BACKGROUNDWastewater management has become a great concern recently due to industrial and domestic discharges containing metals, organic pollutants and pathogenic microbes that contaminate water bodies and also cause waterborne diseases. Although there have been multiple conventional processes for removing contaminants, nanomaterials have recently gained importance for wastewater treatments. RESULTSHere, ZnONPCS with an average size of 10nm was successfully synthesized by using casein as biogenic reducing and capping agent. Removal of three metals and two dyes was investigated and it was found that nearly 90% was removed. Adsorption isotherm data were best fitted with the Langmuir model, and the maximum adsorption capacity (mgg(-1)) was found to be 156.74 for Cd(II), 194.93 for Pd(II), 67.93 for Co(II), 115.47 for methylene blue and 62.19 for congo red. Repeated cycles of regeneration and reuse showed a drop in removal efficiency of 10-13%. Further, nanoparticles also showed efficient photo-degradation of dyes within 240min. Moreover, ZnONPCS demonstrated high antibacterial potential for Escherichia coli in the presence of metals and dyes. CONCLUSIONBiogenic synthesized ZnONPCS demonstrated simultaneous removal of metals, dyes as well as pathogenic microbes, and could be used as a cost-effective and reusable system in various industrial effluent treatments. (c) 2018 Society of Chemical Industry