The Water Research Foundation (WRF) has published a suite of deliverables to help water and wastewater utilities utilize...
Facing a critical corrosion problem, Tony Silva, from the Department of Public Works in Barrington R.I., recently approached Cellinite Technologies to take part in a four-product investigation to find a treatment to reduce hydrogen sulfide from the forced main entering the East Providence Wastewater Treatment Facility.
Barrington has three lift stations, which pump wastewater to the facility through a 24-in. forced main 3.5 miles from the station.
Silva’s facility experienced high levels of hydrogen sulfide, which caused the formation of corrosive acids. The acids corroded the last 200-plus ft of pipe leading to the plant, resulting in catastrophic failure. Measured atmospheric sample levels were reported between 200 and 400 ppm.
Silva and the Barrington Department of Public Works understood how important it was to reduce the hydrogen sulfide levels as the forced main was designed to endure many years of service.
Because the problem occurred en route to the wastewater treatment facility, Silva realized they needed to treat the wastewater at the lift stations so the hazardous hydrogen sulfide levels would not occur while in the pipe. The pump stations are located in residential areas approximately 100 ft from housing, so Silva had to take into consideration a variety of factors: vandalism, security, aesthetics, noise, power and water consumption, equipment, chemical costs, construction and product delivery.
Under these considerations, Silva investigated three other systems to reduce hydrogen sulfide: Bioxide, Bacta-Pur, and potassium permanganate in liquid form and “control release” solid-form sticks.
These mitigating factors addressed earlier eliminated all but Potassium Permanganate CR and Cellinite BioTabs; both are products that do not require power, carry water, construction or dosing equipment.
Silva said the city’s lift stations were treated with 9 lb of BioTabs per day at three locations within the system. The wastewater was tested for aqueous hydrogen sulfide levels and for atmospheric sulfuric acid at the end of the forced main.
Overall, the testing showed a 93.8% reduction of dissolved hydrogen sulfide and a 95.6% reduction of atmospheric sulfuric acid at the end of the forced main. These results were logged after four days of treatment, followed by two days of no treatment over a weekend and three days of a reduced dosage, approximately 3 lb per day.
During the reduced treatment, the hydrogen sulfide and sulfuric acid levels steadily increased to the previously untreated levels.
On the fourth day, the recommended dosage was reinstated. The hydrogen sulfide levels dropped 82.4%, and the sulfuric acid levels dropped 33.3% after one day of treatment. These results verified the reduction was, in fact, due to the addition of the BioTabs.
Seeing these results allowed Silva and the Barrington Department of Public Works to easily adjust daily dosing of the BioTabs to achieve the most efficient treatment of the wastewater while controlling their costs.
In addition to the reduction of hydrogen sulfide and sulfuric acid levels, Barrington experienced a significant reduction in the solid grease and grease cap at their lift station. Before treating the wastewater at the lift stations, the grease cap was a few inches thick.
After two weeks of testing, the operators at the pump station noticed the grease layer looking softer, like marshmallows. After continued use, the grease overall was reduced by 95 to 99%, and what was left of the grease cap became “little grease balls.”
Of the products considered and tested, Cellinite BioTabs were chosen for the estimated annual cost and ease of handling. To apply potassium permanganate, the product had to be lowered into the wet well using a netted bag; whereas the BioTabs were simply dropped into the wastewater.
The BioTabs are solid tablets requiring only gloves for handling; any broken pieces can be easily swept into the wet well.
Other products, although solid, require proper dust masks, eye protection and gloves. When broken, some products can leave a hazardous dust and when wet or moistened, will stain anything the product comes in contact with.
Silva and the Barrington Department of Public Works estimated that their “annual chemical costs” would be $31,000 with the potassium permanganate and $20,000 with the BioTabs.
“We are very pleased with the BioTabs,” Silva said. “I must say, being in the wastewater business for 28 years, I have seen and tried many products that promised to be the solution for my problems. When I heard how simple the solution was, I thought this was another product with false hopes. I cannot tell you how pleased I am that the BioTabs are all they are said to be.”
Barrington continues to use 3.5 lb of solution per day at only one lift station located the farthest down the forced main, and they are keeping their hydrogen sulfide levels between 0 and 20 ppm.
In addition to controlling the hydrogen sulfide levels, they continue to eliminate grease concentration, and a significant odor reduction is also evident.