Cost Of Wastewater Treatment Research Articles

Development of an efficient pretreatment process and multi-functional acetate co-metabolism strategy for the treatment of high strength biogas slurry using a newly isolated Chlorella sorokiniana

The efficient treatment of biogas slurry (BS) to meet the government’s discharge standards is a major challenge for most livestock and poultry enterprises. Although microalgae-based wastewater treatment has many significant benefits over traditional technologies, the poor ammonium tolerance of regular algal species, the pH imbalance during microalgae cultivation, and the complex and expensive BS pretreatment process greatly limit its application in BS treatment. Aimed at these issues, this study firstly isolated a robust Chlorella sp. with strong ammonium and acidic tolerance, as well as heterotrophy ability. To facilitate optimal pH stability and growth enhancement, a co-metabolism cultivation strategy based on the addition of 0.1 g·L-1 acetate in the form of fed-batch was developed. In addition, an efficient pretreatment process integrating ammonia reduction by air stripping with turbidity and chromaticity reduction by acidic precipitation was developed for the elimination of inhibitory factors of microalgal growth in BS. The isolated Chlorella sp. was capable of growing in the pretreated real BS and no growth inhibition was observed even in the undiluted BS. The acetate co-metabolism cultivation strategy obviously enhanced cell growth and pollutant removal and both NH4+ and total phosphorus were reduced to meet the discharge standards of China via 2.5-fold dilutions of BS. The accumulation of high-value biomass could not only fully cover the cost of wastewater treatment, but also bring significant returns. The net profit from treating 1 m3 of BS reached $ 116.2. This study provides a simple and efficient packaged process for the treatment of high strength BS and is expected to greatly reduce the process cost of BS.

Life Cycle Assessment of Industrial Wastewater Treatment Trains

AbstractAlternative technologies to granular activated carbon (GAC) are of interest to improve the sustainability and reduce the cost of munitions wastewater treatment. Research efforts have highlighted GAC alternatives, yet few reports of environmental and economic impacts associated with these technologies are available. Herein, a life cycle assessment (LCA) aids in assessment of environmental impacts associated with six munitions wastewater treatment configurations—specifically GAC, compared to five configurations that include combinations of ion exchange (IX), reverse osmosis (RO), aerobic granular reactors (AGR), UV/H2O2, and ozone technologies. The LCA compares environmental impacts generated by treating 1 m3 of munitions wastewater, impacts by life cycle stage, and effects of IX, RO, and GAC replacement frequency. Results show that IX resin pairs with AGR (for flow‐through treatment) and ozone (for IX regenerant treatment) generated 22 ± 18% less impact than GAC in nine of ten environmental impact categories during production, transportation, and disposal. Treatment trains with ozone or AGR produce 35% less environmental impact than those with UV/H2O2. Production and use stages generate more environmental impacts than transportation and disposal stages for most treatment technologies. This LCA provides insights into the sustainability of six munition wastewater treatment technologies and identifies areas where treatment sustainability can be improved.

Effects of iron-carbon on nitrogen metabolism of floc and aerobic granular sludge

The aerobic granular sludge (AGS) process had been extensively studied for its simultaneous nitrification and denitrification (SND) capabilities. Iron-carbon (IC) had enhanced AGS nitrogen removal efficiency, but the mechanism remained unclear. In this study, four reactors had been added with 50, 30, 10, and 0 g/L of IC. Total nitrogen removal efficiency increased with IC dosage under the same operation mode. IC enhanced sludge ammonia oxidation rate, denitrification rate, and specific oxygen uptake rate, allowing SND to complete 60 min earlier, potentially reducing wastewater treatment costs. Notably, IC eliminated nitrite accumulation in conventional AGS effluent. IC decreased the abundance of genes and enzyme activities related to NOR expression, while increasing those related to NOS, which may mitigate the potential for nitrous oxide formation by microorganisms. In this study, IC acted as an enzymatic reaction activator, affecting granules more than flocs, with the activity gap gradually decreasing with the IC dosage.

