The Florida Keys have long been known for its exotic islands, pristine snorkeling, artistic charm, and a magnificent coral reef. This natural beauty attracts millions of tourists every year. Needless to say, maintaining the quality of the sea water surrounding the keys is essential to the allure and economic viability of the area.
The Key West Southernmost Wastewater Treatment Plant was constructed in 1989, designed and permitted to produce secondary effluent at a rate of 10 million gallons per day (GPD). Prior to this, raw wastewater was discharged directly to the ocean outfall. In fact, it was one of the last raw wastewater discharges to the ocean in the United States. The plant was expected to remove pollutants from wastewater and reduce nutrient levels to 20 milligrams per liter of total nitrogen and 6 milligrams per liter of total phosphorus.
In recent years, the City of Key West has implemented aggressive measures to ensure the reduction of nutrient levels meet or exceed the standards set by the Federal Department of Environmental Protection (FDEP) for advanced wastewater treatment plants. The city has spent more than $67 million over the past five years on sewer capital improvements to rebuild the collection system, replace the ocean outfall with two Class 1 Deep Injection Wells, and upgrade the current Sewer Treatment Plant to an Advanced Wastewater Treatment (AWT) facility.
The Key West wastewater collection system operations and maintenance are contracted out to CH2MHill- Operations Management International (OMI). As part on the ongoing improvement to maintain the high quality standards of the facility, OMI decided that they needed a reliable, versatile, non-intrusive flowmeter that could measure both rate and total of either dirty water or clean water. OMI had experienced numerous failures with Ultrasonic (Doppler Only) flowmeters in the past but were willing to try a Hybrid Ultrasonic due to the flexibility of using it in various applications. OMI’s first area of measurement concern was at each of the five main stations where knowing the rate and the total of the wastewater is crucial in maintaining an efficient facility that encompasses a total of 26 substations.
OMI selected the Blue-White Hybrid Ultrasonic Flowmeter “Sonic-Pro” as there ultrasonic meter of choice primarily because of the flexibility and the communications capability of remote access. The Blue-White Sonic-Pro series Hybrid Ultrasonic Meters can measure any acoustically conductive fluid in any pipe material above two inches. The term “Hybrid” refers to the ability to select either Doppler mode or Transit Time mode. In order for the Doppler mode to be effective, the fluid must contain .02% to 15% (200 – 150,000 PPM) of particles. Conversely, the effectiveness of the Transit Time mode requires relatively clean fluid, containing 0% to 10% (0 to 100,000 PPM) of particles. Additional characteristics of the Sonic-Pro include; a NEMA 4X (IP66) powder coated aluminum enclosure, a UV resistant 320 x 240 pixel QVGA backlit LCD display, a five-button position action tactile switch keypad, and a date/time stamped flow rate/total data in FAT32 file format that is easily imported into Excel. The data outputs include both a 4-20mA and 0-1000 Hz Pulse. Further options encompass process control (three independently configurable 10 amp Form c, NO/NC relays) and external communications (computer connection via RS-232, RS-485, USB, Ethernet).
Gary Rose of Rose Industrial Marketing assisted OMI in the installation and startup of the Sonic-Pro. Initially, the flowmeter was manually configured on site by inputting several key data figures, (e.g., pipe material, pipe outside diameter, pipe thickness, and speed of sound). Once the configuration was completed, it was then saved within the Signal Processing Unit (SPU). If the meter was set in the Transit Time mode, the SPU would have displayed the appropriate transducer spacing. However, in this particular application, the meter was set in the Doppler mode for wastewater. The pipe material was PVC pipe with an outside diameter of 15.32, a wall thickness of .82, and a speed of sound in water at 1505 m/s. The transducers were mounted directly opposite one another on the side wall of the pipe, normal for a Doppler reading. Upon completion of the setup, the configuration was manually activated triggering the flowmeter to enter the run mode. The flow and total rates were immediately displayed reflecting the accurate measurement of wastewater being pumped. The accuracy of the Sonic-Pro in the Doppler mode is +/- 2% of rate at a flow rate greater than 12 ft/second. CH2MHill was amazed at how easily the installation preceded and they were impressed with the capability of the meter to remotely access and upload data logging files via the external communications. Due to this success, CH2MHill-OMI has plans to further implement the Sonic-Pro at the other substations. Additionally, OMI is pleased to have the versatility to incorporate the Sonic-Pro in clean water applications, utilizing the Transit Time mode with an accuracy of +/- 1% of rate a rate greater than 5 ft/second.
At a recent Florida Water Resource conference, the Florida Water Environment Association awarded the City of Key West Wastewater Collection System with four top honors. These awards included a First Place in the Advanced Secondary Treatment category. Blue-White Industries is proud to have their Sonic-Pro Ultrasonic Flowmeters used in integral applications at such a highly recognized wastewater treatment facility.