Department of Water Resources Engineering

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Effect of Pond Depth on Bacterial Mortality Rate
(American Society of Civil Engineers, 1989) Mayo, Aloyce W.
The bactericidal action of solar radiation was investigated in pilot scale waste stabilization ponds under the tropical climate of Dar es Salaam, Tanzania. Bacterial reduction was observed to proceed with increasing direct solar intensity and hydraulic detention time. The mortality rate of faecal coliforms used as test micro-organisms was higher in samples incubated near the surface and decreased rapidly when the samples were incubated at greater depths in the pond. The disappearance rate of faecal coliforms for samples incubated at the pond surface and at a depth of 1.0 m was 1.66 d-1 and 0.37 d-1 respectively. Faecal coliforms were also found to be reduced rapidly in shallow ponds. The mortality rate in 1.0 m and 1.5 m deep ponds was respectively 0.43 and 0.32 d-1. The dieoff rate constant was observed to vary significantly with pond depth but was independent of hydraulic detention time.
Rainwater Harvesting For Domestic Use in Tanzania a Case Study: University of Dar Es Salaam Staff Houses
(Taylor and Francis, 1991) Mayo, Aloyce W.; Mashauri, Damas A.
The bacteriological, chemical and physical analyses of water samples from rainwater cistern system at the University of Dar es Salaam in Tanzania were carried out between October 1988 and December 1989. Faecal coliforms, total coliforms and faecal streptococci were enumerated. The results shows that 86% of the samples were free from faecal coliforms. However, faecal streptococci were obtained in 53% of the samples and 45% of the samples tested for total coliforms were positive. The physical quality of water was found to be appealing during the whole study period with turbidity less than 5 NTU and colour less than 5 mg Pt/l. However, about 54% of the consumers raised objections over the taste of water.
Faecal Coliform and BOD Reduction in Facultative Ponds under Tropical Climatic Conditions
(1992) Mayo, Aloyce W.
Effect of Glucose Loading on the Growth Behavior of Chlorella vulgaris and Heterotrophic Bacteria in Mixed Culture
(Elsevier, 1994) Mayo, Aloyce W.; Noike, Tatsuya
The effect of glucose concentration on the growth of Chlorella vulgaris and heterotrophic bacteria in mixed culture was studied. Granular glucose was fed daily as a source of organic carbon to provide an input concentration ranging from 25–700 mg/l. Growth rates of heterotrophic bacteria and algae increased with glucose loading rate but excessive loading rates were detrimental to the survival of the algae and bacteria. The maximum specific growth rates for the algae and bacteria were 1.58 and 1.70 d−1, respectively. However, the saturation constants were significantly different with values of 27 and 174 mg/l for bacteria and algae, respectively. Under anaerobic conditions, bacterial density and algae growth were significantly affected by accumulation of volatile fatty acids (VFA). Although in low glucose loaded reactors, pH reached as high as 10.6, no significant effect of pH was observed on the survival of Chlorella vulgaris and heterotrophic bacteria. Inorganic carbon production increased with increasing glucose loading rate. When volatile fatty acids accumulated in anaerobic reactors, pH dropped resulting in a shift of equilibrium between H2CO3, HCO3− and CO32− in favor of H2CO3 production, most of which was released as CO2(g) to the atmosphere.
Modeling Coliform Mortality in Waste Stabilization Ponds
(American Society of Civil Engineers, 1995) Mayo, Aloyce W.
The mechanisms of the reduction of fecal coliforms were investigated in pilot-scale and full-scale wastewater stabilization ponds under tropical climatic conditions. Field studies were conducted in pilot and large waste stabilization ponds with pond depths ranging from 1.0 to 1.82 m and hydraulic retention time between 4.3 and 11.2 d, to develop and verify the model. The observation made indicates that sunlight intensity, pond depth, and pH were the key input parameters to the model. In a multifactor developed model, the bacterial mortality rate constant for pH, k(pH) was 0.0135 d-1 and the ratio of rate constant for the light mortality term to light attenuation coefficient k(s)/K was 5.67 x 10(-4) m cm2/cal. The model was successfully verified by simulation with data obtained from field-scale pond systems in Tanzania and from two other pond systems reported in the literature. A brief model application, including the prediction of water pH, is given to aid the designer.
