The sludge produced in the treatment process depends on the type of coagulant and other chemicals used and the suspended particles present in raw water. Discarding this sludge in the landfills poses pollution of both ground and surface water, disturbing the lives in the water and the water quality. The primary potable water provider in Sri Lanka is the National Water Supply and Drainage Board. It focuses on finding ways of disposal, sustainable practices, and possible applications of the water treatment sludge. This research aims to identify the aluminum level in the potable water treatment sludge of the Konduwattuvana water treatment plant in Ampara and to utilize that sludge as an alternative raw material in burnt clay brick manufacturing. The national standards and limitations of the sludge content and the standard brick manufacturing process were followed. To reach the aim, a sequence of tests was conducted, and the brick characteristics are subjected to test for different sludge ratios according to the Sri Lankan Standard of 36:1978 for burnt clay bricks. Experimental results show that the aluminum content in liquid sludge and sludge cake was found to be 231.6 mg.L-1 and 54.9 mg.L-1, respectively, which implies that the sludge contains aluminum. The optimum sludge ratio to produce burnt clay bricks was found to be 10% of the total weight of the brick.

Inhalation of respirable silica particles can cause serious lung diseases (e.g., silicosis and lung cancer), and the toxicity of respirable silica is highly dependent on its crystal form. Common combustion processes such as coal and biomass burning can provide high temperature environments that may alter the crystal forms of silica and thus affect its toxic effects. Although crystalline silica (i.e., quartz, tridymite, and cristobalite) were widely found at different temperatures during the burning processes, the sources and crystal transformation pathways of silica in the burning processes are still not well understood. Here, we investigate the crystal transformation of silica in the coal and biomass combustion processes and clarify the detailed transformation pathways of silica for the first time. Specifically, in coal burning process, amorphous silica can transform into quartz and cristobalite starting at 1100 °C, and quartz transforms into cristobalite starting at 1200 °C; in biomass burning process, amorphous silica can transform into cristobalite starting at 800 °C, and cristobalite transforms into tridymite starting at 1000 °C. These transformation temperatures are significantly lower than those predicted by the classic theory due to possibly the catalysis of coexisting metal elements (e.g., aluminum, iron, and potassium). Our results not only enable a deeper understanding on the combustion-induced crystal transformation of silica, but also contribute to the mitigation of population exposure to respirable silica.

Hydroxyapatite (HAP) is an easily synthesizable, low-cost mineral that has been recognized as a potential material for fluoride removal. Some of the synthesis methods of HAP are quite straightforward and cost-effective, while some require sophisticated synthesis techniques under advanced laboratory conditions. This review assesses the physicochemical characteristics of HAP and HAP-based composites produced via various techniques, their recent development in defluoridation and most importantly, the fluoride removal performances. For the first time, fluoride removal performances of HAP and HAP composites are compared based on partition coefficient (KD) instead of maximum adsorption capacity (Qₘₐₓ), which is significantly influenced by initial loading concentrations. Novel HAP tailored composites exhibit comparatively high KD values indicating the excellent capability of fluoride removal along with specific surface areas above 120 m²/g. HAP doped with aluminium complexes, HAP doped ceramic beads, HAP-pectin nanocomposite and HAP-stilbite nanocomposite, HAP decorated nanotubes, nanowires and nanosheets demonstrated high Qₘₐₓ and KD. The secret of HAP is not the excellent fluoride removal performances but best removal at neutral and near-neutral pH, which most of the defluoridation materials are incapable of, making them ideal adsorbents for drinking water treatment. Multiple mechanisms including physical surface adsorption, ion-exchange, and electrostatic interactions are the main mechanisms involved in defluoridation. Further research work must be focused on upscaling HAP-based composites for defluoridation on a commercial scale.

Arsenic (As) is among the most dangerous metalloids and is harmful to human wellbeing. In this laboratory study, Al(III)-modified kapok fibres (Al-Kapok) were used to remove As(V) from water. The sorbent was characterised using Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM) combined with energy-dispersive X-ray spectroscopy (EDX). Batch experiments were performed to observe the performance of Al-Kapok in the removal of As(V) and to examine the effects of pH, temperature, adsorbent dose, and coexisting ions on the adsorption process. The surface of the sorbent changed after aluminium modification, and the results of the batch experiments showed that the adsorption of As(V) occurred mainly via endothermic-spontaneous chemisorption at the solution and solid interface of Al-Kapok. The As(V) removal efficiency was approximately 76%–84%, and it was slightly affected at pH levels below 8.0. Further study showed that the maximum adsorption capacity of Al-Kapok for As(V) was 118 μg/g at 30 °C and pH 6, and notable adverse effects were caused by the presence of SO42−and PO43−. It was also found that the boundary layer and film diffusion contributed more to As(V) adsorption. After five adsorption/desorption cycles, regeneration recovered approximately 92% of the adsorption capacity of Al-Kapok used. Overall, Al-Kapok appears to be a suitable adsorbent material for the purification of As-contaminated water.

