A Review on Global Recovery Policy of Used Lubricating Oils and Their Effects on the Environment and Circular Economy

Abstract

This manuscript underscores the significance of converting and reusing lubricating oils for dual purposes as both lubricants and fuels. This approach not only benefits the environment, but also contributes to the circular economy. To this end, this article conducts a review and delves into the applications and re-refining techniques employed to recover lubricating oil from waste lubricating oil (WLO). A global overview of waste oil recycling and political feasibility in the marketplace is presented, highlighting country-specific preferences for reusing such oils. Moreover, this manuscript analyzes several studies that utilize recycled oil as fuel in thermal equipment, including diesel engines. The findings indicate that CO emissions increased incrementally under both low- (from 3.22% to 21.23%) and high-load conditions (from 6.6% to 18.2%) compared to diesel fuel. Another study reveals that 10% and 20% blends of transformer oil and diesel exhibit lower fuel consumption than diesel fuel at high loads. In all the cases examined, WLO demonstrated slightly higher emission levels than marine diesel oil (MDO), yet lower than those observed with heavy fuel oil (HFO).

1. Introduction

Lubricating oils play a critical role in reducing friction and wear between metal surfaces, thereby extending equipment lifespan and conserving resources. These oils are categorized into automotive, industrial, process, and marine oils. They are widely used in various sectors, including automotive, industrial, marine, and aviation applications. Typically, lubricating oils comprise 80–90% base oil and 10–20% additives and other compounds [1].

Approximately 50% of the lubricating oils produced are utilized in the automotive, marine, and industrial sectors, with hydraulic oils accounting for up to 20% of the total volume. A portion of these oils eventually becomes waste lubricant oil (WLO) [2]. In the European Union (EU), WLO, classified as hazardous waste, constitutes the most significant liquid hazardous waste stream, amounting to 1.6 million tons in 2017 [3].

This manuscript focuses on a descriptive analysis of existing practices and policies related to the recycling of used lubricating oils. The information presented is largely a compendium of previous data and studies. It is of political interest due to the implications that recycling used lubricating oils has for the circular economy and the preservation of the environment. In the political field, this article highlights the need to establish public policies that encourage the proper management of these hazardous wastes, preventing their indiscriminate disposal into the environment. The implementation of stricter regulations and the setting of recycling targets in the EU member states are some of the recommendations proposed to minimize the environmental impact of these waste oils.

From a policy perspective, this review also emphasizes the importance of international cooperation and the creation of regulatory frameworks that ensure the efficient management of used lubricating oils. This text analyzes various policies implemented in countries such as the U.S., China, and Australia, demonstrating that governments play a key role in creating incentives for recycling these products and reducing environmental risks. This article also highlights that the proper management of waste oils can generate significant economic benefits, such as job creation in the recycling industry and a reduction in the costs associated with environmental pollution.

Table 1. Self-creation based on ChatGPT-4 data.

Lubricants
Application		End User
Manufacturing Companies	Automotive	Internal combustion engines. Lubrication of transmission, differentials, and gearboxes. Hydraulic systems for smooth operation. Wheel bearings and chassis lubrication.
Energy and Utilities	Oil and gas companies. Power generation plants (thermal, hydro, nuclear, wind). Renewable energy operators (e.g., wind farms with turbine gearboxes). Aerospace and marine industry. Agriculture and heavy equipment.	Lubrication systems for all equipment. Turbine oils, jet engines, turbines, and hydraulic systems. Ship engines, gear systems, and hydraulic equipment. Tractor and farm equipment oils.
Food Industry	Food-grade lubricants. Pharmaceutical.	Heat processing equipment (ovens and grills, fryers, steamers and boiling tanks). Raw material processing equipment, tablet press machines, and packaging and labeling equipment.
Electrical and Electronics	Transformer oils. Dielectric oils.	Transformers and circuit breakers for insulation and cooling. Insulation and cooling in high-voltage equipment.
Household and Consumer Goods	Lubricants for appliances. Penetrating oils.	Fans, sewing machines, and bicycles. Loosening rusted bolts and hinges.
Railways and Transport	Railway engine and bearing oils. Greases for tracks and axles.	Locomotives and railcars to reduce wear. Reduce friction in moving parts.

shows the lubricant applications and end users. The indiscriminate disposal of WLO poses a serious threat to the environment, potentially damaging soil, water, and air [4]. High organic content in soil can lead to oil absorption and subsequent migration, contaminating groundwater [5]. Furthermore, elevated concentrations of toxic metals can inhibit plant growth and metabolism, as well as adversely affect reproductive and immune systems [6]. Motor oil from automobiles can contaminate water bodies through illegal dumping or runoff from urban areas [7].

