Department of Civil and Environmental Engineering

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Browsing Department of Civil and Environmental Engineering by Author "Anne, Nakagiri"

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    Abating eutrophication on urban lakes: a case study of Kabaka's Lake, Uganda
    (IWA Publishing Water Practice & Technology, 2023-07) Anne, Nakagiri; Abel, Mutyaba; Charles, Onyutha; Kenan, Okurut
    Eutrophication of water bodies is a challenge in many urban areas. This study measured and modelled quantitatively the pollutant nutrient load of an urban lake (80,596 m2), and assessed both external (constructed wetland) and internal (dredging) eutrophication extenuation measures. For the past 25 years, there has been redistribution (p < 0.005) of the lake's catchment land use, with built-up area increasing by 78.5%, and a reduction in vegetated (37.2%) and water surface (1.8%) areas. A 92.2% reduction in the lakes receiving wetland footprint (p = 0.000003) was noted, with increased nutrient load. The lake's light attenuation was found to be dominated by algae, limited by nitrogen and classified under the oligotrophic class (Trophic State Index < 40), with a threat of eutrophication in an estimated 25 years. Scenario analyses show that the construction of a wetland in the remaining 0.54 hectares of natural wetland will reduce total phosphorus by 35% and total nitrate by 45% (p = 0.05), whereas dredging the lake could reduce them by 80% each (p = 0.0005). Watershed management is the only sustainable solution to control nutrient flow into the lake and enable self-cleansing, factoring in the design of the receiving wetland and groundwater sources.
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    Application of black soldier fly larvae in decentralized treatment of faecal sludge from pit latrines in informal settlements in Kampala city
    (Frontiers in Environmental Science, 2023-02) Richard, Tokwaro; Swaib, Semiyaga; Charles, B. Niwagaba; Anne, Nakagiri; Jotham, Ivan Sempewo; Chimdi, Muoghalu; Musa, Manga
    Introduction: Faecal sludge management (FSM) in urban areas of low-and middle-income countries (LMICs) is not properly implemented due to inaccessibility of sanitation facilities and high faecal sludge (FS) emptying costs, amongst others. Unlike in solid waste and fresh human excreta, use of black soldier fly larvae (BSFL) in treatment of FS from pit latrines - which are the most common sanitation facilities in urban areas of LMICs - has not yet been explored. Moreover, the optimal conditions for efficient FS degradation, such as moisture content, feeding rate and larval density are not yet well known. Against this backdrop, the overarching aim of this study was to determine the effectiveness of BSFL in treating FS under different conditions of moisture content, feeding rate and larval density. Also, the quality of residue left after treatment was assessed. Methods: FS samples were collected from lined and unlined pit latrines in Bwaise I parish in Kampala, Uganda and experiments were set up to feed 10-day old larvae. Results and Discussion: The optimum feeding rate, larval density and moisture content were found to be 50 mg/larvae/day, 1.33 larvae/cm2 and 60%, respectively. The reduction efficiency at optimum conditions were 72% and 66% for FS from lined and unlined pit latrines, respectively. It was further noted that BSFL can feed on FS from pit latrines without dewatering it, hence there is no need for a dewatering unit. The properties of the residue left after treatment were within the allowable limit for use as compost except for helminth egg concentration. Thus, in informal urban settlements, BSFL can be applied for effective treatment of FS from pit latrines while generating good quality residue thereby providing an additional value chain in FSM.
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    Biochar as a novel technology for treatment of onsite domestic wastewater : A critical review
    (Frontiers in Environmental Science, 2023-02) Chimdi, Muoghalu; Prosper, Achaw Owusu; Sarah, Lebu; Anne, Nakagiri; Swaib, Semiyaga; Oliver, Terna Iorhemen; Musa, Manga
    Globally, about 2.7 billion people depend on onsite sanitation systems (OSS) (e.g., septic tanks) for their sanitation needs. Although onsite sanitation systems help in providing primary treatment for domestic wastewater, they don’t effectively remove nutrients, pathogens, and other inorganic contaminants. Previous studies have posited that the use of post treatment systems which incorporate biochar leads to improved contaminant removal efficiency. However, the mechanism through which contaminants are removed and factors potentially affecting the removal are still understudied. To fill this knowledge gaps, this review discusses factors which affect efficiency of biochar in removing contaminants found in onsite domestic wastewater, modifications applied to improve the efficiency of biochar in removing contaminants, mechanisms through which different contaminants are removed and constraints in the use of biochar for onsite wastewater treatment. It was noted that the removal of contaminants involves a combination of mechanisms which include adsorption, filtration, biodegradation, ion exchange, pore entrapment. The combination of these mechanisms is brought about by the synergy between the properties of biochar and microbes trapped in the biofilm on the surface of the biochar. Future areas of research such as the modification of biochar, use of biochar in the removal of antibiotic resistant genes (ARGs), application of wet carbonization methods and resistance of biochar to physical disintegration are also discussed. This study provides useful information that can be applied in the use of biochar for the treatment of wastewater and guide future design of treatment systems for optimized treatment performance.
