Discharge Limits Research Articles

Study on the compatibility of a treated effluent from automobile industry with conventional municipal activated sludge process

AbstractThe on-site-treated effluent from an automobile manufacturing company is discharged into the public sewage system for further treatment. However, the upgrade of the treatment plant to reduce the effluent pollutant load led to the discharge limit for phenols being occasionally exceeded. The concern of the water authority prompted a study to investigate whether the toxicity of phenols could affect the performance of the receiving municipal wastewater treatment plant. To this end, mixtures of the industrial effluent and synthetic municipal wastewater were tested in a laboratory-scale activated sludge system. The bioreactor was fed with increasing ratios of the industrial wastewater in the combined influent (from 10 to 50%) over 7 months. No significant differences were observed in the system performance fed only with the synthetic wastewater (during the acclimation stage) or with the industrial wastewater. The bioreactor achieved average removal efficiencies of 70% for phenols even when half of the combined influent was the industrial wastewater. Bearing in mind the question of phenols, an important drawback was the high uncertainty in their determination by the conventional phenol index method due to the matrix effect. To overcome this a spectrophotometric procedure based on the serial dilutions of each pair of influent and effluent samples has been developed. Although strong microbial selection was observed by the changing bioreactor environment, the industrial effluent was found to be fully compatible with further treatment by conventional activated sludge process.

Machine learning assisted combined systems of wastewater treatment plants with constructed wetlands optimal decision-making

This study proposed an efficient framework for optimizing the design and operation of combined systems of wastewater treatment plants (WWTP) and constructed wetlands (CW). The framework coupled a WWTP model with a CW model and used a multi-objective evolutionary algorithm to identify trade-offs between energy consumption, effluent quality, and construction cost. Compared to traditional design and management approaches, the framework achieved a 27 % reduction in WWTP energy consumption or a 44 % reduction in CW cost while meeting strict effluent discharge limits for Chinese WWTP. The framework also identified feasible decision variable ranges and demonstrated the impact of different optimization strategies on system performance. Furthermore, the contributions of WWTP and CW in pollutant degradation were analyzed. Overall, the proposed framework offers a highly efficient and cost-effective solution for optimizing the design and operation of a combined WWTP and CW system.

Constructed wetland – Microbial fuel cell (CW-MFC) packed with suspended fillers to enhance denitrification with Acorus calamus biomass addition

There is an urgent need to meet strict nitrogen discharge limitation for secondary effluent from wastewater treatment plants, but the nitrogen removal is restricted due to the lack of carbon sources. To address the issues, high-density polyethylene (HDPE) was utilized in the constructed wetland-microbial fuel cell (CW-MFC) for the treatment of low carbon wastewater. Meanwhile, wetland plant biomass was efficiently reclaimed, leading to higher nitrogen removal and bioelectricity generation. CW-MFC with biomass added in the anode attained the maximum total nitrogen (TN) removal of 97.55 % and power density of 2.22 mW/m2 with hydraulic retention time (HRT) of 2d, which were much better than those in CW, CW-MFC with no biomass and CW-MFC with biomass added in the cathode. Owing to the HDPE fillers and Acorus calamus biomass addition in CW-MFC, more than 88 % chemical oxygen demand (COD) and 70 % TN were removed with HRT of 1.5d. In addition, metabolisms related to glycolysis, cellulose degradation and nitrogen were increased in CW-MFC, contributing to the enrichment of denitrifying, electroactive and heterotrophic nitrification-aerobic denitrification (HN-AD) bacteria. This study verifies the feasibility of application of HDPE as the biocarriers in CW-MFC and provides mechanistic insights for the enhancement of nitrogen removal in low carbon wastewater treatment with plant biomass addition.

