Sulfide and arsenic compounds removal from liquid digestate by ferric coagulation and toxicity evaluation

Advanced removal of phosphorus from urban sewage using chemical precipitation by Fe-Al composite coagulants

Phosphorus (P) removal is a significant issue in wastewater treatment. This study applies Fe-Al composite coagulant to the advanced treatment of different P forms in biological effluent. For 90% total P removal, the dosage of FeCl3-AlCl3 composite coagulant reduces by 27.19% and 43.28% than FeCl3 and AlCl3 only, respectively. Changes in effluent P forms could explain the phenomenon of composite coagulant dosage reduction. The suspended P in the effluent of composite coagulant is easier removed by precipitation than single coagulant. In this study, the hydrolysis speciations of Fe3+, Fe2+, and Al3+ at a pH range are calculated by Visual MINTEQ. Changes in the morphology of metal hydroxides correlate with P removal at pH 4-9. Besides, analyses of scanning electron microscope (SEM), Fourier transformed infrared (FTIR), and X-ray photoelectron spectroscopy (XPS) are performed on the coagulation precipitations. Fe2+ reacts directly with P to form flocs of Fe3(PO4)2, and Al2(SO4)3 assists in the sedimentation of the small-volume flocs. Al13 is a significant hydrolysis product of Al3+, and Fe and P would substitute for the peripheral AlVI of the Al13 structure to form stable Fe-O-Al covalent bonds.

Chloride converts lead slag into a bifunctional material to remove heavy metals

Efficient and safe removal of arsenic and lead from industrial wastewater is essential for ecological protection. In this study, we developed a novel method using lead slag as a purifying agent and sodium chloride as a reinforcing agent to remove arsenic and lead from industrial wastewater. Through a combination of experiments and simulations, we elucidated the mechanisms involved in this reaction. The initial concentrations of As and Pb ions in the industrial wastewater were 4333 and 188 mg/L, respectively. After the reaction at 25 °C and a pH ranging from 9.7 to 10, the concentrations of arsenic and lead were reduced to 4.9 mg/L and 0.008 mg/L, respectively, achieving a removal rate of 99.9%. Our experimental results demonstrated that Pb2+ and AsO43- ions released from the lead slag and industrial wastewater reacted with Cl- ions to form Pb5(AsO4)3Cl precipitates, thus effectively eliminating a significant amount of As and Pb species. Simulation studies indicated that Pb5(AsO4)3Cl exhibited exceptional stability below 400 °C and could be directly stored. Additionally, the lead slag, which is rich in silica, played a crucial role in removing and stabilizing As and Pb ions. Under alkaline conditions, silica encapsulated the As and Pb species, adhering to the surface of the Pb-As co-precipitates and forming dense, irregular, small particles with internal and external structures that impeded the efflux of As and Pb ions. This phenomenon was confirmed through scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The kinetics of As and Pb ion removal was consistent with the pseudo-second-order kinetic model, indicating that the removal process was primarily governed by chemical interactions. Lead slag exhibits significant potential and advantages in the removal of As and Pb. This innovative method offers an effective approach to address heavy metal contamination in industrial wastewater, thus contributing to ecological protection.

A critical review on sustainable hazardous waste management strategies: a step towards a circular economy

Globally, industrialisation and urbanisation have led to the generation of hazardous waste (HW). Sustainable hazardous waste management (HWM) is the need of the hour for a safe, clean, and eco-friendly environment and public health. The prominent waste management strategies should be aligned with circular economic models considering the economy, environment, and efficiency. This review critically discusses HW generation and sustainable management with the strategies of prevention, reduction, recycling, waste-to-energy, advanced treatment technology, and proper disposal. In this regard, the major HW policies, legislations, and international conventions related to HWM are summarised. The global generation and composition of hazardous industrial, household, and e-waste are analysed, along with their environmental and health impacts. The paper critically discusses recently adapted management strategies, waste-to-energy conversion techniques, treatment technologies, and their suitability, advantages, and limitations. A roadmap for future research focused on the components of the circular economy model is proposed, and the waste management challenges are discussed. This review stems to give a holistic and broader picture of global waste generation (from many sources), its effects on public health and the environment, and the need for a sustainable HWM approach towards the circular economy. The in-depth analysis presented in this work will help build cost-effective and eco-sustainable HWM projects.

