Preparation of Ceramsite Based on Waterworks Sludge and Its Application as Matrix in Constructed Wetlands

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.

Application of modified water treatment residuals in water and wastewater treatment: A review

Large quantities of sludge known as water treatment residuals (WTRs) are generated from water treatment facilities across the world. Various attempts have been made to reuse these residuals. Among the different applications of WTRs, their reuse in water and wastewater treatment has received more attention. However, direct application of raw WTRs is associated with some limitations. In the last decade, in order to improve their characteristics, numerous investigators have modified WTRs by different methods. This paper reviews the different methods applied to WTRs to enhance their characteristics. The effects of these modifications on their characteristics are explained. The applications of modified WTRs as a filtration/adsorption medium for treating textile/dye wastewater, groundwater containing different anionic and cationic pollutants, storm water runoff, and as a substrate in constructed wetlands are presented in detail. Future research needs are highlighted. The review clearly indicates the potential of different modification methods to improve the removal of a variety of pollutants by WTRs from water and wastewater.

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.

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.

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.

Characterization, Spatial Variation and Management Strategy of Sewer Sediments Collected from Combined Sewer System: A Case Study in Longgang District, Shenzhen

In the urban drainage system, the formation of sewer sediments is inevitable, and the removal of sewer sediments is necessary for system maintenance. Disposal of arisings from sewer sediment removal is becoming a serious environmental issue. The current knowledge of sewer sediments is limited, which is restrained to sewer sediments management. To better understand this municipal waste, the sewer sediments of a combined sewer system in Longgang District, Shenzhen were collected and characterized, and the spatial distribution characteristics of contaminants were analyzed. Based on the bivariate correlation analysis, it is found that many contaminants in sewer sediments have a strong relationship with spatial variables. Compared to the sewer sediments in industrial areas, those in residential areas contain higher concentrations of Hg and phosphorus. The sediments in the sewage conduit also contain more organic matter (OM), phosphorus, Cu, and Ni, and the sediments in the rainwater conduit contain a higher concentration of Cd. Moreover, the sediments produced in different catchments also show huge differences in the content of contaminants. These spatial distribution characteristics may provide help for the further classification of sewer sediments, thereby making the disposal of sediments more targeted. According to the local standards of sludge disposal, land application and incineration are not suitable for managing sewer sediments due to the low OM content and poor lower heating value (LHV). Although sanitary landfill is feasible for sewer sediments disposal, the complicated composition of sewer sediments still poses the risk of polluting the surrounding environment. The management of sewer sediments via the production of building materials is a promising technical route that can avoid the migration of hazardous contaminants and produce valuable products. This study may improve our understanding of sewer sediments and provide a reliable recommendation for sewer sediment management.

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

Municipal sludge is a solid waste material, and resource utilization is the optimal way to dispose of this material. The amount of municipal sludge produced in China is large, and it can be used in the preparation of ceramsite. The content of Al₂O₃ in drinking water treatment sludge is significantly higher than that in wastewater treatment sludge, while the content of K₂O, Na₂O and MgO in the two kinds of sludge is similar. When sludge is used to prepare ceramsite, the amount of sludge in most raw materials for ceramsite is less than 50%. The bulk density of the prepared sludge ceramsite is less than 1000 kg m^-3, and the highest water absorption rate is close to 40%. The leaching content of heavy metals in municipal sludge-based ceramsite is within the standard health safety limit, and heavy metals are better stabilized. The fitting effect of the pseudo-second-order kinetic equation of the dynamic adsorption of sludge ceramsite is obviously better than that of the pseudo-first-order kinetic equation. Sludge ceramsite used in bio-filter media and constructed wetland (CW) substrates is good able to purify wastewater. In the future, the preparation method of municipal sludge ceramsite and purification research of CW substrates based on sludge ceramsite need to be further improved.

