Insight into the role of SO2 on selenium conversion during adsorption by CaO: Theoretical calculation and experimental study.

SO2 can noticeably impact the control of high toxic selenium emissions from flue gas by CaO. Surprisingly, our experiments showed that under certain conditions, SO2 can promote selenium capture by CaO, rather than hinder it. To elucidate the underlying mechanism, a combination of theoretical calculations and experiments was conducted. Thermodynamic equilibrium analysis revealed that gaseous SO2 and solid Ca-S reaction products can promote SeO2 converting to SeO/Se0. The Ca-S products facilitated greater SeO2 conversion compared to SO2. Experimental results demonstrated that selenium adsorption capacity of incompletely sulfurized CaO (CaO with pre-adsorbed SO2) was higher than that of completely sulfurized CaO (Ca-S products), highlighting the importance of adsorption sites of CaO. Density functional theory calculations showed that the pre-adsorbed SO2 hardly affected selenium adsorption energy on the SO2/CaO surface, while completely sulfurized CaO had low selenium adsorption energy, explaining the experimental phenomenon and proving necessary of CaO. Additionally, SeO/Se0 had higher adsorption energy on CaO than SeO2. Overall, the promotion of SO2 on selenium adsorption was primarily affected by two factors: 1) sulfur facilitating SeO2 conversion to SeO/Se0 which can be adsorbed more easily by CaO; 2) sufficient adsorption sites on CaO surface existing for SeO/Se0 adsorption, despite co-adsorption with sulfur.

Co-combustion of Oil Sludge Char with Raw/Hydrothermally Treated Biomass: Interactions, Kinetics, and Mechanism Analysis.

Comprehensive thermochemical treatment (pyrolysis and combustion) is considered to be an efficient method for treatment of oil sludge (OS) or utilization as a heat source. However, combustion of oil sludge char (OSC), the byproduct from OS pyrolysis, is difficult and energy-consuming due to the high ash content and low heating value. In this study, co-combustion of OSC with biomass is proposed, aiming at the efficient thermal treatment with heat recovery. The thermal characteristics, kinetics, and interactive mechanisms of co-combustion of OSC with raw wood (RW) or hydrothermally treated wood (HW) employing thermogravimetric analysis were investigated. The obtained results indicated that RW blending with OSC resulted in negative interactions with decreasing the apparent activation energies (E) of RW, attributed to the inhibited diffusion of volatiles. The developed porous structure in HW effectively promoted volatile matter diffusion. Coupled with the catalytic support by metal oxides in OSC, HW blending yielded positive interactions during co-combustion despite the increased E. The results showed that diffusion models were the most efficient mechanism for OSC/RW combustion. However, chemical reactions were found to be the rate-determining steps for OSC/HW combustion. The catalytic effect of inorganic elements and their physical influence on heat and mass transfer can control the co-combustion performance of OSC and biomass. The findings could offer reference information for understanding OSC co-combustion and provide a basis for implementing and optimizing the co-combustion between biomass and ash-rich waste.

Challenges and practices on waste management and disposal during COVID-19 pandemic.

The COVID-19 pandemic has imposed a global emergency and also has raised issues with waste management practices. This study emphasized the challenges of increased waste disposal during the COVID-19 crisis and its response practices. Data obtained from the scientific research papers, publications from the governments and multilateral organizations, and media reports were used to quantify the effect of the pandemic towards waste generation. A huge increase in the amount of used personal protective equipments (facemasks, gloves, and other protective stuffs) and wide distribution of infectious wastes from hospitals, health care facilities, and quarantined households was found. The amount of food and plastic waste also increased during the pandemic. These factors caused waste treatment facilities to be overwhelmed, forcing emergency treatment and disposals (e.g., co-disposal in a municipal solid waste incinerator, cement kilns, industrial furnaces, and deep burial) to ramp up processing capacity. This paper discussed the ways the operation of those facilities must be improved to cope with the challenge of handling medical waste, as well as working around the restrictions imposed due to COVID-19. The study also highlights the need for short, mid, and longer-term responses towards waste management during the pandemic. Furthermore, the practices discussed in this paper may provide an option for alternative approaches and development of sustainable strategies for mitigating similar pandemics in the future.

