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A special issue of Water (ISSN 2073-4441). This special issue belongs to the section "Wastewater Treatment and Reuse".

Deadline for manuscript submissions: closed (28 February 2023) | Viewed by 38596

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Dr. Ivar Zekker

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Institute of Chemistry, University of Tartu, Ravila 14a, 50411 Tartu, Estonia
Interests: anammox; nitrogen removal; adsorbents; Langmuir; dye removal; wastewater treatment and marine chemistry
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Dear Colleagues,

Wastewater and waste sludge needs efficient treatment technologies, which have low energy input and enable recovering different components from waste. Removal of nitrogen from wastewater to acceptable thresholds is essential for the protection of water bodies from algal blooms and subsequent eutrophication, which may lead to reduced DO concentration and cause death of life forms. NO₂^-/NO₃^- accumulation in humans is traceable to a host of health problems, including cancer. One of the major advancements in the early 1990s was the discovery of anaerobic ammonium oxidation (anammox), which occurs under anaerobic conditions and is characterized by the autotrophic oxidation of ammonium to dinitrogen gas with nitrite serving as an electron acceptor. Waste sludge is produced during water treatment, containing reusable components, such as heavy metals. Biotechnology is considered as an energy-saving and environmentally friendly alternative to pyrometallurgy for the recovery of metals from different residual sludge and compost. Heavy metals are also represented in printed circuit boards (PCBs). However, bacteria-based metal biorecovery processes have their limitations for gold- and platinum-group metals, which can only be solubilized by cyanogenic bacteria producing CN^-(or, alternatively, by less toxic thiosulfate). Well-adapted fungal consortia can achieve approximately the same degree of metal recovery as bacteria, with lower energy consumption at the expense of agitation.

Dr. Ivar Zekker
Guest Editor

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Keywords

Wastewater
Anammox
Mainstream treatment
Heavy metals treatment
Heavy metals recovery

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Research

17 pages, 3965 KiB

Open AccessArticle

The Chemically Modified Leaves of Pteris vittata as Efficient Adsorbent for Zinc (II) Removal from Aqueous Solution

by Qaiser Khan, Muhammad Zahoor, Syed Muhammad Salman, Muhammad Wahab, Muhammad Talha, Abdul Waheed Kamran, Yousaf Khan, Riaz Ullah, Essam A. Ali and Abdul Bari Shah

Water 2022, 14(24), 4039; https://doi.org/10.3390/w14244039 - 11 Dec 2022

Cited by 5 | Viewed by 2097

Abstract

High concentrations of zinc along with other metals are released by steel mills, and this has a number of negative effects on organism health; most notably, neurological symptoms have been recorded with a high risk of brain atrophy. In the current study, Zn (II) was eliminated from steel mill effluent, utilizing chemically processed Pteris vittata plant leaves as a biosorbent. Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermal gravimetric analysis (TGA), and energy dispersive X-ray spectroscopy (EDX) were applied to characterize the chemically modified Pteris vittata leaves, from now onward abbreviated as CMPVL. In order to identify the ideal parameter, batch studies were conducted varying a single parameter affecting the biosorption process at a time, including variations in temperature (293–323 K), initial metal concentration (20–300 mg/L), and adsorbent doses (0.01–0.12 g), pH (2–8), as well as contact time (10–140 min). To describe the isothermal experimental results, a number of models were used including Freundlich, Langmuir, Temkin, Jovanovich, and Harkins–Jura. Among these models, the Langmuir model provided a significant fit to the isotherm data with an R² of 0.9738. The kinetics data were fitted to the pseudo first order, pseudo second order, power function, Natarajan–Khalaf, and intraparticle diffusion models. The highest R² (0.9976) value was recorded for the pseudo second order model. Using the Langmuir isotherm, the highest uptake ability (84.74 mg/g) of Zn was recorded. The thermodynamic investigation, carried out at various temperatures, led to the conclusion that the biosorption process was exothermic and spontaneous in nature. The CMPVL, thus, has the potential to function well as an alternative to existing carbon-based adsorbents in the effective elimination of zinc from aquatic environments. Full article

