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The Effect of Cellular Organic Matter Produced by Cyanobacteria Microcystis Aeruginosa on Water Purification

The Effect of Cellular Organic Matter Produced by Cyanobacteria Microcystis Aeruginosa on Water... J. Hydrol. Hydromech., 57, 2009, 2, 121­129 DOI: 10.2478/v10098-009-0011-3 MARTIN PIVOKONSKÝ, LENKA PIVOKONSKÁ, JITKA BÄUMELTOVÁ, PETRA BUBÁKOVÁ Institute of Hydrodynamics AS CR, v. v. i., Pod Patankou 5, 166 12 Prague 6, Czech Republic; mailto: pivo@ih.cas.cz The aim of this paper is to investigate the influence of COM (Cellular Organic Matter) produced by Microcystis aeruginosa on the process of water purification by destabilisation and subsequent aggregation of the impurity particles. The research was carried out with a raw water into which COM was added. The removal efficiency of the most significant components of COM, i.e. polysaccharides and proteins, was investigated. It was found that the removal efficiency of polysaccharides and proteins was dependent on the reaction conditions (pH, type of destabilisation reagent and its dosage). The removal efficiency of COM was relatively low. It was about 46% and 41% using ferric sulphate and aluminium sulphate aggregation, respectively. In comparison to the other organic components of COM, mainly polysaccharides, the proteins are removed with a higher efficiency. The GPC analyses of the residual COM showed that the proteins of higher molecular weight were aggregated with a higher efficiency. KEY WORDS: AOM (Algal Organic Matter), COM (Cellular Organic Matter), Destabilisation, Aggregation, Reaction Conditions, Water Purification. Martin Pivokonský, Lenka Pivokonská, Jitka Bäumeltová, Petra Bubáková: VLIV BUNCNÝCH ORGANICKÝCH LÁTEK PRODUKOVANÝCH SINICÍ MICROCYSTIS AERUGINOSA NA ÚPRAVU VODY. J. Hydrol. Hydromech., 57, 2009, 2; 23 lit., 9 obr., 1 tab. Cílem práce je opis vlivu buncných organických látek (COM) produkovaných sinicí Microcystis aeruginosa na proces úpravy vody pomocí destabilizace a následné agregace znecisujících pímsí. Výzkum byl uskutecován se syntetickou surovou vodou, do které byly pidány COM získané laboratorní kultivací M. aeruginosa. V prbhu laboratorních test byla sledována pedevsím úcinnost odstranní dvou základních slozek COM, tj. polysacharid a protein. Bylo zjistno, ze tato úcinnost závisí pedevsím na reakcních podmínkách (typu a dávce destabilizacního cinidla a pH). Úcinnost odstranní COM byla pomrn nízká, maximální dosazená úcinnost byla 46% pi destabilizaci pomocí síranu zelezitého a 41% pi pouzití síranu hlinitého. Bylo zjistno, ze s vyssí úcinností jsou odstraovány proteiny, obzvlást pak proteiny s vyssí molekulovou hmotností. KLÍCOVÁ SLOVA: organické látky produkované fytoplanktonem, buncné organické látky, destabilizace, agregace, reakcní podmínky, úprava vody. 1. Introduction Effective removal of natural organic matter (NOM) and especially that produced by a vast development of phytoplankton (Algal Organic Matter ­ AOM) is one of the very significant challenges of the purification of the surface waters (Bernhardt et al., 1985, 1986, 1989; Hoyer et al., 1987; Takaara et al., 2005, 2007; Pivokonsky et al., 2006). Generally, these organic matters can be distinguished into the substances that are released by metabolic activity of micro-organisms ­ the extracellular organic matter (EOM) and the substances released during the process of their decay ­ the intracellular organic matter (COM) (Pivokonsky et al., 2006; Lüsse et al., 1985; Hoyer et al., 1985). The COM represents a specific problem due to the occasional sudden increase in its concentration. A great attention was given to the influence of AOM on the purification of water polluted with different impurities such as aluminosilicates, humic matter, etc. Various studies showed that the influence of EOM on the process of destabilisation and aggregation of the impurity particles could be com121 pared to that of non-ionic polymers (Bernhardt et al., 1985, 1986, 1989; Hoyer et al., 1987). At their low concentrations the efficiency of water purification increases due to the formation of inter-particle bridges between the impurity particles or adsorption to their surfaces. In contrast, at higher concentrations the AOM inhibits the process of destabilisation of the impurity particles by increasing negative charge on their surface. Furthermore, certain substances contained in AOM, primarily proteins, also inhibit the destabilisation process. It is assumed that this results from the formation of higher-valence cation complexes and hydrated ions aided by coordination bonds. The formation of these complexes results in increased consumption of destabilisation reagent and decreasing efficiency of the destabilisation process (Bernhardt et al., 1989). The extent of the inhibition effect of the AOM is dependent upon its composition which is influenced by the kind of organisms and their growth phase (Pivokonsky et al., 2006). The COM are the substances most difficult to remove from the water. The reason is that these organic compounds are released suddenly in large quantities during decay of phytoplankton. Another very important reason is different chemical composition of COM in comparison to the other NOM and EOM (Takaara et al., 2005, 2007; Pivokonsky et al., 2006). The influence of AOM on the destabilisation and aggregation efficiency is not yet adequately explained. The contribution of authors to this theme is presented in this paper. The results obtained by investigating the effect of COM pollution produced by M. aeruginosa on its removal efficiency by coagulation with ferric sulphate and aluminium sulphate purification are summarised in this paper. 2. Material and methods 2. 1 Cyanobacteria cultivation procedure The cyanobacteria Microcystis aeruginosa KUTZ. (ZAPOMELOVA 2006/2) was used in this study. Inoculums of this strain were kindly supplied by the Culture Collection of Algal Laboratory, Institute of Botany, AS CR, v. v. i., Czech Republic. The laboratory strain M. aeruginosa was grown in a 20 l volume of Z medium (pH = 8.5) (Strub and Schweiz, 1961) at 24 °C and regularly shaken by a shaking apparatus operating at 40 rpm. The 16hlight/8h-dark cycle was applied. The cultures were illuminated using four 40W cool-white fluorescent 122 lamps supplying about 6000 lux. All materials and media were sterilized by autoclaving before assembly and operation. The growth of M. aeruginosa was monitored by chlorophyll-a in the culture. Cyanobacterial cells were harvested on 16th day of the cultivation period in the steady-state growth (dominant number of cells was free). 