| Author | Rawintra Eamrat |
| Call Number | AIT Thesis no.EV-14-11 |
| Subject(s) | Septic tanks
|
| 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-14-11 |
| Abstract | On-site sanitation systems are typically installed to treat toilet wastewaters in areas without sewer and centralized treatment systems. There are various designs of the on-site sanitation systems such as one cesspool, two cesspools in series, three cesspools in series and commercial packages or septic tanks. It is widely known that treatment performance of the on-site sanitation systems are not satisfactory in removals of pathogen and organic matters likely due to inappropriate design and operation. One of the main factors affecting treatment performance of the septic tanks were the flow patterns and hydraulic retention times (HRTs). This research aims to investigate the hydraulic conditions occurring in septic tank unit and the effects of HRTs on the system performance. The experiments were conducted with a laboratory-scale septic tank (40 L in size) and actual septic tank (600 L in size) to test the hydraulic conditions occurring by using tracer study. Operating conditions of experimental septic tanks were HRTs at 12, 24 and 48 h. due to limitation of the configuration of the tanks and flow effects. This study used two types of tracer chemicals such as NaCl and Rhodamine dye. A single shot impulse of a tracer chemical was fed at the influent and measurement concentration of the tracer at the effluent. The results of tracer study were determined according to the normalized resident time distribution (RTD) curves showed that the dispersion numbers in the range of 0.017-0.320 and the short-circuit ratios were in the range of 0.014-0.031, indicating the reactors approaching complete-mix conditions and high short-circuiting values. For the experimental of treatment performance of laboratory-scale septic tank under HRT of 24 h and reactor temperature were controlled at 30°C and 40°C, the removal efficiencies of these two laboratory-scale septic tanks were not high and not much different due to the removal mechanism is mainly sedimentation of solids. The percent removal of TCOD, BOD5, TS and TVS were found in the range of 69-76%, 67%, 62-72% and 70-77%, respectively. Moreover, the data of the laboratory-scale actual septic tanks, which revealed unsatisfactory levels of treatment performance having effluent concentration exceeding the discharge standards due to high degree of short-circuiting and improper design and operation. A modified complete-mix model was developed based on the relationship between BOD5 removal efficiencies and HRTs, which fitted well with the laboratory-scale and actual-scale septic tanks data as the correlation coefficient (R2) to be 0.7935 and fitted well when validated with other septic tanks data from previous studies as the correlation coefficient (R2) to be 0.9018. However, the complete-mix model cannot apply for pathogen removals due to the concentration of fecal coliforms were not significantly reduced at the designed HRTs. Therefore, to better protect our environment and minimizing health risks, new generation toilet should be developed that could minimize short-circuiting and improving treatment performance for increasing organic matter and pathogen reduction efficiencies. |
| Year | 2014 |
| 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) | Chongrak Polpasert;Annachatre, Ajit P. |
| Scholarship Donor(s) | Asian Institute of Technology Fellowship |
| Degree | Thesis (M.Sc.) - Asian Institute of Technology, 2014 |