Investigating adsorption of model low-MW AOM components onto different types of activated carbon - influence of temperature and pH value.

Low molecular weight algal organic matter (AOM), as a frequent water contaminant with poor coagulation efficiency, adversely affects the quality of produced water and serves as a source of potentially carcinogenic disinfection by-products. AOM removal from water is inevitable to eliminate the negative health and environmental impacts. This research evaluates the removal of arginine, phenylalanine and aspartic acid, which are amino acids abundant in AOM. Adsorption experiments were performed at 10, 18 and 25 °C and pH 5, 7 and 9 using two different activated carbons (FTL, PIC). Amino acids showed endothermic adsorption behaviour, with a higher removal at higher temperature. Higher temperature increased the diffusion of amino acid molecules, reduced the solution viscosity, or enhanced the hydrophobic interactions contributing to adsorption. The effect of temperature manifested differently during experiments depending on the chemical nature of the amino acids, the pH value and the surface properties of the carbon. Phenylalanine isotherms showed specific waves (Langmuir type 4). pH had a greater effect on arginine adsorption than did temperature. Aspartic acid isotherms exhibited a decrease in adsorption at higher pH values and higher temperatures. The principal mechanisms involved in amino acid adsorption were hydrophobic interactions, electrostatic interactions or hydrogen bonds.

Current knowledge in the field of algal organic matter adsorption onto activated carbon in drinking water treatment.

The increasing occurrence of algal and cyanobacterial blooms and the related formation of algal organic matter (AOM) is a worldwide issue that endangers the quality of freshwater sources and affects water treatment processes. The associated problems involve the production of toxins or taste and odor compounds, increasing coagulant demand, inhibition of removal of other polluting compounds, and in many cases, AOM acts as a precursor of disinfection by-products. Previous research has shown that for sufficient AOM removal, the conventional drinking water treatment based on coagulation/flocculation must be often accompanied by additional polishing technologies such as adsorption onto activated carbon (AC). This state-of-the-art review is intended to serve as a summary of the most current research on the adsorption of AOM onto AC concerning drinking water treatment. It summarizes emerging trends in this field with an emphasis on the type of AOM compounds removed and on the adsorption mechanisms and influencing factors involved. Additionally, also the principles of competitive adsorption of AOM and other organic pollutants are elaborated. Further, this paper also synthesizes previous knowledge on combining AC adsorption with other treatment techniques for enhanced AOM removal in order to provide a practical resource for researchers, water treatment plant operators and engineers. Finally, research gaps regarding the AOM adsorption onto AC are identified, including, e.g., adsorption of AOM residuals recalcitrant to coagulation/flocculation, suitability of pre-oxidation of AOM prior to the AC adsorption, relationships between the solution properties and AOM adsorption behaviour, or AOM as a cause of competitive adsorption. Also, focus should be laid on continuous flow column experiments using water with multi-component composition, because these would greatly contribute to transferring the theoretical knowledge to practice.

A comparison of the character of algal extracellular versus cellular organic matter produced by cyanobacterium, diatom and green alga.

This study investigated characteristics of algal organic matter (AOM) derived from three species (cyanobacterium Microcystis aeruginosa, diatom Fragilaria crotonensis and green alga Chlamydomonas geitleri) which dominate phytoplanktonic populations in reservoirs supplying drinking water treatment plants. Algal growth was monitored by cell counting, optical density and dissolved organic carbon concentration measurements. Extracellular organic matter (EOM) released at exponential and stationary growth phases and cellular organic matter (COM) were characterised in terms of specific UV absorbance (SUVA), peptide/protein and non-peptide content, hydrophobicity and molecular weight (MW). It was found that both EOM and COM were predominantly hydrophilic with low SUVA. COM was richer in peptides/proteins, more hydrophilic (with about 89% of hydrophilic fraction for all three species) and had lower SUVA than EOM. MW fractionation showed that both EOM and COM of all three species contain large portions of low-MW (<1 kDa) compounds and high-MW (>100 kDa) polysaccharides. Peptides/proteins exhibited narrower MW distribution than non-peptide fraction and it widened as the cultures grew. The highest amount of peptides/proteins with a significant portion of high-MW ones (22%) was observed in COM of M. aeruginosa. The results imply that the knowledge of AOM composition and characteristics predetermine which processes would be effective in the treatment of AOM laden water.

Adsorption of cellular peptides of Microcystis aeruginosa and two herbicides onto activated carbon: effect of surface charge and interactions.

In this research, the adsorption of two herbicides, alachlor (ALA) and terbuthylazine (TBA), on granular activated carbon (GAC) in the presence of well-characterized peptide fraction of cellular organic matter (COM) produced by cyanobacterium Microcystis aeruginosa was studied. Two commercially available GACs were characterized using nitrogen gas adsorption and surface charge titrations. The COM peptides of molecular weight (MW) < 10 kDa were isolated and characterized using MW fractionation technique and high-performance size exclusion chromatography (HPSEC). The effect of surface charge on the adsorption of COM peptides was studied by means of equilibrium adsorption experiments at pH 5 and pH 8.5. Electrostatic interactions and hydrogen bonding proved to be important mechanisms of COM peptides adsorption. The adsorption of ALA and TBA on granular activated carbon preloaded with COM peptides was influenced by solution pH. The reduction in adsorption was significantly greater at pH 5 compared to pH 8.5, which corresponded to the increased adsorption of COM peptides at pH 5. The majority of the competition between COM peptides and both herbicides was attributed to low molecular weight COM peptides with MW of 700, 900, 1300 and 1700 Da.