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14 pages, 2348 KiB

Open AccessArticle

Exploring Optimal Pretreatment Approaches for Enhancing Biohydrogen and Biochar Production from Azolla filiculoides Biomass

by Mohamed El-Qelish, Saber A. El-Shafai and Mohamed Mahmoud

Water 2024, 16(21), 3048; https://doi.org/10.3390/w16213048 - 24 Oct 2024

Viewed by 612

Abstract

Mitigating the irreversible consequences of climate change necessitates the application of sustainable energy resources. Hereby, we investigated the biological anaerobic fermentation of Azolla filiculoides biomass for biohydrogen production as a clean renewable energy source. Azolla filiculoides is a widely growing aquatic plant in polluted [...] Read more.

Mitigating the irreversible consequences of climate change necessitates the application of sustainable energy resources. Hereby, we investigated the biological anaerobic fermentation of Azolla filiculoides biomass for biohydrogen production as a clean renewable energy source. Azolla filiculoides is a widely growing aquatic plant in polluted freshwater streams. However, the high non-biodegradable organic matter content in Azolla filiculoides biomass remains challenging in efficiently producing renewable energy, especially when it is being used as the sole donor substrate. In order to overcome this challenge, different pretreatment scenarios (namely, alkali, autoclaving, and ultrasonication) have been employed for enhancing the hydrolysis of Azolla filiculoides biomass to maximize the anaerobic fermentation and, consequently, the biohydrogen production potential. The biohydrogen production potential was 250.5, 398, 414.5, and 439.5 mL-H₂, giving a hydrogen yield of 60.1, 89.6, 92.9, and 107.9 mL-H₂/g-VS, respectively. Gompertz kinetics were applied to estimate the growth parameters of the process, which revealed a good fit with R² ranging from 0.96 to 0.98. The produced digestate was valorized for biochar production, a material that could be applied for water treatment purposes. The produced biochar was characterized using different physical analyses, including FTIR, SEM, EDX, and TEM. The physicochemical characterizations of biochar demonstrate a successful formation of biochar with a highly porous structure and a rough surface, as evidenced by the emergence of significant functional groups (e.g., O-H, C-H, C=C, and C=O) existing on the surface of the biochar. In conclusion, this study harnesses a sustainable approach for the treatment of organic waste streams, which represents a circular economy model by transforming waste materials into valuable products and reducing the reliance on non-renewable resources. Full article

(This article belongs to the Special Issue Biological Treatment of Water Contaminants: A New Insight)

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8 pages, 1493 KiB

Open AccessArticle

Investigating the Potential of River Sediment Bacteria for Trichloroethylene Bioremediation

by Ranjit Gurav, Chang Ji and Sangchul Hwang

Water 2024, 16(20), 2941; https://doi.org/10.3390/w16202941 - 16 Oct 2024

Viewed by 666

Abstract

Trichloroethylene (TCE) is a prevalent groundwater contaminant detected worldwide, and microbes are sensitive indicators and initial responders to these chemical contaminants causing disturbances to their ecosystem. In this study, microbes isolated from San Marcos River sediment were screened for their TCE degradation potential. [...] Read more.

Trichloroethylene (TCE) is a prevalent groundwater contaminant detected worldwide, and microbes are sensitive indicators and initial responders to these chemical contaminants causing disturbances to their ecosystem. In this study, microbes isolated from San Marcos River sediment were screened for their TCE degradation potential. Among the twelve isolates (SAN1-12), five isolates demonstrated TCE degradation within 5 days at 25 °C and 40 mg/L of TCE concentration in the following order: SAN8 (87.56%), SAN1 (77.31%), SAN2 (76.58%), SAN3 (49.20%), and SAN7 (3.36%). On increasing the TCE concentration to 80 mg/L, the degradation efficiency of these isolates declined, although SAN8 remained the prominent TCE degrader with 75.67% degradation. The prominent TCE-degrading isolates were identified as Aeromonas sp. SAN1, Bacillus sp. SAN2, Gordonia sp. SAN3, and Bacillus proteolyticus SAN8 using 16S rRNA sequencing. The TCE degradation and cell biomass of Bacillus proteolyticus SAN8 were significantly improved when the incubation temperature was increased from 25 °C to 30 °C. However, both slightly acidic and alkaline pH levels, as well as higher TCE concentrations, lowered the efficacy of TCE degradation. Nevertheless, these conditions led to an increase in bacterial cell biomass. Full article

(This article belongs to the Special Issue Biological Treatment of Water Contaminants: A New Insight)

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17 pages, 2080 KiB

Open AccessArticle

Optimization of Culture Conditions for Microalgae Treatment Fly Ash Leachate System

by Rong Zhao, Wenjing Pang, Chuanhua Wang, Qiongzhen Chen, Qiang Ke and Qi Wang

Water 2024, 16(16), 2223; https://doi.org/10.3390/w16162223 - 6 Aug 2024

Viewed by 809

Abstract

In order to explore the feasibility of using algae to treat the fly ash leachate from a safe landfill site, leachate samples taken from a certain safe landfill site in Wenzhou City were treated with two different microalgae, Chlorella vulgaris and Scenedesmus obliquus [...] Read more.