2. 2 COM preparation procedure The COM samples were prepared by destruction of the microorganism's cells which were separated from the growth media (2 l samples) on a 0.22 m membrane filter (Millipore, USA) on the 16th day of the cultivation time (the steady-state growth). The separated cells were mixed with ultrapure water (200 ml). The destruction of cells was performed using an ultrasonic homogenizer (HD 3200, 20 kHz, 60W), which was dipped into the beaker containing the separated cells of microorganisms. The efficiency of cells destruction was checked in an optical microscope (Optech B4T, Olympus, Japan). The residual solids (cells) were removed on a 0.22 m membrane filter, and the filtrates concentrated ten-times in a rotary evaporator (Laborota 4000 HB/G1, Heidolph, Germany) at 30 ºC. The concentrated COM was stored at ­18 ºC. 2. 3 COM characterisation procedure Determination of protein portion from the COM The COM consists primarily of carbohydrates and proteins. Therefore, portions of proteins (DOCP) and non-protein (carbohydrates) substances (DOCNP) were measured during the experiments. Proteins were isolated from the COM using H2WO4 as a protein precipitant (Dawson et al., 1986). The protein precipitate was then separated from the dissolved organic matter by filtration through a 0.22 m membrane filters (MF, Millipore, USA) and DOCNP was analysed in the filtrate. The protein portion DOCP is calculated as follows: DOCP = DOCT ­ DOCNP, (1) where DOCT is the total DOC of the COM. The protein precipitations were carried out in triplicate and errors of DOCP were less than 5%. The methodology of determination of protein portion from the COM can be found in Dawson et al. (1986) and Pivokonsky et al. (2006). DOC analysis A Shimadzu TOC-VCPH analyzer was used for organic carbon analysis. Dissolved organic carbon (DOC) was calculated as the difference between the total carbon and inorganic carbon measurements for samples filtered through 0.22 m membrane filter (MF, Millipore). All measurements were conducted in triplicate and errors were less than 2%. Molecular weight fractionation The aqueous COM samples were dialyzed against 0.05M phosphate buffer (pH 7.0) using dialysis membrane (Amersham Bioscience Corp., MW cut off: 10 kDa). The dialyzed samples were applied to the gel permeation chromatography (GPC) for the apparent molecular weight fractionation. The DOCT concentration of all the COM samples was 100 mg l-1 to eliminate potential concentration effects on GPC. The MW fractionation was performed by HPLC system (Agilent 1100 series, Agilent Technologies) with diode array detector (DAD). The Zorbax GF-250 (9.4 mm x 250 mm, 4 m) and GF-450 columns (9.4 mm x 250 mm, 6 m) were used for the GPC. The separation range applied was 4,000­900,000 for globular proteins using GF-250 and GF-450 columns in series. The buffer used for MW fractionation was 0.05M phosphate buffer (pH 7.0). The flow rate of mobile phase was 2.00 ml min-1 at the temperature of 23°C. The sample volume was 20 l. The maximum absorption wavelength (max = 280 nm) was used for measurement of MW of the COM samples. The wavelength of 280 nm was used especially for the protein detection. Data analysis was performed using Agilent Technologies Chemstation software. The system was calibrated using the following gel filtration standards (Sigma-Aldrich Co.): cyanocobalamin (1.35 kDa), ribonuclease-a (13.7 kDa), myoglobin (17 kDa), carbonic anhydrase (29 kDa), albumin (66 kDa), alcohol dehydrogenase (150 kD), -amylase (200 kDa), apoferritin (443 kDa), thyroglobulin (669 kDa) and imunoglobulin (900 kDa). A calibration curve was based on a linear relationship between the retention time and the actual log MW. In all cases, a good linear correlation between the retention time and log MW was observed for the calibration curves (R2 = 0.996). BioRad gel filtration standards of bovine gamma globulin (158 kDa) and chicken ovalbumin (44 kDa) were used as control samples. Standard error was ±1.05 kDa for gamma globulin and ±0.62 for chicken ovalbumin. Reproducibility of the MW fractionation of COM samples was very good, with MW deviations of less than 3% from repeated measurements. 2.4 Coagulation procedure Water The ultrapure water with added NaHCO3 was used in these experiments. The COM of a concentration DOCT = 7.0 mg l-1 was prepared. Other relevant water quality parameters were: pH = 8.3, KNK4.5 = 1.99 mmol l-1, Fe = 0.007 mg l-1, Al = = 0.004 mg l-1. Jar tests The COM removal during water purification was investigated by jar tests. The LMK 8 (Institute of Hydrodynamics, AS CR, v. v. i., Czech Republic) variable speed eight station flocculator with a paddle type stirrer housing standard 2 l beakers fitted with a variable speed drive and equipped with an infinite speed controller and revolution counter was used for jar tests. The tested volume of water in the beakers was 1.5 l. Ferric sulphate and aluminium sulphate were applied as destabilising reagents (coagulants). The procedure consisted of a 1 minute of homogenization agitation ( G = 200 s-1), 15 minutes of aggregation agitation ( G = 70 s-1) and 60 minutes of settling. The effect of coagulation was ascertained by: (i) direct comparison of water quality indicators: content of cation of destabilising reagent (concentration of Fe /cFe/ and Al /cAl/), dissolved organic carbon DOC, pH value and alkalinity (ANC4.5). Methodology of chemical analyses is in details described in Polasek and Mutl, 1995. (ii) determination of the degree of aggregation , calculated according to the relationship C - CF A = 0 , C0 (2) where C0 is the concentration of indicator monitored (Al, Fe, DOC) at the point of testing and CF is the concentration of the same indicator determined in the centrate of the sample C0 after its treatment by centrifugation under defined conditions (3000 rpm, T = 20 min) (Hereit et al., 1980; Polasek and Mutl, 1995). (iii) determination of the test of aggregation, which enables the aggregates formed to be ascribed