A critical review on energy recovery and non-hazardous disposal of oily sludge from petroleum industry by pyrolysis.

This review systematically reports the pyrolysis of oily sludge (OS) from petroleum industry in regards to its dual features of the energy recovery potential and the environmental risks. The petroleum hydrocarbons are the nonbiodegradable fractions in OS that possess hazardous properties, i.e. ignitability and toxicity. Besides, complicated hazardous elements (i.e. N, S and Cl) and heavy metals inherently existing in OS further aggravate the environmental risks. However, the high oil content and heating value of OS contribute to its huge energy resource potential. Considering the energy demand and the environmental pressure, the ultimate purposes of the OS management are to enhance the oil recovery efficiency to minimize the oil content as well as to stabilize the hazardous elements and heavy metals into the solid residue. Among various OS management technologies, pyrolysis is the most suitable approach to reach both targets. In this review paper, the pyrolysis principle, the kinetics and the product distribution in three-phases are discussed firstly. Then the effects of operating parameters of the pyrolysis process on the quality and the application potential of the three-phase products, as well as the hazardous element distribution are discussed. To further solve the dominant concerns, such as the oil content in the solid residue, the pyrolytic oil quality and the migration of hazardous elements and heavy metals, the potentials of the catalytic pyrolysis and the co-pyrolysis with additives are also summarized. Also, the typical pyrolysis reactors are then presented. From the perspective of the energy efficiency and the non-hazardous disposal, the integrated technology combining the pyrolysis and the combustion for the OS management is recommended. Finally, the remaining challenges of OS pyrolysis encountered in the research and the industrial application are discussed and the related outlooks are itemized.

Hydrothermal treatment combined with in-situ mechanical compression for floated oily sludge dewatering.

Due to the high moisture content of the oily sludge, the conventional use of oily sludge treatment presents poor feasibility in industrial applications. Hence, finding an efficient and energy-saving technology is still an urgent need for the dewatering of oily sludge. In this paper, an innovative method combining hydrothermal treatment (HT) and in-situ mechanical compression (MC) for dewatering of floated oily sludge (FOS) was proposed. Series of experiments on HT&MC were conducted to verify the method. 77-96 wt% of water can directly be separated from FOS by the HT&MC treatment under the temperature of 120-240 °C and residence times of 10-60 min. The bound water content in raw and HT&MT treated FOS were measured by employing the differential scanning calorimetry (DSC) to evaluate the dewatering ability. The result of DSC illustrates the freezing peaks shifted from -11.1 °C to -21.2 °C as the diameter of water droplets reduced. Meanwhile, the comprehensive characterization analysis of products, including chemical oxygen demand (COD), NH4+-N, and gas chromatograph (GC) were conducted. All results indicated that HT&MC is advisable for dewatering of oily sludge.

Stochastic economic analysis of coal-alternative fuel production from municipal solid wastes employing hydrothermal carbonization in Zimbabwe.

Hydrothermal carbonization (HTC) is a promising technology for converting high moisture municipal solid waste (MSW) to a safe low-chlorine hydrochar. The key objective is to assess the economic viability of an HTC based MSW management system in Zimbabwe. Previous studies have only used deterministic estimates of hydrochar production costs disregarding uncertainties in their model parameters. Herein, a probabilistic economic analysis is introduced to quantify the uncertainty concerning costs. The goal is to determine factors that will consolidate the venture to achieve a certain level of return. The effectiveness of different investment strategies, namely, a government or private sector-run operation will be tested using Monte Carlo simulations. Results indicate a 55% and 18% probability for a positive Net Present Value (NPV) for a state-run and private operation respectively. A specific investment cost of US$54 - 67 per Mg of MSW treated, a return on investment (ROI) of 5.4-29.0% and internal rate of return (IRR) of 5.2-22.9% can be expected if the project is undertaken by government. The private sector can expect an ROI of -0.8-18.2% at a 90% confidence level and a lower IRR of -2.1-16.2% from US$57 - 71 per Mg of MSW invested. Contingency costs are US$25 per Mg and US$38 per Mg of MSW for the government and private sector respectively at a 100% confidence interval. A 70% rise in collection tariffs or a minimum selling price of US$91/Mg of the hydrochar would ensure a positive NPV for the government-run operation.