BOD5 Removal in Facultative Ponds: Experience in Tanzania
(1996) Mayo, Aloyce W.
This paper discusses the removal of BOD5 in facultative ponds under tropical conditions. Data was collected from pilot and field ponds at the University of Dar es Salaam and was compared to other ponds in Dar es Salaam. Results showed deviations of performance, in some cases, from assumptions made during the design. The permissible organic loading rate for ponds in Dar es Salaam was 450 kg BOD5/ha/d. To reduce concentration of algae in the final effluent, a sunken outlet structure was suggested.
Effects of Temperature and Ph on the Growth of Heterotrophic Bacteria in Waste Stabilization Ponds. Water Research, 30, 447-455
(Elsevier, 1996) Mayo, Aloyce W.; Noike, Tatsuya
This paper presents the effects of temperature and pH on the growth of heterotrophic bacteria in Chlorella vulgaris-heterotrophic bacteria culture. The growth of heterotrophic bacteria was studied at 10, 15, 20 and 30°C, and pH was controlled from 3.0 to 11.5 in a series of fed-batch chemostat reactors supplied with glucose as the sole source of carbon. Samples were analyzed for heterotrophic bacteria by tryptone glucose extract agar in triplicate. The agar pH of 7.0 was the best for enumeration of heterotrophic bacteria. The bacteria grown at pH near neutral were more sensitive to the variation of agar pH than those grown at very alkaline pH. No significant difference in the number of cells capable of forming colonies was noted for incubation temperature of 20 and 35°C, but the lag time for colony formation was longer at 20°C. Samples for enumeration of heterotrophic bacteria collected from algal-bacterial systems such as waste stabilization ponds are recommended to be incubated at 35°C for 72 h. Depending on the pH of the culture, about 86–98% of the cells capable of forming colonies will be visible to the naked eyes after incubation at 35°C for 72 h. At the steady state conditions, heterotrophic bacteria were not sensitive to temperature in the range of 10–20°C. However, at 30°C, a notable competition for glucose between Chlorella vulgaris and heterotrophic bacteria was observed. This competition was responsible for the low bacterial density near neutral pH. No evidence was found to support the view that the discharge of bactericidal substances from Chlorella vulgaris was responsible for reduction of heterotrophic bacteria at high pH.
Effects of Temperature and Ph on the Kinetic Growth of Unialga Chlorella Vulgaris Cultures Containing Bacteria
(1997) Mayo, Aloyce W.
The kinetic growth of unialga Chlorella vulgaris was investigated in mixed-culture fed-batch chemostat reactors, with special reference to temperature and pH. The experiments were carried out at 10 degrees C to 40 degrees C, pH was controlled from 3.0 to 11.5 in a series of reactors, and glucose at a concentration of 75 mg/L was fed as the sole source of organic carbon. The maximum growth rate of 0.50 day(-1) was obtained at pH of about 6.31 to 6.84, and the optimum temperature was 32.4 degrees C. The activation energy of the growth-limiting reaction and the enthalpy change for the enzyme-inactivation reaction were 24.5 and 253.36 kJ/mole, respectively. The saturation constants for hydrogen ion, K-H, and hydroxyl ion, K-OH, were temperature-dependent. At temperatures below optimum, K-H increased when temperature increased, but K-OH decreased. Above the optimum temperature, K-H decreased and K-OH increased with temperature.
Effects of Cell Retention Time, Butyrate Loading Rate and Ph on Oxidation of Butyrate in Aerated Lagoons
(1997) Mayo, Aloyce W.
