Microfluidic paper-based analytical device for measurement of pH using as sensor red cabbage anthocyanins and gum arabic.

The objective of this study was to develop and validate a novel microfluidic paper-based analytical device (µPADpH) for determining the pH levels in foods. Anthocyanins from red cabbage aqueous extract (RCAE) were used as its analytical sensor. Whatman No. 1 filter paper was the most suitable for the device due to its porosity and fiber organization, which allows for maximum color intensity and minimal color heterogeneity of the RCAE in the detection zone of the µPADpH. To ensure the color stability of the RCAE for commercial use of the µPADpH, gum arabic was added. The geometric design of the µPADpH, including the channel length and separation zone diameter, was systematically optimized using colored food. The validation showed that the µPADpH did not differ from the pH meter when analyzing natural foods. However, certain additives in processed foods were found to increase the pH values.

Treatment of pulp and paper mill effluent through combined aerobic and anaerobic suspended fixed-bed bioreactor.

This study explored using ultrafiltration (UF) membranes to treat pulp and paper mill wastewater, implementing a novel Taguchi experimental design to optimize operating conditions for pollutant removal and minimal membrane fouling. Researchers examined four factors: pH, temperature, transmembrane pressure, and volume reduction factor (VRF), each at three levels. Optimal conditions (pH 10, 25°C, 6 bar, VRF 3) led to a 35% reduction in flux due to fouling and high pollutant rejections: total hardness (83%), sulfate (97%), spectral absorption coefficient (SAC254) (95%), and chemical oxygen demand (COD) (89%). Conductivity had a lower rejection rate of 50%. Advanced imaging techniques like atomic force microscopy (AFM) and scanning electron microscopy (SEM) revealed reduced membrane fouling under these conditions. The Taguchi method effectively identified optimal conditions, significantly improving wastewater treatment efficiency and promoting environmental sustainability in the pulp and paper industry. PRACTITIONER POINTS: This study optimized UF membrane conditions for pulp and paper mill wastewater, reducing fouling and enhancing pollutant removal, offering practical strategies for industrial treatment. AFM and SEM provided key insights into membrane fouling and mitigation, promoting real-time diagnosis and optimization for enhanced treatment efficiency. Prioritizing anaerobic fixed-bed systems in wastewater treatment is beneficial for achieving high COD removal efficiency. Optimizing hydraulic retention time (HRT) in these systems can further improve their overall effectiveness and sustainability.

Effect of incubation conditions of cellulase hydrolysis on mechanical pulp fibre morphology.

The mechanical pulp industry is diversifying through the manufacture of high-value paper products, such as microfibrillated cellulose. However, the development of fibre quality is still energy-intensive. Enzymatic hydrolysis is hypothesized to promote fibre cutting, greater fibrillation, and reduce refining energy costs. Despite potential benefits, there is little understanding of the mechanisms behind fibre development during enzymatic hydrolysis of mechanical pulp. This work investigates how incubation pH and temperature during enzymatic hydrolysis impact the refining of mechanical pulp short fibres. Incubation with endoglucanase at pH 5 and 60 °C increased fibre cutting by approximately 20 %. Fibrillation was negatively affected at this condition, resulting in increased slim fines formation with refining. Incubation at pH 8 and 80 °C promoted >15 % reduction in fibre length, despite such conditions being associated with low enzyme activity. The pH variation modified the sedimentation height of the fibres and the conductivity of suspensions, indicating a change in fibre surface charge. Fibre morphology changes were induced by enzyme hydrolysis conducted at conditions representative of the full range of pH and temperature observed in mechanical pulp mills.

Deep Learning-Based Kinetic Analysis in Paper-Based Analytical Cartridges Integrated with Field-Effect Transistors.

This study explores the fusion of a field-effect transistor (FET), a paper-based analytical cartridge, and the computational power of deep learning (DL) for quantitative biosensing via kinetic analyses. The FET sensors address the low sensitivity challenge observed in paper analytical devices, enabling electrical measurements with kinetic data. The paper-based cartridge eliminates the need for surface chemistry required in FET sensors, ensuring economical operation (cost < $0.15/test). The DL analysis mitigates chronic challenges of FET biosensors such as sample matrix interference, by leveraging kinetic data from target-specific bioreactions. In our proof-of-concept demonstration, our DL-based analyses showcased a coefficient of variation of <6.46% and a decent concentration measurement correlation with an r2 value of >0.976 for cholesterol testing when blindly compared to results obtained from a CLIA-certified clinical laboratory. These integrated technologies have the potential to advance FET-based biosensors, potentially transforming point-of-care diagnostics and at-home testing through enhanced accessibility, ease-of-use, and accuracy.

