Optimisation of the coagulation-flocculation process of raw water by optimal design method.

In the present paper, a systematic study of the influence of raw water quality and operating conditions on the effectiveness of the coagulation-flocculation process using aluminium sulphate (AS) is presented. The influence of raw water composition is studied at two levels, fractional factorial designs and a Doehlert uniform shell design to determine the influence of the operating conditions. The analysis of the experimental responses (residual turbidity and minimally AS dose are denoted as (Tu(m)) and (AS(m)), respectively) shows that the parameters which have the greatest influence change depending on the response. It is not always possible, for a given water composition, to obtain simultaneously low residual turbidity and minimally AS dose. However, under the conditions of this study, the search for a criterion of optimisation must bear the minimisation of residual turbidity, because it remains the principal criterion of effectiveness of the process, even, if in a few cases, it results in an increase in the cost of treatment.

Antioxidant activity of flavonoids: efficiency of singlet oxygen (1 delta g) quenching.

Flavonoids, polyphenolic pigments widely present in plants, have been reported to act as scavengers of various oxidizing species. However, most often an overall antioxidant effect was measured. In this paper we report the results of a systematic study of the reactivity of 13 selected flavonoids (from the flavonol, flavone, flavanone and flavane families) with singlet oxygen (1O2(1 delta g)) in order to establish a structure-activity relationship. The rate constants of the chemical reaction of these flavonoids with 1O2(k r) and their rate constants of 1O2 physical quenching (kq) have been determined by kinetic measurements and near-IR singlet oxygen luminescence. The efficiency of the physical quenching is mainly controlled by the presence of a catechol moiety on ring B, whereas the structure of ring C (particularly the presence of a hydroxyl group activating the double bond) is the main factor determining the efficiency of the chemical reactivity of these compounds with 1O2. The total reactivity factor determining the efficiency of the chemical reactivity of these compounds with 1O2. The total reactivity scale is dominated by kq, which is in general higher than kr. (+)-Catechin is the most efficient quencher of the series.