Polyethylene Terephthalate Plastic Waste Research Articles

AspenPlus-based techno-economic analysis of solar-assisted sorption-enhanced gasification for hydrogen and chemicals recovery from polyethylene terephthalate waste

Although the recycling of polyethylene terephthalate (PET) bottles is well-operating in several countries, less than 10% of PET plastic waste was recycled in a closed loop globally, and the rest was discarded as leakage. A process to recover hydrogen and valuable chemicals through solar-assisted PET sorption-enhanced gasification was analyzed. PET steam gasification with CaO and solar-assisted calcium looping processes were already experimentally studied in our previous work to obtain optimized processing conditions. In this paper, the integrated process with product purification, steam power plant, and LiBr-H2O absorption chiller was simulated with Aspen Plus based on previous experimental results to investigate the techno-economic performance. Material flows, energy balance, exergy destruction, and economics were analyzed. Day and night mode operations at different seasons were evaluated based on energy balance and the weather conditions of Naples, Italy. The energy and exergy efficiencies of day and night modes varied between 62%–72%. The annual production yields of hydrogen and benzene were 684 t and 6286 t, respectively. Due to the high production of benzene, its higher price (>1092 €/t) would make the project feasible with a larger than 12% internal rate of return value and competitive break-even hydrogen price (less than 4 €/kg). The results show that this integrated process could be technically and economically feasible. It has the potential to be implemented for hydrogen and benzene recovery from PET plastic waste with sustainable solar heat source and zero fossil CO2 emissions.

Interface-engineering of the Catalysts for Efficient Electrocatalytic Upcycling of Polyethylene Terephthalate Waste

Plastics have become an essential component of our daily lives, but their widespread use has resulted in significant environmental and ecological pollution. Conventional methods for plastic waste treatment are both environmentally unfriendly and energy-intensive. In recent years, the emergence of electrocatalytic degradation technology for plastic waste has opened up new possibilities for converting waste plastics into valuable chemicals, thus promoting the realization of a circular economy for plastics. This review aims to provide an in-depth overview of the fundamental principles and characteristics of interfaces, focusing on the electrocatalytic degradation of ethylene glycol (EG) derived from polyethylene terephthalate (PET). This review primarily examines the two primary methods of electrocatalytic oxidation reactions of PET-derived EG, along with the advancements in interface engineering technology. It delves into the research progress made in interface catalysts for the electrocatalysis of PET-derived EG, while also discussing future research directions. The objective is to delve deeper into the development of effective electrocatalytic degradation catalysts, to address the pressing challenges posed by the ecological environmental crisis and the imperative need for transforming and upgrading PET plastic waste.

Functional upcycling of waste PET plastic to the hybrid magnetic microparticles adsorbent for cesium removal

Accumulation of mismanaged plastic in the environment and the appearance of emerging plastic-derived pollutants such as microplastics strongly demand technologies for waste plastic utilization. In this study, polyethylene terephthalate (PET) from waste plastic bottles was directly utilized to prepare a matrix of an adsorbent for cesium (Cs+) removal. The organic matrix of PET-derived oligomers obtained by aminolysis depolymerization was impregnated with bentonite clay and magnetite nanoparticles (Fe3O4 NPs), playing the roles as a major adsorptive medium for Cs+ removal and as a functional component to primarily provide efficient separation of the hybrid adsorbent from aqueous system, respectively. The obtained hybrid composite microparticles were next tested as an adsorbent for the removal of Cs+ cation from aqueous solutions. The adsorption process was characterized by fast kinetics reaching ca. 60% of the equilibrium adsorption capacity within 5 min and the maximum adsorption capacity toward Cs+ was found to be 26.8 mg/g. The adsorption process was primarily dominated by the cationic exchange in bentonite, which was not significantly affected by the admixture of the competing mono- and divalent cations (Na+, K+, and Mg2+). The proposed approach here exploits the sustainable utilization scenario of plastic waste-derived material to template complex multifunctional nanocomposites that can find applications for pollution cleaning and environmental remediation.

