A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Environmental Engineering and Management

Thesis (M.Sc.) - Asian Institute of Technology, 2019

Goals of this study were to study effects of organic loading rates (OLRs) and carbon/nitrogen ratio (C/N) on the performance of up flow thermophilic septic tank (UTST) for treating toilet wastewater under intermittent feeding pattern, 24 hours of hydraulic retention time and thermophilic condition (50°C) which three laboratory-scale UTST reactors were operated for two months. This study was divided into two phases. Phase I was the study of the performance of three laboratory-scale UTST reactors under 8 kg COD/(m3.d), 4 kg COD/(m3.d) and 2 kg COD/(m3.d) OLR, and operating period of phase I was one month. Fresh excreta collected from Talad Thai (Thai market) was mixed with tap water to dilute the COD concentration to be in the range 2,000 - 8,000 mg/L during phase 1. Performances of each OLR revealed that at 8 kg COD/(m3.d), biogas production was 2.28 ± 2.39 Lid, methane production was 1.56 ± 1.81 Lid which both biogas and methane yield were the highest. Acetic acid and propionic acid were the found mainly and less amount of butyric acid at this OLR which amount of acetic acid, propionic acid and butyric acid were 191.39, 198.04 and 36.12 mg/L, respectively. At 4 kg COD/(m3.d), TCOD and TKN removal efficiencies were the highest which were 74.64 ± 3.20% and 36.71 ± 12.13%, respectively. Butyric acid could not be detected, only acetic acid and propionic acid could be found. The amounts of acetic acid and propionic acid were 142.0 and 83.12 mg/L, respectively. At 2 kg COD/(m3.d), removal efficiency of TCOD and TKN were nearly the same as at 4 kg COD/(m3.d) which were 73.29 ± 3.58% and 36.15 ± 9.39%, respectively. Individual VFAs of2 kg COD/(m3.d) were not much different at 4 kg COD/(m3.d), butyric acid could not be detected. The amounts of acetic acid and propionic acid of this loading rate were 120.78 and 47.07 mg/L, respectively. Phase II of this study was operated for one month, 4 kg COD/(m3.d) was maintained to all reactors under the same conditions as phase 1. Fresh excreta was mixed with tap water and molasses. Moreover, NH4CI was added to maintain TCOD/TKN ratios to be 2511, 1011 and 511. Tendency of TCOD/TKN, TCOD, TKN, ammonia nitrogen (NH3-N) removal efficiencies along with yields and production of biogas and methane were found to be decreasing when TCOD/TKN ratio was decreasing. At 2511 of TCOD/TKN, TCOD,TKN and ammonia nitrogen (NH3-N) removal efficiencies were 74.41 ± 7.09 %,25.41 ± 3.09 %, 23.41 ± 10.70%, respectively and production ofbiogas and methane were 11.67 ± 5.97 and 6.38 ± 3.43 Lid. Yields ofbiogas and methane were 0.138L biogas/g TCODinfluentand 0.076 L CH4/g TCODinfluent. At 1011 of TCOD/TKN, TCOD, TKN and ammonia nitrogen (NH3- N) removal efficiencies were 67.38 ± 6.30%, 18.69 ± 5.04% and 14.05 ± 8.96%, respectively, and production of biogas and methane were 5.17 ± 0.66 and 3.35 ± 0.62 Lid. Yields of biogas and methane were 0.066 L biogas/g TCODinfluent and 0.043 L CH4/g TCODinfluent. At 511 of TCOD/TKN, TCOD, TKN and ammonia nitrogen (NH3-N) removal efficiencies were 53.48 ± 17.88%, 15.04 ± 4.09% and 9.87 ± 9.41 %, respectively and production of biogas and methane were 2.45 ± 0.85 and 1.55 ± 0.61 Lid. Yields of biogas and methane were 0.030 L biogas/g TCODinfluent and 0.019 L CH4/g TCODinfluent.