DC Water Operator case studies
DC Water Operator · Put your knowledge to work in context.
The DC Water Operator credential refers to the District of Columbia's certification for drinking water and wastewater treatment plant and distribution/collection system operators. It is aimed at people who operate, maintain, or supervise water and wastewater infrastructure serving District residents, businesses, and visitors - from treatment plants to the pipes that carry water to taps and sewage to treatment. The DC Water Operator case studies are 5 cases and about 4,122 words.
1Coagulant Underfeed After a Storm in a Conventional Surface-Water Plant
A 12 MGD conventional surface-water plant (rapid mix, flocculation, settling, six dual-media filters) draws from a reservoir. Two days after a 2.5-inch storm, raw turbidity climbed from 3 NTU to 16 NTU, UV254 absorbance rose, and alkalinity fell to 46 mg/L as CaCO3 at pH 7.5.
804 words, about 4 min2Dead-End Chlorine Residual Loss on Unlined Cast Iron
An 8-inch unlined cast-iron dead-end main runs 3,200 feet from a 12-inch transmission main and serves 38 homes on a cul-de-sac. Free chlorine at the plant effluent is 1.15 mg/L; the residual at the last hydrant averages 0.05 mg/L from May through September and 0.4 mg/L in winter.
820 words, about 4 min3Bulking Sludge After a Dewatering Outage
A 4.5 MGD extended-aeration activated sludge plant receives 3.0 MGD with influent BOD5 of 210 mg/L and TSS of 220 mg/L. Mixed liquor in four 0.35 MG aeration tanks has risen to 3,200 mg/L, SVI is 300 mL/g in a 30-minute settleometer test, and the secondary clarifier sludge blanket is at 9.5 feet in a 12-foot sidewater depth.
800 words, about 4 min4Wet-Weather Overflow Risk at a Crippled Pump Station
A 12-inch gravity sewer carries about 1.4 MGD dry-weather flow to a pump station with a 15-foot by 20-foot wet well and three 900 gpm pumps, one of which has its motor out for repair. During a 2-inch-per-hour storm, both available pumps are running continuously, the wet well has risen 0.9 feet in 10 minutes and is now 3.5 feet below the overflow elevation, and a hydrogen sulfide reading at the wet well hatch is 45 ppm.
896 words, about 4 min5UV Transmittance Drop Threatens Cryptosporidium Credit
A 6 MGD conventional plant filters to a UV building with four reactors; three are in service because the fourth reactor's ballast is on backorder. Each reactor is validated by third-party bioassay to deliver a reduction equivalent dose of 40 mJ/cm2 at 2.0 MGD when UV transmittance at 254 nm (1 cm) is 88 percent or higher.
802 words, about 4 min