TiO2/Ti3C2Tx gel microsphere for efficient photocatalytic degradation of organic pollutant with excellent recycling stability

Enhancing the recycling stability of photocatalysts is crucial for practical applications. The significant loss of powder catalyst materials during the recycling process hampers its degradation rate and results in a low reuse rate. Herein, the in-situ prepared TiO2/Ti3C2Tx (TOTC) heterojunction is embedded in gel microsphere (GMS) as a recyclable photocatalyst TOTC@GMS for efficient photocatalytic degradation of Congo red (CR). The experimental results show that the removal rate can reach 99 % in 120 min without any co-catalysts or sacrificial reagents. The GMS can be recycled after rinsing in deionized water for only 2 min, and the removal rate still maintains over 90 % after 25 cycles. Additionally, under natural sunlight exposure, TOTC@GMS achieves a removal rate of 90 % for CR in real water samples. The degradation mechanism is elucidated through hydroxyl radicals (OH) and superoxide radicals (O2−) as the main reactive species, as confirmed by free radical scavenging and electron paramagnetic resonance (EPR) experiments. The degradation products are further analyzed using high-performance liquid chromatography-mass spectrometry (LC-MS), allowing for the deduction of degradation pathways of CR. Furthermore, a phytotoxicity test confirms the non-toxicity of the organic micromolecules generated after degradation. This study presents a practical strategy to improve the recycling stability of photocatalysts, thereby effectively reducing the cost of wastewater treatment.

Ozone/biological aerated filter integrated process for recycled paper mill wastewater: A pilot-scale study

In this study, the effluent from recycled paper mill was treated using a combined ozone (O3) and biological aerated filter (BAF) process. Key operational parameters such as ozone dosage, pH, hydraulic retention time (HRT), volume load and gas-to-water ratio were optimized. Under optimal conditions, with a total ozone dosage of 100 g/m, a gas-to-water ratio of 4:1, and an HRT of 3.0 hours in the BAF, the chemical oxygen demand (COD) and chroma of the treated wastewater were reduced to 44–55 mg/L and 2–4 PCU, achieving removal efficiencies of 70 % and 95 %, respectively. The discharge effluent not only satisfy the new discharge standard of China (GB3544–2008), but also can be used as recycling water. Additionally, the treatment cost of wastewater was ca. 1.3 ¥/m3 in pilot-scale test, significantly decreasing the cost. Ozone pretreatment has a significant effect on wastewater decolorization by disrupting the molecular chemical structure of pollutants, which increase the biochemical properties of biofilm and is beneficial to the sequential BAF treatment. The sludge in the O3/BAF system exhibited increased biomass with minimal filamentous bacteria and higher dehydrogenase activity, confirming stable and robust bacterial growth. GC-MS analysis revealed substantial reduction in pollutant content and diversity post-treatment, although the recalcitrant compound (Z)-13-docosenamide remained relatively high, decreasing from 27.37 % to 21.14 %. The mechanism of the O3/BAF process for the pollutant degradation were also proposed. This study demonstrated that a combination of ozone and fixed biofilm treatment is an efficient and cost-effective treatment, providing the theory and practical applicability for the industrial wastewater.

Pathway reconstruction and metabolic engineering for the de novo and enhancing production of monacolin J in Pichia pastoris.

The statin is the primary cholesterol-lowering drug. Monacolin J (MJ) is a key intermediate in the biosynthetic pathway of statin. It was obtained in industry by the alkaline hydrolysis of lovastatin. The hydrolysis process resulted in multiple by-products and expensive cost of wastewater treatment. In this work, we used Pichia pastoris as the host to produce the MJ. The biosynthesis pathway of MJ was built in P. pastoris. The stable recombinant strain MJ2 was obtained by the CRISPR (clustered regularly interspaced short palindromic repeats)-Cas9 genome-editing tool, and produced the MJ titer of 153.6 ± 2.4mg/L. The metabolic engineering was utilized to enhance the production of MJ, and the fermentation condition was optimized. The MJ titer of 357.5 ± 5.0mg/L was obtained from the recombinant strain MJ5-AZ with ATP-dependent citrate lyase (ACL), glucose-6-phosphate dehydrogenase (ZWF1) and four lovB genes, 132.7% higher than that from the original strain MJ2. The recombinant strain MJ5-AZ was cultured in a 7-L fermenter, and the MJ titer of 1493.0 ± 9.2mg/L was achieved. The results suggested that increasing the gene dosage of rate-limiting step in the biosynthesis pathway of chemicals could improve the titer of production. It might be applicable to the production optimization of other polyketide metabolites.

