Preparation of ceramsite from municipal sludge and its application in water treatment: A review

Sustainable water treatment ceramsite derived from dredged sludge and biomass waste for neutralizing acidic mining wastewater: Mechanisms and efficiency

Porous ceramsite, a typical water treatment material, could be potentially applied for treating acidic mining wastewater (AMW) with alkaline sources. This study aims to evaluate the treatment efficiency and mechanisms of water treatment ceramsite (WTC) derived from dredged sludge, biomass waste, and alkaline sources for neutralizing AMW. WTC with 8% CaCO3 was found to effectively increase the pH of AMW to 7 within 60 min, demonstrating its potential for AMW treatment. Mineralogical analysis revealed that the calcium-rich WTC primarily consisted of quartz, feldspar, and lime, with the decomposition of biomass waste during sintering creating a connecting pore structure that enhanced water treatment efficiency. At high temperatures, CaCO3 decomposed into CaO, the primary alkaline substance responsible for neutralizing AMW. However, excessively high sintering temperatures resulted in increased glassy and feldspar phases, which reduced the reactivity of the ceramsite. This study provides an innovative approach to AMW treatment by transforming solid waste into functional materials, offering a sustainable solution for environmental remediation. The results underscore the potential of WTC as a cost-effective and eco-friendly alternative for mitigating the environmental impacts of mining activities.

Study on the preparation mechanism and dephosphorization effect of SW-ceramsite

To address environmental challenges such as eutrophication caused by excessive phosphorus discharge and low resource utilization of solid waste, this study investigates the factors influencing the physical properties of ceramsite from solid waste (SW-ceramsite) through sintering method, and its adsorption performance. The results shown that under the optimal conditions of additive dosage 9 g/100 g mixture, sintering temperature 1100 °C, heating rate 10 °C/min, and holding time 5 min, the values of breaking and wear rates and void fraction were 0.35% and 69.6%, respectively. Grey relation analysis indicated that the additive dosage was the most influential factor, followed by sintering temperature and heating rate, with holding time being the least impact. The equilibrium adsorption capacity (qe) of SW-ceramsite for phosphorus was 1.85 mg/g. The adsorption process was better described by the Freundlich adsorption isotherm, as well as by the pseudo-first-order and pseudo-second-order kinetic models, and was characterized as non-spontaneous and exothermic. After nine regeneration cycles, The qe of SW-ceramsite decreased by only 0.185 mg/g, with a regeneration loss rate was just 4.988%, suggesting good reusability. The findings suggest that the SW-ceramsite holds promise for treatment of phosphorus-containing wastewater.

Enhanced anaerobic digestion of waste activated sludge using magnetite-modified sludge ceramsite: Performance and microbial dynamics

The effect of magnetite-modified sludge ceramsite on anaerobic digestion of sludge was systematically investigated in this study. The results revealed that the addition of magnetite significantly altered the properties of the ceramsite, while magnetite-modified ceramsite significantly altered the sludge anaerobic digestion process. Biochemical methane production potential experiments demonstrated that the cumulative methane production of the experimental group with moderate ceramsite addition was enhanced by 17.8% compared to the control group without ceramsite. This enhancement was attributed primarily to the favorable pore structure and biocompatibility of the modified ceramsite. The incorporation of magnetite facilitated the enrichment of microorganisms and the reduction of Fe(III), thereby promoting anaerobic digestion. Moreover, the ceramsite exhibited strong buffering capacity, contributing to the enhanced stability of the digestive system. Microbiological analyses revealed that the addition of ceramsite significantly altered the microbial community. Appropriate ceramsite addition resulted in the enrichment of bacteria associated with organic matter degradation and methanogenesis. Furthermore, potential iron-reducing bacteria (Clostridium_sensu_stricto) and bacteria capable of direct interspecies electron transfer (Syntrophomonas) were also enriched in the anaerobic system. This study demonstrates a viable approach for the efficient resource utilization of sludge.

Preparation of high-strength ceramsite from coal gangue, fly ash, and steel slag

Coal gangue (CG) and fly ash (FA) are generated in large quantities worldwide. In this study, high-strength and lightweight aggregate ceramsites were prepared from CG, FA, and steel slag (SS) without any additional chemical additives through high-temperature sintering. The study aimed at determine the sintering mechanism and optimal production process by evaluating the performance of ceramsites produced under various conditions. The results indicated that the ratio of CG, FA, and SS significantly influenced the ceramsites' properties. When the ratio of CG, FA, and SS was 3 : 1 : 1 and the sintering temperature was 1200 °C, the ceramsites demonstrated optimal performance. These ceramsites had a bulk density of 947 kg m-3, an apparent density of 1859 kg m-3, a high compressive strength of 21.17 MPa, and a 1 hour water absorption of 1.35%. The high-strength and lightweight aggregate ceramsites produced from CG, FA, and SS hold promise as construction materials, particularly due to the benefits of waste recycling. This study highlights the potential of utilizing these ceramsites as sustainable alternatives in various construction applications.

Near-Complete Phosphorus Recovery from Challenging Water Matrices Using Multiuse Ceramsite Made from Water Treatment Residual (WTR)

Water treatment residual (WTR) is a burden for many water treatment plants due to the large volumes and associated management costs. In this study, we transform aluminum-salt WTR (Al-WTR) into ceramsite (ASC) to recover phosphate from challenging waters. ASC showed remarkably higher specific surface area (SSA, 70.53 m2/g) and phosphate adsorption capacity (calculated 47.2 mg P/g) compared to previously reported ceramsite materials (< 40 m2/g SSA and < 20 mg P/g). ASC recovered over 94.9% of phosphate across a wide pH range (3 - 11) and generally sustained > 90% of its phosphate recovery at high concentrations of competing anions (i.e., Cl-, F-, SO4 2-, or HCO3 -) or humic acid (HA). We challenged the material with real municipal wastewater at 10°C and achieved simultaneous phosphate (>97.1%) and COD removal (71.2%). Once saturated with phosphate, ASC can be repurposed for landscaping or soil amendment. The economic analysis indicates that ASC can be a competitive alternative to natural clay-based ceramsite, biochar, or other useful materials. Therefore, ASC is an eco-friendly, cost-effective adsorbent for phosphate recovery from complex waters, shedding light upon a circular economy in the water sector.

