Process control in municipal solid waste incinerators: survey and assessment.

As there is only rare and scattered published information about the process control in industrial incineration facilities for municipal solid waste (MSW), a survey of the literature has been supplemented by a number of waste incineration site visits in Belgium and The Netherlands, in order to make a realistic assessment of the current status of technology in the area. Owing to the commercial character, and therefore, the confidentiality restrictions imposed by plant builders and many of the operators, much of the information collected has either to be presented in a generalized manner, and in any case anonymously. The survey was focused on four major issues: process control strategy, process control systems, monitors used for process control and finally the correlation between the 850 degrees C/2 s rule in the European waste incineration directive and integrated process control. The process control strategies range from reaching good and stable emissions at the stack to stabilizing and maximizing the energy output from the process. The main indicator to be monitored, in cases in which the focus is controlling emissions, is the oxygen content in the stack. Keeping the oxygen concentration in a determined range (usually between 8 and 12 vol.%) ensures stable and tolerated concentrations of the gaseous emissions. In the case for which stabilization of energy production is the principal aim, the main controlled parameter is the steam temperature and flow-rate, which is usually related to the fuel energetic input. A lot of other parameters are used as alarm criteria, the most common of which is the carbon monoxide concentration. The process control systems used most commonly feature partially automated classical proportional integral derivative (PID) controllers. New and innovative process control systems, such as fuzzy-logic control systems, are still unknown to most plant managers while their performance is reported to be unsatisfactory in plants in which such systems have been tested or are in use. Monitoring components used in process control are still based on classical tools such as thermocouples. The use of modern and more reliable sensors is very limited due to the high initial investment cost or simply the fear of using non-standard technologies. Complying with the 850 degrees C/2 s rule in the European waste incineration directive generally is seen to be a handicap for the process control, either in terms of cost, or flexibility of reaction, or both, particularly in old incineration facilities where such restrictions were not planned in the design.     

Radiometric and environmental impacts of mill tailings at experimental plant processing unit,Allouga, Egypt

Abstract

Uranium mining and ore processing are known to be harmful to the environment and human health if the waste generated is not managed properly. The aim of the present study is to determine the radiological indices in the mill tailings and review the possible attempts to utilize and minimize its hazardous effect. The activity concentrations of natural radionuclides, ²³⁸U, ²³²Th, ²²⁶Ra, and ⁴⁰K have been measured by gamma spectrometry using HP-Ge detector. The average activity concentrations of ²³⁸U, ²³²Th, ²²⁶Ra, and ⁴⁰K in the tailings wastes were 2071.8, 59.92, 6921.262, and 445. 57?Bq/kg respectively which are higher than the international average limit. The ranges of hazard indices such as Radium equivalent activity (Ra_eq), external hazard index (H_ex), internal hazard index (H_in), γ-radiation hazard index I_γ, Dose rate (nGy/h) and annual effective dose equivalent (AED), were estimated. Uraniumm isotopic ratios in the ore –material and mill tailing samples indicate migration out of radionuclides to the surrounding environment causing contamination and many dangerous diseases. Fairly, all investigated tailing waste samples do not satisfy the universal standards, the studied wastes relatively still have high uranium contents and need reprocessing.     

Synthesis and characterization of drinking water treatment plant sludge-incorporated Portland cement

Kinetic analysis of thermally activated phase transformations in drinking water treatment plant (DWTP) sludge suggests its applicability in the materials of construction. The suggested prediction has already been verified on the sludge-based bricks. The present study deals with incorporating the same sludge in the raw meal for the synthesis of Portland cement clinkers. For this purpose, two raw meals are prepared with varying sludge loadings. The sludge effect on reactivity of the crude mixture is evaluated on the basis of the free lime content sintered at various elevated temperatures. The results of chemical and mineralogical and scanning electron microscopic analyses reveal fine mineralogical contents of Portland clinkers calcined at 1450 and 1500 °C. Moreover, the cements prepared from these clinkers by the introduction of certain proportions of gypsum, depict significant durability. The obtained results elucidate that the studied DWTP sludge-incorporated Portland cement shows considerable potential to be commercialized.     

Cleaner production in the management of water use at a poultry slaughterhouse of Vale do Taquari,Brazil: a case study

This study included the layout characterization for the production process of a poultry slaughterhouse using qualitative and quantitative flow charts for water management; analysis of general parameters for pollution load in the wastewater produced in critical stages of the production process and assessment of environmental impact indicators. Prognoses for cleaner production based on water management were established. The diagnostic stage revealed that the scalding, pre-chilling, separated points of wastewater disposal for the wastewater treatment plant and disposal of treated and non-reused wastewater were critical for water management. Dissolved oxygen depletion and eutrophication account for the major environmental impacts of these wastewaters, resulting in an environmental pressure index of 32.1. The opportunities for cleaner production implementation resulting from this study include the reuse of wastewaters from pre-chilling and chilling for pre-washing of carcasses, since average temperatures of these wastewaters range between 4 and 16 °C. This will contribute to lowering the oil and grease pollution load. Another strategy concerns the standardization of cleaning procedures with rational water use in all work shifts and implementation of water meters on a sector-by-sector basis. In the latter case, which has already been implemented, water consumption was reduced by 13%.     

