Removing Iron and Organic Substances from Water over the Course of Its Treatment with the Application of Average and Highly Alkaline Polyaluminium Chlorides

Abstract

In topic-related literature pertaining to the treatment of water, there is a lack of information on the influence of iron ions in highly basic polyaluminum chlorides on the efficiency of purifying water with increased contents of organic substance. The aim of this work was to determine the changes in the content of organic substances as well as iron compounds in water intended for human consumption following unit treatment processes with particular attention paid to the coagulation process. As coagulants, polyaluminium chloride PAXXL10 with an alkalinity of 70%, as well as polyaluminium chloride PAXXL1911 with an alkalinity of 85% the composition of which also contained iron, were tested. The analysis of the obtained results showed that iron compounds and organic substances were removed to the greatest extent by the coagulation process, which also had a significant influence on the final efficiency of water treatment. The effectiveness of water treatment was determined by the type of tested polyaluminum chloride, which influenced the formation of iron-organic complexes. The reason behind the formation of colored iron-organic complexes during coagulation using PAXXL1911 coagulant was the high pH (approx. 8), at which the functional groups of organic substances, due to their dissociation, are more reactive in relation to iron, and possibly the fact of introducing additional iron ions along with the coagulant.

Suitability of Highly Polymerised Polyaluminium Chlorides (PACls) in the Treatment of Mixture of Groundwater and Surface Water

“…The effectiveness of the coagulation process with the tested coagulants was also evaluated by measuring the electro-kinetic potential ζ (Figure 3), which determines the stability of the colloids. According to reports in the literature [25][26][27] with the increase in the absolute value of the potential ζ, the stability of colloids increases. The coagulation process is mainly based on double layer repulsive potential reduction by neutralisation of surface charge of pollutants, and zeta potential is the parameter that provides the information about the charge neutralisation status [28].…”

“…According to reports in the literature [ 25 , 26 , 27 ] with the increase in the absolute value of the potential ζ, the stability of colloids increases. The coagulation process is mainly based on double layer repulsive potential reduction by neutralisation of surface charge of pollutants, and zeta potential is the parameter that provides the information about the charge neutralisation status [ 28 ].…”

“…The protective colloids of a hydrophilic nature, are created as a result of the adsorption of organic substances on the surface of iron (III) hydroxide. The organic stabilisation of iron colloids results from the formation of an external encasement containing ionised carboxyl groups [27]. According to numerous researchers [5,25,29,30], one of the reasons for iron stabilisation by organic substances in water may be formation of the so called protective colloids of hydrophilic character.…”

“…Analysis of the research results obtained showed that the pH of water during coagulation with the PAXXL1911 coagulant (Z = 85%, Fe = 0.7%) ranged from 7.86 to 8.00 ± 0.1 and with the PAXHP908 (Z = 85%, Fe < 0.01%) ranged from 7.85 to 8.00 ± 0.1 for doses from 1 to 5 mgAl/dm 3 . At these pH values, the functional groups of -COOH and -OH organic substances are more reactive in relation to iron ions and they can form iron-organic complexes [27,[30][31][32][33][34][35][36].…”

“…Although the mechanism of coagulation with non-prehydrolysed and prehydrolysed aluminium salts is the same, the presence of polymeric forms of aluminium in polyaluminium chloride solutions makes them more stable in water, providing more effective removal of impurities and lower concentrations of aluminium remaining in the treated water. In spite of the development of new separation techniques for water treatment, the coagulation process will continue to be the most important water-treatment process for the removal of organic substances [ 24 , 25 , 26 , 27 ].…”