Entrapment of powdered drinking water treatment residues in calcium-alginate beads for fluoride removal from actual industrial wastewater

Amorphous Fe substrate enhances nitrogen and phosphorus removal in sulfur autotrophic process

The autotrophic denitrification of coupled sulfur and natural iron ore can remove nitrogen and phosphorus from wastewater with low C/N ratios. However, the low solubility of crystalline Fe limits its bioavailability and P absorption capacity. This study investigated the effects of amorphous Fe in drinking water treatment residue (DWTR) and crystalline Fe in red mud (RM) on nitrogen and phosphorus removal during sulfur autotrophic processes. Two types of S-Fe cross-linked filler particles with three-dimensional mesh structures were obtained by combining sulfur with the DWTR/RM using the hydrogel encapsulation method. Two fixed-bed reactors, sulfur-DWTR autotrophic denitrification (SDAD) and sulfur-RM autotrophic denitrification (SRAD), were constructed and stably operated for 236 d Under a 5-8-h hydraulic retention time, the average NO3--N, TN, and phosphate removal rates of SDAD and SRAD were 99.04 %, 96.29 %, 94.03 % (SDAD) and 97.33 %, 69.97 %, 82.26 % (SRAD), respectively. It is important to note that fermentative iron-reducing bacteria, specifically Clostridium_sensu_stricto_1, were present in SDAD at an abundance of 58.17 %, but were absent from SRAD. The presence of these bacteria facilitated the reduction of Fe (III) to Fe (II), which led to the complete denitrification of the S-Fe (II) co-electron donor to produce Fe (III), completing the iron cycle in the system. This study proposes an enhancement method for sulfur autotrophic denitrification using an amorphous Fe substrate, providing a new option for the efficient treatment of low-C/N wastewater.

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.

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.

A polymer - zeolite composite for mixed metal removal from aqueous solution

Heavy metals become inevitable pollutants that are toxic to life. Lots of treatment methods are available; adsorption is a cheap option. Metals are mostly found as mixtures in wastewaters. Taking this into account, a natural composite adsorbent aims to remove multiple heavy metals (Pb²⁺, Cu²⁺, Cd²⁺). Alginate was combined with clinoptilolite to form alginate - clinoptilolite (A-C) beads. First, factors influencing the removal efficiency of metals were investigated. Then, continuous column experiments were performed to evaluate the real application potential of the adsorbent. A-C beads preferably adsorbed Pb²⁺. Batch experiments showed metal uptake reached equilibrium after 24 hours and kinetics were compatible with the first-order. Also, pH values near neutral levels were observed to increase heavy metal removal. On the other hand, adsorption equilibrium was well described by the Langmuir model for Cu²⁺ and Cd²⁺ and by the Freundlich model for Pb²⁺. The highest heavy metal uptake was calculated as 2,145 mg /g A-C beads for Pb²⁺. Continuous column operations were suggested to apply low flow rates (<2 mL/min) and heavy metal concentration (<10 mg/L) for effectiveness. A-C beads can be a good candidate for mixed heavy metal removal composed of environmentally friendly and low-cost materials.

Granulation and calcination of alum sludge for the development of a phosphorus adsorbent: From lab scale to pilot scale

Alum sludge, an Al-oxyhydroxide rich waste product from water treatment practices, has the potential to be valorized as a P adsorbent material. However, several challenges currently prevent its application as an adsorbent in industrial setting, i.e. a limited P adsorption capacity due to saturation by organic matter and a fine nature resulting in percolation problems in adsorption bed setups. In this study, granulation and subsequent calcination of alum sludge were proposed to overcome these issues and to improve the P adsorption properties of alum-based adsorbent (ABA) materials. The effect of calcination temperature on the physicochemical properties of granular material was examined using X-ray diffraction, mass-spectroscopy coupled thermogravimetric analysis, Fourier-transform infrared spectrometry and specific surface area analysis, combined with density and crushing strength measurements. The ABA material obtained at 550 °C showed superior P adsorption properties and, therefore, this material was selected for further P adsorption testing and characterization (scanning electron microscopy and sieving). Batch P adsorption tests showed that this material had a maximum P adsorption capacity of 7.27 mg-P g^-1. Kinetic adsorption tests determined the effect of the solid-to-liquid ratio and the granule particle size on the P removal. Finally, the performance of the ABA-550 material was tested in a pilot-scale adsorption setup, using a surface water stream (0.47 mg-P L^-1) at a flow rate of 200 L h^-1. During the test, the P removal efficiency always exceeded 86%, while the material maintained its structural stability. The results of this study illustrate the potential of granulated/calcined ABA materials for P adsorption, paving the way for the industrial application of this novel, sustainable P removal technology.

