Nitrogen removal augmentation of ship sewage by an innovative aerobic-anaerobic micro-sludge MBR technology

Portrait of municipal wastewater of China: Inspirations for wastewater collection, treatment and management

Over the past decades, significant importance has been attached to municipal wastewater treatment in China. But wastewater treatment plants (WWTPs) still grapple with operation inefficiencies due to low influent concentrations. This study comprehensively provides a portrait of Chinese municipal wastewater from the national and province levels, drawing on official data available. The historical trends of main pollutant indexes in WWTPs influent and the corresponding geographical distribution variations during 2007-2020 have been analyzed. Pollutant concentration and wastewater collection rate in northern and western regions were generally higher than southern and eastern regions of China. A wastewater collection rate of approximately 65 % by introducing actual pollutant collection amount has been proposed, demonstrating the practical conditions and problems of Chinese wastewater collection system nowadays. Correlation and redundancy analysis further pinpointed collection rate and rainfall as the paramount factors affecting influent concentrations and pollutant losses, contributing 66.9 % and 29.5 %, respectively. These results indicated that the deteriorated or damaged sewer pipelines, along with mixed or wrong connection of rainwater and wastewater, led to a large amount of extraneous clean water transported into and then treated unnecessarily by WWTPs. A significantly negative correlation between influent chemical oxygen demand (COD) concentration and electricity consumption in WWTPs was disclosed, further emphasizing the importance of increasing influent loading and rehabilitating sewer pipelines to enhance the overall efficiency of wastewater systems. This study helped glean valuable insight into a more efficient and sustainable solution for wastewater treatment and management.

The Environmental Hazards and Treatment of Ship's Domestic Sewage

With the rapid development of the modern shipping field, the damage caused by ship pollution to the global inland waterways and marine ecosystems has attracted extensive attention from the international community. However, there are fewer reviews on the environmental hazards of domestic ship sewage and its treatment, and a systematic summary of the environmental hazards posed by ship domestic sewage and its treatment is lacking. Based on summarizing the various environmental hazards brought about by a ship's domestic sewage and the corresponding treatment methods, this study elaborates, in detail, on the specific hazards of the main toxic and hazardous substances contained in a ship's domestic sewage on the environment and organisms, and the treatment methods of the ship's domestic sewage and their treatment effects, such as membrane bioreactor (MBR). It is also pointed out that MBR has great potential in the direction of ship domestic sewage treatment, and the solution of its membrane pollution and other problems as well as the exploration of the combination of MBR and other treatment methods will become the focus of future research. A theoretical reference is provided for the study of environmental problems caused by domestic sewage from ships and their treatment options.

Evaluating the potential of a new reactor configuration to enhance simultaneous organic matter and nitrogen removal in dairy wastewater treatment

The dairy industry is a very productive sector worldwide and known for producing great volumes of wastewater that is rich in organic matter and nutrients. Apart from fat, the organic matter in such effluents is easily degradable, demanding an external carbon source for conventional denitrification. In this manner, new configurations of reactors promoting a suitable environment for more sustainable nitrogen removal are beyond required-they are paramount. Therefore, the performance of a structured-bed hybrid baffled reactor (SBHBR) with anaerobic and oxic/anoxic chambers was designed and assessed for treating different dairy wastewaters. A combination of baffled and biofilm-structured systems under intermittent aeration was the solution proposed to obtain a new method for nitrogen removal under low COD/TN ratios. The COD/TN ratios tested were 2.1 ± 0.6, 0.84 ± 0.5, and 0.35 ± 0.1 in the inlet of the O/A chambers for operational stages I, II, and III, respectively. The SBHBR provided COD removal efficiencies above 90% in all experimental stages. During stage III, the process had nitrification and denitrification efficiencies of 85.9 ± 17% and 85.2 ± 9%, respectively, resulting in a TN removal efficiency of 74.6 ± 14.7%. Stoichiometric calculations were used to corroborate the activity of bacteria that could perform the anammox pathways as their main mechanisms.