Techno-economic analysis of cleaner alternatives for recovering ammonium chloride from wastewater generated by polyvinyl chloride thermal stabilizer plants

The current conventional process for recovering NH4Cl from wastewater generated by organotin mercaptide-based polyvinyl chloride thermal stabilizer plants through evaporative crystallization is energy intensive and has not yet been discussed. Three energy-saving process variants, namely mechanical vapor recompression (MVR), double-effect evaporation (DEE), and thermal vapor recompression (TVR) processes, have been proposed and evaluated in terms of both technical and economic feasibility, treating the case as a cost-cutting project aimed to avoid off-site wastewater treatment costs. Comparative evaluation has also been carried out with the conventional (CON) process used as a reference. Under the studied conditions, the MVR, DEE, and TVR processes provided energy savings in the ranges of 60%–76%, 35%–43%, and 26%–37%, respectively, confirming that applying the three alternative processes for recovering NH4Cl results in a significantly cleaner and more sustainable recovery process. Under typical conditions and with a plant capacity of 5000 kg/h, the MVR, DEE, and TVR processes required an additional investment of 2.3, 1.0, and 0.2 million USD, respectively, compared to the CON process. The revenue was primarily driven by cost savings due to the elimination of off-site wastewater treatment, which accounted for 86.9% of the total revenue. Sensitivity analysis showed that the off-site wastewater treatment cost was found to be the most influential factor on economic feasibility. When economic targets can be traded off, MVR process is highly recommended as an alternative to the conventional energy-intensive process. If economic feasibility comparable to the conventional process is still targeted, DEE and TVR are recommended. The results of this study dismiss concerns that cleaner processes would have a negative economic impact.

Performance and Mechanism of the Modified Group Regulated the MIL-101(Fe) Type Fenton-like Catalysts.

In order to avoid the disadvantages of the Fenton process in wastewater treatment and reduce the cost of wastewater treatment, a series of MIL-101(Fe)-X (X = -OH, -NH2, -NO2, -H) solid Fenton catalysts were successfully prepared. The performance of these Fenton-like catalysts was studied with the Fenton experiment as a reference and methylene blue (MB) as an organic pollutant. The effects of the H2O2 concentration, catalyst dosage, and reaction pH on catalytic performance were systematically studied. The research had shown that the optimal concentration of H2O2 for catalytic reactions was 0.10 mmol/L and the pH was 3. At this point, their catalytic degradation MB performance was superior to the Fenton reaction and photocatalytic reaction. When the H2O2 participated in the reaction, the performance of MIL-101(Fe)-X (X = -OH, -NH2, -NO2, -H) in catalyzing the degradation of MB followed the rule of -OH > -NH2 > -NO2 > -H. This was due to the synergistic effect of Fenton-like catalysis and photocatalytic degradation in the catalytic degradation of MB. In addition, the electron paramagnetic resonance and electrospray ionization mass spectrometry showed that the hydroxyl radical (·OH) generated during the catalytic process first underwent a redox reaction with the highly electronegative functional groups in the MB molecule, and finally oxidized it to CO2 and H2O. This study successfully prepared commercially applicable Fenton-like catalysts and explored their optimal reaction conditions. This provides a technical reference for wastewater treatment.

