Kinetics of organic matter and fecal micro-organism removal in free water surface constructed wetlands | |
| Author | Khatiwada, Nawa Raj |
| Call Number | AIT Diss. no. EV-99-2 |
| Subject(s) | Constructed wetlands Sewage--Purification--Organic compounds removal |
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Engineering, School of Environment, Resources and Development |
| Publisher | Asian Institute of Technology |
| Abstract | Constructed wetlands are attractive alternatives to solve water pollution problems as they fulfil the requirements of both treatment and waste recycling. This study was undertaken to investigate the organic matter and fecal microorganisms removal kinetics in free-water-surface (FWS) constructed wetlands treating domestic wastewater. The basic kinetic principles were applied to establish the engineering design criteria for the FWS constructed wetlands systems located in the tropical region. The kinetic model of organic matter removal was based on the activity of biofilm bacteria attached to the bed media. Based on the chemical oxygen demand (COD) removal performance and intrinsic biofilm characteristics, the value of effective specific surface area exploited by the biofilm in degrading the influent organic matter was estimated from the biofilm models considering both slab and cylindrical geometries of the media. With the biofilm kinetic model, a typical value of first-order COD removal rate coefficient was estimated as 0.42 day-• or 44 m/yr. The removal kinetics of fecal coliform and bacteriophage was described by the first-order rate equations incorporating the effects of temperature, light and the media filtration. The removal rate coefficient due to media attachment was assessed by a single-collector model previously used for the modelling of colloidal particle transp01t in porous media. The typical first-order fecal coliform and bacteriophage removal rate coefficients were estimated as 1.61 day·• or 168 m/yr and 0.91 day-• or 95 m/yr, respectively. The effluent concentrations of organic matter and fecal microorganisms in the pilot scale constructed wetland units, predicted from both dispersed flow and plug flow equations using model calculated removal rate coefficients, were found comparable with the observed values, suggesting the applicability of both equations in either estimating the hydraulic retention times needed for a desired removal efficiency or predicting the effluent concentrations of FWS constructed wetland systems in operation. The uncertainty of the design equations due to stochastic variability of the input parameters was assessed by the Monte Carlo simulation technique. The probability distributions of the effluent concentrations of organic matter and fecal microorganisms were determined from the repeated deterministic calculations with the random input variables drawn from the probability density functions. The distribution suggested that single point estimates of effluent concentrations based on the mean influent values were merely representing fifty percentiles indicating a larger uncertainty in the long-term prediction. The impact of variability can be minimised by either keeping a nominal safety factor or by designing the units with higher percentiles of input variables. |
| Year | 1999 |
| 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 and Management (EV) |
| Chairperson(s) | Chongrak Polprasert; |
| Examination Committee(s) | Annachhatre, Ajit P. ;Takizawa, Satoshi ;Lin, C. K. ;Haberl, -lng. Raimund; |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 1999 |