Search

This paper introduces the D* Hindsight Deep Q-learning (DH-DQN) algorithm, which combines the D* algorithm and is applied to the port AGV path planning problem. To address the drawbacks of long decision times and large storage space of the D* algorithm, this paper proposes an improved DQN algorithm for a single AGV path planning problem. The Hindsight experience replay algorithm is used to alleviate the problem of slow or non-convergence due to sparse reward space. By selecting the actions planned by the D* algorithm with a certain probability, the DH-DQN algorithm's convergence speed and stability are improved, and its decision time is shorter than the classical D* algorithm. The DH-DQN algorithm is used to control an AGV to perform different tasks in different layouts. Experimental results show that the DH-DQN algorithm not only avoids non-convergence in four different layouts but also converges faster than the classical DQN algorithm. Furthermore, the DH-DQN and DQN algorithms' decision-making process's time comparison under the four layouts reveals that DH-DQN saves 24.91\% of the time in the large-scale environment and 28.08\% in the small-scale environment. Therefore, the DH-DQN algorithm performs well in solving the port AGV path planning problem.

Petrochemical wastewater and produced water from oil and gas operations typically contain an array of organic and inorganic contaminants. The complexity of the wastewater, stringent environmental regulations, and the need for sustainable solutions have driven many research efforts in studying and developing advanced technology or combined treatment processes. On the other hand, the wastewater itself can be resources for water, energy, and other valuable product if appropriate technology is developed to recover them in a cost-effective fashion. The research advances in wastewater treatment and resource recovery technology are reviewed and summarized. For petrochemical wastewater, progresses were made in advanced oxidation, biological processes, and recovery of energy and water from wastewater. For produced water, many efforts were focused on membrane processes, combined systems, and biological treatment. PRACTITIONER POINTS: Significant progress continued to be made on petrochemical wastewater and produced water treatment. Recent technological advances in various treatment processes were summarized. Technologies focusing on resource recovery (e.g., water or energy) were presented.

Drainage from current and historic mining operations remains a persistent environmental problem. Numerous research and development efforts were made in 2019 with a goal to minimize the impact of mine drainage on the environment, while other research endeavors addressed the mine drainage issue from a different perspective, where mine drainage was considered a resource for water and valuable products, such as metals, sulfuric acid, and rare earth elements. Thus, this review has two main sections: (a) focusing on research efforts in mine drainage remediation technology, and (b) emphasizing advances in resource recovery from mine drainage. The first section covers traditional and emerging passive and active treatment technologies. The second section summarizes resource recovery efforts using various technologies, such as selective precipitation, membrane process, and biological systems. PRACTITIONER POINTS: Significant progress continued to be made in the management of mine drainage and related issues. Recent remediation technology advances in mine drainage were presented. Technologies focusing on resource recovery from mine drainage were reviewed.

The effect of treatment temperature on hydrochars properties using P and N enriched agricultural and antibiotic residues as feedstocks via microwave-assisted hydrothermal conversion (MW-HTC) was in...

Wastewater in petrochemical processes and produced water from oil and gas production remain a challenge for the industry to minimize their impact on the environment. Recent research and development of treatment technologies for petrochemical wastewater and produced water from oil and gas industries published in 2018 were summarized in this annual review. Great efforts and progresses were made in various treatment options, including membrane processes, advanced oxidation, biological systems, adsorption, coagulation, and combined processes. PRACTITIONER POINTS: Treatment technologies for petrochemical wastewater are reviewed. Research development in produced water from oil and gas industries is summarized. Reviewed technologies include traditional, advanced, and innovative processes.

Soybean (SB) solid residue after oil extraction was investigated in a hydrothermal modification process to provide an eco-friendly solution to SB solid waste disposal for an actual environmental management effort. SB hydrochars (HCs) were derived either by conventional heating hydrothermal treatment (HTT) under intense conditions (200, 250, and 300 °C for 2 h) or by microwave-assisted hydrothermal treatment (MHTT) under mild conditions (160, 190, and 220 °C for 1 h). Physicochemical properties of SB HCs and the transformation of nitrogen (N) and phosphorus (P) functionalities during HTT and MHTT were characterized using several tools. Ultimate and XPS analyses elucidated N transformation, e.g., 5.51 wt % N of raw SB residue decreased to 3.48 and 3.51 wt % after HTT and MHTT, respectively. The P bioavailability of raw SB (3.46 mg/g) was improved after HTT (26.7 mg/g) and MHTT (10.9 mg/g), depicting the practical application of HCs for soil amendment. Atomic H/C and O/C ratios of SB HCs decreased as treatment temperature increased. HCs showed credible higher heating value (HHV; 22.3–25.5 MJ/kg for HTT and 20.5–22.1 MJ/kg for MHTT), higher than various low-rank coals. Besides, energy densification and fuel ratio improved in intense conditions. The thermogravimetric analysis showed HCs possessed better thermal stability. The improved performance of SB HCs indicated that HTT and MHTT provided a green environmental route of SB waste management, valorization, and utilization.

