This work has examined the effects of pH on the treatment efficiency and biomass production rate of water hyacinth ponds (WHP) treating domestic wastewater. Experiments were carried out outdoor in WHP, working under b...This work has examined the effects of pH on the treatment efficiency and biomass production rate of water hyacinth ponds (WHP) treating domestic wastewater. Experiments were carried out outdoor in WHP, working under batch and subtropical environmental conditions, using pre-treated sewage with pH varying from 5 to 9. It was observed that the plants regulated the pH of the medium to within 6.4 to 7.1 during the treatment processes independently of influent wastewater pH ranges. This adjustment reduced the treatment performances and the biomass production in ponds, the alkaline conditions in ponds being less favorable to the activities of the plants. The optimal removal and biomass production was achieved with influent pH of 7 lying in the above interval. So the optimum influent pH for the growth of plants and the removal of nutrients and organic matters in WHP is within pH 6.4 to pH 7.1.展开更多
Poor wastewater management coupled with lack of sanitation facilities has aggravated the sanitation challenges in developing countries.?This study was aimed at providing information on the current state of sanitation ...Poor wastewater management coupled with lack of sanitation facilities has aggravated the sanitation challenges in developing countries.?This study was aimed at providing information on the current state of sanitation in Cotonou City through surveys. The most common sanitation facilities in the city were septic tanks, latrines and soakaway pits. Mechanical desulging was mainly used (94%) for desludging latrines and septic tanks with a frequency of less than once a year for 73% of the houses;manual desludging was most common for soakaway pits. 84% of sullage generated is disposed without treatment. The only existing stabilization pond plant, managed by a private company SIBEAU, is overloaded;the effluent is poor (up to 2250mg/l BOD5) and does not meet any quality standards. 96% of survey respondents recognise that the sanitation situation in the city is not good;it has to be improved by providing an appropriate and sustainable sanitation management system.展开更多
The growth of duckweed (Spirodela polyrrhiza) was investigated in an outdoor batch system under 15 different conductivities ranging from 200 μS/cm to 3000 μS/cm with average 110 μmol/m2 daylight intensity. The grow...The growth of duckweed (Spirodela polyrrhiza) was investigated in an outdoor batch system under 15 different conductivities ranging from 200 μS/cm to 3000 μS/cm with average 110 μmol/m2 daylight intensity. The growth was performed in an anaerobically treated domestic wastewater using an initial plants population of 50 fronds. Increase in Relative Growth Rate—RGR—(in terms of fresh weight and number of fronds) had a significant non-linear (polynomial) relationship with the conductivity. The maximum RGR related to fresh weight of 0.176 was observed at the conductiviity of 1200 μS/cm while the maximum RGR related to fronds number was 0.193 at the conductivity of 800 μS/cm. The optimum range for duckweeds growth was found to be between conductivities of 600 μS/cm and 1400 μS/cm. The maximal rates of removal of COD of 14.5 mg/day, of 0.65 mg/day, NTK of 15.68 mg/day, faecal coliforms of 100% and turbidity of 80.8% were observed in this range. The COD and PO42- removal rates were highly correlated to the growth rate, with the correlation factor of up to 0.783 and, then to the conductivity. The NTK reduction was positively related to the conductivity.展开更多
A study is presented to evaluate the capabilities of the standard k–ε turbulence model and the k–ε turbulence model with added source terms in predicting the experimentally measured turbulence modulation due to th...A study is presented to evaluate the capabilities of the standard k–ε turbulence model and the k–ε turbulence model with added source terms in predicting the experimentally measured turbulence modulation due to the presence of particles in horizontal pneumatic conveying, in the context of a CFD–DEM Eulerian–Lagrangian simulation. Experiments were performed using a 6.5-m long, 0.075-m diameter horizontal pipe in conjunction with a laser Doppler anemometry （LDA） system. Spherical glass beads with two sizes, 1.5 and 2 mm, were used. Simulations were performed using the commercial discrete element method software EDEM, coupled with the computational fluid dynamics package FLUENT. Hybrid source terms were added to the conventional k–ε turbulence model to take into account the influence of the dispersed phase on the carrier phase turbulence intensity. The simulation results showed that the turbulence modulation depends strongly on the model parameter Cε3. Both the standard k–ε turbulence model and the k–ε turbulence model with the hybrid source terms could predict the gas phase turbulence intensity trend only generally. A noticeable discrepancy in all cases between simulation and experimental results was observed, particularly for the regions close to the pipe wall. It was also observed that in some cases the addition of the source terms to the k–ε turbulence model did not improve the simulation results when compared with those of the standard k–ε turbulence model. Nonetheless, in the lower part of the pipe where particle loading was greater due to gravitational effects, the model with added source terms performed somewhat better.展开更多
Modelling of the agglomeration and deposition on a constricted tube collector of colloidal size particles immersed in a liquid is investigated using the discrete element method （DEM）. The ability of this method to r...Modelling of the agglomeration and deposition on a constricted tube collector of colloidal size particles immersed in a liquid is investigated using the discrete element method （DEM）. The ability of this method to represent surface interactions allows the simulation of agglomeration and deposition at the particle scale. The numerical model adopts a mechanistic approach to represent the forces involved in colloidal suspensions by including near-wall drag retardation, surface interaction and Brownian forces. The model is implemented using the commercially available DEM package EDEM 2.3~, so that results can be repli- cated in a standard and user-friendly framework. The effects of various particle-to-collector size ratios, inlet fluid flow-rates and particle concentrations are examined and it is found that deposition efficiency is strongly dependent on the inter-relation of these parameters. Particle deposition and re-suspension mechanisms have been identified and analyzed thanks to EDEM＇s post processing capability. One-way coupling with computational fluid dynamics （CFD） is considered and results are compared with a two- way coupling between EDEM 2.3 and FLUENT 12.1. It is found that two-way coupling requires circa 500% more time than one-way coupling for similar results.展开更多
文摘This work has examined the effects of pH on the treatment efficiency and biomass production rate of water hyacinth ponds (WHP) treating domestic wastewater. Experiments were carried out outdoor in WHP, working under batch and subtropical environmental conditions, using pre-treated sewage with pH varying from 5 to 9. It was observed that the plants regulated the pH of the medium to within 6.4 to 7.1 during the treatment processes independently of influent wastewater pH ranges. This adjustment reduced the treatment performances and the biomass production in ponds, the alkaline conditions in ponds being less favorable to the activities of the plants. The optimal removal and biomass production was achieved with influent pH of 7 lying in the above interval. So the optimum influent pH for the growth of plants and the removal of nutrients and organic matters in WHP is within pH 6.4 to pH 7.1.
