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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 (31 May 2024) | Viewed by 30401

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Dr. Antonio Albuquerque

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Department of Civil Engineering and Architecture, University of Beira Interior, 6201‐001 Covilhã, Portugal
Interests: nutrient removal; biofilm reactors; algae technology; water reuse; waste valorisation
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Dr. Qiulai He

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Guest Editor

Hunan Engineering Research Center of Water Security Technology and Application, College of Civil Engineering, Hunan University, Changsha 410082, China
Interests: biological wastewater treatment; aerobic granular sludge; in situ sludge reduction; phosphorus removal and recovery; GHGs reduction
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Special Issue Information

Dear Colleagues,

Nitrogen and phosphorous removal remain important and pressing challenges for water utilities with a view to discharging treated effluents into waterways or reusing water. In the last decade, significant advances have been observed in biological nutrient removal (BNR) through nitrification-denitrification pathways, either in wastewater or sludge treatment, using suspended sludge, hybrid flow, or biofilm reactors, with important discoveries on anaerobic ammonium oxidation, partial nitritation (SHARON, OLAND, CANON, and aerobic/anoxic deammonification processes), archaeal nitrification, and co-denitrification, as well as on the influence of the C/N ratio and interrelation between nitrifying, denitrifying, and phosphorus accumulating micro-organisms. Nowadays, research is focused on topics, such as the role of the alga-bacteria consortium in the simultaneous removal of N and P, optimization of nitrification-denitrification and phosphorous removal processes associated with sludge volume reduction, nutrient recovery towards the circular economy, nitrogen removal with minimal carbon demand, diversion of carbon for increasing biomethane production and lower carbon footprint, and reduction of greenhouse emissions. Therefore, this Special Issue aims to bring the most recent and innovative research on BNR, taking into account new challenges on sustainable water reuse, reduction of greenhouse emissions, circular economy, and needs in upgrading or retrofitting existing facilities.

Main topics are:

New developments and challenges in BNR;
Granular sludge for BNR;
Biological phosphorus removal in sludge acid fermentation;
Greenhouse emissions reduction in BNR;
Nutrient recovery;
Algal technology for BNR;
Modelling advances in BNR;
Sludge treatment and reduction technologies in BNR.

The Special Issue on “Nitrification-Denitrification Processes in Bioreactors for Wastewater and Sludge Treatment” is now open for submissions to be published as part of journal Water.

Dr. Antonio Albuquerque
Dr. Qiulai He
Guest Editors

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Keywords

wastewater treatment
biological nutrient removal
nitrification-denitrification
phosphorous removal
nitrogen removal
water reuse
sludge treatment

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Published Papers (11 papers)

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Research

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13 pages, 2921 KiB

Open AccessArticle

Added Biochars Promoted Nitrogen and Phosphorus Removal from Ecological Ditches at Low Temperature

by Guangsha Bai, Si Pang, Dongsu Bi, Siqi Wang, Min Cai, Lingqi Kong, Zheng Shen and Yalei Zhang

Water 2024, 16(8), 1191; https://doi.org/10.3390/w16081191 - 22 Apr 2024

Cited by 1 | Viewed by 2053

Abstract

The global issue of ecological ditches being poor in removing nitrogen and phosphorus under cold winter temperatures has been identified. This study introduced three types of biochar (reed, rice, and corn) into ecological ditch sediments via two application methods: rhizosphere and mixed addition. The purpose was to explore how these methods affect the removal of nitrogen and phosphorus, as well as their influences on microbial communities in sediments. The results indicated that the addition of biochar to ecological ditches significantly enhanced the removal of nitrogen and phosphorus. Among the three types of biochar, the mixed addition of corn biochar yielded the greatest results, achieving removal rates of 77.1% for total nitrogen (TN), 93.3% for NH₄⁺-N, and 90.3% for total phosphorus (TP). The growth of Vallisneria natans was greatly improved by the mixed addition method, resulting in an average increase of 154%. This improvement was superior to the rhizosphere addition group, which led to a growth increase of 125%. In comparison, the control group (CK) showed a decrease of 4.8% in growth. Different methods of biochar addition resulted in changes in the physicochemical properties and stoichiometry of the plants. Microbial analyses showed that the addition of biochar reduced the diversity and abundance of the substrate microbial community. Full article

(This article belongs to the Special Issue Nitrification-Denitrification Processes in Bioreactors for Wastewater and Sludge Treatment)

