Water Supply and Environmental Engineering
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Browsing Water Supply and Environmental Engineering by Author "Agizew, Nigussie (PhD)"
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Item Effects of Pressure Change on Water Quality: Case of Akaki Phase 3B Water Supply Distribution System in Addis Ababa, Ethiopia(Addis Ababa University, 2017-12) Yetnayet, Tsegaye; Agizew, Nigussie (PhD)Water network performance is defined as the ability to deliver a required quantity of water under sufficient pressure and an acceptable level of quality. Systems that have big transmission line may have problem on changes of pressure in the distribution system. Because pressure rate changes have been too much between water treatment plant and dead ends in distribution system. This study is to analyze the effects pressure changes on the water quality in water distribution systems for case study of Akaki phase 3B water supply system was assessed. Efforts were also made to identify the relationship between the residual chlorine and pressure in the distribution of the water supply network systems using Water Cad software /tool to model water distribution system. Accordingly, simulation results show that, for maximum and minimum pressures were used as base to evaluate the hydraulic performance; and simulation results for minimum residual chlorine were used as base to assess water quality transformation in distribution system. Pressure has a direct relationship with residual chlorine. Pressure change has been causing to increase chlorine consumption more. The result of pressure changes among others can decrease in chlorine content and hydraulic factors, because the systems may be extensive and thus possess complex networks and hangs in quantity cause pressure of flow. Hence hydraulic changes (pressure) could affect of water quality in the water distribution system.Item Greywater Treatment Using Banana Peel Biochar and Sand Filtration(Addis Ababa University, 2019-10) Biruktawit, Gebremeskel; Agizew, Nigussie (PhD); Zerihun, Getaneh (Mr.) Co-AdvisorSand has been used for long time to treat greywater. However, biochar might be an alternative to replace the sand for greywater treatment and also reduce the amount of organic waste disposed into the environment. In this study the biochar was produced from banana peel and the purpose was to evaluate and compare the performances of biochar, sand and sand with biochar in reducing turbidity, COD, N, P, fecal coliform and pH. The biochar and sand were packed to a depth of 27 cm into columns with a diameter of 7 cm but in case of sand with biochar the depth was 13.5 cm for sand and the remaining was filled by biochar. The columns were fed with synthetic and real greywater. Synthetic greywater was used for optimization of biochar particle size and pH. Real greywater was fed to the column by taking the optimum biochar particle size and pH and compared with, sand and sand with biochar for four days. Biochar was prepared in three different sizes: Fine, medium and coarse with a size of below 1mm, between 1-3 mm and above 3mm, respectively. Fine particle size of biochar showed more removal efficiency than medium and coarse sized particles. The average performance of fine medium and coarse particle size was 88%, 71.2% and 39.3% for turbidity 54.8%,36.5% and 23.1% for COD,62.2%, 23.4% and 12.6% for N and 52%,18.4% and 9.4% for P respectively. But in all particle sizes of biochar effluent pH and EC values were found to be more than that of the influent. For the optimization of pH values that varied from 5 to 10 were tested. The results of the analysis showed that the highest removals of turbidity (89%), COD (55%), N (94%) and P (78.8%) were achieved at pH value of 7. Fine biochar (FBC) showed better removal efficiency when compared to that of sand and biochar with sand (FBCS). The average performance efficiencies of FBC, sand and FBCS were 95%, 67%, and 79% for turbidity, 81%, 19% and 56% for ammonium, 71%, 28% and 50% for phosphate 50 %, 61% and 46% for COD and 90%, 80% and 87% for fecal coliform respectively. The findings of this paper indicate that transformation of banana peel into biochar has a double advantage of treating greywater and minimizing the amount of waste that is disposed into the environment.Item Impacts of Land Use/Cover on Surface Water Quantity and Quality (Case of Akaki Catchment, Ethiopia)(Addis Ababa University, 2019-09-05) Tesfakiros, Atsbha; Agizew, Nigussie (PhD)Evaluating the impacts of land use on surface water quality and