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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 (15 June 2023) | Viewed by 40759

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Prof. Dr. Yongjun Sun

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Guest Editor

College of Urban Construction, Nanjing Tech University, Nanjing 211816, China
Interests: flocculation and flocculants; coagulation and coagulants; industrial wastewater treatment; domestic sewage treatment; advanced oxidation technology
Special Issues, Collections and Topics in MDPI journals

Dr. Kinjal J. Shah

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Guest Editor

College of Urban Construction, Nanjing Tech University, Nanjing 211816, China
Interests: green chemistry; environmental sustainability; water treatment; microplastic
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The urban wastewater treatment process generally determines the degree of wastewater purification and the corresponding treatment method after the urban wastewater is used or discharged, considering the natural purification capacity of the water body. Treated wastewater, whether used in industry, agriculture or to supplement groundwater, must meet relevant water-quality standards. A large amount of sludge generated during wastewater treatment is not treated and disposed of effectively, causing great harm to the environment in the form of solid waste. The primary disposal methods for traditional sludge include landfill, incineration, discharge into the sea, and agricultural use. However, traditional treatment methods also have some disadvantages, which cannot be used for resource utilization of sludge and cannot meet the current technical requirements of sludge treatment. The treatment and disposal of sewage sludge should be considered comprehensively in terms of pollution, health and safety, and economic benefits. New sludge-treatment technologies with energy recovery and utilization will play an irreplaceable role in sludge treatment and disposal. This Special Issue mainly focuses on applying the Nexus approach to resource management to achieve a global water environment system.

Prof. Dr. Yongjun Sun
Prof. Dr. Kinjal J. Shah
Guest Editors

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Keywords

water-energy-nexus
municipal wastewater
sludge treatment

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Published Papers (11 papers)

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Research

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12 pages, 3762 KiB

Open AccessArticle

Analysis of the Partial Nitrification/Anammox Performance and Microbial Structure of Low C/N Wastewater by A²/O Process

by Lei Ye, Yanhao Zhou, Liangdong Tang, Sixing Chen and Xianguang Zhao

Water 2023, 15(12), 2300; https://doi.org/10.3390/w15122300 - 20 Jun 2023

Viewed by 2301

Abstract

Given the carbon limitation of low C/N wastewater, the improvement of nitrogen-removal efficiency remains a challenging task of municipal wastewater treatment plants (WWTPs) in China. In this study, a partial nitrification/anammox (PN/A) system was established to facilitate the anaerobic-anoxic-aerobic (A²/O) treatment of low C/N (C/N = 3) wastewater with insufficient carbon sources. Effects of dissolved oxygen (DO) concentration and internal reflux ratio on nitrogen-removal efficiency and pathway were investigated. Under the optimal DO (0.5–0.8 mg·L⁻¹) and internal reflux ratio (250%), the highly efficient NH₄⁺-N removal (97.21%) and TN removal (80.92%) were achieved based on PN/A. Moreover, the relative abundance of ammonia-oxidizing bacteria (Nitrosomonas) was 3 times higher than the abundance of nitrite-oxidizing bacteria (Nitrospira) in phase V, which was the main cause of PN in the reactor. Anaerobic ammonia-oxidizing bacteria (Candidatus Brocadia, Pirellula, and Gemmata) were also found and considered as the key microbes involved in anammox. This study reports that the A²/O process can achieve advanced nitrogen removal of low C/N wastewater based on PN/A by optimizing conventional process parameters. The outcomes of this study may provide practical engineering applications as a reference for nitrogen removal based on the A²/O process. Full article

(This article belongs to the Special Issue Water-Sludge-Nexus)

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16 pages, 3822 KiB

Open AccessArticle

Impact of Dissolved Oxygen on the Performance and Microbial Dynamics in Side-Stream Activated Sludge Hydrolysis Process

by Lu Qin, Dongqi Wang, Zhe Zhang, Xiaoxiao Li, Guodong Chai, Yishan Lin, Cong Liu, Rui Cao, Yuxin Song, Haiyu Meng, Zhe Wang, Hui Wang, Chunbo Jiang, Yuan Guo, Jiake Li and Xing Zheng