Utilization of mixed organic-plastic municipal solid waste as renewable solid fuel employing wet torrefaction.

The largest obstacles in the utilization of municipal solid waste (MSW) as solid fuel in developing countries such as Indonesia are its high water content, irregular size and shape, and difficulty-to-sort due to the mix of plastic and organic waste. Based on literature study, wet torrefaction could be an appropriate pre-treatment process for mixed MSW because it requires no initial drying and mixed organic-plastic MSW can be processed without initial sorting. In this research, experiments were conducted to investigate the effect of wet torrefaction on increasing the fuel properties of mixed MSW. Based on field survey, the composition of the analyzed sample was: leaf litter (34.67%), food waste (23.33%), vegetable waste (14.33%), fruit waste (11.00%), and non-recycled plastic (16.67%). The experiments were conducted in a 2.5-L stirring reactor temperature variation (150, 175, 200 and 225 °C) with several holding times and solid loads. The result showed that wet torrefaction at a temperature of 200 °C with holding time of 30 min and solid load of 1:2.5 was the optimum condition, producing solid product with uniform physical shape, small particles and homogeneous particle size distribution, HHV of 33.01 MJ/kg and energy yield of 89%. The wet torrefaction process is not only suitable to convert the mixed MSW into renewable high energy density solid fuel, but it can also be used to produce separate organic product that can be used as solid fuel and plastic product that can be prepared for other treatments, such as pyrolysis to produce liquid fuel or recycling.

Preparation of high surface area sludge-based activated hydrochar via hydrothermal carbonization and application in the removal of basic dye.

Conventional methods to produce sludge activated carbon require high-energy due to high moisture content and poor dewaterability of the wet sludge. Recently hydrothermal carbonization (HTC) has been emerged as a promising thermo-chemical wet biowaste conversion technology for the valorization by converting these precursors into high value-added products such as a nanostructured carbon. In this study, sludge-based activated hydrochars (SAC) were prepared from high moisture content (88.9%) wastewater sludge (without pre drying) via HTC followed by physical (P-SAC) and chemical (C-SAC) activation with CO2 and KOH, respectively. Further, the effects of HTC temperatures (170, 200, 230 and 260 °C) and the activation methods on the physicochemical characteristics of hydrochar and SACs were investigated through ultimate analysis (CHNO), SEM, BET, BJH, FT-IR, Boehm back titration and zeta potential. The result showed that KOH-activation at 700 °C could significantly enhance the surface area of hydrochars (from 6.3 to 1613.9 m2/g) compared with CO2-activation even at 900 °C (261.6 m2/g). The mesopore P-SAC prepared from hydrochar at lower HTC temperature due to the presence of ash content. While, the negatively charged microspores C-SAC (VTotal: 0.88 cm3/g and Vmicro/VTotal: 73.3%) with high SBET was synthesized at higher HTC temperature. Prepared hydrochars were applied for the removal of a basic dye (such as methylene blue, MB) from aqueous solution. Based on Langmuir isotherm model (R2>99.4%), the maximum monolayer MB adsorption capacity of hydrochar, P-SAC and C-SAC were 63.3, 122.4, and 588.2 mg/g, respectively at pH > 8.0. The MB adsorption on C-SACs followed the pseudo-second-order kinetic model and a spontaneous endothermic reaction from 298 to 328 K. The commercial ACs also was compared with our materials and found that produced activated hydrochars showed superior results for MB removal. Therefore, HTC can be the potential carbonization method for wet biomass conversion to valuable carbonaceous material in a cost-effective way.

