Development of a biofilm photobioreactor for treatment of septic tank effluent | |
| Author | Chawalit Chaiwong |
| Call Number | AIT Diss. no.EV-21-02 |
| Subject(s) | Biofilms Wastewater--Treatment Septic tanks--Environmental aspects |
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Environmental Engineering and Management, School of Environment, Resources and Development |
| Publisher | Asian Institute of Technology |
| Abstract | Domestic wastewater, especially septic tank effluent, is a one of sanitation issues in developing countries. The effluent form septic tanks containing high amount of water pollutions such as organics, nutrients and pathogens is discharged into the environments; consequently, this could result in several environmental and human health problems. The biofilm photobioreactors (BPBRs) could achieve high organic and nutrient removal rates via algal-bacterial symbiotic reactions e.g., biological organic degradation, biomass assimilation of nutrient matters (nitrogen and phosphorus) and simultaneous nitrification/denitrification. Determination of optimal operating conditions and development of integrated kinetic models for designing and operating the suitable BPBR system as a post treatment technology for treatment of the effluent from septic tank were proposed in this study. In this research, the experiments of the BPBRs units with low-cost attached-growth media were continuously carried out with various conditions i.e. wavelengths of light, hydraulic retention times (HRTs) and loading rates of organic (OLRs), nitrogen (NLRs) and phosphorus (PLRs) and light intensities in different operating stages i.e., stages I-V during about 20 months. The operating stages I and II were conducted in order to investigate effects of wavelengths of light including sole blue (wavelengths of 400-500nm) and red (wavelengths of 600-700 nm) lights and the mixed lights (blue and red) on the performance of the BPBRs. Examining impacts of the operating conditions of HRTs (2-12 days), OLRs (35-175 mgCOD/(L.d)), NLRs (8-45 mgN/(L.d)), PLRs ((0.8- 4.0 mgP/(L.d)) on the treatment and biomass production performances of the BPBR systems were achieved during the operating stages III and IV. The various light intensities (50 - 300 µmol/(m2 .s)) affecting the BPBR performance were studied in the stage V. The experimental results revealed that during the stages I and II, the BPBR with mixed blue and red lights (50:50 ratio) performed highest treatment efficiencies of 85, 87 and 84 % for organics (COD), nitrogen (TN) and phosphorus (TP), respectively, comparing with other BPBRs quipped with sole wavelengths of light, namely, the blue and red lights. These results were also corresponding to the results of biomass production rates in the BPBR units. Moreover, based on the results of nitrogen and phosphorus mass balance analyses of the BPBRs, about 80% (11.3 mgN/(L.d)) and 78 % (0.62 mgP/(L.d)) of the TN and TP removals, respectively were achieved via biomass assimilation in the BPBRs, suggesting its possibility of nutrient recovery via the produced biomass. Accordingly, the mixed blue and red lights was considered to be optimal wavelengths of light for the further experiments during the operating stages III-V. In the experimental stage III, the HRT of 6 days were found as an optimal condition for the BPBRs performing 72, 87 and 81 % for the treatment efficiencies of organics (COD), nitrogen (TN) and phosphorus (TP) concentrations, respectively. Moreover, in the stages IV-V, the experimental results were observed that increases in the OLRs, NLR sand PLRs as well as lighting conditions (e.g., light intensities and daily light integral (DLI)) resulted in enhanced organic and nutrient removal rates, namely ORRs, NRRs and PRRs. Based on the overall derived experimental results of the organic and nutrient treatment performance, the HRT, OLR, NLR, PLR and light intensity of 6 days, 60 mgCOD/(L.d),15 mgN/(L.d) and 1.2 mgP/(L.d) and 150 µmol/(m2 .s), respectively were considered as optimum operating conditions for the BPBRs in treating septic tank effluent. Moreover, as those above-mentioned conditions having effects on the BPBR performance, kinetic models integrated with those factors for COD, TN and TP removals were developed using the multiple regression analysis. Consequently, the developed models were found to be applicable in predicting the performance of the treatment system (R2>0.8). Besides, results of validation of the developed models using the data from literatures were found to be satisfactory with R2 more than 0.9, indicating that they can be applicable in designing and operating the BPBR system for treatment of wastewater. However, experimental studies on a pilot-scale BPBR system are recommended be further conducted for evaluating the practicability of developed kinetic models and the BPBRs system as a post-treatment technology treating septic tank effluent. |
| Year | 2021 |
| 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;Shipin, Oleg;Salin, Krishna R. |
| Scholarship Donor(s) | Royal Thai Government;Asian Institute of Technology Fellowship |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2021 |