Wastewater Treatment – Then and Now

dec.ny.sedbasinIn 1909, the city of Santa Monica was featured in the Municipal Journal and Engineer for their nine-month operation of a magneto-electrolytic sewage purification plant. The theory at the time was that charging sewage with electricity was sufficient to render the sewage safe and free of disease. According to the article, the cost for the city averaged $400 per month, and the plant received inquiries from “all parts of the globe.” Unfortunately, this method was not as effective as the proponents had claimed; municipalities eventually moved past magneto-electrolytic purification.


Today, our wastewater treatment methods are much more complex and vary by plant and region. Wastewater treatment generally involves three stages: Primary, Secondary and Tertiary treatment. Today we’ll look at Pretreatment and Primary treatment methods that are commonly used nationwide.


Wastewater Treatment.OKPretreatment usually involves removing large debris, such as trash, tree limbs, leaves, and branches from wastewater. This is done through screening, grit removal, and fat and grease removal in some cases. Some plants utilize flow equalization basins to dilute and distribute batch discharges of toxic or high-strength waste. Equalization basins  typically include provisions for bypass and cleaning, and may also include aerators.


treated sludgeIn the Primary treatment stage, sewage flows through large tanks, commonly called “pre-settling basins”, “primary sedimentation tanks” or “primary clarifiers”. The tanks are used to settle sludge, while grease and oils rise to the surface and are skimmed off. Primary settling tanks are usually equipped with mechanically driven scrapers that continually drive the collected sludge towards a hopper in the base of the tank where it is pumped to sludge treatment facilities. The sludge produced is often treated to be reused as agricultural fertilizer.


Stay tuned for our post on Secondary and Tertiary Treatment.