Enhanced primary wastewater treatment by sludge recycling

Abstract

This paper describes the development of a cost‐effective modified primary treatment method which can significantly increase the removal of both finely‐divided and soluble organic matter without resorting to the use of any chemical coagulants or secondary treatment method. It involves the recycling of a small portion of the settled primary sludge and then mixing it, after brief aeration, with raw sewage for a short period to induce biosorption and flocculation/enmeshment of various types of pollutants, thereby settling them together with the recycled sludge particles. During operation, the raw sewage is NOT subjected to any aeration; only a small aeration tank for sludge pre‐aeration and a flocculation tank for sludge‐sewage mixing are added; thus, the energy for the improved treatment method will not be too much higher than the conventional primary treatment method. Yet, the removal of both COD and SS can be improved significantly as compared to the conventional method. The increased removal is mainly attributed to the effective biosorption/flocculation and settling of colloidal particles and this suggestion has been substantiated by the data of particle analysis.

Key words:

• Biosorption
• particle analysis
• COD removal
• sludge recycling
• flocculation/enmeshment
• primary waste treatment

Notes

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