Hyperproduction of extracellular polymeric substance in Pseudomonas fluorescens for efficient chromium (VI) absorption

A novel extracellular polymeric substance (EPS) with flocculating activity produced by Pseudomonas fluorescein isolated from soil was studied in this paper. Firstly, atmospheric and room temperature plasma (ARTP) was applied to get a mutant of P. fluorescein with higher EPS production. A mutant T4-2 exhibited a 106.48% increase in flocculating activity compared to the original strain. The maximum EPS yield from T4-2 was enhanced up to 6.42 g/L, nearly 10 times higher than the original strain on a 3.6-L bioreactor with optimized fermentation conditions. Moreover, the flocculating activity of the mutant reached 3023.4 U/mL, 10.96-fold higher than that of T4. Further identification showed that EPS from mutant T4-2 was mainly composed of polysaccharide (76.67%) and protein (15.8%) with a molecular weight of 1.17 × 105 Da. The EPS showed excellent adsorption capacities of 80.13 mg/g for chromium (VI), which was much higher than many reported adsorbents such as chitosan and cellulose. The adsorption results were described by Langmuir isotherm and pseudo-second-order kinetic model. The thermodynamic parameters (ΔG0, ΔH0 and ΔS0) revealed that the adsorption process was spontaneous and exothermic. Adsorption mechanisms were speculated to be electrostatic interaction, reduction, and chelation.

Comparative Assessment of Nitrogen Concentration Effect on Microalgal Growth and Biochemical Characteristics of Two Chlorella Strains Cultivated in Digestate

Microalgae have been recently recognized as a promising alternative for the effective treatment of anaerobic digestion effluents. However, to date, a widely applied microalgae-based process is still absent, due to several constraints mainly attributed to high ammonia concentrations and turbidity, both hindering microalgal growth. Within this scope, the purpose of the present study was to investigate the performance of two Chlorella strains, SAG 211-11b and a local Algerian isolate, under different nitrogen levels, upon ammonia stripping. The experiments were performed on cylindrical photobioreactors under controlled pH (7.8 ± 0.2) and temperature (25 ± 2 °C). Cultures were monitored for biomass production and substrate consumption. After sampling at the beginning of the stationary phase of growth (12th day) and after the maturation of the cells (24th day), an analysis of the produced biomass was conducted, in terms of its biochemical components. The local isolate grew better than C. vulgaris 211-11b, resulting in 1.43 mg L−1 biomass compared to 1.02 mg L−1 under 25 mg NH4-N L−1, while organic carbon and nutrient consumption varied between the two strains and different conditions. Concerning biomass quality, a high initial NH4-N concentration led to high protein content, while low nitrogen levels favored fatty acid (FA) accumulation, though the production of pigments was inhibited. In particular, the protein content of the final biomass was determined close to 45% of the dry weight in all experimental scenarios with adequate nitrogen, while proteins decreased, and the fatty acids approached 20% in the case of the local isolate grown on the substrate with the lowest initial ammonium nitrogen (25 mg NH4-N L−1). The novelty of the present work lies in the comparison of a microalga with industrial applications against a local isolate of the same species, which may prove to be even more robust and profitable.

Understanding the by-product formation potential during phenol oxidation from in-situ electro-generated radicals by microalgae harvesting

Advanced oxidation processes have gained colossal attention owing to the prospect of accessible mineralization, but by-product formation and its toxicity evaluation are still inconclusive. The present study demonstrated the performance of electrochemical oxidation process supported with graphite electrodes for the oxidation of phenol from modulated coke oven wastewater. The results suggested that the hydrogen peroxide along with the in-situ synthesized oxidizing agents has the ability to increase the phenol mineralization 1.5 times and by-product toxicity potential on microalgae, Scenedesmus sp. CBIIT(ISM) also revealed that chlorophyll-a synthesis has increased after the electro-oxidation process in coke oven wastewater. The experimental results for phenol mineralization and by-product formation were validated using a mass spectrophotometer.