18155b9e610ffbdcf8b

Air Pollution Control in Municipal Solid Waste Incinerators

Municipal solid waste (MSW) remains a major problem in modern societies, even though the significant efforts to prevent, reduce, reuse and recycle. At present, municipal solid waste incineration (MSWI) in waste-to-energy (WtE) plants is one of the main management options in most of the developed countries. The technology for recovering energy from MSW has evolved over the years and now sophisticated air pollution control (APC) equipment insures that emissions comply with the stringent limits established in developed countries. This chapter shows the role of incineration in WtE processes in the ambit of MSW management, giving an overview of the MSWI technologies and APC devices used for cleaning the gaseous emissions. The main focus is on the key air pollutants, such as dioxins and furans. At the end, the impact of emission on health risks is also briefly considered