Selection of Various Indications of Tempering Lubricant Concentration Reuse in the Wet Rolling Process

ABSTRACTDiscarded tempering lubricants retained significant reuse potential, making their recycling a vital step in reducing resource wastage and wastewater treatment costs in the strip steel industry. Hence, developing an accurate, rapid evaluation indicator for recycled fluid concentration was essential for facilitating this process. Research showed that among common evaluation indicators for metal fluids, three—electrical conductivity, refractive index and total base number (TBN)—due to their high linear correlation with tempering lubricant concentration (R2 > 0.995), could be utilised to monitor the dynamic changes in the concentration of tempering lubricants. Subsequent experiments on reused tempering lubricants revealed that electrical conductivity, significantly altered by iron powder (7%–24% variance), and refractive index, impacted by hydraulic oil (3% deviation), highlighted contaminant challenges; yet, filtration effectively mitigated iron powder's effect on TBN. Finally, A 17‐day reused tempering lubricants simulation demonstrated consistent effectiveness of the three indicators in monitoring the need to update tempering lubricant concentration. However, in terms of sensitivity, precision, and particularly stability and relative mean deviation, the TBN concentration evaluation indicator outperformed, with TBN (3.38%) < Refractive Index (7.92%) < Electrical Conductivity (11.05%). This indicates the TBN method's superior stability over conductivity and refractive index methods, with its accuracy deviation below 2%, making it a stable, simple and reliable metric worthy of broader adoption.

Treatment of Wastewaters with Different Ammonium Concentrations in a Sequencing Batch Reactor by Nitritation and Denitritation Processes

In the treatment of industrial and municipal wastewaters, biological nitrification and denitrification processes have been widely applied methods. However, in recent years, experimental studies have been carried out on nitritation and denitritation processes in order to reduce the cost of wastewater treatment. In this study, the removal of synthetic wastewaters containing ammonium at various concentrations through nitritation and denitritation processes was investigated in a sequence batch reactor (SBR). The SBR was operated at a low dissolved oxygen concentration of 0.7±0.2 mg/L, while the initial pH level and temperature were kept constant at 7.5 and 25 ℃, respectively, which were below the defined optimal level for nitritation. For the initial concentrations of 100, 150, and 200 mg NH4-N/L, 91, 142, and 180 mg NOx-N were produced, respectively with the specific nitritation rates of 0.69, 0.95, and 0.81 mg NH4-N/mg MLVSS.hour. Considering the operating conditions of nitritation, approximately NO2-N/NOx-N ratio of 80% could be considered as successful with the combined effect of DO limitation and NH3 inhibition on the nitrite oxidizing bacteria. During the first days of nitritation and denitritation processes, change of nitrogen concentrations was negligible because the adaptation of organisms to the oxic and anoxic conditions. After completing nitritation stage, denitritation was carried out by using methanol as an electron donor for the initial concentrations of 91, 142, and 180 mg/L of NOx-N in 96, 120 and 264 hours of reaction times, respectively.

An optimal standalone wind-photovoltaic power plant system for green hydrogen generation: Case study for hydrogen refueling station

Sustainability goals include the utilization of renewable energy resources to supply the energy needs in addition to wastewater treatment to satisfy the water demand. Moreover, hydrogen has become a promising energy carrier and green fuel to decarbonize the industrial and transportation sectors. In this context, this research investigates a wind-photovoltaic power plant to produce green hydrogen for hydrogen refueling station and to operate an electrocoagulation water treatment unit in Ostrava, Czech Republic's northeast region. The study conducts a techno-economic analysis through HOMER Pro® software for optimal sizing of the power station components and to investigate the economic indices of the plant. The power station employs photovoltaic panels and wind turbines to supply the required electricity for electrolyzers and electrocoagulation reactors. As an off-grid system, lead acid batteries are utilized to store the surplus electricity. Wind speed and solar irradiation are the key role site dependent parameters that determine the cost of hydrogen, electricity, and wastewater treatment. The simulated model considers the capital, operating, and replacement costs for system components. In the proposed system, 240 kg of hydrogen as well as 720 kWh electrical energy are daily required for the hydrogen refueling station and the electrocoagulation unit, respectively. Accordingly, the power station annually generates 6,997,990 kWh of electrical energy in addition to 85595 kg of green hydrogen. Based on the economic analysis, the project's NPC is determined to be €5.49 M and the levelized cost of Hydrogen (LCH) is 2.89 €/kg excluding compressor unit costs. This value proves the effectiveness of this power system, which encourages the utilization of green hydrogen for fuel-cell electric vehicles (FCVs). Furthermore, emerging electrocoagulation studies produce hydrogen through wastewater treatment, increasing hydrogen production and lowering LCH. Therefore, this study is able to provide practicable methodology support for optimal sizing of the power station components, which is beneficial for industrialization and economic development as well as transition toward sustainability and autonomous energy systems.