Electrocatalytic denitrification biofilter for advanced purification of chlorophenols via ceramsite-based Ti/SnO2-Sb particle electrode: Performance, microbial community structure and mechanism

In response to the demand for advanced purification of industrial secondary effluent, a new method has been developed for treating chlorophenol wastewater using the novel ceramsite-based Ti/SnO2-Sb particle electrodes (Ti/SnO2-Sb/CB) enhanced electrocatalytic denitrification biofilter (EDNBF-P) to achieve removal of chlorophenols (CPs), denitrification, and reduction of effluent toxicity. The results showed that significantly improved CPs and TN removal efficiency at low COD/N compared to conventional denitrification biofilter, with CPs removal rates increasing by 0.33%-59.27% and TN removal rates increasing by 12.53%-38.92%. Under the conditions of HRT = 2h, 3V voltage, charging times = 12h, and 25 °C, the concentrations of the CPs in the effluent of EDNBF-P were all below 1 mg/L, the TN concentration was below 15 mg/L, while the effluent toxicity reached the low toxicity level. Additionally, the Ti/SnO2-Sb/CB particle electrodes effectively alleviated the accumulation of NO2--N caused by applied voltage. The Silanimonas, Pseudomonas and Rhodobacter was identified as the core microorganism for denitrification and toxicity reduction. This study validated that EDNBF-P could achieve synergistic treatment of CPs and TN through electrocatalysis and microbial degradation, providing a methodological support for achieving advanced purification of chlorophenol wastewater with low COD/N in industrial applications.

High efficiency of drinking water treatment residual-based sintered ceramsite in biofilter for domestic wastewater treatment

Aluminum (Al)-based drinking water treatment residue (DWTR) has often been attempted to be recycled as dominant ingredient to produce sintered ceramsite for water treatment. This study aimed to determine the long-term performance of DWTR-based ceramsite in treating domestic wastewater based on a 385-d biofilter test and by using physicochemical, metagenomic, and metatranscriptomic analyses. The results showed that the ceramsite-packed biofilter exhibited high and stable capability in removing phosphorus (P) and chemical oxygen demand (COD), with removal efficiencies of 92.6 ± 3.97% and 81.1 ± 14.0% for total P and COD, respectively; moreover, 88-100% of ammonium-nitrogen (N) was normally converted, and the total N removal efficiency reached 80-86% under proper aeration. Further analysis suggested that the forms of the removed P in the ceramsite were mainly NH4F- and NaOH-extractable. Microbial communities in the ceramsite biofilter exhibited relatively high activity. Typically, various organic matter degradation-related genes (e.g., hemicellulose and starch degradations) were enriched, and a complete N-cycling pathway was established, which is beneficial for enriching microbes involved in ammonium-N conversion, especially Candidatus Brocadia, Candidatus Jettenia, Nitrosomonas, and Nitrospira. In addition, the structures of the ceramsite had high stability (e.g., compressive strength and major compositions). The ceramsites showed limited metal and metalloid pollution risks and even accumulated copper from the wastewater. These results demonstrate the high feasibility of applying ceramsite prepared from Al-based DWTR for water treatment.

Effectiveness of a novel composite filler to enhance phosphorus removal in constructed wetlands

Improving the adsorption performance of wetland fillers is of great significance for enhancing pollutant removal in constructed wetlands. Currently, limited by complex preparation processes and high costs, large numbers of high adsorption fillers studied in lab are difficult to be applied in practical engineering. In this study, a newly low-cost and efficient phosphorus removal composite wetland filler (CFB) is prepared by using industrial and agriculture waste (steel slag and oyster shells) and natural ore (volcanic rock) as raw materials. The results show that phosphorus removal efficiency was largely enhanced by synergistic effects of steel slag, oyster shells, and volcanic rock, and it was mainly influenced by the proportion of each component of CFB. Based on the fitting of the classical isothermal equation, the adsorption capacity of CFB is 18.339 mg/g. The adsorption of phosphorus by CFB is endothermic and spontaneous, and there are heterogeneous surfaces and multi-layer adsorption processes, as well as pH value and temperature, are free from the influence on CFB phosphorus removal. During the practical wastewater application experiments, the phosphorus removal rate of the CFB-filled constructed wetland apparatus (CW-A) can reach 94.89% and is free from the influence on the removal of other pollutants (COD, TN, and NH3-N) by the system. Overall, the prepared CFB is of excellent decontamination effect, an extremely simple preparation process, low cost, and sound practical engineering application potential, providing new ideas and approaches for enhancing the phosphorus removal capacity and waste resource utilization of constructed wetland systems.

Adsorption of Phosphate by Two-Step Synthesis of Ceramsite from Electrolytic Manganese Residue/Dredged Sludge

Carrying out research on the management of electrolytic manganese residue (EMR) is necessary to maintain the environment and human health. The dredged sludge (DS) and water hyacinth (WH) generated from dredging projects are potential environmental threats, and therefore suitable methods need to be found for their treatment. In this study, ceramsite was prepared by a two-step low-temperature firing method using DS and EMR as raw materials, WH as a pore-forming additive, and aluminate cement as a binder for the adsorption of phosphorus from wastewater. The optimal ratio and process parameters of the ceramsite were determined by mechanical and adsorption properties. The static adsorption experiments were conducted to study the effect of ceramsite dosage and solution pH on the removal of phosphorus. At the same time, dynamic adsorption experiments were designed to consider the influence of flow rate on its actual absorption effect, to explore the actual effect of ceramsite in wastewater treatment, and to derive a dynamic adsorption model that can provide technical support and theoretical guidance for environmental management.

Preparation of ceramsite using solid residue from anaerobic digestion of waste activated sludge and its enhancing effect on catalytic ozonation

Anaerobic digestion is an environmentally friendly method for reclaiming waste activated sludge. However, it cannot be overlooked that the solid residue generated from this process can still pose environmental risks and impose economic pressure on society. To mitigate and recycle the solid residue, this study utilized it as a primary raw material for manufacturing ceramsite with potential applications in wastewater treatment. The optimal ratio of solid residue to fly ash was demonstrated to be 6:4 with an additional 15% of clay supplementing the raw ceramsite materials. Furthermore, the optimal sintering process was established as preheating at 300 °C for 25 min followed by sintering at 1085 °C for 10 min, as determined through an L16 (44) Orthogonal test. The prepared ceramsite demonstrated advantageous performance parameters that exceeded the standards outlined in the Chinese industry standard CJ/T 299-2008 for water treatment artificial ceramsite. When utilized in an ozonation system, the ceramsite exhibited remarkable catalytic activity for phenol degradation by promoting the decomposition of molecular O3 into hydroxyl radicals. Additionally, it displayed minimal leaching of heavy metals and lower application costs. These findings emphasize its attractiveness in water and wastewater treatment processes and present a practical strategy for reclaiming this solid residue.

