Performance intensification of the coagulation process in drinking water treatment

Surface water pollution has increased, owing to industrial development and population growth. Consequently, it is important to find alternative drinking water treatment strategies, which cater for changes in the quality of raw water. This study compared the efficiency of different coagulants in treating raw water that feeds a drinking water treatment plant (WTP). Using jar testing equipment and a number of physicochemical parameters, an investigation was conducted to establish optimum conditions for aluminium chloride (A),  ferric chloride (B), and chitosan (C), and their performance compared with aluminium sulphate (D), which is the coagulant used at the WTP. The turbidity removal efficiencies for the single coagulants were in the order: B (95.7%) > A (94.7%) > C (94.4%), at optimum coagulant doses of 60, 50, and 0.6 mg/L, respectively. The coagulants achieved high removal efficiencies for turbidity, total dissolved solids (TDS), ultraviolet absorbance at 254 nm (UV254) and conductivity under acidic conditions. For dual coagulants, there was a  gradual increase in the removal efficiencies of the tested parameters with increasing pH. Combined coagulants were more effective compared to single coagulants, with highest removal efficiencies being exhibited by the A/C combination. Overall, the coagulants proved to be suitable alternatives to D, since they had comparable performances

Visible light photodegradation of methyl orange and Escherichia coli O157:H7 in wastewater

Water pollution due to dyes and pathogens is problematic worldwide, and the disease burden is higher in low-income countries where water treatment facilities are usually inadequate. Thus the development of low-cost techniques for the removal of dyes and pathogens in aquatic systems is critical for safeguarding human and ecological health. In this work, we report the fabrication and use of a photocatalyst derived from waste from coal combustion in removing dyes and pathogens from wastewater. Higher TiO2 loading of the photocatalyst increased the removal efficiency for methyl orange (95.5%), and fluorine-doping improved the disinfection efficacy from 76% to 95% relative to unmodified material. Overall, the work effectively converted hazardous waste into a value-added product that has potential in point-of-use water treatment. Future research should focus on upscaling the technique, investigating the fate of the potential of the photocatalysts for multiple reuse, and the recovery of TiO2 in treated water. Significance: • The study provides a pathway for the fabrication of a value-added product from coal fly ash waste.• The use of the proposed nanocomposite material for wastewater treatment represents a potentially affordable, simple, and sustainable technology for point-of-use water treatmen

Natural organic matter in aquatic systems – a South African perspective

Natural organic matter (NOM) is a complex heterogeneous mixture of humic (HS) and non-humic substances which are widespread in the aquatic environment. Other constituents are amino acids, aliphatic and aromatic hydrocarbons containing oxygen, nitrogen and hydroxyl groups. It is the combination and proportions of these motifs which give NOM its overall polarity and reactivity. Its main origins include soils, residues of fauna and flora, microbial excrements and anthropogenic faecal loads, agriculture activities and urban landscapes. Due to the different origins of the precursor material and the extent of transformation it undergoes, the composition of NOM in different water bodies varies. Characterization methods for NOM can be divided into three broad categories namely: (i) direct measuring methods, which measure the amount of organic matter in the sample; (ii) spectrometric methods, which measure the amount of radiation absorbed and or released by chromophores; and (iii) fractionation methods, which separate NOM according to size and polarity. South Africa has 6 distinct water quality regions, and each region has a unique NOM character and quantity. Existing water treatment plants do not remove NOM to levels low enough to inhibit the formation of disinfection by-products (DBPs). Currently, research is focusing more on the use of alternative techniques for NOM removal; these include advanced oxidation processes (AOPs), nanomaterials, and ceramic membranes. While NOM is well studied in other parts of the world, to the best of our knowledge, there is no state-of-the-art investigation of the occurrence and removal of NOM in South African source waters. This review aims at (i) synthesizing literature on the nature, occurrence and ecological impact of NOM, (ii) evaluating the removal of NOM in the six different water quality regions of South Africa, and (iii) suggesting novel approaches that can be used to remove NOM in South Africa.Keywords: advanced oxidation, ceramic membranes, disinfection byproducts, treatability, water treatmen

Investigating the fate of natural organic matter at a drinking water treatment plant in South Africa using optical spectroscopy and chemometric analysis

