|Title:||Novel vegetated sequencing batch biofilm reactor for treating suburban domestic wastewater|
|Subject:||Hong Kong Polytechnic University -- Dissertations.|
Sewage -- Purification.
Sewage -- Purification -- Biological treatment.
|Department:||Department of Civil and Structural Engineering|
|Pages:||xix, 268 leaves : ill. ; 30 cm.|
|Abstract:||Common small-scale domestic wastewater treatment systems such as waste stabilization ponds, lagoons and constructed wetlands are limited to usages in rural areas with small wastewater flows due to their large land requirements and relatively low pollutant treatment efficiencies. Though constructed wetland has gained most popularity among the various biological wastewater treatment methods with its successful applications in small communities worldwide, its large footprint and long retention time restrict it from serving beyond the rural areas to the suburban areas with larger wastewater flows, in where conventional municipal treatment facilities are too costly to be installed. In this study, a practical and affordable wastewater treatment system serving small community in suburban areas was studied. The principal of the system studied capitalizes on the pollutant removal mechanisms of the soil-plant-microbial interactions of constructed wetlands. The short comings of conventional constructed wetland were attempted to be eliminated by optimizing the operating conditions for equivalent treatment efficiency. The system studied is a vegetated sequencing batch biofilm reactor integrated with the rhythmical movement of wastewater and air like that of a sequencing batch reactor. The controlling factors of pollutant removals being studied included plant, contact time, rhythmical movement of air/wastewater, dissolved oxygen and temperature. Nutrients in the domestic wastewater, which cause environmental nuisance like eutrophication, was targeted to be gotten rid of by the process. Bench experiments were designed and carried out on the medium, namely coal slag and the plant, namely Cyperus alternifolius in the system. Two parallel systems were set up in both laboratory-scale and pilot-scale. The data from the lab-scale experiments were used to establish the nutrient mass balances and to understand the conversion efficiencies of pollutants through different removal mechanisms. Adsorption and microbial degradation dominated in the removal processes at different stages of operation for different pollutants while plant uptake played a minor role. The planted systems in the laboratory-scale experiment showed enhanced ammonia nitrogen removal over the unplanted system. With the longest contact time being tested in the pilot system, the treatment systems achieved around 60 % removal efficiency for carbonaceous matters. The removals of ammonia nitrogen and phosphorus were about 50 and 40 %, respectively, while the removal of total suspended solids was approaching 80 %. Multivariate regression, first-order kinetics and mass balance models were developed for the prediction of effluent concentration of ammonia nitrogen. The sensitivities of the controlling factors in the mass balance model, including influent ammonia nitrogen concentration, contact time, temperature and dissolved oxygen, were analysed. With the in-depth understandings of the effects of operating conditions on the system performance, contour plots were prepared from the ammonia nitrogen removal predictive model under two temperature ranges of temperate climate. The required contact time for achieving any desired levels of removal efficiencies could be predicted under different influent concentrations. Treating the domestic wastewater from small community, specifically in suburban areas, the system was found to be cost-effective compared to the conventional activated sludge processes and constructed wetlands, for equivalent treatment efficiencies.|
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