Alternative fuels have been investigated for their environmental benefits [8], with environmental regulations encouraging research into alternative energy sources [9,10,11], with waste lubricant oil being a potential option. The Waste Framework Directive (WFD) mandates measures to address the environmental and health impacts of waste generation and management, promoting resource efficiency and the transition to a circular economy [12]. The WFD requires EU countries to implement measures for the treatment, separate collection, and proper handling of waste oils.

The global lubricant market was valued at $157.6 billion in 2021 and is projected to reach $182.6 billion by 2025 [13]. Figure 1 shows the global demand in 2024 [14]. As oil quality deteriorates over time, it becomes unsuitable for further use and must be replaced. Approximately 50% of fresh lubricating oil becomes WLO, with the remainder lost through combustion, evaporation, leakage, and residue in containers. In 2017, approximately 4.3 million tonnes of lubricating and industrial oils were placed on the EU market, with about 1.64 million tonnes of waste oils collected, representing 38% of the total [15].

Recycling WLO offers several benefits, including reducing the need for harsh chemicals to clean up oil spills and providing a source of alternative energy. It also helps conserve crude oil resources and alleviate environmental stress. However, improper disposal or recycling of waste oils from vehicles, engines, hydraulic systems, and gearboxes can contaminate the environment.

Among the re-refining techniques for recovering lubricating oil from WLO, the acid/clay process is the oldest and most common, capable of producing high-quality lubrication stocks but generating significant volumes of petroleum-contaminated acid clay sludge [16].

Recent studies [17,18] describe advanced solvent-based processes where optimized solvent mixtures (such as combinations of 1-butanol, isopropanol, and methyl ethyl ketone) are used to extract high-quality base oil from waste lubricants. When this step is followed by vacuum distillation, the process can separate light fractions (often used as fuel oil) from heavier contaminants. This dual-step approach not only improves the yield and quality of re-refined oil, but also minimizes energy input compared to older thermal methods.

Table 2. Application and re-refining techniques for recovering lubricating oil from WLO.

Process	Author	Application
Acid/clay	Izza, H. et al., 2018 [16]	Good quality lubrication stocks.
Solvent extraction process	Al-ZahraniIm and Putra MD., 2013 [19]	Re-refining WLO.
Super-critical fluid extraction	Liu Y et al., 2005 [20]	Re-refining WLO.
Hydrotreating	Emam EA et al., 2013 [21]	Re-refining WLO.
Thin wiped film evaporation	Saleem HJ et al., 2020 [22]	Re-refining WLO.
Membrane technology	Widodo S et al., 2020 [23]	Re-refining WLO.
Recycled waste oils	Naima K., 2013 [24]	Shipping industry.
Characterization of Used Lubricant Oil	Carlos Sánchez-Alvarracín et al., 2021 [25]	Analysis of options for its regeneration.
Solvent extraction	Nancy Kamil Zgheib and Hosni Takache, 2021 [17]	Simulation and feasibility study.
Recent Advances in Reclamation of Used Lubricant Oil	Krunal Rajeshkumar et al., 2022 [26]	Industry (included marine and aerospace).
Review on Recycle of Waste Lubricant	Harshit Mandloi et al., 2023 [18]	Industry (included marine and aerospace).
Analysis of Recycled Used Engine Oil	Negasa Abdena Alemu et al., 2025 [27]	Industry (included marine and aerospace).

and

Table 3. Application and re-refining techniques for recovering fuel oil from WLO.

