Rapid urban growth has resulted in an increase in the amount and heterogeneity of waste produced [1]. Consequentially, the complexity of waste produced poses waste management challenges, resulting in up to 95% of the waste produced worldwide ending up in landfills [2]. The preference of landfilling in many countries over other waste disposal methods is often because of economic reasons [3]. One important environmental impact of landfills is the generation of leachate, a liquid concentrated with contaminants produced when waste dumped undergoes a series of biological and physicochemical transformations [4]. The leachate accumulates at the bottom of the landfill and percolates through the soil, where it increases the risk of ground and surface water pollution as well as soil pollution. Moreover, even after closure, landfills continue to produce contaminated leachate for 30–50 years [5].

Most cities in developing countries are battling waste management challenges. In Sub-Saharan Africa, waste generated annually is estimated to be approximately 62 million metric tons [6]. Of the approximately 2 million metric tons of waste produced annually in Zimbabwe, much of it is destined for landfills. Unfortunately, most of the landfill sites are non-engineered, resulting in serious threats to human health and the environment. Due to poor waste management, most urban areas of most countries have been affected by public health hazards such as the 2008–2009 cholera outbreak, which was a direct consequence of a breakdown in municipal services, including irregular refuse collection, among other factors [7].

If not properly treated and safely disposed of, landfill leachate could be an impending source of surface and groundwater contamination, causing adverse impacts to receiving waters. Several studies have found evidence of groundwater pollution in the Matsheumhlope aquifer, one of Bulawayo’s biggest groundwater sources, caused by leachate from the Richmond landfill site [8]. Another study done by Teta and Hikwa in 2017 ascertained the presence of and high accumulation of metals in weeds growing at the landfill and groundwater from nearby boreholes, which contained high amounts of lead and cadmium above the WHO standards for drinking water [9]. Considering the ongoing water challenges across the country, leachate management is crucial in preventing contamination of the dwindling resource.

Preventive solid waste management practices such as separation of toxic wastes at their source, recycling of dangerous wastes, and waste minimization are much needed in managing landfill leachate quality. Over the last decades, new and advanced sustainable technologies for landfill leachate have received growing interest as they offer better removal of leachate pollutants, thus protecting the environment. By utilizing these new technologies, difficult parameters are much easier to treat nowadays.  Despite the growing population, the Richmond landfill site remains the destination for most of the city’s solid waste. The aging landfill continues to release leachate into unlined ponds, which is a major environmental concern.

Landfills remain one of the cheapest methods for managing municipal solid waste in most parts of the world. Unfortunately, non-engineered landfill sites pose serious threats to groundwater from either biological, chemical, or physiochemical processes or are associated with volatile gases escaping into the environment. This also makes it quite difficult to harness the waste resources into valuable products as part of the circular economy. Additionally, poor waste management systems present a potential threat to groundwater resources in the form of pollution, which has already been observed in Bulawayo.

Landfills such as Richmond influence its surrounding environment, with groundwater pollution being one of the main concerns. All the city's industrial and domestic solid waste is disposed of at an unlined landfill in Richmond. The landfill overlies a shallow, unconfined aquifer, risking contamination of subsurface water in nearby residential areas. Bulawayo is heavily dependent on borehole water to augment its erratic piped water supplies; therefore, contamination of sub-surface water could pose a serious public health concern. Studies carried out by Teta [9] in monitoring wells around the landfill have linked the presence of heavy metals and organic compounds in groundwater to the leachate from the land fill. Currently, leachate produced from the landfill site is directed to leachate ponds, where it is left to evaporate into the atmosphere, thus increasing the likelihood of groundwater pollution. As part of efforts to address the status quo, researching the remediation of landfill leachate is a significant area of interest for the country, as it will create a sustainable way of handling its generation and a closed-loop approach through investigating possibilities of treating leachate using available materials.

Study Site Description

The study was carried out at the Richmond landfill site in Bulawayo, Zimbabwe. All the domestic and industrial waste generated by the city is disposed of at the Richmond landfill site. The landfill was commissioned in 1994 and is still in use to date. It is located on a former gravel excavation site that is characterized by highly porous gravel soils. The landfill is lined with compacted layers of clay and clay ash. The leachate produced by the landfill drains into leachate ponds through underground drains located around the landfill, where it is left to evaporate into the atmosphere without further treatment for safe disposal. The leachate ponds are not membrane-lined except for the base layer of compacted clay, thus increasing the risk of groundwater contamination. 

Sampling and Sample Preparation

The banana peels, maize cobs, and eggshells sourced from local markets were dried, pulverized, sieved to produce 125 and 425 µm particle sizes, carbonized at 4500 C, and activated with 80% phosphoric acid to produce activated carbon. Jar tests were carried out using the different activated carbon materials and the characterized leachate. The results were then entered and analysed.

Physic-Chemical Parameters

Samples collected were analysed for the following physic-chemical parameters: pH, turbidity, conductivity, and total suspended solids (TSS). Samples were also subjected to the AAS to test for Iron (Fe), Copper (Cu), and Nickel (Ni). 

Instrumentation and Equipment

The research was conducted using resources and equipment from Bulawayo City Council Water Pollution Control Laboratory, Criterion Waterworks, and Zimbabwe School of Mines.

                  Table 1: Equipment Used During Experimental Procedures.

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