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11 pages, 3283 KiB

Open AccessArticle

Using Natural and Artificial Microalgal-Bacterial Granular Sludge for Wastewater Effluent Polishing

by Yihang Wang, Penghui Sun, Min Lin, Qiulai He and Bin Ji

Water 2023, 15(14), 2605; https://doi.org/10.3390/w15142605 - 18 Jul 2023

Cited by 6 | Viewed by 3236

Abstract

Marimo is a type of microalgal-bacterial granular sludge (MBGS) that exists in natural water bodies. For the first time, this paper explored the feasibility of marimo in real wastewater effluent polishing, focusing on nutrient removal as compared with MBGS. The results showed that the color of marimo gradually darkened during a 21-day experiment, and the chlorophyll content increased significantly. Although marimo and MBGS showed fairly similar removal performance in terms of NO₃⁻-N and TN, marimo exhibited better phosphate removal as compared to MBGS. Marimo and MBGS contained different algae but the same bacterial phylum of Proteobacteria, including denitrifiers. In addition, marimo had a higher relative abundance of nitrite reductase than MBGS, suggesting that the denitrification process might also happen in addition to assimilation. This study is expected to initiate the application of marimo for wastewater effluent polishing and reclamation, shedding light on nature-based wastewater self-purification technology in the era of carbon neutrality. Full article

(This article belongs to the Special Issue Nitrification-Denitrification Processes in Bioreactors for Wastewater and Sludge Treatment)

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15 pages, 3983 KiB

Open AccessArticle

Roles of Granular Sludge Size Restricting and Organic Degradation in an Extended Filamentous AGS System Using Agnail Aeration Device

by Jun Liu, Songbo Li, Weiqiang He, Qiulai He, Xiangzhou Meng, Liangliang Wei, Heng Liang and Jun Li

Water 2023, 15(11), 2009; https://doi.org/10.3390/w15112009 - 25 May 2023

Cited by 1 | Viewed by 1785

Abstract

This work investigated the role of an agnail device (manually made from a comb) on sludge size restriction and organic degradation in extended filamentous aerobic granular sludge-sequencing batch reactors (AGS-SBRs) with artificial wastewater. Two identical SBRs (R1 and R2) were employed in this experiment. Extended filamentous AGS with a large size was achieved in both SBRs by seeding the dewatering the sludge on day 40. R1 (the control) did not use the agnail aeration device, and the extended filamentous AGS system was finally disintegrated. However, R2 promptly employed the agnail device on days 56–59, the extended filamentous AGS size obviously decreased from 4.8 mm to 2.5 mm, and the dominant filamentous species, including Proteobacteria, Acidobacteria, and Choroflexi, gradually shrank at a low level, acting as a framework for AGS recovery. This was because enough nutrients diffused into the inside of small sludge for the filamentous living. Simultaneously, the sludge volume indexes (SVI₅ and SVI₃₀) sharply decreased from 155.8–103.9 to 51.7–46.6 mL/g, and the mixed liquid suspended solids (MLSSs) and extracellular polymeric substances (EPSs) in R2 both increased and were kept at 5816 mg/L and 69.1 mg/g·MLVSS, respectively. These contributed to enhancing the sludge’s structural stability to avoid AGS failure. COD and NH₄⁺-N in R2 were both degraded by simultaneous nitrification and denitrification (SND) processes throughout the experiment, which was not significantly influenced before or after the agnail aeration device was employed. These results indicate that the agnail device can effectively restrict AGS size and limit the extended filamentous overgrowth with nutrient diffusion into the sludge’s interior, which can prevent AGS disintegration. In addition, this device had no significant influence on organic degradation. Full article

(This article belongs to the Special Issue Nitrification-Denitrification Processes in Bioreactors for Wastewater and Sludge Treatment)

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15 pages, 1837 KiB

Open AccessArticle

Controlling Nitrogen Removal Processes in Improved Vertical Flow Constructed Wetland with Hydroponic Materials: Effect of Influent COD/N Ratios

by Elackiya Sithamparanathan, Nora B. Sutton, Huub H. M. Rijnaarts and Katarzyna Kujawa-Roeleveld

