Comparison of the doses of coagulants ensuring a similar degree of reduction in the concentration of total iron (76%), colour (60%), turbidity (95%) and TOC (27%) in water samples in which hydrogen peroxide was used as the oxidising agent, confirmed unambiguously the greatest effectiveness of coagulant PAX XL-60, and among the non-hydrolyzed coagulants, a preliminarily greater effectiveness of aluminium sulphate (VI) than iron (III) sulphate (VI) (except for reduction in turbidity) (Table 4).
Analysis of the results of the studies presented in Table 5 showed that irrespective of the oxidising agent used, an increase in the effectiveness of coagulation and sedimentation in the removal of Fe(III) resulted in an increase in the degree of the removal of TOC, which proves the removal of Fe(III) together with the organic substances, and thus, the occurrence of iron in iron-organic bonds in water.
Hydrogen peroxide was the least useful oxidising agent.
Regardless of the oxidising agent the best results in the removal of pollutants in the coagulation process were produced by the coagulant: pre-hydrolysed polyaluminium chloride PAX XL-60, and the worst by the iron coagulant: iron (III) sulphate (VI).
An analysis of the research results also shows that when groundwater with an increased content of organic substances is treated, the coagulation process for polyaluminium chloride should be aided with a chemical oxidising agent, preferably with a potassium manganate (VII) because apart from iron(III) hydroxide, manganese (IV) oxide is also produced in the process of oxidation.
The impact of the type of oxidising agent: a) dissolved oxygen and KMn[O.sub.4], b) [H.sub.2][O.sub.2] and KMn[O.sub.4], c) dissolved oxygen and [H.sub.2][O.sub.2] on the effects of the removal of pollutants in the coagulation process (SAL, PAX XL-60, PIX-112) and 2-hour sedimentation