Carbon emission calculation of three biological nitrogen removal processes: A case of rare earth element tailings wastewater in Southern Jiangxi, China

Global warming has been caused by greenhouse gases (GHGs) released by human activity. Traditional sewage treatment uses much energy to achieve discharge limits in the water treatment industry, producing many GHG emissions. In this study, the emission factor approach and mass balance method are used to calculate the carbon emission equivalent of nitrification and denitrification, anaerobic ammonia oxidation, and microalgae assimilation using a rare earth tailings (REEs) wastewater example. The results show that, among the three denitrification processes, the traditional nitrification and denitrification method has the greatest carbon emission equivalent (16.23 kgCO2/kgN). Direct causes include N2O emissions, which account for 48 % of the total carbon emission equivalent. The anaerobic ammonia oxidation process produces the carbon dioxide equivalent of 0.02 kgCO2/kgN. Carbon emission comparable to microalgal assimilation is −3.23 kgCO2/kgN. The anaerobic ammonia oxidation process can thus greatly reduce carbon emissions when compared to the conventional nitrification and denitrification processes, whilst microalgae assimilation can result in negative carbon emissions.

Treatment of food processing industries wastewaters using a new clay-based inorganic membrane: Performance evaluation and fouling analysis

BackgroundCeramic membranes are intensely extending their applicability in wastewater treatment due to their excellent resistance to corrosive environment, anti-fouling nature, and longer lifetime. To further widen the usage of ceramic membranes despite of their high cost, development of inexpensive ceramic membranes is highly anticipated. MethodA novel inexpensive Fuller's earth clay ceramic membrane's performance was evaluated in treating the wastewater obtained from two food processing industries, namely the dairy industry and palm oil industry, by varying the applied pressure from 0.35 – 2 bar. Furthermore, the fouling mechanism concerning the microfiltration of wastewater was identified with the help of Hermia's pore blocking models. Significant FindingsThe prepared novel Fuller's earth clay ceramic membrane significantly reduced COD content below the permissible discharge limit (< 200 mg/L) for dairy and palm oil industry wastewaters at a pressure of 0.35 bar. Notably, 98 – 99 % removal of turbidity and suspended solids was achieved. Also, the total phosphorus content was brought down below the permissible discharge limit of 5 mg/L. From fouling analysis, it was inferred that the cake filtration model appropriately fits the obtained experimental results, confirming the anti-fouling nature of the fabricated clay membrane in treating food process industries' wastewater.

Treatment of greywater with nanofiltration for nutrient removal – 2-year experience from Helsingborg

Abstract Source-separated sanitation and greywater treatment have become an increasingly attractive alternative to traditional wastewater management systems in recent years due to their potential to combat water scarcity, ease resource recovery, and meet tightening effluent demands. In Helsingborg, Sweden, source-separated wastewater from the new city district of Oceanhamnen is being collected and treated in a new treatment plant (RecoLab) to test, among other issues, how efficient greywater treatment can be in achieving low discharge limits for pollutants. The greywater treatment consists of activated sludge treatment, drum filter micro-sieving, and nanofiltration. In the first two years of operation, the robustness of the treatment system during periods with extreme conditions, e.g., very low and very high organic matter concentrations, was tested. The combination of biological treatment and nanofiltration has achieved stable effluent concentrations below 10 mg/L chemical oxygen demand, 2 mg/L total nitrogen, and 0.2 mg/L total phosphorus as average values for 22 months of operation with an average flow of 43 m3/day. The treatment system for greywater treatment thus shows the possibility to achieve low discharge limits and meet the new proposed effluent demands of the EU Urban Wastewater Treatment Directive.

Design, implementation, and evaluation of a short rotation coppice system for wastewater treatment and resource recovery in India

Despite growing health concerns and increasing water scarcity, adequate wastewater treatment and reuse remains limited in India. Low-cost, decentralised, and nature-based on-site sanitation systems could play a key role in a circular water approach. This paper evaluates the performance of a Wastewater Fertigated Short Rotation Coppice (wfSRC) system based on willow, poplar, and bamboo species as a potential solution, offering low-cost, efficient water treatment, and high biomass production. Through a full-scale wfSRC pilot plant (250 m3·day−1 municipal wastewater on 6864 m2) established at Aligarh Muslim University, Uttar Pradesh, India, treatment capacities, biomass production rates, and contamination tolerance of different willow, poplar, and bamboo species were investigated. The chemical compositions of incoming wastewater, percolation water, soil, and biomass were monitored regularly. Despite the high load, all plant sections of the wfSRC system showed efficient removal of wastewater-originated pollutants. BOD5 and COD removal efficiencies were up to 99% and 95% respectively. Removal efficiencies for PO4-P reached 93% and for TN 91%. In general, total nitrogen and phosphate loads appear to be the limiting design parameters under the conditions at Aligarh to meet all discharge limits in India. Biomass production was projected to be >225 tDM·ha−1·yr−1 for bamboo, 65 tDM·ha−1·yr−1 for willow, and 206 tDM·ha−1·yr−1 for poplar. The pilot, conducted from March 2022 to June 2023, showcased how these densely planted agroforestry systems can effectively treat wastewater through natural processes such as oxidation, microbial degradation, and plant uptake. The findings demonstrate wfSRC's potential to serve as a nature-based, sustainable approach to wastewater treatment, particularly beneficial for suburban and rural areas in India and similar regions worldwide. This paper also provides recommendations for future implementation of wfSRC systems, emphasizing the need for careful planning regarding plant selection, system design, and operational strategies to maximize treatment efficiency and biomass production.