A portable lateral flow distance-based paper sensor for drinking water hardness test.

Hardness is one of the basic parameters of water, and a high-level hardness of drinking water may be harmful to human health. Thus, it is very important to monitor drinking water hardness. In this work, a portable lateral flow distance-based paper sensor for the semi-quantitative detection of drinking water hardness is demonstrated. In the presence of Ca2+/Mg2+, the hydrogel can be formed via the chelation between sodium alginate and Ca2+/Mg2+, inducing a phase separation process. The viscosity change of the sodium alginate solution is directly related to the Ca2+/Mg2+ concentration and can be determined by the water lateral flow distance on test strips. The sensor successfully realizes the quantification of Ca2+ and Mg2+ in the range of 0-10 mmol L-1 and 4-20 mmol L-1, respectively. The recoveries are found varied from 95% to 108.9%. The water hardness is acceptable for drinking if the Cr values lies in the range of 0.259 to 0.419, and it is high with the Cr value above 0.595. Remarkably, the performance of the sensor is comparable with the commercial kit for real water samples, which avoids the subjective judgment. Overall, this method provides a portable approach for semi-quantitative detection of drinking water hardness with the merits of convenience and low cost, which shows great potential for the potential application.

Wearable electrochemical device based on butterfly-like paper-based microfluidics for pH and Na+ monitoring in sweat.

A wearable potentiometric device is reported based on an innovative butterfly-like paper-based microfluidic system, allowing for continuous monitoring of pH and Na+ levels in sweat during physical activity. Specifically, the use of the butterfly-like configuration avoids evaporation phenomena and memory effects, enabling precise and timely biomarker determination in sweat. Two ad hoc modified screen-printed electrodes were embedded in the butterfly-like paper-based microfluidics, and the sensing device was further integrated with a portable and miniaturized potentiostat, leveraging Bluetooth technology for efficient data transmission. First, the paper-based microfluidic configuration was tested for optimal fluidic management to obtain optimized performance of the device. Subsequently, the two electrodes were individually tested to detect the two biomarkers, namely pH and Na+. The results demonstrated highly promising near-Nernstian (0.056 ± 0.002 V/dec) and super-Nernstian (- 0.080 ± 0.003 V/pH) responses, for Na+ and pH detection, respectively. Additionally, several important parameters such as storage stability, interferents, and memory effect by hysteresis study were also investigated. Finally, the butterfly-like paper-based microfluidic wearable device was tested for Na+ and pH monitoring during the physical activity of three volunteers engaged in different exercises, obtaining a good correlation between Na+ increase and dehydration phenomena. Furthermore, one volunteer was tested through a cardiopulmonary test, demonstrating a correlation between sodium Na+ increase and the energetic effort by the volunteer. Our wearable device highlights the high potential to enable early evaluation of dehydration and open up new opportunities in sports activity monitoring.

Fabrication of highly fluorescent graphene quantum dots for quantification of As3+ ion using modified cellulose paper.

Easy, economical, and swift detecting tools are very demanded for assaying various chemical species. The introduction of label-free paper-based read-out devices has significantly reached the demand of analytical science for target analytes assays. Herein, a facile, and disposable inexpensive paper-based sensing tool was fabricated for sensing As3+ ion using graphene quantum dots (GQDs) as a fluorescent reader. The CA-GQDs were synthesized using citric acid (CA) as a precursor via the pyrolysis method, further physisorbed on the cellulose substrate for sensing of As3+ via aggregation-based fluorescence "turn-off" mechanism. The linear range for quantitating As3+ ion is in the range of 0.05-50 µM with a detection limit of 10 nM. The practical application of the CA-GQDs-based analytical platform was verified by assaying As3+ ion in water samples. The CA-GQDs-embedded paper strip can be easily extended for assaying of As3+ ion, which meets the demand for monitoring of As3+ ion in real samples.

Humidity-enhanced microfluidic plasma separation on Chinese Xuan-papers.

