The geopolymer concept has gained wide international attention during the last two decades and is now seen as a potential alternative to ordinary Portland cement; however, before full implementation in the national and international standards, the geopolymer concept requires clarity on the commonly used definitions and mix design methodologies. The lack of a common definition and methodology has led to inconsistency and confusion across disciplines. This review aims to clarify the most existing geopolymer definitions and the diverse procedures on geopolymer methodologies to attain a good understanding of both the unary and binary geopolymer systems. This review puts into perspective the most crucial facets to facilitate the sustainable development and adoption of geopolymer design standards. A systematic review protocol was developed based on the Preferred Reporting of Items for Systematic Reviews and Meta-Analyses (PRISMA) checklist and applied to the Scopus database to retrieve articles. Geopolymer is a product of a polycondensation reaction that yields a three-dimensional tecto-aluminosilicate matrix. Compared to unary geopolymer systems, binary geopolymer systems contain complex hydrated gel structures and polymerized networks that influence workability, strength, and durability. The optimum utilization of high calcium industrial by-products such as ground granulated blast furnace slag, Class-C fly ash, and phosphogypsum in unary or binary geopolymer systems give C-S-H or C-A-S-H gels with dense polymerized networks that enhance strength gains and setting times. As there is no geopolymer mix design standard, most geopolymer mix designs apply the trial-and-error approach, and a few apply the Taguchi approach, particle packing fraction method, and response surface methodology. The adopted mix designs require the optimization of certain mixture variables whilst keeping constant other nominal material factors. The production of NaOH gives less CO₂ emission compared to Na₂SiO_3, which requires higher calcination temperatures for Na₂CO₃ and SiO_2. However, their usage is considered unsustainable due to their caustic nature, high energy demand, and cost. Besides the blending of fly ash with other industrial by-products, phosphogypsum also has the potential for use as an ingredient in blended geopolymer systems. The parameters identified in this review can help foster the robust adoption of geopolymer as a potential “go-to” alternative to ordinary Portland cement for construction. Furthermore, the proposed future research areas will help address the various innovation gaps observed in current literature with a view of the environment and society.

Hazardous waste materials and their management are of prime importance to society. This article gives an overview of the current practices that relate to hazardous waste management. It looks at issues concerning the transboundary or international movement of harmful materials from industrialized nations to the developing and emerging world. This study has shown that Africa, most notably Nigeria, has become a dumping ground for hazardous waste materials as a result of the high importation of scrap computers and electronic devices into the country. The public health hazards, such as birth deficiencies, cancers, and even infectious diseases such as human immunodeficiency virus (HIV) and Hepatitis B and C, respectively, have been traced to the improper management of these waste materials. The review highlights a few models on hazardous waste management as developed by previous literature, which gives a hierarchy, ranging from source reduction, recycling, and landfill options. Studies reveal that hazardous waste management in Africa must revolve around wealth creation, economic, and environmental sustainability. The study provided evidence that the recycling option has high potentials in the areas of energy recovery. The data collected show South Africa to be the most advanced in the African continent in the field of hazardous waste management. For a sustainable environment, keen attention must be paid to hazardous waste management globally.

This paper presents a brief description of some existing models of facility location problems (FLPs) in solid waste management. The study provides salient information on commonly used distance functions in location models along with their corresponding mathematical formulation. Some of the optimization techniques that have been applied to location problems are also presented along with an appropriate pseudocode algorithm for their implementation. Concerning the models and solution techniques, the survey concludes by summarizing some recent studies on the applications of FLPs to waste collection and disposal. It is expected that this paper will contribute in no small measure to an integrated solid waste management system with specific emphasis on issues associated with waste collection, thereby boosting the drive for effective and efficient waste collection systems. The content will also provide early career researchers with some necessary starting information required to formulate and solve problems relating to FLP.

The effects of poor solid waste management practices in many developing countries have been identified in the literature. This study focuses on understanding the public perception and attitudes of people towards local waste management practices. Five Local Government Areas in Ogun State, Nigeria, were selected based on population, landmass, spatial location, and distribution. The study used a survey that looked into the socio-demographics, household characteristics, and standard solid waste disposal practices at the household and municipal levels. Factors such as frequency of waste collection, presence of environmental task force/protection agency, and level of effectiveness of such task force/agency were all investigated. The study verified the impact of people’s attitudes towards waste management, as well as the effects of monitoring and control on the management of waste. The results showed that significant factors such as age, income, and education levels affect the perceptions, practices, and attitudes of the people towards solid waste management. An average of 36.6% of the people in the selected local governments dispose of their solid wastes at open dumps, with the majority of the residents (54.4%) still with the opinion that sanitation services are too costly and should be the prerogative of the local and state governments to carry out. These outcomes resonate that more efforts by the government and relevant stakeholders should be put into proper enforcement of environmental laws, as well as creating awareness on proper solid waste management practices in schools and public places.

This paper reviews the partnership between the public and the private sectors in providing efficient solid waste management (SWM) services. While the responsibility of providing SWM services lies with the public sector, the sector has not been able to meet the demand for efficient service delivery, especially in developing countries. In a bid to increase efficiency and lower costs incurred in rendering these services, the involvement of the private sector has been sought. With a focus on major Nigerian cities, partnerships between the local government and private operators in SWM have been analysed based on the level to which the partnership has improved the SWM services. This paper provides an understanding that the success of any public-private partnership relies on the extent to which all stakeholders perform their duties. If the public sector is slack in monitoring and supervising the activities of the private operators, the latter may focus on profit generation while neglecting efficient service delivery. Also, legislation is an important part of SWM. Without the right legislation and enforcement, waste generators will not be mandated to dispose their waste properly. The public sector as a facilitator is responsible for creating an environment for private operators to function, particularly through legislation, enforcement and public sensitization.

Agricultural products such as cassava produce huge amounts of waste when processed into consumable goods. The waste generated is generally considered to contribute largely to environmental pollution. This study therefore investigates the waste management practice that is adopted by cassava processors in Ogun State, Nigeria. Five local government areas (LGAs) dominant in processing cassava were selected for the study on the basis of spatial location distribution, landmass, and population. The survey involved the use of structured questionnaires administered to cassava processors of the selected LGAs. The Statistical Package for Social Sciences (SPSS) software application and descriptive statistics were used for data analysis. Results of the analysis show that the majority (70%) of the cassava processors are females. Cassava peel constitutes 10% of the waste produced, of which 91% is heaped at refuse dumps in most communities. Results also reveal that 86.3% of cassava residues are used for animal feeds. Other findings show that the peels, when dried, are used as biofuel for cooking and there is a significant potential for biogas production. From the data captured from respondents during the study, most processors are willing to pay for an improved waste management system. The study therefore recommends the proper waste management of cassava waste to minimize environmental pollution.