An integrated process for struvite recovery and nutrient removal from ship domestic sewage

Marine pollution caused by the untreated and substandard discharge of ship domestic sewage has received widespread attention. A novel integrated process for struvite recovery and nutrient removal from ship domestic sewage (SRNR-SDS) based on seawater magnesium source was developed in this study. Removal efficiencies of the total nitrogen (TN) and total phosphorus (TP) for the activated sludge unit in SRNR-SDS process were approximately 67.61% and 41.35%, respectively, under the salinity of 7.85 g/L. The coupling-induced struvite crystallization unit significantly improved the removal efficiency of TN and TP, and the scanning electron microscopy and X-ray diffraction demonstrated that magnesium ammonium phosphate (MAP) crystals were successfully formed on the surface of zeolite. The SRNR-SDS process had an ideal performance for pollutant removal and MAP recovery under the optimal hydraulic retention time of 20 h. The effluent concentrations of COD, NH₄⁺-N, TN and TP in SRNR-SDS process were approximately 34.73 mg/L, 4.31 mg/L, 10.07 mg/L and 0.23 mg/L, respectively, which meet the Chinese and international ship sewage discharge standards. SRNR-SDS process has obvious environmental, social and economic benefits, which could save 6.20%∼57.14% of the operation cost of ship domestic sewage treatment via MAP recovery. The results could provide theoretical and technical support for the development and application of ship sewage treatment process with the functions of pollutant removal and resource recovery.

Wastewater treatment for ships experiencing large temperature changes： the activated sludge/membrane-biofilm reactor

A particular challenge to treatment systems for ship wastewater comes from low and variable temperatures. We evaluated the temperature response (35-15 °C) of a novel biological treatment system involving activated sludge followed by a membrane-biofilm reactor: the activated sludge/membrane-biofilm reactor (AS-ABfMemR). In this study, a pilot-scale AS-ABfMemR achieved over 96% chemical oxygen demand (COD) and 94% total nitrogen (TN) removal from a ship wastewater (550-960 mgCOD·L^-1 and 52-77 mgTN·L^-1) with a continuous operation with a hydraulic retention time of 12 h at 25 °C. The effluent COD and TN concentrations met IMO discharge standards at temperatures as low as 17 °C, which reduced the energy consumption for wastewater heating. The COD and TN removals of the biofilm stage became important (up to 34% and 35%, respectively) at low temperatures, and this compensated for the deterioration in performance of the aerobic sludge. The genus Azospira dominated in the biofilm's denitrification removal for TN at low temperature. In addition, the buildup of trans-membrane pressure was so slow that backwashing was not needed over the 90 days of continuous operation. These conclusions indicate that the pilot-scale AS-ABfMemR technology is an effective way for real ship sewage treatment under temperature variations.

A hydroponic plants and biofilm combined treatment system efficiently purified wastewater from cold flowing water aquaculture

Recently, more and more cold flowing water aquaculture has been adopted, but its wastewater treatment is always ignored, which causes great pressure on the environment. In this study, a compound in-situ treatment system that applied hydroponic plants and biofilm was constructed to treat the wastewater produced by cold flowing water culture of sturgeon. The removal efficiency of the nutrients from culture and the microbial composition in water and biofilm were tested, the correlation between the water quality indexes and bacterium was analyzed, and the abundance of nitrogen and phosphorus cycling genes was quantified. The results show that the system respectively achieved 90%, 100%, 100%, 100% and 48% removal efficiency of NH₄⁺-N, NO₃^--N, TN, TP and COD which were produced by experimental sturgeon culture. Chinese cabbage (Brassica rapa var. chinensis) and water dropwort (Oenanthe javanica) showed obvious growth in the four plants, which contributed to the removal of nutrients from wastewater. Besides, in the biofilm, Proteobacteria, Bacteroidetes and Verrucomicrobia became the top three dominant flora at the phylum level, and Flavobacterium, Rhodoferax, Sphaerotilus and Chitinimonas became the top four dominant flora at the genus level, which promoted the removal of nitrogen in the wastewater. The FAPROTAX analysis result shows that the highest functions within the carbon and nitrogen metabolisms were significantly identified in the biofilm, such as chemoheterotrophy, aerobic chemoheterotrophy and nitrate reduction. Further, the abundance of denitrifying genes (narG and napA) was higher than the nitrifying related genes (nxrB and amoA), indicating the more active denitrifying process. In summary, the compound in-situ treatment system efficiently removed nutrients from cold flowing water aquaculture. And the combined purification of hydroponic plants and biofilm which is rich in denitrifying bacterium plays an essential role in this process.