Enhanced biomethane production from waste activated sludge anaerobic digestion by ceramsite and amended Fe2O3 ceramsite

Wastes recycling and reutilization technique could simultaneously fulfill waste control and energy recovery sustainably, which has attracted increasing attention. This work proposed a novel waste reuse technology utilizing ceramsite and amended Fe2O3-ceramsite made from waste activated sludge (WAS) as additives to promote the yield of methane from WAS anaerobic digestion (AD). Experimental results demonstrated that compared to the control (85.05 ± 0.2 mL CH4/g-VS), the cumulative methane yield was effectively enhanced by 14% and 40% when ceramsite and Fe2O3-ceramsite were added. Further investigation revealed that ceramsite, especially the Fe2O3-ceramsite, enriched the populations of key anaerobes involved in hydrolysis, acidification, and methanogenesis. Meanwhile, potential syntrophic metabolisms between syntrophic bacteria and methanogens were confirmed in the Fe2O3-ceramsite AD system. Mechanisms studies exhibited that ceramsite and Fe2O3-ceramsite reinforced intermediate processes for methane production. The favorable pore structure, enhanced Fe (III) reduction capacity and conductivity also contributed a lot to the AD process.

Co-utilization of iron ore tailings and coal fly ash for porous ceramsite preparation: Optimization, mechanism, and assessment

Maximizing the utilization of industrial by-products, such as iron ore tailings (IOTs) and coal fly ash (CFA), is crucial toward sustainable development. This study provides a meticulous insight into the optimization, mechanism, and assessment of the co-utilization of IOTs and CFA for the preparation of porous ceramsite. Micro-CT results revealed that the prepared ceramsite exhibited an exceptional porosity, peaking at 56.98%, with a wide range of pore diameters (3.55-959.10 μm) under optimal conditions (IOTs content at 76%, preheating at 550 °C for 15 min, and sintering at 1177 °C for 14 min), while maintaining good mechanical properties (water adsorption of 1.28%, comprehensive strength of 8.75 MPa, apparent density of 1.37 g/cm3, and bulk density of 0.62 g/cm3). The primary parameters affecting the porosity were identified and ranked as follows: sintering temperature > IOTs content > sintering time. The formation and growth of pores could be attributed to the equilibrium relationship between the liquid-phase surface tension and the gas expansion force, accompanied by pore wall thinning and pore merging. Notably, the prepared ceramsite is both ecologically feasible and economically rewarding, boasting a profit margin of 9.47 $/ton. The comprehensive life cycle assessment (LCA) conducted further highlights the potential of its large-scale implementation for promoting sustainable development. This study provides an innovative strategy for the co-utilization of IOTs and CFA, with advantages such as cost-effectiveness, ecological feasibility and scalability of production.

Structural and functional perspectives of carbon filter media in constructed wetlands for pollutants abatement from wastewater

Constructed wetlands (CWs) represent the most viable artificial wastewater treatment system that works on the principles of natural wetlands. Filter media are integrally linked to CWs and have substantial impacts on their performance for pollutant removal. Carbon-derived substrates have been in the spotlight for decades due to their abundance, sustainability, reusability, and potential to treat complex contaminants. However, the efficiency and feasibility of carbon substrates have not been fully explored, and there are only a few studies that have rigorously analyzed their performance for wastewater treatment. This critical synthesis of the literature review offers comprehensive insights into the utilization of carbon-derived substrates in the context of pollutant removal, intending to enhance the efficiency and sustainability of CWs. It also compares several carbon-based substrates with non-carbon substrates with respect to physiochemical properties, pollutant removal efficiency, and cost-benefit analysis. Furthermore, it addresses the concerns and possible remedies about carbon filtration materials such as configuration, clogging minimization, modification, and reusability to improve the efficacy of substrates and CWs. Recommendations made to address these challenges include pretreatment of wastewater, use of a substrate with smaller pore size, incorporation of multiple filter media, the introduction of earthworms, and cultivation of plants. A current scientific scenario has been presented for identifying the research gaps to investigate the functional mechanisms of modified carbon substrates and their interaction with other CW components.

A review on fabricating functional materials by electroplating sludge: process characteristics and outlook

As the end product of the electroplating industry, electroplating sludge (ES) has a huge annual output and an abundant heavy metal (HM). The effective disposal of ES is attracting increasing attention. Currently, the widely used ES disposal methods (e.g. landfill and incineration) make it difficult to effectively control of HMs and synchronously utilise metal resources, leading to a waste of metal resources, HMs migration, and potential harm to the environment and human health. Therefore, techniques to limit HMs release into the environment and promote the efficient utilisation of metal resources contained within ES are of great interest. Based on these requirements, material reuse is a great potential means of ES management. This review presents an overview of the process flows, principles and feasibilities of the methods employed for the material reuse of ES. Several approaches have been investigated to date, including (1) additions in building materials, (2) application in pigment production, and (3) production of special functional materials. However, these three methods vary in their treatment scales, property requirements, ability to control HMs, and degree of utilisation of metal resources in ES. Currently, the safety of products and costs are not paid enough attention, and the large-scale disposal of HMs is not concordant with the effective management of HMs. Accordingly, this study proposes a holistic sustainable materialised reuse pattern of ES, which combines the scale and efficiency of sludge disposal and pays attention to the safety of products and the cost of transformation process for commercial application.

New strategy of drinking water sludge as conditioner to enhance waste activated sludge dewaterability: Collaborative disposal

Drinking water sludge (DWS) and waste activated sludge (WAS) are usually treated separately. With the continuous deepening understanding of the characteristics of two types sludge, the research and application of the collaborative disposal is worth considering. The heated modification DWS (HDWS) rich in inorganic matter and aluminum (Al₂O₃) can be used as a conditioner to enhance WAS dewaterability using its properties with physical skeleton and chemically catalyzed ozone (O₃). The results showed that the minimum values of capillary water time (CST) and specific resistance filtration (SRF) for WAS were 20.9±2.40 s and 1.07±0.19×10¹³ m/kg at pH=4, O₃ dosage=60 mg/g VS and HDWS dosage=700 mg/g VS, corresponding to the reduction of sludge cake water content (Wc) to 60.37±0.97 %. The mechanism of HDWS+O₃ enhanced WAS dewaterability was systematically elucidated through pyridine-infrared analysis and density functional theory (DFT) calculations. The surface of Al₂O₃ in HDWS had more Lewis acidic sites, and the oxygen atoms of O₃ combined with Al atoms to form Al-O bonds and undergo electron transfer, while O₃ molecules dissociated to produce more hydroxyl radicals (·OH). With the oxidation of ·OH, the extra-microcolony/cellular polymers (EMPS/ECPS) structure were destroyed and became looser, promoting the conversion of internal moisture to free moisture. Zeta potential tended to zero, particle size increased, and the surface was more hydrophobic. Correlation analysis revealed that the component content, protein (PN) secondary structure and molecular weight (MW) in ECPS were positively and more strongly correlated with the sludge dewaterability compared to EMPS. The discovery of HDWS+O₃ applied to effectively enhance WAS dewaterability provided an inspiring perspective on the emerging DWS and WAS co-processing disposition.