The first step in blood testing necessitates blood separation to obtain an adequate volume of plasma. Traditional centrifugation is bulky, expensive and electricity-powered, which is not suitable for micro-scale blood plasma separation in point-of-care testing (POCT) cases. Microfluidic paper-based plasma separation devices present a promising alternative for plasma separation in such occasions. However, they are limited in terms of plasma yield, which hinders analyte detection. Herein, we proposed a humidity-enhanced paper-based microfluidic plasma separation method to address this issue. Specifically, paper was first treated by blood-typing antibodies, then samples of whole blood were introduced into the prepared paper. After waiting for 5 min for RBC agglutination and plasma wicking under high humidity, micro-scale plasma separation from whole blood was achieved. As a result, an extremely high plasma yield of up to 60.1% could be separated from whole blood through using Xuan-paper. Meanwhile, the purity of plasma could reach 99.99%. Finally, this innovative approach was effortlessly integrated into distance-based glucose concentration detection, enabling rapid determination of blood glucose levels through naked-eye observation. Considering the simplicity and inexpensiveness of this method, we believe that this technology could be integrated to more paper-based microfluidic analytical devices for rapid and accurate detection of plasma analytes in POCT.

A dual colorimetric-electrochemical microfluidic paper-based analytical device for point-of-care testing of ischemic strokes.

A novel microfluidic paper-based analytical device with dual colorimetric and electrochemical detection (dual µPAD) was developed for the assessment of transferrin saturation (TSAT) in samples from ischemic stroke patients. TSAT was calculated from the ratio between transferrin-bound iron, which was colorimetrically measured, and the total iron-binding capacity, which was electrochemically measured. To this end, a µPAD was smartly designed, which integrated both colorimetric and electrochemical detection reservoirs, communicating via a microchannel acting as a chemical reactor, and with preloading/storing capabilities (reagent-free device). This approach allowed the dual and simultaneous determination of both parameters, providing an improvement in the reliability of the results due to an independent signal principle and processing. The µPADs were validated by analyzing a certified reference material, showing excellent accuracy (Er ≤ 5%) and precision (RSD ≤ 2%). Then they were applied to the analysis of diagnosed serum samples from ischemic stroke patients. The results were compared to those provided by a free-interference method (urea-PAGE). Impressively, both methods exhibited a good correlation (r = 0.96, p < 0.05) and no significant differences were found between them (slope 1.0 ± 0.1 and the intercept 1 ± 4, p < 0.05), demonstrating the excellent accuracy of our approach during the analysis of complex samples from ischemic stroke patients, using just 90 µL of clinical samples and taking less than 90 min in comparison with the 18 hours required by the urea-PAGE approach. The developed fully integrated colorimetric-electrochemical µPAD is a promising ready to use reagent-free device for the point-of-care testing of TSAT, which can be used to assist physicians in the fast diagnosis and prognosis of ischemic strokes, where the decision-time is crucial for the patient's survival.

Chemical profiling of paper recycling grades using GC-MS and LC-MS: An exploration of contaminants and their possible sources.

Paper packaging made with recycled paperboard is used to pack various consumer goods that can include amongst others, electronics, toys, food, cosmetics, and stationery. Chemical profiling of the various paper recycling grades used in the manufacture of recycled paperboard was undertaken to investigate possible sources of contaminants and their propagation in the paper recycling chain. Pre-consumer, retail and post-consumer paper-based materials were collected at papermills, corrugators, grocery stores, household waste, solid waste disposal sites and recycling facilities. In the GC-MS analysis, phthalates, long-chain aliphatic compounds, and fatty acids were the most commonly detected compounds whilst phthalates and bisphenols featured most prevalently in the LC-MS analysis. The factors that were identified as likely contributors to the detection of the different chemical compounds included the presence of wood derivatives, the use of certain chemical additives during manufacturing, and exposure of paper to contaminants from consumers, other goods and the environment. Waste mingling, recovery, sorting and reprocessing into recycled paper were also shown to influence the chemical profile of paper materials. Sparse partial least squares-discriminate analysis indicated that newspaper and office paper had unique chemical constituents, whilst cartons were shown to have higher variability. By looking at key stages of paper recycling, this study showed that the possible persistence and transformation of chemical compounds in additives must be evaluated when considering the recyclability of paper-based materials. Further, it highlighted that different separation approaches may be required to reduce contaminant exposure opportunities in post-consumer paper materials.

Assessing the resource potential of paper and board in lightweight packaging waste sorting plants through manual analysis and sensor-based material flow monitoring.

