Water Supply and Environmental Engineering

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Browsing Water Supply and Environmental Engineering by Author "Agizew Nigussie (PhD)"

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    Optimization of Up-flow Anaerobic Sludge Blanket Reactor: A case of Kality Wastewater Treatment Plant, Ethiopia
    (Addis Ababa Univeristy, 2024-08) Johnny Girma; Agizew Nigussie (PhD); Asie Kemal (PhD)
    Enhancing the performance of an up-flow anaerobic sludge blanket reactor (UASB) for unregulated sewage treatment by optimising its operating parameters at a moderate temperature is contingent upon controlling variables like temperature, pH, organic loading rate (OLR), and hydraulic retention time (HRT). The primary goal of the study was to improve the performance of the Kality Wastewater Treatment Plant (WWTP), which uses a UASB reactor through optimization of operational parameters. To do this, controllable operational parameters were optimised, toxic heavy metals concentrations were measured in the unit processes like UASB reactor, Trickling filter, and secondary clarifier. Samples were also tested at downstream irrigated soil and plants for toxic heavy metals concentration. Eventually, the UASB reactor was modelled using general process simulation (GPS-X). Sixty experimental data sets were collected during the rainy seasons (June, July and August) and dry seasons (February, March and April). Central composite design-response surface method (CCD-RSM) tool was used for optimization of operational parameters. Using this CCD-RSM, a temperature of 21.58°C, OLR of 2.99kg COD/m3.d, HRT of 4.37hrs and pH of 6.3 operational parameters were achieved during the rainy seasons. Experimental triplications were conducted using the rainy seasons optimized parameters and about 92.70% Chemical Oxygen Demand(COD), 99.06% Total Suspended Solid(TSS), and 94.50% volatile suspended solid (VSS) were achieved . For dry season’s data, CCD-RSM gave raise optimized operational parameters of temperature (23.04°C), OLR (2.23kg COD/m3.d), pH (7.5), and HRT (11.43hrs). Using optimized operational parameters, experimental triplications were conducted and achieved a removal efficiencies 84.07%COD, 99.89%TSS, and 100%VSS which is much higher than the removal efficiency set by Kality WWTP manual (55% COD, 55%BOD5 and 70%TSS). At the halfway point of the HRT, the reactor's process wellbeing was assessed by measuring the VFA to alkalinity ratio, VSS to TSS ratio, mixed liquor suspended solids (MLSS), and mixed liquor volatile suspended solids (MLVSS). Moreover, because of point and non-point sources of wastewater to the treatment plant multiple issues that have public and environmental health significance could be observed. One of the issue is the evaluation of the WWTP’s unit processes for toxic heavy metals. They were evaluated for toxic heavy metals removal since the existence of higher concentration of these metals in WWTP’s unit processes significantly affects the wellbeing of microorganisms through significant change of pH and the formation of complex compound which precipitate and corrodes the distribution pipes. The second issue is associated with the prevalent use of the treated effluent for irrigation by local farmers. Data were collected to identify and quantify toxic heavy metals in treatment plant’s effluent, irrigated soil, and vegetables. The laboratory tests revealed that majority of the toxic heavy metals were present in the samples analyzed (Chromium, Cadmium, Arsenic, Copper, Lead, and Manganese) and the unit processes were inefficient to remove these metals. Furthermore, a model describing the main biological processes occurring in the UASB reactors was developed. General Process Simulation-X (GPS-X) was used in this experimental research since it is the best tool for simulation and optimization of WWTP processes. Before simulation, influent characterization was done for mass balance around the secondary clarifier which was helpful for calibrating the GPS-X model. The sensitivity analysis result showed that model parameters like kinetic (Maximum Specific Growth Rate on Substrate, Maximum Growth Rate for Ammonia Oxidizer, Maximum Growth Rate for nitrite Oxidizer, Maximum growth rate of PAO) and stoichiometric (Ammonia-oxidizer yield, and Nitrite-Oxidizer yield) values were the most sensitive parameters to calibrate the UASB reactor but the most influential model parameter was kinetic value (heterotrophic maximum specific growth rate). Average absolute relative error (ARE) was used to evaluate the best fit between the measured and simulated data sets. ARE values for COD, TSS and ammonia-nitrogen being less than 7-15% showed that the model was calibrated. Finally the calibrated model was validated based on actual dry seasons data sets collected experimentally. As the simulated results showed acceptable model performances, the developed model can be used by operators, designers and researchers for further studies.
