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Low-molecular-weight organics, i.e., phloroglucinol ͑P͒, resorcinol ͑R͒, and p-hydroxybenzoic acid ͑PHBA͒, were selected as the target compounds to evaluate their removal and precursor reduction efficiency by coagulation under the presence of high-molecularweight compounds. The results of this investigation reveal that turbidity removal efficiencies can achieve 95% and above, but the total organic carbon removal for P, R, and PHBA are not remarkable, which are less than 20%. The chlorine demand after 168 hour is: PХPHBAϾ R Ͼ humic acids ͑HA͒ Ͼ tannic acid ͑TA͒; while the order of trihalomethanes ͑THM͒ formation is R Ͼ P Ͼ PHBAϾ HA Ͼ TA, which is strictly dependent upon the nature of the model compounds. By applying the developed dissolved organic carbon ͑DOC͒ removal model, both the maximum adsorption capacity and the residual DOC can be well predicted after coagulation. In this developed model, the adsorption capacity ͑a͒ is a function of the sorbable part of organic compounds ͑f sorbable ͒, which can be expressed as: a = e 2.67f sorbable , both shown in nature and synthetic water samples. The f nonsorb increased as the molecular weight ͑MW͒ of the target compounds decreased, suggesting that low-MW target compounds could not be easily adsorbed on the flocs.

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