Process	Author	Application
Reprocessed into fuel	Pawlak Z et al., 2010 [28]	Burning in engines
Reprocessed into fuel	Becthold RL., 1976 [29]	Combustion in diesel engines
Reprocessed into fuel	Tajima et al., 2001 [30]	Combustion in diesel engines (as Heavy Fuel, HFO)
Reprocessed by pyrolysis and catalytic cracking as diesel-like fuel	Arpa et al., 2010 [31]	Effects on engine performance and exhaust emissions
Reprocessed as diesel-like fuel	Wang and Ni, 2017 [32]	Analysis of combustion and emission performance
Pretreated used automobile lubricating oil and a distillate fuel oil	Garbina et al., 2016 [33]	Marine diesel engine performance
Recovery waste lube oils	Singhabhandhu A., 2010 [34]	Energy conversion plants
Recovered waste lubricating oils	Breyer S, et al., 2017 [35]	Alternative fuel in diesel engines
Pyrolysis Process	Bisrul Hapis Tambunan et al., 2023 [36]	Alternative fuel
Physical characterization	Robert Silaban et al., 2024 [37]	Experimental study
Physical characterization	Zami Furqon et al., 2025 [38]	Alternative fuel
Investigations on a Diesel Engine Run	Pranav Kumar et al., 2020 [39]	Use as biodiesel blend

summarize the procedures and applications for recycling waste oil.

Re-refining technologies aim to convert waste lubricating oil (WLO) into a reusable product—typically a base oil suitable for new lubricant formulations or, in some cases, fuel oil. The main process routes include the following:

(a)

Acid/Clay Treatment. In acid/clay treatment, WLO is treated with an acid (e.g., sulfuric, acetic, phosphoric, or formic acid) to precipitate contaminants and degrade undesirable additives [16]. This method is attractive due to its simplicity and low capital cost, making it suitable for facilities with lower throughput.

(b)

Solvent Extraction. Solvent extraction separates the base oil from contaminants by exploiting differences in solubility [24]. Its near-ambient operating conditions reduce energy demands compared with thermal processes. On the other hand, it requires skilled operators and robust solvent recovery systems to minimize solvent losses and environmental emissions.

(c)

Vacuum Distillation (often as a downstream process). Following a primary treatment (such as solvent extraction), vacuum distillation is used to separate oil fractions based on their boiling points.

(d)

Hybrid and Emerging Methods (such as membrane filtration and pyrolysis). Recent advances have explored combining solvent extraction with vacuum distillation (or with other techniques) to optimize both recovery and quality [33].

From the above, newer processes (such as integrated solvent extraction followed by vacuum distillation, pyrolysis with catalytic cracking, and membrane-based separation) have enhanced the efficiency and yield of oil recycling. In many cases, these advanced technologies enable the re-refining process to use approximately one-third the energy required for refining virgin crude oil [26].

The recovery and utilization of used lubricating oil represent a significant step towards sustainable resource management and a circular economy. This paper explores two key aspects of WLO in resource governance: its environmental impact and its potential as a fuel source. By conceptualizing WLO as a governance mechanism within resource management, we highlight its importance in environmental and energy contexts. We also analyze the political motivations behind WLO systems, revealing their dual nature in facilitating both sustainability information flow and alternative fuel utilization.

2. Methodology

The methodology applied in this study is described in Figure 2. A selection of sources and a literature search were carried out using recognized academic databases (Scopus, Web of Science, PubMed, Google Scholar, etc.). Inclusion and exclusion criteria were applied, along with search strategies using keywords and Boolean operators. The articles were classified according to their approaches, methodologies, and findings. Throughout this section, the current global status of waste oil recycling, global political feasibility in the marketplace, and research design will be reviewed, highlighting recent developments, methodologies used and current challenges. The objective is to provide a critical synthesis that will identify emerging trends and possible future lines of research.

2.1. Current Global Status of Waste Oil Recycling

Pioneering research into waste oil recycling began in Europe and the United States during the 1960s, leading to the accumulation of valuable experience. Western countries have since maintained a dominant position in the waste oil recycling industry and the broader petroleum sector. This leading role can be attributed to supportive policies and government incentives.

In contrast, China’s waste oil recovery rate remains relatively low, influenced by factors such as national and local regulations, inefficiencies in upstream collection, downstream technological limitations, and other constraints [40].

