A pilot study on the removal of ammonia from aqueous solution using the integration of struvite synthesis and breakpoint chlorination

Herein, a pilot study on the removal of ammonia from surface water using the integration of struvite precipitation and breakpoint chlorination is reported. A two staged pilot plant with a capacity of 1000 liters (1 m3) per run (LPR) was utilized, of which Stage 1 comprised struvite precipitation and Stage 2 comprised breakpoint chlorination. Optimum conditions (i.e., Stage 1) for struvite precipitation were 110 mg/L of Mg and P dosage (concentration), 150 rpm of mixing speed, 60 minutes of contact time, and lastly, 120 minutes of sedimentation, while optimum condition for the breakpoint chlorination (i.e., Stage 2) were 30 minutes of mixing and an 8:1 Cl2-NH4+ weight ratio. The synergistic effects of this hybrid system proved to be effective, with Stage 1 increasing the pH from 6.8 to 10.1, reducing Mn (≥97.0%) and Fe (≥99.6%) concentrations steeply, and concomitantly deactivated E coli and TPC to ≥ 99% and ≥91%, respectively, while ammonia was reduced from 5.4 mg/L to 2.7 mg/L-N (51.8 %). In Stage 2, i.e., breakpoint chlorination, ammonia was reduced from 2.7 mg/L to 0.02 mg/L-N whilst fully depleting residual microorganisms. Finally, the OPEX amounted to $ 0.31/m3; however, there is a potential for cost savings (≈53.2%) by replacing Kh2PO4 with waste phosphoric acid. Lastly, the results from this techno-economic evaluation study showed great potential compared to similar technologies, making this approach a game-changer towards the prudent management of elevated levels of ammonia amongst other problematic contaminants

Photocatalytic activity of Gd2O2CO3·ZnO·CuO nanocomposite used for the degradation of phenanthrene

Multimetal oxides nanocomposite photocatalysts based on Gd2O2CO3·ZnO·CuO were prepared by a co-precipitation method and carefully characterized using a range of analytical techniques. More specifically, analysis by X-ray diffraction and electron microscopies confirmed the identity and quality of the as-synthesized powders. The photocatalytic degradation activities of these nanocomposites towards phenanthrene were then investigated by measuring the effects of catalyst dosage, irradiation time, and oxidant addition. In addition, the pseudo first-order kinetic model was used to determine the rate constant of the degradation reaction. Optimum dosages of 0.6, 0.6, and 0.4 gL−1 were recorded when using CuO, Cu–CuO/ZnO, and Gd2O2CO3·ZnO·CuO, respectively. In addition, the Gd2O2CO3·ZnO·CuO composite exhibited a higher removal efficiency than both Cu–CuO/ZnO and the pure CuO nanoparticles. Furthermore, the addition of oxidants influenced the removal of phenanthrene from solution. Finally, the photocatalytic degradation data followed pseudo first-order kinetics as defined by the Langmuir–Hinshelwood model, which allowed prediction of the faster degradation rate by the Gd2O2CO3·ZnO·CuO nanocomposite. The newly synthesized nanocomposite could therefore be considered for the removal of phenanthrene and related polycyclic aromatic hydrocarbons from contaminated wate

Mineralogy and Leaching Characteristics of Coal Ash from a Major Brazilian Power Plant

The feed coals, fly ashes and bottom ashes collected from seven different units in a major Brazilian PF power plant have been subjected to comprehensive mineralogical, geochemical, and petrographic studies, to investigate the links between feed coal and ash characteristics. Ashes from two of the units were collected while the coal was being co-fired with oil as part of the boiler start-up procedure, allowing the impact of oil co-firing on ash characteristics also to be evaluated. High proportions of unburnt carbon and high proportions of retained sulphur were found in the fly ashes produced during oil co-firing, probably reflecting less efficient combustion and associated lower combustion temperatures. Higher concentrations of a number of relatively volatile trace elements were also noted in these fly ashes, compared to the fly ashes collected from units under normal operating conditions. The fly ashes produced during oil co-firing gave rise to acid pH conditions in water-based leaching tests, in contrast to the alkaline pH associated with fly ashes produced during normal operations. This probably reflects higher SO3 contents relative to total CaO + MgO for the co-fired ash samples. Many trace elements that are typically mobilised as cations were also more abundant in leachates from the co-fired fly ashes. This is due, most likely, to the more acid pH conditions involved. Despite similar or even higher total concentrations, however, elements that are typically released from coal ash as oxy-anions were less mobile from the co-fired fly ashes than from the normally-fired fly ash materials

Environmental assessment and nano-mineralogical characterization of coal, overburden and sediment from Indian coal mining acid drainage

The deterioration of environmental conditions is the major contributory factor to poor health and quality of life that hinders sustainable development in any region. Coal mining is one of the major industries that contribute to the economy of a country but it also impacts the environment. The chemical parameters of the coal, overburden, soil and sediments along with the coal mine drainage (CMD) were investigated in order to understand the overall environmental impact from high sulphur coal mining at northeastern coalfield (India). It was found that the total sulphur content of the coal is noticeably high compared to the overburden (OB) and soil. The volatile matter of the coal is sufficiently high against the high ash content of the soil and overburden. The water samples have a High Electrical Conductivity (EC) and high Total Dissolve Solid (TDS). Lower values of pH, indicate the dissolution of minerals present in the coal as well as other minerals in the mine rejects/overburden. The chemical and nano-mineralogical composition of coal, soil and overburden samples was studied using a High Resolution-Transmission Electron Microscopy (HR-TEM), Energy Dispersive Spectroscopy (EDS), Selected-Area Diffraction (SAED), Field Emission-Scanning Electron Microscopy (FE-SEM)/EDS, X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Raman and Ion-Chromatographic analysis, and Mössbauer spectroscopy. From different geochemical analysis it has been found that the mine water sample from Ledo colliery has the lowest pH value of 3.30, Tirap colliery samples have the highest electrical conductivity value of 5.40 ms cm−1. Both Ledo and Tirap coals have total sulphur contents within the range 3–3.50%. The coal mine water from Tirap colliery (TW-15B) has high values of Mg2+ (450 ppm), and Br− (227.17 ppm). XRD analysis revealed the presence of minerals including quartz and hematite in the coals. Mineral analysis of coal mine overburden (OB) indicates the presence both of pyrite and marcasite which was also confirmed in XRD and Mossbauer spectral analysis. The presented data of the minerals and ultra/nano-particles present shows their ability to control the mobility of hazardous elements, suggesting possible use in environmental management technology, including restoration of the delicate Indian coal mine areas