Kinetics of a fixed bed reactor with immobilized microorganisms for the removal of organic matter and phosphorous

The biodegradation of domestic wastewater contaminants has been carried out using microorganisms immobilized in sodium alginate gel (Alg-Na). A fixed bed reactor with immobilized microorganisms was used for the treatment of domestic wastewater. A wastewater pretreatment was carried out to remove the larger particulate matter, which consisted of a reactor packed with different materials (anthracite, zeolite, and activated carbon). Later, a second reactor packed with balls with immobilized microorganisms was used to eliminate organic matter and nutrients. 2.5% w/v of Alg-Na was used as a support to immobilize the microorganisms. According to the results, a total phosphorus (TP) and chemical oxygen demand (COD) removal of 94.26% and 78.25% was obtained, respectively. In addition, the degradation rate for both organic matter and phosphorous was studied by using the kinetic model for fix bed reactor. © 2020 Water Environment Federation PRACTITIONER POINTS: Phosphorous and organic matter removal by adsorption and immobilized microorganisms. High removal efficiency of phosphorous and organic matter was found. An innovative wastewater treatment alternative is proposed. Kinetic model for fixed bed reactor is also proposed for scaling-up purposes.

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.

Porous, pH-Responsive, and Reusable Hydrogel Beads of Bovine Serum Albumin_Au Hybrid as Smart Nanofactories for the Removal of Organic and Inorganic Pollutants from Water: A Detailed Demonstration by Spectroscopy and Microscopy

The availability of potable water is one of the major concerns in many countries today. This brings in a need to design molecular scaffolds suitable for efficient adsorption of the contaminants present in water. In this paper, an unprecedented strategy is demonstrated in order to synthesize highly porous bovine serum albumin_Au (BSA_Au) beads and was employed for the removal of water contaminants. The beads stored in acidic medium (Bead_a) and in basic medium (Bead_b) selectively adsorb anionic and cationic species that includes organic dyes and inorganic species, respectively, by showing a pH-responsive behavior. This phenomenon bestowed the beads with the recyclability and reusability as demonstrated for eight cycles wherein almost 100% efficiency is retained by the beads without any deterioration. The porous nature of these beads is retained even after switching the pH for several cycles of adsorption-desorption processes as judged based by the SEM data. Thus, the reported beads are demonstrated for their selective and efficient removal of both organic and inorganic contaminants from water wherein the beads can be recycled by triggering pH changes that would also release the captured species. The biologically benign beads act as reusable smart nanofactories in the purification of water from industrial contaminants.

Granulation of drinking water treatment residuals as applicable media for phosphorus removal

Recycling drinking water treatment residuals (DWTR) show promise as a strategy for phosphorus (P) removal; however, powdered DWTR is not an ideal practical medium due to clogging. This study granulates DWTR by entrapping powdered DWTR in alginate beads. Results show that granular DWTR has an appreciable amount of mesopores along with a Brunauer-Emmett-Teller (BET) surface area of 43.8 m²/g and total pore volume of 0.049 cm³/g. Most metals (e.g., Al, Ba, Be, Cd, Co, Cr, Mn, Ni, Pb, and Zn) in granular DWTR became more stable and granular DWTR could be considered non-hazardous material. Further analysis indicates that the granular DWTR has strong P adsorption capability with a maximum adsorption capacity of 19.70 mg/g as estimated by the Langmuir model. Good P adsorption may be attributed to the formation of Fe-PO₄ and Al-PO₄ associated with the amorphous state of enormous iron and aluminum in granular DWTR. More importantly, granular DWTR exhibits good mechanical stability and maintained its shape with weight loss below 12.49% after three recycling rounds. Overall, granular DWTR appears to serve as better media for phosphorus removal in water treatment structures such as wetlands.

Fabrication of granular activated carbons derived from spent coffee grounds by entrapment in calcium alginate beads for adsorption of acid orange 7 and methylene blue

Biomass-based granular activated carbon was successfully prepared by entrapping activated carbon powder derived from spent coffee grounds into calcium-alginate beads (SCG-GAC) for the removal of acid orange 7 (AO7) and methylene blue (MB) from aqueous media. The dye adsorption process is highly pH-dependent and essentially independent of ionic effects. The adsorption kinetics was satisfactorily described by the pore diffusion model, which revealed that pore diffusion was the rate-limiting step during the adsorption process. The equilibrium isotherm and isosteric heat of adsorption indicate that SCG-GAC possesses an energetically heterogeneous surface and operates via endothermic process in nature. The maximum adsorption capacities of SCG-GAC for AO7 (pH 3.0) and MB (pH 11.0) adsorption were found to be 665.9 and 986.8mg/g at 30°C, respectively. Lastly, regeneration tests further confirmed that SCG-GAC has promising potential in its reusability, showing removal efficiency of more than 80% even after seven consecutive cycles.