Nitrogen removals in vertical flow constructed wetland with low-cost substrata treating fecal sludge | |
| Author | La Thien Luan |
| Call Number | AIT Thesis no.EV-08-17 |
| Subject(s) | Constructed wetlands Sewage--Purification--Nitrogen removal |
| Note | A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineer in Environmental Engineering and Management |
| Publisher | Asian Institute of Technology |
| Abstract | Raw fecal sludge (FS) contains high concentration of pollutants. Improper disposal of FS caused serious typically problems in both rural and urban areas of developing countries such as health impacts, water pollution, air pollution, etc. Vertical-flow constructed wetland (VFCW) was known as a low-cost treatment option which could achieve high nitrogen (N) removal efficiency, but likely the major cost is due constructed wetland (CWs) the substrata i.e. sand or gravel. Minimize construction cost of CWs by determining alternative substrata is a focus of the study. The experiments employed five lab-scale and one pilot-scale VFCW units. Four lab-scale units were designed with different low-cots substrata such as plastic filters (circular shape, CW-PF), broken brick (CW-B), plastic bottle segments (CW-PB) and charcoal (CW-C) that were used to compare treatment performance with conventional substrata (small gravel, CW-G). Pilot-scale unit (CW-PS) had same substrata as used in CW-G to determine scale-up effect on treatment performance. Every units were operated by feeding FS intermittently loading at a frequency of once a week and 6 days percolate impoundment. Lab-scale units were fed at the solid loading rate of 250kg total solids (TS)/m².yr (corresponding to about 8m³ /wk at pilot-scale unit). To investigate nitrification and denitrification rates, five in-situ VFCW units were installed with the similar substrata arrangement of the lab-scale units. After operating for 6 months, accumulated sludge layer onto substrata bed was measured of 28-41 cm (42-47% of TS mass balance), but clogging problem was only observed in CW-PF unit. About 40-43% water was lost via evapotranspiration and retained into substrata bed. Yield of cattails was calculated in range of 1.97-3.06kg DW/m².yr. Some cattails death was occurred in CW-PF and CW-B at 3rd month and in CW-G, CW-PB, CW-PS at 6th month, but no death plant observed in CW-C. All VFCW units could achieve high efficiency in treating FS in ranges of 93.2%-96.7% for TS and suspended solids (SS); 97.2%-98.8% for Total chemical oxygen demand (TCOD) and Biochemical oxygen demand at 5 days (BOD5); and 95.5%-98.7% for Total Kjeldahl nitrogen (TKN) and Total nitrogen (TN). Removal efficiencies CW-C was stable and higher than other units of 0.2-1.1% (TS), 0.8-1.3% (BOD5), 0.7-1.5% (TCOD), 1.9-2.6% (TKN) and 1.5-2.4% (TN). CW-B and CW-PB could obtain removal efficiencies relatively low as compared with those of CW-C and CW-G. It was differed significantly from TN removal efficiencies of pilot-scale unit and CW-G (p<0.01). Nitrogen removals via nitrification and denitrification were observed at the range of 52.4-98.7gN/m².wk and 17.0-19.9gN/m².wk, respectively. Based on the N mass balance in every VFCW units, N mass in percolate, plant uptake and accumulated into accumulated sludge were accounted of 2.4% -4.4%, 0.2%-0.3% and 17.7%-20.0%, respectively. N conversion via for nitrification was 13.9%-26.2% and via denitrification of 3.8%-5.3% of total N mass. Unaccounted N mass was about of 47.4-56.6% possibility due to ammonia volatilization and retention into substrata bed. The study has demonstrated that some low-cost substrata can replace with conventional substrata to reduce construction cost. Charcoal was achieved the best treatment performance. Besides removal efficiencies of broken brick and plastic bottle are lower than conventional substrata but they could consider with lowest construction cost. Thus, broken brick and plastic bottle segment are suitable in cots to apply at developing countries to resolved raw FS, solid waste of construction and plastic waste problems. |
| Year | 2008 |
| 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 and Management (EV) |
| Chairperson(s) | Thammarat Koottatep; |
| Examination Committee(s) | Preeda Pakpian;Nowarat Coowanitwong; |
| Scholarship Donor(s) | Ministry of Education and Training (MOET), Vietnam;Asian Institute of Technology Fellowship; |
| Degree | Thesis (M.Eng.) - Asian Institute of Technology, 2008 |