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    Performance Assessment of Sewer Network in Addis Ababa: The Case of Kality Catchment
    (Addis Ababa University, 2023-12) Getye Fekadu; Agizew Nigussie (PhD)
    Urban development usually exerts enormous pressure on the existing sewer network systems. The deficiency in the performance of the sewer network becomes one of the most critical issues in the sewer system sector that requires immediate action. Kality Catchment sewer system has problems related to sewer system coverage, manholes overflow, and capacity deficiency. The main objective of this study is to assess the performance of existing sewer network in Kality’s Catchment with respect to pipe capacity (depth/rise), and surcharge using Bentley SewerGEMS CONNECT. Both primary and secondary data were collected and TOOLS such as Arc GIS, AutoCAD, Microsoft Office Excel, and Geographic positioning system (GPS) were used. Model analyses were conducted under three possible scenarios. The wastewater generations for the first and second scenarios were estimated based on water consumption bill data by considering active and potential sewer customers for both scenarios, respectively. Additionally, a projected wastewater generation was derived from land use data for the third scenario. The sewer system coverage in the Kality Catchment was estimated to be 17.63%, showing only the proportion of active sewer customers relative to water customers in the study area. The steady-state analysis of the sewer network, considering peak flow conditions, revealed that approximately 1.01%, 1.49%, and 4.16% of pipes exceeded their capacity (d/D) (>90%) values. This accounts for lengths of 5,415.10m, 7,956.20m, and 22,249.10m for the first, second, and third scenarios respectively. Additionally, approximately 2.88%, 3.74%, and 8.35% of pipes experienced surcharge, accounting for lengths of 15,372.40m, 20,019.10m, and 44,654.50m for the respective scenarios. The pipe capacity (d/D) exceeded when the d/D ratio reached 0.9(90%), and surcharge occurred when the water level rose above 15cm of the manhole rim elevation during peak flow conditions. These locations with deficiencies in both pipe capacity (d/D) and surcharge covered lengths of 1,691.90m, 5,334.80m, and 17,577.50m for the first, second, and third scenarios respectively. It is recommended that the utility upgrade the existing sewer network, as well as expand a new sewer system and connect to the system unserved areas and customers.
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    Quantifying Water Loss Components and Conducting Performance Indicator-Based Assessment for Addis Abeba Water Distribution System
    (Addis Ababa University, 2024-04) Fikirte Girma; Agizew Nigussie (PhD)
    Water loss in urban water distribution systems is a significant global challenge, leading to wastage, revenue losses, and contamination risks. The Addis Ababa Water Distribution System (AAWDS) faces similar challenges, a significant portion of the water supplied to people doesn’t reach its intended users. Despite the critical importance of mitigating water loss, assessment practices and understanding of different causes and factors influencing the amount and type of water loss in a distribution system is limited. This study aims to assess and quantify total water losses in the AAWDS, and evaluating system performance. The research examines both real and apparent losses, with a focus on metering accuracy degradation rates and failures, especially in DN 15 mm customer meters, which constitute a large proportion of utility meters. The study identifies a high meter failure rate (0.59%/year) in the system, with water losses due to DN 15mm meter failure estimated at 0.53% of the annual non-revenue water (NRW), equivalent to 470,081𝑚3 /year. Using comparative billing analysis methodology, the research determines meter accuracy degradation rates for different meter models and calculates annual water losses due to meter inaccuracies, totaling US$1.5 million per year. Additionally, the study adopted two techniques, Minimum Night Flow Analysis and Calibration Process Water GEMs V10 Calibrator Software, were used to estimate leakages in district-metered areas situated around Kasanchis area, revealing a daily water loss 756 𝑚3. Leakage identification in the water distribution system of the DMA resulted in shortlisting of 5 points. The research also proposes 12 performance indicators for evaluating the system's efficiency, with some successfully tested on a branch utility of AAWSA. The findings emphasize the need of integrated water meter management (IWMM), leakage detection with calibrator software, and the utility's use of appropriate water loss performance indicators