PREDICTIVE REAL TIME CONTROL OF SURCHARGED INTERCEPTORS: IMPACT OF SEVERAL CONTROL PARAMETERS1

ABSTRACT: A global predictive real time control strategy minimizing overflow volumes from combined sewers during rainfall was applied to control flows entering the Marigot interceptor (Laval, Canada) for 23 rain events that occurred in this urban area during the summer of 1989. Different surcharge intensities were allowed in the sewer. The duration of the control horizon as well as the location and number of control regulators were varied to assess the impact of these parameters on total overflow volumes and on control safety. Due to the high propagation speed of flow waves in pressurized conduits, it was found that five‐ minute control horizons were sufficient to ensure control performance and safety when important surcharges were permitted in the interceptor and when the controlled regulators were located where pressurized flow occurred. It was also found that it is possible to reduce the number of controlled regulators by placing them at locations intercepting the largest volumes of water during rain periods.     

Dynamics of copper and zinc sedimentation in a lagooning system receiving landfill leachate

This study characterises the sediment dredged from a lagooning system composed of a settling pond and three lagoons that receive leachates from a municipal solid waste (MSW) landfill in France. Organic carbon, carbonate, iron oxyhydroxides, copper (Cu) and zinc (Zn) concentrations were measured in the sediment collected from upstream to downstream in the lagooning system. In order to complete our investigation of sedimentation mechanisms, leachates were sampled in both dry (spring) and wet (winter) seasonal conditions. Precipitation of calcite and amorphous Fe-oxyhydroxides and sedimentation of organic matter occurred in the settling pond. Since different distributions of Zn and Cu concentrations are measured in sediment samples collected downstream in the lagooning system, it is suggested that these elements were not distributed in a similar way in the leachate fractions during the first stage of treatment in the settling pond, so that their sedimentation dynamics in the lagooning system differ. In the lagoons, it was found that organic carbon plays a major role in Cu and Zn mobility and trapping. The presence of macrophytes along the edges provided an input of organic matter that enhanced Cu and Zn scavenging. This edge effect resulted in a two-fold increase in Cu and Zn concentrations in the sediment deposited near the banks of the lagoons, thus confirming the importance of vegetation for the retention of Cu and Zn in lagooning systems.     

History of Bioengineering Techniques for Erosion Control in Rivers in Western Europe

Living plants have been used for a very long time throughout the world in structures against soil erosion, as traces have been found dating back to the first century BC. Widely practiced in Western Europe during the eighteenth and nineteenth centuries, bioengineering was somewhat abandoned in the middle of the twentieth century, before seeing a resurgence in recent times. Based on an extensive bibliography, this article examines the different forms of bioengineering techniques used in the past to manage rivers and riverbanks, mainly in Europe. We compare techniques using living material according to their strength of protection against erosion. Many techniques are described, both singly and in combination, ranging from tree planting or sowing seeds on riverbanks to dams made of fascine or wattle fences. The recent appearance of new materials has led to the development of new techniques, associated with an evolution in the perception of riverbanks. This study was part of a research project on river bioengineering funded by the French Ministère de l’Ecologie, de l’Energie, du Développement Durable et de l’Aménagement du Territoire, Direction Générale de la Prévention des Risques.     

The anthropogenic atmospheric elements fraction: A new interpretation of elemental deposits on tree barks

The superficial deposit on the bark surface of several trees (mainly Fraxinus excelsior L.) was sampled in the experimental station of the university campus in Grenoble (France). Its composition was studied by scanning electron microscopy–energy dispersive X-ray emission (SEM–EDX) and, after digestion, by inductively coupled plasma-mass spectrometry (ICP-MS). The deposit was composed of 81.3% ± 7.4 organic matter, 9.4% ± 4.9 of geogenic minerals issued from the atmosphere (atmospheric geogenic fraction: AGF) and 9.3% ± 2.7 of a mixture of elements which was called anthropogenic atmospheric elements fraction (AAEF). The SEM–EDX analysis showed the presence of particles of geogenic compounds such as different types of silicates, phosphates, carbonates, sulphates, oxides and also particles of metals such as iron or of alloys of Fe–Zn, Fe–Ni, Ni–Cr and Ca sulphates or phosphates. Typical spheres of “fly ashes” composed of pure iron or Al-silicates were detected. Using the SEM–EDX analysis of the deposit and the average local soil composition, an empiric formula for the AGF (without polluting elements) was chosen, which presented a clear analogy with the global formula of the upper continental crust. In the same way, a formula for the pure organic matter fraction was chosen. Withdrawing the elements corresponding to these two fractions allows a tentative estimation of the content of the AAEF which was supposed to better represent the elemental anthropogenic contamination issued from the atmosphere. In the station, most of Sb, Cd, Sn, Pb, Cu, V and Zn were found in the AAEF. This AAEF composition was compared to that of the deposit in a highway tunnel where Pb and Cu were at a very high level. The meaning and the limits of the AAEF concept were critically discussed.