Fabrication of activated carbon from polyethylene terephthalate plastic waste (PET) and their application for the removal of organic dyes in aqueous solution by chemical method

Synthetic plastics are found in all manufacturing industries and in daily life because plastic products bring convenience to life. Polyethylene terephthalate (PET) is one of the most popular synthetic plastics with increasing consumption. Every year, the huge amount of PET plastic waste is discharged into the environment. Therefore, it is necessary to have an effective solution for PET plastic waste. In this study, PET waste plastic was utilized to fabricate activated carbon using the chemical activating approach. H3PO4 acid was used as activating agent. The influence of impregnation rate of PET waste platic with H3PO4, activating temperature, activating time on the surface areas of activated carbon was investigated. The prepared activated carbon was well-characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), FTIR, and BET. The activated carbon prepared from the :PET plastic waste revealed high absorption toward methylene blue in aqueous solution in a wide range of pH solutions. The fabrication of activated carbon from the plastic waste not only address the environmental issues, but also produce high-value activated carbon for the environmental remediation.

Improving Performance in Mixture Porous Asphalt: Application Polyethylene-Terephthalate (PET) and Lawele Granular Asphalt (LGA)

Plastic has various types, one of which is PET (Polyethylene Terephthalate) plastic, which is often used as a raw material for plastic bottles. One type of asbuton that is often used for road pavement is LGA (Lawele Granular Asphalt) asphalt. Repairs by adding asbuton to the porous asphalt mixture need to be done. This is because porous asphalt has several weaknesses, namely low strength or stability compared to other asphalt mixtures. The addition of PET and LGA waste to porous asphalt is a topic in this article. This research design uses a quantitative design with a type of experimental research. The results of the study concluded that: (1) The results of testing the characteristics of the constituent ingredients of the porous asphalt mixture meet the specifications of SNI, and (2) The test results of the addition of PET (Polyethylene Terephthalate) plastic and LGA (Lawele Granular Asphalt) to porous asphalt mixture meet the specifications by RSNI 2 Design and Implementation of Porous Asphalt Mixture 2012. It is hoped that this research can be an alternative to the mixture of PET plastic waste and LGA asbuton in a porous asphalt mixture. In addition, the newness of this material is expected to also help the construction of roads.

The Potential of Bacillus altitudinis B538 and Alcaligenes faecalis B947 in PET and PCL Plastic Degradation

Polyethylene terephthalate (PET) plastic is the most widely used type of plastic that produces waste and causes various environmental and health problems. The treatment of PET plastic waste with chemically and mechanically recycling approaches still has shortcomings, so biological processing using microorganisms or enzymes has new potential. Two bacterial isolates from the Indonesian Culture Collection of National Research and Innovation Agency (InaCC, BRIN), namely isolate InaCC B538 and InaCC B947, were further observed for their potential in PET plastic degradation. Firstly, both isolates were determined by the molecular marker 16S rDNA. The potential of both isolates was measured with following method: 10 days of degradation using PET and PCL substrates, esterase enzyme activity assay, and observation of the PET plastic surface using Scanning Electron Microscope (SEM). Species identification was performed using DNA sequencing of 16S rDNA. InaCC B538 and InaCC B947 were closely related to Bacillus altitudinis TBMAX41 and Alcaligenes faecalis AN-13, respectively. InaCC B947 isolate has a better potential in degrading PET plastic and PCL with a degradation percentage of 0.32% for PET plastic and 3.22% for PCL film for 10 days, respectively, and esterase activity of 0.06 U/ml; while InaCC B538 did not cause weight loss of PET and 2.49% for PCL, respectively, with esterase activity of 0.04 U/ml. The degradation of PET plastic by the isolates InaCC B947 was able to cause damage to the plastic surface leading to the degradation of PET plastic.

Sustainable solar-and electro-driven production of high concentration H2O2 coupled to electrocatalytic upcycling of polyethylene terephthalate plastic waste