(This article belongs to the Special Issue Recent Advances in Bioreactors and Heavy Metals Removal/Recovery during Waste Post-treatment)

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17 pages, 4217 KiB

Open AccessFeature PaperArticle

Statistical Modeling and Optimization of Process Parameters for 2,4-Dichlorophenoxyacetic Acid Removal by Using AC/PDMAEMA Hydrogel Adsorbent: Comparison of Different RSM Designs and ANN Training Methods

by Irvan Dahlan, Emillia Eizleen Md Azhar, Siti Roshayu Hassan, Hamidi Abdul Aziz and Yung-Tse Hung

Water 2022, 14(19), 3061; https://doi.org/10.3390/w14193061 - 28 Sep 2022

Cited by 5 | Viewed by 1853

Abstract

In this study, the response surface methodology (RSM) and artificial neural network (ANN) were employed to study the adsorption process of 2,4-dichlorophenoxyacetic acid (2,4-D) by using modified hydrogel, i.e., activated carbon poly(dimethylaminoethyl methacrylate) (AC/PDMAEMA hydrogel). The effect of pH, the initial concentration of 2,4-D and the activated carbon content on the removal of 2,4-D and adsorption capacity were investigated through the face-centered composite design (FCCD), optimal design and two-level factorial design. The response surface plot suggested that higher removal of 2,4-D and adsorption capacity could be achieved at the higher initial concentration of 2,4-D and lower pH and activated carbon content. The modeling and optimization for the adsorption process of 2,4-D were also carried out by different design methods of RSM and different training methods of ANN. It was found that among the three design methods of RSM, the optimal design has the highest accuracy for the prediction of 2,4-D removal and adsorption capacity (R² = 0.9958 and R² = 0.9998, respectively). The numerical optimization of the optimal design found that the maximum removal of 2,4-D and adsorption capacity of 65.01% and 65.29 mg/g, respectively, were obtained at a pH of 3, initial concentration of 2,4-D of 94.52 mg/L and 2.5 wt% of activated carbon. Apart from the optimization of process parameters, the neural network architecture was also optimized by trial and error with different numbers of hidden neurons in the layers to obtain the best performance of the response. The optimization of the neural network was performed with different training methods. It was found that among the three training methods of the ANN model, the Bayesian Regularization method had the highest R² and lowest mean square error (MSE) with the optimum network architecture of 3:9:2. The optimum condition obtained from RSM was also simulated with the optimized neural network architecture to validate the responses and adequacy of the RSM model. Full article

(This article belongs to the Special Issue Recent Advances in Bioreactors and Heavy Metals Removal/Recovery during Waste Post-treatment)

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12 pages, 2518 KiB

Open AccessArticle

Enhanced Adsorption of Rhodamine B on Biomass of Cypress/False Cypress (Chamaecyparis lawsoniana) Fruit: Optimization and Kinetic Study

by Salma Gul, Hajera Gul, Maria Gul, Rozina Khattak, Gul Rukh, Muhammad Sufaid Khan and Hani Amir Aouissi

Water 2022, 14(19), 2987; https://doi.org/10.3390/w14192987 - 23 Sep 2022

Cited by 19 | Viewed by 2314

Abstract

Many industries use various dyes to beautify their products and discharge the waste into the water without proper treatment. Such wastewater is not only dangerous for aquatic life but it is also toxic to human life and can cause numerous problems, such as skin diseases, and some dyes are carcinogenic or even mutagenic as well. Rhodamine-B (RhB) is one of those synthetic organic dyes which is widely used in textile, paper making, leather manufacturing, stained glass work, cosmetics, and many other industries owing to its high tinting strength, high stability, and bright colour. Therefore, it is essential to either remove or reduce its concentration before releasing it into aquatic streams, as well as to minimize or control the cause of several diseases. Several physical and chemical methods have been used for the removal of different dyes from wastewater; nevertheless, adsorption is one of the best techniques used for the removal of dyes due to its high efficiency and low cost. In this regard, we used Chamaecyparis lawsoniana (C. lawsoniana) fruit as a bio-adsorbent for the removal of RhB from an aqueous solution. An 85.42% dye adsorption was achieved at optimized conditions (pH 2, 40 ppm initial dye concentration, 105 min, and 50 mg adsorbent). Adsorption occurs by pseudo-second-order kinetics, according to kinetic studies. Several samples from various sources, including tap water, distilled water, river water, and filtered river water, were tested for RhB removal, and the study revealed good results even in river water. Thus, C. lawsoniana fruit can be used for its real-world application. Full article