The effect of coal alternative fuel from municipal solid wastes employing hydrothermal carbonization on atmospheric pollutant emissions in Zimbabwe.

The vast increase of municipal solid waste (MSW) generated in Zimbabwe coupled with a severe energy crisis have made waste-to-energy technology more attractive and necessary. Coal-alternative solid fuel production from MSW though hydrothermal carbonization can play a critical role to improve both waste management and energy supply. Moreover, MSW conversion to a carbon neutral solid fuel that can be burnt in existing coal-fired power stations might reduce greenhouse gas (GHG) emissions despite GHG releases from waste collection, waste conversion to fuel, and fuel transportation processes. The purpose of this paper is to investigate present MSW generation in Zimbabwe, its characteristics as a fuel source, and the impact of coal-alternative solid fuel production from MSW using hydrothermal carbonization technology on GHG and other air pollutant emissions. Four different scenarios based on the balance between fuel supply and demand were tested in this paper. The results suggest 0.54 ±â€¯0.14 kg/capita/day of MSW generation in Zimbabwe and about 1051.7 ±â€¯270.7 Gg of annual MSW generation from the current urban population. 289.3 Gg of coal-alternative solid fuel production was expected from domestic MSW collectable in urban areas. The model predicted that co-burning of alternative fuel in coal-fired power plants could reduce the methane potential of household waste from 62,200 to 15,800 Mg CH4 per year. Under the best possible scenario, it could reduce SOx emissions by 4.2%, CH4 emissions by 4.5%, CO2 emissions by 3.1%, and Global Warming Potential by 2.2%. On the other hand, NOx emissions would increase by 18%. If without additional installation of air pollutant control devices in power plants, waste-to-energy generates a trade-off between global warming and acid rain. In addition, geological locations generate a large demand/supply gap of alternative fuel and regulate maximum available consumption of alternative fuel.

Characterization and application of microalgae hydrochar as a low-cost adsorbent for Cu(II) ion removal from aqueous solutions.

Hydrochar prepared from the hydrothermal liquefaction of microalgae is characterized and investigated for copper removal from aqueous solution. Two hydrochars were prepared at 210 °C (HD210) and 250 °C (HD250). The effect of the initial solution pH, the initial Cu(II) concentration, the contact time, and the temperature will be investigated. According to the elemental analysis, the volatile matter in the hydrochars was lower and ash content was higher than those of microalgae. Also, pore characteristic analysis revealed that the surface area of the HD250 was higher than that of the HD210 suggesting a higher potential for the adsorption process. FTIR analysis and Boehm titration showed that both hydrochars contained oxygen-containing functional groups (OFG) on the surface which were effective for the copper removal. The adsorption experiments indicated that the amount of copper adsorbed reached a maximum value at the pH of 5 which was considered as the optimum solution pH. In addition, HD250 had a higher amount of copper adsorption than that of HD210 at all values of the solution pH. The adsorption data at the optimum solution pH was well fitted by the Langmuir's isotherm model and the adsorption process could be well described by the pseudo-2nd order kinetic model. Moreover, thermodynamic analysis revealed that copper adsorption onto the hydrochar was a physical endothermic process.

Rapid screening of inorganic and organic anions in liquid by-products from hydrothermal treatment of biomass by capillary electrophoresis.

A simple and rapid capillary electrophoresis method with capacitively coupled contactless conductivity detection (CE-C4 D) for the simultaneous determination of inorganic and organic anions in liquid product obtained from the hydrothermal treatment of biomass residues is presented. Under the optimal analytical conditions, limits of detection ranged from 1.8 to 9.4 µM for most target solutes and 53 µM for citrate. Relative standard deviations were below 0.5% for migration times and within 0.6-6.5% for peak areas for all solutes. The proposed method was successfully applied for the rapid determination and screening of inorganic and organic anions in liquid product produced following differing hydrothermal treatment temperatures for banana and pineapple biomass, and the contribution of organic acid formation to acidity in the liquid was evaluated. CE-C4 D could be a suitable method for the optimization or tailoring of HTT conditions for desired liquid product composition, and additionally for determination of the best variety(s) of biomass to use in such processes.

