Dye tracing of the Lusaka karstified aquifer system: implications towards urban groundwater quality protection.

Management of groundwater resources requires a large amount of data, coupled with an understanding of the aquifer system behavior. In developing countries, the scarcity in groundwater data has led to aquifers being managed according to rule-of-thumb standards or even abandoned as unmanageable at times. Groundwater quality protection thus has been through prescribed separation distances often without due regard for internal and boundary characteristics that affect response rates of groundwater movement, attenuation of pollutants, and recharge. In this study, we examine the boundary characteristics of the highly vulnerable karst aquifer system in the rapidly expanding city of Lusaka using a dye tracer technique. We investigate the flow dynamics (magnitude and direction) of groundwater using dye tracer dyes (fluorescein and rhodamine) spiked in pit latrines and observed at discharge springs. The results provide irrefutable evidence that pit latrines are a source and a pathway to contamination of groundwater. Dye tracer movement in groundwater was rapid, estimated at 340 and 430 m/day for fluorescein and rhodamine, respectively, through interconnected conduit density. The vadose zone (epikarst) tends to store diffuse recharge before release to the phreatic zone. These rapid groundwater movements render regulatory separation minimum distances of 30 m between abstraction wells and pit latrines/septic tanks in such environments to be an ineffective means of reducing contamination. The policy focus in the protection of groundwater quality should henceforth be on robust sanitation solutions especially for low-income communities that recognize the socio-economic diversity.

Anthropogenic influences on Zambian water quality: hydropower and land-use change.

The Zambezi River Basin in Southern Africa is undergoing rapid development and population growth. Agricultural intensification, urbanization and future development of hydropower dams will likely lead to a degradation of surface water quality, but there have been few formal assessments of where, how and why these changes impact specific water quality parameters based on in situ data spanning a large region. We sampled a large suite of biogeochemical water quality parameters at 14 locations in four field campaigns in central and southern Zambia in 2018 and 2019 to characterize seasonal changes in water quality in response to large hydropower dams and human landscape transformations. We find that the major rivers (Zambezi and Kafue) are very clean with extremely low concentrations of solutes, but suffer from thermal changes, hypoxia and loss of suspended sediment below dams. Smaller tributaries with a relatively large anthropogenic landcover footprint in their catchments show signs of pollution in the form of higher concentrations of nutrients and dissolved ions. We find significant relationships between crop and urban land cover metrics and selected water quality metrics (i.e. conductivity, phosphorus and nitrogen) across our data set. These results reflect a very high-quality waterscape exhibiting some hotspots of degradation associated with specific human activities. We anticipate that as agricultural intensification, urbanization and future hydropower development continue to accelerate in the basin, the number and extent of these hotspots of water quality degradation will grow in response. There is an opportunity for governments, managers and industry to mitigate water quality degradation via investment in sustainable infrastructure and practice, such as wastewater treatment, environmental dam operations, or riparian protection zones.

Biosorption of Pb (II) and Zn (II) from aqueous solution by Oceanobacillus profundus isolated from an abandoned mine.

The present study investigated biosorption of Pb (II) and Zn (II) using a heavy metal tolerant bacterium Oceanobacillus profundus KBZ 3-2 isolated from a contaminated site. The effects of process parameters such as effect on bacterial growth, pH and initial lead ion concentration were studied. The results showed that the maximum removal percentage for Pb (II) was 97% at an initial concentration of 50 mg/L whereas maximum removal percentage for Zn (II) was at 54% at an initial concentration of 2 mg/L obtained at pH 6 and 30 °C. The isolated bacteria were found to sequester both Pb (II) and Zn (II) in the extracellular polymeric substance (EPS). The EPS facilitates ion exchange and metal chelation-complexation by virtue of the existence of ionizable functional groups such as carboxyl, sulfate, and phosphate present in the protein and polysaccharides. Therefore, the use of indigenous bacteria in the remediation of contaminated water is an eco-friendly way of solving anthropogenic contamination.

Efficacy of biocementation of lead mine waste from the Kabwe Mine site evaluated using Pararhodobacter sp.

Biocementation of hazardous waste is used in reducing the mobility of contaminants, but studies on evaluating its efficacy have not been well documented. Therefore, to evaluate the efficacy of this method, physicochemical factors affecting stabilized hazardous products of in situ microbially induced calcium carbonate precipitation (MICP) were determined. The strength and leach resistance were investigated using the bacterium Pararhodobacter sp. Pb-contaminated kiln slag (KS) and leach plant residue (LPR) collected from Kabwe, Zambia, were investigated. Biocemented KS and KS/LPR had leachate Pb concentrations below the detection limit of < 0.001 mg/L, resisted slaking, and had maximum unconfined compressive strengths of 8 MPa for KS and 4 MPa for KS/LPR. Furthermore, biocemented KS and KS/LPR exhibited lower water absorption coefficient values, which could potentially reduce the water transportation of Pb2+. The results of this study show that MICP can reduce Pb2+ mobility in mine wastes. The improved physicochemical properties of the biocemented materials, therefore, indicates that this technique is an effective tool in stabilizing hazardous mine wastes and, consequently, preventing water and soil contamination.

Solidification of sand by Pb(II)-tolerant bacteria for capping mine waste to control metallic dust: Case of the abandoned Kabwe Mine, Zambia.

Environmental impacts resulting from historic lead and zinc mining in Kabwe, Zambia affect human health due to the dust generated from the mine waste that contains lead, a known hazardous pollutant. We employed microbially induced calcium carbonate precipitation (MICP), an alternative capping method, to prevent dust generation and reduce the mobility of contaminants. Pb-resistant Oceanobacillus profundus KBZ 1-3 and O. profundus KBZ 2-5 isolated from Kabwe were used to biocement the sand that would act as a cover to prevent dust and water infiltration. Sand biocemented by KBZ 1-3 and KBZ 2-5 had maximum unconfined compressive strength values of 3.2 MPa and 5.5 MPa, respectively. Additionally, biocemented sand exhibited reduced water permeability values of 9.6 × 10-8 m/s and 8.9 × 10-8 m/s for O. profundus KBZ 1-3 and KBZ 2-5, respectively, which could potentially limit the entrance of water and oxygen into the dump, hence reducing the leaching of heavy metals. We propose that these isolates represent an option for bioremediating contaminated waste by preventing both metallic dust from becoming airborne and rainwater from infiltrating into the waste. O. profundus KBZ 1-3 and O. profundus KBZ 2-5 isolated form Kabwe represent a novel species that has, for the first time, been applied in a bioremediation study.