Water 2023, 15(6), 1074; https://doi.org/10.3390/w15061074 - 10 Mar 2023

Cited by 2 | Viewed by 2749

Abstract

Discharge of nitrogen (N) with wastewater causes eutrophication in surface water. On the other hand, nutrient-rich wastewater can be valuable for agriculture. Tailoring N removal or conservation is important to meet the requirements of different water end uses. Improved vertical flow constructed wetlands with hydroponic materials (CWH) as substrata were developed at lab scale in a greenhouse and studied to optimize N removal in CWH. This study investigated the effect of influent COD/N ratios of 5/1 and 15/1 on the removal or conservation of N in CWHs with Syngonium as vegetation and three substrata, pumice, cocopeat, and mineral wool. CWH with pumice showed the highest TN removal at both COD/N ratios. The Syngonium plant significantly contributed to the additional 50% TN removal in CWH. Nitrification of above 90% was observed at both studied COD/N ratios, indicating sufficient oxygenation due to the vertical pulse flow operated CWH. The denitrification process was enhanced at a higher COD/N ratio of 15/1 compared to 5/1 by around 10–40%. The occurring nitrification and denitrification indicate the coexistence of aerobic and anaerobic conditions in CWH, and balancing these conditions is necessary for future applications to remove N for its specific end use, i.e., irrigation water (high standards) or discharge to surface water (low standards). Full article

(This article belongs to the Special Issue Nitrification-Denitrification Processes in Bioreactors for Wastewater and Sludge Treatment)

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13 pages, 2946 KiB

Open AccessArticle

The Pretreatment of Micro-Polluted Source Water through Phototrophic Biofilms under Variant Light Conditions

by Hong-Yi Li, Runze Xu, Ting-Feng Liu and Zhi-Xin Hu

Water 2023, 15(4), 621; https://doi.org/10.3390/w15040621 - 5 Feb 2023

Cited by 1 | Viewed by 2503

Abstract

The imbalance of inorganic nutrients in micro-polluted source water poses a huge threat to aquatic environments and human health. To pretreat micro-polluted source water, some biological reactors have been conducted at lab-scale. However, using phototrophic biofilms to pretreat micro-polluted source water at pilot-scale has yet to be explored, and the effects of light on the practical operation of phototrophic biofilms are poorly understood. In this study, the potential of pretreating micro-polluted source water by phototrophic biofilms was explored. The high light intensity (4500 lx, 60.75 μmol/m²/s) promoted the growth of phototrophic biofilms and the secretion of extracellular polymeric substance. The removal efficiency of inorganic nitrogen and total phosphorus in synthetic micro-polluted water was 56.82% and 40.90%, respectively. When interacting with actual micro-polluted source water, the nutrients in the actual micro-polluted source water were reduced by the stable pilot-scale phototrophic biofilms. The final concentration of effluent nutrients was lower than the Grade II surface water quality standard in China. Therefore, using phototrophic biofilms as a pretreatment facility in water treatment plants is a promising solution to this issue. Full article

(This article belongs to the Special Issue Nitrification-Denitrification Processes in Bioreactors for Wastewater and Sludge Treatment)

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13 pages, 2805 KiB

Open AccessArticle

Results of Adding Sludge Micropowder for Microbial Structure and Partial Nitrification and Denitrification in a Filamentous AGS-SBR Using High-Ammonia Wastewater

by Jun Liu, Dong Xu, Weiqiang He, Qiulai He, Wenhai Chu, Songbo Li and Jun Li

Water 2023, 15(3), 508; https://doi.org/10.3390/w15030508 - 27 Jan 2023

Cited by 2 | Viewed by 2561

Abstract

This work investigated the roles of sludge micropowder addition in microbial structure and partial nitrification and denitrification (PND) in an extended filamentous aerobic granular sludge-sequencing batch reactor (AGS-SBR) using high-ammonia wastewater. Type 1683 Acinetobacter with a high percentage became the dominant extended filaments, remarkably shifted and remained at a low level, acting as a framework for AGS recovery after micropowder addition. The sludge volume index (SVI₅) decreased from 114 to 41.7 mL/g, mixed liquid suspended solids (MLSS) and extracellular polymers (EPS) both increased and balanced at 6836 mg/L and 113.4 mg/g•MLVSS, respectively. COD and NH₄⁺-N were degraded to certain degrees in the end. However, the effluent NO₂⁻-N accumulated to the peak value of 97.6 mg/L on day 100 (aeration stage), then decreased and remained at 45.3 mg/L with development of the stirring and micropowder supplemented in the SBR on day 160 (anoxic stage), while the influent NO₂⁻-N always remained at zero. Interestingly, the influent/effluent NO₃⁻-N both remained at zero throughout the whole experiment. These results demonstrated that PND was successfully obtained in this work. Sludge micropowder addition not only restrained the extended filaments’ overgrowth, but also contributed to PND realization with carbon released. Citrobacter and Thauera played an essential role in the PND process for high-ammonia wastewater treatment. Running condition, wastewater characteristic, and sludge structure played an important role in microbial composition. Full article