Co-gasification of bituminous coal and hydrochar derived from municipal solid waste: Reactivity and synergy.

In this work, the influences of gasification temperature and blended ratio on co-gasification reactivity and synergy of Shenfu bituminous coal (SF) and municipal solid waste-derived hydrochar (HTC) were investigated using TGA. Additionally, active alkaline and alkaline earth metal (AAEM) transformation during co-gasification was quantitatively analyzed by inductively coupled plasma optical emission spectrometer for correlating synergy on co-gasification reactivity. The results showed that higher char gasification reactivity existed at higher HTC char proportion and gasification temperature, and the main synergy behaviour on co-gasification reactivity was performed as synergistic effect. Enhanced synergistic effect at lower temperature was mainly resulted from more obviously inhibiting the primary AAEM (i.e. active Ca) transformation, and weak synergistic effect still existed at higher temperature since more active K with prominent catalysis was retained. Furthermore, more active HTC-derived AAEM remaining in SF sample during co-gasification would lead to enhanced synergistic effect as HTC char proportion increased.

Adenocarcinoma arising in multiple hyperplastic polyps in a patient with Helicobacter pylori infection and hypergastrinemia during long-term proton pump inhibitor therapy.

We report a case of developing multiple adenocarcinoma foci in multiple hyperplastic polyps in a patient with Helicobacter pylori infection and hypergastrinemia during long-term proton pump inhibitor (PPI) therapy. A 57-year-old man, who was undergoing hemodialysis for chronic renal failure, underwent an upper gastrointestinal endoscopy to elucidate the cause of anemia. Atrophic gastritis with H. pylori infection and multiple adenocarcinoma foci in multiple hyperplastic polyps were found in the endoscopic and histological examinations. Enterochromaffin-like micronests and parietal cell protrusion in the background of the polyps suggested the existence of hypergastrinemia. The serum gastrin level was markedly high-10,206 pg/ml (normal range 37-172 pg/ml). The cause of this marked hypergastrinemia was not autoimmune gastritis and gastrinoma. After discontinuing PPI therapy and successful eradication of H. pylori, the serum gastrin level decreased to normal range. These findings indicate that hypergastrinemia may be caused by long-term PPI therapy in patients with H. pylori infection. This case suggests that hypergastrinemia may mediate gastric carcinogenesis in patients with H. pylori infection.

Evaluation of hydrothermal treatment in enhancing rice straw compost stability and maturity.

In order to evaluate the hydrothermal treatment (HTT) in enhancing compost stability and maturity of lignocellulosic agricultural residues, a bin-scale (90 L) composting of rice straw with and without "HTT" was performed. The rice straw compost product with "HTT" after 6 weeks of composting can be considered stable and adequate for field application as expressed by pH of 8.4, "EC value" of 2.96 dS m(-1), C/N ratio of 12.5, microbial activity of <8.05 mg CO2 g(-1) OM d(-1), NH4(+)-N content of 93.75 mg kg(-1) DM and finally, by "GI" of >83%. However, compost may prove phytotoxic if used as growing media for EC sensitive plants. As for rice straw compost product without "HTT", the high microbial activity (>12.28 mg CO2 g(-1) OM d(-1)) even after 14 weeks of composting suggests that the residue has not stabilized yet and is far away from stability and maturity, although a higher GI (>100%) was observed.

Nitrogen evolution during the co-combustion of hydrothermally treated municipal solid waste and coal in a bubbling fluidized bed.