Driven by the increasing urgency for energy conservation and environmental protection, WLO is re-refined into lubricating oil. In 2019, Europe consumed 3.8 million tons of lubricating oil, with approximately 13% derived from re-refined WLO. A significant portion (61%) of collected WLO is regenerated into base oils, with 24% used for fuel production, 11% for direct energy recovery in various industries, and the remainder incinerated as hazardous waste [41]. In 2019, 27 waste oil regeneration plants in the EU28 treated 1.5 million tons of waste oils.

In the United States, the entities responsible for collecting, treating, and recycling waste oils are often integrated. The DIY sector, a significant source of waste oil pollution, can mitigate its environmental impact by utilizing these oils as fuel [42].

Australia’s Product Stewardship for Oil (PSO) scheme has successfully collected and recycled over 4300 million liters of lubricating oils and greases, exceeding the volume of oil released in the 2010 Deepwater Horizon disaster [43]. The PSO Scheme has played a crucial role in environmental protection and public health, transforming used oil into valuable products [44].

Despite these successes, significant quantities of used oil remain unaccounted for. In 2018, an estimated 1624 million liters of used oil were unaccounted for, representing approximately 31% of the total generated. Additionally, a substantial portion of collected used oil, estimated between 18% and 28%, is legally burned annually [42].

Research into waste oil collection, characterization, and reuse techniques in Latin American countries is limited [39]. Mexico and Brazil are leading the region in reusing used lubricant oils. Mexico’s Bravo Energy recovers around 100 million liters of used oil annually, while Brazil consumes approximately 1 billion liters of lubricating oil per year, with a significant portion derived from automobiles. Ecuador possesses a substantial amount of waste transformer oil suitable for reuse, particularly in powering diesel engines. In recent years, the country has also explored the use of various industrial oils, including transformer oils, hydraulic oil, and brake fluids [25].

2.2. Global Political Feasibility in the Marketplace

A single liter of waste oil can contaminate up to one million liters of water in rivers, lakes, and streams, posing a significant threat to aquatic ecosystems. Furthermore, if left untreated on the ground, waste oil can severely contaminate soil. Taking into account these circumstances, measures are being taken at the global level, as we will see below. The EU has established broad principles through the Waste Framework Directive (2008/98/EU) [42] that require member states to treat waste oils in accordance with a strict waste hierarchy. This framework emphasizes the need to collect waste oils separately, prevent their mixing with other wastes, and prioritize regeneration over energy recovery or disposal. In practice, EU countries are required to ensure that waste lubricating oils are managed in ways that both protect human health and promote resource conservation. The EU’s average waste oil collection rate is approximately 82% [44]. However, a 2020 report by member states [45] highlights the lack of robust statistical information on waste oil collection and management, hindering the establishment of mandatory EU collection targets.

The Waste Framework Directive [46] requires the European Commission to consider measures for waste oil treatment, particularly promoting waste oil regeneration. The reason for this is that recycling used oil is often more energy-efficient than producing new lubricating oil from virgin crude oil, and it supports numerous jobs [47]. Federal strategies are being implemented to improve the collection of used lubricating oil, with 18 specific opportunities identified. At the same time, virgin lubricant producers are adapting to policies that facilitate a level playing field for customers purchasing base stocks.

In this sense, Italy’s National Consortium of Waste Oils (CONOU) is a leading case study in which lubricant producers are required to contribute to a fund used to finance the collection and re-refining of used oil. Similar incentive-based models exist in Spain, Portugal, and France, where subsidies or contribution fees help cover the costs of collection and re-refining.

In contrast, countries such as Germany and the United Kingdom rely more on market forces and standards rather than direct subsidies. Here, the regulatory framework encourages investment in high-quality re-refining facilities through standards for emission reductions and energy savings.

In the U.S., the Environmental Protection Agency (EPA) has established specific requirements under 40 CFR part 279 that govern the management of used oil. These regulations set standards for storage, transportation, and processing, ensuring that used oil is not improperly disposed of and is directed toward re-refining or beneficial reuse (for example, as fuel or base oil) [42]. At the federal level, the U.S. Department of Energy (DOE) has developed strategies to increase the beneficial reuse of used lubricating oil that include policy recommendations, data collection initiatives, and incentives to promote a “closed-loop” recycling system.