(This article belongs to the Special Issue Recent Advances in Bioreactors and Heavy Metals Removal/Recovery during Waste Post-treatment)

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12 pages, 2138 KiB

Open AccessFeature PaperArticle

Efficient Removal of Methyl Red Dye by Using Bark of Hopbush

by Salma Gul, Mansha Kanwal, Raina Aman Qazi, Hajera Gul, Rozina Khattak, Muhammad Sufaid Khan, Fatima Khitab and Andrey E. Krauklis

Water 2022, 14(18), 2831; https://doi.org/10.3390/w14182831 - 11 Sep 2022

Cited by 32 | Viewed by 4036

Abstract

Methyl red (MR) dye, one of the azo dyes, is mutagenic and its persistence has negative effects on the environment and people’s health. The current work is the first to demonstrate that methyl red dye can be removed effectively and sustainably, utilizing biomass derived from the bark of the Dodonaea viscosa (Hopbush) plant. The Hopbush bark shows effective adsorption of MR, upto 73%, under optimized conditions in an aqueous medium. The experimental conditions were optimized by examining the effect of time, initial dye concentration, pH and ionic strength on the adsorption process in an aqueous medium. Maximum (i.e., 73%) adsorption of MR removal (500 ppm) was observed in highly acidic conditions (pH = 1) at a contact time of 75 min. The pseudo-second-order kinetic model and Freundlich adsorption isotherm appeared to be the most appropriate for characterizing the MR’s adsorption onto the bark of the D. viscosa plant. Furthermore, it was shown that bark powder outperformed animal charcoal, silica gel, and powdered flowers, as well as the leaves of the same species, in terms of adsorption capacity. Thus, a natural adsorbent that is inexpensive and readily available—the bark of the D. viscosa plant—can be used to effectively remove harmful dyes from contaminated water and protect water resources from harmful pollutants. Full article

(This article belongs to the Special Issue Recent Advances in Bioreactors and Heavy Metals Removal/Recovery during Waste Post-treatment)

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17 pages, 4137 KiB

Open AccessArticle

Removal of Chromium (VI) from the Steel Mill Effluents Using the Chemically Modified Leaves of Pteris vittata as Adsorbent

by Qaiser Khan, Muhammad Zahoor, Syed Muhammad Salman, Muhammad Wahab, Muhammad Talha and Abdul Waheed Kamran

Water 2022, 14(17), 2599; https://doi.org/10.3390/w14172599 - 23 Aug 2022

Cited by 3 | Viewed by 2072

Abstract

Chromium (Cr), a metal that is released in appreciable amounts from the steel industry into water bodies, is not only the main causative agent of lung cancer in human but also negatively affects the metabolic activities of plants. Keeping in view the hazardous effects of Cr(VI), the present study was aimed to eliminate it from industrial effluents of steel mills installed in Dargai District Malakand, Pakistan, using chemically modified Pteris vittata plant leaves as an adsorbent. The instrumental techniques such as FTIR, surface area analysis, SEM, TGA and EDX were used to evaluate surface functionality, morphology, thermal stability and elemental composition of the modified leaves. To identify the ideal conditions for the biosorption process, batch adsorption tests were carried out under varied conditions of pH, contact time, initial metal concentration, biosorbent dose, as well as temperature. Various models, such as those of Freundlich, Jovanovich, Temkin, Langmuir, and Harkins–Jura, were utilized to explain the isothermal experimental data. The high value of R² (0.991) was exhibited by the Langmuir model. Pseudo-first-order, power function, pseudo-second-order, intraparticle diffusion, and Natarajan–Khalaf models were employed to obtain an insight into kinetics of the process. The highest R² value, close to unity was recorded with pseudo-second order. At pH = 2, the best elimination of Cr was observed with maximum uptake capacity q_max(66.6 mg/g) as calculated from the Langmuir isotherm. The thermodynamic analysis, which was conducted at different temperatures, showed that the nature of this sorption process was exothermic and spontaneous. The modified leaves-based biosorbent could be used as an alternative adsorbent for effective Cr elimination from water, and its use could be extended to other heavy metals and organic pollutants as well, and further experimentation are needed in this regard. Full article

