Ionizing irradiation grafting of natural polymers having applications in wastewater treatment

Ionizing irradiation grafting of natural polymers having applications in wastewater treatment M.R. Nemțanu and M. Brașoveanu National Institute for Lasers, Plasma and Radiation Physics, Electron Accelerator Laboratory, 409 Atomiștilor St., P.O. Box MG-36, 077125 Bucharest-Măgurele, Romania In this chapter, graft copolymerization of acrylamide onto starch induced by simultaneous electron beam irradiation as free radical initiator without additional chemicals was performed. The results showed that the level of grafting was influenced by the monomer-to-starch ratio and less by the irradiation dose. Flocculation performances of the synthesized copolymers were evaluated in coagulation-flocculation experiments at laboratory scale in order to remove the organic load of wastewater from the meat industry. Thus, in coagulation-flocculation process the copolymer aqueous solutions showed good efficiency to improve different water quality indicators (total suspended solids, chemical oxygen demand and fatty maters) as a function of the irradiation dose and copolymer dosage used as a flocculant. Hence, starch-graft copolymers having good flocculating ability can be rapidly produced with good yields by simultaneous electron beam irradiation with low doses and no additional chemicals. Keywords: electron beam; starch; flocculation performance 1. General remarks Treatment of industrial and municipal wastewaters is one of the major challenges of our society in terms of maintaining essential resources available and suitable with providing a healthy environment. Flocculants are used for liquid-solid separation processes in wastewater treatment by acting on a molecular level on the surfaces of the particles to reduce repulsive forces and increase attractive forces [1]. Although the synthetic polymeric flocculants are highly efficient even in very small quantities, main problems associated with their use are the lack of biodegradability making them unfriendly to the environment [2] and high operation costs. The current environmental considerations impose rigorous environmental protection measures and sustainable progress that minimize the impact of wastes on the environment. Therefore, there is a strong demand to develop economically viable and eco-friendly replacements of conventional synthetic flocculants, based upon the renewable organic materials that are low cost and degrade naturally when are released into the environment [1]. On the other hand, the fast society development of the last decades led to the requirement to use the renewable raw materials more and more. Thus, modification of natural polymers in order to be used in the wastewater treatment is a continuous concern of researchers and technologists. The chemical combination of organic synthetic polymer with natural polymer produces organic natural polymer hybrid materials with desirable properties of both components [3]. In this way, grafting is the most effective way of regulating the properties of natural polysaccharides, which can be tailor-made according to the needs and produce high efficient graft copolymers [2]. The graft copolymers essentially combine the best properties of both components and possess unique properties compared to the original components. Additionally, they are biodegradable to some extent and reasonably shear stable because of the attachment of flexible synthetic polymers onto the rigid polysaccharide backbone [4]. Promising alternative copolymers have been synthesized and tested for their application as flocculating agents for treatment of different wastewaters. Modification of natural polymers such as starch [5], amylopectin [6], cellulose [7], chitosan [8], alginate [9], psyllium [10], tamarind [4], inulin [11] has been investigated as an attractive alternative in flocculation processes. Starch is one of the most abundant and renewable natural polysaccharides in the world, having application in many industries like food, pharmaceuticals, cosmetics, papermaking, textile, and so on. It is composed of two polymers of anhydroglucose units, namely amylose and amylopectin, whose composition depends on botanical source. Modification of starch by grafting various monomers onto it is an effective way to improve its properties, thereby enlarging the range of its utilization and profiting by its biodegradable nature. Acrylamide is one of the most grafted vinyl monomers onto starch substrates, and their water-soluble copolymers are good flocculants. A serious drawback of acrylamide and its homopolymer (polyacrylamide) is