quantity based on temporal and spatial variation using the integrated watershed (SWAT) and water quality models (WASP) were the aims of this study. SWAT model’s performance was assessed using Nash– Sutcliffe coefficient (NSE) and coefficient of determination (R ) with the help of SWAT CUP software. The model was calibrated from 1989 to 1994 and validated from 1995 to 1997 for stream flow using the 1989 land use/land cover map. The monthly calibration and validation results showed (NSE = 0.74, R 2 = 0.55) respectively. Annual stream flow was evaluated on the years 1989, 2003 and 2016 and the result shows that it increases by 10.1% from (1989-2003) and by 30.3% from (1989-2016) on the downstream of Little Akaki river (reach 51). This is because urbanization increases by 63.7% and forestland decreases by 61.6% from the upstream to the downstream of the river. Sediment load decreased by 98.2% when urbanization is increased by 35.2% and barren lands decreased by 37.3% from (1989-2016). It also increased by 82.6% when urbanization increased by 53.5% and barren land decreased by 32.4% from (1989-2016). pH, Temperature, TSS, NH4-N, NO2-N, TN and TP decreases its quality by 5.9%, 0.8%, 7.0%, 59.2%, 67.0%, 34.5% and 45.9% from upstream to downstream of Great Akaki river. This is because of built up area increases by 45.7% and forestland decreases by 28.5% from upstream to downstream of Great Akaki River. Water quality of the rivers was evaluated temporally and the results showed that pH, Temperature, TSS, NH4-N, NO2-N, TN and TP decreases its quality by 5.29%, 9.11%, 48.47%, 45.88%, 43.28%, 47.1% and 17.69% respectively from (1989-2016) on little Akaki river. When the simulated result are compared to water quality guide lines pH, TSS, NH4-N, TN and TP exceeds the guideline by 2.9%, 85.8%, 5.2%, 2.3%, & 0.2% on downstream of little Akaki and by 11.1%, 87.3%, 10.7%, 31.6% & 7.35 Great Akaki rivers respectively.Item Optimum Coagulant Dose Prediction for Water Treatment using Artificial Neural Network (Case of Legedadi Water Treatment Plant)(Addis Ababa University, 2022-04) Eyerusalem, Alemayehu; Agizew, Nigussie (PhD)Water obtained from surface or subsurface sources is crucial for life. But direct use of raw water has serious health risks. Different water treatment processes can be used to make the raw water safe for domestic purposes. Coagulation and Flocculation is one of the treatment stages used to remove colloidal particles through the use of chemicals (coagulants) that enable the formation of larger flocs that can be easily removed by sedimentation and filtration. Determination of the optimum coagulant dosage is important to meet the required water quality. For instance, a high coagulant dosage may lead to high residual chemical in the treated water, high sludge volume, and increased load on the filter units. All these can result in poor water treatment performances, high operational costs, and process complications. Jar test has been used widely to determine the optimal coagulant dosage for a given water quality. However, this practice has some drawbacks such as it is time-consuming, the probability of making errors is high and it is impractical for highly variable raw water turbidity. Consequently, the need to develop new tools and techniques to determine optimum coagulant dosage becomes important. However, quantifying the relationship between the process inputs and output in the water treatment unit process is very difficult with the existing process model. Thus, Artificial Neural Network was used to develop the models in this research as it is a robust technique that allows the development of a multi-variable and complex non-linear relationship. ANN Multi-Linear Perceptron type with one hidden layer was used to simulate the jar test for the optimum coagulant dosage forecasting. Two models were developed and their performances were evaluated based on Root mean squared error (RMSE) and coefficient of determination (R 2 ). The first model which enables prediction of turbidity for a given coagulant dosage and other factors was the process model. The second model which allows determination of optimum coagulant dosage to attain the desired turbidity level is the Inverse Process Model. The RMSE and R 2 values were found to be 0.0748 NTU and 0.6121, respectively for the Process model. For the Inverse Process model the RMSE and R 2 values were found to be 0.225mg/l and, 0.9823, respectively. These indicate that a good performance of the ANN-based model to simulate the jar test could be obtained. The models can be used