Water 2023, 15(11), 1977; https://doi.org/10.3390/w15111977 - 23 May 2023

Cited by 5 | Viewed by 2711

Abstract

Dissolved oxygen (DO) plays an important role in the performance of biological wastewater treatment systems. This study investigated the effect of the DO concentration on nutrient removal performance and microbial community structure in side-stream activated sludge hydrolysis (SSH) and conventional anaerobic/anoxic/aerobic (A²O) processes. The results showed that the change in DO had little effect on the removal performance of chemical oxygen demand (COD), and the removal efficiencies were about 90% for both reactors. Compared with the high DO level (4.1–6.9 mg/L), the A²O and SSH reactors had better nitrogen removal performance at low (0.5–2.2 mg/L) and moderate (2.2–3.9 mg/L) DO levels, with ammonia (NH₄⁺-N) removal efficiencies of 88–89% and 89–91%, respectively, and total nitrogen (TN) removal efficiencies of 74–76% and 75–81%, respectively. Directly reducing the DO concentration from high to low reduced the phosphate removal efficiencies of the A²O and SSH reactors from 80.2% and 86.2% to 63.1% and 70.6%, respectively, while re-elevating the DO concentration to moderate levels significantly improved the phosphate removal efficiencies to 94.6% and 96.0%, respectively. Compared to the A²O reactor, the SSH reactor had more stable and better nutrient removal performance under different DO conditions, partly due to the additional carbon sources produced through the sludge fermentation in the side-stream reactor. The decrease in the DO concentration resulted in a decrease in the relative abundance of Acinetobacter but an increase in the relative abundance of Competibacter, potentially leading to the deterioration in phosphorus removal. Full article

(This article belongs to the Special Issue Water-Sludge-Nexus)

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18 pages, 4710 KiB

Open AccessArticle

Y-Type Zeolite Synthesized from an Illite Applied for Removal of Pb(II) and Cu(II) Ions from Aqueous Solution: Box-Behnken Design and Kinetics

by Kinjal J. Shah, Jiacheng Yu, Ting Zhang and Zhaoyang You

Water 2023, 15(6), 1171; https://doi.org/10.3390/w15061171 - 17 Mar 2023

Cited by 4 | Viewed by 2305

Abstract

A Y-type zeolite was prepared from illite clay, which was activated and synthesized by a solid-phase alkali fusion technique with reduced reaction conditions and crystal methods. The optimal synthesis conditions were investigated using the Box-Behnken design for a NaOH/illite (mass ratio) of 1:2, an activation temperature of 185 °C, and an activation time of 2.7 h. The synthesized Y-type zeolites were characterized by various analytical techniques such as FT-IR, XRD, and SEM, and the results obtained show that small amounts of quartz and P-type zeolites are present in the synthesized products. The mixture was classified as a zeolitic mineral admixture (ZMA). The adsorption performance of ZMA on Pb(II) and Cu(II) in solution was evaluated by batch adsorption experiments. The results showed that ZMA had good adsorption performance for Pb(II) and Cu(II), with maximum adsorption amounts of 372.16 and 53.46 mg/g, respectively. From the investigation, it was concluded that the adsorption process is chemisorption occurring in monomolecular layers and relying on electrostatic adsorption, ion exchange and complexation of hydroxyl groups on the ZMA surface for heavy metal cations. The ZMA reusability result shows that sodium chloride has the ability to regenerate the active site by restoring the ion exchange capacity without significant loss of Pb(II) and Cu(II) adsorption. Full article

(This article belongs to the Special Issue Water-Sludge-Nexus)