文摘Poor wastewater management coupled with lack of sanitation facilities has aggravated the sanitation challenges in developing countries.?This study was aimed at providing information on the current state of sanitation in Cotonou City through surveys. The most common sanitation facilities in the city were septic tanks, latrines and soakaway pits. Mechanical desulging was mainly used (94%) for desludging latrines and septic tanks with a frequency of less than once a year for 73% of the houses;manual desludging was most common for soakaway pits. 84% of sullage generated is disposed without treatment. The only existing stabilization pond plant, managed by a private company SIBEAU, is overloaded;the effluent is poor (up to 2250mg/l BOD5) and does not meet any quality standards. 96% of survey respondents recognise that the sanitation situation in the city is not good;it has to be improved by providing an appropriate and sustainable sanitation management system.
文摘The growth of duckweed (Spirodela polyrrhiza) was investigated in an outdoor batch system under 15 different conductivities ranging from 200 μS/cm to 3000 μS/cm with average 110 μmol/m2 daylight intensity. The growth was performed in an anaerobically treated domestic wastewater using an initial plants population of 50 fronds. Increase in Relative Growth Rate—RGR—(in terms of fresh weight and number of fronds) had a significant non-linear (polynomial) relationship with the conductivity. The maximum RGR related to fresh weight of 0.176 was observed at the conductiviity of 1200 μS/cm while the maximum RGR related to fronds number was 0.193 at the conductivity of 800 μS/cm. The optimum range for duckweeds growth was found to be between conductivities of 600 μS/cm and 1400 μS/cm. The maximal rates of removal of COD of 14.5 mg/day, of 0.65 mg/day, NTK of 15.68 mg/day, faecal coliforms of 100% and turbidity of 80.8% were observed in this range. The COD and PO42- removal rates were highly correlated to the growth rate, with the correlation factor of up to 0.783 and, then to the conductivity. The NTK reduction was positively related to the conductivity.
文摘A study is presented to evaluate the capabilities of the standard k–ε turbulence model and the k–ε turbulence model with added source terms in predicting the experimentally measured turbulence modulation due to the presence of particles in horizontal pneumatic conveying, in the context of a CFD–DEM Eulerian–Lagrangian simulation. Experiments were performed using a 6.5-m long, 0.075-m diameter horizontal pipe in conjunction with a laser Doppler anemometry （LDA） system. Spherical glass beads with two sizes, 1.5 and 2 mm, were used. Simulations were performed using the commercial discrete element method software EDEM, coupled with the computational fluid dynamics package FLUENT. Hybrid source terms were added to the conventional k–ε turbulence model to take into account the influence of the dispersed phase on the carrier phase turbulence intensity. The simulation results showed that the turbulence modulation depends strongly on the model parameter Cε3. Both the standard k–ε turbulence model and the k–ε turbulence model with the hybrid source terms could predict the gas phase turbulence intensity trend only generally. A noticeable discrepancy in all cases between simulation and experimental results was observed, particularly for the regions close to the pipe wall. It was also observed that in some cases the addition of the source terms to the k–ε turbulence model did not improve the simulation results when compared with those of the standard k–ε turbulence model. Nonetheless, in the lower part of the pipe where particle loading was greater due to gravitational effects, the model with added source terms performed somewhat better.
文摘Modelling of the agglomeration and deposition on a constricted tube collector of colloidal size particles immersed in a liquid is investigated using the discrete element method （DEM）. The ability of this method to represent surface interactions allows the simulation of agglomeration and deposition at the particle scale. The numerical model adopts a mechanistic approach to represent the forces involved in colloidal suspensions by including near-wall drag retardation, surface interaction and Brownian forces. The model is implemented using the commercially available DEM package EDEM 2.3~, so that results can be repli- cated in a standard and user-friendly framework. The effects of various particle-to-collector size ratios, inlet fluid flow-rates and particle concentrations are examined and it is found that deposition efficiency is strongly dependent on the inter-relation of these parameters. Particle deposition and re-suspension mechanisms have been identified and analyzed thanks to EDEM＇s post processing capability. One-way coupling with computational fluid dynamics （CFD） is considered and results are compared with a two- way coupling between EDEM 2.3 and FLUENT 12.1. It is found that two-way coupling requires circa 500% more time than one-way coupling for similar results.
