By Prof. Bob Andoh

Many developers and municipalities have invested in filtering systems to meet the US EPA mandate for reducing these storm water runoff problems. Their experiences reveal a fundamental flaw in the design of conventional “down flow” filtration. The capital investment in these immense systems — sometimes spanning whole football fields in size — is tremendous and regular maintenance is cost-prohibitive.

By Prof. Bob Andoh

Across the United States, wastewater treatment plant operators face a common problem that threatens the effectiveness of their plants. It’s grit. Grit erodes mechanical equipment and accumulates in channels and process chambers causing capacity and operational problems. Grit accumulation in primary and secondary process basins diminishes a plant’s performance, reduces its treatment capacity, and increases operational and maintenance costs. Grit is a continuous and common problem, which impacts treatment plants worldwide. However, the solution which will most effectively remove it can vary by plant.

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 Dr. Bob Andoh

For years municipalities around the globe have invested in stormwater treatment systems to remove pollutants from runoff. Whether they are used for stand-alone treatment or as pretreatment devices to keep our infiltration bays from clogging, these “sedimentation devices” have an important role in stormwater treatment. Yet a troubling problem has emerged and become more apparent: many proprietary treatment systems don’t hold what they catch. When flows increase, previously captured pollutants can re-suspend and discharge right out of the system. Moreover, many communities are not aware of this phenomenon — known as “washout” — leaving them with a false sense of security about the ability to keep their waterways clean.