Removal of THM precursors from a high-alkaline surface water by enhanced coagulation and behaviour of THMFP toxicity on D.magna

摘要

This study evaluates the effectiveness of polyaluminium chloride (PAC1) compared to aluminium sulphate (alum)and ferric chloride (FeCl_3) to remove THM precursors and reduce THM formation potential of two samples (S1 andS2) from a surface water resource with low TOC (<3mg/l),high alkalinity (180 mgCaCO_3/l) and pH (8.0),to complywith stringent Italian limits for TTHMs (30 mug/1).The effectiveness of the coagulants used was evaluated bymeasurements of turbidity,TOC,UV absorbance at 254 nm wavelength (UV_(254)),and total trihalomethanes formationpotential (TTHMFP),as well as by monitoring their toxicity behaviour using a standardized,reliable,and time-savingbiotest (Daphnia magna acute immobilization test) in raw,coagulated,and chlorinated samples.PAC1 was the mosteffective coagulant to remove turbidity for both samples (S 1 and S2);however,it did not reduce NOM as effectivelyas FeCl_3 and alum.For S2,PAC1 was more selective for bromoform removal than FeCl_3.None of the coagulant dosesapplied could reduce TTHMs to the required limits,not even high doses (80 mg/1).Toxicity test results displayeddifferent behaviour due to coagulant type and dose.The toxicity of raw chlorinated water could be reduced by a slightlybut significant degree by enchanced coagulation.This study showed the necessity of NOM characterization to optimizethe coagulation process as well as integrating it with an advanced pre-/post-treatment technology to obtain safe water.