Water Pollution Problems Research Articles

Impact of Improper Waste Disposal on Surface and Ground Water

Pollution in water occurs when harmful substance (often chemicals or biological) contaminate streams, river, lakes, oceans or other bodies of water, degrading water quality and rendering it unhealthy to humans, animal and the environment. The widespread problem of water pollution is jeopardizing our health. Water pathogens, in form of disease-causing bacteria and viruses from human and animal waste, are a major reason of illness from contaminated drinking water. Owing to the improper treatment facilities, waste is often discharged into the surface and ground water sources. Water bacteria can be limited by recycling used plastic, standard disposal of chemicals, oils or non-biodegradable items and proper collection and transportation of solid waste to a processed disposal site. In addition, waste water should be treated properly to prevent adverse health risk of the user of both surface water and ground water in the aquatic ecosystems.

Preparation of temperature-responsive smart sponge and its application in oil-water separation and dye adsorption

At present, researchers are committed to studying new intelligent response materials to deal with severe water pollution problems. Using PU sponge as the substrate, dopamine was first modified to construct a rough surface while introducing active groups. The monomer N-isopropylacrylamide (NIPAM) and itaconic acid (IA) were grafted and polymerized onto the polydopamine coating on the sponge surface by vinyltrimethoxysilane (VTMS). The obtained DINA-PU sponge has good temperature response and switchable wettability characteristics, and has good adsorption-desorption cycle function. Moreover, a micro-filtration device was designed to separate heavy (light) oil-water mixtures. The separation efficiency can reach more than 95% and 99% for heavy and light oil-water, respectively. In addition, the adsorption capacity of the material for methylene blue (MB) can reach 660mg·g-1. The separation efficiency in the oil-water separation-dye adsorption integrated separation experiment can reach more than 99%.

New challenges regarding the environmental and sanitary condition of Ukrainian water bodies

Today Ukraine is faced with new challenges that have a significant impact on natural water bodies and aquaculture. As a result of hostilities, there is an additional pressure on aquatic ecosystems. Unfortunately, large territories with important fishery complexes of Ukraine are either occupied, located in the war zone, or mined. Currently it is impossible to carry out comprehensive monitoring investigations into the actual environmental condition of inland water bodies of Ukraine. Therefore, in order to establish a true picture of the state of the water fund of Ukraine, an analytical review of publications was performed. Unfortunately, after the large-scale hostilities on the territory of Ukraine, a significant number of water bodies changed their status according to saprobic indicators. The situation is difficult with the reservoirs of the Dnipro River Cascade, which accumulate all pollutants released into the water from the catchment area. The destruction of the Kakhovka Hydroelectric Power Station led to a massive killing of all biota, including fish. The reservoirs are mostly polluted by biogenic, organic and surface-active substances, oil products, phenols, pesticides, and heavy metals. Even in the pre-war period, the problem of water pollution required immediate decisions, and with the beginning of the full-scale war, it became one of the most urgent tasks for Ukraine. Today, Ukraine’s water bodies suffer from pollution by pyrogens, fuel, and lubricants after rocket attacks and even from the total destruction of fish farms, water reservoirs, i.e., the Kakhovka Reservoir. Therefore, monitoring of the environmental condition of inland water bodies of Ukraine will provide an opportunity to assess their real condition and, in the future, to select the complex of methods aimed for their restoration.

Water pollution: causes, impacts and current efforts to address the issues of water pollution along river Meizimera-kihihi, Kanugu District,Uganda.

Pollution refers to the addition of harmful substances to that level where they cause an effect on the environment, it has three major categories such as water, soil, and air pollution but this report is on water pollution. It occurs when harmful substances contaminate water bodies such as, groundwater, rivers, lakes, and oceans rendering them unfavorable for various purposes for example drinking, recreation, and support to aquatic life. Globally, over 80% of wastewater worldwide is discharged into the water bodies without adequate treatment. In Africa, lack of clean water and sanitation is a significant challenge in many countries, affecting approximately 319 million people. Thus, water pollution is one of the types of pollution that has been threatening the lives of living organisms. Implementing effective policies and strategies can have a profound impact on the environment and local communities. By reducing pollution levels and improving water quality, we can create a healthier environment and decrease the incidence of waterborne diseases, leading to improved health and well-being for residents. The research on water pollution in the River Meizimera Kihihi has important implications for future research, policy and governance, human health, the environment, and communities and society. In conclusion, effective policies can foster community involvement, raise awareness, and promote collective action to address water pollution. By achieving clean water and sanitation (SDG 6), we can contribute to the broader sustainable development goals. This research has important ramifications for future research, policy and governance, human health, the environment, communities, and society. This study investigated the problems of water pollution, its causes, its impact, and the current effort to address the issues along the river of Meizimera-kihihi, Kanugu district, Uganda. Recommendations were made, which included encouraging the adoption of sustainable agricultural practices, industrial processes, and waste management strategies to minimize pollution.