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    Contributions of human activities and climatic variability to changes in river Rwizi flows in Uganda, East Africa
    (MDPI, 2021-09) Charles, Onyutha; Resty, Nyesigire; Anne, Nakagiri
    This study employed Soil and Water Assessment Tool (SWAT) to analyze the impacts of climate variability and human activities on River Rwizi flows. Changes in land use and land cover (LULC) types from 1997 to 2019 were characterized using remotely sensed images retrieved from Landsat ETM/TM satellites. SWAT was calibrated and validated over the periods 2002–2008 and 2009–2013, respectively. Correlation between rainfall and river flow was analyzed. By keeping the optimal values of model parameters fixed while varying the LULC maps, differences in the modeled flows were taken to reflect the impacts of LULC changes on rainfall–runoff generation. Impacts due to human activities included contributions from changes in LULC types and the rates of water abstracted from the river as a percentage of the observed flow. Climate variability was considered in terms of changes in climatic variables such as rainfall and evapotranspiration, among others. Variability of rainfall was analyzed with respect to changes in large-scale ocean-atmosphere conditions. From 2000 to 2014, the portion of River Rwizi catchment area covered by cropland increased from 23.0% to 51.6%, grassland reduced from 63.3% to 37.8%, and wetland decreased from 8.1% to 4.7%. Nash–Sutcliffe Efficiency values for calibration and validation were 0.60 and 0.71, respectively. Contributions of human activities to monthly river flow changes varied from 2.3% to 23.5%. Impacts of human activities on the river flow were on average found to be larger during the dry (14.7%) than wet (5.8%) season. Using rainfall, 20.9% of the total river flow variance was explained. However, climate variability contributed 73% of the river flow changes. Rainfall was positively and negatively correlated with Indian Ocean Dipole (IOD) and Niño 3, respectively. The largest percentages of the total rainfall variance explained by IOD and Niño 3 were 12.7% and 9.8%, respectively. The magnitude of the correlation between rainfall and IOD decreased with increasing lag in time. These findings are relevant for developing River Rwizi catchment management plans.
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    The relationship between water pressure variations and drinking-water quality in small water supplies: A case of Mukono District, Uganda
    (Environmental Challenges, 2023-09) Kenan, Okurut; Jamiru, Ntumwa; Anne, Nakagiri; Jo, Herschan; Aime, Tsinda; Rosalind, Malcolm; Dan, J Lapworth; Kathy, Pond
    The supply of a safe and adequate quantity of water is essential for human health and socioeconomic devel- opment. Physiochemical and microbiological quality of water supplied in piped distribution systems can be affected by long water residence times and travel distances. This may be due to low pressure, reservoir storage and insufficient disinfection in the system among other causes. As such, large schemes usually have mechanisms of improving the quality of water along supply and/or distribution networks at reservoir and other points. In contrast, small, piped water supply schemes rarely have the infrastructure and resources to monitor and provide treatment to the water in distribution. The objective of this study was to assess the variation of water quality and water pressure along the supply network in small, piped water systems. The study used mixed methods of quantitative water quality and pressure assessments, alongside stakeholder interviews, to investigate the vari- ability of water pressure and specific water quality parameters across the distribution network, and reliability of supply in two different small water supply schemes in the study area of Mukono, Uganda. Results showed water pressure in small, piped water supply networks have minimal influence on variation of selected water quality parameters in smaller (< 4000 m travel distances) and well operated and maintained systems. A pressure drop from 82.2 m to 22.5 m changed Turbidity by < 1, Apparent Color by < x10 and Total Dissolved Solids by < x102. Proper management of supply systems to ensure optimal residual and continuous pressure can safeguard the quality of water in the distribution systems of small piped water networks against intrusion of contaminants. Good management practice that utilizes historical operational data with continuous capacity development and training support on water quality and pressure fluctuations can significantly improve system performance to meet acceptable standards.