The treatability of butyrate in aerated lagoon was investigated in continuous laboratory-scale aerated reactors at 35°C. The effects of cell retention time, organic loading rate and pH on cellular growth and oxidation rate of butyrate were investigated. The cell retention time was varied in series of bioreactors from 1.5 to 8.0 days and influent pH was varied from 4.0 to 7.0. Butyrate loading rate of up to 3 kg/m3/d as soluble organic carbon was investigated. The analysis showed that the maximum specific growth rate of heterotrophic bacteria was 2.1 d-1, yield coefficient was 0.51, bacterial decay coefficient was 0.133 d-1 and cell maintenance coefficient was 0.262 d-1. The maximum specific substrate utilization rate, half-rate saturation constant and substrate inhibition constant were 1.22 mg SOC/mg POC/d, 7.8 mg SOC/L, and 5900 mg SOC/L, respectively. Butyrate removal rate was influenced by loading rate, but was independent of the mode of variation of butyrate loading rate. No evidence was found to support the view that total butyrate concentration influenced the density of heterotrophic bacteria. However, the concentration of undissociated butyrate was found to significantly affect the density of heterotrophic bacteria. In the alkaline pH range, heterotrophic bacteria increased as butyrate concentration increased. Densities of heterotrophic bacteria as high as 1.1×1010 cfu/mL were observed when effluent pH was 8.4, but decreased to 3×103 cfu/mL when effluent pH decreased to 4.3.
Modelling Diurnal Variation of Dissolved Oxygen in Waste Stabilization Ponds
(Elsevier, 2000) Kayombo, S.; Mbwette, T. S. A.; Mayo, Aloyce W.; Katima, Jamidu; Jørgensen, S. E.
The dissolved oxygen sub model was developed in order to depict the combined influence of light, pH, temperature and carbon dioxide on the processes of dissolved oxygen (DO) production and utilization in secondary facultative waste stabilization ponds (SFWSP). The model was formulated based on Chen and Orlob (Chen, C.W., Orlob, G.T., 1975. In: Patten, B.C. (Ed.), Systems Analysis in Ecology, Vol. 3. Academic Press, New York, pp. 476–588.), and was modified to include the influence of pH and carbon dioxide. The forcing functions to the DO model were light intensity, carbon dioxide, temperature and pH. It was found that temperature, light and pH influence the process of photosynthesis based on the multiplicative formulation of forcing functions. The model was calibrated and validated by using the average daily data from SFWSP1 and 11. The model yielded a linear regression coefficient of 0.87 during calibration and 0.78 during validation. Based on the model results the rate of production of DO with relation to dry algal biomass was 1.599 mg DO/mg dry weight, which is equivalent to 35.905 mg DO/mg chlorophyll-a. Such correlation between the observed data and model prediction indicates that the assumption inherent in the mathematical model formulation of the processes is valid for the description of DO production and usage in the ponds.
Constructed Wetland at the University of Dar Es Salaam
(Elsevier, 2000) Mashauri, Damas A.; Mulungu, Deogratias M. M.; Abdulhussein, B. S.
Following lack of investment in wastewater treatment, high investment and maintenance cost, conventional treatment systems have not been used in Tanzania. On the other hand, cost effective wastewater treatment methods like the use of septic tanks, soak pits, drainage fields and waste stabilization ponds are widely applied. One of the methods of achieving compliance using conventional treatment systems at low cost, producing treated water pollution free and fostering a community responsibility for wastewater treatment involves the use of natural or constructed wetlands. To date, no wetlands have been used for treating wastewater in Tanzania. Therefore in an attempt to promote the use of constructed wetland for wastewater treatment, a horizontal flow constructed wetland at the University of Dar es Salaam was commissioned for treatment of wastewater effluent from the University waste stabilization ponds (WSP).This paper presents results obtained from a constructed wetland (CW) installed at an outlet of the WSP of the University of Dar es Salaam. The field tests were conducted at low and high filtration rates 0.27 m/h and 2.3 m/h respectively for a period of 4 weeks. Treatment effectiveness was evaluated which indicated high mean removal efficiencies; 80% for SS, 66% for COD, 91% for faecal coliforms (FC) and 90% for total coliforms (TC) achieved at the low filtration rate. Thus, wetlands if properly designed, operated and maintained can provide an efficient and economical means of upgrading the quality of secondary treated wastewater to an acceptable level.