Seasonal Rise in the Contents of Microcystin-LR and Odorous Substances Due to Cyanobacterial Blooms in a Drinking Water Reservoir Supplying Xinyang City, China.

Cyanobacterial blooms have become a serious water pollution problem in many parts of the world, and the monitoring and study of the impacts of biotoxins on human health are of vital importance. In this study, the contents of microcystin-LR, 2-methylisoborneol, and geosmin were measured in water and sediment samples from Nanwan Reservoir, China, by means of bimonthly sampling between February and December 2023. The physicochemical and hydrochemical factors and phytoplankton dynamics in the reservoir were also investigated. The results showed that the overall mean concentration of microcystin-LR (0.729 μg/L) in summer approached the guiding standard (1 μg/L) set by the WHO for drinking water. Furthermore, the content of 2-methylisoborneol (143.5 ng/L) was 14 times higher than the national standard (10 ng/L). The results of laboratory cultures showed that lower light levels and medium temperatures were suitable for the growth of Microcystis and Planktothricoides but higher temperatures promoted the synthesis and release of microcystin-LR and 2-methylisoborneol. In addition, the results of co-cultures showed that the growth of Planktothricoides was inhibited by Microcystis. Our results suggest that cyanobacterial bloom and the presence of the metabolites 2-methylisoborneol and microcystin-LR can decrease the drinking water quality of Nanwan Reservoir.

Microbial fuel cells: A potent and sustainable solution for heavy metal removal

The global water pollution problem is becoming increasingly crucial. One of the major contributors to water pollution is the presence of heavy metals. Heavy metals pose significant threat to both humans and all ecosystems. Various factors influence the removal of heavy metals from wastewater, including pH, temperature, natural organic matter (NOM), and ionic strength, which vary based on the chemical properties of the pollutants. More effective and modern approaches receive attention and extensively researched to substitute traditional methods such as adsorption, membrane filtration, and chemical-based separation. Among these methods, Microbial fuel cells (MFCs) are particularly intriguing. This review article focuses on MFCs and their potential applications in various fields, including clean water production. MFCs represent an innovative technology that not only generates electricity, but also demonstrates significant potential for heavy metal removal from wastewater. Cathodic chamber of MFCs effectively reduces heavy metals, while organic substrates act as carbon and electron donors in the anodic chamber. Through various mechanisms, including direct and indirect metal reduction, biofilm formation (metal sequestering), electron shuttling, and synergistic interactions among microbial communities, microorganisms exhibit remarkable efficiency in removing metals. Studies showed that dual- and single-chamber MFCs could efficiently remove a range of heavy metals, including chromium, cobalt, copper, vanadium, mercury, gold, selenium, lead, magnesium, manganese, zinc, and sodium, while simultaneously generating electricity, achieving high removal efficiencies ranging from 25% to 99.95%. This range of efficiency varies depending on the specific contaminant being targeted, the concentration of the contaminant, as well as the operating conditions such as pH and temperature. Moreover, MFCs demonstrated a wide range of power outputs, typically ranging from 0.15 W/m² to 6.58 W/m², depending on the specific configuration and conditions. These findings underscore the potential of MFCs as a sustainable and efficient approach for both wastewater treatment and energy generation.

