Wastewater Management

Worcester manages wastewater and run-off by three means: sanitary sewer system, surface sewer, and combined sewer system. Students travelled to the Upper Blackstone Water Pollution Abatement District’s Upper Blackstone Wastewater Treatment Facility (UBWWTF )in Millbury to study how Worcester and surrounding towns manage and treat their waste water (“sewage”). While the surface sewer system in Worcester directs stormwater to the nearest waterway, the combined sewer system collects both sewage and stormwater sewage in 4 square central miles of the city and directs it along with sewage from homes and businesses to the UBWWTF. The plant averages 30+ million gallons a day using “primary”, physical treatment (settling through gravity), “secondary” biological treatment ( decomposition and absorption of organics, fine solids, dissolved metals, ammonia, phosphorous by microbes living in the aeration tanks followed by a second round of settling), and chemical treatment (chlorine disinfection). Treated water flows into the Blackstone River, making up over 60% of the total headwater flow volume at points in the summer. In 2007, the plant removed 6,238 tons of suspended solids from the waste stream. Sludge is incinerated on-site using various air pollution controls (scrubbers, electrostatic precipitation, oxidation). Other systems data include annual heat energy demand (2007) of 69 million cubic feet of gas and 16.2 million kWh. Currently, the plant is undergoing a $ 180 million renovation to deal in part with EPA regulations regarding phosphorous and nitrogen pollution.

In the event of heavy rain the combined sewer system can become overwhelmed leading to Combined Sewer Overflows (CSOs) that pollute local waterways. In 1980, Worcester built the Quinsigamond Ave Combined Sewer Overflow Treatment Facility (QACSOTF), which pumps sewage from the combined system to the UBWWTF during dry periods and treats the sewage during heavy rains by using bar screens, settling, and disinfection before capacity exceeding flow is discharged into the Blackstone River.

For more information on the UBWWTF go to UBWPAD

For more information on the QACSOTF go to DPW (click on city departments-public works-combined sewer overflow treatment)

Worcester Water Filtration Plant (II)

Environmental Science students visit the city’s water filtration plant in Holden, MA. Pictures above display i) the role that computers play in monitoring and managing each treatment step, ii) plant manager Bob Hoyt fielding a question from upper school science teacher ,Paul Elkins – in the room for coagulation (fast mixing of aluminum sulfate and cationic polymer binds to debris, forming flocs, which after going through slow mixing, or flocculation, will be filtered out by the top layer of the direct filtration beds (comprised of 5 feet coal, 1 foot sand, 1 foot gravel) and de-ozonation (excess ozone needs to be converted back to O2 before being released outside)- and iii) students peering over the direct filtration beds (filtering water at a rate of about 6 gallons/sf/minute). Typically, the plant reaches it annual maximum during the summer, with 32+ MGD, well below its maximum capacity of 50 +MGD. If and when a water main breaks, the plant will have to compensate for the water pressure drop and lost water by increasing filtration rates by a few MGD. The city is working to mitigate the contamination threat from “cross connections” which is when non-potable water (contaminated with pesticides, chlorine, industrial materials, etc.) back-flows into the water distribution systems due to negative pressure. For more information click on the Water page above and previous water post

Worcester Municipal Water Filtration System (click photos)

Over 2.5 billion people in the world lack access to sanitary water. As a result millions of people die every year due to water related illness. Living and going to school in Worcester we enjoy some of the highest quality water in the world. The Worcester Water Filtration Plant filters about 22 million gallons of water every day by collecting water from 10 reservoirs (containing 8 billion gallons) located throughout the Blackstone and Nashua River Watersheds, running it through a 10-step filtration process, and then using gravity and pumps to deliver it through 600 miles of piping to Worcester and surrounding towns. Worcester water meets every EPA Safe Drinking Water Act standard, with the exception of a few detected cases of lead due to old piping in homes ( the solution to which is to simply run the faucet for at least 30 seconds to flush out stagnant water before filling up larger water containers). Click on Worcester’s Water Quality Report 2006 below, for a detailed report.

Worcester Water Quality Report 2006

Photos clockwise from top left.

1) Holden Reservoir #1 (729 Million Gallons) view to the south. 2) Water entering the plant. Students look down into the mirrored plant designed 2 60 in. diameter intake pipes, each of which have a rated capacity of 50 MGD.3) Air must be dessicated to prevent corrosion of ozone generating tubes. 4) Students looking into a $300,000 ozone generator used to break down organic membranes thus disinfecting and improving the taste of water. 5) View of ozone generating tubes: long glass tubes with metal coating conducting electricity contact pressurized dry air to break apart O2 and then form O3 (ozone), which is a ground level lung irritant and smog forming compound but in the upper atmosphere a UV ray absorbing compound as well as effective water sanitizer. 6) Excess O3 is converted back to O2. 7) Flocculation, slow mixing with aluminum sulfate and ionic polymer to create flocs that will be unable to pass through the next step. Students look down into a direction filtration tank where 5.3 gallons of water per square foot per minute are being filtered through five feet of anthracite coal, one foot of sand, and one foot of gravel. 9) A graph shows the difference in turbidity (measure of cloudiness) as result coagulation (rapid mixing) and flocculation.