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11 pages, 1626 KiB

Open AccessArticle

Exploration and Optimisation of High-Salt Wastewater Defluorination Process

by Dianhua Chen, Minyan Zhao, Xinyuan Tao, Jing Ma, Ankang Liu and Mingxiu Wang

Water 2022, 14(23), 3974; https://doi.org/10.3390/w14233974 - 6 Dec 2022

Cited by 2 | Viewed by 2408

Abstract

The typical lime precipitation method is used to treat high-concentration fluorine-containing wastewater. In this way, the fluorine in the wastewater can be removed in the form of CaF₂. Thus, this method has a good fluoride removal effect. In this study, calcium hydroxide was used to adjust the pH and achieve a significant fluoride removal effect at the same time. The removal rate of fluoride ion decreases gradually with the increase in the concentration of sulphate in the raw water. When the synergistic defluorination cannot meet the requirements of water production, adding a step of aluminium salt flocculation and precipitation can further reduce the fluoride ion concentration. According to the feasibility of the actual project, this study improves the lime coagulation precipitation defluorination process on this basis, and the combined process is synchronised. In the process optimisation, barium chloride is added to remove the influence of sulphate radicals in the water, and then, the pH is adjusted to 5–6. The fluoride ion concentration in high-salt wastewater can be reduced from 446.6 mg/L to 35.4 mg/L by defluorination after pre-treatment whose removal rate was 92.1%. The combined process synchronously removes fluorine and purifies the water quality to a certain extent. Indicators such as COD, total phosphorus, ammonia nitrogen, and chloride ions in wastewater are reduced, and the removal rate is increased by 35.5% under the same conditions. This scheme improves the wastewater treatment effect without increasing the existing treatment equipment. Thus, it achieves a better defluorination effect and reduces the dosage of chemicals as much as possible, which is conducive to lowering the discharge of sludge after treatment. Full article

(This article belongs to the Special Issue Water-Sludge-Nexus)

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16 pages, 4372 KiB

Open AccessArticle

Nitrogen Doped Cobalt Anchored on the Used Resin-Based Catalyst to Activate Peroxymonosulfate for the Removal of Ibuprofen

by Cheng Wang, Guangzhen Zhou, Yanhua Xu, Peng Yu and Yongjun Sun

Water 2022, 14(22), 3754; https://doi.org/10.3390/w14223754 - 18 Nov 2022

Cited by 3 | Viewed by 1928

Abstract

The ion exchange resin is mainly composed of carbon, and it can form carbon material after calcination in the isolation of oxygen. Meanwhile, the nitrogen doping of metal-based carbon materials has attracted extensive attention in activating peroxymonosulfate (PMS) to produce active groups in the degradation of refractory organic pollutants. In this study, the used D001 resin served as the source of carbon material and catalyst carrier, cobalt ions adsorbed by impregnation, and then mixed with dicyandiamide and carbon balls formed by calcined (N-Co/D001CB). After nitrogen doping, cobalt exists in the form of cobalt sulfide with high crystallinity, and the serious problems of skeleton shrinkage and internal blockage are significantly alleviated. Under certain catalytic reaction conditions, the degradation rate of ibuprofen in one hour was more than 95%, which was significantly higher than that of cobalt. Finally, quenching experiments found that SO₄⁻· is the main pathway for pollutant degradation, followed by ·OH, and there also exists the contributions of ·O₂⁻ and ¹O₂. In summary, the catalyst was prepared easily and had efficient catalytic activity, but it also recycled its resources with a low disposal cost of used D001CB, realizing the purpose of recycling waste materials and applying them in pollutant treatment. Full article

(This article belongs to the Special Issue Water-Sludge-Nexus)

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18 pages, 3963 KiB

Open AccessEditor’s ChoiceArticle

Study on the Application of Shell-Activated Carbon for the Adsorption of Dyes and Antibiotics

by Jinlong Wang, Rui Wang, Jingqian Ma and Yongjun Sun

Water 2022, 14(22), 3752; https://doi.org/10.3390/w14223752 - 18 Nov 2022

Cited by 24 | Viewed by 4863

Abstract

In this study, we prepared homemade fruit shell-activated carbon (SAC) with efficient adsorption of new pollutants and used it in the removal of methylene blue dye (MB) and ofloxacin antibiotic (OFL) in water. We fitted the experimental data for MB and OFL adsorption with isothermal and kinetic models and performed extensive characterization to study the properties of SAC. We also studied the effects of solution pH, dosage amount, initial concentration, and coexisting ions on the adsorption capacity. The results show that SAC has a rich pore structure, and electrostatic interactions are its main adsorption mechanism. Adjusting the solution pH by changing the SAC dosage and removing the K⁺, SO₄²⁻, and Cu²⁺ could increase the removal of MB and OFL to 99.9% and 97.6%, respectively. In addition, the adsorption capacity of SAC for MB remained at more than 50% of the initial state after three iterations of adsorption regeneration, showing a good regeneration ability. These results show the potential of SAC in replacing conventional activated carbon to remove new pollutants. Full article