Fecal Coliform Mortality in Water Hyacinths Ponds
(2000) Mayo, Aloyce W.; Kalibbala, Martin
The effects of various environmental factors, sedimentation and attachment of faecal coliforms on water hyacinths, Eichhornia crassipes, were investigated in a pilot-scale water hyacinths pond. This investigation was conducted to evaluate the role of solar intensity, pH, dissolved oxygen, temperature, sedimentation, and attachment of faecal bacteria on Eichhornia crassipes on disappearance of bacteria in a water hyacinths pond. A mathematical model that used the plug flow philosophy and incorporated aforementioned factors to predict faecal coliform mortality rate was developed. The proposed multifactor model satisfactorily predicted mortality rate of faecal coliforms in a pilot-scale water hyacinths constructed wetland. The environmental factors such as solar intensity and pH were the key factors if the coverage of water hyacinths is minimum, but attachment of bacteria to water hyacinths played a major role in a wetland fully covered with water hyacinths.
Modelling Nitrogen Transformation and Removal in Primary Facultative Ponds
(Elsevier, 2002) Senzia, M. A.; Mayo, Aloyce W.; Mbwette, T. S. A.; Katima, Jamidu; Jørgensen, S. E.
This paper presents a dynamic rational model for nitrogen transformation in primary facultative ponds. The results show that, the dominant mechanism for nitrogen removal was sedimentation of organic nitrogen (9.7%). The major nitrogen transformation route was through mineralization (19.2%) followed by ammonia uptake by microorganisms (17.4%) and nitrification (2.4%). Denitrification process was another possible route for removal of nitrogen (4.1%), but volatilisation played a negligible role (0.1%). Approximately 38.8% of nitrogen flowing to primary facultative pond did not undergo any transformation. It was further found out that 8.3% of influent nitrogen was unaccounted for, which might be lost through seepage to the ground or evaporation. Nitrogen contained in microorganisms accounted for 50% of the total nitrogen in the final effluent.
Estimation of Soil Erosion in the Pangani Basin Upstream of Nyumba ya Mungu Reservoir
(2002) Mtalo, Felix W.; Ndomba, Preksedis M.
Diurnal Cycles of Variation of Physical–Chemical Parameters in Waste Stabilization Ponds
(Elsevier, 2002) Kayombo, S.; Mbwette, T. S. A.; Mayo, Aloyce W.; Katima, Jamidu; Jørgensen, S. E.
Diurnal fluctuations of pH, dissolved oxygen (DO), water, air temperature and sunlight intensity were investigated in the waste stabilization ponds at the University of Dar es Salaam. The variation of these parameters followed the diurnal pattern of light intensity. The rate of oxygen production based on first order linear regression analysis was between 0.02 and 0.36 mg/l per h with high production rate being observed in secondary facultative ponds. The rate of utilization of dissolved oxygen (total respiration) during the night by the microbial population in the pond ranged between 0.016 and 0.435 mg/l per h. The average rate of increase of pH during the day was 0.0006–0.243 units of pH per h, and the rate of decrease was 0.0003–0.101 units of pH per h. The ponds receiving low organic loading showed high diurnal variation of physical–chemical parameters. The relationship between average hourly DO and pH followed a polynomial trend with the coefficient of regression (R2) ranging from 0.76 to 0.82. It may be concluded that the diurnal variation of the parameters in the WSPs is due to hourly and daily variation of light intensity.