Application Research on the Use of Multiple Comparison Methods in The Evaluation of the Effectiveness of Total Nitrogen and Total Phosphorus Reduction Measures

With the problem of water pollution becoming increasingly serious, excessive discharge of nitrogen and phosphorus has become a key factor affecting water quality and ecological balance. In order to evaluate the effectiveness of different pollution reduction measures in total nitrogen and total phosphorus control, this study evaluates multiple best management practices (BMPs) using multiple comparison methods, in particular Tukey HSD testing. The results of the statistical analysis of the reduction effects of the different measures showed that all the treatment groups with measures were significantly better than the control group without measures. In particular, BMP 8, BMP 7 and BMP 6 showed the best reduction effects. This study not only provides a scientific basis for pollution control decisions, but also lays the foundation for follow-up research, highlighting the importance of multiple comparison methods in environmental science.

Adsorption of Chromium (VI) and Lead (II) in Synthetic Solutions Using Tamarindus Indica Fruit Peel

The problem of water pollution persists and, in some cases, has been getting worse since many of the industries that are currently installed in developing countries do not comply with established standards. In order to reduce water pollution, various environmental standards have been established that aim to regulate the introduction of contaminating agents into water and, thereby, control the degree of alteration of the quality of the vital liquid. Adsorption allows minimizing the generation of toxic waste and the recovery of the metal. The objective of the work was to study the bioadsorption of Cr (VI) and Pb (II) using the dry peel of <i>Tamarindus indica</i>. We worked at different pH values and concentration levels. The determination of the chemical-physical parameters was carried out at the Empress Geominera Oriente. Adsorption isotherms were performed using the Langmuir, Freundlich and Dubinin-Radushkevich models, resulting in the maximum bioadsorption capacity of Cr (VI) and Pb (II) by biomass being 3.83 and 15.63 mg/g, respectively. reaching maximum removal percentages of 90.8%. The values of mean free energy of adsorption obtained from the Dubinin-Radushkevich model in Cr (VI) and Pb (II) were 10,000 kJ/mol, respectively, showing that, for these experimental conditions, the adsorption process is of a chemical nature.

Detection of Chemical Contaminants in Water for Irrigation Systems: A Systematic Review

Water pollution is a detrimental issue that occurs when there are bad changes in water quality parameters. It directly disrupts water usage and poses a danger to society, environment, economy, and agriculture. Water quality should be monitored to alert authorities on water pollution, so that action can be taken quickly. Improper water management pollutes rivers and lakes in Malaysia such as Klang River, Semenyih River, Kim Kim River, Slim River, and others. Various techniques are introduced to detect contaminants in water such as electronic sensors, biosensor approaches, laboratory analysis, and optical techniques. The functionality tool varies depending on the specific contaminants or parameters that are targeted, and the resources allocated. Several common contaminant types are found in polluted water including heavy metals, organic and inorganic chemicals, industrial pollutants, suspended solids, and others. The objective of the review is to study various non-optical and optical contaminant detection methods in water to identify the strengths and weaknesses of the methods. In this review, water pollution problems mainly due to the agricultural sector in several countries are discussed. Besides, conventional, and modern methods are compared in terms of parameters, complexity, and reliability. We believe that conventional methods are costly and complex, whereas modern methods are also expensive but simpler with real-time detection. Recent contaminant detection methods in water are also reviewed to study any loopholes in the latest methods. We found that the spectroscopy method based on light propagation theory is suitable and one of the promising methods for chemical contaminants detection for water quality analysis. This method offers fast analysis time, high sensitivity detection, non-invasive analysis, provides reliable data, and others. Undoubtedly, some contaminants in water can be challenging to be identified rapidly and confidently even though there are numerous tools and techniques available for water quality analysis. Thus, the review is important to compare previous methods and to improve current chemical contaminants detection analysis in terms of reliability with a minimum operating system and cost effectiveness.

Development and fabrication of graphene oxide and reduced graphene oxide incorporated MnFe2O4@Bi2WO6 nanocomposite for efficient degradation of antibiotic drug as water contaminant under visible-light illumination