(This article belongs to the Special Issue Recent Advances in Bioreactors and Heavy Metals Removal/Recovery during Waste Post-treatment)

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16 pages, 5030 KiB

Open AccessFeature PaperArticle

Biological Mineralization of Methyl Orange by Pseudomonas aeruginosa

by Asad Ullah Khan, Muhammad Zahoor, Mujaddad Ur Rehman, Abdul Bari Shah, Ivar Zekker, Farhat Ali Khan, Riaz Ullah, Ghadeer M. Albadrani, Roula Bayram and Hanan R. H. Mohamed

Water 2022, 14(10), 1551; https://doi.org/10.3390/w14101551 - 12 May 2022

Cited by 28 | Viewed by 4722

Abstract

Due to its recalcitrant and carcinogenic nature, the presence of methyl orange (MO) in the environment is a serious threat to human and animal life and is also toxic to plants. MO being recalcitrant cannot be effectively reclaimed from industrial effluents through physical and chemical approaches. Biological methods on the other hand have the potential to degrade such dyes because of their compatibility with nature and low chances of adverse effects on the environment. Bacteria, due to their fast growth rate and capability of surviving in extreme environments can effectively be used for this purpose. In the current research study, Pseudomonas aeruginosa was isolated and characterized using 16rRNA from textile wastewater. In the preliminary tests it was found that Pseudomonas aeruginosa has the ability to degrade and mineralize methyl orange effectively. The physicochemical conditions were then optimized, in order to get maximum degradation of MO which was achieved at 37 °C, a pH of 7, a low salt concentration of 0.1 g/15 mL, a high carbon source of 0.6 g/15 mL, and 72 h experimental time. In a single set of experiments where all these optimum conditions were combined, 88.23% decolorization of the selected dye was achieved. At the end of the experimental cycle, the aliquots were homogenized and filtered. The filtrates were subjected to FTIR and GC-MS analysis where azo linkage breaking was confirmed from the FTIR spectra. The filtrates were then extracted with ethyl acetate and then passed through a silica gel column. On the basis of Rf value (TLC plates used) similar fraction were combined which were then subjected to NMR analysis. The compounds detected through GC-MS, peaks were not observed in proton and C-13 NMR. Instead, solvent and some impurity peaks were present, showing that complete mineralization of the dye had occurred due to the action of different bacterial enzymes such as azoreductase, peroxidases, and classes on MO. The prosed mechanism of complete mineralization is based on spectral data that needs to be verified by trapping the individual step products through the use of appropriate inhibitors of individual enzymes. Full article

(This article belongs to the Special Issue Recent Advances in Bioreactors and Heavy Metals Removal/Recovery during Waste Post-treatment)

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20 pages, 4845 KiB

Open AccessFeature PaperArticle

Adsorption-Membrane Hybrid Approach for the Removal of Azithromycin from Water: An Attempt to Minimize Drug Resistance Problem

by Muhammad Wahab, Muhammad Zahoor, Syed Muhammad Salman, Abdul Waheed Kamran, Sumaira Naz, Juris Burlakovs, Anna Kallistova, Nikolai Pimenov and Ivar Zekker