related to the biodegradability. Their lack of biodegradability is compensated by grafting onto starch backbone. The methods of synthesis of grafted polysaccharides are: (1) conventional redox reactions by use of chemical free radical initiator (i.e., ceric ions, manganic ions, potassium persulphate) [5,8], (2) radiation routes involving ionizing radiation as gamma rays [12,13] or electron beam [14] and non-ionizing radiation as ultraviolet light [15] or microwave radiation [11,16] as free radical generator, (3) plasma method [17], and (4) enzymatic method [18] using the enzyme as an initiator. However, radiation induced grafting provides practical benefits in terms of product properties, large processing temperature range, environmental protection and costs. Electron beam (EB) irradiation is a green powerful tool for synthesis/modification/functionalization of advanced materials that feature unique properties. EB induced grafting has major advantages over conventional methods. It is fast, occurs in the absence of an initiator or other 270

chemical catalysts and produces low byproduct levels and hazards [19]. Moreover, EB processing requires low cost that involves the indirect operating costs and the applied irradiation dose, which depends on the beam power, the efficiency of its use and the conversion factor of the beam power from the facility consumption power [20]. Limited information can be found on the starch grafting by e-beam irradiation to produce flocculating materials. The purposes of this study were: (1) to modify starch by grafting acrylamide using EB irradiation in order to synthesize water-soluble copolymers having flocculation abilities, and (2) to investigate the efficiency of the grafted copolymers as flocculation agents. 2. Experimental 2.1 Materials Unmodified regular corn starch (approx. 73% amylopectin and 23% amylose) was purchased from Sigma-Aldrich (St. Louis, MO, USA) and acrylamide from Alfa Aesar (Germany). Other chemicals were of analytical grade and purchased from SC Chimreactiv SRL (Romania). 2.2 Synthesis of the starch-grafted acrylamide copolymers Starch aqueous solutions were prepared by dissolving corn starch (St) in distilled water with continuously magnetic stirring on a water bath at 75-80 o C for 30 min, and the obtained solutions were cooled at room temperature (25 o C). Acrylamide (AMD) was added to starch aqueous solution with further stirring at room temperature for 30 min, resulting in a starch:acrylamide (St:AMD weight ratios = 1:1.1, 1:2.2 and 1:3.3) homogenous aqueous solutions. Therefore, both the monomer (AMD) and substrate (starch) were exposed simultaneously to EB irradiation. The irradiations were carried out at ambient temperature and pressure by using linear electron accelerator ALIN-10 (INFLPR, Bucharest-Magurele, Romania) of 6 MeV mean energy, with irradiation doses D, 2D and 6D. A high-energy electron beam generator of 1-10 MeV is preferred for practicing grafting polymerization because it penetrates deep into the materials, allowing a thicker layer of material to be irradiated [14]. After irradiation, irradiated mixtures were kept at room temperature for 24 hours. After that, according to literature [21,22], the samples were precipitated in excess of ethanol and then washed several times with aqueous ethanol (30% vol.) to remove totally the residual monomer and homopolymers. The resulted copolymers (St-g-AMD) were dried in oven at 55 o C for 20 hours. 2.3 Characterization of graft copolymers The graft copolymers were characterized by elemental analysis, rheology and infrared spectroscopy. 2.3.1 Elemental analysis Elemental analysis of samples was carried out using an elemental analyzer Flash 2000 (Thermo Fischer Scientific, UK). The calibration curve was made with cystine, methionine, sulphanilamide (4-aminobenzenesulphonamide) and BBOT (2,5-bis(5-ter-butyl-2-benzo-oxazol-2-yl) thiophene). The grafting parameters such as monomer conversion (C%) and grafting percentage (GP%) were evaluated according to the following equations: C m m St AMD % 5.071 N% (1) mamd GP m m St AMD % 5.071 N% (2) mst where: N% is the determined nitrogen percentage of grafted copolymer after removal of homopolymer, m St and m AMD are the amounts (in grams) of native starch and acrylamide, respectively, introduced into the grafting reaction. 2.3.2 Rheological analysis Rheological measurements were carried out on aqueous suspensions of 0.5% starch and copolymers at different shear rates (0-1082 s -1 ) and 28 o C using HAAKE VT 550 rotational viscosimeter (ThermoHaake, Germany) with NV coaxial cylinder. The obtained data were analysed with RheoWin v.3.5 software. 271