to optimize the coagulation process within the available raw water turbidity range of Legedadi Water Treatment Plant.Item Performance Assessment of Horizontal Subsurface Constructed wetland for the treatment of Winery wastewater(Addis Ababa University, 2019-06) Sunamawit, Aweke; Agizew, Nigussie (PhD)Wastewater from human dwellings and activities has been a primary target of many treatment technologies, including constructed wetlands. Constructed wetland technologies for wastewater treatment is characterized by specific conditions enabling simultaneous various physical and biochemical processes that are responsible for the removal and retention of pollutants. Thanks to its advantages such as simple construction, easy operation and cost effective maintenance, there is growing interest in the use of this technology for the treatment of wastewater from different sources including industries. The specific characteristic of industrial wastewater (new pollutants, extreme concentration, low biodegradability, high toxicity) is a challenge for the application of constructed wetlands, and therefore research is necessary to assess their viability and optimize their design and operation. This study was undertaken to establish the efficacy of horizontal subsurface constructed wetlands in purifying winery wastewater, and to examine the effect of water depth and vegetation on the treatment efficiency. The study used four pilot scale cells with water depth of 40 cm and 80 cm that were operated at the same hydraulic residence time of ten days. Two cells were planted with local macrophyte (bossarus aethopium) and the other two were left unplanted to be used as control. The constructed wetlands exhibited good removal efficiency with respect to all the major pollutants monitored i.e. COD, BOD, TSS, TDS, TKN, NH4 + . The data analysis indicated that the shallow wetland cells with a water depth of 40 cm had significantly higher performance for the removal of COD, BOD, TKN and NH4 + - 3- , NO3 , TP and PO4 than the 80 cm deep cells. Also, the planted wetland cells showed better removal efficiency for the organic matter and nutrient than the unplanted cells. The findings of this study showed positive results towards the use of HSSFCWs for the treatment of winery wastewater. The 40cm deep planted cell had better overall performance compared to the other cells and hence was used to design a large scale constructed wetland for Awash winery. STELLA modeling tool was used to simulate the hydrologic dynamics of the large scale constructed wetland.Item Performance Evaluation and Model-Based Optimization of Membrane Bioreactors: The Case of Addis Ababa Package Treatment Plant(Addis Ababa University, 2017-11) Mahlet, Melaku; Agizew, Nigussie (PhD)Addis Ababa Water and Sewerage Authority invested 750 million ETB for installing membrane bioreactor units in the city. This new technology is expected to double the wastewater treatment capacity of the city. Evaluating the performance of the units is necessary in estimating the likelihood of meeting this expectation and predicting the sustainability of the treatment plants. This research explores performance of the installed plants and suggests optimal operational strategies to enhance the denitrification capacity of the plant while minimizing energy cost. Measures of performance were effluent quality and membrane filtration processes. In order to evaluate the effluent quality, samples were collected both in dry and wet seasons. The MBR module was evaluated using recorded data of Transmembrane Pressure (TMP), flux & permeability of five-month operation. Activated sludge model no1 based simulation was used to determine the optimal operation strategy. To ensure energy reduction while improving the treated water quality; the suitability of intermittent aeration was explored using the developed model. The average COD removal efficiency was 97%. The ammonium effluent concentration was always lower than 0.5 mg/L. However, absence of anoxic tank resulted in poor denitrification with consequently increase nitrate effluent concentration over 100 mg/l. The treated wastewater was found to be completely clear of fecal coliform; making the treated water suitable for reuse. The MBR filtration showed stable but low permeability condition. The average operational TMP was less than 20mbar. However, flux and permeability plot showed the plant was operating with decreasing trend over time and maximum of 80LMH/bar. This suggests the need for frequent cleaning or construction of a primary tank. Results from the ASM1 