In order to explore the feasibility of using algae to treat the fly ash leachate from a safe landfill site, leachate samples taken from a certain safe landfill site in Wenzhou City were treated with two different microalgae, Chlorella vulgaris and Scenedesmus obliquus, and the effectiveness of each treatment was evaluated in terms of its efficiency of pollutant removal. The effects of conditions such as pretreatment of leachate by sterilization, the initial concentration of leachate, and the addition of nutrients on pollutant removal efficiency and algae growth were studied. Sterilization of the leachate was found to have a relatively small impact on the growth of C. vulgaris and S. obliquus, as well as the removal of pollutants from the leachate. Therefore, sterilization treatment may not be necessary for engineering applications. Algal growth and the removal of pollutants were optimal when the leachate was used at a concentration of 10%, but when the leachate concentration was 30% or higher, the growth of both algae was weakened. The inclusion of 0.2 g/L K₂HPO₄·3H₂O and 0.06 g/L ammonium ferric citrate in the system led to higher algal growth and pollutant removal. The chlorophyll a levels of C. vulgaris and S. obliquus were 555.53% and 265.15%, respectively, and the nitrogen removal rates were also the highest, reaching 59.51% and 56.69%, respectively. This study optimized the cultivation conditions of a microalgae treatment leachate system, providing technical support and a theoretical basis for the practical engineering of a harmless treatment of leachate. Full article

(This article belongs to the Special Issue Biological Treatment of Water Contaminants: A New Insight)

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26 pages, 8963 KiB

Open AccessArticle

Enhanced Biological Nitrate Removal from Groundwater in Humid Tropical Regions Using Corn Cob-Based Permeable Reactive Barriers: A Case Study from Panama

by Graciela Cecilia Sánchez Hidalgo, Maria De Los Ángeles Ortega and Euclides Deago

Water 2024, 16(12), 1668; https://doi.org/10.3390/w16121668 - 12 Jun 2024

Viewed by 1269

Abstract

Nitrate contamination in groundwater is a global concern due to its widespread presence and consequential social, environmental, and economic ramifications. This study investigates the efficacy of biological denitrification in a humid tropical setting, utilizing corn cob in batch and column tests to assess [...] Read more.

Nitrate contamination in groundwater is a global concern due to its widespread presence and consequential social, environmental, and economic ramifications. This study investigates the efficacy of biological denitrification in a humid tropical setting, utilizing corn cob in batch and column tests to assess nitrate removal under varying conditions. Batch tests demonstrated the nitrate removal efficiencies of 93.14%, 91.58%, 90.77%, and 98.74% for initial concentrations of 22.18 ± 2.82 mg/L, 27.3 mg/L, 69.1 ± 1.2 mg/L and 115.08 ± 1.88 mg/L, respectively. In the column test, the removal efficiency was 99.86%, 87.13%, and 74%, and the denitrification rate was 32.82, 53.43, and 83.53 mg NO₃⁻-N/L d, for a hydraulic retention time (HRT) of 24 h, 16 h, and 7 h, respectively. Predominantly, nitrate removal occurred via biological denitrification, particularly favoring a 24 h HRT. The corn cob effectively removed high nitrate concentrations of up to 115 mg NO₃⁻-N/L. Scanning electron microscopy and Fourier transform infrared spectroscopy revealed surface characteristic changes of the carbon source pre- and post-denitrification. This research sheds light on the potential of biological denitrification using corn cob in humid tropical environments, offering a promising avenue for addressing nitrate contamination challenges in groundwater systems. Full article

(This article belongs to the Special Issue Biological Treatment of Water Contaminants: A New Insight)

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15 pages, 4937 KiB

Open AccessArticle

Mechanism of Crude Oil Biodegradation in Bioreactors: A Model Approach

by Carlos Costa and Nicolás Millán

Water 2024, 16(12), 1653; https://doi.org/10.3390/w16121653 - 10 Jun 2024

Cited by 1 | Viewed by 1088

Abstract

Oil-degrading bacteria have the ability to degrade alkanes present in crude oil because of a special enzymatic system, the alkane hydroxylase complex (AlkH). The mechanism for the transport and degradation of alkanes present in crude oil remains unclear, especially related to the first [...] Read more.

