Characterization of fly ash ceramic pellet for phosphorus removal

Evaluation of compressive strength and phosphate fixation characteristics of wastewater filter media using coal bottom ash and oyster shells

The excessive concentration of phosphate in coastal areas results in environmental problems such as red tide and eutrophication. Filter media (FM) is used in wastewater treatment facilities to decrease phosphate concentration. This study aims to investigate the optimal mixing ratio for high compressive strength and phosphate fixation ability using coal bottom ash (CBA) and oyster shells (OS) -derived FM. Compressive strength experiments were conducted using mixed CBA and OS with different mixing ratios, 1:3 (GBO13), 1:1 (GBO11), and 3:1 (GBO31). The highest compressive strength of 0.93 MPa was observed in GBO11. GBO11 had similar elemental proportions with Portland cement, promoting a pozzolanic reaction and forming calcium-silicate-hydrate. The phosphate fixation capability of GBO11 was evaluated through an up-flow column filtration experiment. GBO11 fixed phosphate through precipitation and adsorption, and the maximum amount of phosphate fixation was estimated to be 1.403 mg-P/g. This study demonstrates that the combination of CBA and OS can be promising FM with high compressive strength and phosphate fixation properties.

Promoted removal of phosphate by layered double hydroxides combined with bacteria: Application of novel carriers in biofilm reactor

Layered double hydroxides (LDHs) were used as carriers for the microbial consortium in sequencing biofilm batch reactor (SBBR) without inoculation to promote the removal of phosphate. The adsorption capacity of [Zn-Al]-LDH was significantly better than that of [Mg-Al]-LDH. The pollutants removal performance and behavior of microorganisms in LDH-SBBRs were also investigated. LDH-SBBRs showed improved removal efficiencies of COD, phosphate and TP with a low C/N ratio. Microscopic images show that biofilm formed rapidly in LDH-SBBRs. SEM-EDS detected abundant carbon and phosphorus, implying that biomass and phosphorus accumulate on LDH carriers. The microbial compositions of the three SBBRs indicate that the LDHs carriers improved the biodiversity of biofilm in the bioreactors. Synergistic effects of adsorption and biodegradation between well-structured LDHs and microorganisms led to an improved phosphate removal performance of LDH-SBBR. The results also demonstrate that [Zn-Al]-LDH carrier is the best for improving SBBR phosphate removal.

Phosphorus removal from wastewater using electric arc furnace slag aggregate

Electric arc furnace (EAF) slag aggregate, a waste by-product of the steel industry, exhibited a high potential for phosphorus (P) removal and had attracted considerable attention. The main objectives of this study were to evaluate the performance of using EAF slag aggregate as an adsorbent for P removal and identify its P removal capacity. A series of batch tests showed that P removal capacity of EAF slag increases gradually with the increase of pH with a range of 2-10, while the highest P removal capacity (1.94 mg/g) can be obtained at pH 12. The adsorption kinetics of P on EAF slag can be described by pseudo-second-order kinetic equations. Isothermal adsorption simulations showed that the best fitted model was the Freundlich model with a correlation coefficient of 0.9825. A continuous flow column experiment feeding a synthetic influent containing 15 mg P/L was operated for 60 days and the P removal efficiency was greater than 95% with a P removal capacity of 1.6 mg P/g slag. The results obtained in this study showed that EAF slag could act as an efficient adsorbent for P removal. Calcium phosphate precipitation depends on the release of Ca²⁺ and OH^- by the dissolution of calcium oxide in EAF slag was found to be the dominant removal mechanism for P removal.

Evaluation of advanced phosphorus removal from slaughterhouse wastewater using industrial waste-based adsorbents

Slaughterhouse wastewater (SWW) contains high concentrations of phosphorus (P) and is considered as a principal industrial contaminant that causes eutrophication. This study developed two kinds of economical P removal adsorbents using flue gas desulfurization gypsum (FGDG) as the main raw material and bentonite, clay, steel slag and fly ash as the additives. The maximum adsorption capacity of the adsorbent composed of 60% FGDG, 20% steel slag, and 20% fly ash (DSGA2) was found to be 15.85 mg P/g, which was 19 times that of the adsorbent synthesized using 60% FGDG, 30% bentonite, and 10% clay (DSGA1) (0.82 mg P/g). Surface adsorption, internal diffusion, and ionic dissolution co-existed in the P removal process. The adsorption capacity of DSGA2 (2.50 mg P/g) was also evaluated in column experiments. The removal efficiency was determined to be higher than 92% in the first 5 days, while the corresponding effluent concentration was lower than the Chinese upcoming SWW discharge limit of 2 mg P/L. Compared with DSGA1, DSGA2 (synthesized from various industrial wastes) showed obvious advantages in improving adsorption capacity of P. The results showed that DSGA2 is a promising adsorbent for the advanced removal of P from SWW in practical applications.

