By Professor Robert Andoh

Burgeoning commercial and industrial development is putting increased pressure on drainage systems. Land and vegetation act as a natural filtration system during storms. The conversion of open space to impervious materials such as roads, buildings, and parking lots increases the volume of runoff and the risk of downstream flooding. Worse, too fast an influx of water into the drain overtaxes combined sewage systems, causing untreated sewage to spill out into waterways.

Until recently, most developers and municipalities in the U.S. relied on end-of-pipe solutions such as large detention tanks, deep tunnel storage systems, and high rate treatment facilities to combat urban flooding problems. However, these large, structurally intensive systems are extremely costly to purchase and to maintain.

To alleviate these challenges, many in the U.S. are now looking to an alternative approach long relied on in Europe and the U.K. More than 16,000 vortex flow controls, also known as vortex “valves”, are installed around the world to manage water flow in stormwater storage schemes, stormwater sewers, combined sewers and wastewater treatment plants. These novel devices are useful for many applications, including inlet control and stormwater storage.

By Prof. Bob Andoh

Current estimates of the costs required to address combined sewer overflow (CSO) problems are in the $50 billion range and rising. The majority of the cost is made up of chambers and other equipment required to separate solids and disinfect the much higher volume of stormwater-sewage mix that is generated during heavy rains. These estimated costs are based on the use of conventional technology, which requires relatively large sedimentation and contact tanks in order to achieve the level of solids separation or disinfection needed to meet applicable environmental regulations.

Hydrodynamic vortex separators (HDVSs) have been identified as a possible means of reducing the capital expenditures required to address CSOs. A key advantage is that a single HDVS is capable of both solids separation and disinfection, providing a significant reduction in the capital expenditures required to handle CSOs. Another advantage is that the flow properties of a single HDVS can be optimized to greatly improve the efficiency of both solids separation and contact disinfection compared to conventional technology. This means that HDVSs can handle the same CSO volume as conventional contact tanks that are 5 times larger. The resulting reduction in tank size and construction costs typically reduces overall project costs by about 50%.

By Robert Y.G. Andoh, Mike Faram and Dave Scott

Water industry officials throughout Europe – and in a growing number of municipalities in North America – tend to think of vortex valves as a novel technology for outlet flow control on a stormwater detention system. Most of these 17,000+ valves installed around the world are, in fact, implemented on stormwater detention schemes because use of a valve can reduce the required storage volume by up to 50% while still meeting the maximum discharge requirement. But vortex valves actually have many other uses in stormwater, wastewater and combined sewer systems. These versatile devices tackle a number of other problems, including erosion control, re-oxygenation of water and flow equalization in wastewater treatment plants.

By Prof. Bob Andoh 

Communities with CSO issues lack adequate funds to undertake the required level of capital and operations and maintenance investments without a potential near doubling of local rates and fees. Conventional systems are costly and this, coupled with the funding constraints and issues of affordability, clearly highlights the need for more innovative, cost-effective and sustainable “alternative approaches” to resolving the current collection systems and wastewater treatment needs and challenges.

The use of satellite treatment systems located within collection systems provides the scope for resolving some of the challenges in urban wastewater infrastructure provision in a cost-efficient manner as demonstrated in Saco, Maine, and Columbus, Georgia. Monitoring and operation of these full scale systems has confirmed that high-rate processes such as vortex separator, either on its own or followed by compressed media filter, can be used to remove the gross solids and the lighter fraction of fine particulates while passively optimizing in-system storage.