Characterization of the Physical Chemistry Properties of Iron-Tailing-Based Ceramsite

In order to deal with the problems of resource waste and environmental pollution caused by solid waste, iron tailings (mainly SiO₂, Al₂O₃ and Fe₂O₃) were used as the main raw material to create a type of lightweight and high-strength ceramsite. Iron tailings, dolomite (industrial grade, purity 98%) and a small amount of clay were combined in a N₂ atmosphere at 1150 °C. X-ray fluorescence spectrometry (XRF), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and a themogravimetric analysis (TGA) were performed and the specific surface area was analyzed to determine the strength and adsorption of the ceramsite. The results of the XRF showed that SiO₂, CaO and Al₂O₃ were the main components of the ceramsite, with MgO and Fe₂O₃ also included. The results of the XRD and SEM-EDS showed that the ceramsite contained several kinds of minerals and was mainly composed of akermanite, gehlenite and diopside, and that the morphology of the internal structure of the ceramsite was mainly massive and contained a small number of particles. The ceramsite could be used in engineering practice to improve the mechanical properties of materials and meet the requirements of actual engineering for the strength of materials. The results of the specific surface area analysis showed that the inner structure of the ceramsite was compact and that there were no large voids. The voids were mainly medium and large, with a high stability and strong adsorption ability. The TGA results showed that the quality of the ceramsite samples will continue to increase within a certain range. According to the XRD experimental results and experimental conditions, it was speculated that in the part of the ore phase containing Al, Mg or Ca in the ceramsite, the elements underwent relatively complex chemical reactions with each other, resulting in the formation of an ore phase with a higher molecular weight. This research provides the basis of characterization and analysis for the preparation of high-adsorption ceramsite from iron tailings and promotes the high-value utilization of iron tailings for waste pollution control.

Ceramsite made from drinking water treatment residue for water treatment: A critical review in association with typical ceramsite making

The use of ceramsite to construct filtration systems (e.g., biofilters) is a common method for water treatment. To promote such applications, the development of low-cost, high-performance, and environmentally friendly ceramsites has received increasing attention from scientists, and a critical step in the development is the preparation of raw materials. As an inevitable and non-hazardous by-product during potable water production, drinking water treatment residue (DWTR) is typically recycled to make water treatment ceramsite to promote recycling in filtration systems. This study aims to bridge the knowledge gap regarding DWTR in making ceramsites for water treatment. The results suggest that the fabrication methods for DWTR-based ceramsite can be generally classified into sintering and non-sintering procedures. For the sintering method, owing to the heterogeneous properties (especially aluminum, iron, and calcium), DWTR has been applied as various sub-ingredients for raw materials preparations. In contrast, for the non-sintering method, DWTR is commonly applied as the main ingredient, and natural curing, physical crosslinking, and thermal treatment methods have been typically adopted to make ceramsite. However, DWTR-based ceramsites tend to have a high adsorption capability and favorable microbial effects to control different kinds of pollution (e.g., phosphorus, nitrogen, and organic matter). Future work is typically recommended to thoroughly evaluate the performance of DWTR-based ceramsite-constructed filtration systems to control water pollution concerning the making procedures, the potential to control pollution, the stability, and the safety of raw DWTR-based ceramsite, providing systematic information to design more proper planning for beneficial recycling.

Recent Research on Municipal Sludge as Soil Fertilizer in China: a Review

Due to the annual increase in wastewater treatment in most Chinese cities, a major environmental issue has arisen: safe treatment, disposal, and recycling of municipal sludge. Municipal sludge has a high content of carbon and essential nutrients for plant growth; hence, it has gained interest among researchers as a soil fertilizer. This study discusses the potential usage of municipal sludge as soil fertilizer (indicators include nitrogen (N), phosphorus (P), and trace elements) along with its shortcomings and drawbacks (potentially toxic elements (PTEs), organic matter (OM), pathogens, etc.) as well as reviews the latest reports on the role of municipal sludge in land use. The use of municipal sludge as a soil fertilizer is a sustainable management practice and a single application of sludge does not harm the environment. However, repeated use of sludge may result in the accumulation of harmful chemicals and pathogens that can enter the food chain and endanger human health. Therefore, long-term field studies are needed to develop ways to eliminate these adverse effects and make municipal sludge available for agricultural use.

Enhanced nickel removal and synchronous bioelectricity generation based on substrate types in microbial fuel cell coupled with constructed wetland: performance and microbial response

In this study, an attempt was made to clarify the impact of substrates on the microbial fuel cell coupled with constructed wetland (CW-MFC) towards the treatment of nickel-containing wastewater. Herein, zeolite (ZEO), coal cinder (COA), ceramsite (CER), and granular activated carbon (GAC) were respectively introduced into lab-scaled CW-MFCs to systematically investigate the operational performances and microbial community response. GAC was deemed as the most effective substrate, and the corresponding device yielded favorable nickel removal efficiencies over 99% at different initial concentrations of nickel. GAC-CW-MFC likewise produced a maximum output voltage of 573 mV, power density of 8.95 mW/m², and internal resistance of 177.9 Ω, respectively. The strong adsorptive capacity of nickel by GAC, accounting for 54.5% of total contaminant content, was mainly responsible for the favorable nickel removal performances of device GAC-CW-MFC. The high-valence Ni²⁺ was partially reduced to elemental Ni⁰ on the cathode, which provided evidence for the removal of heavy metals via the cathodic reduction of CW-MFC. The microbial community structure varied considerably as a result of substrates addition. For an introduction of GAC into the CW-MFC, a remarkably enriched population of genera Thermincola, norank_f__Geobacteraceae, Anaerovorax, Bacillus, etc. was noted. This study was dedicated to providing a theoretical guidance for an effective regulation of CW-MFC treatment on nickel-containing wastewater and accompanied by bioelectricity generation via the introduction of optimal substrate.