The recycling of paper and board (PB) yields economic and environmental advantages compared to primary paper production. However, PB from lightweight packaging (LWP) waste is currently not comprehensively reintegrated into the paper value stream. To develop an adapted recycling process for PB from LWP, PB quantities, qualities, and fluctuations ranges in LWP are required. Currently, no sufficient database is available. Therefore, we developed a methodical approach and conducted a case study to access the PB potential in LWP sorting plants using manual analysis and sensor-based material flow monitoring. Differences resulting from seasonal variations, materials from different settlement structures, and fluctuation ranges in LWP composition over two weeks have been investigated. PB contents in the input of 6.5 wt% (ww) and 5.9 wt% (ww) were determined for winter and summer sampling campaigns, respectively. The PB product stream amounted to 5.7 wt% (ww, winter) and 4.8 wt% (ww, summer). Around 45 wt% (ww) of PB from the PB product stream was classified as misplaced by the consumer and should have been discarded in separate paper collections. Based on the determined PB quantities and qualities, a potential of usable and in the PB product stream available PB in LWP was determined. The technically available and usable PB potential in German LWP waste amounts to 89,000 to 100,000tons per year (average PB yield of around 65 wt% (ww)). The methodical approach can be adapted for sorting plant balances. The results can contribute to developing an adapted recycling process for PB from LWP.

Intermittent lysis on a single paper-based device to extract exosomal nucleic acid biomarkers from biological samples for downstream analysis.

As the role of exosomes in physiological and pathological processes has been properly perceived, harvesting them and their internal components is critical for subsequent applications. This study is a debut of intermittent lysis, which has been integrated into a simple and easy-to-operate procedure on a single paper-based device to extract exosomal nucleic acid biomarkers for downstream analysis. Exosomes from biological samples were captured by anti-CD63-modified papers before being intermittently lysed by high-temperature, short-time treatment with double-distilled water to release their internal components. Exosomal nucleic acids were finally adsorbed by sol-gel silica for downstream analysis. Empirical trials not only revealed that sporadically dropping 95 °C ddH2O onto the anti-CD63-modified papers every 5 min for 6 times optimized the exosomal nucleic acids extracted by the anti-CD63 paper but also verified that the whole deployed procedure is applicable for point-of-care testing (POCT) in low-resource areas and for both in vitro (culture media) and in vivo (plasma and chronic lesion) samples. Importantly, downstream analysis of exosomal miR-21 extracted by the paper-based procedure integrated with this novel technique discovered that the content of exosomal miR-21 in chronic lesions related to their stages and the levels of exosomal carcinoembryonic antigen originated from colorectal cancer cells correlated to their exosomal miR-21.

Paper-Based Microfluidic Analytical Device Patterned by Label Printer for Point-of-Care Blood Glucose and Hematocrit Detection Using 3D-Printed Smartphone Cassette.

This study presents a portable, low-cost, point-of-care (POC) system for the simultaneous detection of blood glucose and hematocrit. The system consists of a disposable origami microfluidic paper-based analytical device (µPAD) for plasma separation, filtration, and reaction functions and a 3D-printed cassette for hematocrit and blood glucose detection using a smartphone. The origami µPAD is patterned using a cost-effective label printing technique instead of the conventional wax printing method. The 3D-printed cassette incorporates an array of LED lights, which mitigates the effects of intensity variations in the ambient light and hence improves the accuracy of the blood glucose and hematocrit concentration measurements. The hematocrit concentration is determined quantitatively by measuring the distance of plasma wicking along the upper layer of the origami µPAD, which is pretreated with sodium chloride and Tween 20 to induce dehydration and aggregation of the red blood cells. The filtered plasma also penetrates to the lower layer of the origami µPAD, where it reacts with embedded colorimetric assay reagents to produce a yellowish-brown complex. A color image of the reaction complex is captured using a smartphone inserted into the 3D-printed cassette. The image is analyzed using self-written RGB software to quantify the blood glucose concentration. The calibration results indicate that the proposed detection platform provides an accurate assessment of the blood glucose level over the range of 45-630 mg/dL (R2 = 0.9958). The practical feasibility of the proposed platform is demonstrated by measuring the blood glucose and hematocrit concentrations in 13 human whole blood samples. Taking the measurements obtained from commercial glucose and hematocrit meters as a benchmark, the proposed system has a differential of no more than 6.4% for blood glucose detection and 9.1% for hematocrit detection. Overall, the results confirm that the proposed µPAD is a promising solution for cost-effective and reliable POC health monitoring.

Decentralized food safety and authentication on cellulose paper-based analytical platform: A review.