Removal of perfluoroalkyl acids from aqueous media by surfactant-modified clinoptilolites.

Perfluoroalkyl and polyfluoroalkyl substances (PFASs) are environmentally persistent, bioaccumulating, and toxic compounds that have attracted global attention. It is challenging to reduce the residual concentrations of these compounds to safe discharge limits. In this study, batch experiments were performed to evaluate natural clinoptilolite and clinoptilolites modified (MC) with cetylpyridinium chloride (CPC-MC), didodecyldimethylammonium bromide (DDAB-MC), hexadecyltrimethylammonium bromide (HDTMA-MC), and tetramethylammonium chloride (TMA-MC) as cost-effective aqueous PFAS adsorbents. The removal capacities of the adsorbents for the majority of the PFASs decreased in the following order: DDAB-MC > CPC-MC ≫ modified natural clinoptilolite with hexadecyltrimethyl ammonium bromide (HDTMA-MC) ≫ modified natural clinoptilolite with tetramethylammonium chloride (TMA-MC) ≈ natural clinoptilolite modified with NaCl (NC). In particular, CPC-MC and DDAB-MC reduced PFASs concentration in 50μg/L by up to 98% for perfluorooctane sulphonate. Within 30min, CPC-MC (30.5μg/L) and DDAB-MC (32.1μg/L) met the PFOS water quality criterion of 36μg/L in inland surface waters. Both adsorbents met this criterion at the highest solution volume (40mL) and 0.125g/L (solid-to-liquid ratio of 1:8). PFASs with short hydrocarbon chains competed more for adsorption. PFASs with sulphonate functional groups were also adsorbed more than carboxyl groups in single- and multi-PFAS solutions. The modified surfaces of clinoptilolites controlled PFAS adsorption through hydrophobic and electrostatic interactions. PFAS removal with surfactant-modified clinoptilolites is cost-effective and protects aquatic environments by using surplus natural materials.

Table Olive Manufacturing Wastewater Treatment Using the Peroxymonosulfate/Fe(III) System

Wastewater generated in table olive manufacturing processes (WWTOMP) is a seasonal waste difficult to manage due to the high salinity content. The treatment of WWTOMP has been accomplished by including a precoagulation stage with aluminum sulfate, oxidation using the peroxymonosulfate/Fe(III) system, and a final aerobic biological stage. The optimum conditions of precoagulation led to a chemical oxygen demand removal rate of roughly 30–35% without the need for pH adjustment. The peroxymonosulfate(PMS)/Fe(III) system was thereafter applied to the effluent after coagulation. The addition of PMS lowered the initial pH to acidic conditions (pH = 1.5–2.0). Under these operating conditions, the initial PMS concentration and the initial Fe(III) dose showed optimum values. An excess of the oxidant and/or the catalyst partially inhibited the process efficiency, and pH exerted a significant influence. COD removal was substantially increased as the pH of the solution was moved toward circumneutral values in the interval 5–4. Moreover, at pH values of 5 and 7, PMS was capable of reducing COD without the need for Fe(III) presence. The direct oxidation of organics by PMS or the generation of chloride-based oxidants (Cl2 or HClO) is suggested to occur in parallel to the radical attack from PMS decomposition. An attempt to biologically reduce the final COD to discharge limits failed, mainly due to the high salinity content; however, the 1:2 dilution led to the reduction in COD from 6 to 2 g L−1. Acclimated sludges or saline content reduction should be first considered.