The coexistence of per- and polyfluoroalkyl substances (PFASs) and heavy metals have been found in soils. However, the interaction between the combined pollutants in soils remains unclear. In this study, the adsorption processes of single and combined Cr(VI) and chlorinated polyfluoroalkyl ether potassium sulfonate (F–53 B) in red, yellow and black soils were simulated. When compared with the single F–53 B and Cr(VI), the adsorption amount of the combined F–53 B and Cr(VI) on soils changed with the types of soils. The interactions between F–53 B and Cr(VI) in soils affected their adsorption behavior. The adsorption of the combined F–53 B and Cr(VI) best fit second-order kinetics and the Freundlich equation. Moreover, aluminum and iron oxides are highly correlated with adsorption of F–53 B and Cr(VI). Both F–53 B and Cr(VI) can form complexes with aluminum and iron oxides through electrostatic interactions, but PFOS could be bridged with iron oxides to form an inner sphere complex and with aluminum oxides to form an outer sphere complex. The coexistence of F–53 B and Cr(VI) could change the fluorescent group of dissolved organic matter (DOM) in soils due to the complexation between F–53 B and DOM. In addition, F–53 B increased the acid-soluble portion of Cr and decreased its residual form, which promoted the environmental risk of Cr in soils.

Lead-zinc slag (LZS) is a solid waste product that is rich in silicon and aluminum and has enormous resource potential for functional environmental functional geopolymer materials. Unfortunately, the solidification mechanism of heavy metals in geopolymers is still unclear, which is detrimental to the heavy metal solidification of LZS. In this study, we comprehensively studied and demonstrated the solidification mechanisms of Pb and Zn in geopolymers, based on the preparation of high-performance LZS-based geopolymers (compressive strength up to 89.3 MPa, and Pb and Zn solidification efficiency up to 93.1% and 90.0%, respectively). Thereafter, the solidification mechanism differences between Pb and Zn were explained by electronegativity and ion potential. Due to the ionic potential order of Zn²⁺> Pb²⁺> Na⁺, both Zn²⁺ and Pb²⁺ could exchange with Na⁺ in the geopolymer. In addition, due to the electronegativity order of Pb > Si > Zn, Pb could attack the [SiO₄] structure and form covalent bonds in the Pb–O structure, while Zn did not (shown by Raman spectroscopy). As a result, Pb simultaneously solidified in the geopolymer through covalent bonding and ion exchange, while Zn was solidified mainly by ion exchange. Thus, this work provides new perspectives and ideas for the solidification mechanisms of heavy metals in geopolymers.

The present study aims to determine the associations of multiple plasma metal levels and plasma microRNAs (miRNAs) with diabetes risk, and further explore the mediating effects of plasma miRNAs on the associations of plasma metal with diabetes risk. We detected plasma levels of 23 metals by inductively coupled plasma mass spectrometry (ICP-MS) among 94 newly diagnosed and untreated diabetic cases and 94 healthy controls. The plasma miRNAs were examined by microRNA Array screening and Taqman real-time PCR validation among the same study population. The multivariate logistic regression models were employed to explore the associations of plasma metal and miRNAs levels with diabetes risk. Generalized linear regression models were utilized to investigate the relationships between plasma metal and plasma miRNAs, and mediation analysis was used to assess the mediating effects of plasma miRNAs on the relationships between plasma metals and diabetes risk. Plasma aluminum (Al), titanium (Ti), copper (Cu), zinc (Zn), selenium (Se), rubidium (Rb), strontium (Sr), barium (Ba), and Thallium (Tl) levels were correlated with elevated diabetic risk while molybdenum (Mo) with decreased diabetic risk (P < 0.05 after FDR multiple correction). MiR-122–5p and miR-3141 were positively associated with diabetes risk (all P < 0.05). Ti, Cu, and Zn were positively correlated with miR-122–5p (P = 0.001, 0.028 and 0.004 respectively). Ti, Cu, and Se were positively correlated with miR-3141 (P = 0.003, 0.015, and 0.031 respectively). In addition, Zn was positively correlated with miR-193b-3p (P = 0.002). Ti was negatively correlated with miR-26b-3p (P = 0.016), while Mo and miR-26b-3p were positively correlated (P = 0.042). In the mediation analysis, miR-122–5p mediated 48.0% of the association between Ti and diabetes risk. The biological mechanisms of the association are needed to be explored in further studies.