Food safety and authenticity analysis play a pivotal role in guaranteeing food quality, safeguarding public health, and upholding consumer trust. In recent years, significant social progress has presented fresh challenges in the realm of food analysis, underscoring the imperative requirement to devise innovative and expedient approaches for conducting on-site assessments. Consequently, cellulose paper-based devices (PADs) have come into the spotlight due to their characteristics of microchannels and inherent capillary action. This review summarizes the recent advances in cellulose PADs in various food products, comprising various fabrication strategies, detection methods such as mass spectrometry and multi-mode detection, sampling and processing considerations, as well as applications in screening food safety factors and assessing food authenticity developed in the past 3 years. According to the above studies, cellulose PADs face challenges such as limited sample processing, inadequate multiplexing capabilities, and the requirement for workflow integration, while emerging innovations, comprising the use of simplified sample pretreatment techniques, the integration of advanced nanomaterials, and advanced instruments such as portable mass spectrometer and the innovation of multimodal detection methods, offer potential solutions and are highlighted as promising directions. This review underscores the significant potential of cellulose PADs in facilitating decentralized, cost-effective, and simplified testing methodologies to maintain food safety standards. With the progression of interdisciplinary research, cellulose PADs are expected to become essential platforms for on-site food safety and authentication analysis, thereby significantly enhancing global food safety for consumers.

Degradation of paper-based boxes for food delivery in composting and anaerobic digestion tests.

This study evaluated the fate of food delivery boxes when subjected to biological treatments, reproducing at the lab-scale the conditions of full-scale plants. Four paper-based boxes were composted: two made of paper only, one coupled with polylactic acid (PLA), and one with a barrier coating. One paper only box and the box with PLA were also investigated for their anaerobic degradability with biochemical methane potential (BMP) and semi-continuous tests. During composting, the boxes were not recognisable inside the compost after four (paper only boxes), eight (box with PLA), and twelve (box with barrier coating) weeks. In BMP tests, the paper only box showed a degradability similar to that of food waste (92 %), while the box with PLA degraded only at 76 %. Furthermore, undigested pieces of PLA were found in semi-continuous tests. Accordingly, paper resulted suitable for biological treatments, while the presence of PLA or other barrier coatings can be critical.

Multi-dimensional microfluidic paper-based analytical devices (µPADs) for noninvasive testing: A review of structural design and applications.

The rapid emergence of microfluidic paper-based devices as point-of-care testing (POCT) tools for early disease diagnosis and health monitoring, particularly in resource-limited areas, holds immense potential for enhancing healthcare accessibility. Leveraging the numerous advantages of paper, such as capillary-driven flow, porous structure, hydrophilic functional groups, biodegradability, cost-effectiveness, and flexibility, it has become a pivotal choice for microfluidic substrates. The repertoire of microfluidic paper-based devices includes one-dimensional lateral flow assays (1D LFAs), two-dimensional microfluidic paper-based analytical devices (2D µPADs), and three-dimensional (3D) µPADs. In this comprehensive review, we provide and examine crucial information related to paper substrates, design strategies, and detection methods in multi-dimensional microfluidic paper-based devices. We also investigate potential applications of microfluidic paper-based devices for detecting viruses, metabolites and hormones in non-invasive samples such as human saliva, sweat and urine. Additionally, we delve into capillary-driven flow alternative theoretical models of fluids within the paper to provide guidance. Finally, we critically examine the potential for future developments and address challenges for multi-dimensional microfluidic paper-based devices in advancing noninvasive early diagnosis and health monitoring. This article showcases their transformative impact on healthcare, paving the way for enhanced medical services worldwide.

Streamlined integrated protein isoelectric focusing using microfluidic paper-based device.

An innovative integrated paper-based microdevice was developed for protein separation by isoelectric focusing (IEF), allowing for robust design thanks to a 3D-printed holder integrating separation channel, reservoirs, and electrodes. To reach robustness and precision, the optimization focused on the holder geometry, the paper nature, the reservoir design, the IEF medium, and various focusing parameters. A well-established and stable pH gradient was obtained on a glass-fiber paper substrate with simple sponge reservoirs, and the integration of the electrodes in the holder led to a straightforward system. The separation medium composed of water/glycerol (85/15, v/v) allowed for reducing medium evaporation while being an efficient medium for most hydrophobic and hydrophilic proteins, compatible with mass spectrometry detection for further proteomics developments. To our knowledge, this is the first report of the use of glycerol solutions as a separation medium in a paper-based microdevice. Analytical performances regarding pH gradient generation, pI determination, separation efficiency, and resolution were estimated while varying the IEF experimental parameters. The overall process led to an efficient separation within 25 min. Then, this methodology was applied to a sample composed of saliva doped with proteins. A minimal matrix effect was evidenced, underscoring the practical viability of our platform. This low-cost, versatile and robust paper-based IEF microdevice opens the way to various applications, ranging from sample pre-treatment to integration in an overall proteomic-on-a-chip device.