Ultrafiltration after primary settler to enhance organic carbon valorization: Energy, economic and environmental assessment

A membrane-based alternative consisting of introducing an ultrafiltration step after the primary settler of the Carraixet WWTP (Valencia, Spain) is analyzed. This alternative aim at increasing the organic carbon valorization in the anaerobic digestion and reducing the aeration requirements in the biological reactor. A comparison is made between the current WWTP and the membrane-based alternative based on their energy balances and applying the life cycle costing and life cycle assessment methodologies. Assessment of the membrane-based alternative shows a reduction in the energy demand of 0.053 kWh per kg of COD removed due to a decrease of the aeration needs and a higher methane production in the anaerobic digestion. However, a bypass stream of 25 % to the reactor is needed to guarantee enough COD for a proper nitrogen removal to accomplish with discharge limits. The improvement in the energy balance allowed a reduction in OPEX of €0.013 per kg of COD removed, while the implementation of the membrane system represents CAPEX of €0.105 per kg COD removed. Finally, membrane-based alternative shows a better environmental performance in all the categories evaluated with ReCiPe 2016. Specifically, lower N2O emissions allowed a reduction of 0.3 kg CO2eq per kg of COD removed.

Assessing wet season water quality and health risks of Chaobai River: impacts of natural weathering and anthropogenic activities in a small urban watershed

ABSTRACT Small urban watersheds are susceptible to external influences, facing increased solute inputs during high-flow periods without sufficient dilution. This study determined the sources of major ions in the Chaobai River, which is the essential surface water source of North China. The dominant river water type was HCO3-Ca·Mg based on the Piper diagram. PCA and ion ratios revealed that natural weathering (evaporate dissolution, carbonate, and silicate weathering by carbonic and sulfuric acid) and anthropogenic activities (urban domestic sewage and industrial effluent) were the dominant factors affecting the chemical composition. Sodium adsorption ratio (SAR), soluble sodium percentage (Na%), and residual sodium carbonate (RSC) assessments indicated potential sodium and moderate salinity hazards. Meanwhile, the non-carcinogenic health risks of riverine solutes evaluated by health risk assessment need to be noticed, particularly for children. The limitation of urban sewage discharge is crucial for improving water quality in urban watershed and needs further studies.

Partial nitritation/anammox applied to real anaerobically pretreated domestic sewage under subtropical climate: aeration strategies and nitrogen cycle bacteria

ABSTRACT The combination of sewage anaerobic treatment and partial nitritation/anammox process (PN/A) can make wastewater treatment plants energetically self-sufficient. However, PN/A application has been a challenge in low-nitrogen wastewaters and it is little explored in anaerobically pretreated domestic sewage, as well as aeration strategies and the PN/A feasibility at ambient temperature. This study investigated PN/A in a sequential batch reactor (SBR) treating real anaerobically pretreated domestic sewage. After the startup, SBR was fed with real wastewater and operated at 35°C and at ambient temperature (20–31°C) without total nitrogen (TN) removal decrease (71 ± 8 and 75 ± 6%, respectively). The median ammonium and TN removals were 68 ± 21 and 59 ± 9%, respectively with 7 min on/14 min off strategy, which represents 12.3 ± 4.2 mg L−1 N-NH4 + effluent, which is lower than Brazilian discharge limits. The qPCR results showed anammox abundance in the range of 108–109 n° copies gVSS−1. Thus, results were very promising and showed the feasibility of the PN/A process for treating real anaerobically pretreated domestic sewage at ambient temperature.