Mitigation of caffeine micropollutants in wastewater through Ag-doped ZnO photocatalyst: mechanism and environmental impacts.

Micropollutants, such as caffeine (M-CF), pose a significant threat to ecosystems and human health through water and food sources. The utilization of metal oxide-based photocatalysts has proven to be an effective treatment method for the removal of organic pollutants. This study explores the efficacy of Ag-doped ZnO (Ag/ZnO) for removing M-CF from wastewater. The characterization of Ag/ZnO underscores the crucial role of band gap energy in the photocatalytic degradation process. This parameter influences the separation of electrons and holes (e-/h+) and the generation of reactive radicals. Under solar light, Ag/ZnO demonstrated markedly superior photocatalytic activity, achieving an impressive degradation efficiency of approximately 93.4%, in stark contrast to the 53.2% occurred by ZnO. Moreover, Ag/ZnO exhibited a remarkable degradation efficiency of M-CF in wastewater, reaching 83.5%. A key advantage of Ag/ZnO lies in its potential for recovery and reuse in subsequent treatments, contributing to a reduction in operational costs for industrial wastewater treatment. Impressively, even after five cycles, Ag/ZnO maintained a noteworthy photodegradation rate of M-CF at 78.6%. These results strongly suggest that Ag/ZnO presents a promising solution for the removal of micropollutants in wastewater, with potential scalability for industrial and large-scale applications.

Perspectives on sustainable process control optimization through reusability of non-regenerated Fenton sludge in landfill leachate treatment

The production of iron-rich waste (Fenton sludge) and the high chemical dosage required in the Fenton-based advanced oxidation process (AOP) harm the environment, making disposal challenges and the technique unsustainable. Thus, finding adequate Fenton sludge (FS) reuse alternatives is critical to addressing the Fenton process's drawbacks in addition to environmental protection. This study signifies that FS could be employed satisfactorily without requiring costly regeneration operations or chemical dosages, such as landfill leachate, during wastewater treatment. In this study, two sets of experiments were carried out utilizing the most often used optimization tools: design of experiments (DOE) (central composite design (CCD)/response surface methodology (RSM). Under optimized conditions, reasonably high chemical oxygen demand (COD) removal of 62 %, total suspended solids (TSS) removal of >95 %, and colour removal of >80 % was obtained after 48 min of reaction time with 84 mL/L sludge reused at pH 3.6. The method's key influencing factors were sludge volume, pH, and reaction time. Furthermore, reused FS exhibited lower toxicity and total volatile solids, indicating that sludge reuse is superior to direct disposal. According to the techno-economic analysis, using non-regenerated sludge as proposed reduces toxic iron-based waste and total wastewater treatment costs.

Resourceful application and mechanism of oyster shell-microalgae synergistic system：Sustainable treatment of harsh low carbon nitrogen ratio actual wastewater

Microalgal technology holds great promise for both low C/N wastewater treatment and resource recovery simultaneously. Nevertheless, the advancement of microalgal technology is hindered by its reduced nitrogen removal efficiency in low C/N ratio wastewater. In this work, microalgae and waste oyster shells were combined to achieve a total inorganic nitrogen removal efficiency of 93.85% at a rate of 2.05 mg L−1 h−1 in low C/N wastewater. Notably, over four cycles of oyster shell reuse, the reactor achieved an average 85% ammonia nitrogen removal extent, with a wastewater treatment cost of only $0.092/ton. Moreover, microbial community analysis during the reuse of oyster shells revealed the critical importance of timely replacement in inhibiting the growth of non-functional bacteria (Poterioochromonas_malhamensi). The work demonstrated that the oyster shell - microalgae system provides a time- and cost-saving, environmental approach for the resourceful treatment of harsh low C/N wastewater.

