Recycling & Waste Management

Waste water Recycling

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Introduction to Wastewater Treatment Processes

Wastewater treatment is closely related to the standards and/or expectations set for the effluent quality. Wastewater treatment processes are designed to achieve improvements in the quality of the wastewater. The various treatment processes may reduce:

·        Suspended solids (physical particles that can clog rivers or channels as they settle under gravity)

·        Biodegradable organics (e.g. BOD) which can serve as “food” for microorganisms in the receiving body.

·        Pathogenic bacteria and other disease causing organisms These are most relevant where the receiving water is used for drinking, or where people would otherwise be in close contact with it; and

·        Nutrients, including nitrates and phosphates. Widely used terminology refers to three levels of wastewater treatment: primary, secondary, and tertiary (or advanced).

·        Primary (mechanical) treatment is designed to remove gross, suspended and floating solids from raw sewage. It includes screening to trap solid objects and sedimentation by gravity to remove suspended solids. This level is sometimes referred to as “mechanical treatment”, although chemicals are often used to accelerate the sedimentation process.

·        Secondary (biological) treatment removes the dissolved organic matter that escapes primary treatment. This is achieved by microbes consuming the organic matter as food, and converting it to carbon dioxide, water, and energy for their own growth and reproduction. The biological process is then followed by additional settling tanks (“secondary sedimentation", see photo) to remove more of the suspended solids.

·        Tertiary treatment is simply additional treatment beyond secondary! Tertiary treatment can remove more than 99 per cent of all the impurities from sewage, producing an effluent of almost drinking-water quality.