Tetracyclines are one category of extensively applied antibiotics. Meantime, owing to misapplication and inappropriate disposal, they are mostly discovered in wastewater, which causes a series of environmental contamination and stated a threat to a person's health and security. The present study investigates the photodegradation of tetracycline using MnFe2O4@Bi2WO6/graphene oxide, GO, and MnFe2O4@Bi2WO6/reduced graphene oxide, RGO, and MnFe2O4@Bi2WO6 nanocomposites as permanent photocatalyst with the aid of visible light. A facile microwave assisted combustion method was applied in solid state rapidly, conveniently to fabricate MnFe2O4@ Bi2WO6–GO and MnFe2O4@ Bi2WO6–rGO nanocomposites at low power 150 W and in time 10 min with very low amount of glycine (as fuel). Consequently, XRD, EDX Mapping, DRS, PL, TEM, FESEM, FTIR, VSM, BET and UV–Visible spectrophotometric analysis demonstrated characteristic of nanocomposites and specifications of existent photocatalyst. Magnetic investigations revealed that the MnFe2O4@ Bi2WO6-GO and MnFe2O4@ Bi2WO6–RGO nanocomposites can be easily separated from the solution by an external magnetic field. MnFe2O4@ Bi2WO6–GO nanocomposites were discovered with high specific surface area 73.83 m2/g than MnFe2O4@Bi2WO6–RGO nanocomposites with specific surface area 17.75 m2/g. Highest photocatalytic activity was determined for the MnFe2O4@ Bi2WO6–GO (catalyst-0.10 g/l, tetracycline antibiotic concentration 10 mg/l and at pH = 4) within 25 min of visible light irradiation without using any oxidizing agent. The investigation of kinetic study revealed that kinetic parameter specified to photodegradation and experimental outcomes follow first-order model. the superoxide, hydroxyl radicals, ℎ+ holes and light are the principal demonstrates of the reaction mechanism for the effective degradation of tetracycline drug. The evaluation of MnFe2O4@ Bi2WO6–GO and MnFe2O4@ Bi2WO6–RGO magnetic catalysts has proposed the encouraging and significant role of nanocomposites in perilous pharmaceuticals refinement from industrial wastewater and also, magnetically photocatalyst attributes can be used as a potent separable tool for eliminating water pollution problems in the various industry.

Construction of LED-light-driven Z-scheme WO3/Bi12O15Cl6 heterojunction for photocatalytic degradation and antimicrobial

In order to alleviate the problem of water pollution, a novel Z-scheme WO3/Bi12O15Cl6 heterojunction was successfully designed to remove organic pollutants and bacteria from water bodies. Various characterization proved that WO3/Bi12O15Cl6 composites were successfully prepared. Photocurrent and electrochemical impedance (EIS) results verified the formation of heterojunctions could facilitate charge separation and migration. Under LED irradiation, the best sample 5 % WO3/Bi12O15Cl6 was able to remove 76.0 % tetracycline (TC) in 120 min and 98.9 % rhodamine B (RhB) in 90 min and kill Escherichia coli (E. coli) in 50 min. A possible mechanism of photocatalysis was proposed through active species removal experiments and the corresponding characterization. This research offers a new path to construct effective Z-scheme heterojunctions, which is a promising option for wastewater purification.

Phycoremediation: a path towards heavy metal bioremediation from wastewater

AbstractHeavy metals (HMs) have emerged as a significant and complex water pollution problem globally. These pollutants are particularly concerning due to their teratogenic, mutagenic, poisonous and carcinogenic properties, as well as their non‐biodegradability. Traditional removal techniques often fall short in addressing these issues, leading to a search for more effective solutions. One promising alternative is the phycoremediation process, which employs microalgae to remove HMs from wastewater. This method is not only cost‐effective but also environmentally friendly, offering the additional benefits of nutrient recovery from polluted water and conversion into value‐added products. This review delves into the capabilities of microalgae in remediating HM‐polluted water, examining the various factors and methods that affect the process. Key improvements that can enhance the efficiency of phycoremediation include immobilizing microalgae to increase their stability and longevity, utilizing binary cultures to harness synergistic effects and implementing cellular and genetic modifications to boost HM uptake and resilience. Moreover, the integration of algorithms and artificial intelligence can optimize phycoremediation processes by predicting and controlling environmental conditions, enhancing the precision and effectiveness of HM removal. The combination of these advanced strategies holds promise for overcoming the limitations of conventional methods, positioning phycoremediation as a viable solution for mitigating HM contamination in water bodies. © 2024 The Author(s). Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI).

