In the removal of ammonia with a dose of chlorine followed by contact with activated carbon, pH determines the major chlorine species. The studies reported herein indicate that a pH value near 4.5 should be avoided, because NHCI2 predominates and thus 10 parts by weight of chlorine are required for each part of NH3-N oxidized to N2. At a slightly higher pH and using acclimated and activated carbon, the portion of mono-chloramine increases and the chlorine required per unit weight of NH3-N oxidized should approach 7.6 parts, ignoring the chlorine demand resulting from other substances. However, further testing should be used to verify this conclusion in each case.
Laboratory studies at Blue Plains in Washington (Pressley et al., 1970 and 1973), in which buffered distilled ammonia nitrogen solutions of 20 mg/l concentrations were subject to breakpoint-chlorination dosages, showed a definite optimum pH for breakpoint in the range of pH 6 to 7. The chlorine dosage at optimum pH levels were found to be 8:1 (chlorine to ammonium-N).
The reaction rate has not been measured quantitatively, but it has been noted that the reaction is very rapid (Morris, 1965). The optimum pH for the reaction rate is 8.3, but at pH 6-7 the reaction is completed in 0.2 seconds.
There is no evidence that normal variations in the temperature of waste water effluents and initial mixing conditions affect the nitrogen removal by this process.
Organic nitrogen is to a certain extent removed by the breakpoint-chlorination according to Brown and Caldwell (1975), while Taras (1953) has reported a very slow reduction of amino acids.
Nitrate and nitrogen chloride are occasionally found in the effluents from the breakpoint-chlorination process.
An increasing level of pretreatment decreases the amount of chlorine required to achieve breakpoint, as demonstrated in Table 8.2, where results reported by Pressley et al. (1973) and Brown and Caldwell (1975) are summarized. Increase of total dissolved solid will generally imply a higher chlorine to ammonium-N ratio.
The application of activated carbon for dechlorination is recommended, as it serves several functions other than removal of residual chlorine. Carbon, as demonstrated in Section 8.1, can effectively catalyze the chemical reactions and remove soluble organics through adsorption. Table 8.2.
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