Transactions of the American Society of Civil Engineers, vol. LXXII, June, 1911 / Water Purification Plant, Washington, D. C. Results of Operation.

Metadata

Gutenberg ID

27632

Title

Transactions of the American Society of Civil Engineers, vol. LXXII, June, 1911 / Water Purification Plant, Washington, D. C. Results of Operation.

Language

en

Book source

Project Gutenberg

Description max 80 words

This technical report details the five-year operational results of Washington, D.C.'s slow sand filtration plant. Authored by E. D. Hardy, it offers engineers a data-driven analysis of cost, efficiency, and water quality, featuring extensive tables on turbidity, bacterial counts, and sand replacement methods.

Summary up to 500 words

Presented to the American Society of Civil Engineers in 1911, this paper by E. D. Hardy offers a comprehensive review of the Washington Filtration Plant, which had been in continuous operation since October 1905. The facility, drawing water from the Potomac River via the Washington Aqueduct, utilizes 29 slow sand filters with a total capacity of 15 million gallons. Hardy details the plant's evolution from manual sand scraping to more efficient hydraulic replacement techniques adopted in 1909, which significantly lowered resanding costs and improved sand compactness. The report provides extensive data on turbidity reduction, highlighting that raw water turbidity fluctuates dramatically, often necessitating the closure of intake gates at Great Falls to exclude excessive mud. Hardy notes that while clarification begins in three settling reservoirs, fine clay particles often require filtration; however, filtration efficiency is heavily influenced by temperature. Data tables demonstrate that colder water yields higher turbidity in the effluent, with the filtered water turbidity at temperatures below 40°F being practically twice that of water filtered at temperatures above 70°F. This aligns with theoretical principles regarding sedimentation rates and water viscosity. Bacterial analysis reveals that while bacterial counts are uniformly low for eight to nine months of the year, they increase during winter months. This correlates closely with turbidity spikes, though typhoid death rates remain comparatively low even during periods of poorer water quality. Hardy discusses the potential for sand segregation when using hydraulic replacement methods but concludes that for the high-quality summer water, this poses little issue, whereas it could be critical for polluted winter supplies. Consequently, Hardy advocates for preliminary coagulation treatment to maintain water quality year-round. Following a campaign to educate engineers against coagulants, an appropriation was secured in 1910 to build a coagulating plant, which was subsequently tested during periods of high turbidity. The paper concludes that despite winter operational challenges, the water supply remains safe, and the plant's methods represent a significant advancement in municipal water purification.

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Categories

• Civil Engineering
• Water Treatment