In Situ Colorimetric LAMP Based on One-Step Modified Filter Paper to Screen Human Papillomavirus (HPV)16/18 from Clinical Samples.

Cervical cancer is among the most common malignant tumors in women. The development of rapid screening techniques plays an important role in early screening for cancer treatment. We have developed an HPV screening method, which effectively combines the high-efficiency nucleic acid enrichment of chitosan-modified filter paper and the rapid visual detectability of colorimetric LAMP, along with the enhancement of the tolerance ability of the pH-sensitive LAMP reagent to acidic original samples, making the detection of HPV 16/18 easy to carry out and reliable, which is helpful for the epidemiological prevention and control strategies of HPV-induced cancer. This technique can simultaneously exhibit the "in situ amplification" capability of chitosan-modified filter paper and the nontemperature cycle dependence of visual LAMP detection. Therefore, DNA extraction and amplification can be performed efficiently and quickly within a single reaction where all DNA is concentrated in the QF paper disc. By embedding amino-modified filter paper into the plastic chip, a simple and reliable disposable chip was prepared for rapid HPV16 and HPV18 detection from clinical endometrial samples, and the results were 100% consistent with clinical diagnosis. More importantly, even after the sample was diluted 100-fold, HPV16/18-infected cells could be accurately identified, showing the advantages of the system in early cancer screening. Moreover, for endometrial samples containing plenty of cells, the filter paper could be used to enrich cells by filtration, preventing the acidic fluid from impacting pH-induced colorimetric LAMP detection and realizing direct amplification for HPV identification without nucleic acid extraction. This easy-to-operate system that can analyze a wide range of samples will be suitable for routine on-site HPV screening, dramatically extending the applications and utility for rapid, near-patient nucleic acid testing.

Performance evaluation of ICX reactor in treatment of paper mill wastewater: a case study in South Vietnam.

This study evaluates the performance of the Internal Circulation eXperience (ICX) reactor in treating high-strength paper mill wastewater in the south of Vietnam. The ICX reactor effectively managed organic concentrations (sCOD) of up to 11,800 mg/L. Results indicate a volumetric loading rate (VLR) of 26.8 kg/m3 × day, achieving processing efficiency exceeding 81% while consistently maintaining volatile fatty acids (VFA) below 300 mg/L. The study employed Monod and Stover-Kincannon kinetic modeling, revealing dynamic parameters including Ks = 56.81 kg/m3, Y = 0.121 kgVSS/kgsCOD, Kd = 0.0242 1/day, µmax = 0.372 1/day, Umax = 151 kg/m3 × day, and KB = 175.92 kg/m3 × day, underscoring the ICX reactor's superior efficiency compared to alternative technologies. Notably, the reactor's heightened sensitivity to VFA levels necessitates influent concentrations below 1,400 mg/L for effective sludge treatment. Furthermore, the influence of calcium on treatment efficiency requires post-treatment alkalinity maintenance below 19 meq/L to stabilize MLVSS/MLSS concentration. Biogas production ranged from 0.6 to 0.7 Nm3 biogas/kg sCOD; however, calcium impact diminished this ratio, reducing overall treatment efficiency and biogas production. The study contributes valuable insights into anaerobic treatment processes for complex industrial wastewaters, emphasizing the significance of controlling VFA, calcium, and alkalinity for optimal system performance.

"Research paper mills": A factory outlet for dubious research.

The primary objective of any research, regardless of its domain such as health, technology, psychology, or any other subject, is to enhance the overall well-being of individuals. Rigorous processes are involved in conducting research ethically and in communicating its outcomes to society. However, as publishing research has become a mandatory requirement for career advancement and appointments, academics are resorting to several unethical practices to get substandard work published quickly. Consequently, predatory publishing markets have emerged, which publish data that is falsified and fabricated, along with plagiarised textual matter. The emergence of "paper mills" is a further step in the corruption of research, where a group of persons or automated systems generate papers for publication. Anyone desirous of publishing a paper can purchase one, akin to any desired fast-moving consumer product, with the added guarantee of publication in indexed journals. Therefore, paper mills and their unethical modus operandi are discussed in this paper in detail, with relevant examples. The article unfolds the consequences of publishing such fraudulent research papers and concludes with the challenges in combating paper mills.