The removal dynamics of biodegradable dissolved organic carbon (BDOC) and natural organic matter (NOM) polarity fractions at a water treatment plant (WTP) in South Africa was studied using UV-Vis absorbance, fluorescence excitation-emission matrix, and two-dimensional synchronous fluorescence spectroscopy (SFS). This study gave insights into the transformation of NOM due to treatment processes. The objectives of the study were: (i) to use chemometric analysis and two-dimensional SFS correlations to investigate the evolution of NOM arising from treatment processes, and (ii) to access the chemical profile dynamics of polarity and BDOC fractions throughout the treatment train. The UV254 absorbance, which indicates aromaticity, reduced by 45% along the WTP. Gaussian fitting of UV-Vis data showed a decreasing trend in intensity and number of bands along the treatment process. The removal efficiency of NOM components followed the order: humiclike (HL) > tyrosine-like (TYL) > fulvic-like (FL) > tryptophan-like (TPL) > microbial-like (MBL). At the source, the relative distribution of the hydrophobic (HPO), hydrophilic (HPI), and transphilic (TPI) fractions was 45%, 31%, and 24%, respectively. The HPI was recalcitrant to treatment, and the TYL component of the HPI fraction was conjectured to be a disinfection byproduct limiting reagent. The HL and FL components of the BDOC fraction were the major substrates for bacterial growth. According to two-dimensional-SFS correlation, TYL, TPL, and MBL varied concurrently across the treatment stages. Used for the first time in South Africa, the robustness of a multi-dimensional approach of optical methods coupled with chemometric tools for the assessment of the fate of NOM along the treatment processes was revealed by this study.Keywords: biodegradable dissolved organic, carbon, natural organic matter, optical spectroscopy, two-dimensional correlations, water treatmen

Insects, Rodents, and Pets as Reservoirs, Vectors, and Sentinels of Antimicrobial Resistance

This paper reviews the occurrence of antimicrobial resistance (AMR) in insects, rodents, and pets. Insects (e.g., houseflies, cockroaches), rodents (rats, mice), and pets (dogs, cats) act as reservoirs of AMR for first-line and last-resort antimicrobial agents. AMR proliferates in insects, rodents, and pets, and their skin and gut systems. Subsequently, insects, rodents, and pets act as vectors that disseminate AMR to humans via direct contact, human food contamination, and horizontal gene transfer. Thus, insects, rodents, and pets might act as sentinels or bioindicators of AMR. Human health risks are discussed, including those unique to low-income countries. Current evidence on human health risks is largely inferential and based on qualitative data, but comprehensive statistics based on quantitative microbial risk assessment (QMRA) are still lacking. Hence, tracing human health risks of AMR to insects, rodents, and pets, remains a challenge. To safeguard human health, mitigation measures are proposed, based on the one-health approach. Future research should include human health risk analysis using QMRA, and the application of in-silico techniques, genomics, network analysis, and ’big data’ analytical tools to understand the role of household insects, rodents, and pets in the persistence, circulation, and health risks of AMR

Photocatalytic Activity and Reusability of F, Sm³⁺ Co-Doped TiO₂/MWCNTs Hybrid Heterostructure for Efficient Photocatalytic Degradation of Brilliant Black Bis-Azo Dye

A global freshwater pollution catastrophe is looming due to pollutants of emerging concern (PECs). Conventional water treatment methods are limited in removing PECs such as pharmaceuticals and dye house effluent from aquatic systems. This study provides an effective potential solution by developing an innovative wastewater treatment method based on solar-light-responsive semiconductor-based photocatalysts. A sol-gel synthesis technique was used to produce Fluorine-Sm3+ co-doped TiO2 (0.6% Sm3+) (FST3) photocatalysts. This was followed by loading multi-walled carbon nanotubes (MWCNTs) in the range of 0.25 to 1 wt% into the FST3 matrix. Solid state UV-visible spectroscopy measurements showed a bathochromic shift into the visible light region after the co-doping of TiO2, whereas XRD analysis confirmed the presence of predominantly anatase polymorphs of TiO2. The FT-IR and EDX results confirmed the presence of the F and Sm3+ dopants in the synthesised photocatalysts. XRD and TEM measurements confirmed that the crystallite sizes of all synthesised photocatalysts ranged from 12–19 nm. The resultant photocatalysts were evaluated for photocatalytic degradation of Brilliant Black BN bis-azo dye in aqueous solution under simulated solar irradiation. FST3 completely degraded the dye after 3 h, with a high apparent rate constant (Ka) value (2.73 × 10−2 min−1). The degree of mineralisation was evaluated using the total organic carbon (TOC) technique, which revealed high TOC removal (82%) after 3 h and complete TOC removal after 4 h. The incorporation of F improved the optical properties and the surface chemistry of TiO2, whereas Sm3+ improved the quantum efficiency and the optical properties. These synergistic effects led to significantly improved photocatalytic efficiency. Furthermore, incorporating MWCNTs into the F and Sm3+ co-doped TiO2 (0.6% Sm3+) improved the reaction kinetics of the FST3, effectively reducing the reaction time by over 30%. Recyclability studies showed that after 5 cycles of use, the FST3/C1 degradation efficiency dropped by 7.1%, whereas TiO2 degradation efficiency dropped by 33.4% after the same number of cycles. Overall, this work demonstrates a sustainable and efficient dye-removal technique