(This article belongs to the Special Issue Nitrification-Denitrification Processes in Bioreactors for Wastewater and Sludge Treatment)

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10 pages, 2249 KiB

Open AccessArticle

Nutrients’ Removal from Mariculture Wastewater by Algal–Bacterial Aggregates Developed from Spirulina platensis

by Xiaohua Fu, Qianrong Jiang, Xiaojing Yang, Lihong Liu, Li Liu, Jingshi Li, Siyang Li, Qijin Luo, Jianyu Chen, Ziwen Zhao and Gang Liu

Water 2023, 15(3), 396; https://doi.org/10.3390/w15030396 - 18 Jan 2023

Cited by 4 | Viewed by 3538

Abstract

As an important alternative to alleviate the shortage of wild fishery resources, mariculture is facing increasing challenges on the wastewater treatment, mainly due to the salinity brought from seawater and low nutrient concentration. In this study, Spirulina platensis (S. platensis) was adopted as the target algae stain for synthetic mariculture wastewater treatment, which exhibited excellent adaptability to high-saline wastewater during a 40 days’ adaptive culture. Then, the microalgae stain was inoculated into photo-bioreactors with different uplift airflow velocity (UAV) to achieve microalgal aggregation. After 10 days of pre-cultivation and a 30-day granulation process, the maximum nutrient removal rates by S. platensis were 86.5% of TN (to 3.4 mg/L), 98.1% of TP (to 0.1 mg/L) and 95.8% of DOC (to 5.5 mg/L), with 3.5 g/L of biomass content in synthetic wastewater. Analysis of phosphorus and EPS content showed that higher protein content in tightly bound EPS and enhanced P accumulation was accompanied with the microalgal aggregation processes, and P was mainly distributed in the residual rather than the EPS part of microalgal aggregates, indicating that the development of aggregates from suspension S. platensis would benefit not only biomass separation, but also phosphorus recovery, being a potential treatment for simultaneously removing nutrients and recovering mariculture wastewater. Full article

(This article belongs to the Special Issue Nitrification-Denitrification Processes in Bioreactors for Wastewater and Sludge Treatment)

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15 pages, 2958 KiB

Open AccessArticle

Sequential Nitrification—Autotrophic Denitrification Using Sulfur as an Electron Donor and Chilean Zeolite as Microbial Support

by A. Barahona, J. Rubio, R. Gómez, C. Huiliñir, R. Borja and L. Guerrero

Water 2023, 15(1), 95; https://doi.org/10.3390/w15010095 - 28 Dec 2022

Cited by 4 | Viewed by 2942

Abstract

Sequential nitrification–autotrophic denitrification (SNaD) was carried out for ammonium removal in synthetic wastewater (SWW) using sulfur as an electron donor in denitrification. Four reactors were operated in batch mode, two with zeolite (1 mm size) used as microbial support and two without support, to assess the effect of the zeolite addition in the SNaD. Aeration, anoxic, and anaerobic cycles were established, where 96% removal of NH₄⁺-N (oxidized to nitrite or nitrate) was achieved in nitrification, along with 93% removal of NO₃⁻-N in denitrification for the SNaD with zeolite. It was observed that the use of zeolite assists in buffering reactor load changes. Inhibition caused by nitrite accumulation in the denitrification stage was minimized by increasing the nitrogen concentration in the SWW. The results obtained in this study are the basis for the development of ammonium removal by simultaneous nitrification–autotrophic denitrification using a single reactor. Full article

(This article belongs to the Special Issue Nitrification-Denitrification Processes in Bioreactors for Wastewater and Sludge Treatment)

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13 pages, 2093 KiB

Open AccessArticle

Removal of N and P in a Rotating Biological Contactor Plant: Case Study Agnita, Romania

by Eniko Gaspar, Ioan Munteanu and Silviu Sintea

Water 2022, 14(22), 3670; https://doi.org/10.3390/w14223670 - 14 Nov 2022

Cited by 2 | Viewed by 2709

Abstract

The wastewater treatment plant of Agnita, Romania was designed with a rotational biological contactor system for a population of approximately 9500, but for environmental protection reasons it must comply with regulations concerning nitrogen and phosphorus designed for larger communities. In order to achieve the prescribed limits for these pollutants, we have used a 40% FeCl₃ solution, continuously added to the distributor, without changes in flow or equipment. Its use boosts the removal of ammonia nitrogen, and phosphorus, bringing them within the limits and with reasonable cost. To determine the ferric chloride to be used we considered, aside from the pollutant load, the water temperature, and introduced a new parameter: specific removal power that enabled us to optimize the volume of FeCl₃. A major contribution to nitrogen removal was achieved by the denitrification bacteria favored by the presence of ferric ions, which also precipitate phosphorus. The results of this study, performed since September 2021, enable us to continue to use this method and enlarge its application to other plants owned by the local operator. Full article