Smart anti‐fouling and self‐repairing polymer brushes for efficient oil–water separation

AbstractThe increasing water pollution problem poses a demand for oil–water separation materials, but preparing separation materials with high efficiency and excellent durability remains a great challenge. In this work, we use a diblock polymer brush of polydimethylsiloxane (PDMS) and poly(N,N‐dimethylaminoethyl methacrylate) (PDMAEMA) based on cotton fabric to prepare oil–water separation membranes with high efficiency, good durability, and intelligent self‐repairing properties. Lubricating PDMS brushes reduces the fouling adhesion due to its low surface energy and high flexibility. pH‐responsive PDMAEMA brushes provide good hydrophobicity and an intelligent self‐repairing effect. The prepared Co‐PDMS‐PDMAEMA has high oil flux (>30,000 L m−2 h−1) and high separation efficiency (>99%) even after 10 cycles and its surface character can be recovered under acidic conditions. Overall, the modified cotton fabric made by such a versatile technique is promising in oil–water separation.

Assessment of nutrient differences in detached soil particles between cropland and revegetated abandoned land

AbstractCropland (CRL) abandonment is a worldwide phenomenon of land use change with significant impacts on agro‐ecosystems. This research attempts to deepen the analysis of the positive and negative effects arising by focusing on the changes in soil properties and the amount and composition of soil particles detached after several periods of rainfall and the resulting exported sediment that occurs in abandoned areas with natural revegetation compared to CRL. The study was carried out in an agroforestry catchment with a temperate climate, on which CRL and abandoned land with natural vegetation were compared. The soil was sampled along two representative hillslopes integrating elements of the landscape and land use/land covers. Sediments were collected after seven periods in which flood events were recorded during the period July 2016 to December 2017, using artificial‐lawn mats. Soil and sediment composition (texture, soil organic carbon [SOC] and nutrients [total nitrogen and total phosphorous]) under both land uses were assessed and compared and related to rainfall characteristics using principal component analysis. Nutrient enrichment factors in the sediments compared to soils were also evaluated. The results highlight that after abandonment, SOC increased significantly, reaching contents almost three times higher than in CRL. Consequently, soil erodibility decreased, resulting in substantially lower sediment generation after erosive rainfall events. On average, sediment generation was three times lower in abandoned areas than in CRL, despite their steeper slopes. Soil total nitrogen also increased on abandoned lands, reaching values about twice as high as those in CRL. However, total phosphorous content was almost twice as high in CRL than in abandoned land posing a potential risk for water due to higher erosion rates recorded in CRL. The results confirmed the association of phosphorous with smaller particles and also demonstrated the total phosphorous‐SOC link in abandoned land. Furthermore, the effect of rainfall intensity on phosphorous mobilisation was confirmed, whilst nitrogen losses were mainly related to the total amount of rainfall recorded. In a scenario of increasing extreme precipitation, both total amount and increased precipitation intensity may exacerbate water pollution problems following nutrient loss in cultivated areas. This research contributes to identifying the impacts on agroforestry systems within the current context of converting natural areas into cultivated land, whilst in other regions revegetated natural areas are developed from abandoned agricultural land.

The Representative Kanpur Tannery’s Ganges Water Pollution Problem

The Representative Kanpur Tannery’s Ganges Water Pollution Problem

Study on the treatment of black and odorous water bodies by aeration combined with sulfur-iron autotrophic denitrification MBBR

ABSTRACT As China's economy grows rapidly, there is a growing problem of rural water pollution, particularly regarding black and odorous water bodies. However, the current treatment technologies have proven inadequate in both nitrogen and phosphorus removal, primarily due to the insufficient carbon-to-nitrogen ratio in these black and odorous water bodies, resulting in low nitrogen removal efficiency. To address this challenge, the study proposes a novel treatment process, namely ‘aeration + sulfur-iron autotrophic denitrification MBBR’. This innovative approach was compared with the traditional ‘aeration + MBBR’ treatment process and blank control group over an 18-day experimental period. Ten water quality indicators were monitored and compared, including odor, turbidity, DO, pH, COD, BOD5, NH3-N, NO3-N, TN, and TP. The results revealed satisfactory performance of both treatment processes in terms of odor, turbidity, DO, COD, BOD5, and NH3-N indicators. However, significant disparities were observed in denitrification and phosphorus removal, with the new process achieving removal rates of 85.65 and 78.02%, respectively, compared to −2.30 and −4.05% for the existing process. Furthermore, the new process met the surface water class IV quality standard for all 10 monitored indicators, indicating its potential for effectively addressing the issue of black and odorous water in rural China.