Recycling of antibiotic mycelial fermentation residue (AR), a hazardous waste material, into high-performance heavy metal remediation material is an emerging research hotspot. The inorganic composition of biomaterials represents their capacity to immobilize heavy metals. In this study, to improve the Pb immobilization capacity, lincomycin mycelial fermentation residue (LR, a type of AR) was pyrolyzed in CO2 or N2 gas under different temperatures to adjust the carbon and phosphorus composition of its biochar. Results indicate that both activation temperature and gas type can significantly influence the transformation of LR carbon and phosphorus-containing groups. At high temperatures, the activation gas significantly controlled changes in carbonate and available phosphorus; however, this process was less successful at low temperatures. CO2 gas clearly inhibited the degradation of carbonate, but promoted consumption of the carbon matrix and released organism-combined phosphorus. Results suggest that CO2-activated biochar at 700 °C exhibited the strongest Pb immobilization capacity of 454 mg/g in aqueous solution and the highest Pb immobilization rate of 60% in soil, due to its more sites (carbonate and available phosphorus) for Pb stabilization. This study provides an effective method for transforming waste AR into a high-performance material for metal stabilization.

Nano-MgO carbon composites (MCs) demonstrated great potential in phosphate immobilization to resolve phosphorus reuse and eutrophication problems, but the mechanisms of phosphate immobilization are still unclear. In this study, MCs were fabricated via CO2 activation of hydrochar materials, and the activation mechanisms were first investigated through analysis of pyrolysis gases and porosity. The results indicate that MgO particles (pyrolysis products of MgCl2) catalyzed the consumption of the carbon matrix but blocked the development of carbon matrix pores. Furthermore, phosphate immobilization by MCs increased with the increase of MgO loading content. More importantly, XPS and TEM-EDX profiles demonstrate that solution and surface precipitations regulated phosphate immobilization by MCs. Solution precipitation mainly contributed to a MgHPO4 precipitate, while in surface precipitation the carbon matrix served as a bridge for H2PO4− transmission to MgO particles to produce a Mg(H2PO4)2 precipitate. Also, with the decrease of carbon content, surface precipitation became dominant due to the shortened distance. This contributes to the improvement of phosphate immobilization by MCs, which was found to be even higher than pure MgO. Compared with N2 activated MC, CO2 activated MC showed much higher phosphate immobilization potential attributed to the surface precipitation reaction. The results of this study will guide the development of more efficient MC materials for phosphate recovery.

The beneficial utilization of biomass wastes and residues for environmental remediation is the focus of many research efforts towards environmental sustainability. In this study, agricultural residue (soybean, (SB)) and a biopolymer (chitosan, (CS)) were examined for enhanced heavy metals (HMs) removal. Specifically, SB, CS, and mixtures of SB and CS at different mass ratios (SB:CS) were treated to obtain hydrochars (HCs) via microwave-assisted hydrothermal treatment (Mw-HTT). Synthesized HCs were subsequently characterized by elemental analysis (EA), SEM/EDX, XRD, FT-IR, XPS, and sequential extraction to estimate nitrogen (N) and phosphorus (P) transformation during Mw-HTT. The N remained same in CS HCs and decreased in SB HCs based on EA results, and sequential extraction indicated that P decreased after Mw-HTT in SB and CS HCs. Lead (Pb(II)) adsorption was carried out using as-synthesized HCs, and experimental results were examined using standard adsorption isotherm and kinetic models. The R2 value (≥ 0.960) with acceptable n and Kf confirmed that Freundlich isotherm was suitable. For adsorption kinetics, pseudo-2nd-order model showed R2 ≥0.94 and good agreement between calculated and actual adsorption capacities, providing insights into adsorption mechanisms for CS, SB, and SB:CS HCs. It was found that N and P transformed during Mw-HTT, which played a role in Pb(II) removal from solutions.

Suspension roasting followed by magnetic separation is a promising method to upgrade oolitic hematite ore. An oolitic hematite ore was roasted using suspension roasting technology at different temperatures. The phase transformation for iron minerals was investigated by XRD and Mossbauer spectrum, and the characteristics of roasted product were analyzed by VSM and SEM-EDS. Results indicate that the magnetic concentrate is of 58.73% Fe with iron recovery of 83.96% at 650 °C. The hematite is rapidly transformed into magnetite during the roasting with transformation ratio of 92.75% at 650 °C. Roasting temperature has a significant influence on the phase transformation of hematite to magnetite. The transformation ratio increases with increased temperature. After roasting, the magnetic susceptibility is significantly improved, while iron ore microstructure is not altered significantly.

The recent research and development on mine drainage published in 2017 was summarized in this review. In particular, this review was focused on three main aspects: 1) mine drainage and its environmental impact, 2) prediction and prevention, and 3) treatment technologies. The first section covers physiochemical characterization, microbiological characterization, and environmental impacts. The second section includes mine drainage prediction and prevention. The final section focuses physiochemical treatment, biological treatment, passive treatment, and beneficial uses of mine drainage and treatment wastes.