simulation indicated that intermittent aeration with aerobic-anoxic cycle of 43/54 min was the optimum duration. The proposed operational strategy increased the total nitrogen removal efficiency from 42% to 71% without affecting COD removal. These results indicate that creating optimal aerobic/anoxic conditions within the existing reactor is the most competitive solution to upgrade the MBR treatment plant.Item Recovery of Nitrogen and Phosphorous From Source Separated Urine Using Biochar(Addis Ababa University, 2019-10) Ephrata, Tewhibo; Agizew, Nigussie (PhD); Zerihun, Getaneh (Mr.) Co-AdvisorNutrients mainly nitrogen and phosphorous exist in wastewater excessively. If uncontrolled, they lead to eutrophication problem which has adverse impacts on the social, economic and ecological values of surface water bodies. Urine is a significant contributor of phosphorus and nitrogen found in domestic waste water. Therefore, recovery of these nutrients from urine removes the excess amount of nutrients and prevents environmental pollution. In addition removal of Phosphorus in wastewater treatment plants is costly and limits its recovery and use as a resource. Recovery of nutrients from source separated urine would increase the efficiency in nitrogen and phosphorous removal and reuse capacity. The objective of this research was to examine different parameters affecting the recovery of nitrogen and phosphorous through adsorption process by using biochar produced from corn cob(CC), coffee husk(CH) and water hyacinth(WH) and determine nutrient recovery efficiencies of each biochar from human urine. In this research, the impacts of different parameters which can affect nutrient recovery from source separated urine using biochar were examined to get optimal values. The nutrient recovery process was conducted under different pH (3-8), biochar dosage (0.2-1g) and contact time (30-150min.) on urines of different storage time (15days, 1 month and 2 month). The optimum working values of pH and contact time were 6 and 60 minutes, respectively. The optimum dosages were 0.4g, 0.6g and 0.8g for 15 days, 1 month and 2 months stored urine. Highest NH4 + 3— -N and PO4 P recoveries were obtained from urine that had two months of storage time. Therefore, urine with two months storage time was selected as optimal. Under these optimum values, the nitrogen recovery efficiencies of biochars produced from CC, CH and WH were 94.13%, 77.99% and 85.78%, respectively. The recovery efficiencies of phosphorous from human urine were 68.60%, 71.14% and 57.72 % using CC, CH and WH, respectively. CC produced biochar was the best compared to CH and WH biochars. Biochars produced from wastes have good potentials for nutrient recovery from source separated urines. Besides, the use of waste as resource is in line with sustainable waste management and contributes to environmental pollution control.Item Recovery of Phosphorus and Nitrogen from Domestic Wastewater through Struvite Precipitation using Conical Fluidized Bed Reactor(Addis Ababa University, 2019-10) Azeb, Wujira; Agizew, Nigussie (PhD); Zerihun, Getaneh (Mr.) Co-AdvisorRecovery of nutrients as struvite before it forms and accumulates is in line with sustainable wastewater management. It prevents water pollution and enables use of the nutrients as fertilizer to increase agricultural productivity. A bench-scale fluidized bed reactor (FBR) was used to recover phosphate (PO4) and ammonium (NH4) through struvite crystallization, from synthetic wastewater and aerobic digester domestic wastewater supernatant collected from, Haile Garment Addis Ababa and Oromia Condominium Wastewater Treatment Plant. Struvite crystallization is a promising nutrient recovery method. Its recovered precipitate can be used as a slow release fertilizer and raw material for chemical industry. The objective of this research was to examine the influence of different parameters affecting the performance of FBR for phosphorus (P) and nitrogen (N) removal and recovery efficiencies. In this study, the impacts of important factors on nutrient recovery in a laboratory scale (FBR) were examined using synthetic wastewater to get optimal values. The nutrient recovery of the FBR from real wastewater was also evaluated by using the optimum parameter values. The recoveries of PO4 and NH4 were evaluated by changing the values of the following parameters: pH (7.5-10), molar ratio of Mg/P (0.75-1.75), Hydraulic retention time (HRT = 15hr), and settling time (15-90min). The optimum values of pH, Mg/P, HRT, and settling time were found to be 