Emulsified oil fouling resistant cellulose acetate-MoS2-nanocomposite membrane for oily wastewater remediation

This study evaluated the performance stability of amphiphilic cellulose acetate-MoS2-nanocomposite membranes (CMN) on oil removal and flux, oil fouling trends, as well as MoS2's catalytic peroxidase-like efficiency for oily wastewater treatment. When H2O2 was present in the feed, the membrane consistently achieved oil removal rates as high as 83.12 %, with only <10 % flux decline over an 80-minute filtration. During longer-term filtration of 4–6 h, the CMN membrane also exhibited significantly lower overall flux decline rates compared to the neat membrane with flux decline rates of 16.27 %, which was half of the cellulose membrane flux of 39.38 %. The fouling resistant performance was underpinned by the generation of reactive oxygen species (ROS) via catalytic reactions of MoS2 and H2O2. Coumarin was use as ROS scavenging agent and confirmed that the ROS amount was affected by the MoS2 and H2O2 dosages. The CMN membrane achieved the oil removal to the permissible discharge limit for low concentration wastewater. As a low-pressure membrane, it offered advantages of less energy consumption and continuously operating mode without frequent chemical cleaning and desorption. These findings support the CMN membrane's potential as a promising solution for treating industrial oily wastewater.

Experimental study on environmental chemical effect and purification treatment of waste slurry in horizontal directional drilling

The waste slurry generated during Horizontal Directional Drilling (HDD) has detrimental effects on water sources, soil, and organisms. Existing studies lack quantitative analysis and assessment of the environmental hazards of waste slurry. The treatment of waste slurry is usually done by physical curing or chemical curing agents. The treatment effect of these treatments is unsatisfactory or not environmentally friendly enough. Research on the application of Microbially Induced Calcite Precipitation (MICP) in waste slurry purification can help provide innovative solutions. This study began by acquiring the basic properties, mineral composition, and particle size distribution of the waste slurry through experiments. The effects of different concentrations of waste slurry on soil chemical properties were compared, including the measurement of total dissolved solids (TDS), turbidity, and heavy metal ion concentrations of waste slurry supernatant. Additionally, the environmental impact of the waste slurry was assessed from an electrochemical, turbidity, and ionic composition perspectively. A combination formulation containing 2.8 wt% urease, 5 wt% urea, and 3.5 wt% calcium chloride was used to purify the waste slurry. The supernatant of the MICP treated waste slurry undergoes electrochemical testing to evaluate the effectiveness of MICP technology for slurry treatment. The findings indicate that both chemical additives and stratum contaminants significantly contribute to slurry pollution. When the waste slurry constitutes more than 40 wt% of the soil mass fraction, the electrical conductivity (EC) of the soil surpasses the threshold of 1000 μs/cm, and the pH level rises to approximately 9.5, rendering it unsuitable for plant growth. Moreover, the TDS, turbidity, and heavy metal ion concentrations in the waste slurry supernatant exceed the permissible environmental discharge limits. Notably, the concentration of arsenic (As) exceeds the national standard by 18 times, cadmium (Cd) by 20 times, and selenium (Se) by 208 times, posing a high risk of environmental pollution. However, the comparison of ion concentrations in the supernatant before and after MICP treatment reveals that MICP demonstrates effective cementation and co-precipitation of heavy metal ions. MICP purified 66.6 % of arsenic (As), all cadmium (Cd), 75 % of phosphorus (P), and 76 % of selenium (Se) from the waste slurry supernatant. The results of this research contribute to the quantitative evaluation of the environmental hazards of waste slurry. It also helps to promote the application of MICP in waste slurry purification.

Simulation assisted process simplification and energy recovery from a cryptic biological nutrient removal plant

In this study, simulation-based analysis is conducted for nitrogen removal mechanism in a biological nutrient removal plant designed in an encrypted manner. In the first phase, the simulation study elucidates how nitrogen removal occurs in a complex design using a series of 4 carousel bioreactors with additional nitrate recycle. It is demonstrated that pre-anoxic volume fed with limited internal recirculation only would not be sufficient to meet the discharge Total Nitrogen (TN) limit of 10 mg N/L. However, the addition of simultaneous nitrification-denitrification (SND) processes in aerobic reactors enables compliance with TN discharge limits. In the second phase, the configuration is simplified by means of process simulation, where the complex design is streamlined by eliminating internal recycle while achieving nitrogen removal through the SND process. Plant data confirmed that the simplified configuration can achieve nitrogen removal providing the same discharge quality. The simulations resulted that TN concentration achieved at the plant effluent is comparable, while effluent total phosphorus concentration is decreased by approximately 50 % due to increased activity of Phosphorus Accumulating Organisms (PAOs) under reduced sludge retention time (SRT). In the third phase, the application of the SND process in the field using a simplified and new activated sludge configuration yields similar results to the simulation. According to plant records, 28 % energy savings and an equivalent chemical cost reduction of €945,000 per year were achieved with the new process configuration.