Immobilization of by-product sulfate salt slag from high-salt organic wastewater with fly ash in lightweight aggregate ceramsite

The lightweight aggregate ceramsite (LAC) was prepared from by-product sulfate salt slag (BPSS) of high-salt organic wastewater with fly ash. The BPSS fixation rate, leaching toxicity, morphological structures and potential environmental risks of heavy metals in LAC were investigated. BPSS can be fixed in LAC when the mass ratio of Fly ash: Kaolin: clay was 7:1:2, the addition of BPSS was 28%, the heating rate was 8°C min^-1, and the calcination temperature was 1100°C. The characteristics of the LAC met the requirements for Chinese lightweight aggregate standards (GB/T17431.2-2010). The Total Organic Carbon (TOC) content of the aqueous leaching liquor in LAC was less than 0.5 mg·L^-1. And the fixation rate of heavy metal was more than 99%, which meets the requirements of GB 5085.3-2007. The BPSS immobilization mechanisms were mainly related to the formation of new crystal phases, including Leucite (KAlSi₂O₆), Albite (Na₂O·Al₂O₃·6SiO₂), Potash Feldspar (K₂O·Al₂O₃·6SiO₂), Jadeite (NaAlSi₂O₆), Hauyne ([Na,Ca]₈[Si,Al]₁₂O₂₄[SO₄]₂), Nosean (Na₈Al₆Si₆O₂₄SO₄), and Sodalite (Na₈Al₆Si₆O₂₄[MnO₄]₂) by incorporation of heavy metals in high-temperature curing reaction. This work provides an effective method for the harmless treatment and recycling of by-product salt residues from high-salt organic wastewater.

Adsorption Characteristics of Phosphate Based on Al-Doped Waste Ceramsite: Batch and Column Experiments

Phosphorus widely existing in rainfall and wastewater impacts the water environment. In this study, sludge, cement block, and coal fly ash were employed as ceramsite material to synthesize Al-doped waste ceramsite (Al-ceramsite) for removing phosphate (PO₄^3--P) from aqueous solutions. Batch static adsorption-desorption experiments were designed to investigate the effect of various parameters such as Al-ceramsite dosage, PO₄^3--P concentration, temperature, initial pH, coexisting ions, and desorbents on the removal of PO₄^3--P. Also, the fate of PO₄^3--P removal efficiency in actual rainwater was studied through dynamic adsorption column experiments using Al-ceramsite. Results showed that Al-ceramsite could remove PO₄^3--P efficiently under the optimum parameters as follows: Al-ceramsite dosage of 40 g/L, initial PO₄^3--P concentration of 10 mg/L, temperature of 25 °C, and pH of 5. Besides that, the Al-ceramsite could completely remove PO₄^3--P in actual rainwater, and the effluent PO₄^3--P concentration was lower than the environmental quality standards for surface water Class Ⅰ (0.02 mg/L). The adsorption characteristics of Al-ceramsite on PO₄^3--P by X-ray photoelectron spectroscopy (XPS) were further explained. As a result, ligand exchange and complexation were confirmed as the main PO₄^3--P removal mechanism of Al-ceramsite. Thus, Al-ceramsite was prepared from industrial waste and has shown excellent potential for phosphorus removal in practical applications.

Basic Research on Co-treatment of Municipal Solid Waste Incineration Fly Ash and Municipal Sludge for Energy-Saving Melting

MSWI fly ash and municipal sludge are solid wastes. Melting vitrification treatment was a resource utilization method. However, the flow temperature of grate furnace MSWI fly ash and municipal sludge was high (>1325 °C), which increased the energy consumption in the melting process. MSWI fly ash contained a large amount of CaO, and municipal sludge contained a large amount of SiO₂, Al₂O₃, and Fe₂O_3. The temperature of melting vitrification can be reduced using these two kinds of CITY garbage as raw materials to change the proportion of ingredients. The eutectic characteristics of MSWI fly ash and municipal sludge and the phase diagrams of CaO-SiO₂-Al₂O₃ (C-S-A) and CaO-SiO₂-Al₂O₃-Fe₂O₃ (C-S-A-F) were analyzed in this paper. It established a low melting point mixing system. The results showed that when the amount of municipal sludge was 50-70%, the flow temperature of the mixtures was <1215 °C, which was significantly lower than that of MSWI fly ash (1490 °C) and municipal sludge (1325 °C). The optimal range of low melting point components was 14.1-36.3% CaO, 21.6-40.4% SiO₂, 6.7-12.6% Al₂O₃, and 6.3-11.4% Fe₂O₃. At 400-1400 °C, the minerals in the mixtures mainly changed as follows: CaCO₃ + SiO₂ + Al₂O₃ → Ca₂SiO₄ + Ca₃SiO₅ + Ca₂Al₂SiO₇ + Ca₃Al₂O₆ + Ca₁₂Al₁₄O₃₃ → CaAl₂Si₂O₈. In the melting experiment, with the increase in temperature, most of the phases in the mixtures might become amorphous. Therefore, the low melting point phase anorthite (CaAl₂Si₂O₈) only accounted for a small part of the final molten product.

Mixture Design and Mechanical Properties of Recycled Mortar and Fully Recycled Aggregate Concrete Incorporated with Fly Ash

Recycled aggregate concrete (RAC) is a sort of green, low carbon, environmental protection building material, its application is of great significance to the low carbonization of the construction industry. The performance and strength of RAC are much lower than natural aggregate concrete (NAC), which are the key factors restricting its application. Class F fly ash is a cementitious material that is considered environmentally hazardous. In this paper, appropriate water-binder (w/b) ratios were found through a mortar expansion test at first. The compressive strength of recycled mortar incorporated with class F fly ash was further studied. On this basis, the mechanical properties of nine groups of fully recycled aggregate concrete (FRAC) with a w/b ratio of 0.3, 0.35, and 0.4, and fly ash replacement ratios of 0, 20%, and 40%, were studied. The influence of the w/b ratio and fly ash replacement ratio on mechanical properties was analyzed and compared with previous research results. In addition, the conversion formulas between the splitting tensile strength, flexural strength, and compressive strength of FRAC were fitted and established. The research results have a certain guiding significance for the mixture design of FRAC and further application of class F fly ash.