Modelling of Flood Flows in Rufiji River Basin, Tanzania
(2002) Mkhandi, Simon H.; Kachroo, Raj; Mtalo, Felix W.
A simulation procedure applied to select a suitable statistical procedure to model flood flows in Rufiji River basin in Tanzania is presented. In this paper, a flood frequency procedure refers to the combination of a probability distribution with a suitable method of parameter estimation. A predictive ability test based on bias between observed and predicted flows is used to select the suitable procedure. Based on the results of the simulation, the most suitable statistical frequency procedures for modelling flood flows for the homogeneous regions of Rufiji basin seem to be log-Pearson type 3/method of moments (LP3/MOM) and Pearson type 3/method of probability weighted moments (P3/PWM). The two procedures gave the lowest bias values for different return periods and sample sizes considered in the sUidy. The study is based on the data from 42 sites in the basin
Comparison of Forest Canopy Interception Models Combined with Penman-Monteith Equation.
(2002) Mulungu, Deogratias M. M.; Shiiba, Michiharu; Ichikawa, Yutaka
Three models of interception process: Rutter model with Deardorff's power function, Deardorff model and Modified Kondo model, each in combination with Penman-Monteith equation applied to the same climatic forcing over the year of simulation were compared. The modification of the Kondo's model done in our study includes the water balance component, between storms evaporation and transpiration including the power function, storage changes and the canopy drainage. The comparison was meant for assessing the simple Modified Kondo model developed in Japan and demonstration of the importance of the power function. The Penman-Monteith equation was the kernel for determination of evaporation and transpiration rates. Its use in this study was proposed because it has been widely used in Japan and in experimental sites and therefore can be used as a basis for comparison. Since much interest was on net rainfall, the control volume for the water accounting was between top of the canopy and above the ground surface and hence does not include soil moisture and transpiration. Results showed that forest canopy evaporation ranged from 22 to 29% of gross rainfall. Much model prediction differences were observed in winter, with lower rainfall intensity where wet canopy storages or rainfall did not meet the potential (atmospheric) evaporation demand. The annual net rainfall and transpiration ranged from 71 to 78% of gross rainfall and from 727 to 733 mm respectively. The adopted power function had significant impact on transpiration rate and small impact on evaporation rate for the Modified Kondo model. The Modified Kondo model predicted fairly close to the two models and therefore can be used for providing hourly input into hydrological models. The differences in the predicted hydrological fluxes resulted from the different model for mulations especially throughfall coefficients and drainage functions.
Platinum Catalysed Wet Oxidation of Phenol in a Stirred Slurry Reactor: A Practical Operation Window
(Elsevier, 2003) Masende, Z. P. G.; Kuster, B. F. M.; Ptasinski, Krzysztof J.; Janssen, Frans J. J. G.; Katima, Jamidu H. Y.; Schouten, J. C.
The catalytic performance of graphite supported platinum (5 wt.%) catalyst in liquid phase oxidation has been studied using a continuous flow stirred tank slurry reactor (CSTR) in order to determine the proper operation window. The study was carried out in a temperature range of 120–180 °C and in a total pressure range of 1.5–2.0 MPa. Other operational variables employed were oxygen partial pressure (0.01–0.8 MPa), initial phenol feed concentration (0.005–0.07 M), and catalyst concentration from 1 to 10 kg m−3. It was found that the extent of oxygen coverage on the platinum surface determines the reaction pathway and selectivity to CO2 and H2O. Complete oxidation of phenol to CO2 and H2O could be achieved at 150 °C when the reaction proceeds within the range of weight specific oxygen loads of 0.15–0.35 mol s−1 kgPt−1 and at stoichiometric oxygen excess in the range of 0–80%. The activity of the platinum catalyst remained high when the residual partial pressure of oxygen in the reactor was kept below 150 kPa. Higher residual oxygen partial pressure resulted into deactivation of the platinum catalyst (over-oxidation), which was temporary and could be reversed at reducing conditions. The formation of p-benzoquinone, followed by the formation of polymeric products was also favoured at higher oxygen load, which resulted into permanent deactivation of the platinum catalyst (poisoning). While the platinum surface was vulnerable to poisoning by carbonaceous compounds when insufficient oxygen was used, a fully reduced platinum surface favoured the formation of acetic and succinic acids which are difficult to oxidize. Higher temperatures can enhance the activity of the platinum catalyst, while at lower temperatures catalyst deactivation occurs with increased formation of polymeric products and lower selectivity to CO2 and H2O. In order to maintain the catalyst within the proper operation window, a CSTR is the preferred reactor.