Petrochemical and oil & gas industries are crucial for global economy while great attention is needed for the related contamination and its impact on the environment. Papers reviewed herein represent the recent research and development on petrochemical wastewater and produced water from oil & gas industry, published in 2017 and beginning of 2018 globally. In the petrochemical wastewater, progresses were made in characterization, physicochemical treatment and biological treatment. In the oil & gas produced water, efforts were made on the characterization, the environmental impact and treatment options.

Oolitic iron ore is a refractory mineral resource of great importance due to its vast abundance in light of the dwindling supply of high quality iron ores globally. In this study, an oolitic iron ore was isothermally reduced by coal at 1423 K–1573 K, and the reduction kinetics and mechanisms were investigated using the thermogravimetry (TG) technique. The characteristics of reduced samples were analyzed by scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and X-ray diffraction (XRD). It was found that the reduction temperature and C/O molar ratio had significant influence on the degree of iron oxide reduction and its reduction rate, and the coal-based reduction could be divided into the initial, middle, and final stages. The reaction kinetic models were proposed to represent the reduction of oolitic iron ore using coal. The hematite in the ore was reduced to metallic iron in the sequence of Fe2O3 → Fe3O4 → FeO (FeAl2O4, Fe2SiO4) → Fe. The mechanisms of reduction changed with reduction time. As reduction progressed, the oolitic structure was gradually destroyed, and the metallic iron aggregated concurrently. The rate controlling mechanisms during oolitic iron ore reduction were a combination of interfacial chemical reaction and solid state diffusion.

Mine drainage from the mining of mineral resources (coal, metals, oil sand, or industrial minerals) remains as a persistent environmental problem. This review summarizes the scientific literature published in 2014 on the technical issues related to mine drainage or mine water in active and abandoned coal/hard rock mining sites or waste spoil piles. Also included in this review is the water from oil sand operations. This review is divided into the four sections: 1) mine drainage characterization, 2) prediction and environmental impact, 3) treatment technologies, 4) oil sand water. Many papers presented in this review address more than one aspect and different sections should not be regarded as being mutuallyexclusive or all-inclusive.

Mixtures of oolitic iron ore and coal with different C/O molar ratios (1.5, 2.0, 2.5, and 3.0) were heated from 600 to 1300 °C at four heating rates (5, 10, 15, and 20 °C min−1). The degree of reduction and reduction rate were calculated from the measurements of weight loss and off-gas composition using thermogravimetry technique and NDIR gas analyzer. The kinetic parameters (the activation energy, pre-exponential factor, and reduction model) were determined by Ozawa–Flynn–Wall kinetic method and by Satava–Sestak method. It was found that, as temperature increased, the degree of reduction increased, while the reduction rate rapidly increased first, subsequently stabilized, and then decreased. The non-isothermal reduction of oolitic iron ore with coal was significantly influenced by both heating rate and C/O molar ratio, although the impact of the latter was much less. The values of activation energy estimated by Ozawa–Flynn–Wall method ranged from 159.2 to 169.6 kJ mol−1. The mechanism function for the non-isothermal coal-based reduction of oolitic iron ore was D5 reaction model. The non-isothermal kinetic models for coal-based reduction of oolitic iron ore were proposed based on the obtained kinetic parameters. The iron oxide in the oolitic ore was reduced to metallic iron in the sequence of Fe2O3 → Fe3O4 → FeO (FeAl2O4, Fe2SiO4) → Fe. Phase change and reduction mechanism shift were observed during the reduction.

This review summarizes the recent research and development pertaining to the topic of mine drainage which were published in 2016 and early 2017. The review includes three main sections: Mine Drainage and its Environmental Impact, Prediction and Prevention, and Treatment Technologies. The first section covers the characterization of mine drainage and its related environmental impacts, including three subsections focused on physiochemical characterization, microbiological characterization, and environmental impacts. The second section of the review is divided into two subsections focused on either the prediction or prevention of acid mine drainage. The final section focuses on treatment technologies for mine drainage, including physiochemical treatment, biological treatment, passive treatment, and beneficial uses of mine drainage and treatment wastes.

This review provides a snapshot of papers published in 2015 relevant to the topic of mine drainage generation and control options. The review is broken into 3 sections: Generation, Prediction and Prevention, and Treatment Options. The first section, mine drainage generation, focuses on the characterization of mine drainage and the environmental impacts. As such, it is broken into three subsections focused on microbiological characterization, physiochemical characterization, and environmental impacts. The second section of the review is divided into two subsections focused on either the prediction or prevention of acid mine drainage. The final section focuses on treatment options for mine drainage and waste sludge. The third section contains subsections on passive treatment, biological treatment, physiochemical treatment, and a new subsection on beneficial uses for mine drainage and treatment wastes.