(This article belongs to the Special Issue Nitrification-Denitrification Processes in Bioreactors for Wastewater and Sludge Treatment)

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Review

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14 pages, 606 KiB

Open AccessReview

Promoting Aquatic Health in Constructed Wetlands: Removal of Pathogens and Nitrogen

by Zihang Yang, Yuanchun Zou, Xiaoyan Zhu and Xiuli Yu

Water 2024, 16(7), 917; https://doi.org/10.3390/w16070917 - 22 Mar 2024

Cited by 4 | Viewed by 2127

Abstract

Due to urbanization and population growth, freshwater resources have become a long-term concern for most developing countries. With the growth of population, the demand for fresh water is increasing and the requirement for sewage treatment is also increasing. In recent years, the demand for sewage recycling has increased sharply. Constructed wetlands (CWs) are an effective sewage treatment system with low energy consumption, minimal maintenance requirements, and a low operation cost, which will meet the current demand for the removal of nutrients and pathogens. The application of CWs in sewage treatment has attracted more and more attention because it is also a nature-based solution (NbS). These systems are capable of removing not only nitrogen (N) and phosphorus (P), but also pathogen indicators, such as fecal coliform and Escherichia coli. The presence of these indicators also suggests the influx of other pathogens into aquatic systems, thereby threatening aquatic ecological health. However, research on the removal of pathogens in CWs is relatively scare and their removal mechanisms are not fully understood. Despite their widespread application, the role of plants in CWs, particularly in the specific mechanism of pathogens and nitrogen removal, remains largely unknown. This article will help us to better understand this technology and provide help for our further research. In this paper, the coupled denitrification mechanism between microorganisms and plants in the process of nitrogen transformation was discussed. Plants affect nitrogen transformation microorganisms by releasing oxygen and secretions from their roots and provide substrates for bioremediation. The removal effects of different types of CWs on pathogen and nitrogen species were also summarized. Overall, the removal effect of subsurface flow wetlands outperforms that of surface flow wetlands, with multi-stage wetland systems being the most effective. The main factors affecting the removal of pathogens and nitrogen species in CWs include plants, substrates, operating parameters, UV radiation, temperature, water composition, and pH. Finally, the research frontiers on the removal of pathogens in CWs were prospected. Full article

(This article belongs to the Special Issue Nitrification-Denitrification Processes in Bioreactors for Wastewater and Sludge Treatment)

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14 pages, 279 KiB

Open AccessReview

The Inhibition of Engineered Nano-ZnO in the Biological Nitrogen Removal Process: A Review

by Teng-Fei Ma, Hong-Xi Ma, Jin Wu, Yi-Chang Yu, Ting-Ting Chen, Yuan Yao, Wei-Ling Liao and Li Feng

Water 2024, 16(1), 17; https://doi.org/10.3390/w16010017 - 20 Dec 2023

Cited by 2 | Viewed by 1622

Abstract

Engineered nano-ZnO is extensively utilized in both production and daily life, leading to its inevitable entry into the wastewater treatment system through various pathways. Nitrogen removal microorganisms in wastewater treatment systems are highly susceptible to environmental impacts. The antibacterial properties of nano-ZnO can impede the biological nitrogen removal (BNR) process and adversely affect the nitrogen removal performance. A comprehensive understanding of the inhibitory effect and mechanism of nano-ZnO on the BNR process is crucial in devising appropriate countermeasures to ensure optimal nitrogen removal performance. This review provides an overview of the sources of nano-ZnO in the environment, its impact on the BNR process, and the inhibition mechanism, and proposes potential methods that can mitigate the inhibitory effect of nano-ZnO. Additionally, future prospects are also discussed. This review serves as a foundation for a deeper understanding of the inhibition of engineered nano-ZnO on the BNR process and aids in guiding efforts to maintain the nitrogen removal performance in the presence of engineered nano-ZnO. Full article

(This article belongs to the Special Issue Nitrification-Denitrification Processes in Bioreactors for Wastewater and Sludge Treatment)

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