2.3.3 Fourier transform infrared (FTIR) spectroscopy FTIR spectra of samples were recorded on a Tensor 27 FTIR spectrometer (Bruker Optik GmbH, Germany) room temperature in the frequency range of 4000-600 cm -1 with an average of 64 scans at a resolution of 4 cm -1. The background spectrum was recorded in air (with no sample) and subtracted from the sample spectra. The collected spectra were analysed with Opus v. 6.5. software. Samples were dissolved in water and then dried as a film in order to be measured by using the attenuated total reflectance (ATR) accessory. 2.4 Flocculation study Flocculation investigation was performed on wastewater collected from a meat processing plant. Quality parameters such as ph, total suspended solids (TSS), chemical oxygen demand (COD) and fatty matters (FM) were measured in accordance with standardized methods to investigate the effect of the polymer addition on the degree of purification of wastewater. Synthesized graft copolymers (0.1% aqueous solution) of dosages 0.5-1.5 mg/l were tested in experiments, and the flocculation efficiency (FE) for each quality indicator was calculated according to the formula: C0 C FE 100 (%) (3) C 0 where: C 0 and C are the concentrations (in mg/l) of respective parameter before and after the wastewater treatment. The results reported are expressed by means of values ± standard deviation of three measurements, except the flocculation study. Processing of experimental data was performed using Microcal TM Origin TM v.8.0 (Microcal Software, Inc., Northampton, MA, USA) and Microsoft Excel 2010 (Microsoft Corporation, Redmond, WA, USA). 3. Results and Discussion The synthesized copolymers were evaluated from physicochemical and functional points of view. Their characterization through rheology, elemental analysis, FTIR and SEM was performed to point out the grafting level. Further, their functionality as flocculant agents was examined on real wastewater from the meat industry. 3.1 Effect of irradiation dose and monomer concentration on grafting and viscosity Some characteristics of the graft copolymers synthesized under EB field by varying the irradiation dose (free radical generator) and the concentration of AMD (monomer) are displayed in Table 1. Three different sets (S1-S3) of graft copolymers were synthesized so that a series of three graft copolymers was obtained for each monomer ratio by varying the irradiation dose. The copolymerisation mechanism of AMD onto starch by simultaneous exposure of both monomer and substrate in aqueous solution to the EB involves mainly the formation of free-radical sites in both chemical species initiated by an indirect effect due to the water (solvent). Nasef and Guven [23] stated that the diluting solvent plays a crucial role in affecting the accessibility of the monomer to the grafting sites and the mechanism of grafting, including initiation, propagation of the growing chain and termination steps. In the present, study water is the solvent, and it absorbs most of the e-beam energy leading to its radiolysis characterized by formation of highly reactive entities, e aq, H, OH, H 2 O, H 2, O*, as a result of primary effects (excitation, dissociation and ionization). Then, the hydroxyl radicals attack the St and AMD molecules generating their macroradicals that combine further yielding the graft copolymer. The conversion of AMD ranged from 49 to 90% and grafting percentage ranged from 54 to 294% as a function of irradiation dose and monomer-to-starch ratio. The results indicate that monomer conversion improved by increasing the irradiation dose for each tested monomer ratio and thus the irradiation dose of 6D gave the highest conversion, C = 90.0±0.8% for the highest AMD concentration. However, the linear correlation C% = f(irradiation dose) reduced as the AMD concentration increased. In other words, the monomer conversion and irradiation dose were strongly positive correlated (r ~ 0.976) at low concentration of AMD and no significant correlated (r ~ 0.674) at the highest monomer concentration. At a constant irradiation dose, the increase of monomer conversion was good dependent (r > 0.900) on AMD concentration introduced into grafting reaction. In a similar manner, the grafting percentage increased both by increasing of irradiation dose at constant AMD concentration and by increasing of AMD concentration at constant irradiation dose. A similar trend was observed for the other grafting systems using ionizing radiation [12,24,25]. The grafting parameters increased with the increase in the concentration of monomer, because more monomers are available and can react at the grafting site in the starch trunk polymer [26]. Graft copolymers were soluble in cold water unlike native starch. All studied samples of 0.5% aqueous solutions of St and graft copolymers had Newtonian behaviour. Viscosity is strongly related to the molecular weight of polymer so 272

