December 2013, Vol. 25, No.12

Problem Solvers

Road reconstruction with green infrastructure scheme

Heavy-duty porous asphalt and vortex separators control stormwater  
   

Problem: A reconstructed high-traffic, lakeside road needed improved stormwater controls.  

Solution: Installing heavy-duty porous asphalt and vortex separators eliminated either captured pollutant-laden water or separated out much of the contaminants. 

  

When a four-lane wide, 1.6 km- (mile-) long stretch of Warren County’s Beach Road located along the southern shore of Lake George in New York needed to be reconstructed, it presented the opportunity to implement innovative and protective measures to reduce the effects of polluted stormwater runoff. The existing roadway originally drained directly to the lake, resulting in the deposition of roadway contaminants such as salt, sediment, and the deleterious particles that are attached to the sediment directly into the lake. 

The project is a major step in protecting the pristine nature and water quality of the lake, which is of paramount importance to Warren County, Lake George, and the nearby New York State Department of Environmental Conservation’s (NYSDEC) Million Dollar Beach, a pair of favorite summer tourist destinations. 

To address this concern, Thomas Baird, project manager and chief engineer in the Albany office of Barton & Loguidice (Syracuse, N.Y.), and his project team designed a solution for the road surface and drainage involving a heavy-duty, pervious pavement system coupled with conveyance relief areas and offsite contamination protection systems. 

  

Infiltrate what’s possible  

The porous pavement system was designed to capture and store 125 mm (5 in.) of rain in a 24-hour period, and then allow the stormwater to infiltrate the subgrade below. The relief areas would convey any excess runoff from larger storms that may occur into a drainage network that discharges directly into Lake George. 

This design offered the best solution given the challenges of the project, which included property acquisition restraints, continuous high traffic, the close proximity to the lake, the flatness of the site, and the high potential for offsite contamination.  

  

Capture and treat the rest  

As a highway reconstruction project, the original project scope did not include separate stormwater quality treatment structures in the relief areas, though the project team recommended a more proactive and fail-safe approach for improved runoff quality. Intersecting roadways that are paved with conventional impervious pavement would generate sediment-laden runoff that could overburden the pervious pavement in certain areas. In other areas, runoff from the conventional pavement would not flow over any pervious pavement and would instead be discharged directly into the lake without treatment. 

Even with the many brands of stormwater treatment devices approved for use using Federal Highway Administration, New York State Department of Transportation, and Warren County funds, the design team had a particular vortex separator in mind as a best fit for the project. 

However, publicly bid projects using public funds carry requirements for competitive opportunities. Once the project was out to public bid, the contractor selected the Downstream Defender® based on the stringent requirements of the project and what the project site demanded. This is the same choice the project team had come to, so the design team approved the plan and the project proceeded into the construction phase. 

The Downstream Defender is an advanced vortex separator, manufactured by Hydro International (Portland, Maine) and designed to remove hydrocarbons, total suspended solids, and their associated pollutants, such as metals, from stormwater runoff. It is a low-headloss separator, making it a good fit for this project due to the limited elevation in the drainage profile. 

  

Building the system  

The precast, offsite design and construction, and small footprint of the vortex separators were key factors in it being chosen — the site was limited in both space and elevation. The separators’ inlet/outlet configuration requires very little hydraulic drop and fit within the overall drainage profile, and the round shape allowed more flexibility for inlet/outlet pipe angle orientation. 

Three units were installed in the first phase of the project — a 1.8-, 2.4-, and 3-m (6-, 8-, and 10-ft) unit — each one size larger than what the NYSDEC design standards required. (See figure, p. 84.) 

The design team elected to use one model size larger in the two smaller 1.8- and 2.4-m (6- and 8-ft) locations because they expected high concentrations of sediment to be present in the off-site generated runoff, and the separator systems discharge directly into the lake. With the larger units, there is little concern that they would be overburdened between cleanings, which will take place twice a year. The relative costs were minimal to achieve a reasonable factor of safety in sediment storage and with that assurance also came a higher water quality treatment rate. 