India has implemented legislative strategies [48] to formalize the collection and recycling of waste lubricating oil. With hundreds of registered recycling facilities spread across the country, these policies aim to bring the recycling sector into the formal economy, reduce environmental contamination, and harness economic benefits from converting waste into valuable products.

In China [43], policy measures often include tax waivers and other financial incentives to promote the recycling of used oil. Such incentives help lower the cost of processing and encourage investments in recycling technology. Conversely, Brazil has taken a more prohibitive stance; for example, certain regulations ban the burning of used oil entirely, pushing stakeholders toward re-refining or other environmentally sound recycling methods. Thus, while the petroleum industry has made efforts to promote policy development and implementation, the vast geographic area and varying levels of investment and understanding in waste oil recycling and regeneration have hindered progress. These disparities have presented significant challenges for the waste oil recycling industry.

Some Middle Eastern countries have also begun to develop policies targeting the recycling of lubricating oil [49]. In these regions, the focus is often on reducing environmental pollution and managing waste in an increasingly urbanized context. Incentives in these markets may include subsidies for re-refining facilities or mandates that require industrial users to source a percentage of their fuel from recycled oil.

Finally, WLO converted to fuel in countries with less stringent regulations may be exported to countries or regions with stricter standards. Therefore, a comprehensive assessment of the economic benefits of re-refining and combustion policies is necessary, considering the potential environmental liabilities associated with used oils contaminated with polychlorinated biphenyls. Additionally, individual waste management strategies can influence national policies and guide future research and investments.

2.3. Research Design

The increasing consumption of lubricating oils leads to the accumulation of WLO, which poses environmental hazards. Recycling WLO into fuel offers a sustainable alternative to disposal.

To assess the energy and environmental implications of WLO management, a comprehensive research project that focuses on the environmental and energy impacts of re-refining used oil is necessary. This research should consider two primary pathways: collection and disposal versus fuel use. Collecting used oil is preferable to disposal as it recovers a valuable resource and prevents potential drinking water and soil contamination [48]. However, it is essential to quantify the proportion of fresh lubricating oil that becomes used lubricating oil (ULO) and the losses incurred through combustion, evaporation, leakage, and container residue.

To draw informed conclusions, a thorough analysis of the characteristics of by-product fuel oil (BFO) and reprocessed used lubricating oil (RULO) is necessary. While studies have shown similarities between the two fuels, RULO exhibits lower reactivity and larger sprayed particle diameters compared to BFO, particularly during cold start-up combustion [50].

In 2006, the European Union consumed approximately 5.8 million tons of lubricating oil, generating around 3 million tons of ULO [51]. Driven by increasing energy conservation and environmental concerns, ULO has been re-refined into lubricating oil. In 2014, Europe consumed 3.8 million tons of lubricating oil, with approximately 13% derived from re-refined ULO [52].

The suitability of ULO as a fuel depends on the specific application. For instance, in the case of modern oil burners, research should consider factors such as filtration to remove large particles and preheating to reduce viscosity. These elements should form the basis for the design of such a system.

A 2007 study by an independent third-party test company [53] revealed low levels of unburned hydrocarbons and carbon monoxide (CO) but higher levels of sulfur dioxide (SO₂). Additional EPA testing can provide a general emissions profile to inform research planning.

When considering the use of ULO in diesel engines, it is crucial to recognize the diverse applications of diesel engines in power generation, agriculture, automobiles and transportation. These engines are favored for their low specific fuel consumption, fuel economy, and relatively low emissions, excluding particulate matter (PM) and nitrogen oxide (NO_x) [41,42,43,44,45,46,47,48,49,50,51,52,53,54].

The increasing cost of petroleum, dwindling fossil fuel reserves, and stringent pollution regulations have spurred interest in alternative energy sources, including biofuels, waste oils, and biomass for diesel engines [55].

An experimental study [56] investigated the use of waste transformer oil blended with petroleum products in diesel engines. The results revealed the following:

• Increased load leads to decreased brake-specific fuel consumption for all blends (10% to 40%).
• Blends of 10% and 20% exhibit lower fuel consumption than pure diesel at high loads.
• Blends of 30% and 40% have higher fuel consumption than pure diesel.
• The 10% blend displays higher brake thermal efficiency than pure diesel at high loads, while the 20% blend exhibits similar efficiency.
• Higher blends (30% and 40%) demonstrate lower thermal efficiency due to the lower calorific value of transformer oil.