Synthesis of eco-friendly ZnO-based heterophotocatalysts with enhanced properties under visible light in the degradation of organic pollutants

Abstract Heterogeneous photocatalysts have been widely used for the removal of various organic pollutants from wastewater. The main challenge so far resides in the sustainability of the process, with regard to the synthesis and the application under visible light. In this study the precipitated materials from the Moringa oleifera seed (MO), groundnut shells (GS) and apatite (A) agrowastes were functionalized with zinc oxide (ZnO) and silver (Ag) solution, to produce a novel bioheterophotocatalysts. Various analytical techniques such as scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDS), photoluminescence (PL) and X-ray diffraction (XRD) were used for the characterization of the novel photocatalysts. It was proven that agrowastes can also enhance the photocatalytic activity of a ZnO-based photocatalyst as pure metals. The combination of MO/GS/A/ZnO/Ag in a 1:1:1 ratio resulted in a lower band gap of 1.59 eV, as compared to the band gap of 2.96 eV for ZnO/Ag. These photocatalysts' efficiency was also tested on the photodegradation of polycyclic aromatic hydrocarbon (PAHs) derived from coal leaching in various water sources such as acidic mine drainage, alkaline mine drainage and sewage wastewater. From MO/GS/A/ZnO/Ag, the removal efficiency was found to be 69.59%, 61.07% and 61.68%, compared to 52.62%, 37.96 and 44.30% using ZnO/Ag in acidic mine drainage, alkaline mine drainage and sewage wastewater for 60 min under solar irradiation

An understanding of lump coal physical property behaviour (density and particle size effects) impacting on a commercial-scale Sasol-Lurgi FBDB gasifier

Thermal processes which utilize coarse coal, such as fixed-bed gasification and chain grate stoker boilers, are dependant on a stable particle size for stable operation. During coarse coal utilization, thermal fragmentation of lump coal (upon heating) produces hydrodynamic effects (pressure drop fluctuations) manifesting itself in a variety of ways, and include: channel-burning and solids elutriation. Primary thermal fragmentation occurring in the drying zone of a fixed-bed reactor is primarily a function of moisture content release with ensuing particle size reduction. Large particles tend to fragment more than finer particles, thus leading to hydrodynamic problems. From fragmentation studies it was elucidated that a thermal “stable size” is reached through the process of thermal fragmentation for optimum heat transfer and utilization during the drying and pyrolysis zone regions of the coarse coal utilization process. In this paper, the Sasol-Lurgi MK IV FBDB gasifier turn-out physical property profiles (bulk density and particle size distribution) results will be discussed. It was found that these profiles provided significant insight into the complex heterogeneous nature of the coal transformation processes occurring within the fixed-bed reactor. In the case of the bulk density profile, a shrinking core and flaking mechanism was proposed to explain the increase in density occurring in the bottom half of the gasifier. The +25 mm size fraction distribution profile was found to clearly show the fragmentation effects occurring within the reactor. Primary fragmentation was inferred as the mechanism responsible for causing breakage of this size fraction down to a remaining ca. 15% +25 mm fraction. The significant breakage of the coarse +25 mm fraction is expected to influence unstable gasifier conditions in the top part of the gasifier, due to pressure drop fluctuations caused by void packing. A good correlation was obtained for the relationship between bulk density versus the −25 mm + 6.3 mm size fraction content, indicating that the bed-packing density is highly dependent on the relative abundance of this intermediate size fraction. The −6.3 mm size fraction distribution profile was found to not be significantly different between the four reaction zones identified in the gasifier. Breakage of the coarser +6.3 mm sizes occurred continuously, and could possibly be related to breakage caused by the ash-grate when sampling. The Ergun Index was successfully used to profile the fragmentation zones identified and to show areas within the gasifier where pressure drop and resultant instability occurs. This is the first-ever identification of this phenomenon occurring within a fixed-bed gasifier and is expected to lead to significant optimization challenges to ensure better stabilit

Reduction of salinity of water using acrylamide-based polyampholyte

Polyampholytes are charged macromolecules, which carry both acidic and basic groups. These groups dissociate, leaving ions on chains and counter ions in solution, under appropriate conditions, such as in aqueous solutions. After ionization occurs, there are positively and negatively charged groups on the polymer chain. Polyampholytes are able to absorb high dosages of anions and cations adequately and would ultimately be the best alternative for the reduction of salinity in water. In this study polyampholites with different ratio of cationic groups were synthesized and tested for the removal of sulphate from solution. High cationic Polyampholytes showed great sulphate absorption capacities and could remove 100% of sulphate content. These Polyampholytes are able to function on a relatively low dosage and over a short period of time. Polyampholytes may be a good solution towards the implementation of desalination plant