to one of the four basic size-categories, namely: nonaggregated particles (NA), primary aggregates (PR), micro-aggregataes (MI) and macroaggregates (MA). The technologically significant categories of particles are determined according to the following relationships: C - C5 C - C60 C - C60 F MA = 0 , MI = 5 , PR = 60 , C0 C0 C0 C NA = 60 F , (3­6) C0 organic matter is relatively low and reaches its highest value of about DOCT = 0.45 with ferric sulphate and DOCT = 0.41 with aluminium sulphate (Figs. 4 and 5). Maximum aggregation efficiency is attained in the range of high dosage of destabilisation reagent when a considerable Fe and Al concentrations remain non-aggregated (Figs. 2 and 3). and MA + MI + PR + NA = 1, (7) where C0, C5 and C60 ­ the concentrations of the monitored determinant measured in the samples taken at the beginning of sedimentation, after 5, and 60 minutes of sedimentation and C60F ­ a concentration of the monitored determinant measured in concentrate of the C60 sample after its treatment by centrifugation under defined conditions (3000 rpm, T = 20 min) (Hereit et al., 1980; Polasek and Mutl, 1995). 3. Results and discussion The results of COM characterisation show that the COM of M. aeruginosa is composed of protein and non-protein organic matters. The protein portion determined as DOCP was measured to be about 59.9% of DOCT in the COM and the non-protein organic is the balance of 40.1%. The proteins characterized by 21, 85, 234, 359, 470 kDa and more than 900 kDa were identified in the M. aeruginosa COM (Fig. 1). The protein concentration in the raw water was DOCP = 4.12 mg l-1 and non-protein concentration was DOCNP = 2.86 mg l-1. The character of the COM produced by cyanobacteria M. aeruginosa and other cyanobacteria and green algae are discussed in sufficient details in literature (Pivokonsky et al., 2006). The dependence of removal of the COM produced by M. aeruginosa on dosage of destabilisation reagent is shown in Figs. 2 and 3. It is evident that residual concentration of total organic matter (DOCT) drops up to a dosage of 0.160 mmol l-1 (90 mg l-1) with ferric sulphate and 0.105 mmol l-1 (70 mg l-1) with aluminium sulphate aggregation. Thereafter residual concentrations of DOCT remain virtually unchanged. The aggregation efficiency of 124 Fig. 1. GPC profile for the COM in raw water. Obr. 1. GPC profil COM v surové vod. In contrast to the curves of residual concentration of organic matter (DOCT), the concentration curves of residual Fe and Al have a quite distinct optimum (cFe = 0.12 mg l-1, cAl = 0.16 mg l-1) as shown in Figs. 2 and 3. The residual Fe reaches its maximum cFe = 1.23 mg l-1 at a dosage around 0.018 mmol l-1 (10 mg l-1) Fe2(SO4)3 9H2O and pH = 7.56. With a further increase in dosage, the residual Fe gradually decreases up to its minimum cFe = 0.12 mg l-1 at a dosage of 0.125 mmol l-1 (70 mg l-1) and pH = 6.33. A further increase in ferric sulphate dosage results in another sharp increase in residual Fe up to cFe = = 1.91 mg l-1 which is reached at a dosage of 0.178 mmol l-1 (100 mg l-1) and pH = 5.43 and thereafter increases gradually until alkalinity of the water was fully utilised (Fig. 2) at a dosage of about 0.231 mmol l-1 (130 mg l-1). The residual Al reaches its maximum cAl = 1.29 mg l-1 at a dosage around 0.030 mmol l-1 (20 mg l-1) Al2(SO4)3 18H2O and pH = 7.58 (Fig. 3). After reaching this maximum, residual Al gradually decreases to its lowest value cAl = 0.16 mg l-1 which is attained at a dosage of 0.075 mmol l-1 (50 mg l-1) and pH = 6.67. With a further increase in dosage, the residual Al gradually increases until alkalinity of the water (ANC4.5) is fully utilised (Fig. 3) at a dosage of about 0.210 mmol l-1 (140 mg l-1). Fig. 2. Dependence of residual Fe and DOCT on ferric sulphate dosage. Obr. 2. Závislost zbytkového zeleza a DOCT na dávce síranu zelezitého. mg l-1 is attained at a dosage of 0.178 mmol l-1 (100 mg l-1) of ferric sulphate whilst in the case of aluminium sulphate the lowest DOCT = 4.2 mg l-1 is attained at a dosage of 0.195 mmol l-1 (130 mg l-1). It is evident from the results obtained that the efficiency of COM aggregation is dependent on pH values. It was found that the dissolved organic substances are the most efficiently separated in a pH ranging between 5.0 and 6.5 and sometimes even at pH < 5.0 (Edzwald et al., 1982; Edwards and Amirtharajah, 1985; Polasek and Mutl, 1995, 2005; Gregor et al., 1997; Pivokonska and Pivokonsky, 2007). The pH value influences also the prevailing type of Fe-hydroxopolymer which is mainly characterized by the magnitude of surface charge. The charge magnitude determines efficiency of a hydroxopolymer as destabilisation reagent (Polasek and Mutl, 1995, 2005). Fig. 3. Dependence of residual Al and DOCT on aluminium sulphate dosage. Obr. 3. Závislost zbytkového hliníku a DOCT na dávce síranu zelezitého. Fig. 4. Dependence of Fe and DOCT on ferric sulphate dosage. Obr. 4. Závislost Fe a DOCT na dávce síranu zelezitého. The efficiency of Fe-aggregation is about Fe = = 0.90 in a dosage range between 0.071 and 0.178mmol l-1 (40 and 100 mg l-1). The maximum aggregation efficiency Fe = 0.92 is attained at a dosage of 0.160 mmol l-1 (90 mg l-1) (Fig. 4). Similarly, the efficiency of Al-aggregation is about Al = 0.90 also in a dosage range between 0.060 and 0.150 mmol l-1 (40 and 100 mg l-1). However, the maximum Al = 0.92 is attained at a dosage of 0.060 mmol l-1 (40 mg l-1) (Fig. 5). Comparison of the residual Fe and Al ions shows that the lowest Fe concentration is attained at a dosage of 0.125 mmol l-1 (70 mg l-1) whereas the lowest Al concentration is attained at a dosage of 0.075 mmol l-1 (50 mg l-1). In contrast to that the lowest residual DOCT = 3.6 Fig. 5. Dependence of Al and DOCT on aluminium sulphate dosage. Obr. 5. Závislost Al a DOCT na dávce síranu hlinitého. Figs. 6 and 7 show comparison of the changes in residual protein (DOCP) and non-protein (DOCNP) organic matters with ferric and aluminium sulphate dosages. In the case of ferric sulphate (Fig. 6) DOCP gradually decreases with dosage to around 1.5 mg l-1 at a dosage of 0.089 mmol l-1 (50 mg l-1) and with a further increase in dosage it decreases very slowly to a concentration of 1.07 mg l-1 which is attained at a dosage around 0.160 mmol l-1 (90 mg l-1) and