Warren County, the project’s sponsor and lead agency, also received funding from the New York State Environmental Facilities Corporation’s Green Innovation Grant Program to support these green innovations, and to set up a testing program to ensure actual results. 

When the $7.5-million project is completed, Beach Road will be the first heavy-traffic roadway in New York State paved with porous asphalt. Beach Road will be under a 3-year monitoring program to measure runoff volumes and quality of the discharge. The two additional units specified would be installed along the porous pavement in a subsequent construction phase should area rainfall amounts increase, if the area’s watershed significantly increases the volume of stormwater runoff, or if the porous pavement is not renewed or replaced at the end of its life cycle. 

“The Beach Road project is a model for integrating green and gray stormwater management techniques for a cost-effective, low-impact design. This public–private initiative is raising the bar for projects in sensitive areas, where satisfying the minimum is simply not enough,” Baird said.  

  

  

Anaerobic treatment benefits Thailand sugar cane mill 
  

Problem : A sugar cane mill needed a wastewater treatment process. 

Solution : Install an anaerobic wastewater treatment system that transforms wastes into energy. 

  

Reusing wastes has produced many rewards for a sugar cane mill located in Khon Kaen, Thailand. The United Farmer and Industry Co. Ltd. (Chaiyaphum, Thailand) mill was commissioned to be built earlier this year. The mill was designed for a capacity of 3500 m3/d containing 22,750 kg/d chemical oxygen demand (COD).  

Because sugar cane processing now uses less water than it has in the past, the wastestream has an increased concentration of carbon. This higher carbon content in the wastestream enabled the mill to use an anaerobic system to produce biogas while its effluent volume decreased. 

 “We are now getting toward the stage where instead of having a series of huge anaerobic and aerobic lagoons impacting the environment, we can treat the effluent in contained anaerobic reactors where biogas is extracted and influent wastewater is cleaned of most of its impurities without release to the environment,” said Jean Pierre Ombregt, CEO of Global Water Engineering (GWE; Bangkok). Large lagoons result in odor, land use, and environmental leaching, he added. 

After examining anaerobic systems, the mill installed GWE’s anaerobic wastewater treatment system, the ANUBIXTM B reactor.  

During the anaerobic biological treatment process, bacteria break down organic material without oxygen. GWE’s system, a closed reactor operating under regulated temperatures and specific process control parameters, is designed to optimize waste consumption and gas generation during the process. The reactor includes an influent screen, equalization, acidity control, anaerobic treatment, biogas flare, and two-stage biogas sweetening through the Bio-SulfurixTM followed by activated carbon filtration. The medium- to high-loading rate upflow anaerobic sludge bed reactor is used at the mill for most low- to medium-strength influent containing mainly soluble carbohydrates. 

The system, which can be installed at any facility with a biological waste stream with high organic carbon or high COD of natural origin, produces a high-quality effluent and biogas. The mill has achieved a minimum 85% removal of COD with loads reduced from 6500 mg/L to 975 mg/L COD.  

“In addition to substantial environmental benefit ... the United Farmers Plant achieves a supply of green energy that delivers energy savings virtually in perpetuity,” Ombregt said.   

Typically, 1 ton of COD anaerobically digested generates 350 Nm3 of methane, which equals approximately 312 L of fuel and can generate about 1300 kWh of green electricity, according to Ombregt. At the mill, biogas production currently is building to 9000 Nm3/d, 75% of which is methane. The biogas is used to fuel several steam boilers.  

Since installation, the factory has experienced permanent and ongoing purchased fuel savings. Typical installations like this one produce enough green energy to pay for the cost of installation in 1 to 2 years, Ombregt said. In addition to wastewater treatment and cost savings, the facility has reduced its carbon footprint. 