QUANTITATIVE IN-SITU MONITORING OF ORGANOHALOGEN COMPOUNDS IN DOMESTIC SEWAGE RESULTING FROM THE USE OF HYPOCHLORITE BLEACH

A field monitoring program was carried out on the sewage of five large apartment blocks in the city of Parma, Italy, to verify under realist ic conditions existing laboratory data and model calculations on organ ohalogen formation by domestic hypochlorite (NaOCl) bleach usage. The average adsorbable organic halogens (AOX) level was determined for thr ee distinct experimental phases: an ''undisturbed period,'' a ''no ble ach period,'' and a ''controlled bleach usage period.'' The study invo lved participation of the site inhabitants in the second and third pha ses. In line with what could be predicted from the hypochlorite chemis try, an effect of the use of hypochlorite bleach on the AOX concentrat ion in domestic sewage was detected. In a laboratory simulation conduc ted in parallel with the field study, the degree of NaOCl-to-AOX conve rsion ranged from 0.75 to 2.25% (w/w). The degree of conversion in the field study itself was of the order of 1.5% (or 0.075% when expressed for a typical bleach product containing 5% NaOCl). Under the specific conditions of the site, the difference in average AOX concentration i n sewage between the ''no bleach'' and the ''undisturbed'' bleach use period was of the order of 37 mu g . l(-1) (P < 0.05). The average ble ach-related AOX emission at the study site was around 7 mg .(inhabitan t . day)(-1). Overall, these figures correspond well with existing lit erature data. Linking the measured amounts of AOX with available ecoto xicity data for treated domestic effluents and their organohalogen con stituents, it can be considered unlikely that the organohalogens forme d by domestic bleaching will exert or trigger any adverse environmenta l effect. Copyright (C) 1996 Elsevier Science Ltd