Mathematical modeling of dissolved oxygen in fish ponds

A mathematical model was developed to predict the effects of wind speed, light, pH, Temperature, dissolved carbon dioxide and chemical oxygen demand (COD) on Dissolved Oxygen (DO) in fish ponds. The effects of organic feeds, aeration and fish activity were added to the model developed by Kayombo et al. for Waste Stabilization Ponds (Ecological Modelling 127(2000): 21 - 31) to reflect the situation in fish ponds. Model calibration and validation was done by use of average DO, pH, temperature, COD, CO2 and algae biomass data measured from RETCO fish ponds in Dar es Salaam; and light intensity data were adopted from Kayombo et al. (2000). Model results showed a linear relationship between simulated DO and measured DO in fish pond (r2 = 0. 87) for model calibration and (r2 = 0.88) for model validation. Simulation results also showed a general decrease of DO with time in 13 days by 28 and 38% for first and second batch, respectively. Thus, the model developed in this study could be used to predict the DO dynamics in fish ponds. Based on the model results, successful cultivation of healthy fish may require that retention time for water in the fish pond be 10 days.Key words: Calibration, light, pH, substrate, temperature, validation

Performance of Solanum incunum Linnaeus as natural coagulant and disinfectant for drinking water

The paper reports the performance of Solanum incunum Linnaeus as coagulant and disinfectant for water purification. The coagulation-flocculation experiment was carried out using a Phipps and Bird PB-700™ Jar Tester. Results show that coagulation depends on Fe(II) content and disinfectant on bioactive natural product compounds from the plant. Turbidity removals were 96, 97 and 75% for raw water with turbidity of 450, 300 and 105 NTU, respectively. Fecal coliform removal increased with coagulant concentration, displayed a maximum removal of 99% at 2.2 × 10-4 g/ml. LD50 ranged from 0.62-2.6 × 10-5 g/ml, which were within the range of optimum coagulation concentration of 2.2 × 10-5 g/ml. Turbidity and SO42- concentrations for the treated water conforms to the Tanzanian Standards and WHO guidelines for drinking water, while fecal coliform counts exceeded the recommended values. The results suggest that S. incunum is promising as coagulant and disinfectant product for water purification.Key words: Coagulant, disinfection, fecal coliform, Solanum, turbidity, water

Wetlands for wastewater treatment and subsequent recycling of treated effluent : a review

Due to water scarcity challenges around the world, it is essential to think about non-conventional water resources to address the increased demand in clean freshwater. Environmental and public health problems may result from insufficient provision of sanitation and wastewater disposal facilities. Because of this, wastewater treatment and recycling methods will be vital to provide sufficient freshwater in the coming decades, since water resources are limited and more than 70% of water are consumed for irrigation purposes. Therefore, the application of treated wastewater for agricultural irrigation has much potential, especially when incorporating the reuse of nutrients like nitrogen and phosphorous, which are essential for plant production. Among the current treatment technologies applied in urban wastewater reuse for irrigation, wetlands were concluded to be the one of the most suitable ones in terms of pollutant removal and have advantages due to both low maintenance costs and required energy. Wetland behavior and efficiency concerning wastewater treatment is mainly linked to macrophyte composition, substrate, hydrology, surface loading rate, influent feeding mode, microorganism availability, and temperature. Constructed wetlands are very effective in removing organics and suspended solids, whereas the removal of nitrogen is relatively low, but could be improved by using a combination of various types of constructed wetlands meeting the irrigation reuse standards. The removal of phosphorus is usually low, unless special media with high sorption capacity are used. Pathogen removal from wetland effluent to meet irrigation reuse standards is a challenge unless supplementary lagoons or hybrid wetland systems are used

Environmental-energy analysis and the importance of design and remanufacturing recycled materials

This paper proposes a framework that interrelates the life cycle of the product, remanufacturing and recycling for plastics. The paper analyses the different chemical processes of recycling polymer wastes. We introduce a thermodynamic calculation of the energy consumed and CO2 emissions for all types of waste(municipal, electronic, vehicle). The remanufacturing process could reduce the amount of CO2 emissions through feedback to the product design stage with robust platforms that extend the product life cycle. In order to meet the requirements of remanufacturing we combine mechanical and chemical recycling solutions. These recycling processes must undergo a thermodynamic analysis to optimize energy and decrease the minimum CO2 emissions, i.e. recycling processes in line with the ultimate objective, which isthe reduction of CO2 emissions and slowing a part of the problem global warming