Nitrogen evolution was studied during the co-combustion of hydrothermally treated municipal solid wastes (HT MSW) and coal in a bubbling fluidized bed (BFB). HT MSW blending ratios as 10%, 20% and 30% (wt.%) were selected and tested at 700, 800, 900 °C. Emissions of NO and N2O from blends were measured and compared with the results of mono-combustion trials. Moreover, concentrations of precursors like NH3 and HCN were also quantified. The results are summarized as follows: NO emissions were predominant in all the cases, which rose with increasing temperature. The blending of HT MSW contributed to the NO reduction. N2O emissions decreased with temperature rising and the blending of HT MSW also presented positive effects. At 30% HT MSW addition, both NO and N2O emissions showed the lowest values (391.85 ppm and 55.33 ppm, respectively at 900 °C). For the precursors, more HCN was detected than NH3 and both played important roles on the gas side nitrogen evolution.

Absorptive removal of biomass tar using water and oily materials.

Water is the most common choice of absorption medium selected in many gasification systems. Because of poor solubility of tar in water, hydrophobic absorbents (diesel fuel, biodiesel fuel, vegetable oil, and engine oil) were studied on their absorption efficiency of biomass tar and compared with water. The results showed that only 31.8% of gravimetric tar was removed by the water scrubber, whereas the highest removal of gravimetric tar was obtained by a vegetable oil scrubber with a removal efficiency of 60.4%. When focusing on light PAH tar removal, the absorption efficiency can be ranked in the following order; diesel fuel>vegetable oil>biodiesel fuel>engine oil>water. On the other hand, an increase in gravimetric tar was observed for diesel fuel and biodiesel fuel scrubbers because of their easy evaporation. Therefore, the vegetable oil is recommended as the best absorbent to be used in gasification systems.

A simple expression for the apparent reaction rate of large wood char gasification with steam.

A simple expression for the apparent reaction rate of large wood char gasification with steam is proposed. Large char samples were gasified under steam atmosphere using a thermo-balance reactor. The apparent reaction rate was expressed as the product of the intrinsic rate and the effective factor. The effective factor was modified to include the effect of change in char diameter and intrinsic reaction rate during the reaction. Assuming uniform conversion ratio throughout a particle, the simplified reaction scheme was divided into three stages. In the initial stage, the local conversion ratio increases without particle shrinkage. In the middle stage, the particle shrinks following the shrinking core model without change in the local conversion ratio. In the final stage, the local conversion ratio increases without particle shrinkage. The validity of the modified effective value was confirmed by comparison with experimental results.

A comparison of co-combustion characteristics of coal with wood and hydrothermally treated municipal solid waste.

In this work, thermogravimetric analysis was used to investigate the co-combustion characteristics of wood and municipal solid waste (MSW) with Indian coal. Combustion characteristics like volatile release, ignition were studied. Wood presented an enhanced reaction rate reflecting its high volatile and low ash contents, while MSW enhanced ignition behavior of Indian coal. The results indicate that blending of both, wood and MSW improves devolatization properties of coal. Significant interaction was detected between wood and Indian coal, and reactivity of coal has improved upon blending with wood. On the other hand, MSW shows a good interaction with Indian coal leading to significant reduction in ignition temperature of coal and this effect was more pronounced with higher blending ratio of MSW. Hence MSW blending could more positively support the combustion of low quality Indian coal as compared to wood, due to its property of enhancement of ignition characteristics.

Effects of the reforming reagents and fuel species on tar reforming reaction.

In this study, using wood chips and polyethylene (PE) as fuels, the effects of air and/or steam as reagents on the tar reforming were clarified quantitatively with a simulated gasifier/reformer apparatus of a two-staged gasification process. The results show that when only steam or air was supplied into the reformer, the tar residual rate (defined as the ratio of the tar amount in the reformed gas to the tar amount in the pyrolysis gas) and the carbon particulate concentration in both reformed gases produced from pyrolysis gases of wood chips and PE decreased with the increase of the steam ratio (H(2)O/C, 0-1.0) or the air ratio (ER, 0-0.30). Supplying steam into the reformer to suppress carbon particulate formation for PE pyrolysis gas is more effective than for wood chips pyrolysis gas. Comparing with the results of steam only reforming, the effect of air supply on reduction of the tar residual rate was more significant, while that on suppression of carbon particulate formation was smaller.