(This article belongs to the Special Issue Water-Sludge-Nexus)

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18 pages, 5539 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Adsorption of Methylene Blue by Coal-Based Activated Carbon in High-Salt Wastewater

by Jinlong Wang, Jingqian Ma and Yongjun Sun

Water 2022, 14(21), 3576; https://doi.org/10.3390/w14213576 - 7 Nov 2022

Cited by 25 | Viewed by 4877

Abstract

High-salt printing and dyeing wastewater is a difficult industrial wastewater to treat. Coal-based activated carbon (CBAC) can be used as an adsorbent to treat high-salt printing and dyeing wastewater and realize the resource utilization of CBAC. In this study, simulated wastewater that contained methylene blue (MB) was used as the research object, and CBAC was used as the adsorbent. The effects of CBAC dosage, NaCl concentration, coexisting ions, adsorption time, MB concentration, humic acid concentration, and solution pH on the adsorption performance of CBAC with MB were discussed. The results showed that when the CBAC dosage was 0.6 g/L, the solution pH was greater than 6, the adsorption time was 8 h, the adsorption temperature was 308 K, and the MB concentration was 10 mg/L. Thus, the maximum adsorption capacity of CBAC with MB was obtained. The maximum adsorption capacity and removal rate were 15.5 mg/L and 90%, respectively. High-salt wastewater can inhibit the adsorption of methylene blue by coal-based activated carbon. In addition, 20 g/L of NaCl reduced the adsorption capacity of coal-based activated carbon by 1.8 mg/g. Compared to the other coexisting ions, the influence of the presence of Cu²⁺ and Fe³⁺ on the removal of methylene blue was greater. However, when Cu²⁺, Fe³⁺ and high-salt wastewater coexist, the inhibition effect decreases. Full article

(This article belongs to the Special Issue Water-Sludge-Nexus)

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14 pages, 2114 KiB

Open AccessArticle

Pretreatment Hydrolysis Acidification/Two-Stage AO Combination Process to Treat High-Concentration Resin Production Wastewater

by Shengping Cao, Weiwei Jiang, Minyan Zhao, Ankang Liu, Mingxiu Wang, Qu Wu and Yongjun Sun

Water 2022, 14(19), 2949; https://doi.org/10.3390/w14192949 - 20 Sep 2022

Cited by 3 | Viewed by 2286

Abstract

The rapid development of the resin industry has led to a large amount of high-concentration resin production wastewater, which has created serious water pollution problems while limiting the development of related enterprises. In this study, a combined pretreatment hydrolysis acidification/two-stage anaerobic oxic (AO) process for high-concentration resin production wastewater was constructed, and the effect of operation time on the treatment efficiency of the hydrolysis acidification and the two-stage AO unit was investigated using chemical oxygen demand (COD), total nitrogen (TN), and NH₃-H (ammonia nitrogen) as indicators. The effect of operation time on the treatment efficiency of the hydrolysis acidification and the two-stage AO unit was investigated. Results showed that the pretreatment of “alkaline digestion + ozone oxidation” could effectively remove volatile phenols and phenolic organic pollutants from the wastewater. The average removal rates of COD, TN, and NH₃-H (ammonia nitrogen) of resin production were 91.96%, 85.35%, and 85.67%, respectively. The average concentrations of final biochemical effluent were 404.7, 21.4, and 11.4 mg/L, respectively. Full article

(This article belongs to the Special Issue Water-Sludge-Nexus)

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16 pages, 3928 KiB

Open AccessFeature PaperArticle

Study on the Breeding and Characterization of High-Efficiency Oil-Degrading Bacteria by Mutagenesis

by Pan Zhang, Zhaoyang You, Tianfang Chen, Li Zhao, Jianguo Zhu, Weihong Shi, Qinwei Meng and Yongjun Sun