Oil-degrading bacteria have the ability to degrade alkanes present in crude oil because of a special enzymatic system, the alkane hydroxylase complex (AlkH). The mechanism for the transport and degradation of alkanes present in crude oil remains unclear, especially related to the first step in hydrocarbons oxidation. In this work, we present a novel model of the crude oil biodegradation mechanism by considering the contact between the oil drop and the cell and calculating the mass transfer coefficients in three oleophilic bacteria (B. licheniformis, P. putida and P. glucanolyticus). The mass transfer coefficients are evaluated under critical time conditions, when the kinetics and mass transport are in balance, and the difference in the values obtained (k_L α = 1.60 × 10⁻³, 5.25 × 10⁻⁴ and 6.19 × 10⁻⁴ m/d, respectively) shows the higher value of the mass transfer coefficient and higher biodegradation potential for B. licheniformis. Because the morphology of the cells has been analyzed by optical and electron microscopy, in the proposed model, the increase in the size of the cells in P. glucanolyticus compared to P. putida exhibits higher values of the mass transfer coefficients and this is attributed, as a novel statement, to a bigger window for alkanes transport (contact area) when the external area of the cell is bigger. Full article

(This article belongs to the Special Issue Biological Treatment of Water Contaminants: A New Insight)

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14 pages, 2771 KiB

Open AccessArticle

Treatment of Slaughterhouse Wastewater through a Series System: Upflow Anaerobic Reactor and Artificial Wetland

by Andrés A. Galindo Montero, Yeison M. Berrio Arrieta and Estefany V. Pimienta Serrano

Water 2024, 16(5), 700; https://doi.org/10.3390/w16050700 - 27 Feb 2024

Cited by 2 | Viewed by 1574

Abstract

Slaughterhouse wastewater is characterized by high concentrations of organic matter. This creates a need to explore methods for its treatment before discharge. This study evaluated the efficiency of an integrated treatment process consisting of a laboratory-scale upflow anaerobic sludge blanket reactor and a [...] Read more.

Slaughterhouse wastewater is characterized by high concentrations of organic matter. This creates a need to explore methods for its treatment before discharge. This study evaluated the efficiency of an integrated treatment process consisting of a laboratory-scale upflow anaerobic sludge blanket reactor and a pilot-scale horizontal subsurface flow wetland. This treatment was used for (i) the removal of organic matter through anaerobic–aerobic microbiological processes, (ii) the conversion of organic matter from hydraulic processes, and (iii) for bioremediation and phytoremediation. The treatment system was evaluated at hydraulic retention times (HRTs) of 7.5, 5.0, and 2.5 d; during the investigation, the influence of the HRTs on the removal efficiency of the system was evaluated. High efficiencies of 85% and 75% were obtained for COD_T and BOD, respectively, at an HRT of 7.5 d. The highest overall efficiency for the removal of total solids was observed at an HRT of 2.5 d. The results obtained confirm the feasibility of implementing the suggested system as an alternative for the adequate and sustainable treatment of slaughterhouse wastewater, and the system can be applied to slaughterhouses with similar conditions to those in this study. Full article

(This article belongs to the Special Issue Biological Treatment of Water Contaminants: A New Insight)

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11 pages, 13026 KiB

Open AccessArticle

Acceleration of Aerobic Granulation in Sidestream Treatment with Exogenous Autoinducer

by Eunae Jang, Kyung Jin Min, Eunyoung Lee, Hanna Choi and Ki Young Park

Water 2023, 15(12), 2173; https://doi.org/10.3390/w15122173 - 8 Jun 2023

Cited by 3 | Viewed by 1599

Abstract

Aerobic granular sludge (AGS) is a special type of biofilm formed by the self-aggregation of microorganisms and extracellular polymers and is considered a promising technology for wastewater treatment. However, new strategies are still being proposed as to how to improve the extracellular polymeric [...] Read more.