Environmental impact, treatment technology and monitoring system of ship domestic sewage: A review

Marine pollution caused by the substandard discharge of domestic sewage from ships has received considerable attention in recent years. Thus, the research and application of efficient treatment and supervision system of domestic ship sewage are matters of considerable interest in marine pollution prevention. The environmental impacts of black and grey water on marine and river environments were reviewed to emphasize the urgency and importance of sewage treatment. Development and changes of emission indexes revealed the emphasis on marine environmental protection and domestic sewage discharge. Based on summarizing the difficulties of high salinity, high organic load and poor stability in ship sewage treatment, the technologies of physical-, chemical- and biochemical-based processing were reviewed. Case study of online monitoring system was displayed to provide research trends. The challenges and future perspectives were also provided to promote supervision and disposal of domestic sewage from ships.

Functional genera for efficient nitrogen removal under low C/N ratio influent at low temperatures in a two-stage tidal flow constructed wetland

A two-stage tidal flow constructed wetland (referred to as TFCW-A and TFCW-B) was used to treat low chemical oxygen demand/total nitrogen (COD/TN or simply C/N) ratio influent at low temperatures (<15 °C). The influence of the flooding-resting time (A: 8 h-4 h, B: 4 h-8 h) and effluent recirculation on nitrogen removal and microbial community characteristics were explored. TFCW-B achieved optimal average nitrogen removal efficiency with effluent recirculation (96.05% ammonium nitrogen (NH₄⁺-N); 78.43% TN) and led to nitrate nitrogen (NO₃^--N) accumulation due to the lack of a carbon source and longer resting time. Ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) were inhibited at low temperatures. Except for nrfA, AOA, AOB, narG and nirS were separated by the flooding-resting time rather than by spatial position. Furthermore, the dominant genera in TFCW-A were Arthrobacter, Rhodobacter, Pseudomonas, and Solitalea, whereas prolonging resting time promoted the growth of Thauera and Zoogloea in TFCW-B. Spearman correlation analysis showed that Zoogloea and Rhodobacter had the strongest correlations with other genera. Moreover, the NH₄⁺-N concentration was significantly positively influenced by Arthrobacter, Rhodobacter, Pseudomonas, and Solitalea but negatively influenced by Thauera and Zoogloea. There was no significant correlation between TN and the dominant genera. This study not only provides a practicable system for wastewater treatment with a low C/N ratio but also presents a theoretical basis for the regulation of microbial communities in nitrogen removal systems at low temperatures.

Simulation and prediction of electrooxidation removal of ammonia and its application in industrial wastewater effluent

A FLUENT software able to predict and assess the electrooxidation of ammonia from the simulation of ammonia concentration and flow field distribution was developed in this study. The flow field-based models of ammonia removal were simulated and modified through the experimental results. The parameter of reaction constant k is corrected to 0.00195, and the modified model fitted well with experimental values, with the error less than 4%. The electrode depth of 4 cm was assessed to be optimal for ammonia removal based on the comparison of the simulation results on ammonia concentration and flow field distribution. The prediction result applied in the industrial wastewater treatment indicated that complete could be achieved at 0.27 Ah/L, and about 50% of total nitrogen was removed at 0.8 Ah/L. About 7% of chloride ions were converted into inorganic by-products, indicating low biological toxicity and risk on environment. The energy consumption increased with the promotion of removal efficiency of total nitrogen, requiring 5.4 kWh/m³ to remove 50% total nitrogen at 0.8 Ah/L. The results show the practicability and feasibility of this FLUENT software tool on the simulation and prediction of electrooxidation process, which can provide the simulation parameter settings for the subsequent application. PRACTITIONER POINTS: A FLUENT software based on the simulation of ammonia concentration and flow field distribution was able to predict and assess ammonia electrooxidation. A modified model is provided with a rate constant k of 0.00195 and the distinction of 4% with experimental results. The optimal electrode depth was predicted to be 4 cm via the obtained model. Complete ammonia and about 50% of total nitrogen could be at 0.27 Ah/L and 0.8 Ah/L, receptively. About 7% of chloride ions were converted into inorganic by-products in industrial wastewater with high chloride.