Exhaust gas temperatures were higher for the blends compared to pure diesel. The exhaust gas temperature of diesel fuel is 182C at high load, while the exhaust gas temperature of the 10%, 20%, and 30% blends is 187C, 188C, and 193C, respectively.

Another study [57] suggested that medium-speed engines are more suitable for burning alternative fuel derived from recycled lubricating oil (AFO) than heavy fuel oils. While AFO exhibited poorer combustion performance than distillate fuel, it outperformed residual heavy fuel oils. However, AFO emitted more smoke and particles than distillate fuel oil (DFO) but less NO_x. Fuel consumption and energy efficiency were not significantly improved with AFO, although advanced injection timing could enhance fuel economy.

A marine multicylinder turbocharged diesel engine was tested with waste lube oil-based alternative oil (AFO) [58]. The engine performed well with AFO, meeting marine emission regulations and combustion standards. Combustion and injection analysis indicated that AFO’s blend of light and heavy components facilitated rapid ignition but delayed combustion completion. AFO exhibited lower fuel mass consumption due to its higher lower heating value, but energy efficiency remained comparable to DFO. AFO emitted significantly less NO_x and slightly higher CO emissions than DFO, while smoke opacity was higher but not concerning.

Table 4. Specification details of test engine.

Engine type	TV1, 4S, Diesel engine
Power (kW)	3.5 kW
Bore × Stroke (mm × mm)	87.5 × 110
Compression ratio	17.5:1 (Range 12:1–22:1)
Injection pressure	200 bar
Injection timing	23 bTDC

shows the specifications of the tested engine.

Table 5. Brake specific fuel consumption (BSFC), CO, NO_x and smoke opacity emissions.

Type of Fuel	Brake Termal Efficiency (BTE, %). Full Load Condition	BSFC kg/kWh		CO Emissions g/kWh		NOx Emissions ppm		Smoke Opacity Full Load
		Low Load	High Load	Low Load	High Load	Low Load	High Load	%
DIESEL	30.60	0.391	0.263	4.96	3.61	91	460	65.0
JBDULO10	29.13	0.413	0.266	5.12	3.85	120	583	55.2
JBDULO20	29.40	0.423	0.278	5.49	3.92	117	570	57.4
JBDULO30	28.42	0.441	0.291	5.84	4.16	115	561	60.4
JBDULO40	28.10	0.541	0.391	6.84	5.16			64.9

shows the results of a study [59] that compared the brake thermal efficiency (BTE), brake specific fuel consumption (BSFC), CO, NO_x, and smoke opacity emissions of diesel, distilled used lubricating oil (DULO), and Jatropha biodiesel (JB) mixtures (JBDULO10, JBDULO20, JBDULO30, and JBDULO40).

Table 5 shows that CO emissions increased simultaneously with low load conditions by 3.22%, 10.68%, 17.74%, and 21.23%, and to final load conditions by 6.6%, 8.5%, 15.23%, and 18.2% compared with diesel fuel. Biodiesel has a lower heat of evaporation, which decreases the heat transfer, causing a low cooling effect on the combustion chamber [60]. The overall efficiency is increased, and CO emission is decreased. The reason for this is that the rapid addition of DULO in the Jatropha biodiesel blends reduces the overall cetane number when compared with diesel fuel [33,61]. The NO_x emissions of JBDULO20 are reduced by 17.31% at full load conditions compared with JB. Increasing the DULO concentration with JB decreases nitrogen oxide emissions compared with diesel. This is due to the higher cooling effect liberated by the latent heat of vaporization of DULO, which is highly useful to reduce the emissions of oxides of nitrogen [62,63]. Further increasing the DULO concentration in JB causes high cylinder pressure, and the cylinder temperature increases NO_x formation.

The results of these studies demonstrate the potential benefits of utilizing recycled oil as a fuel. However, in light of market pressures for the use of WLO as fuel, EU legislation suggests prioritizing regeneration over direct burning or fuel production. This approach aligns with the goal of reducing environmental impacts compared to the production of virgin base oil from crude.

