Development of nitrogen transformation model for vertical flow constructed wetland treating faecal sludge | |
| Author | Atitaya Panuvatvanich |
| Call Number | AIT Diss. no.EV-10-01 |
| Subject(s) | Constructed wetlands Sewage sludge Sewage--Purification--Nitrogen removal |
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Engineering in Environmental Engineering and Management |
| Publisher | Asian Institute of Technology |
| Series Statement | Dissertation ; no. EV-10-01 |
| Abstract | Faecal sludge (FS) typically contains high concentrations of pathogens and be contaminated with several other pollutants, which could also be valuable nutrients (especially N) for agricultural use. Vertical flow constructed wetland (VFCW ) is regarded as a promising treatment option, and technically feasible for sludge dewatering, stabilisation and humification . Knowledge of nitrogen (N) transformation in VFCW system could be useful to further system design or development. The main objective of study is to comprehensively determine N transformation pathways and kinetics of the processes corresponding to each form of N such as organic nitrogen ( O rg - N), ammonia nitrogen (NH 4 - N) and nitrite+nitrate nitrogen (NOx - N) in VFCW. The residence time distribution (RTD) analysis was applied as a tool for determining hydraulic behavior of VFCW units under different feeding and drainage patterns and under different hydraulic loading rates (HLR). Tracer experiments were undertaken in lab oratory - scale VFCW systems to examine RTD . The experimental results showed that the drainage pattern could affect hydraulic behavior. Free drainage pattern, percolate impounding w ould cause the increase in HRT by about 1.6 times of those of free drainage. No significant difference in the hydraulic behaviour could be observed at the continuously - fed VFCW units at HLRs varying between 0.025 and 0.300 m 3 /m 2 .d . Hydraulic behaviour of VFCW c ould be then described as moderate dispersion by which tank - in - series ( TIS ) model would precisely describe the hydraulic behaviour, whereas the delay - TIS model could be applied at HLRs lower than 0.050 m 3 /m 2 .d . The exper iments on N transformation were divided into 2 runs : the 1 st run – VFCW units were fed with high N wastewa ter (HNWW) at NH 4 - N of about 300 mg/L (AIT campus wastewater added with Ammonium Chloride (NH 4 Cl )) and the 2 nd run – FS was fed at solid loading rate (SLR) of 250 kg TS/ m 2 year. Seven units of laboratory - scale VFCW were installed and operated at different mode s i.e. drainage patterns (free v.s. percolate impounding); sludge accumulation layer (0, 10, 20 cm); sand layer depth (10, 20, 40 cm). N mass balance in VFCW units was determined in order to identify N transformation pathways. About 25% and 34% of T N mass from HNWW were disappeared in sand and gravel layer s, respectively. Approximately 50% of TN mass accumulated in sludge layer, w hereas 13% wa s disappeared in sand layer and 14% were decreased in gravel layer of VFCW units treating FS. Ammonia volatilization from the accumulated sludge layer was about 0.035 – 0.037 g N/m 2 .week , which was only 0.01% of TN losses in VFCW treating both HNWW and FS. Plant uptake was ranged from 0.07 – 0.23 and 0.15 – 0.29 g N/m 2 week in VFCW units treating HNWW and FS, repectively . Nitrification reaction could occur in both sand and gravel layer s, amounting to the range s of 6.21 – 8.81 g N/m 2 week ( 13% ) and 4.38 – 8.77 g N/m 2 week ( 9.5% ) of TN influent for HNWW experiment and ranged from 5.12 – 17.19 g N/m 2 week ( 3% ) and 2.78 – 4.69 g N/m 2 week ( 1% ) of TN influent for FS experiment . Denitrification reaction could also occur in both sand and gravel layer s which ranged from 5.21 – 8.27 g N/m 2 week ( 7% ) and 5.81 – 8.57 g N/m 2 week ( 9.8% ) of TN disappearance for HNWW experiment and ranged from 5.90 – 16.26 g N/m 2 week ( 6% ) and 2.21 – 5.01 ( 8% ) of TN disappearance for FS experiment . Based on hydraulic and N mass flow studies, N transformation model s w ere developed by applying compartment analysis technique. The sequen tial - N model deserves serious considerations for describing the reactivity of different N species incorporates to the iv sequential N transformations. Actual field data from lab experiments were used to calibrate a proposed N transformation model. The N tra nsformation model satisfactorily predicts the mean effluent mass for O rg - N , NH 4 - N and NOx - N . The underestimated O rg - N and NH 4 - N mass as well as the overestimated NOx - N mass are validat ed from both VFCW units treating HNWW and FS. The investigations on decay rate of O rg - N, NH 4 adsorption and nitrification capacity of filter material s are recommended by considering VFCW configuration , operating conditions and model development for enhanced nitrogen recovery or removal. With the unde rstandings of N transformation in VFCW units obtained from this study, recommendations for future research and field application are list as follows: i) Investigation on N decay rate from accumulated sludge, ii) Investigations on NH 4 adsorption and nitrifi cation capacity of the VFCW media , iii) The compartmentalized models should be modified by incorporating the effects of N and BOD loadings together with other factors such as pH, DO and sand depth and iv) Long term study on demonstrated VFCW system in term of operation, economic and social acceptance. |
| Year | 2010 |
| Corresponding Series Added Entry | Asian Institute of Technology. Dissertation ; no. EV-10-01 |
| Type | Dissertation |
| 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 ;Preeda Parkpian ;Ranamukhaarachchi, S. L. ;Kone, Doulaye |
| Scholarship Donor(s) | Velux Foundation ;Swiss Federal institute of Aquatic Science and Technology (Eawag), Switzerland |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2010 |