Phosphorus Removal from Wastewater: The Potential Use of Biochar and the Key Controlling Factors

In recent years, a large volume of literature has been published regarding the removal of phosphorus (P) from wastewater. Various sorbing materials, such as metal oxides and hydroxides, carbonates and hydroxides of calcium (Ca) and magnesium (Mg), hydrotalcite, activated carbon, anion exchange resins, industrial solid wastes and organic solid wastes, have been suggested for P removal. Many of these sorbents are expensive and/or may cause some environmental problems. In contrast, biochar, as an economical and environmentally friendly sorbing material, has received much attention in recent years and has been used as a novel sorbent for the removal of different organic and inorganic pollutants. Biochar is a type of sustainable carbonaceous material that is produced from the thermal treatment of agricultural organic residues and other organic waste streams under oxygen free conditions. This paper reviews the potential use of biochar and the key controlling factors affecting P removal from wastewater. The ability of biochar to remove P from wastewater depends on its physical and chemical properties. Some of the most important physicochemical properties of biochar (structural characteristics, electrical conductivity (EC), mineral composition, pH, zeta potential, cation exchange capacity (CEC) and anion exchange capacity (AEC)) are affected by the feedstock type as well as temperature of pyrolysis and the P sorption capacity is highly dependent on these properties. The P removal is also affected by the water matrix chemistry, such as the presence of competing ions and bulk pH conditions. Finally, several recommendations for future research have been proposed to facilitate and enhance the environmental efficiency of biochar application.

Influence of Activators on Mechanical Properties of Modified Fly Ash Based Geopolymer Mortars

The aim of this work was to study the influence of the type of activator on the formulation of modified fly ash based geopolymer mortars. Geopolymer and alkali-activated materials (AAM) were made from fly ashes derived from coal and biomass combustion in thermal power plants. Basic activators (NaOH, CaO, and Na₂SiO₃) were mixed with fly ashes in order to develop binding properties other than those resulting from the use of Portland cement. The results showed that the mortars with 5 mol/dm³ of NaOH and 100 g of Na₂SiO₃ (N5-S22) gave a greater compressive strength than other mixes. The compressive strengths of analyzed fly ash mortars with activators N5-S22 and N5-C10 (5 mol/dm³ NaOH and 10% CaO) varied from 14.3 MPa to 5.9 MPa. The better properties of alkali-activated mortars with regular fly ash were influenced by a larger amount of amorphous silica and alumina phases. Scanning electron microscopy and calorimetry analysis provided a better understanding of the observed mechanisms.

Utilization potential of fly ash and copper tailings in concrete as partial replacement of cement along with life cycle assessment

Fly ash (FA) and copper tailings (CT) both are, anthropogenic wastes, spread all over the globe due to rapid growth in thermal power plants and progressive increase in the demand of copper. This study examines the feasibility of combined utilization of FA and CT in concrete as a partial replacement of cement by assessing compressive strength, cost, and environmental impact. Morphology and constituent minerals of FA and CT have been identified to understand the utilization potential. Subsequently, the concrete has been designed for 30 MPa target strength as per IS 10262:2009 for different mix proportions of FA and CT. Improvement (up to 8.27% compared to the control mix) in the compressive strength has been observed at combined replacement of 10% FA and 5% CT. The cost of concrete can also be reduced up to 16% without compromising its compressive strength. The environmental impact assessment of the modified concrete mix proportions has also been performed using life cycle assessment (LCA) as per ISO 14040:2006. Effect of all raw materials, electricity, and water consumption have been considered from their cradle to grave approach. One cubic meter concrete has been taken as a functional unit in LCA. Notable reduction has been observed in the chosen midpoint categories up to 38% in climate change, up to 32.6% in human toxicity, up to 33.6% in ozone depletion, up to 31.9% in agriculture land occupation, water depletion up to 34.3%, fossil depletion up to 34.8%, particulate matter up to 35.4%, and metal depletion up to 25.2%.

Comprehension of heavy metal stability in municipal solid waste incineration fly ash with its compositional variety: A quick prediction case of leaching potential

In the current work, a quick prediction of the heavy metal (HM) leaching potential in municipal solid waste incineration fly ash (MSWI FA) was developed based on the statistical data between the HM leaching behaviors and the compositional variety in FA from China. In the comparison of the surveyed (508 data points) leaching concentrations, Pb and Cd leaching amounts in FA exceeded the Toxicity Characteristic Leaching Procedure (TCLP) limits most frequently. Moreover, the chemical compositions (pH and soluble chlorine (S-Cl)) of FA were proposed to have significant linear correlations with the Pb and Cd leaching. This corresponded to the chemical fraction change of the HM (risk assessment code (RAC)), which was relative to the pH of FA and chloride. This suggests that the HM stability can be evaluated by these factors. To verify this hypothesis, principal component analysis (PCA) and multiple linear regressions were used to evaluate the relationship between 5 indices and the leaching concentrations of Pb and Cd in 160 MSWI FA samples after stabilization/solidification from eastern China. It is indicated that pH, S-Cl and free CaO were the critical variables in Pb and Cd leaching. Accordingly, a new index, Φ, combined with the logistic model was proposed to predict the leaching potential. It is revealed that the high risk of the exceeding the limits for HM leaching occurred when Φ was below 12.5. Our results assess the HM stability in MSWI FA with its compositional variety in a statistical way, which gives an approach for the quick prediction of HM leaching potential.