The photoelectro-reforming of poly (ethylene terephthalate) (PET) waste coupled with the synthesis of hydrogen peroxide (H2O2) poses significant implications for environmental and energy engineering, yet it presents substantial with challenges. A strategy offering an energy efficient photo-electrolysis is reported, which couples oxygen reduction reaction (ORR) with oxidation reaction of PET hydrolysate (glycol, EGOR), utilizating a porous hollow double-shell with oxygen vacancies Z-scheme Mo2N-Co3O4@Fe2O3/PVDF/NF cathode and a Co3O4/NF anode within a cell electrolyser. The H2O2 concentration by hydrophobic photocathode (3.4 wt%) significantly surpasses that of hydrophilic electrode (1.9 wt%), attributing to the hydrophobic modified enhances the mass transfer and utilization efficiency of O2. The Mo2N-Co3O4@Fe2O3 has photothermal effect by introducing Mo2N with local surface plasmon resonance (LSPR) for the direct synthesis of high concentration H2O2 (21.4 wt%). The photoelectro-reforming of PET by photoanode yields the value-added products such as terephthalic acid (PTA) and potassium diformate (KDF) with a high Faradic efffciency (89 %). Notably, EGOR assistes the ORR, resulting in a yield of H2O2 by ORR that is significantly improved at least three times in comparison to the water oxidation reaction coordinated with ORR. This research contributes to a feasible methodology for H2O2 production, and the transformation of plastics and other waste materials into value-added chemicals.

Utilization of Plastic Waste in Reinforcing Sandy Soil for Sustainable Engineering Applications

Large quantities of polyethylene terephthalate (PET) plastic are discarded into the environment during production, application, and disposal. Although current clean-up strategies aim to mitigate the adverse impacts of PET pollution, efforts struggle to keep up with the escalating amount of PET waste. This accumulation of PET waste poses significant threats to ecosystems worldwide. One recycling method for PET plastic waste involves its utilization in soil reinforcement applications within civil engineering. By incorporating PET plastic waste to reinforce poor-quality sands, sustainable construction practices can be promoted in civil engineering infrastructures, addressing multiple aspects of sustainability, including engineering, economic, social, and environmental considerations. The experimental work conducted in this research involved sieve analysis, proctor compaction test, California Bearing Ratio (CBR) test, and direct shear box test. The sand was reinforced with varying percentages of PET plastic waste flakes, namely 5, 10, and 15 %, with respect to the weight of the soil sample taken for the test, and laboratory tests were performed on the samples. Including PET plastic flakes enhanced various soil properties, such as shear strength and friction angle. It also improved the CBR value of the composite, making it suitable for pavement construction. The reduction in dry density further supports the application of the composite in lightweight structures. In conclusion, the geotechnical material obtained from the soil-PET plastic waste composite can be utilized in various geotechnical projects, including landfills and slope stabilization.

The Effect of 0.8% Polyethylene Terephthalate Plastic Waste Substitution on the Flexural Strength on K-175 Concrete

The use of plastics in daily life continues to increase in a variety of uses. One of the most commonly used plastic that is difficult to decompose is Polyethylene Terephthalate (PET) plastic. In recent years, such as the construction industry, has been trying to reuse the waste as construction material. Therefore, this research aims to contribute by exploring the effect of PET plastic fiber substitution as fine aggregate on the flexural strength of concrete. PET plastic fibers were used at 0.8% as partial replacement of fine aggregates and then chopped to a size of 5 cm long, 1-3 mm wide. The test results indicate that concrete containing 0.8% PET plastic fiber as a substitution of fine aggregate has a higher flexural strength value of 4.32% which is better than normal concrete. Therefore, using recycled PET fiber in concrete is needed as an eco-friendly and sustainable construction material in the future in order to minimize PET plastic waste and replace it as a concrete constituent material.

Green Synthesis of CoZn-Based Metal-Organic Framework (CoZn-MOF) from Waste Polyethylene Terephthalate Plastic As a High-Performance Anode for Lithium-Ion Battery Applications.

The recycling of discarded polyethylene terephthalate (PET) plastics produced metal-organic frameworks can effectively minimize environmental pollution and promote sustainable economic development. In this study, we developed a method using NaOH in alcohol and ether solvent environments to degrade PET plastics for synthesizing terephthalic acid. The method achieved a 97.5% degradation rate of PET plastics under a reaction temperature of 80 °C for 60 min. We used terephthalic acid as a ligand from the degradation products to successfully synthesize two types of monometallic and bimetallic CoZn-MOF materials. We investigated the impact of different metal centers and solvents on the electrochemical performance of the MOF materials. The result showed that the MOF-DMF/H2O material maintained a specific capacity of 1485.5 mAh g-1 after 100 cycles at a current density of 500 mA g-1, demonstrating excellent rate capability and cycling stability. In addition, our finding showed that the performance difference might be attributed to the synergistic effect of bimetallic Co2+ and Zn2+ in MOF-DMF/H2O, rapid lithium-ion diffusion and electron transfer rates, and the absence of coordinating solvents. Additionally, the non-in situ X-ray powder diffraction, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy analysis results showed that lithium storage in the MOF-DMF/H2O electrode mainly depended on the aromatic C6 ring and carboxylate portions of the organic ligands in different charge and discharge states. Lithium ions can be reversibly inserted/removed into/from the electrode material. The physical adsorption on the MOF surface through electrostatic interactions enhanced both capacity and cycling stability. This research provides valuable insight for mitigating solid waste pollution, promoting sustainable economic development, and advancing the extensive applications of MOF materials in lithium-ion batteries.

