Chlorination - concepts and methods.
Chlorination is employed to prevent the growth of bacteria and algae and to destroy organic contaminants. The chlorinating agent can be either calcium or sodium hypochlorite but more often chlorine gas is used. Chlorination can be carried out either by the chlorine ammonia or the break point process. In the former the chlorine reacts with ammonia, already present or added, to produce chloramines. In the latter, chlorine is added until there is residual free chlorine in addition to combined chlorine in the form of mono, di, or trichloramines. By the break point method ammonia is removed within 1 min at pH 7.3. Organic matter may also be oxidized at this pH but a contact time of 4 h may be necessary. Typical doses are: for the removal of ammonia, 10 x NH3 N; for the removal of iron (optimum pH 7.0), 0.64 x Fe content; for the removal of manganese (optimum pH 10), 1.3 x Mn content; and for the control of bacteria, algae, and slime organisms, 1.0 to 10.0 ppm. The fouling of ion exchange resins with organic matter can be minimized by chlorination but some resins cannot tolerate more than 0.3 ppm of residual chlorine. Excess chlorine can be destroyed with SO2. The chlorinator consists of a device to maintain a constant pressure across a rotameter and a control valve. The gas is fed into the water by a vacuum injector which automatically closes the chlorine valve if the vacuum is broken. The capacity of the chlorinator (kg chlorine/day) may be calculated from the flow of water/day x level of chlorine (ppm) x 10-6. Chlorinators with capacities between 1.3 and 3600 kg/24 h are available. Manual control can be used to treat a constant flow of water to a constant level but automatic control is necessary for variable flow and/or variable demand situations.
Keywords: brewing chlorination disinfectant equipment