From January t o July, 1972, six municipal sewage treatment plants were routinely monitored for the efficiency of heavy metals removal. municipalities served ranged from a small agricultural community to an industrial city. Four basic plant types were studied: 1 ) Primary w i t h sludge digestion; 2) Primary w i t h sludge f i l t r a t i o n ; 3) Trickling-filter secondary w i t h sludge digestion; and 4) Activated-sludge secondary with sludge digestion. Composite samples from the influent, effluent, and sludge were homogenized, acid-digested, and analyzed by atomic absorption spectrophotometry f o r Cd, Cr, Cu, Zn, and Pb. The efficiency of heavy metals removal and the relationship between heavy metals removal and suspended solids removal are discussed.

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