Shape-memory polyurethane elastomer originated from waste PET plastic and their composites with carbon nanotube for sensitive and stretchable strain sensor

Chemical recycling of polyethylene terephthalate (PET) bottles is prospective for reducing waste plastics. The transformation of waste PET into valuable composites in high efficiency still remains a formidable challenge. Here we report the synthesis of polyurethane elastomer (PUE) by using the degraded products from waste PET via one-pot chain extended process. Then, the composites composed of PUE as substrate with carbon nanotubes as fillers are applied in fabricating stretchable strain sensor. The results show that the degraded product was successfully introduced into the polyurethane chains. The PUE chains showed disordered stacking as the degraded product content increased, with the modulus and elongation at break were up to 763.9 %. The composites assembled strain sensors exhibited stable sensing performance and excellent durability after 1000 cycles at 20 % tensile strain. This may supply a path to efficiently recycle waste PET plastic into valuable and functional composites, and even devices.

In situ growth of MIL-101 (Fe) on waste PET plastic slices for effective arsenic removal

Converting waste Polyethylene terephthalate (PET) plastic into value-added metal–organic frameworks (MOFs) has emerged as a prospective solution to plastic upcycling. Within this work, MIL-101(Fe)@PET was fabricated via microwave method. The as-prepared MIL-101(Fe)@PET performed high removal efficiency (100 %) toward three arsenic pollutants at low concentration (1 mg/L) within 60 min. The maximum adsorption capacity of MIL-101(Fe)@PET toward 4-aminophenylarsonic acid (ASA), hydroxy-3-nitrobenzenearsonic acid (ROX) and As(V) were 320.6, 476.5, 240.0 mg g−1, respectively. Further, the household water purifiers filter was assembled adopting the as-prepared MIL-101(Fe)@PET as absorbent. MIL-101(Fe)@PET filter performed higher arsenic removal efficiency than active carbon filter and commercial filter. The adsorption behaviors of MIL-101(Fe)@PET toward arsenic was found to be fitted with pseudo-second-order kinetic models and Langmuir isotherm models. The possible adsorption mechanism was proposed. The developed strategy provides a new method in the application of MOFs-based materials and upcycling waste plastics.

Expression and engineering of PET-degrading enzymes from Microbispora, Nonomuraea, and Micromonospora.

Mismanagement of PET plastic waste significantly threatens human and environmental health. Together with the relentless increase in plastic production, plastic pollution is an issue of rising concern. In response to this challenge, scientists are investigating eco-friendly approaches, such as bioprocessing and microbial factories, to sustainably manage the growing quantity of plastic waste in our ecosystem. Industrial applicability of enzymes capable of degrading PET is limited by numerous factors, including their scarcity in nature. The objective of this study is to enhance our understanding of this group of enzymes by identifying and characterizing novel enzymes that can facilitate the breakdown of PET waste. This data will expand the enzymatic repertoire and provide valuable insights into the prerequisites for successful PET degradation.