thereafter it remains unchanged. In contrast, DOCNP is reduced by 0.4 mg l-1 at a dosage of 0.018 mmol l-1 (10 mg l-1). of 0.018 mmol l-1 (10 mg l-1) of ferric sulphate and with increasing dosage it remains unchanged. In contrast, in the case of aluminium sulphate the residual DOCNP decreases very slowly with dosage to its lowest residual concentration DOCNP = 2.24 mg l-1 at a dosage of 0.231 mmol l-1 (130 mg l-1). It is evident from comparison of the removal of DOCP and DOCNP that the reduction in COM (DOCT) is mainly the result of the removal of protein organic matter (DOCP). Low aggregation efficiency of the non-protein organic substances is likely the result of both the electric-neutrality of polysaccharide molecules and the fact that they contain a large quantity of OH ions owing to which a compact hydration layer is formed around them (Rinaudo, 2001). The low aggregation efficiency of neutral hydrophilic organic matter (polysaccharides) was confirmed also by other researchers (Croue et al., 1993; Kim and Yu, 2004; Pivokonska and Pivokonsky, 2007). Fig. 6. Dependence of DOCT, DOCNP and DOCP on ferric sulphate dosage. Obr. 6. Závislost DOCT, DOCNP a DOCP na dávce síranu zelezitého. In the case of aluminium sulphate (Fig. 7) DOCP gradually decreases up to a dosage of 0.075 mmol l-1 (50 mg l-1) and then it drops to a value of 2.06 mg l-1 at a dosage of 0.105 mmol l-1 (70 mg l-1), (pH = = 6.76 to 6.17 and ANC4.5 = 0.81 to 0.45 mmol l-1). With further increase in dosage DOCP remains unchanged. This sudden drop in the residual DOCP concentrations indicates the optimum reaction conditions at which this drop is most likely the result of adsorption of these compounds onto the hydrolysis products of destabilisation reagents (Polasek and Mutl, 1995). Similarly, in the case of ferric sulphate, Fig. 6 shows such a sudden improvement in the residual DOCP concentrations also between dosages 0.120 and 0.135 mmol l-1 (80 and 90 mg l-1), (pH = 6.00 ­ 5.80 and ANC4.5 = 0.32 ­ 0.22 mg l-1). The changes in non-protein organic matter (polysaccharides) concentration with dosage of the destabilisation reagents are also interesting. Its concentration drops to DOCNP = 2.54 mg l-1 at a dosage 126 Fig. 7. Dependence of DOCT, DOCNP and DOCP on aluminium sulphate dosage. Obr. 7. Závislost DOCT, DOCNP a DOCP na dávce síranu hlinitého. The residual COM concentrations attained with both destabilisation reagents were subjected to fractionation of protein MW. The concentration of proteins identified at a dosage at which the maximum aggregation efficiency is attained, i.e. D = 0.178 mmol l-1 (100 mg l-1) Fe2(SO4)3 9H2O (Fe = 1.90 mg l-1, DOCT = 3.61 mg l-1, DOCP = 1.07 mg l-1) and D = 0.195 mmol l-1 (130 mg l-1) Al2(SO4)3 18H2O (Al = 3.77 mg l-1, DOCT = 4.22 mg l-1, DOCP = 2.06 mg l-1) are compared in Tab. 1. The effect of cellular organic matter produced by cyanobacteria Microcystis aeruginosa on water purification T a b l e 1. Efficiency of protein aggregation. T a b u l k a 1. Úcinnost agregace protein. Protein MW [kDa] 21 85 234 359 470 > 900 Suma Raw water DOCPI [mg l-1] 0.41 0.70 0.66 0.95 0.41 0.99 4.12 Purified water Fe2(SO4)3 9H2O (D = 100 mg l-1) DOCPI DOCPI [mg l-1] [-] 0.27 0.34 0 1 0.21 0.68 0.59 0.38 0 1 0 1 1.07 0.74 Purified water Al2(SO4)3 18H2O (D = 130 mg l-1) DOCPI DOCPI [mg l-1] [­] 0.18 0.56 0.57 0.19 0.53 0.20 0.78 0.18 0 1 0 1 2.06 0.50 The area of the peaks of each identified protein was recalculated from the DOCP concentration to a DOCPI (DOC concentration of protein identified using molecular weight fractionation) for the determination value of the aggregation efficiency DOCPI (aggregation efficiency of DOC concentration of protein identified using molecular weight fractionation). It is evident from this comparison that no proteins of MW of 470 kDa and higher than 900 kDa are found in the purified water using both destabilisation reagents. Higher efficiency in the removal of high molecular organic matter, which is proven also by other authors (Chin et al., 1994; Chow et al., 1999), is most likely associated with their structure and the presence of dissociated functional groups on their surface. In the case of ferric sulphate all proteins of MW = 85 kDa are removed. On the contrary, a higher efficiency in the aggregation of proteins of the lowest MW = 21 kDa is attained with aluminium sulphate. It is also evident from these results, as already discussed above, that a higher total efficiency in the aggregation of proteins is attained with ferric sulphate. Monitoring of the size-distribution of aggregates formed by the test of aggregation (Hereit et al., 1980; Polasek and Mutl, 1995) offers one of the best method for the interpretation of the results of jar tests. Figs. 8 and 9 show the development of aggregates formed by both destabilisation reagents under the same hydrodynamic conditions. The residual portion of non-aggregated particles NA corresponds to the course of residual Fe and Al concentrations. As it is evident from Fig. 8 the lowest NA = 0.10 portion was attained with ferric sulphate dosages between 0.071 and 0.142 mmol l-1 (40 and 80 mg l-1). The highest portion of macro-aggregates MA = 0.58 is attained at a dosage of 0.018 mmol l-1 (10 mg l-1) and thereafter it decreases with increasing dosage. As the portion of macro-aggregates decreases the portion of non-aggregated particles gradually increases with increasing dosages. The development of Al-formed aggregates is illustrated in Fig. 9. The lowest portion of NA = 0.16 is attained with aluminium sulphate dosage between 0.075 and 0.150 mmol l-1 (50 and 100 mg l-1). The highest portion of macro-aggregates MA was formed at a dosage of 0.075 mmol l-1 (50 mg l-1). Most probably the relatively high portion of macro-aggregates formed during jar test is caused by the fact that under certain circumstances the COM substances may behave like non-ionic and anionic polyelectrolytes, which by means of the resultant adhesion enable formation of large aggregates (Bernhardt et al., 1986, 1989; Hoyer et al., 1987). Fig. 8. Dependence of size distribution of formed aggregates on ferric sulphate dosage. Obr. 8. Závislost velikostní distribuce tvoených agregát na dávce síranu zelezitého. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Hydrology and Hydromechanics de Gruyter