Fluoride (F) is an emerging pollutant that originates from multiple sources and adversely affects plant growth and nutrient bioavailability in soil. This greenhouse study investigated the effects of soil F (0, 10, 20, 50, 100, 200 mg kg⁻¹) on morpho-physiological growth characteristics of wheat, soil F contents, and bioavailability and uptake of F, phosphorus (P), sulphur (S), potassium (K), calcium (Ca), magnesium (Mg), aluminium (Al), iron (Fe), manganese (Mn), silicon (Si) and zinc (Zn) by wheat. Higher F significantly reduced plant height and number of leaves particularly at early growth stages and increased visible leaf injury index. Powdery mildew infestation coincided with leafy injury and was higher in elevated soil F treatments. Fluoride treatments (>50 mg kg⁻¹) significantly increased water (H₂O)- and calcium chloride (CaCl₂)-extractable F contents in soil. Water-extractable soil F contents from soil in all concentration were higher than CaCl₂-extractable F. This increased F bioavailability resulted in significantly higher F uptake and accumulation in live leaves, dead leaves and grains of wheat which followed order: live leaves > dead leaves > grains. Leaf injury index and number of dead leaves correlated significantly positively with soil H₂O- and CaCl₂-extractable F contents. Patterns of nutrient (P, K, S) and trace metals (Al, Ca, Mg, Fe, Mn, Si, Zn) varied significantly with F concentrations and between live and dead leaves, and grains except for Zn. Dead leaves generally had higher nutrients and trace metals than live leaves and grains. Fluoride contents in live leaves, dead leaves and grains showed positive correlations with nutrient elements but negative with trace metals. Number of dead leaves correlated negatively with Al, Ca, Fe, Mg, S and Si but positively with P and Zn contents in dead leaves whereas leaf injury index showed positive correlation with Fe, K, P, Si, Zn, S but negative with Al, Ca and Mg contents. These observations provided evidence of higher F uptake and associated impairment in nutrient and trace metal accumulation which caused leaf injury accompanied by powdery mildew infestation in wheat. However, further research in the region is required to confirm the relationship between F pollution, leaf injury and trace metal accumulation in crops under field conditions.

Rapid growth in population and industrialization causes the worldwide crisis for potable water, which is emphasizing on researchers to find an alternative way. Solar still is a solar energy-based device facing the problem of low productivity. The motive of the present investigation is to improve the productivity of triangular pyramid solar still by incorporating triangular cross-sectional aluminium hollow-fins and wool cloth wick-fins. In two sets of experiments, the performance of the triangular pyramid solar still with hollow-fins, wick-fins, and without fins has been compared for the case of partially and fully submerged fins. The total distillate outputs per day (including nocturnal duration) from stills for the case of partially submerged fins were: 2.5674 L/m² (12.36% higher) with hollow-fins, 2.5481 L/m² (11.51% higher) with wick-fins, and 2.2850 L/m² for without fins. For the case of partially submerged fins, the productivity was observed higher for the still with wick-fins during morning hours (9:00 h to 13:00 h), whereas for the still with hollow-fins during afternoon hours (14:00 h to 17:00 h). For the case of fully submerged fins, total distillate outputs per day (including nocturnal duration) from stills were: 2.2529 L/m² (9.00% higher) with hollow-fins, 2.3042 L/m² (11.49% higher) with wick-fins, and 2.0668 L/m² for without fins. For the still with hollow-fins and wick-fins, efficiency was improved by 13.22% and 15.70% in the case of partially submerged fins, and 17.36% and 29.34% in the case of fully submerged fins. The enhancement in the efficiency of the still with wick-fins and hollow-fins was observed higher for the case of fully submerged fins than the case of partially submerged fins.

Domestic wastewater is an important alternative source of water in the face of a growing discrepancy between water availability and demand. The use of techniques that enable the urban reuse of treated sewage is essential to make cities more sustainable and resilient to water scarcity. The main goal of this study was to evaluate the performance of an electrocoagulation-flotation system in the treatment of domestic wastewater for urban reuse. The study was performed using raw domestic wastewater samples. The electrocoagulation-flotation system was a cylindrical reactor with aluminum electrodes. The treatment conditions involved agitation at 262.5 rpm, electrical current of 1.65 A, electrolysis time of 25 min, an initial pH of 6, and inter-electrode distance of 1 cm. Overall, the electrocoagulation-flotation system was highly efficient for removal of apparent color (97.9%), chemical oxygen demand (82.9%), turbidity (95.8%), and orthophosphate phosphorous (> 98.2%). The electrocoagulation-flotation system had a consumption of electrical energy ranging from 9.5 to 13.3 kWh m⁻³, electrode mass from 294.7 to 557.0 g m⁻³, and hydrochloric acid from 4.3 to 6.6 L m⁻³. Sludge production in the system ranged from 1,125.7 to 1,835.7 g m⁻³. Treated wastewater had a satisfactory quality for several urban reuse activities. The electrocoagulation-flotation system showed potential to be used for domestic wastewater treatment for urban reuse purposes.