Biochemical oxygen demand (BOD) is defined as ............ in ppm of O2.
(1) Required to sustain life
(2) The amount of oxygen required by bacteria to break down the organic matter present in a certain volume of a sample of water.
(3) The amount of oxygen required by anaerobic bacteria to break down the inorganic matter present in a certain volume of a sample of water.
(4) Required photochemical reaction to degrade waste