Table 1 Synthetic details of native starch and graft copolymers. Sample Conversion (%) Grafting Percentage (%) Viscosity (mpa s) Native starch (St) - - 1.8±0.1 Set S1 D(St-g-AMD) 49.2±1.4 53.7±1.6 2.2±0.1 2D(St-g-AMD) 57.2±3.0 62.3±3.3 2.8±0.2 6D(St-g-AMD) 69.1±4.7 75.5±5.2 2.9±0.1 Set S2 D(St-g-2AMD) 71.9±0.8 156.6±1.8 3.1±0.1 2D(St-g-2AMD) 82.7±1.7 180.1±3.6 3.0±0.0 6D(St-g-2AMD) 88.1±0.5 192.2±1.0 3.4±0.2 Set S3 D(St-g-3AMD) 76.2±4.4 249.1±14.3 4.4±0.2 2D(St-g-3AMD) 89.6±1.3 293.4±4.3 3.7±0.2 6D(St-g-3AMD) 90.0±0.8 294.1±2.7 3.8±0.2 that higher viscosity involves higher molecular weight. Native starch had the apparent viscosity of 1.8±0.1 mpa s while the viscosities of the graft copolymers ranged from 2.2 to 4.4 mpa s (Table 1). As expected, the viscosities of synthesized copolymers were greater than that of native starch used as an initial substrate, which can be explained by higher molecular weight of the copolymers than native starch due to the grafting of the polyacrylamide (pamd) branches on the starch backbone. When the percentage of starch is small in comparison to the pamd, it is then very likely that the increase of viscosity with the amount of AMD is due to an increase of the pamd side chain molecular weight [27]. Thus, pamd chains are assumed to be generated by increasing the AMD concentration. Consequently, at constant irradiation dose, the effect of AMD on the viscosity showed an increase in viscosity with increasing the amount of AMD (r > 0.950). The increase in viscosity with the increased amount of AMD resulted from the increase in the molecular weight of the pamd side chain. However, in the series S3 of samples with the highest AMD concentration, the viscosity was lower with irradiation dose increasing than expected. According to Radoiu et al. [28], during irradiation several processes involving monomer polymerisation, chain branching and cross-linking and degradation of the polymer already formed and even a competition among all these phenomena, which affect the final structure of the polymer, can occur. As all copolymers of this series were water-soluble, the crosslinking process was minimized. At the same time, we excluded a reduction in the molecular weight of the pamd side chain since the monomer conversion and grafting ratio (based on nitrogen content) indicated good results correlated with our expectations. Thus, the decrease in viscosity at higher AMD concentration and higher irradiation dose could be due to the partial cleavage of the starch glycosidic linkages resulting from increasing in the irradiation dose, and this leads to a decrease in molecular weight of starch molecules. On the other hand, although high irradiation doses generally cause degradation of St and/or formed copolymer, one should also take into sort of consideration the formation of shorter average chains of pamd that can give lower molecular weight. These shorter pamd chains result from the increase in the number of active sites on substrate with the irradiation dose for the same AMD concentration. Consequently, an irradiation dose is considered optimum when it is able to initiate a few grafting sites resulting in longer pamd chains. 3.2 Elemental analysis No presence of nitrogen was detected in native starch by elemental analysis. On the other hand, the nitrogen content ranged from 5 to 14% for graft copolymers (Table 2). Therefore, the presence of nitrogen in all synthesized copolymers confirmed that AMD have indeed grafted on the starch backbone, increasing with irradiation dose and AMD concentration. According to Jyothi et al. [29], there is a significant positive correlation between grafting ratio and nitrogen content in the grafted starches so that the higher grafting level corresponds to higher nitrogen content. Table 2 Elemental analysis results. Sample C (%) H (%) O (%) N (%) Native starch 40.30±0.19 6.52±0.07 49.23±0.09 - Set S1 D(St-g-AMD) 42.40±0.06 6.70±0.18 42.87±0.97 5.07±0.15 2D(St-g-AMD) 42.48±0.23 6.74±0.08 39.95±1.82 5.88±0.31 6D(St-g-AMD) 42.77±0.26 6.68±0.11 39.71±0.69 7.12±0.49 Set S2 D(St-g-2AMD) 43.84±0.22 6.93±0.11 36.85±0.38 9.72±0.11 2D(St-g-2AMD) 43.59±0.12 6.99±0.06 34.81±0.72 11.17±0.22 6D(St-g-2AMD) 43.76±0.17 6.99±0.04 33.79±0.05 11.92±0.06 Set S3 D(St-g-3AMD) 44.26±0.14 7.12±0.06 35.44±0.71 11.51±0.66 2D(St-g-3AMD) 45.86±3.46 7.32±0.51 31.71±0.52 13.98±0.90 6D(St-g-3AMD) 44.12±0.02 7.16±0.07 31.87±1.02 13.59±0.13 273