Synthesis, structure and photocatalytic property of a novel Zn(II) coordination polymer based on in situ synthetized pyridine-3,4-dicarboxylhydrazidate ligand

One new pyridine-3,4-dicarboxylhydrazidate-coordinated compound [Zn(pdh)] 1 (pdh = pyridine-3,4-dicarboxylhydrazidate) was obtained under the hydrothermal conditions. Noteworthily, the pdh molecules in the title compound originated from the ligand in situ reaction between organic pyridine-3,4-dicarboxylic acid (pdca) and N₂H₄·H₂O. X-ray single-crystal diffraction analysis revealed that the pdh ligands exhibit a special μ₄-bridging mode in compound 1, which link Zn(II) centers into a 2D layered structure. The photocatalysis analysis indicates that it is a potential visible light catalyst. In addition, the solid photoluminescence property of compound 1 was also investigated.

Multiple draft tubes airlift loop membrane bioreactor as an efficient system for acidic 7-amino cephalosporanic acid (7-ACA) wastewater treatment

In this study, a lab-scale multiple draft tubes airlift loop membrane bioreactor (Mt-ALMBR) was used for treating acidic 7-amino cephalosporanic acid (7-ACA) wastewater under different pHs (3.54-6.20) and hydraulic retention time (HRT) (48 h, 36 h, 24 h and 16 h). During about 200 days operation, under HRT of 48 h and pH condition about 6.0, the optimum average COD and BOD₅ removal rates were reach to 84.4 ± 2.1% and 94.9 ± 0.8%, and the highest 7-ACA removal rate also observed as 77.6%. Biodegradation, membrane rejection, hydrolysis and sludge adsorption were the four main pathways of 7-ACA removal. With the increase of pH, biodegradation, membrane rejection and hydrolysis had significant positive impacts on 7-ACA removal, while adsorption had a negative impact. Moreover, mathematical models for 7-ACA removal rate and pH were calculated to guide the operation of Mt-ALMBR. Biodegradation was the main pathway to remove 7-ACA when pH was >4.17.

Landfill leachate as an additional substance in the Johannesburg-Sulfur autotrophic denitrification system in the treatment of municipal wastewater with low strength and low COD/TN ratio

Johannesburg-Sulfur autotrophic denitrification (JHB-SAD) system was investigated for the combined treatment of leachate and municipal wastewater with low strength and low COD/TN ratio. The average removal efficiencies for chemical oxygen demand (COD), total nitrogen (TN) and total phosphorus (TP) were 85.2%, 96.2% and 75.8%, respectively. The municipal wastewater and leachate (dosing of 2.1‰, v/v) can be treated via the JHB-SAD system to achieve efficient nutrients removal. The mass balance calculations suggested that 58.1-69.8% TN was removed in JHB unit and 32.9-41.2% TN in SAD unit. Further, the denitrifying phosphorus removal process occurred in the anoxic zone. EEM-PARAFAC analysis found that the protein-like materials were more efficiently removed than fulvic-like materials in JHB-SAD system. The tryptophan-like materials had the most positive linear relationship with the COD concentrations. The bacterial community was difference between JHB and SAD unit. Furthermore, bacteria abundance relating to nitrogen removal increased with additional leachate.

Influence of salinity on the biological treatment of domestic ship sewage using an air-lift multilevel circulation membrane reactor

Recently, strict standards for ship domestic sewage discharge have been implemented by the International Maritime Organization (IMO). The high salinity of ship sewage was considered a key factor influencing the removal efficiency of ship sewage treatment systems. In the present study, the salinity effect on the removal of chemical oxygen demand (COD) and ammonia nitrogen (NH₄⁺-N) from ship domestic sewage was investigated by using a novel air-lift multilevel circulation membrane reactor (AMCMBR). Enzyme activity analysis and wavelet neural network (WNN) models were built to determine the mechanisms of the process. The experimental results indicate that high salinity levels (> 21 g/L) had a negative impact on COD and NH₄⁺-N removal efficiencies, and low saline concentrations (≤ 21 g/L) caused a negligible effect. The COD and NH₄-N removal efficiencies were 84% and 97%, respectively, at a salinity of 21 g/L, which were higher than those at low salinities (i.e., 7 g/L and 14 g/L). Invertase and nitrate reductase had a close relationship with removal performance, and they can be considered important indicators reflecting the operation effort under saline environments. With high predictive accuracies, the constructed WNN models simulated the complex COD and NH₄⁺-N removal processes well under different saline concentrations, ensuring the long-term stable operation of the AMCMBR under different salinities.