Development of a novel multi-soil layering based constructed wetland treating solar septic tank effluent | |
| Author | Prattana Suksiri |
| Call Number | AIT Thesis no.EV-17-16 |
| Subject(s) | Constructed wetlands septic tanks |
| 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-17-16 |
| Abstract | Disposal of untreated black water poses an environmental threat and leads to the contamination of the water bodies. Solar septic tank which was a modification of conventional septic tank with solar-heated water was considered to be an effective on-site sanitation technology. Even though the solar septic tank is proposed to increase the removal efficiency of pollutants, effluent from solar septic tank does not still meet the national discharged standards of Thailand. Post-treatments such as soil absorption systems or constructed wetlands to remove the contaminants from the effluent is required. The post-treatment systems normally require large land areas, which are not suitable for dense urban areas. To overcome the limitations, the study of a multi-soil-layer system based constructed wetland (MSL-CW) was developed and applied for post-treatment of the septic tank effluent. This study aimed to investigate the performance of MSL-CW operating at different hydraulic retention time (HRT) for treating solar septic tank effluent and to develop and validate kinetic model of MSL-CW which was compared with controlling unit as a vertical flow constructed wetland (VFCW). These experiments were carried out in laboratory scale. The MSL pilot (high 60 cm, width 40 cm, length 40 cm) was composed of red soil mixed with sawdust and charcoal at ratio of 80, 10 and 10%, respectively, on dry weight basis, and the permeable layers were composed of zeolite. In addition, the controlling unit used the general soil containing the less Fe content as media in VFCW. Vetiver grasses were planted in these systems. Four systems were operated at varied hydraulic retention time (HRT) of 10, 20,36 and 20 hrs (MSL-CW1, MSL-CW2, MSL-CW3 and VFCW, respectively). The effluent of solar septic tank had an average chemical oxygen demand (COD), biochemical oxygen demand (BOD5), ammonia nitrogen (NH3-N), total suspended solids (TSS) and total phosphorus (TP) concentration of 197.72±36.76, 71.54±21.23, 57.76±6.45, 53.81±13.13 and 5.88±1.28 mg/L, respectively. The experimental results showed that MSL-CW unit operating at the HRT of 20 h could remove TCOD, BOD, NH3-N, TSS and TP better than the VFCW unit. The HRT of 10 h resulted in the lowest TCOD, BOD, NH3-N, TSS and TP removal efficiencies of 77, 79, 94, 70% and 75%, while the HRT of 36 h resulted about 84 % for TCOD, 85 % for BOD, 97 % for NH3-N, 85 % for TSS and 90 % for TP, respectively. The MSL-CW3 with HRT 36 hours showed significantly (p values < 0.05) effect on effluent treatment. These results showed the effective of MSL-CWs for treating the septic tank effluent to meet the standard. To develop a design platform, the combined first order kinetic and complete-mixed equation was applied to the MSL-CW system. The k values of TCOD, BOD and NH3-N removal rates determined from the first order kinetic equation of these experimental results were found to be 1.42, 1.54 and 10.33 d-1, respectively. The first order kinetic model was validated satisfactorily with the literature data of the MSL-CW for treating wastewater. These k values could be used for MSL-CW system design for treating septic tank effluents and other on-site sanitation systems. To identify the contribution of microorganisms in the removal mechanism, the microbial community compositions and diversities of the multi-soil layering based constructed wetland and vertical flow constructed wetland using PCR and Mi-seq techniques revealed the distributions of AOA (Nitrososphaera cluster) and AOB (Nitrosospira and Nitrosomonas cluster) that involved to NH3-N removal efficiency. The MSL-CW3 found that percent abundant of AOA and AOB higher than VFCW4 effect to also higher in NH3-N removal efficiency. Moreover, the MSL-CW3 detected anaerobe bacteria groups in SMBs and aerobe bacteria groups in PLs that effected to TCOD and BOD5 removal efficiencies. |
| Year | 2017 |
| 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) | Chongrak Polprasert;Shipin, Oleg V.; |
| Scholarship Donor(s) | Royal Thai Government Fellowship; |
| Degree | Thesis (M.Eng.) - Asian Institute of Technology, 2017 |