The Effect of Cellular Organic Matter Produced by Cyanobacteria Microcystis Aeruginosa on Water Purification

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10.2478/v10098-009-0011-3
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J. Hydrol. Hydromech., 57, 2009, 2, 121­129 DOI: 10.2478/v10098-009-0011-3 MARTIN PIVOKONSKÝ, LENKA PIVOKONSKÁ, JITKA BÄUMELTOVÁ, PETRA BUBÁKOVÁ Institute of Hydrodynamics AS CR, v. v. i., Pod Patankou 5, 166 12 Prague 6, Czech Republic; mailto: pivo@ih.cas.cz The aim of this paper is to investigate the influence of COM (Cellular Organic Matter) produced by Microcystis aeruginosa on the process of water purification by destabilisation and subsequent aggregation of the impurity particles. The research was carried out with a raw water into which COM was added. The removal efficiency of the most significant components of COM, i.e. polysaccharides and proteins, was investigated. It was found that the removal efficiency of polysaccharides and proteins was dependent on the reaction conditions (pH, type of destabilisation reagent and its dosage). The removal efficiency of COM was relatively low. It was about 46% and 41% using ferric sulphate and aluminium sulphate aggregation, respectively. In comparison to the other organic components of COM, mainly polysaccharides, the proteins are removed with a higher efficiency. The GPC analyses of the residual COM showed that the proteins of higher molecular weight were aggregated with a higher efficiency. KEY WORDS: AOM (Algal Organic Matter), COM (Cellular Organic Matter), Destabilisation, Aggregation, Reaction Conditions, Water Purification. Martin Pivokonský, Lenka Pivokonská, Jitka Bäumeltová, Petra Bubáková: VLIV BUNCNÝCH ORGANICKÝCH LÁTEK PRODUKOVANÝCH SINICÍ MICROCYSTIS AERUGINOSA NA ÚPRAVU VODY. J. Hydrol. Hydromech., 57, 2009, 2; 23 lit., 9 obr., 1 tab. Cílem práce je opis vlivu buncných organických látek (COM) produkovaných sinicí Microcystis aeruginosa na proces úpravy vody pomocí destabilizace a následné agregace znecisujících pímsí. Výzkum byl uskutecován se syntetickou surovou vodou, do které byly pidány COM získané laboratorní kultivací M. aeruginosa. V prbhu laboratorních test byla sledována pedevsím úcinnost odstranní dvou základních slozek COM, tj. polysacharid a protein. Bylo zjistno, ze tato úcinnost závisí pedevsím na reakcních podmínkách (typu a dávce destabilizacního cinidla a pH). Úcinnost odstranní COM byla pomrn nízká, maximální dosazená úcinnost byla 46% pi destabilizaci pomocí síranu zelezitého a 41% pi pouzití síranu hlinitého. Bylo zjistno, ze s vyssí úcinností jsou odstraovány proteiny, obzvlást pak proteiny s vyssí molekulovou hmotností. KLÍCOVÁ SLOVA: organické látky produkované fytoplanktonem, buncné organické látky, destabilizace, agregace, reakcní podmínky, úprava vody. 1. Introduction Effective removal of natural organic matter (NOM) and especially that produced by a vast development of phytoplankton (Algal Organic Matter ­ AOM) is one of the very significant challenges of the purification of the surface waters (Bernhardt et al., 1985, 1986, 1989; Hoyer et al., 1987; Takaara et al., 2005, 2007; Pivokonsky et al., 2006). Generally, these organic matters can be distinguished into the substances that are released by metabolic activity of micro-organisms ­ the extracellular organic matter (EOM) and the substances released during the process of their decay ­ the intracellular organic matter (COM) (Pivokonsky et al., 2006; Lüsse et al., 1985; Hoyer et al., 1985). The COM represents a specific problem due to the occasional sudden increase in its concentration. A great attention was given to the influence of AOM on the purification of water polluted with different impurities such as aluminosilicates, humic matter, etc. Various studies showed that the influence of EOM on the process of destabilisation and aggregation of the impurity particles could be com121 pared to that of non-ionic polymers (Bernhardt et al., 1985, 1986, 1989; Hoyer et al., 1987). At their low concentrations the efficiency of water purification increases due to the formation of inter-particle bridges between the impurity particles or adsorption to their surfaces. In contrast, at higher concentrations the AOM inhibits the process of destabilisation of the impurity particles by increasing negative charge on their surface. Furthermore, certain substances contained in AOM, primarily proteins, also inhibit the destabilisation process. It is assumed that this results from the formation of higher-valence cation complexes and hydrated ions aided by coordination bonds. The formation of these complexes results in increased consumption of destabilisation reagent and decreasing efficiency of the destabilisation process (Bernhardt et al., 1989). The extent of the inhibition effect of the AOM is dependent upon its composition which is influenced by the kind of organisms and their growth phase (Pivokonsky et al., 2006). The COM are the substances most difficult to remove from the water. The reason is that these organic compounds are released suddenly in large quantities during decay of phytoplankton. Another very important reason is different chemical composition of COM in comparison to the other NOM and EOM (Takaara et al., 2005, 2007; Pivokonsky et al., 2006). The influence of AOM on the destabilisation and aggregation efficiency is not yet adequately explained. The contribution of authors to this theme is presented in this paper. The results obtained by investigating the effect of COM pollution produced by M. aeruginosa on its removal efficiency by coagulation with ferric sulphate and aluminium sulphate purification are summarised in this paper. 2. Material and methods 2. 1 Cyanobacteria cultivation procedure The cyanobacteria Microcystis aeruginosa KUTZ. (ZAPOMELOVA 2006/2) was used in this study. Inoculums of this strain were kindly supplied by the Culture Collection of Algal Laboratory, Institute of Botany, AS CR, v. v. i., Czech Republic. The laboratory strain M. aeruginosa was grown in a 20 l volume of Z medium (pH = 8.5) (Strub and Schweiz, 1961) at 24 °C and regularly shaken by a shaking apparatus operating at 40 rpm. The 16hlight/8h-dark cycle was applied. The cultures were illuminated using four 40W cool-white fluorescent 122 lamps supplying about 6000 lux. All materials and media were sterilized by autoclaving before assembly and operation. The growth of M. aeruginosa was monitored by chlorophyll-a in the culture. Cyanobacterial cells were harvested on 16th day of the cultivation period in the steady-state growth (dominant number of cells was free). 