One of the most promising approaches in wastewater treatment technology to purify water from cyclic organic compounds and bacteria simultaneously is to use semiconductor nanoparticle based photocatalysts. Ni-doped SnO2 nanoparticles were obtained via co-precipitation method, synthesis procedure was developed to obtain nanoparticles with the same size and shape, but different concentrations of dopant ions and various amounts of defects. It was established that amount of defects, including oxygen vacancies, can be regulated via variation of the synthetic procedure. Obtained nanoparticle samples were tested as photocatalysts on a methylene blue solution under different light sources, including cheap widely available LED lightbulbs. More than 80% of methylene blue degradation was achieved within 60 min. The key parameter affecting the nanoparticles photocatalytic activity, namely the vacancies and defects amounts ratio, was revealed for the first time for three types of photocatalytic procedure (various light sources and stirring methods). Antibacterial activity against E.coli bacteria was studied under bubble stirring, the inhibition activity close to 60% after two hours of irradiation was shown and can be predicted by taking into account the oxygen vacancies and defects amounts ratio and the interaction energy of oxygen molecule with nanoparticle surface. The way for the rational design of simple in production photocatalyst for wastewater treatment was formulated based on experimental and computational data.