We present the technical and engineering design of a medium energy (10 MeV) and high average power (1000 kW) electron-beam accelerator intended for irradiation treatment of high-volume industrial and municipal wastewater. The accelerator uses a ${\mathrm{Nb}}_{3}\mathrm{Sn}$ superconducting radio-frequency (SRF) cavity for producing the high average beam power with $>90%$ rf to beam efficiency. The design of the accelerator is tailored for industrial settings by adopting the cryocooler conduction-cooling technique for the SRF cavity instead of a conventional liquid helium bath cryosystem. The technical design is supplemented with a detailed analysis of capital and operating cost of the accelerator. The designed accelerator can treat up to 12 million gallons per day of wastewater, requires capital of $\ensuremath{\sim}$8\text{ }\text{ }\mathrm{M}$ for construction, and has $\ensuremath{\sim}13.5\text{ }\text{ }\textcent{}/\mathrm{ton}/\mathrm{kGy}$ in material processing cost.