2. 2 COM preparation procedure The COM samples were prepared by destruction of the microorganism's cells which were separated from the growth media (2 l samples) on a 0.22 m membrane filter (Millipore, USA) on the 16th day of the cultivation time (the steady-state growth). The separated cells were mixed with ultrapure water (200 ml). The destruction of cells was performed using an ultrasonic homogenizer (HD 3200, 20 kHz, 60W), which was dipped into the beaker containing the separated cells of microorganisms. The efficiency of cells destruction was checked in an optical microscope (Optech B4T, Olympus, Japan). The residual solids (cells) were removed on a 0.22 m membrane filter, and the filtrates concentrated ten-times in a rotary evaporator (Laborota 4000 HB/G1, Heidolph, Germany) at 30 ºC. The concentrated COM was stored at ­18 ºC. 2. 3 COM characterisation procedure Determination of protein portion from the COM The COM consists primarily of carbohydrates and proteins. Therefore, portions of proteins (DOCP) and non-protein (carbohydrates) substances (DOCNP) were measured during the experiments. Proteins were isolated from the COM using H2WO4 as a protein precipitant (Dawson et al., 1986). The protein precipitate was then separated from the dissolved organic matter by filtration through a 0.22 m membrane filters (MF, Millipore, USA) and DOCNP was analysed in the filtrate. The protein portion DOCP is calculated as follows: DOCP = DOCT ­ DOCNP, (1) where DOCT is the total DOC of the COM. The protein precipitations were carried out in triplicate and errors of DOCP were less than 5%. The methodology of determination of protein portion from the COM can be found in Dawson et al. (1986) and Pivokonsky et al. (2006). DOC analysis A Shimadzu TOC-VCPH analyzer was used for organic carbon analysis. Dissolved organic carbon (DOC) was calculated as the difference between the total carbon and inorganic carbon measurements for samples filtered through 0.22 m membrane filter (MF, Millipore). All measurements were conducted in triplicate and errors were less than 2%. Molecular weight fractionation The aqueous COM samples were dialyzed against 0.05M phosphate buffer (pH 7.0) using dialysis membrane (Amersham Bioscience Corp., MW cut off: 10 kDa). The dialyzed samples were applied to the gel permeation chromatography (GPC) for the apparent molecular weight fractionation. The DOCT concentration of all the COM samples was 100 mg l-1 to eliminate potential concentration effects on GPC. The MW fractionation was performed by HPLC system (Agilent 1100 series, Agilent Technologies) with diode array detector (DAD). The Zorbax GF-250 (9.4 mm x 250 mm, 4 m) and GF-450 columns (9.4 mm x 250 mm, 6 m) were used for the GPC. The separation range applied was 4,000­900,000 for globular proteins using GF-250 and GF-450 columns in series. The buffer used for MW fractionation was 0.05M phosphate buffer (pH 7.0). The flow rate of mobile phase was 2.00 ml min-1 at the temperature of 23°C. The sample volume was 20 l. The maximum absorption wavelength (max = 280 nm) was used for measurement of MW of the COM samples. The wavelength of 280 nm was used especially for the protein detection. Data analysis was performed using Agilent Technologies Chemstation software. The system was calibrated using the following gel filtration standards (Sigma-Aldrich Co.): cyanocobalamin (1.35 kDa), ribonuclease-a (13.7 kDa), myoglobin (17 kDa), carbonic anhydrase (29 kDa), albumin (66 kDa), alcohol dehydrogenase (150 kD), -amylase (200 kDa), apoferritin (443 kDa), thyroglobulin (669 kDa) and imunoglobulin (900 kDa). A calibration curve was based on a linear relationship between the retention time and the actual log MW. In all cases, a good linear correlation between the retention time and log MW was observed for the calibration curves (R2 = 0.996). BioRad gel filtration standards of bovine gamma globulin (158 kDa) and chicken ovalbumin (44 kDa) were used as control samples. Standard error was ±1.05 kDa for gamma globulin and ±0.62 for chicken ovalbumin. Reproducibility of the MW fractionation of COM samples was very good, with MW deviations of less than 3% from repeated measurements. 2.4 Coagulation procedure Water The ultrapure water with added NaHCO3 was used in these experiments. The COM of a concentration DOCT = 7.0 mg l-1 was prepared. Other relevant water quality parameters were: pH = 8.3, KNK4.5 = 1.99 mmol l-1, Fe = 0.007 mg l-1, Al = = 0.004 mg l-1. Jar tests The COM removal during water purification was investigated by jar tests. The LMK 8 (Institute of Hydrodynamics, AS CR, v. v. i., Czech Republic) variable speed eight station flocculator with a paddle type stirrer housing standard 2 l beakers fitted with a variable speed drive and equipped with an infinite speed controller and revolution counter was used for jar tests. The tested volume of water in the beakers was 1.5 l. Ferric sulphate and aluminium sulphate were applied as destabilising reagents (coagulants). The procedure consisted of a 1 minute of homogenization agitation ( G = 200 s-1), 15 minutes of aggregation agitation ( G = 70 s-1) and 60 minutes of settling. The effect of coagulation was ascertained by: (i) direct comparison of water quality indicators: content of cation of destabilising reagent (concentration of Fe /cFe/ and Al /cAl/), dissolved organic carbon DOC, pH value and alkalinity (ANC4.5). Methodology of chemical analyses is in details described in Polasek and Mutl, 1995. (ii) determination of the degree of aggregation , calculated according to the relationship C - CF A = 0 , C0 (2) where C0 is the concentration of indicator monitored (Al, Fe, DOC) at the point of testing and CF is the concentration of the same indicator determined in the centrate of the sample C0 after its treatment by centrifugation under defined conditions (3000 rpm, T = 20 min) (Hereit et al., 1980; Polasek and Mutl, 1995). (iii) determination of the test of aggregation, which enables the aggregates formed to be ascribed to one of the four basic