Optimization of municipal solid waste management systems towards sustainability

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Wastewater purification using advanced functionalized nanoparticles

Publication . Noorimotlagh, Zahra; Silva, Adriano S.; Díaz de Tuesta, Jose Luis; Mirzaee, Seyyed Abbas; Martínez, Susana Silva; Gomes, Helder

Environmental pollution is rapidly increasing due to population growth, industrialization, urbanization, etc. Anthropogenic activities have increased pollution in all sections of the environment (i.e., soil, air, water, and wastewater). There is great importance attached to resolving this complicated situation, which could effectively reduce the negative impacts of anthropogenic activities on the environment. Nanotechnology, especially functionalized nanoparticles (FNPs), is emerging as an effective solution to environmental pollution at the global scale. The extraordinary chemical and physical properties of materials at the nanometer scale enable new and innovative applications in the environmental sector. Although manufactured metal-based NPs are being produced, concern about their toxicity is increasing. To resolve the toxicity of NPs, functionalization of the materials appears to be a possible solution. The functionalization of NPs, as well as the metal core, can be varied according to the problem being targeted. This chapter discusses detailed information about the fabrication methods of FNPs used for environmental purification, especially wastewater treatment. Their scope in the environment, which includes cleaning up existing pollution, is also discussed. A critical evaluation of the challenges and future needs for a safe environment are also explored.

2023Book part

Restricted access

Execution time as a key parameter in the waste collection problem

Publication . Silva, Adriano S.; Pereira, Ana I.; Lima, José; Silva, Adrián; Gomes, Helder

Proper waste management has been recognized as a tool for the green transition towards a more sustainable economy. For instance, most studies dealing with municipal solid wastes in the literature focus on environmental aspects, proposing new routes for recycling, composting and landfilling. However, there are other aspects to be improved in the systems that deal with municipal solid waste, especially in the transportation sector. Scholars have been exploring alternatives to improve the performance in waste collection tasks since the late 50s, for example, considering the waste collection problem as static. The transition from a static approach to a dynamic is necessary to increase the feasibility of the solution, requiring faster algorithms. Here we explore the improvement in the performance of the guided local search metaheuristic available in OR-Tools upon different execution times lower than 10 seconds to solve the capacitated waste collection problem. We show that increasing the execution time from 1 to 10 seconds can overcome savings of up to 1.5 km in the proposed system. Considering application in dynamic scenarios, the 9 s increase in execution time (from 1 to 10 s) would not hinder the algorithm’s feasibility. Additionally, the assessment of the relation between performance in different execution times with the dataset’s tightness revealed a correlation to be explored in more detail in future studies. The work done here is the first step towards a shift of paradigm from static scenarios in waste collection to dynamic route planning, with the execution time established according to the conclusions achieved in this study.

2023Conference paper

Open access

Execution time experiments to solve capacitated vehicle routing problem

Publication . Silva, Adriano S.; Lima, José; Pereira, Ana I.; Silva, Adrián; Gomes, Helder

Studies dealing with route optimization have received considerable attention in recent years due to the increased demand for transportation services. For decades, scholars have developed robust algorithms designed to solve various Vehicle Routing Problems (VRP). In most cases, the focus is to present an algorithm that can overcome the shortest distances reported in other studies. On the other hand, execution time is also an important parameter that may limit the feasibility of the utilization in real scenarios for some applications. For this reason, in this work, a Guided Local Search (GLS) metaheuristic available in open-source OR-Tools will be tested to solve the Augerat instances of Capacitated Vehicle Routing Problems (CVRP). The stop criterion used here is the execution time, going from 1 s (standard) to 10 s, with a last run of 360 s. The numerical results demonstrate that increasing the execution time returns significant improvement in distance optimization. However, the optimization found considering high execution times can be expensive in terms of time, and not feasible for situations demanding faster algorithms, such as in Dynamic Vehicle Routing Problems (DVRP). Nonetheless, the GLS has proven to be a versatile algorithm for use where distance optimization is the main priority (high execution times) and in cases where faster algorithms are required (low execution times).