Abatement of humic acid from aqueous solution using a carbonaceous conjugated microporous polymer derived from waste polystyrene

Humic acid (HA) is a major constituent of natural organic matter (NOM) found in water systems. Although NOM generally does not have any known harmful effects to humans, it imparts repulsive organoleptic properties to water, reacts with disinfectants to produce toxic products, and interferes with the efficiency of water treatment processes. The removal of NOM and related compounds from water is therefore important to render water potable and suitable for other applications. In this work, a hitherto unreported carbonaceous conjugated microporous polymer (CCMP) prepared through the organic-polymeric-precursor-controlled carbonization of hypercrosslinked post-consumer waste polystyrene (WPS) was evaluated for its capacity to remove HA from synthetic wastewater. This advanced material retained the morphology of the precursor material, while its porosity and chemical integrity were significantly improved. The approach is an environmentally friendly way of handling WPS while at the same time remediating NOM-contaminated water. Overall, with a maximum adsorption capacity of 340 mg/g in batch experiments, and a maximum initial removal rate of 95.7% in column experiments, the results showed that CCMP can be used for the remediation of HA-contaminated water at high pH.College of Engineering, Science and Technolog

Removal of dissolved organic matter from raw water using zero valent iron

Please follow the DOI link at the top of this record to access the full-text on the publisher's websiteThere are a limited number of potentially scalable low-cost treatment methods for removing organic pollutants in water. In this study, a magnetic zero valent iron-carbonaceous conjugated microporous polymer nanocomposite (ZVI-CCMP) was synthesized from ZVI and waste polystyrene via the liquid phase reduction method, and used in a batch system for the removal of dissolved organic carbon (DOC) in water from a water treatment plant (WTP) in Pretoria, South Africa. The results were compared to the DOC removal efficiency of the WTP. The surface morphology of the nanocomposites as characterized using scanning electron microscopy showed heterogeneous ZVI nanastructures dispersed on the CCMP surface. Fourier transform infrared spectroscopy showed that the functional groups on the ZVI-CCMP surface were predominantly C]C and C-C from quinonoid motifs, aliphatic chain conjugation, and C-S groups originating from the introduced sulphonic moieties. Batch experiment data indicated that ZVI-CCMP adsorbed significantly (p=0.01) more DOC than ZVI, demonstrating the synergistic effect of ZVI activation. Whereas the WTP removed up to 24.3% DOC, ZVI and ZVI-CCMP removed 64 and 75%, respectively after a contact time of 30 min. Thus, compared to the processes used by the WTP, batch experiments using ZVI and ZVI-CCMP were 41 (p=0.00) and 52% (p=0.01) superior, respectively, demonstrating the potential of these materials to be upscaled for pilot and real life applications. While polystyrene has been used in the ZVI composites and the synthesis and evaluation of ZVI decorated carbon based materials has been widely studied, ZVI-CCMP based materials have not been reported. The objectives were: (1) to synthesise and characterise ZVI-CCMP nanocomposites; (2) to evaluate the removal of DOC in real water samples by ZVI and ZVI-CCMP; and (3) to compare the relative efficiency of ZVI-CCMP to that of the water treatment process through the measurement of DOC. Using CCMP nanocomposites to treat water is potentially a low-cost and environmentally friendly alternative for reducing the adverse public health and environmental risks associated with waste polystyrene.College of Engineering, Science and Technolog