Aerobic granular sludge (AGS) is a special type of biofilm formed by the self-aggregation of microorganisms and extracellular polymers and is considered a promising technology for wastewater treatment. However, new strategies are still being proposed as to how to improve the extracellular polymeric substances (EPS) production that influences the formation of AGS. Recently, the acceleration of aerobic granulation using autoinducers such as N-acyl-homoserine lactone (AHL)-mediated quorum sensing has been reported. However, it is not yet fully understood due to knowledge gaps on the correlations depending on the type of AHL used. In this study, to evaluate the effects of various AHL on the AGS formation of activated sludge, the secretion of extracellular polymeric substances, biofilm formation, and sludge characteristics were comprehensively investigated. Among the AHL types, tightly bound EPS (TB-EPS) and loosely bound EPS (LB-EPS) in the reactor with C8-HSL added were 18.49 and 74.07 mg/g VSS, respectively, which represented increases of 3.15% and 53.76% compared to the control group. Additionally, C8-HSL increased the relative hydrophobicity and biomass volume by 153% and 218%, respectively. As a result, AHL had a positive effect on biomass content, an increase in sludge size, and an improvement in sludge sedimentation in the early stage of granulation, and C8-HSL was found to be the most suitable for initial granulation among AHL types. Full article

(This article belongs to the Special Issue Biological Treatment of Water Contaminants: A New Insight)

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Review

Jump to: Research

14 pages, 4714 KiB

Open AccessReview

Research Trends and Future Prospects of Constructed Wetland Treatment Technology in China

by Yuyang Liu, Bo Feng and Yu Yao

Water 2024, 16(5), 738; https://doi.org/10.3390/w16050738 - 29 Feb 2024

Cited by 1 | Viewed by 2703

Abstract

With the intensification of water pollution problems worldwide, constructed wetlands, as a green, efficient, and energy-saving wastewater treatment technology, have gradually attracted the wide attention of scholars at home and abroad. In order to better understand and master the research trends of constructed [...] Read more.

With the intensification of water pollution problems worldwide, constructed wetlands, as a green, efficient, and energy-saving wastewater treatment technology, have gradually attracted the wide attention of scholars at home and abroad. In order to better understand and master the research trends of constructed wetland treatment technology in China and promote its development, the literature from 2000 to 2023 in the CNKI database and the Web of Science (WoS) database (located in China) were selected as research objects. Then, CiteSpace software (6.2.R4) was used to visualize and analyze the literature, revealing the research trends and hot areas of constructed wetland treatment technology in China. Then, the optimized way of operation effect of constructed wetland was discussed to provide a theoretical and technical basis for the wide application of constructed wetland technology in our country. The results indicate that the annual publication volume of research on constructed wetlands in China is showing a rapid upward trend. Among them, the Chinese literature mainly focuses on how to improve the application effect of constructed wetlands on nitrogen and phosphorus removal of rural domestic wastewater by matching different wetland plants or developing combined processes. The English literature from the Web of Science (WoS) database mainly focuses on how to remove emerging pollutants, such as heavy metals and resistance genes in wastewater in China, by changing the filling matrix and microbial community structure or developing new processes, and the related mechanisms have been discussed. One of the hot spots for the future research of constructed wetlands in China is to vigorously develop microbial fuel cells, and try to overcome the problem of poor purification efficiency of constructed wetlands under complex conditions such as low temperature, low carbon-nitrogen ratio, and high pollution load. In order to strengthen its application, the specific optimization methods can be divided into two categories: self-optimization strategies such as increasing oxygen supply and transfer, providing electron donor matrix, preventing matrix blockage, and combination processes coupled with anaerobic treatment and other technologies. Full article

(This article belongs to the Special Issue Biological Treatment of Water Contaminants: A New Insight)

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12 pages, 1616 KiB

Open AccessReview

Cometabolism of Chlorinated Volatile Organic Compounds and 1,4-Dioxane in Groundwater

by Catherine Clark and Lee K. Rhea

Water 2023, 15(22), 3952; https://doi.org/10.3390/w15223952 - 14 Nov 2023

Cited by 2 | Viewed by 1818

Abstract

This article provides an overview of the bioremediation of groundwater plumes containing admixtures of chlorinated volatile organic compounds (CVOCs) and 1,4-dioxane. The remediation of these plumes has historically focused on the reductive dechlorination of the CVOCs. Many of the remaining plumes are relatively [...] Read more.

This article provides an overview of the bioremediation of groundwater plumes containing admixtures of chlorinated volatile organic compounds (CVOCs) and 1,4-dioxane. The remediation of these plumes has historically focused on the reductive dechlorination of the CVOCs. Many of the remaining plumes are relatively large, and contaminant concentrations are diluted below the concentrations that can sustain reductive dechlorination. Cometabolic processes can decrease contaminant concentrations below the thresholds needed to support direct metabolism but typically require the addition of a substrate, such as high-purity propane. Relatively intensive site characterization and monitoring is necessary to implement bioremediation. Full article

(This article belongs to the Special Issue Biological Treatment of Water Contaminants: A New Insight)

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