Clogging patterns in vertical flow constructed wetland treating combined sewer overflows under different organic loadings | |
| Author | Juthamas Siriporn Na Rajasima |
| Call Number | AIT Thesis no.EV-12-25 |
| Subject(s) | Combined sewers Constructed wetlands |
| Note | A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Environmental Engineering and Management |
| Publisher | Asian Institute of Technology |
| Series Statement | Thesis ; no. EV-12-25 |
| Abstract | Combine sewer overflows (CSOs) typically contains with high concentration of SS and the fluctuated flows due to the nature of rainfall and the runoff behavior of catchment area. Vertical flow constructed wetland (VFCW) is considered in the treatment option for treating CSOs. However, the extremely loads of SS can result in the clogging of bed filter which will reduce the performance of its system and operation time. For investigating the effect of organic loadings, five lab-scale VFCWs of dimensions 1.3 m in height and 0.25 m in diameter were operated by continuous feeding. The HLRs were varied with time from 0.9 to 15 m³/m²d for simulating the rainfall event. Each layer of filter bed contained sand, small and large gravel layer, which the heights are 0.1, 0.15 and 0.35m, respectively. The wastewater was synthesized for two different concentrations of COD and NH4-N which were 180 and 360 mg/L for COD and 19.5 and 39 mg/L for NH4-N. Then it was introduced to each unit by peristaltic pumps. For the treatment efficiencies were done by analyzing chemical oxygen demand (COD), ammonia nitrogen (NH4-N), dissolved oxygen (DO) and total suspended solids (TSSs) of influent and effluent. In addition to the changed of substratum characteristics were investigated by measuring the effective porosity, hydraulic conductivity and the thickness of solid accumulation on wetland surface. Most of pollutants were removed in sand layer especially for SS, which the removal rate was more than 60%. Whereas the treatment performance of NH4-N was very low accounting for about 25% for lower NH4-N units and 10% for higher NH4-N units. For the COD removal was shown the directly proportional with SS removal. Additionally the DO level was decrease in sand filter when the solid accumulation on wetland surface was occurred. The decreasing of hydraulic conductivity was observed in the 360 mg/L of COD unit with non-SS fed system and SS-fed units. Moreover, the correlation between the decreasing hydraulic conductivity and pore space reduction was found very high in the first five weeks for COD 360 mg/L units and first seven week for COD 180 mg/L unit, after that the correlation coefficient was decrease as a result of more accumulated on wetland surface. The fastest clogging was observed in the highest COD concentration with SS-fed. The clogging mathematical model was developed by considered the accumulation of fixed and volatile solid, biofilm and bound water within pore spaces. Monod’s equation was used in this model for calculated the volume of biofilm. The batch experiment was set for obtaining the values of μmax, kd and KS which are equal to 0.166 day-1, 0.001 day-1 and 545.34 mg/L respectively. However, this model can be affected by solid accumulation on wetland media which can result in decreasing of clogging time. Therefore, model’s outcomes were not reliable due to they were calculated from the model which considered only the reduction of pore spaced. |
| Year | 2012 |
| Type | Thesis |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Department of Energy and Climate Change (Former title: Department of Energy, Environment, and Climate Change (DEECC)) |
| Academic Program/FoS | Environmental Engineering (EV) |
| Chairperson(s) | Thammarat Koottatep; |
| Examination Committee(s) | Preeda Pakpian;Shipin, Oleg V.; |
| Scholarship Donor(s) | Royal Thai Government Fellowship; |
| Degree | Thesis (M.Sc.) - Asian Institute of Technology, 2012 |