Alum sludge as an efficient sorbent for hydrogen sulfide removal: Experimental, mechanisms and modeling studies

Construction of 3D network aluminum sludge-based hydrogel beads: combination of macroization, amino functionalization, and resource utilization

An aluminum sludge-based composite material was constructed against the problems of phosphorus pollution and the waste of aluminum sludge resources. Utilizing metal Ce doping and hydrogel microbeads with pore preparation, the adsorption performance of the original sludge was improved. Meanwhile, the macroscopic body was constructed, and on this basis, polyethyleneimine (PEI) was introduced to complete the amino functionalization further to enhance the adsorption of phosphorus by the adsorbent, and NH-CeAIS-10 microbeads were successfully prepared. In adsorption, microbeads with larger specific surface area and richer functional groups are better choice compared to original sludge. The results of SEM, BET, FT-IR, and XPS analyses indicate that the adsorption of phosphorus by the microbeads is mainly achieved through electrostatic interactions, ligand exchange, and the formation of inner-sphere complexes. According to the Langmuir model, the maximum phosphorus adsorption capacity of NH-CeAIS-10 was 29.56 mg g-1, which was four times higher compared to native aluminum sludge. This also confirms the significant enhancement of phosphorus adsorption through the modification of aluminum sludge. Besides, in dynamic adsorption column experiments, the material exhibited up to 99% removal in simulated wastewater for up to 30 days, demonstrating the great adsorption potential of NH-CeAIS-10 in engineering applications.

Regulation of ash slagging behavior of palm oil decanter cake by alum sludge addition

Combustion of palm oil decanter cake (PODC) is a propitious alternative waste to energy means. However, the mono-combustion of PODC prompt severe ash slagging behavior which give rise to reduction in heat transfer and also shorten the lifespan of combustion reactors. In this study, alum sludge (AS) was introduced at different proportion of 30%, 50% and 70% to revamp the slagging characteristics of PODC during combustion. The addition of AS improved ash fusion temperature of PODC during co-combustion as ash fusion temperature increased significantly under high AS dosage. Slagging and fouling indices showed that at 50% AS addition, slagging tendency of the co-combustion ashes can be ignored. The predictive model for PODC-AS combustion showed good correlation coefficient with 0.89. Overall, co-combustion of PODC and AS is an ideal ash related problem-solving route. The proposed PODC slagging preventive method by AS was based on: (1) limited amount of aluminum content in PODC-AS system resulted in development of refractory ash (2) reduction in proportion of basic oxide which act as ash bonding glue played important role in the regulation of slagging (3) reduction of cohesive bond by formation of spongy and porous structure which prevented ash slagging.

Development of microwave-assisted nitrogen-modified activated carbon for efficient biogas desulfurization: a practical approach

Removal of H₂S (hydrogen sulfide) from biogas is anticipated for higher energy conversion of methane (CH₄), while reducing the detrimental impacts of corroding the metal parts in the plant and its hazardous effect on humans and the environment. The introduction of microwave (MW) heating and nitrogen-modification could generate superior adsorbent features, contributing to high H₂S removal. Up to date, there is no work reported on the influence of physicochemical characteristics of nitrogen-modified carbon synthesized via MW and conventional heating (TH) methods and their performance in H₂S removal. Palm shell activated carbon (PSAC) was functionalized with nitrogen groups via urea impregnation, followed by the synthesis of MW and TH at 950 °C, 500 ml/min of N₂ flow rate and 30 min of heating time. MW and TH heating effects on the modified PSAC adsorbent were analysed and compared towards hydrogen sulfide (H₂S) removal. PSAC with nitrogen functionalization produced using MW heating (PSAC-MW) demonstrates superior performance, with an adsorption capacity of 356.94 mg/g. The adsorbent sample generated using MW heating exhibited notable properties, including a large surface area and a sponge-like structure, with new pores developed within the current pores. Instead of that, there was an observation of 'hot spot' appearance during the MW heating process, which is believed to be responsible for the development of physical and chemical characteristics of the adsorbent. Thus, it is believed that MW heating was assisted in the development of the adsorbent's properties and at the same time contributed to the high removal of H₂S at low adsorption temperature. The utilization of biomass-based adsorbent (PSAC) for H₂S removal can address the lignocellulosic waste disposal problem, while mitigating the H₂S release from the biogas production plants thus has several environmental merits. This indirectly contributed to zero-waste generation, while overcoming the adverse effects of H₂S.

Sewage sludge ash-derived materials for H2S removal from a landfill biogas

H₂S removal is a key step for biogas cleaning because this component can lead to premature corrosion of the equipment and its cleaning has a significant cost. The aim of the present work was to assess the use of sewage sludge derived ash (SSA)-materials for H₂S removal from a landfill biogas. SSA and mixtures made with SSA, activated carbon (AC) and sand were tested for H₂S removal. The best removal efficiency was obtained with the mixture 80%m SSA and 20%m AC, while SSA alone was not a good adsorbent under tested experimental conditions. The materials characterization helped the adsorption mechanism understanding. Indeed, results highlighted that SSA presence stabilizes the pH on a basic range, favorable for H₂S dissociation into HS^- then its chemisorption. On the other hand, with the microporosity of AC, the contact surface between H₂S and oxygen was sufficiently large for chemisorption kinetics. It also appeared that the mixture with sand and AC adorbs non selectively H₂S but also other volatile organic pollutants present in biogas. Contrariwise, with SSA/AC mixtures, H₂S seems to be selectively chemisorbed.

