Photocatalytic degradation of slaughterhouse wastewater (SHWW) through TiO2 and Ag-TiO2 catalysts alone and in combination with hydrogen peroxide (H2O2) under both UV irradiation and sunlight, and photocatalytic inactivation of pathogens and their regrowth potential in treated SHWW have been investigated in this study. The slaughterhouse wastewater characteristics, including BOD (1078.45 mg/l), COD (2024.5 mg/l) and total nitrogen (83.07 mg/l) were found extremely higher than National Environmental Quality Standards (NEQs) for BOD (80 mg/l), COD (150 mg/l) and nitrogen (40 mg/l). Thus, the wastewater requires treatment for safe disposal into water bodies. The performance of catalysts (TiO2, Ag-TiO2) alone or combined with other processes was a function of process conditions such as pH of the reaction medium, dose of catalyst, treatment time and type of light source. Catalysts performed well in acidic medium (pH 3) and efficiency of catalysts increased with increasing catalyst dose and treatment time only up to their optimum values. The application of TiO2 and Ag-TiO2 catalysts under UV irradiation (400 W lamp) for the degradation of slaughterhouse wastewater at optimal process conditions (pH 3; catalyst dose of 1 g/l; treatment time of 40 min), resulted in 87.02% BOD, 72.34% COD and 63.89% nitrogen removals and 89.98% BOD, 75.01% COD and 65.09% nitrogen removals respectively. Silver doped titanium dioxide (Ag-TiO2) catalyst performed better than TiO2 as silver doping on TiO2 significantly enhances photocatalytic activity and working under sunlight. Under optimum conditions (pH 3, catalyst dose of 1.5 g/l and sunlight exposure time of 90 min), Ag-TiO2 catalyst yielded 85.16% BOD, 73.0% COD and 63% total nitrogen (TN) removal from SHWW, whereas TiO2 showed maximum BOD, COD and nitrogen removal efficiency in the tune of 50%, 40% and 37%, respectively under optimum conditions ((pH 3, catalyst dose of 1.5 g/l and sunlight exposure time of 120 min). The degradation efficiency of Ag-TiO2 combined with H2O2 (Ag-TiO2/H2O2), irrespective of the mode of applications (mobilized, immobilized) and source of light used (UV irradiation, sunlight), was found to be spectacular due to the increase of both synergetic and sustained release of powerful oxidizing hydroxyl radicals of TiO2 nano-particles and H2O2 together with silver ions and electron-hole separations at the surface of nano TiO2 by the silver ions. Thus, under optimum conditions (pH 3, 1 g/l catalyst dose, 40 min UV irradiation exposure time and 0.5 ml/l H2O2) and (pH 3, catalyst dose 1.5 g/l, 90 min sunlight exposure time and 1 ml/l H2O2), maximum BOD, COD and nitrogen removal efficiencies reached to 95.08%, 86.66% and 73.51% and 94.15%, 84.34 % and 72.31% under UV irradiation and sunlight, respectively. The application of TiO2 catalyst showed 99.9% elimination of pathogens (total coliform, fecal coliform and escherichia coli) under UV irradiation time of 15 min. Almost same removal efficiency was achieved with TiO2 under sunlight exposure time of 100 min. The disinfection efficiencies of Ag-TiO2 alone and combined processes like TiO2/H2O2, and Ag-TiO2/H2O2, irrespective of light source used (UV irradiation, sunlight) were however amazing due to the synergetic photocatalytic antibacterial activity of TiO2 nano-particles and H2O2 together with silver ions and complete removal of pathogens was obtained at very short treatment time under both UV irradiation and sunlight. The dominance of processes, like Ag-TiO2, TiO2/H2O2 and Ag-TiO2/H2O2 to eliminate pathogens over TiO2 alone under both UV irradiation and sunlight with regard to regrowth of pathogens in slaughterhouse wastewater treated with these processes validated by the fact that there was no regrowth in Ag-TiO2, TiO2/H2O2 and AgTiO2/H2O2 treated SHWW samples in the presence of nutrients and favorable temperature (35oC) even after 21 days period of time. It appears from the results that synergetic photocatalytic degradation and antibacterial activities make Ag-TiO2/H2O2 system potentially applicable to treat slaughterhouse wastewater under both light sources.