3. Discussion and Conclusions

Government policy plays a pivotal role in both collection and regeneration. In Europe, the Waste Framework Directive and complementary national measures (including EPR schemes (such as Italy’s CONOU model) have been instrumental in increasing both collection rates and the proportion of oil that is re-refined or converted into fuel. In the United States, EPA regulations (40 CFR Part 279) along with initiatives from the Department of Energy (e.g., the 2020 “Used Oil Management and Beneficial Reuse Options” report) have provided frameworks and incentives for more sustainable recycling practices.

In emerging markets like India, recent legislative changes under Extended Producer Responsibility have begun formalizing the recycling sector. Meanwhile, some countries in Asia and the Middle East have introduced tax waivers or subsidies to encourage both collection and processing, thereby improving the economics of converting waste oil into fuel.

Recent technological advances in integrated process designs are enabling more efficient recycling of used lubricating oil. These technologies not only produce high-quality base oil for lubricant manufacture but also generate fuel oil fractions that offer economic and environmental benefits. Current data indicate gradual improvements in collection and regeneration rates (driven by both market factors and supportive policy measures), while ongoing research continues to optimize processes for lower energy consumption and reduced emissions.

Across these diverse policy approaches, several common themes emerge. Regarding environmental protection and resource conservation, by mandating the proper collection, treatment, and re-refining of used oil, policies help to prevent soil and water contamination and reduce the environmental footprint of lubricant production. On the other hand, financial instruments such as subsidies, tax credits, and EPR schemes help to offset the costs associated with re-refining technologies. These incentives not only make recycling more competitive against the production of virgin oil, but also stimulate investment in cleaner, more efficient processing technologies.

Effective policies often rely on robust data and standardized reporting of accurate data on oil losses, collection rates, and processing efficiency, enabling continuous improvement in policy design and implementation. Ultimately, well-designed policies can shift market behavior, encouraging both industry and consumers to view used lubricating oil not as waste but as a valuable resource. This contributes to the broader circular economy, where materials are continually reused, reducing overall reliance on non-renewable resources. However, policies on recycling lubricating oil and its use as fuel vary widely by country, reflecting differences in regulatory frameworks, market conditions, and environmental priorities. The EU has implemented comprehensive directives and EPR schemes; the U.S. relies on a mix of federal regulations and state incentives; and countries in Asia and the Middle East use a combination of financial incentives and prohibitions to steer market behavior. These diverse policy approaches are crucial for ensuring that waste lubricating oil is managed sustainably, thereby protecting the environment, conserving energy, and providing economic benefits through the development of a robust recycling industry. By studying and comparing these policies, stakeholders can identify best practices and design more effective, region-specific strategies to promote the recycling and beneficial reuse of lubricating oil.

Significant changes have been implemented in both the U.S. and EU regarding oil recycling, including differential incentive payments for used oil returned for re-refining compared to other re-processing routes. However, the market price of used oil is influenced by various factors, including its multiple potential end-uses. In this study, the treatment of used oil has been analyzed under two aspects: (i) its reuse as lubricating oil and (ii) its reuse as fuel.

Regarding reusing oil as fuel, as outlined in the European Green Deal Communication [64], the EU aims to achieve a climate-neutral and circular economy.

In the United States, used oil-fired space heaters have been part of used oil management for over four decades. The space heater industry estimates that approximately 100,000 U.S. businesses actively use space heaters (with a maximum capacity of no more than 0.5 million kJ per hour) [64]. The industry, including manufacturers, employs over 1000 people and supports thousands of additional jobs through vendors and channel partners.

The selection of a treatment route should consider factors such as the lubricant market, energy consumption, distance to treatment facilities, operational costs, final product quality, and technological advances.

Typically, most countries impose identical taxes on manufactured oil, regardless of whether it is produced from virgin or recycled oil. Additionally, the refund paid on recycled oil is independent of its ultimate end-use, whether as fuel oil, marine diesel oil, or re-refined oil. However, the inclusion of bio-based lubricants in the used oil collection stream can negatively impact the re-refining process, leading to technical complications. Careful consideration should be given to the costs and benefits of tax incentives that encourage the re-refining of used motor oil.

