In storm drains of coastal cities, anaerobic conditions result in the production of odorous hydrogen sulfide. A proposed solution to the odor emission problem is to introduce iron-based granules into the storm drain that oxidize the odorous hydrogen sulfide to odorless substances. The granules can be regenerated by reacting with oxygen in sea water. At high tide, rapidly opening a gate installed at the downstream end of the storm drain discharging into the sea generates a dam break flow. The current study investigates the feasibility of the dam break flow to assist with the recovery of exhausted chemicals by suspending the solid mixture and hence providing opportunities for the granules to react with the oxygen in the sea water.

The study is based on a new set of experiments th...[ Read more ]

In storm drains of coastal cities, anaerobic conditions result in the production of odorous hydrogen sulfide. A proposed solution to the odor emission problem is to introduce iron-based granules into the storm drain that oxidize the odorous hydrogen sulfide to odorless substances. The granules can be regenerated by reacting with oxygen in sea water. At high tide, rapidly opening a gate installed at the downstream end of the storm drain discharging into the sea generates a dam break flow. The current study investigates the feasibility of the dam break flow to assist with the recovery of exhausted chemicals by suspending the solid mixture and hence providing opportunities for the granules to react with the oxygen in the sea water.

The study is based on a new set of experiments that were carried out in the Water Resources Laboratory at HKUST by building a semi-infinite reservoir representing the sea (8.0 m long and 2.0 m wide) and a storm drain (6.6 m long, 0.3 m wide, 0.35 m high and slope 1:20) into the towing tank. The dam break flow was generated by lifting the gate that separated the storm drain from the reservoir in 0.3 s.

Iron granule regeneration experiments, in which the H₂S removal capacity of the granules was obtained, confirmed the capability of dam break flows to assist with the regeneration. The recovery potential varies with distance into the channel from very good to poor. The recovery potential is enhanced by increasing the number of dam break events and the time of inundation for the sediment and iron particle mixture in the water. Sediment transport and preliminary hydrodynamic experiments were carried out to understand the bulk flow behavior and sediment movements induced by the dam break. An imaging technique was used to obtain observations and measurements of the flow depth. The results showed that the suspension of sediments decreases rapidly with distance from the gate and the difference in the behavior of the flow and the sediments for an initially dry or wet storm drain was small. The recovery potential of iron granules is therefore not significantly affected by the different dam break flow types with good regeneration potential close to the gate under both flow conditions.

To understand the detailed hydrodynamics of the dam-break flow from an infinite reservoir into a positively inclined channel of finite width, experiments were carried out in which a PIV and LIF system were used to measure the flow velocity and flow depth respectively. The results highlighted the effects of the infinite reservoir on the flow behavior, including the presence of cross-waves, large free surface waves, and the absence of divergence in the flow. For an initially wet channel, the initial partial blockage results in a smaller flow rate into the channel, but the flow has the same features as those for the initially dry channel. The effect of the smaller flow rate becomes smaller with distance along the sloping channel.