Laboratory experiments were carried out to examine the effects of chelating agents on heavy metal extraction from slightly contaminated dredged sediments from the port of Livorno (Italy). Ethylene diamine tetraacetate (EDTA), citric acid (CA) and humic substances (HS) were tested in two different concentrations each: 120 and 480, 500 and 2,000, 500 and 1,000 mg/l, respectively. Solubilisation of heavy metals (Cu and Zn) was observed for both EDTA and HS in the extraction kinetic experiments: 58% of the total Cu and 50% of the total Zn in the sediment were mobilised from the solid matrix using EDTA (480 mg/l) and 32% of the total Cu and 5% of the total Zn, using HS (1,000 mg/l). It was observed that solubilized metal levels were positively related to the chelating agent concentration. HS performance in the heavy metals mobilisation and phyto-toxicity tests was considered promising. HS represent an innovation in enhanced phytoextraction techniques: they can be considered an environmentally non-impacting bioagronomic amendment. CA induced no significant effects on heavy metal mobilisation and it also negatively affects seed germination (Germination Index<40%). Laboratory experiments with plants showed that none of the treatments significantly affected the biomass production and a trend could only be detected for the heavy metal uptake into shoots of Paspalum vaginatum sp. Transplantation of seashore paspalum is useful as a pre-treatment of contaminated dredged sediments, since it is a salttolerant species and it can be easily adaptable on a nutrient poor and fine textured medium.
Aeration represents the main part of energy consumption in the low-load activated sludge process. Because of its ability to remove the various kinds of pollution (carbonaceous, nitrogenous) with a high dependability level, this process is the most widespread throughout France, particularly in its tropical overseas regions. A previous study led the authors to set up a graph which links energy savings and effluent quality (carbonaceous and nitrogenous pollution removal). This graph appears useful as well to monitor biological phosphorus removal in the low-load activated sludge process including an anaerobic basin.
In order to optimize pollution removal and energy savings, ORP regulation has been carried out since January 1983 on the Yffiniac plant (West of France). It was preferred to dissolved oxygen (D.O.) regulation because of the low values of D.O. observed in this plant and the difficulties of operating D.O. regulation.
A laboratory and full-scale study shows that ORP regulation is possible and particularly accurate as a contribution to optimizing pollution removal, energy savings and operating conditions. Since then other ORP Regulations have been installed. The observations we made specify which cases lend themselves to successful ORP regulation.
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