Water 2021, 13(14), 1969; https://doi.org/10.3390/w13141969 - 18 Jul 2021

Cited by 50 | Viewed by 4795

Abstract

In this study, activated carbon (AC) and magnetic activated carbon (MAC) were prepared from Dalbergia sissoo sawdust for the removal of antibiotic Azithromycin (AZM) from aqueous solution. The effect of initial concentration, contact time, pH, adsorbent dosage, and the temperature were investigated for both the adsorbents. The optimum AZM concentration, contact time, pH and adsorbents dosages were found to be 80 mg/L, 120 min, 6 and 7 (pH, respectively, for AC and MAC), and 0.1 g (for both AC and MAC), respectively. The isothermal data of both sets of experiments correlated well with the Langmuir isotherm model, while the kinetic data with the pseudo-second-order model. The adsorption of AZM on both adsorbents was found to be favorable, which is evident in the values of the thermodynamic parameters (ΔH = −26.506 and −24.149 KJ/mol, ΔS = 91.812 and 81.991 J/mol K, respectively, for AC and MAC). To evaluate the effect of AC and MAC on the membrane parameters, a continuous stirred reactor was connected with ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO) membranes. High % retention and improved permeate flux (around 90%) were obtained for AC/UF, AC/NF AC/RO, MAC/UF, MAC/NF, and MAC/RO treatments. The percent retention of AZM observed for AC/UF, AC/NF AC/RO was higher than MAC/UF, MAC/NF, and for MAC/RO hybrid processes due to greater surface area of AC than MAC. Full article

(This article belongs to the Special Issue Recent Advances in Bioreactors and Heavy Metals Removal/Recovery during Waste Post-treatment)

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13 pages, 8177 KiB

Open AccessEditor’s ChoiceArticle

Palladium-Supported Zirconia-Based Catalytic Degradation of Rhodamine-B Dye from Wastewater

by Salma Jabeen, Muhammad Sufaid Khan, Rozina Khattak, Ivar Zekker, Juris Burlakovs, Sergio S. dC Rubin, Makarand Madhao Ghangrekar, Anna Kallistova, Nikolai Pimenov, Muhammad Zahoor and Gul Shahzada Khan

Water 2021, 13(11), 1522; https://doi.org/10.3390/w13111522 - 28 May 2021

Cited by 46 | Viewed by 3672

Abstract

The catalytic activity of Pd/ZrO₂ was studied in terms of the degradation of rhodamine-B dye in the presence of hydrogen peroxide. Pd/ZrO₂ was prepared by impregnation method, calcined at 750 °C and characterized by XRD, SEM and EDX. The catalyst showed good catalytic activity for dye degradation at 333 K, using 0.05 g of the catalyst during 5 h. The reaction kinetics followed the pseudo-first order kinetics. The Freundlich, Langmuir and Temkin isotherms were applied to the data and the best fit was obtained with Freundlich isotherm. Thermodynamic parameters, like ΔH, ΔG and ΔS were also calculated. The negative values of ΔH (−291.406 KJ/mol) and Gibbs free energy (ΔG) showed the exothermic and spontaneous nature of the process. The positive ΔS (0.04832 KJ/mol K) value showed suitable affinity of catalyst for dye degradation. The catalyst was very stable, active and was easily separated from the reaction mixture by filtration. It can be concluded from the results that the prepared catalyst could be effectively used in dyes degradation/removal from water subjected to further validation and use for various dyes. Full article

(This article belongs to the Special Issue Recent Advances in Bioreactors and Heavy Metals Removal/Recovery during Waste Post-treatment)

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15 pages, 21523 KiB

Open AccessArticle

Preparation of Activated Carbon from the Wood of Paulownia tomentosa as an Efficient Adsorbent for the Removal of Acid Red 4 and Methylene Blue Present in Wastewater

by Sultan Alam, Muhammad Sufaid Khan, Wahida Bibi, Ivar Zekker, Juris Burlakovs, Makarand M. Ghangrekar, Gourav Dhar Bhowmick, Anna Kallistova, Nikolai Pimenov and Muhammad Zahoor