Nationwide review of heavy metals in municipal sludge wastewater treatment plants in China: Sources, composition, accumulation and risk assessment

Systematically analyzing the problem of heavy metals in the municipal sludge, a meta-analysis of nine metals was undertaken to distinguish the sources and sinks of those with the impact of their accumulation on the environment. Municipal sludge was rich in N, P and K nutrients, was found to contain heavy metals comprising the descending order Zn > Mn > Cu > Cr > Pb > Ni > As > Cd > Hg. The forms, in which heavy metals accumulated in geographical regions, were characterized. The geographical distribution of heavy metals in the sludge showed a significant difference, with higher accumulation in Eastern and Southern regions, however, the risk evaluations showed the higher risk of heavy metals accumulation in Eastern and Western regions. Agricultural, industrial and traffic activities, and storm water pipeline sediments were identified as the main sources of heavy metals in the sludge. The correlation analysis elucidated the role of the total organic carbon in the accumulation of heavy metals in sludge. Municipal sludge is endowed with resource properties due to the detection of heavy metal contents thresholds in household products and its own resource-attributable enrichment behavior, which requires deduction of environmental risks.

Study on the Properties and Heavy Metal Solidification Characteristics of Sintered Ceramsites Composed of Magnesite Tailings, Sewage Sludge, and Coal Gangue

With the rapid development of industry, the disposal of industrial solid waste needs to be solved urgently in China. Thus, an effective disposal method should be proposed to recycle these solid wastes in an environmentally friendly and sustainable manner. In this paper, ceramsite was prepared from sewage sludge (SS), magnesite tailings (MTs), and coal gangue (CG). The influence of the material ratio and sintering temperature on the properties of the ceramsite was investigated. The results show that the ceramsite had better properties when the following parameters were used: a ratio of SS: CG: MT of 4.5:4:1.5; a sintering temperature of 1250 °C; a compressive strength of 11.2 MPa (or it can be rounded to 11; our major remark relates to significant figures, and they should be up to 2-3 figures, according to measurement errors); a water absorption of 3.54%; and apparent and bulk densities of 1.19 and 0.81 g/cm3, respectively. The strength was superior to more than twice the 900-density grade prescribed by the Chinese national standard. After sintering, most of the heavy metals in the ceramsite mainly existed in the form of residue state (FD), meaning that they were highly stable. The leaching concentrations of Zn and Ni from the ceramsite were 0.72 and 0.25 mg/L lower than the prescribed regulatory limits (2.0 and 0.1 mg/L). The overall pollution toxicity index (OPTI) was only 240, less than that of raw pellets, indicating that the environmental risk is low. Not only did the ceramsite, prepared from SS, CG, and MT, exhibit excellent chemical properties, but it also proved to be an environmentally safe material. Therefore, it is an effective approach to realize the collaborative treatment of SS, CG, and MT by preparing ceramsite.

Co-Utilization of Sewage Sludge and Rice Husk in Ceramsite Preparation with Selective Adsorption Capacity to Pb

Realizing the green recycling of sludge is an important link to effectively solve the problem of sludge disposal. In this paper, sewage sludge (SS) and rice husk (RH) were utilized as raw materials in preparing novel ceramsite (SRC) for the treatment of lead-containing wastewater, and its adsorption mechanism was explored. The results showed that the optimal preparation conditions were 40% RH + 60% SS mixture, a sintering temperature of 1190 °C, and a sintering time of 20 min. The basic properties of SRC met Chinese artificial ceramsite filter material standards for water treatment (CJ/T 299-2008). Under optimum adsorption conditions (pH = 6, 1 g/L SRC dosage, 20 mg/L Pb(NO)3 concentration, 18 h), the removal rate of Pb2+ reached 94.7%, and the equilibrium adsorption capacity was 18.94 mg/g. The adsorption process was more consistent with the pseudo-second-order kinetic model and the Langmuir isotherm model, indicating that the adsorption process was dominated by chemisorption. Thermodynamic parameters (ΔH0 > 0, ΔG0 < 0, ΔS0 > 0) indicated that the adsorption reaction was spontaneous and endothermic. The possible adsorption mechanisms are as follows: (1) SRC is rich in layered mesoporous structure, which provides sufficient reaction sites for Pb adsorption; (2) the sintered lawsonite and muscovite can strongly attract Pb and then form a new phase (Pb10[Si2O7]3(OH)2); (3) Pb2+ can bond with the Si−O- bond in aluminosilicates, and the introduction of Pb elevates the degree of polymerization of aluminosilicates in turn, indicating that the adsorption process is stable.

Fabrication of Pd/Sludge-biochar electrode with high electrochemical activity on reductive degradation of 4-chlorophenol in wastewater

Effective treatment and utilization of sludge contribute to achieve conventional carbon emission reduction and resource recovery, which is of great significance to realize carbon neutralization of WWTPs. Sludge carbonization derived biochar has attracted more interest because of high potential as catalytic materials. Therein, sludge-derived electrode exhibits a promising potential in the case of sludge utilization for electrocatalysis, however, electrocatalytic performance of the already reported sludge-derived electrode is unsatisfactory due to insufficient active sites. In this study, an efficient Pd/sludge-biochar loaded foam nickel (Pd-SAC@Ni) was successfully fabricated using simple pyrolysis and solidification method, and exhibited remarkable electrocatalytic performance for 4-chlorophenol (4-CP) degradation. Furthermore, the morphology, element distribution and crystal composition were characterized by SEM, EDS, XPS and XRD. The Pd-SAC@Ni electrode exhibited superior electrocatalytic performance than Ni, SAC@Ni, Pd-Ni electrodes. The reduction rate of 98.9% was achieved at current density of 5 mA cm^-2, 4-CP concentration of 0.8 mM and initial pH of 7.0. Also, Pd-SAC@Ni electrode showed desirable reusability and achieved 98% of 4-CP removal after multiple runs of experiments. Moreover, the active hydrogen species (H*) generation capacity of electrodes was determined using tert-butanol (TBA) as trapping agent. The mechanism analysis demonstrated that direct reduction process and indirect reduction process both involved in the 4-CP degradation process, and their contribution were 19.5% and 80.5%, respectively. Then, the intermediates formed in the electrochemical degradation of 4-CP were revealed by HPLC and the plausible degradation pathway was proposed. This study provides a cost-effective approach for preparing sludge biochar electrode, and explored a novel way to promote resourceful utilization of sludge for carbon neutrality.