System-Based Protection Method for High-Voltage Pulse Generator Switching Units in Biomass Electroporation

Background High-voltage pulsed electric field (PEF) technology has emerged as a promising technique for enhancing cell membrane permeabilization for biotechnological and medical applications. Given the parametric instability and low resistivity of biomass when used it as an electrical load, it is imperative for the switching unit to meet specific requirements in terms of load capacity and protection against overloads and short circuits. Methods To construct generators capable of producing high-voltage pulses in the microsecond and millisecond duration ranges, we are incorporating a switching unit that employs a hardware-software method to safeguard critical transistors against overloads and short-circuit currents. Our strategy revolves around utilizing the energy storage capacitor (ESC) both as a means of energy storage and as a current sensor. By monitoring the voltage drop during discharge, we can accurately estimate current parameters. The occurrence of an excessively rapid discharge from the ESC serves as an indicator of a short circuit. The microcontroller calculates ESC discharge limits based on preset parameters within a defined timeframe. Should this limit be exceeded, the system promptly interrupts to address the pulse responsible for the short circuit and halts the further supply of remaining pulses to the load. This sophisticated approach ensures the protection and integrity of the system in the face of potential overloads or short circuits. Results Applying a systemic approach in the design of the presented implementation of protection for key transistors in the switching node from overload and short-circuit current for high-voltage pulse generators (HVPG) in the microsecond and millisecond duration ranges allows for a simpler circuit solution. In this case, the system approach also provides a unified control principle when implementing the considered option for organizing protection, regardless of the number and type of transistors or solid-state switching modules used and connected in parallel. Conclusions The configuration and protective circuitry presented in the article are specifically tailored for shielding switching elements from short-circuit currents, with a primary focus on their application in high-voltage pulse generators (HVPG). These generators are commonly employed in the high-voltage pulse treatment of diverse and unstable loads during the electroporation of biomass. The technical solution expounded in the article is intended for use in the switching nodes of HVPG, particularly those with discharge circuits constructed based on a direct capacitive discharge scheme. Notably, this protection configuration introduces local innovation and is characterized by the circuit's simplicity, achieved through the effective utilization of existing system resources. This protective variant for HVPG switches is particularly well-suited for devices utilized in versatile technological installations with relatively lower performance levels.

Machine learning facilitated the conceptual design of an alum dosing system for phosphorus removal in a wastewater treatment plant

Wastewater treatment plants (WWTPs) face challenges in controlling total phosphorus (TP), given more stringent regulations on TP discharging. In particular, WWTPs that operate at a small scale lack resources for real-time monitoring of effluent quality. This study aimed to develop a conceptual alum dosing system for reducing TP concentration, leveraging machine learning (ML) techniques and data from a full-scale WWTP containing incomplete TP information. The proposed system comprises two ML models in series: an Alert model based on LightGBM with an accuracy of 0.92, and a Dosage model employing a voting algorithm through combining three ML algorithms (LightGBM, SGD, and SVC) with an accuracy of 0.76. The proposed system has demonstrated the potential to ensure that 88.1% of the effluent remains below the TP discharge limit, which outperforms traditional dosing methods and could reduce overdosing from 61.3 to 12.1%. Furthermore, the SHapley Additive exPlanations (SHAP) analysis revealed that incorporating the output features from the previous cycle and utilizing the results of the Alert model as the input features for dosage prediction could be an effective method for data with limited information. The findings of this study have practical applications in improving the efficiency and effectiveness of TP control in small-scale WWTPs, providing a valuable solution for complying with stringent regulations and enhancing environmental sustainability.

Microalgae-Based Remediation of Real Textile Wastewater: Assessing Pollutant Removal and Biomass Valorisation.

