Effects of various configurations of the on-site wastewater treatment units on hydraulic characteristics | |
| Author | Pluem Chuaychoo |
| Call Number | AIT Thesis no.EV-18-25 |
| Subject(s) | Sewage disposal plants Sanitation--Thailand |
| Note | A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering in Environmental Engineering and Management |
| Publisher | Asian Institute of Technology |
| Series Statement | Thesis ; no. EV-18-25 |
| Abstract | On - site sanitation systems are served as a primary sedimentation unit of the toilet wastewater which its removal mechanism is solid sedimentation. Solid sedimentation is influenced by internal hydraulic conditions of the tank. Hydraulic s of the tank are influenced by 1) tank shape, 2) tank dimensions, 3) baffle, and 4) pipe works. Hence, this study aimed to determine hydraulic characteristics which are affected by different tank configurations. The experimental tanks consisted of 600 L full scale circular, cylindrical, and rectangular tanks which each shape had two configurations of with and without baffle. Circular tanks were used to simulate commercial septic tanks, cylindrical tanks were simul ated as a cesspool system which is widely used in Thailand , and rectangular tanks were simulated as a constructed septic tank. Tracer study was a tool to determine hydraulic characteristics such as mean residence time, dispersion number, short - circuiting index, hydraulic efficiency ( l ), and dead space. In this study, NaCl was used as a tracer chemical and was injected into the reactor by pulse injection. NaCl effluent concentrations were analyzed and plotted on RTD curves. As a result, mean residence time varied between 18 hours to 28 hours which the tanks without baffle provided less mean residence time that the tanks with baffle. Dispersion numb ers were found to be in the range of low dispersion to high dispersion. Short - circuiting indexes were approximately 0.005 to 0.05 which showed that the tracers exit the tank very shortly after the injection and the total time spent were much greater and every tank was classified as short - circuited. Hydraulic efficiencies ( l ) were under 0.4 which every tank indicated poor hydraulic efficiency. Dead spaces were found to be in between 6 – 26 percent of the total volume of the tank. Tanks dimension such as water depth, flow length and surface area influenced the hydraulic characteristics by, deeper tank provide d more dispersion and reduce short - circuit, longer flow increased mean residence time and reduce dead space, more surface area provide longer mean residence time, and hydraulic efficiency ( l ) reduced dispersion degree and dead space. Another experiment was Hydraulic Efficiency test (according to EN 12566 - 1 standard). The aim of this ex periment was to determine solid retention capacity of a testing tank by using polystyrene beads to simulate solids. As a result, the tanks without baffle could obtain hydraulic efficiencies in the range between 80 – 9 0 percent which were less than the standard of 99.5 percent, whereas the tanks with baffle could obtain 98.9 – 99.9 percent. This means that the baffle walls help in retaining the solids. Vari ations of solid loadings and flow rates influenced by reducing hydraulic efficiencies of the tanks with ba ffle as the increasing of solid loadings and flow rates. However, these variations did not affect the hydraulic efficiencies of the tanks without baffle. It was found that tank dimensions did not affect hydraulic efficiencies, the important thing is hydraulic characteristics instead. Nonetheless, sedimentation is not th e only key of treatment in on - site wastewater treatment system. There is a need to combine high mixing in order to stimulate microbial activity and low mixing to let the solids to sediment before exiting the tank. To enhance effectiveness of the on - site sa nitation facilities’ performance , at least, septic tank should have two compartments which are mixing and sedimentation parts. Mixing part should provide long residence time , high mixing, and less dead space for effectiveness of biodegradation and reductio n in sludge stabilization. Another compartment is to allow residual solids to settle in order to increase the effectiveness of treatment and reduce environmental pollution. |
| Year | 2018 |
| Corresponding Series Added Entry | Asian Institute of Technology. Thesis ; no. EV-18-25 |
| 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) | Shipin, Oleg V.;Hongchai Kanabkaew; |
| Scholarship Donor(s) | Royal Thai Government Fellowship; |
| Degree | Thesis (M. Sc.) - Asian Institute of Technology, 2018 |