Water 2022, 14(16), 2544; https://doi.org/10.3390/w14162544 - 18 Aug 2022

Cited by 4 | Viewed by 2191

Abstract

In the present study, a high-efficiency petroleum hydrocarbon-degrading bacterium MX1 was screened from petrochemical wastewater sludge, and MX1 was identified using morphological, physiological, and biochemical experiments and combined with 16S rDNA. Results showed that the the MX1 strain belongs to Enterobacter sp. The degradation conditions were an incubation time of 18 days, temperature of 30 °C, pH of 7, and salinity of 2% (w/v), and the degradation proportion was 37.41% for 7 days. The combination of microwave and ultraviolet mutagenesis yielded the strain MXM3U2. The mutant strain had a petroleum hydrocarbon breakdown efficiency of 56.74% after 7 days of culture, and this value was 51.66% higher than the original strain. The number of strains and the rate of degradation of n-alkanes (C16, C24, C32, and C40) decreased steadily with the increase in carbon chains in the degradation test. GC/MS (Gas chromatography mass spectrometry) results showed that in the process of degrading crude oil, the hydrocarbons with carbon number C < 24 were degraded first, followed by hydrocarbons with carbon number C > 24. The strains had a good degradation effect on pristane, naphthalene, and phenanthrene. In this study, a high-efficiency petroleum hydrocarbon-degrading bacterium was screened via microwave-ultraviolet composite mutagenesis technology. Full article

(This article belongs to the Special Issue Water-Sludge-Nexus)

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Review

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22 pages, 1270 KiB

Open AccessReview

Research Progress of High-Salinity Wastewater Treatment Technology

by Lei Guo, Yiming Xie, Wenquan Sun, Yanhua Xu and Yongjun Sun

Water 2023, 15(4), 684; https://doi.org/10.3390/w15040684 - 9 Feb 2023

Cited by 36 | Viewed by 10040

Abstract

With the continuous expansion of industrial enterprises, a large amount of high-salt wastewater with complex components is produced. Direct discharge will cause great harm to the ecosystem and waste a large amount of potential salt resources. This paper summarizes the source, water quality characteristics, and environmental impact of high-salinity wastewater, and introduces the desalination and treatment technologies of high-salinity wastewater. The desalination technology of high-salinity wastewater mainly includes two processes: concentration and crystallization, obtaining concentrated solution through membrane concentration or thermal concentration and then carrying out crystallization treatment on the concentrated solution, thereby realizing the recovery of salt. The advanced treatment technologies of high-salinity wastewater were analyzed, including physicochemical treatment, biological treatment, and coupling treatment. Catalytic ozonation is one of the most widely used physicochemical technologies for the advanced treatment of high-salinity wastewater. Biological treatment processes operating in the presence of halotolerant bacteria show excellent performance at high salinity. High salinity has a negative impact on the performance of various physicochemical processes and biological treatment technologies. However, high salinity has little effect on the performance of a coupled system designed to treat high-salinity wastewater. In this review, the effect of salinity on the scaling and corrosion of equipment is also illustrated. It is suggested that the research direction of high-salinity wastewater should be to develop new membrane materials and catalysts, develop salt-tolerant microorganisms, explore high-efficiency and energy-saving physico–chemical–biochemical combination processes, improve the treatment efficiency of high-salinity organic wastewater, and reduce treatment costs. Full article

(This article belongs to the Special Issue Water-Sludge-Nexus)

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18 pages, 3105 KiB

Open AccessReview

Advances in Chemical Conditioning of Residual Activated Sludge in China

by Yankai Liang, Rui Wang, Wenquan Sun and Yongjun Sun

Water 2023, 15(2), 345; https://doi.org/10.3390/w15020345 - 13 Jan 2023

Cited by 7 | Viewed by 3462

Abstract

Municipal sludge is characterized by high organic matter content, high viscosity, and fine particles, resulting in poor dewatering performance. This article analyzes the composition and properties of municipal sludge, examines the factors affecting the dewatering performance of sludge and the mechanisms corresponding to each influencing factor, and introduces chemical conditioning in detail. Chemical conditioning includes flocculation conditioning, oxidation conditioning, acid-base conditioning, and aggregate conditioning. The principles and applications of existing sludge conditioning technologies are systematically analyzed. By comparing the advantages and disadvantages of different technologies, it is pointed out that the key to developing sludge conditioning technology lies in developing a more appropriate combination of the sludge conditioning and dewatering process according to the sludge quality of different municipal wastewater treatment plants, taking into account their local environment, input costs, subsequent sludge disposal methods, and other factors, and further optimizing the sludge dewatering process by developing new efficient and environmentally friendly sludge conditioning agents. Full article

(This article belongs to the Special Issue Water-Sludge-Nexus)

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