size-categories, namely: nonaggregated particles (NA), primary aggregates (PR), micro-aggregataes (MI) and macroaggregates (MA). The technologically significant categories of particles are determined according to the following relationships: C - C5 C - C60 C - C60 F MA = 0 , MI = 5 , PR = 60 , C0 C0 C0 C NA = 60 F , (3­6) C0 organic matter is relatively low and reaches its highest value of about DOCT = 0.45 with ferric sulphate and DOCT = 0.41 with aluminium sulphate (Figs. 4 and 5). Maximum aggregation efficiency is attained in the range of high dosage of destabilisation reagent when a considerable Fe and Al concentrations remain non-aggregated (Figs. 2 and 3). and MA + MI + PR + NA = 1, (7) where C0, C5 and C60 ­ the concentrations of the monitored determinant measured in the samples taken at the beginning of sedimentation, after 5, and 60 minutes of sedimentation and C60F ­ a concentration of the monitored determinant measured in concentrate of the C60 sample after its treatment by centrifugation under defined conditions (3000 rpm, T = 20 min) (Hereit et al., 1980; Polasek and Mutl, 1995). 3. Results and discussion The results of COM characterisation show that the COM of M. aeruginosa is composed of protein and non-protein organic matters. The protein portion determined as DOCP was measured to be about 59.9% of DOCT in the COM and the non-protein organic is the balance of 40.1%. The proteins characterized by 21, 85, 234, 359, 470 kDa and more than 900 kDa were identified in the M. aeruginosa COM (Fig. 1). The protein concentration in the raw water was DOCP = 4.12 mg l-1 and non-protein concentration was DOCNP = 2.86 mg l-1. The character of the COM produced by cyanobacteria M. aeruginosa and other cyanobacteria and green algae are discussed in sufficient details in literature (Pivokonsky et al., 2006). The dependence of removal of the COM produced by M. aeruginosa on dosage of destabilisation reagent is shown in Figs. 2 and 3. It is evident that residual concentration of total organic matter (DOCT) drops up to a dosage of 0.160 mmol l-1 (90 mg l-1) with ferric sulphate and 0.105 mmol l-1 (70 mg l-1) with aluminium sulphate aggregation. Thereafter residual concentrations of DOCT remain virtually unchanged. The aggregation efficiency of 124 Fig. 1. GPC profile for the COM in raw water. Obr. 1. GPC profil COM v surové vod. In contrast to the curves of residual concentration of organic matter (DOCT), the concentration curves of residual Fe and Al have a quite distinct optimum (cFe = 0.12 mg l-1, cAl = 0.16 mg l-1) as shown in Figs. 2 and 3. The residual Fe reaches its maximum cFe = 1.23 mg l-1 at a dosage around 0.018 mmol l-1 (10 mg l-1) Fe2(SO4)3 9H2O and pH = 7.56. With a further increase in dosage, the residual Fe gradually decreases up to its minimum cFe = 0.12 mg l-1 at a dosage of 0.125 mmol l-1 (70 mg l-1) and pH = 6.33. A further increase in ferric sulphate dosage results in another sharp increase in residual Fe up to cFe = = 1.91 mg l-1 which is reached at a dosage of 0.178 mmol l-1 (100 mg l-1) and pH = 5.43 and thereafter increases gradually until alkalinity of the water was fully utilised (Fig. 2) at a dosage of about 0.231 mmol l-1 (130 mg l-1). The residual Al reaches its maximum cAl = 1.29 mg l-1 at a dosage around 0.030 mmol l-1 (20 mg l-1) Al2(SO4)3 18H2O and pH = 7.58 (Fig. 3). After reaching this maximum, residual Al gradually decreases to its lowest value cAl = 0.16 mg l-1 which is attained at a dosage of 0.075 mmol l-1 (50 mg l-1) and pH = 6.67. With a further increase in dosage, the residual Al gradually increases until alkalinity of the water (ANC4.5) is fully utilised (Fig. 3) at a dosage of about 0.210 mmol l-1 (140 mg l-1). Fig. 2. Dependence of residual Fe and DOCT on ferric sulphate dosage. Obr. 2. Závislost zbytkového zeleza a DOCT na dávce síranu zelezitého. mg l-1 is attained at a dosage of 0.178 mmol l-1 (100 mg l-1) of ferric sulphate whilst in the case of aluminium sulphate the lowest DOCT = 4.2 mg l-1 is attained at a dosage of 0.195 mmol l-1 (130 mg l-1). It is evident from the results obtained that the efficiency of COM aggregation is dependent on pH values. It was found that the dissolved organic substances are the most efficiently separated in a pH ranging between 5.0 and 6.5 and sometimes even at pH < 5.0 (Edzwald et al., 1982; Edwards and Amirtharajah, 1985; Polasek and Mutl, 1995, 2005; Gregor et al., 1997; Pivokonska and Pivokonsky, 2007). The pH value influences also the prevailing type of Fe-hydroxopolymer which is mainly characterized by the magnitude of surface charge. The charge magnitude determines efficiency of a hydroxopolymer as destabilisation reagent (Polasek and Mutl, 1995, 2005). Fig. 3. Dependence of residual Al and DOCT on aluminium sulphate dosage. Obr. 3. Závislost zbytkového hliníku a DOCT na dávce síranu zelezitého. Fig. 4. Dependence of Fe and DOCT on ferric sulphate dosage. Obr. 4. Závislost Fe a DOCT na dávce síranu zelezitého. The efficiency of Fe-aggregation is about Fe = = 0.90 in a dosage range between 0.071 and 0.178mmol l-1 (40 and 100 mg l-1). The maximum aggregation efficiency Fe = 0.92 is attained at a dosage of 0.160 mmol l-1 (90 mg l-1) (Fig. 4). Similarly, the efficiency of Al-aggregation is about Al = 0.90 also in a dosage range between 0.060 and 0.150 mmol l-1 (40 and 100 mg l-1). However, the maximum Al = 0.92 is attained at a dosage of 0.060 mmol l-1 (40 mg l-1) (Fig. 5). Comparison of the residual Fe and Al ions shows that the lowest Fe concentration is attained at a dosage of 0.125 mmol l-1 (70 mg l-1) whereas the lowest Al concentration is attained at a dosage of 0.075 mmol l-1 (50 mg l-1). In contrast to that the lowest residual DOCT = 3.6 Fig. 5. Dependence of Al and DOCT on aluminium sulphate dosage. Obr. 5. Závislost Al a DOCT na dávce síranu hlinitého. Figs. 6 and 7 show comparison of the changes in residual protein (DOCP) and non-protein (DOCNP) organic matters with ferric and aluminium sulphate dosages. In the case of ferric sulphate (Fig. 6) DOCP gradually decreases with dosage to around 1.5 mg l-1 at a dosage of 0.089 mmol l-1 (50 mg l-1) and with a further increase in dosage it decreases very slowly to a concentration of 1.07 mg l-1 which is attained at a dosage around 0.160 mmol l-1 (90 mg l-1) and thereafter it remains unchanged. In