Water 2021, 13(11), 1453; https://doi.org/10.3390/w13111453 - 22 May 2021

Cited by 50 | Viewed by 5849

Abstract

Paulownia tomentosa, a woody plant that is widely found in Pakistan and in other regions of the world, was used as a raw material to prepare activated carbon using chemical and physical activation methods. Adsorption of the dyes- acid red 4 and methylene blue onto the prepared activated carbon were analyzed by batch experiments. The impacts of different adsorption parameters such as pH, temperature, contact time, initial dye concentration and adsorbent dosage were also evaluated. Equilibrium data were fitted into various isotherm models such as: Langmuir, Temkin and Freundlich. High regression values were achieved with Langmuir isotherm model. Different kinetic adsorption models such as pseudo-first-order, pseudo-second-order and intra-particle diffusion model models were applied. The adsorption kinetics was found to be best-fitted into pseudo-second-order kinetic model. The optimum pH for acid red 4 was around 1 while for methylene blue it was 8. The optimum adsorbent dosage was 0.3 g for both dyes used. The activation energy (E_a) values were 30.57 and 3.712 kJ/mol, respectively for acid red 4 and methylene blue while the enthalpy (ΔH) and entropy (ΔS) values were correspondingly as 24.88/1.1927 kJ/mol and −2843.32/−0.329 J·mol/K for the mentioned dyes. The experimental result showed that the prepared activated carbon was the best in the removal of acid red 4 and methylene blue from aqueous media and therefore, could be preferably used as cheap adsorbent in wastewater treatment. Full article

(This article belongs to the Special Issue Recent Advances in Bioreactors and Heavy Metals Removal/Recovery during Waste Post-treatment)

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16 pages, 1112 KiB

Open AccessFeature PaperArticle

Start-Up of Anammox SBR from Non-Specific Inoculum and Process Acceleration Methods by Hydrazine

by Ivar Zekker, Oleg Artemchuk, Ergo Rikmann, Kelvin Ohimai, Gourav Dhar Bhowmick, Makarand Madhao Ghangrekar, Juris Burlakovs and Taavo Tenno

Water 2021, 13(3), 350; https://doi.org/10.3390/w13030350 - 30 Jan 2021

Cited by 65 | Viewed by 5616

Abstract

Biological nutrient removal from wastewater to reach acceptable levels is needed to protect water resources and avoid eutrophication. The start-up of an anaerobic ammonium oxidation (anammox) process from scratch was investigated in a 20 L sequence batch reactor (SBR) inoculated with a mixture of aerobic and anaerobic sludge at 30 ± 0.5 °C with a hydraulic retention time (HRT) of 2–3 days. The use of NH₄Cl, NaNO₂, and reject water as nitrogen sources created different salinity periods, in which the anammox process performance was assessed: low (<0.2 g of Cl⁻/L), high (18.2 g of Cl⁻/L), or optimum salinity (0.5–2 g of Cl⁻/L). Reject water feeding gave the optimum salinity, with an average nitrogen removal efficiency of 80%, and a TNRR of 0.08 kg N/m³/d being achieved after 193 days. The main aim was to show the effect of a hydrazine addition on the specific anammox activity (SAA) and denitrification activity in the start-up process to boost the autotrophic nitrogen removal from scratch. The effect of the anammox intermediate hydrazine addition was tested to assess its concentration effect (range of 2–12.5 mg of N₂H₄/L) on diminishing denitrifier activity and accelerating anammox activity at the same time. Heterotrophic denitrifiers’ activity was diminished by all hydrazine additions compared to the control; 5 mg of N₂H₄/L added enhanced SAA compared to the control, achieving an SAA of 0.72 (±0.01) mg N/g MLSS/h, while the test with 7.5 mg of N₂H₄/L reached the highest overall SAA of 0.98 (±0.09) mg N g/MLSS/h. The addition of trace amounts of hydrazine for 6 h was also able to enhance SAA after inhibition by organic carbon source sodium acetate addition at a high C/N ratio of 10/1. The start-up of anammox bacteria from the aerobic–anaerobic suspended biomass was successful, with hydrazine significantly accelerating anammox activity and decreasing denitrifier activity, making the method applicable for side-stream as well as mainstream treatment. Full article

(This article belongs to the Special Issue Recent Advances in Bioreactors and Heavy Metals Removal/Recovery during Waste Post-treatment)

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