Nitrogen and Phosphorus Removal Efficiency and Denitrification Kinetics of Different Substrates in Constructed Wetland

Constructed wetlands (CWs) are generally used for wastewater treatment and removing nitrogen and phosphorus. However, the treatment efficiency of CWs is limited due to the poor performance of various substrates. To find appropriate substrates of CWs for micro-polluted water treatment, zeolite, quartz sand, bio-ceramsite, porous filter, and palygorskite self-assembled composite material (PSM) were used as filtering media to treat slightly polluted water with the aid of autotrophic denitrifying bacteria. PSM exhibited the most remarkable nitrogen and phosphorus removal performance among these substrates. The average removal efficiencies of ammonia nitrogen, total nitrogen, and total phosphorus of PSM were 66.4%, 58.1%, and 85%, respectively. First-order continuous stirred-tank reactor (first-order-CSTR) and Monod continuous stirred-tank reactor (Monod-CSTR) models were established to investigate the kinetic behavior of denitrification nitrogen removal processes using different substrates. Monod-CSTR model was proven to be an accurate model that could simulate nitrate nitrogen removal performance in vertical flow constructed wetland (VFCWs). Moreover, PSM demonstrated significant pollutant removal capacity with the kinetics coefficient of 2.0021 g/m2 d. Hence, PSM can be considered as a promising new type of substrate for micro-polluted wastewater treatment, and Monod-CSTR model can be employed to simulate denitrification processes.

Influence of Ceramsite with Assembly Unit of Sludge and Excavated Soil on the Properties of Cement Concrete

The application of sludge in the manufacture of ceramic material provides an outlet for waste disposal. In this study, we aimed to produce a new lightweight aggregate applications in concrete. The influence of burning temperature on the ignition loss rate, cylinder compressive strength, and the water absorption rate of ceramsite mixed with sludge and excavated soil was investigated. The slump flow, apparent density, and mechanical strength (flexural and compressive strengths) of cement concrete with ceramsite were determined. Moreover, the chloride ion permeability coefficient and the thermal conductivity were tested. Finally, scanning electron microscopy, X-ray diffraction, and thermal analysis were applied to analyze the mechanisms of the properties of ceramsite. Results show that the ignition loss rate and the burning temperature are in a quadratic relationship. The cylinder compressive strength shows a positive quadratic relationship with the burning temperature. However, the water absorption rate negatively correlates with the burning temperature. The addition of sludge can increase the ignition loss rate and cylinder compressive strength of ceramsite. Meanwhile, the effect of sludge on the water absorption rate is the opposite. Ceramsite decreases the slump flow and the apparent density of cement concrete. Cement concrete with 10% ceramsite shows the highest mechanical strength and the lowest chloride ion migration coefficient. Correction of the chloride ion migration coefficient and the content of ceramsite was performed as an exponential equation. Ceramsite exerts a negative effect on the thermal conductivity of cement concrete. Concrete with sludge ceramsite shows higher slump flow, apparent density, mechanical strength, and resistance to chloride ion penetration and thermal conductivity than concrete sludge with clay ceramsite. The mullite content of sludge ceramsite is higher than that of clay ceramsite. Additionally, sludge ceramsite exhibits a denser structure than that of clay ceramsite.

Ceramsite production using water treatment residue as main ingredient: The key affecting factors identification

As an inevitable by-product of potable water production, drinking water treatment residue (DWTR) recycling to make ceramsite can provide both environmental and economic benefits in constructing filtration treatment system for water environment remediation. Given the varied properties of DWTR from different waterworks, this study aims to identify the key factors affecting ceramsite production from DWTR as main ingredient based on five different DWTR with using clay as the auxiliary material. The results showed that of sintering temperature (500-1000 °C), DWTR:clay ratio (5:5 to 9:1), sintering time (5-60 min), and granule diameter (5-15 mm), the sintering temperature was the key parameter. Increasing temperatures from 500 to 1000 °C gradually promoted DWTR sintering by enhancing Si and Al crystallization, which typically increased the formation of SiO₂ and CaAl₂Si₂O₈ crystals in ceramsite. Ceramsites made from different DWTR tended to have different properties, mainly resulting from varied contents of Si (20.2%-48.6%), K (0.0894%-2.39%), Fe (4.56%-14.3%), and loss on ignition (11.7%-39.5%). During ingredients preparation to produce up-to-standard ceramsite, supplying additional Si and diluting loss on ignition were necessary for all DWTR, while supplying K and diluting Fe may be required for specific DWTR, due to the potential varied DWTR compositions caused by different water production processes applied (e.g., type of flocculants). Further toxicity characteristic leaching procedure analysis indicated the increased leaching of Cu. However, DWTR based ceramsite was identified as non-hazardous material; even, sintering treatment reduced the leachability of Ba, Be, Cd, and Cr. DWTR based ceramsite also had relatively high specific surface area (22.1-50.5 m²/g) and could adsorb Cd, Cu, and Pb from solution. Overall, based on appropriate management, DWTR can be recycled as the main ingredient in the production of ceramsite for water environment remediation.

Optimize the Preparation of Novel Pyrite Tailings Based Non-sintered Ceramsite by Plackett-Burman Design Combined With Response Surface Method for Phosphorus Removal

The large amount of untreated pyrite tailings has caused serious environmental problems, and the recycling of pyrite tailings is considered as an attractive strategy. Here, we reported a novel non-sintered ceramsite prepared with pyrite tailings (PTNC) as the main active raw material for phosphorus control, and the dosage effect of ingredients on total phosphorus (TP) removal ability was investigated. The results from Plackett-Burman Design (PBD) suggested the dosages of dehydrated sludge, sodium bicarbonate, and cement were the factors which significantly affect the TP removal ability. The Box-Behnken Design (BBD) based response surface methodology was further employed, and it indicated the interactions between different factors, and the optimized recipe for PTNC was 84.5 g (pyrite tailings), 10 g (cement), 1 g (calcined lime), 1 g (anhydrous gypsum), 3 g (dehydrated sludge), and 0.5 g (sodium bicarbonate). The optimized PTNC was characterized and which presented much higher specific area (7.21 m²/g) than the standard limitation (0.5 m²/g), as well as a lower wear rate (2.08%) rather than 6%. Additionally, the leaching metal concentrations of PTNC were far below the limitation of Chinese National Standard. The adsorption behavior of TP on PTNC was subsequently investigated with batch and dynamic experiments. It was found that the calculated max adsorption amount (q_max) was about 7 mg/g, and PTNC was able to offer a stable TP removal ability under different hydraulic retention time (HRT). The adsorption mechanism was discussed by model fitting analysis combined with XRD and SEM characterization, and cobalt phosphide sulfide was observed as the newly formed substance through the adsorption process, which suggested the existing of both physical and chemical adsorption effect. Our research not only offered an economic preparation method of ceramsite, but also broadened the recycling pathway of pyrite tailings.

