Investigation of Chromium Removal Efficiency from aqueous Solution Using of Powdered Activated Carbon Produced using Ultrasonic Waves oleh Fatemeh Alsadat Arghavan, Rasoul Khosravi, Ali Akbar Taghizadeh, Mahmoud Taghavi, Athar Entezari, Monireh Khazaei, Reza Ali Fallahzadeh