contrast, DOCNP is reduced by 0.4 mg l-1 at a dosage of 0.018 mmol l-1 (10 mg l-1). of 0.018 mmol l-1 (10 mg l-1) of ferric sulphate and with increasing dosage it remains unchanged. In contrast, in the case of aluminium sulphate the residual DOCNP decreases very slowly with dosage to its lowest residual concentration DOCNP = 2.24 mg l-1 at a dosage of 0.231 mmol l-1 (130 mg l-1). It is evident from comparison of the removal of DOCP and DOCNP that the reduction in COM (DOCT) is mainly the result of the removal of protein organic matter (DOCP). Low aggregation efficiency of the non-protein organic substances is likely the result of both the electric-neutrality of polysaccharide molecules and the fact that they contain a large quantity of OH ions owing to which a compact hydration layer is formed around them (Rinaudo, 2001). The low aggregation efficiency of neutral hydrophilic organic matter (polysaccharides) was confirmed also by other researchers (Croue et al., 1993; Kim and Yu, 2004; Pivokonska and Pivokonsky, 2007). Fig. 6. Dependence of DOCT, DOCNP and DOCP on ferric sulphate dosage. Obr. 6. Závislost DOCT, DOCNP a DOCP na dávce síranu zelezitého. In the case of aluminium sulphate (Fig. 7) DOCP gradually decreases up to a dosage of 0.075 mmol l-1 (50 mg l-1) and then it drops to a value of 2.06 mg l-1 at a dosage of 0.105 mmol l-1 (70 mg l-1), (pH = = 6.76 to 6.17 and ANC4.5 = 0.81 to 0.45 mmol l-1). With further increase in dosage DOCP remains unchanged. This sudden drop in the residual DOCP concentrations indicates the optimum reaction conditions at which this drop is most likely the result of adsorption of these compounds onto the hydrolysis products of destabilisation reagents (Polasek and Mutl, 1995). Similarly, in the case of ferric sulphate, Fig. 6 shows such a sudden improvement in the residual DOCP concentrations also between dosages 0.120 and 0.135 mmol l-1 (80 and 90 mg l-1), (pH = 6.00 ­ 5.80 and ANC4.5 = 0.32 ­ 0.22 mg l-1). The changes in non-protein organic matter (polysaccharides) concentration with dosage of the destabilisation reagents are also interesting. Its concentration drops to DOCNP = 2.54 mg l-1 at a dosage 126 Fig. 7. Dependence of DOCT, DOCNP and DOCP on aluminium sulphate dosage. Obr. 7. Závislost DOCT, DOCNP a DOCP na dávce síranu hlinitého. The residual COM concentrations attained with both destabilisation reagents were subjected to fractionation of protein MW. The concentration of proteins identified at a dosage at which the maximum aggregation efficiency is attained, i.e. D = 0.178 mmol l-1 (100 mg l-1) Fe2(SO4)3 9H2O (Fe = 1.90 mg l-1, DOCT = 3.61 mg l-1, DOCP = 1.07 mg l-1) and D = 0.195 mmol l-1 (130 mg l-1) Al2(SO4)3 18H2O (Al = 3.77 mg l-1, DOCT = 4.22 mg l-1, DOCP = 2.06 mg l-1) are compared in Tab. 1. The effect of cellular organic matter produced by cyanobacteria Microcystis aeruginosa on water purification T a b l e 1. Efficiency of protein aggregation. T a b u l k a 1. Úcinnost agregace protein. Protein MW [kDa] 21 85 234 359 470 > 900 Suma Raw water DOCPI [mg l-1] 0.41 0.70 0.66 0.95 0.41 0.99 4.12 Purified water Fe2(SO4)3 9H2O (D = 100 mg l-1) DOCPI DOCPI [mg l-1] [-] 0.27 0.34 0 1 0.21 0.68 0.59 0.38 0 1 0 1 1.07 0.74 Purified water Al2(SO4)3 18H2O (D = 130 mg l-1) DOCPI DOCPI [mg l-1] [­] 0.18 0.56 0.57 0.19 0.53 0.20 0.78 0.18 0 1 0 1 2.06 0.50 The area of the peaks of each identified protein was recalculated from the DOCP concentration to a DOCPI (DOC concentration of protein identified using molecular weight fractionation) for the determination value of the aggregation efficiency DOCPI (aggregation efficiency of DOC concentration of protein identified using molecular weight fractionation). It is evident from this comparison that no proteins of MW of 470 kDa and higher than 900 kDa are found in the purified water using both destabilisation reagents. Higher efficiency in the removal of high molecular organic matter, which is proven also by other authors (Chin et al., 1994; Chow et al., 1999), is most likely associated with their structure and the presence of dissociated functional groups on their surface. In the case of ferric sulphate all proteins of MW = 85 kDa are removed. On the contrary, a higher efficiency in the aggregation of proteins of the lowest MW = 21 kDa is attained with aluminium sulphate. It is also evident from these results, as already discussed above, that a higher total efficiency in the aggregation of proteins is attained with ferric sulphate. Monitoring of the size-distribution of aggregates formed by the test of aggregation (Hereit et al., 1980; Polasek and Mutl, 1995) offers one of the best method for the interpretation of the results of jar tests. Figs. 8 and 9 show the development of aggregates formed by both destabilisation reagents under the same hydrodynamic conditions. The residual portion of non-aggregated particles NA corresponds to the course of residual Fe and Al concentrations. As it is evident from Fig. 8 the lowest NA = 0.10 portion was attained with ferric sulphate dosages between 0.071 and 0.142 mmol l-1 (40 and 80 mg l-1). The highest portion of macro-aggregates MA = 0.58 is attained at a dosage of 0.018 mmol l-1 (10 mg l-1) and thereafter it decreases with increasing dosage. As the portion of macro-aggregates decreases the portion of non-aggregated particles gradually increases with increasing dosages. The development of Al-formed aggregates is illustrated in Fig. 9. The lowest portion of NA = 0.16 is attained with aluminium sulphate dosage between 0.075 and 0.150 mmol l-1 (50 and 100 mg l-1). The highest portion of macro-aggregates MA was formed at a dosage of 0.075 mmol l-1 (50 mg l-1). Most probably the relatively high portion of macro-aggregates formed during jar test is caused by the fact that under certain circumstances the COM substances may behave like non-ionic and anionic polyelectrolytes, which by means of the resultant adhesion enable formation of large aggregates (Bernhardt et al., 1986, 1989; Hoyer et al., 1987). Fig. 8. Dependence of size distribution of formed aggregates on ferric sulphate dosage. Obr. 8. Závislost velikostní distribuce tvoených agregát na dávce síranu zelezitého.

Journal

Journal of Hydrology and Hydromechanics – de Gruyter

Published: Jun 1, 2009

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