Modifications for Extending the Treatment Capacityby Noah Galil, Technion Inst of Technology, Haifa, Israel,
Abstract: An approach for minimizing influences of increasing raw wastewater flow rates is proposed, based on modifying existing primary sedimentation units, by transforming them to flocculation - sedimentation units; the secondary biotreatment unit is kept without any modification. The idea is to improve removals of suspended solids and colloidal matter, most of it of organic origin, at the primary treatment stage, for protecting the biotreatment and limiting the total load to soluble organics mainly. Experimental results obtained on a pilot unit, operated in the previous stages of the project, using hydrated lime as flocculant, showed removals of suspended solids up to 90 percent and total BOD up to 50. The settling velocities of lime flocculated matter enabled to operate primary sedimentation on the same existing unit, at 1.7 times higher hydraulic load than the usually used on plain sedimentation. High solids concentrations, 10 percent and more, were obtained in the primary chemical sludge when lime dose was set for pH values of 9.5 to 10.0. The total sludge production, by both treatment stages, indicated that existing sludge facilities could support an increase of 60-70 percent in the raw wastewater flow rates, after modifying the primary treatment stage to lime flocculation - sedimentation. The main economic advantage in the proposed modification consist on significantly lower investment, considerably lower energy and land area requirements, as compared to the alternative of constructing new additional units similar to the existing ones.
Subject Headings: Flocculation | Solid mechanics | Lime | Turbidity | Sludge | Flow rates | Organic matter
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