Iron-Based Water Treatment Residuals: Phase, Physicochemical Characterization, and Textural Properties

Groundwater treatment residuals (GWTRs) are safe waste materials generated during drinking water treatment. GWTRs are mainly deposited in landfills, but the preferred solution should be reused or utilized for some components. To ensure proper sludge management, it is important to provide quality, chemical composition, and texture characteristics of GWTRs. Therefore, in this study, we aimed to investigate and compare the features of GWTRs collected from four water treatment plants. GWTRs were characterized by X-ray diffraction (XRD); scanning electron microscopy (SEM) with energy dispersion spectroscopy (EDS); Fourier transform infrared spectroscopy (FTIR); thermogravimetric, differential thermogravimetric, and differential thermal analysis (TG, DTG, and DTA, respectively); X-ray fluorescence (XRF); inductively coupled plasma optical emission spectrometry (ICP-OEP); specific surface area (S_BET) measurement; and determination of the isoelectric point (pH_IEP). According to the results, GWTRs are poor crystalline materials that are predominantly composed of ferrihydrite with minor calcite and quartz admixture. They formed heterogeneously mixed particles with irregular shapes. They were mainly composed of iron oxides (32-55%), silica (4-28%), calcium oxide (4-17%), and manganese oxides (0.3-4.0%). They were found to be mesoporous with a large specific surface area. Due to their composition and texture characteristics, GWTRs demonstrate good adsorption properties toward different compounds such as heavy metals and metalloids.

Two-stage hybrid constructed wetland-microbial fuel cells for swine wastewater treatment and bioenergy generation

A newly emerged alum sludge-based hybrid constructed wetland-microbial fuel cells (CW-MFCs), i.e. vertical upflow CW coupled MFC as 1st stage and horizontal subsurface flow CW coupled MFC as 2nd stage (VFCW-MFC + HSSFCW-MFC), was firstly developed for swine wastewater treatment and electricity generation. Swine wastewater and multi-set air-cathodes were applied to investigate the pollutants removal behavior and the power production. Six-month trial suggested that the overall removal efficiency of SS, COD, NH₄⁺-N, NO₃^--N, TN, TP and PO₄^3--P was 76 ± 12.4, 72 ± 7.4, 59 ± 28.3, 69 ± 25.6, 47 ± 19.7, 85 ± 9.5 and 88 ± 8.7%, respectively. The two stages hybrid system (VFCW-MFC + HSSFCW-MFC) continuously generated electrical power with average voltages of 0.44 ± 0.09 and 0.34 ± 0.09 V, and power densities of 33.3 ± 13.81 and 9.0 ± 2.5 mW/m³ in 1st and 2nd stage, respectively. The average net energy recovery (NER) of 1st stage and 2nd stage is in turn 0.91 ± 0.16 and 2.76 ± 0.70 Wh/kg·COD. It indicates that the hybrid CW-MFCs has higher removal efficiency than single stage CW-MFC, while 1st stage plays the major role both in pollutants removal and power generation.

Application of Alum Sludge in Wastewater Treatment Processes: “Science” of Reuse and Reclamation Pathways

Alum sludge (AlS) refers to the inevitable by-product generated during the drinking water purification process, where Al-salt is used as a coagulant in the water industry. It has long been treated as “waste”, while landfill is its major final disposal destination. In fact, AlS is an underutilized material with huge potential for beneficial reuse as a raw material in various wastewater treatment processes. In the last two decades, intensive studies have been conducted worldwide to explore the “science” and practical application of AlS. This paper focuses on the recent developments in the use of AlS that show its strong potential for reuse in wastewater treatment processes. In particular, the review covers the key “science” of the nature and mechanisms of AlS, revealing why AlS has the potential to be a value-added material. In addition, the future focus of research towards the widespread application of AlS as a raw material/product in commercial markets is suggested, which expands the scope for AlS research and development.

Granulation of Drinking Water Treatment Residues: Recent Advances and Prospects

Beneficial reuse of drinking water treatment plant residues (WTRs) has been intensively studied worldwide in the last decades, but few engineering applications can be found. The majority of WTRs were directly reused in cake form (after dewatering), e.g., alum sludge cake as main substrate used in constructed wetlands (CWs), or oven dried and ground powdery form, e.g., sorbent for pollutant removal. However, WTRs reuse in such forms has several drawbacks, i.e., difficulty of recovering and easy clogging (in CWs), which result in limited WTRs engineering applications. Granulation or pelleting could widen and be a wiser WTRs reuse route and also seems to be a promising strategy to overcome the “application bottleneck” issues. In the literature, a number of trials of WTRs granulation have been reported since 2008, including sintering ceramsite, gel entrapment and newly emerged techniques. Hence, there is a need to overlook these studies and promote WTRs granulation for further development. To this end, this review firstly provides a piece of updated comprehensive information and critical analysis regarding WTRs granulation/pelleting technology. It aims to enhance WTRs granulation studies in the developing stage and thus enlarge WTRs engineering applications.