Unveiling the synergistic potential of g-C3N4-MWCNT/In2O3 nanocomposite for enhanced organic pollutant degradation and cancer cell inhibition under visible light irradiation

The surge in industrial activities and a substantial increase in antibiotic usage, has led to the further deterioration of global water pollution problems. Focusing on this current scenario, we synthesize the g-C3N4-MWCNT/In2O3 (GMI) ternary composite to utilize for the photocatalytic degradation of levofloxacin (LF) antibiotic and crystal violet (CV) dye under visible light. The photocatalytic degradation of CV (15 mgL⁻1) and LF (40 mgL⁻1) was 99.7 % and 87.4 % respectively, in just 15 and 100 min of irradiation with GMI-0.2 nanocomposite. The removal rates of CV and LF with GMI-0.2 nanocomposite were 14.61 and 4.85 times more rapid than those observed with In2O3. Similarly, compared to g-C3N4, the removal rates for CV and LF were 7.34 and 3.98 times higher when using GMI-0.2 nanocomposite. The trapping experiments and ESR measurements indicated that O2•⁻ was the predominant active species responsible for the photocatalytic degradation processes. In order to explain the degradation processes, a feasible photocatalytic mechanism for GMI ternary composite was proposed. The mechanism was based on the calculations of the band gaps and edge potentials of the synthesised materials as well as the findings of the quenching experiments. The GMI-0.2 nanocomposite was also used to treat human lung cancer cells, and it was discovered that cell viability with 100 µg/mL of the photocatalyst was lowest in both dark (36 %) and in visible light (20 %).

Cobalt germanium hydroxides with asymmetric electron distribution and surface hydroxyl groups for superb catalytic degradation performances

Peroxymonosulfate (PMS)-based advanced oxidation processes (AOPs) are attractive approaches for solving the global problem of water pollution, due to the generation of highly-active reactive oxygen species (ROS). Therefore, highly-efficient PMS activation is crucial for promoting the catalytic degradation of environmental pollutants. Here, bimetallic CoGeO2(OH)2 nanosheets with abundant surface hydroxyl groups (CGH) were synthesized via a simple hydrothermal route for PMS activation and degradation of various organic contaminants for the first time. The abundant surface hydroxyl groups (≡Co–OH/≡Ge–OH) could promptly initiate PMS to generate highly-active species: singlet oxygen (1O2), sulfate radicals (SO4·−) and hydroxyl radicals (HO•), while the asymmetric electron distribution among Co–O–Ge bonds derived from the higher electronegativity of Ge than Co further enhances the quick electron transfer to promote the redox cycle of Co2+/Co3+ and Ge2+/Ge4+, thereby achieving an outstanding catalytic capability. The optimal catalyst exhibits nearly 100 % catalytic degradation performance of dyes (Methylene blue, Rhodamine B, Methyl orange, Orange II, Methyl green) and antibiotics (Norfloxacin, Bisphenol A, Tetracycline) over a wide pH range of 3–11 and under different coexisting anion conditions (Cl−, HCO3–, NO3–, HA), suggesting the excellent adaptability for practical usage. This study could potentially lead to novel perspectives on the remediation of water areas such as groundwater and deep-water areas.

Composite Copolymer Beads Incorporating Red Mud for Water Amendment by Adsorption—Oxidation Processes

We face significant environmental pollution problems due to various industries, such as the aluminum industry, which generates large amounts of red mud (RM) waste, or agriculture, in which case the use of pesticides creates huge water pollution problems. In this context, the present study offers a better perspective to originally solve both environmental issues. Thus, the main target of the study referred to using RM waste as a filler for preparing composite copolymer beads. Thereafter, this can achieve significant removal of water pollutants due to their adsorption/oxidation characteristics. As evidenced by the changes in chemical structure and composition, thermal stability, morphology, and porosity, RM was homogenously incorporated in poly(acrylonitrile-co-acrylic acid) beads prepared by wet phase inversion. The final assessment for the removal of pesticides by adsorption and oxidation processes was proven successful. In this regard, 2,4-dichlorophenoxyacetic acid was chosen as a model pollutant, for which an adsorption capacity of 16.08 mg/g composite beads was achieved.

A Review of Different Predictive Models for Water Pollution Problems

A Review of Different Predictive Models for Water Pollution Problems