Enhancing wastewater treatment efficiency: A hybrid technology perspective with energy-saving strategies

The study aimed to investigate how hybrid technology, combined with various intermittent aeration (IA) strategies, contributes to reducing the energy costs of wastewater treatment while simultaneously ensuring a high treatment efficiency. Even with IA subphases lasting half as long as those without aeration, and oxygen levels reduced from 3.5 to 1.5 mg O2/L, pollutants removal efficiency remains robust, allowing for a 1.41-fold reduction in energy consumption (EO). Hybrid technology led to a 1.34–fold decrease in EO, along with improved denitrification efficiency from 74.05 ± 4.71 to 81.87 ± 2.43 % and enhanced biological phosphorus removal from 35.03 ± 4.25 to 87.32 ± 3.64 %. The high nitrification efficiency may have been attributed to the abundance of Pseudomonas, Acinetobacter, and Rhodococcus, which outcompeted the genera of autotrophic nitrifying bacteria, suggesting that the hybrid system is favorable for the growth of heterotrophic nitrifiers.

Joint Modeling and Operational Optimization of a Reverse Osmosis-Mechanical Vapor Recompression System for Coal-Fired Power Plant Wastewater.

The operation of coal-fired power plants generates a large amount of wastewater. With the issuance of increasingly strict drainage standards, the cost of wastewater treatment is increasing, and the need to reduce the cost of wastewater treatment is becoming increasingly urgent. Thus, based on the principles of reverse osmosis (RO) and mechanical vapor recompression (MVR) in wastewater treatment, the operational optimization of an RO-MVR joint system was studied in this work with the consideration of reducing the operating costs of wastewater treatment under given operational conditions. Firstly, based on the basic principles of RO and MVR, corresponding mechanism models were established and their accuracy was verified. Then, an economic model of the RO-MVR joint system was established, with the goal of minimizing the water production unit price and daily operating costs of the joint system for optimization analysis. Finally, we analyzed the cost and water production performance of the RO-MVR joint system before and after optimization under different operating conditions. The results show that this optimization based on the RO-MVR joint system will reduce the unit price of water production to 3.16 CNY/m3, with the daily operating costs being decreased by 22% compared to before optimization. This result helps to reduce the cost of zero-discharge wastewater treatment in coal-fired power plants.

River water quality management using an integrated multi-objective optimization-simulation approach based on bankruptcy rules.

The aim of this research is to allocate the river's self-purification (acceptance capacity of pollution) fairly between the beneficiaries (pollutant sources) using bankruptcy theory. For this purpose, four bankruptcy rules (CAE, CEL, P, and TAL) were called using the link of the water quality simulation model (QULA2Kw) to an evolutionary optimization algorithm (multi-objective imperialist competition algorithm (MOICA)). The objective functions were reducing polluters' wastewater treatment costs and preventing biochemical oxygen demand (BOD) violations of the standard level along the river. The applicability of the approach is demonstrated by the case study that was carried out on the Dez River in Iran. According to the results, the CEL scenario is the most effective method for the Dez River when taking into account the most optimal state for both objective functions (selecting the best compromise solution from the Pareto front). This is because it has the lowest violation value of the standard level for BOD along the river when compared to other scenarios. Alternatively, when considering Solution 20, which focuses on the maximum cost of treating the polluters while staying within the acceptable level of pollution in the river, the results indicated that the CEA rule emerged as the most favorable option. This is due to its lower treatment cost (156.9 (1000$)) and higher pollution discharge to the river (681.91 g/s).

Using ohmic heating to shorten the tempering time for frozen fish

SummaryThawing is necessary to restore the freshness of fish before cooking because fish is often frozen to retain its freshness. Frequently, fish is partially thawed (or ‘tempered’) as it is easier to handle in this form than fully thawed fish. However, the conventional tempering techniques – immersion in water and still air tempering – take a long time and alter the fish's characteristics. Hence, the aim of this study was to use the heat generated inside the frozen fish, or ohmic heating, to alter the tempering process. Compared with conventional tempering operations, in this study, three voltage levels (20, 30 and 40 V/cm) were used for ohmic tempering. The fish quality and yield findings revealed that 30‐V/cm ohmic heating was more appropriate, even though ohmic heating at 40 V/cm provided the shortest tempering time. The main operating expense for ohmic tempering was the power cost of USD 58.5/100 kg, whereas the major operating expense for water immersion was the cost of water supply and wastewater treatment, which was around USD 108/100 kg. By using ohmic heating instead of still air and water immersion to temper the frozen fish, not only was less time required while retaining the freshness of the fish but the cost of tempering was also reduced.