The Tolerance of Anoxic-Oxic (A/O) Process for the Changing of Refractory Organics in Electroplating Wastewater: Performance, Optimization and Microbial Characteristics

In order to investigate the tolerance of an anoxic-oxic (A/O) process for the changing of refractory organics in electroplating wastewater, optimize the technological parameters, and reveal the microbial characteristics, a pilot-scale A/O process was carried out and the microbial community composition was analyzed by high-throughput sequencing. The results indicated that a better tolerance was achieved for sodium dodecyl benzene sulfonate, and the removal efficiencies of organic matter, ammonia nitrogen (NH4+-N), and total nitrogen (TN) were 82.87%, 66.47%, and 53.28% with the optimum hydraulic retention time (HRT), internal circulation and dissolved oxygen (DO) was 12 h, 200% and 2–3 mg/L, respectively. Additionally, high-throughput sequencing results demonstrated that Proteobacteria and Bacteroidetes were the dominant bacteria phylum, and the diversity of the microbial community in the stable-state period was richer than that in the start-up period.

Evaluation of Bed Depth Reduction, Media Change, and Partial Saturation as Combined Strategies to Modify in Vertical Treatment Wetlands

The aim of this work was to evaluate the performance of vertical subsurface flow treatment wetlands (VSSF TWs) for treating rural domestic wastewater when strategies such as bed depth reduction and media change are used in combination with bottom saturation. Two treatment wetland systems were implemented: normal (VF-N), with a bed depth of 1.0 m, and modified (VF-M), with a bed depth of 0.5 m and a bottom layer of natural zeolite. Schoenoplectus californicus was used as experimental plant. These two treatment systems were operated at a hydraulic loading rate of 120 mm/d in two phases. Phase I did not use bottom saturation, while Phase II involved a bottom saturation of the zeolite layer of the VF-M system. The results show that bed depth reduction did not have a significant effect (p > 0.05) in terms of organic matter, solids, and ammonium removal. Conversely, it had a significant influence (p < 0.05) on phosphate as well as a negative effect on pathogen removal. This influence could be explained by initial media capacity for phosphorus removal and filtration importance in the case of pathogens. Partial saturation only had a positive influence on total nitrogen removal. The addition of a bottom layer of natural zeolite showed no positive effect on nutrient removal. The plant showed adaptation and positive development in both VF-N and VF-M. The water balance showed that water loss was not influenced by bed depth reduction. Therefore, according to the previous results, a combination of the proposal modifications to VSSF TWs can be introduced for treating rural domestic wastewater.

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.

Treatment of microcystin (MC-LR) and nutrients in eutrophic water by constructed wetlands: Performance and microbial community

Cyanobacterial harmful algal blooms and microcystins (MCs) pollution pose serious threat to aquatic ecosystem and public health. Planted and unplanted constructed wetlands (CWs) filled with four substrates (i.e., gravel (G-CWs), ceramsite (C-CWs), iron-carbon (I-CWs) and slag (S-CWs)) were established to evaluate nutrients and a typical MCs variant (i.e., MC-LR) removal efficiency from eutrophic water affected by the presence of plant and different substrate. The response of the microbial community to the above factors was also analyzed in this study. The results indicate that the presence of plant can generally enhance nutrients and MC-LR removal efficiency in CWs, except for I-CWs. Throughout the experiment, all CWs exhibited good nitrogen removal efficiency with removal percentages exceeding 90%; TP and MC-LR average removal efficiency of C-CWs and I-CWs were greater than G-CWs and S-CWs irrespective of the presence of plant. The best MC-LR removal efficiency under different MC-LR loads was observed in planted C-CWs (ranged from 91.56% to 95.16%). Except for I-CWs, the presence of plant can enhance relative abundances of functional microorganisms involved in nutrients removal (e.g., Comamonadaceae and Planctomycetaceae) and MCs degradation (e.g., Burkholderiaceae). The microbial community diversity of I-CWs was simplified, while the relative abundance of Proteobacteria was highest in this study. The highest relative abundances of Comamonadaceae, Planctomycetaceae and Burkholderiaceae were observed in planted C-CWs. Overall, ceramisite and iron-carbon were more suitable to be applied in CWs for nutrients and MC-LR removal. This study provides a theoretical basis for practical application of CWs in eutrophication and MCs pollution control.

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.