Miami Dade County

Odor and Corrosive Control Pilot Study

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Introduction

 

AUS conducted a cursory pilot study for the treatment of sulfide within a sludge transmission line from the North Miami WWTP. The transfer line runs for approximately 10.4 miles from the North Miami plant to the 9th Street Pump Station. Approximately one half of the transmission line is a force main that runs from the North Miami plant through a 16″ line to a 72″ gravity line at 25th Street and Biscayne Blvd. It is within the force main portion of the transmission of sludge that sulfide is generated in considerable quantity. Odalog hydrogen sulfide readings at the point at which the sludge transmission line goes from force main to gravity were off scale within the atmosphere of the gravity pipe at over 1,000 ppm. It is, therefore, not surprising that the gravity sewer line from this point has suffered catastrophic damage due to sulfide related corrosion. It is also reasonable to assume that the sulfide related odors that come from the 0th Street Pump Station are largely the result of the hydrogen sulfide laden sludge are well documented. Levels in excess of 400 ppm in the atmosphere are often fatal. Levels in excess of 1,000 ppm that exist within the gravity line at 36th Street certainly pose a significant life threatening hazard to workers and extreme care should be required for those individuals who may be exposed to gases from this line.

 

Methods Tested

AUS tested two chemical approaches for the treatment of sludge with the transmission line. The first approach tested a catalyzed oxidation method that produces hydroxyl radicals known to rapidly treat sulfide (Odor Terminator II Method). This method can work with either hydrogen peroxide or oxygen as the oxidant of choice. The catalyst is an organic catalyst that reacts with the oxidant to form free radicals. While this method is excellent for rapid control of sulfide, it does not have a long-term residual effect. It is typically best suited for shorter retention times within sewer force mains of under 3 hours. Since the retention time within the force main portion of the transmission line was something over 3 hours, it was determined that it should be tried first.

The second method tested also relies on hydrogen peroxide or oxygen as on oxidant but has long-term residual treatment capacity. The process, known as the Odor Terminator I Process, is designed for long-term treatment in force mains from ~ 2 hours to greater than 24 hours of retention time. The oxygen generated from peroxide or from direct injection of oxygen reacts with the catalyst to produce free radicals for treatment of sulfide on contact. A slower acting oxidant is also present that reacts with the catalyst over time for long-term treatment. The mere presence of an oxidant within the force main also acts to prevent further development of sulfide.

Conclusion

 

Results generally indicated that Odor Terminator II catalyst along with peroxide treatment reduced the amount of sulfide within the system but did not completely control the problem. Given the distance and retention time involved, this result indicates that limits of the technology were tested resulting in a mediocre outcome. It was obvious from the Odor Terminator II study that a more long lasting oxidant would be required to achieve the results needed. A switch from Odor Terminator II to Odor Terminator I achieved this goal. Good control of sulfide entering the 9th Street Pump Station was quickly realized after the switch to Odor Terminator I. Tests within the atmosphere for hydrogen sulfide at 9th Street were well down. Regular peaks of 80 to 90 ppm of hydrogen sulfide were noted before treatment using the Aqua Odalog air monitoring system. Average hydrogen sulfide levels of approximately 5 ppm were noted in the air with Odor Terminator I treatment in the air immediately above incoming wastewater. Both Aqua and Miami Dade test equipment indicated very low levels of hydrogen sulfide within the 9th Street Pump Station building atmosphere while Odor Terminator I Treatment continued. Tests of the water entering the Pump Station confirmed low levels of sulfide in the water (<0.8 mg/l sulfide).