In situ production of bacterial nanocellulose-activated carbon composites from pear juice industry wastewater by two new Komagataeibacter intermedius and Komagataeibacter xylinus isolates for heavy metal removal

Fruit juice industry generates a large amount of wastewater, which contains substantial waste activated carbon for juice turbidity removal. Due to the low concentrations of useful compounds in the wastewater, the cost for the extraction is extremely high. Two new bacterial nanocellulose (BNC) producing strains were isolated and identified. These strains produced 6.11 and 1.38 folds BNC from pear juice wastewater than from a conventional medium, respectively. BNC spontaneously encapsulated the suspended waste activated carbon particles during the fermentation, flocculating and collecting the particles without additional filtration or centrifugation processes. FE-SEM, FT-IR, TGA and XRD showed that the fiber diameters, chemical structure, thermal stability and crystallinity of BNC produced from the pear juice wastewater supernatant was similar to that from the conventional medium. FE-SEM revealed the three-dimensional package structure of the BNC-activated carbon composite, and XRD showed that the crystallinity of the composite was improved up to 86%. The BNC-activated carbon composite exhibited excellent adsorption performance towards heavy metals, and the maximum adsorption capacities for Cu2+ and Zn2+ were 20.71 mg/g and 76.92 mg/g within 60 min, respectively. Especially, compared to activated carbon, the adsorption capacity of the composite for Zn2+ was improved for 25.01%. This study utilized pear juice wastewater as an alternative medium to produce BNC at lower cost, and reduced BOD and wastewater treatment costs. Additionally, BNC encapsulated residual activated carbon left over in the wastewater, preventing dust pollution and enabling recycling of the waste activated carbon, and formed a composite with excellent heavy metal absorption capacity.

Enhanced synergistic system for the persulfate activation under visible light using novel N–ZnO photocatalyst supported on Lantana camara-based biochar

Herein, a novel nitrogen-doped ZnO photocatalyst supported on biochar (N–ZnO@LBC) was synthesized using the Lantana camera as a green source of biochar. The synthesized photocatalyst was applied as an activator of persulfate (PS) for the photodegradation of methylene blue (MB) under visible light irradiation. The properties of the synthesized photocatalyst were explored before and after photocatalysis using different characterization analyses. The results revealed that the nitrogen doping of ZnO@LBC could reduce the band gap energy from 2.83 eV to 2.78 eV resulting in higher activity under visible light. The synergetic effect of the N–ZnO@LBC/PS/visible process was investigated under various reaction conditions. Surprisingly, about 95.7% of MB photodegradation could be achieved using N–ZnO@LBC/PS/visible process under optimal conditions. Moreover, a prediction model with an excellent correlation between the actual and predicted data (R2 = 0.9844) was established to forecast MB removal. Interestingly, the scavenging tests exhibited that various reactive species could induce MB degradation in an order of O2−• > h+ > SO4−• >•OH with the highest contribution of O2−•. Additionally, the presence of functional hydroxyl groups in the N–ZnO@LBC structure could lead to the generation of additional radicals as confirmed by FT-IR analysis after photocatalysis. The reusability test showed that the photocatalyst could be reused for up to five cycles without a significant loss in the photocatalytic activity indicating its high stability. The cost of wastewater treatment by N–ZnO@LBC/PS/Visible process was estimated to be US$ 9.79/m3 based on an economic analysis. It worth mentioning that the proposed process was investigated for the degradation of other dyes including Congo red (CR) and methyl orange (MO) and the efficiencies were 65.41% and 59.23% for CR and MO, respectively. Overall, the proposed process could be a promising and cost-effective approach for the degradation of various dyes in real applications.