9, 1.5:1, 2hr, and 30min respectively. Under these optimum values, the P and N removal efficiencies of conical FBR from synthetic and real wastewater were 97% and 95% and 67.2% and 64.7%, respectively. Moreover, different techniques were used to enhance nutrient recovery efficiency including use of a reactor that has three parts and insertion of cones in each part. The findings of the study show pH, Mg/P molar ratio, HRT, and settling time to be important factors that influence Phosphorus and nitrogen removal efficiency in FBR. A conical FBR with three distinct parts gives a good nutrient recovery through struvite precipitation.Item Recovery of Phosphorus and Nitrogen from Source-Separated Urine: Process Optimization in Bench-Scale(Addis Ababa University, 2018-06) Johnny, Girma; Agizew, Nigussie (PhD); Zerihun, Getaneh (Mr.) Co-AdvisorThe main focus of this research is to investigate about the possibility of Nutrient recovery in the form of Magnesium Ammonium Phosphate (Struvite) by determining optimum PH, optimum dosage, suitable mixing time, mixing speed , precipitation time ,and storage time from source separated stored human urine. A laboratory test was conducted using Jar test for the stored human urine. Struvite formation was PH dependent reaction and the experiment was started with PH optimization having six different pH values from PH 6 to 11. The experimental result showed that at PH 10 the percentage removal for N -N and PO4-P was 87.07% and 91.55% respectively, which is greater than other PH’s which implied that the optimum PH was PH 10. Using PH 10 as optimum PH, the determination of optimum dosage (P04-p:M )ratio was conducted using six different mass ratios, i.e. 1:1, 1:2, 1:3, 1:4, 1:5 and 1:6. The result of the experiment showed that, at PH10 and P04-P:M dosage of 1:1, the percentage removal of NH4-N and P04-P was 90.54% and 77.49% respectively which showed the optimum dosage was 1:1. Laboratory tests were also done to determine the optimum mixing time and mixing speed and found to be 30minutes and 60rpm respectively .Two samples were tested to determine the optimum incubation period to recover nitrogen and phosphorus for 25 and 30 days and found to be on 20th and 19th day respectively. Furthermore Basaka water was also used as source of Mg +2 to recover Nitrogen and Phosphorus and about 36% of Phosphorus was recovered and ultimately struvite was produced by the designed stirred reactor.Item Wetlands as Nature Based Solutions for In Situ Water Purification: The Case of Urban Wetlands, Jimma, Ethiopia(Addis Ababa University, 2018-07) Adey, Sileshi; Agizew, Nigussie (PhD)Nature provides valuable solution to tackle different socio- environmental challenges. Wetlands have a potential to purify water which is mainly influenced by its hydro-system, including landform setting and the water regime, and different biogeochemical processes. In East Africa, it’s estimated that approximately 80% of wastewater is discharged untreated or partially treated. Although there are some studies dealing with the water purifying effect of wetlands, its application for in-situ water purification is still in its infancy. The main objective of this study is to determine the effect of natural riverine wetlands to reduce nutrient and organic pollutant concentrations. And to assess the difference among the study wetlands. A cross sectional study on water samples collected from different locations before entering the wetlands, within the wetlands and after passing through the wetlands, was conducted between February 5 and February 25, 2017. Data collection check list and standard field protocol were used to collect data from three urban wetlands (urban downstream wetland and two urban upstream wetlands). After compiling, data analysis was done using R statistical software. The results of this study showed a lower concentration of nutrients, and BOD in sites after joining the wetlands compared to those before the confluence of the wetland. This implied the presence of pollution attenuation by the wetlands. Among the three wetlands, the one located in the urban downstream revealed a higher level pollution. The PCA model showed nutrient and pollution gradient along its axis. Urban downstream wetland was positively correlated with nutrients as shown in the PCA biplot. In conclusion, the study revealed the potential of urban wetlands to reduce/ attenuate pollution from the water which passes through them. However, discharging unlimited amount of nutrients and other toxicants to wetlands may affect the functioning of wetlands