Water quality soft-sensor prediction in anaerobic process using deep neural network optimized by Tree-structured Parzen Estimator

● Hybrid deep-learning model is proposed for water quality prediction. ● Tree-structured Parzen Estimator is employed to optimize the neural network. ● Developed model performs well in accuracy and uncertainty. ● Usage of the proposed model can reduce carbon emission and energy consumption. Anaerobic process is regarded as a green and sustainable process due to low carbon emission and minimal energy consumption in wastewater treatment plants (WWTPs). However, some water quality metrics are not measurable in real time, thus influencing the judgment of the operators and may increase energy consumption and carbon emission. One of the solutions is using a soft-sensor prediction technique. This article introduces a water quality soft-sensor prediction method based on Bidirectional Gated Recurrent Unit (BiGRU) combined with Gaussian Progress Regression (GPR) optimized by Tree-structured Parzen Estimator (TPE). TPE automatically optimizes the hyperparameters of BiGRU, and BiGRU is trained to obtain the point prediction with GPR for the interval prediction. Then, a case study applying this prediction method for an actual anaerobic process (2500 m³/d) is carried out. Results show that TPE effectively optimizes the hyperparameters of BiGRU. For point prediction of COD_eff and biogas yield, R² values of BiGRU, which are 0.973 and 0.939, respectively, are increased by 1.03%–7.61% and 1.28%–10.33%, compared with those of other models, and the valid prediction interval can be obtained. Besides, the proposed model is assessed as a reliable model for anaerobic process through the probability prediction and reliable evaluation. It is expected to provide high accuracy and reliable water quality prediction to offer basis for operators in WWTPs to control the reactor and minimize carbon emission and energy consumption.     

Enhanced photocatalytic activities of silicon nanowires/graphene oxide nanocomposite: Effect of etching parameters

Homogeneous and vertically aligned silicon nanowires (SiNWs) were successfully fabricated using silver assisted chemical etching technique. The prepared samples were characterized using scanning electron microscopy, transmission electron microscopy and atomic force microscopy. Photocatalytic degradation properties of graphene oxide (GO) modified SiNWs have been investigated. We found that the SiNWs morphology depends on etching time and etchant composition. The SiNWs length could be tuned from 1 to 42 µm, respectively when varying the etching time from 5 to 30 min. The etchant concentration was found to accelerate the etching process; doubling the concentrations increases the length of the SiNWs by a factor of two for fixed etching time. Changes in bundle morphology were also studied as function of etching parameters. The SiNWs diameter was found to be independent of etching time or etchant composition while the size of the SiNWs bundle increases with increasing etching time and etchant concentration. The addition of GO was found to improve significantly the photocatalytic activity of SiNWs. A strong correlation between etching parameters and photocatalysis efficiency has been observed, mainly for SiNWs prepared at optimum etching time and etchant concentrations of 10 min and 4:1:8. A degradation of 92% was obtained which further improved to 96% by addition of hydrogen peroxide. Only degradation efficiency of 16% and 31% has been observed for bare Si and GO/bare Si samples respectively. The obtained results demonstrate that the developed SiNWs/GO composite exhibits excellent photocatalytic performance and could be used as potential platform for the degradation of organic pollutants.     

Maximising the net social benefit of the construction of post‐disaster alternative housing projects

The widespread destruction that follows large‐scale natural disasters, such as Hurricane Katrina in August 2005, challenges the efficacy of traditional temporary housing methods in providing adequate solutions to housing needs. Recognising these housing challenges, the Congress of the United States allocated, in 2006, USD 400 million to the Department of Homeland Security to support Alternative Housing Pilot Programs, which are intended to explore the possibilities of providing permanent and affordable housing to displaced families instead of traditional temporary housing. This paper presents a new methodology and optimisation model to identify the optimal configurations of post‐shelter housing arrangements to maximise the overall net socioeconomic benefit. The model is capable of quantifying and optimising the impacts of substituting temporary housing with alternative housing on the social and economic welfare of displaced families as well as the required additional costs of doing so. An application example is presented to illustrate the use of the model and its capabilities.     

Applying physicochemical approaches to control phosphogypsum heavy metal releases in aquatic environment

One of the most important sources of solid waste in the Mediterranean Basin ecosystem originated from the phosphate fertilizer industries, which discharge phosphogypsum (PG) directly into aquatic environments or are stacked on stockpiles. The present study investigates metal release from PG under the influence of variable pH, increasing PG mass content, and complexing organic matter ligands. Major ions from PG leachates, grain size and charge, main functional groups along with metal leachability (Pb, Cd, Cr, Cu, and Zn) were determined using ion chromatography, laser diffraction, zetameter, Fourier transform infrared spectroscopy, and atomic absorption spectroscopy, respectively. The complete dissolution of PG recorded is at 2 g/L. Saturation and supersaturation with respect to PG may occur at concentrations of 3 and 4 g/L, respectively, revealing a clustering phenomenon leading to heavy metal encapsulation within the aggregates. Organic ligands such as citrate may trigger the cationic exchange within the PG suspension leading to ion release. As these factors are considered as specific process involving the release of contaminants from PG during storage under natural conditions, this study could set the foundations for PG remediation in aquatic environment. Organic ligands under controlled pH conditions could be utilized in treating fertilizer industrial wastes by taking into consideration the particularity of the receiving area, thus decreasing metal hazardous impact on natural media.     

Synthesizing of magnesium and nickel nanoparticles from spent methane dry reforming catalyst using sol–gel method: process flow diagram development

Journal of Material Cycles and Waste Management - This study aims to recover Ni and Mg from spent catalysts of dry methane reforming. Huge amounts of spent catalyst are produced every year....