Suitability of Constructed Wetlands and Waste Stabilisation Ponds in Wastewater Treatment: Nitrogen Transformation and Removal
(2003) Senzia, M. A.; Mashauri, Damas A.; Mayo, Aloyce W.
It is estimated that 90% of sewage in cities in developing countries are today discharged untreated into water bodies. In Tanzania, pollution of rivers such as Karanga, Njoro and Rao in Moshi; Mirongo in Mwanza and Themi in Arusha is the cause of frequent disease outbreaks in communities downstreams. Solutions to effluent crisis can be found by its proper treatment and disposal. The principal objective of wastewater treatment is to allow effluents to be disposed without danger to human health or unacceptable damage to the ecology of receiving water bodies. Field investigations were made on pilot scale horizontal subsurface flow constructed wetlands (CW) units located downstream of waste stabilisation ponds (WSP). Six units filled with gravel of 6–25 mm diameters in equal proportion, which gave an initial hydraulic conductivity of 86 m/d were used. While four units covering surface area of 40.7 m2 each, were located downstream of primary facultative pond, the other two units with surface area 15.9 m2 each were located downstream of maturation pond. An attempt was made to compare the output of mathematical models for Phragmites and Typha macrophytes located downstream of primary facultative pond. Based on total inflow nitrogen of 1.457 gN/m2 d, while Phragmites has shown a removal of 54%, Typha had a removal of 44.2%. Furthermore, while the system downstream of primary facultative pond has accretion as a major pathway, accounting for 19.1% of inflow nitrogen, the system downstream of maturation pond has denitrification as its major removal mechanism accounting for 20.5%. In this paper, a comparison of land required by CW and WSP based on the amount of water to be treated is made.
Effects of Substrate Concentrations on the Growth of Heterotrophic Bacteria and Algae in Secondary Facultative Ponds
(Elsevier, 2003) Kayombo, S.; Mbwette, T. S. A.; Katima, Jamidu H. Y.; Jørgensen, S. E.
This paper presents the effect of substrate concentration on the growth of a mixed culture of algae and heterotrophic bacteria in secondary facultative ponds (SFPs) utilizing settled domestic sewage as a sole source of organic carbon. The growth of the mixed culture was studied at the concentrations ranging between 200 and 800 mg COD/l in a series of batch chemostat reactors. From the laboratory data, the specific growth rate (m) was determined using the modified Gompertz model. The maximum specific growth rate (mmax) and half saturation coefficients (Ks) were calculated using the Monod kinetic equation. The maximum observed growth rate (mmax) for heterotrophic bacteria was 3.8 day 1 with Ks of 200 mg COD/l. The mmax for algal biomass based on suspended volatile solids was 2.7 day 1 with Ks of 110 mg COD/l. The mmax of algae based on the chlorophyll-a was 3.5 day 1 at Ks of 50 mg COD/l. The observed specific substrate removal by heterotrophic bacteria varied between the concentrations of substrate used and the average value was 0.82 (mg COD/mg biomass). The specific substrate utilization rate in the bioreactors was direct proportional to the specific growth rate. Hence, the determined Monod kinetic parameters are useful for the definition of the operation of SFPs.

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