In conclusion, this article highlights the importance of storing used oil from an environmental point of view in order to identify optimal oil recycling policies as well as incentive payments for used oil returned for re-refining. This manuscript also highlights how several studies conclude that increased load leads to decreased brake-specific fuel consumption for all blends, that blends exhibit lower fuel consumption than pure diesel at high loads, and that a small quantity of blend displays higher brake thermal efficiency than pure diesel at high loads. Higher blends demonstrate lower thermal efficiency due to the lower calorific value of transformer oil.

On the other hand, exhaust gas temperatures are higher for the blends compared to pure diesel. Conclusions from another study show that medium-speed engines are more suitable for burning alternative fuel derived from recycled lubricating oil than heavy fuel oils.

As regards emissions, another study shows that CO emissions increase with low load conditions compared with diesel fuel and that increasing the DULO concentration with JB reduces nitrogen oxide emissions compared with diesel.

The indiscriminate disposal of waste lubricating oils (WLOs) into the environment poses a significant risk to ecosystems. Therefore, it is imperative to implement strategies for proper storage and reuse, such as re-refining into lubricating oil or utilizing it as a fuel source.

This analysis highlights the importance of a holistic circular economy approach to waste management. Both the European Union and the United States have prioritized the design, collection and recycling of WLO. EU countries, in particular, exhibit a strong inclination toward recycling WLO, with competition between regeneration and energy recovery. While market pressures favor the use of WLO as a fuel, EU legislation prioritizes policies that promote regeneration over direct combustion or fuel production. Numerous studies have demonstrated that regeneration reduces the environmental impact compared to the production of virgin base oil from crude. Table 1 summarizes key factors to consider when selecting a treatment route, including lubricant market dynamics, energy consumption, and operational costs. Additionally, research has explored policies that optimize the allocation of used lubricating oil.

When used as a fuel, WLO has been shown to produce lower pollutant emissions than heavy fuel oil (HFO). While comparisons with other fuels like distilled diesel or biofuels yield similar results, the optimal policy often involves independent air quality regulations for residual fuel oil and marine diesel oil combustion.

The disposal of WLO into the environment poses a significant risk to ecosystems. For this reason, a holistic circular economy approach, encompassing lubricant production, consumption, generation, collection, and recycling, should be adopted for waste management systems. EU countries are currently grappling with the competition between regeneration and energy recovery.

In conclusion, policies that promote lubrication oil recycling offer significant benefits for both the environment and the circular economy. Increased recycling activities not only contribute to environmental sustainability, but also stimulate job creation and foster further research into waste oil utilization.

In conclusion, indiscriminate disposal of waste lubricating oil (WLO) poses a significant hazard to the environment and humans. WLO can be harnessed to generate valuable energy fuel and chemicals as an alternative to the depleting reserve of fossil fuel sources. Different methods/techniques exist for recycling or regenerating WLO. Each has its advantages and disadvantages over others for the process parameters such as the reaction time, temperature, pressure, etc., on the product’s yield and composition. A few available techniques that have commercial applicability have been defined in this manuscript. However, it is essential to carry out the economic assessment of a technique to determine its feasibility to scale up. A holistic approach via modifying the existing dataset on the life cycle assessment of WLO processing technologies for known regions/countries could be conducted to estimate the effect of the WLO management/processing model in other regions.

The choice among re-refining technologies for used lubricating oil depends on a complex interplay of technical parameters and economic and environmental considerations. Acid/clay treatment offers simplicity and low cost but with significant sludge generation, whereas solvent extraction provides high recovery yields and product quality at the expense of increased operational complexity and solvent management. Vacuum distillation remains a critical downstream process for achieving the required purity levels, and emerging hybrid systems are promising routes to overcome individual method limitations. Ultimately, process optimization (through detailed evaluation of solvent compositions, oil-to-solvent ratios, operating temperatures, pressures, and residence times) is key to developing cost-effective and environmentally sustainable re-refining processes.

Some state governments have further strengthened these efforts by establishing incentive programs (such as recycling incentive payments to collection centers and matching grants) to encourage efficient collection and proper disposal. These measures are designed not only to protect the environment, but also to stimulate market demand for re-refined oil products, whether used for fuel or for further processing into lubricants.