2023Conference paper

Restricted access

Plastic waste-derived carbon nanotubes: Influence of growth catalyst and catalytic activity in CWPO

Publication . Roman, Fernanda; Silva, Adriano S.; Tuesta, Jose L. Diaz de; Baldo, Arthur P.; Lopes, Jessica P.M.; Gonçalves, Giane; Pereira, Ana I.; Praça, Paulo; Silva, Adrián; Faria, Joaquim L.; Bañobre-López, Manuel; Gomes, Helder

Low-density polyethylene (LDPE) was used in this work to grow carbon nanotubes (CNTs) by chemical vapor deposition (CVD) over catalysts based on Ni, Fe and Al, synthesized either by co-precipitation (C) or wet impregnation (I) methods, with CNT yields in the range of 16–33 %. The morphology of the CNTs was directly influenced by the route used for the CVD catalyst synthesis, with co-precipitation-derived CVD catalysts resulting in CNT samples with curly walls. CNTs were purified with H2SO4 (10–50 wt.%) to remove attached metal particles. All synthesized materials (CVD-catalysts, as-synthesized CNTs, and purified CNTs) were tested as catalysts in the catalytic wet peroxide oxidation (CWPO) of paracetamol (PCM), chosen as a model pharmaceutical compound. Removals of 100 % of PCM in 8 h and 71 % of total organic carbon (TOC) in 24 h were achieved, with an H2O2 consumption efficiency of 76 % in 24 h for purified CNT (CNT@NiFeAl-C-P). The same CVD-catalyst (NiFeAl-C) was used to grow CNTs using real LDPE waste, and it was tested under the same reaction conditions, resulting in a PCM and TOC abatement of 90 % and 65 %, respectively. The synthesis of CNTs using LDP waste was a good alternative, given the environmental benefits associated with its reintroduction into the economic cycle as a material with higher value than initially (upcycling).

2025Journal article

Open access

Carbon-Coated Magnetic Catalysts for Enhanced Degradation of Nitrophenols: Stability and Efficiency in Catalytic Wet Peroxide Oxidation

Publication . Baldo, Arthur P.; Bezerra, Ana J.B.; Silva, Adriano S.; Silva, Ana P. F.; Roman, Fernanda; Çaha, Ihsan; Bañobre-López, Manuel; Deepak, Francis Leonard; Gomes, Helder

Nitrophenols are persistent organic pollutants that pose serious environmental and health risks due to their toxic and lipophilic nature. Their persistence arises from strong aromatic stability and resistance to biodegradation, while their lipophilicity facilitates bioaccumulation, exacerbating ecological and human health concerns. To address this challenge, this study focuses on the synthesis and characterization of two different types of hybrid multi-core magnetic catalysts: (i) cobalt ferrite (Co-Fe2O4), which exhibits ferrimagnetic properties, and (ii) magnetite (Fe3O4), which demonstrates close superparamagnetic behavior and is coated with a novel and less hazardous phloroglucinol–glyoxal-derived resin. This approach aims to enhance catalytic efficiency while reducing the environmental impact, offering a sustainable solution for the degradation of nitrophenols in aqueous matrices. Transmission electron microscopy (TEM) images revealed the formation of a multi-core shell structure, with carbon layer sizes of 6.6 ± 0.7 nm for cobalt ferrite and 4.2 ± 0.2 nm for magnetite. The catalysts were designed to enhance the stability and performance in catalytic wet peroxide oxidation (CWPO) processes using sol–gel and solution combustion synthesis methods, respectively. In experiments of single-component degradation, the carbon-coated cobalt ferrite (CoFe@C) catalyst achieved 90% removal of 2-nitrophenol (2-NP) and 96% of 4-nitrophenol (4-NP), while carbon-coated magnetite (Fe3O4@C) demonstrated similar efficiency, with 86% removal of 2-NP and 94% of 4-NP. In the multi-component system, CoFe@C exhibited the highest catalytic activity, reaching 96% removal of 2-NP, 99% of 4-NP, and 91% decomposition of H2O2. No leaching of iron was detected in the coated catalysts, whereas the uncoated materials exhibited similar and significant leaching (CoFe: 5.66 mg/L, Fe3O4: 12 mg/L) in the single- and multi-component system. This study underscores the potential of hybrid magnetic catalysts for sustainable environmental remediation, demonstrating a dual-function mechanism that enhances catalytic activity and structural stability.

2025Journal article

Open access