Ultrafiltration membrane fabricated from polyethylene terephthalate plastic waste for treating microalgal wastewater and reusing for microalgal cultivation

Current study had made a significant progress in microalgal wastewater treatment through the implementation of an economically viable polyethylene terephthalate (PET) membrane derived from plastic bottle waste. The membrane exhibited an exceptional pure water flux of 156.5 ± 0.25 L/m2h and a wastewater flux of 15.37 ± 0.02 L/m2h. Moreover, the membrane demonstrated remarkable efficiency in selectively removing a wide range of residual parameters, achieving rejection rates up to 99%. The reutilization of treated wastewater to grow microalgae had resulted in a marginal decrease in microalgal density, from 10.01 ± 0.48 to 9.26 ± 0.66 g/g. However, this decline was overshadowed by a notable enhancement in lipid production with level rising from 181.35 ± 0.42 to 225.01 ± 0.11 mg/g. These findings signified the membrane's capacity to preserve nutrients availability within the wastewater; thus, positively influencing the lipid synthesis and accumulation within microalgal cells. Moreover, the membrane's comprehensive analysis of cross-sectional and surface topographies revealed the presence of macropores with a highly interconnected framework, significantly amplifying the available surface area for fluid flow. This exceptional structural attribute had substantially contributed to the membrane's efficacy by facilitating superior filtration and separation process. Additionally, the identified functional groups within the membrane aligned consistently with those commonly found in PET polymer, confirming the membrane's compatibility and efficacy in microalgal wastewater treatment.

Insight the influence of the catalyst basicity on glycolysis behavior of Polyethylene terephthalate (PET)

Although polyethylene terephthalate (PET) is one of the most prevalent plastics, a cumulative disposal of PET waste has caused adverse effects on both economy and environment. Catalytic glycolysis of PET waste has emerged as a prevalent and sustainable pathway to address this problem. Due to the limitations of recovery and recycling, the catalytic development trend for PET glycolysis has recently changed from homogenous to heterogeneous designs. Herein, metal oxides with different basicity, including calcium, cerium, and cobalt, were supported on alumina and first employed in the glycolysis process of waste PET plastic. A plausible mechanism is proposed and reveals the correlation between the basicity of as-prepared catalyst and glycolysis performances. Among these catalysts, 10%Ce/Al2O3 exhibited a complete conversion of waste PET with the highest selectivity to the main product BHET. There is no significant drop in catalytic activity after five consecutive runs. Furthermore, the excellent quality of the monomer product BHET was confirmed via different analysis techniques. This work has contributed to a promising notion for engineering efficient heterogeneous catalysts of PET recycling technology.

Catalytic upgrading of PET to acid by engineering bimetallic AuCu/CNT catalyst

AbstractBACKGROUNDRecycling waste polyethylene terephthalate (PET) plastic can prolong its life cycle, reduce the consumption of non‐renewable resources, prevent plastic pollution and also protect the ecological environment. Traditional chemical recycling of waste PET plastic can depolymerize PET into terephthalic acid (TPA) and ethylene glycol (EG).RESULTSA strategy was proposed to directly depolymerize PET into TPA and acid, which shows significantly higher values than conventional EG. This is achieved over a carbon nanotube (CNT)‐supported AuCu catalyst (AuCu/CNT) prepared using an evaporative impregnation method. Comprehensive analyses of the catalyst were conducted using X‐ray diffraction, N2 adsorption/desorption, transmission electron microscopy, X‐ray photoelectron spectroscopy, H2‐temperature=programmed reduction, and so on. It was found that Cu species in the AuCu/CNT catalyst mainly existed in the form of CuO, forming new reaction adsorption sites and providing active AuCu alloy sites, thereby improving the catalytic performance of AuCu/CNT. This results in simultaneously superior acid selectivity and EG conversion over AuCu/CNT compared with Au/CNT and Cu/CNT.CONCLUSIONThis study indicates that the hydrolysis of PET is highly significant in preparing value‐added products. © 2023 Society of Chemical Industry.

Electrocatalytic upcycling of polyethylene terephthalate plastic to formic acid coupled with energy-saving hydrogen production over hierarchical Pd-doped NiTe nanoarrays

Electrochemical upcycling of plastic waste to high-value chemicals is an ideal approach for the valorization of waste resources. In this study, we report the electro-reforming of polyethylene terephthalate (PET) plastic hydrolysate to valuable formate and hydrogen. Pd-deposited hierarchical aligned NiTe nanoarrays on Ni foam (Pd-NiTe/NF) is developed for oxidation of PET hydrolysate at anode and hydrogen evolution at cathode, with the overpotentials of 0.019 and 1.35 V at 10 and 100 mA cm-2, respectively. In co-electrolysis system, the Pd-NiTe/NF exhibits high Faradaic efficiencies for concurrent production of value-added formate (95.6%) and H2 (98.6%). The high activity and stability of Pd-NiTe/NF can be ascribed to that the interfacial heterostructures by incorporating Pd atoms and the strongly interfacial electronic interactions of between Pd and NiTe can synergistically promote PET-derived ethylene glycol to formate oxidation and hydrogen evolution. This work shows promising prospect in electro-reforming PET plastic waste to valuable chemicals.