Ecological floating bed for decontamination of eutrophic water bodies: Using alum sludge ceramsite

In this study, a combined ecological floating bed (C-EFB) with alum sludge ceramsite (ASC) was designed to improve the water purification effect of traditional ecological floating beds (T-EFBs). During the ASC preparation stage, alum sludge was shaped into a ball, air-dried, and fired under 600 °C. The physical and chemical properties of the ASC meet the requirements of Artificial Ceramsite Filter Materials for Water Treatment (CJ/T229-2008). This study investigated the increased capability of this new-type artificial substrate (ASC) on the removal of chemical oxygen demand (COD), ammonia nitrogen (NH4+-N), total phosphorus (TP), and total nitrogen (TN) from eutrophic landscape water. Compared with the T-EFB, the C-EFB owns a higher purification efficiency. The highest average efficiency of COD, NH4+-N, TN and TP removals during the four operating stages was 78.2%, 58.1%, 46.7% and 53.2%, respectively, in the C-EFB, which were all higher than those of 53.5%, 32.4%, 27.2% and 25.8%, respectively, for the T-EFB. Among them, the C-EFB showed a higher advantage in the removal of TP. The results showed that the potential benefits of utilizing ASC in seriously eutrophic bodies of water.

Co-utilization of lake sediment and blue-green algae for porous lightweight aggregate (ceramsite) production

Lake sediment and algal sludge with large output posed significant environmental risks. In this work, an idea of co-utilization of both solid wastes for the production of ceramsite (a sort of porous lightweight aggregates as building materials) was proposed and validated for the first time. The treatment process contained a dewatering step by a flocculation-pressure filtration method, and a sintered ceramsite preparation step. Effects of flocculant type and dosage on the dewatering performance were studied in the first step. An environmental-friendly amphoteric starch flocculant with a dosage of 12 mg/(g dried sample) was found to achieve the best dewatering performance. Effects of raw material mass ratio, sintering temperature and time in the second step were investigated. Under the optimal conditions (60 wt% of dewatered sediment; 20 wt% of dewatered algal sludge; 20 wt% of additives (fly ash: calcium oxide: kaolin = 2:1:2); sintering temperature: 1100 °C; time: 35 min), the obtained ceramsite met the Chinese National Standard as a qualified building material, with reliable environmental safety according to the leaching results for both heavy metals and microcystins. Both environmental and economic benefits of the proposed treatment were assessed. The process completely followed the rules of "reduction, harmlessness and resource utilization" for solid waste treatment and disposal; Meanwhile, the profit of the proposed ceramsite production could be more than 2.3 US dollar/m³. The co-utilization method in this work acted as a good example for the comprehensive management of solid wastes in water-rich areas.

Nitrogen and phosphorus removal in simulated wastewater by two aquatic plants

Water pollution control is the focus of environmental pollution control. Ecological water treatment is widely used because of its low cost and landscape effect, and has no pollution. Aquatic plants have attracted wide attention because of their low cost and high level of resource utilization. In order to study the effects of emergent and submerged plants on the removal of different concentrations of wastewater, and the effect of pollutants on plant growth, two common aquatic plants found in Northeast China (Iris ensata Thunb. and Potamogeton malaianus Miq.) were selected. Under static conditions, the removal efficiency of nitrogen and phosphorus in wastewater with different concentrations by two kinds of plants was studied. The results showed that the removal rate of total nitrogen (TN) in medium- and high-pollutant concentration water samples and total phosphorus (TP) in medium- and low-pollutant concentration water with I. ensata reached more than 75%. The removal rate of TN in the medium-pollutant concentration water with P. malaianus reached 71.4%, while the removal efficiency of TN and TP in the low-pollutant concentration water was higher than 80%. In the Nanhu Park Lake samples, I. ensata had the highest removal rates of TN (80.38%) and TP (85.62%). This study shows that both I. ensata and P. malaianus can be used as aquatic plants to restore the water quality of urban lakes. This research provides an important basis for the phytoremediation and treatment of urban domestic wastewater and urban surface water bodies in Northern China.

Response surface optimization, combustion characteristics and kinetic analysis of mixed fuels of Fenton/CaO conditioned municipal sewage sludge and rice husk

The co-combustion characteristics and kinetics of Fenton/CaO conditioned MSS, and biomass rice husk (RH) are studied by thermogravimetry, and the condition optimization was carried out by response surface methodology (RSM). The results show that the mixed fuel with RH is helpful to decrease T_i and T_b values and increase combustion characteristic index (CCI). The CCI of MSS after conditioning is 0.59-0.88 times lower than that of the pure MSS. In addition, the total E_m of S2, MSS/RH mixed combustion after Fenton/CaO conditioning is lower, the combustion reactivity is stronger. According to RSM, the optimum conditions are considered to be: RH mixing ratio 56%, Fenton/CaO conditioner dosage 147 mg g^-1 dry solids, heating rate 30 K min^-1, the maximum CCI 25.3305 × 10^-7%² °C^-3 min^-2, and the minimum E_m 10.6403 kJ min^-1. This study supplies new insights into combustion technology of sludge.

Study on clogging mechanisms of constructed wetlands from the perspective of wastewater electrical conductivity change under different substrate conditions

Constructed wetland (CW) has obvious advantages in wastewater treatment of medium and small towns. However, there is a lack of health monitoring research on CW system clogging. The electrical conductivity (EC) of wastewater purified by CW is related to the concentration of pollutants, which can reflect the CW clogging. The objectives of this study are to reveal the mechanisms of CWs substrate clogging from the perspective of wastewater EC changes, and provide an important reference for the health evaluation of CWs. The EC changes of nine CWs substrates (quartz sand, zeolite, gravel, coarse sand, straw biochar, sludge biochar, clay ceramsite, fly ash ceramsite and shale ceramsite) under different conditions (purified water, wastewater and wastewater + NaCl) were tested, and comparative analysis was used to reveal the influence of different substrate materials on the change of wastewater EC. The results show that the adsorption ability of substrate material isn't the main factor affecting the EC of wastewater, and the soluble component in the material is the important factor to cause the difference of EC increment. Under the condition of 0.4-1.0 g L^-1 NaCl concentration, the adsorption of substrate materials had little effect on the EC of wastewater, and the effect of NaCl used in CW tracer experiment was good. Quartz sand, coarse sand, gravel and sludge biochar have little influence on the change of wastewater EC. Other materials that have great influence on the change of wastewater EC can be treated by modifying or controlling the mixing ratio. The results are of great significance to reveal the clogging state of CW system and to carry out health assessment research.