The textile industry generates highly contaminated wastewater. It severely threatens local ecosystems without proper treatment, significantly diminishing biodiversity near the discharge point. With rapid growth rates, microalgae offer an effective solution to mitigate the environmental impact of textile wastewater, and the generated biomass can be valorised. This study sets out to achieve two primary objectives: (i) to assess the removal of pollutants by Chlorella vulgaris from two distinct real textile wastewaters (without dilution) and (ii) to evaluate microalgal biomass composition for further valorisation (in a circular economy approach). Microalgae grew successfully with growth rates ranging from 0.234 ± 0.005 to 0.290 ± 0.003 d-1 and average productivities ranging from 78 ± 3 to 112.39 ± 0.07 mgDW L-1 d-1. All cultures demonstrated a significant reduction in nutrient concentrations for values below the legal limits for discharge, except for COD in effluent 2. Furthermore, the pigment concentration in the culture increased during textile effluent treatment, presenting a distinct advantage over conventional ones due to the economic value of produced biomass and pigments. This study underscores the promise of microalgae in textile wastewater treatment and provides valuable insights into their role in addressing the environmental challenges the textile industry poses.

Phytoremediation of an integrated poultry and aquaculture wastewater using sub-surface constructed wetland planted with Phragmites karka and Typha latifolia

This study focused on assessing the effectiveness of vertical subsurface constructed wetlands (VSFCW) in purifying integrated poultry and aquaculture wastewater (PAW) in a tropical region. This evaluation encompassed the treatment of physico-chemical, heavy metal, and microbiological pollutants across three distinct climatic seasons and hydraulic retention time (HRT: 21 days). Parameters such as BOD (29.50 mg/L), COD (56.67 mg/L), Zn (2.97 mg/L), Cr (0.24 mg/L), Cu (1.78 mg/L), Pb (0.21 mg/L), total fecal coliform (866.67 cfu/mL), total coliform (1666.67 cfu/mL), E. coli (1133.33 cfu/mL), and Salmonella/Shigella (700 cfu/mL) exceeded the discharge limits for wastewater into nearby surface water bodies. Significant removal efficiencies were observed for all parameters tested in the CW planted with both Phragmites karka and Typha latifolia. The macrophytes showed similar removal efficiencies for all tested parameters, and there was no significant difference in the initial concentrations of the parameters based on the experimental season, except for microbial properties. This suggests that weather conditions did not significantly impact the concentration of physical and chemical properties in the wastewater. Consequently, this study successfully demonstrates the potential of using a VSFCW for effective treatment of PAW.

A mechanistic evaluation for total removal of toxic hexavalent and trivalent chromium from water by oxygen vacancy-engineered nanocomposite

Oxygen vacancy-engineered nanocomposites are emerging materials in adsorption and photocatalysis research. This study evaluated total toxic Chromium removal by a nanocomposite of core-shell zeolite A@oxygen-vacant ZnO1−X (ZA@ZnO1−X) from water using its coexisting dual characteristics. ZA@ZnO1−X has removed 98.3% of total Cr, achieving a discharge limit of 0.05 ppm of Cr(VI) after the photoreduction and adsorption simultaneously. The detailed structural and physicochemical properties of synthesized ZA@ZnO1−X nanocomposite show higher BET surface area, oxygen-vacant percentage, and visible light photoactivity than the sole ZnO1−X nanosheet. The photocatalytic reduction efficiency (PRE) effect is systematically studied on varying operational variables like pH, citric acid (CA), Cr(VI) concentration, catalyst load, presence of anions, and radical scavengers. ZA@ZnO1−X removed Cr(VI) and Cr(III) simultaneously by 98.5% PRE with a catalyst load of 4 g/l, CA= 5 mM, pH= 5.06 under halogen light irradiation (300 W, 240 V) for 50 mins. This experimental study evaluates the prominent role of oxygen vacancy of ZA@ZnO1−X for photocatalytic reduction of Cr(VI) and enhanced adsorption of Cr(III). The kinetic study reveals adsorption of both Cr(VI) and Cr(III) follows pseudo-second-order kinetics, whereas photoreduction of Cr(VI) follows pseudo-first-order kinetics. A possible mechanism of total Cr removal is sketched, supporting enhanced adsorption due to unsaturated Zn atoms and unpaired e- at the oxygen defect site, followed by photoreduction by photogenerated e- and CO2-• radical. The ZA@ZnO1−X performance is reduced by only 2.5% after five consecutive runs without deformation. The easy regeneration process makes it suitable for toxic total Cr removal, avoiding any secondary pollution.