Sustainable Waste Management Breakthrough: Transforming Plastic Waste into Eco-Friendly Briquette Charcoal

Plastic waste has emerged as an important environmental concern. Among the various types of plastic waste, such as Polyethylene Terephthalate (PET) and Polypropylene (PP), these two contribute the most to the overall plastic waste problem need to be efficiently managed. The purpose of this research is to study the manufacture of briquettes from PET and PP plastic waste with the help of starch adhesive. This research is expected to reduce the negative impact of plastic waste. In this study, the data to be obtained were the calorific value of the briquettes, ash content, moisture content, volatile content and bound carbon content. The results show that the best raw material combination in terms of the calorific value of the resulting charcoal briquettes is the raw material mixture with the addition of PET. The results of the PET type plastic briquettes were superior with the results of the calorific value test of 10.129 cal/gram, the proximate test results of 3.11% ash content, 4.98% moisture content, 65.31% volatile matter content, and 78% bound carbon content 79%. While the PP type plastic briquettes obtained a calorific value test result of 9,949 cal/gram, the calorific value was lower than the PET type plastic briquettes.

Performance of clay soil reinforced with PET plastic waste subjected to freeze-thaw cycles for pavement subgrade application

The freeze-thaw (F-T) cycle is a common weathering process that often occurs in cold climates, and it can deteriorate the mechanical performance of the subgrade soil, leading to pavement failure and economic loss. Plastic wastes have been adopted as a soil reinforcement element to improve the geotechnical properties and stability of expansive clay soils used as subgrade material. Previous research has mainly focused on the application of polyethylene terephthalate (PET) plastic waste to soil reinforcement under ambient temperature, but few studies have investigated the geotechnical performance of expansive clay soils reinforced with PET plastic waste under freeze-thaw conditions for pavement subgrade application. Moreover, there is a lack of knowledge on the dynamic properties of expansive clays modified with PET plastics exposed to the F-T process. This study conducted a series of mechanical experiments, including repeated load triaxial tests and unconfined compressive strength tests, for the first time to investigate the mechanical performance of expansive clay soil reinforced with different percentages of PET strips (i.e., 0, 1, 1.5, and 2% by the weight of dry soil) after being exposed to 0, 2, 5, and 8 F-T cycles. The experimental results showed that the F-T process significantly reduced the compressive strength and resilient modulus. However, the compressive strength and resilient modulus of the PET strips-reinforced samples were higher than those of the unreinforced samples after F-T cycles. The optimum content of PET strips was found to be 1% by weight of dry soil, as it exhibited the highest strength and stiffness under various F-T cycles.

Biodegradation of polyethylene terephthalate (PET) by diverse marine bacteria in deep-sea sediments.

PET plastic waste entering the oceans is supposed to take hundreds of years to degrade and tends to accumulate in the deep sea. However, we know little about the bacteria capable of plastic degradation therein. To determine whether PET-degrading bacteria are present in deep-sea sediment, we collected the samples from the eastern central Pacific Ocean and initiated microbial incubation with PET as the carbon source. After enrichment with PET for 2 years, we gained all 15 deep-sea sediment communities at five oceanic sampling sites. Bacterial isolation for pure culture and further growth tests confirmed that diverse bacteria possess degradation ability including Alcanivorax xenomutans BC02_1_A5, Marinobacter sediminum BC31_3_A1, Marinobacter gudaonensis BC06_2_A6, Thalassospira xiamenensis BC02_2_A1 and Nocardioides marinus BC14_2_R3. Furthermore, four strains were chosen as representatives to reconfirm the PET degradation capability by SEM, weight loss and UPLC-MS. The results showed that after 30-day incubation, 1.3%-1.8% of PET was lost. De-polymerization of PET by the four strains was confirmed by the occurrence of the PET monomer of MHET and TPA as the key degradation products. Bacterial consortia possessing PET-degrading potential are prevalent and diverse and might play a key role in the removal of PET pollutants in deep oceans.