3.3 FTIR analysis The FTIR spectrum of native corn starch showed typical complex vibrational modes due to the pyranose ring of the glycosidic unit in the region below 800 cm -1 [30]. In addition, the spectrum displayed a broad absorption band in the region of 3290 cm -1, indicating the presence of intermolecular hydrogen bonded hydroxyl group having polymeric association. Other characteristic peaks were also identified at 2926 cm -1 (C-H stretching), at 1413 cm -1 ( CH 2 scissoring) and 1352 cm -1 ( CH 2 twisting), at 1642 cm -1 (O-H vibrations from bound water molecules) and the triplet band for the -CH 2 -O-CH- stretching absorption at 1151, 1078 and 1024 cm -1. Fig. 1 FTIR spectra of native starch and some synthesized copolymers. The grafting onto St was confirmed by comparing the spectra of the native starch with those of the grafted starches. In all cases, the spectra of the graft copolymers showed characteristic absorption bands of the starch substrate. The appearance of a shoulder at 3188-3200 cm -1 and other characteristic absorption bands found at 1651-1661 cm -1 and 1604-1612 cm -1 were attributed to N-H stretching, C=O bands and N-H bending bands of the pamd CONH 2 groups (Fig. 1). Additionally, the new peak found at 1442-1446 cm -1 is due to C-N bending vibrations [31,32]. The presence of these vibrations was not observed in the spectrum of the St, being the proof of grafting reaction. Moreover, it was noticed that the increase of AMD concentration led to an absorbance decrease of the starch characteristic triplet band at around 1151, 1078 and 1024 cm -1 concomitantly with a clear increase of absorption band found at 1604-1612 cm -1 (N-H band). These results are consistent with previous literature on the graft copolymerization of AMD onto polysaccharide substrates [11,16,27,29,31-34]. 3.5 Flocculation efficiency in wastewater from a meat processing plant The results presented within the previous sections demonstrate the physicochemical and structural changes of St and indicate the occurrence of EB induced grafting. Hence, the efficiency of the graft copolymers as flocculation agents was further investigated at laboratory scale in order to remove the organic load of wastewater collected from a meat processing plant. Meat processing wastewater is usually heavily loaded with organic and inorganic materials that create severe problems, making it a problematic effluent to treat before its discharge to public sewerage. This loading depends very much on the type of production and facilities, and wastewater has a high strength in terms of biochemical oxygen demand, chemical oxygen demand, suspended solids, fatty matters (fat, oil and grease), nitrogen and phosphorus, compared to domestic wastewaters [35,36]. Among physico-chemical processes, coagulation-flocculation is one of the most widely used solid-liquid separation process for the removal of suspended and dissolved solids, colloids and organic matter present in industrial wastewaters [37,38]. In the present study, flocculation performances of the graft copolymers were evaluated in coagulationflocculation experiments using inorganic coagulants (200 mg/l CaCO 3 and 200 mg/l Al 2 (SO 4 ) 3 ) and various dosages (0.5-1.5 mg/l) of 0.1% aqueous solution of flocculants (graft copolymers). The quality indicators quantified were ph, total suspended solids, chemical oxygen demand, and fatty matter in suspension. Table 3 shows the characteristics of raw wastewater and the permissible levels of water quality indicators according to the Romanian national guideline. Table 3 Characteristics of the raw wastewater used in experiments. Parameter Raw wastewater Maximum allowed level* ph 7.7 6.5-8.5 TSS (mg/l) 562 350 COD (mg O 2 /L) 1055 500 FM (mg/l) 246 30 *Romanian National Regulation NTPA 002/2005 Quality indicators of wastewaters discharged to urban sewerage systems 274

All synthesized copolymers used in coagulation-flocculation process showed good efficiencies ranging 86-98% for TSS, 88-90% for COD and 55-89% for FM (Fig. 2) and ph values of 7.8-8.2 as a function of the irradiation dose and copolymer dosage used as a flocculant. More precisely, the coagulation removed around 84% of TSS, 87% of COD and 50% of FM, while the flocculation step had additional removal capacity of 2-14% for TSS, 1-4% for COD and 5-39% for FM. a) b) c) Fig. 2 Flocculation efficiencies on a) total suspended solids, b) chemical oxygen demand and c) organic matters. In certain cases, a decrease in the removal efficiency of the studied indicators was noticed as the increase in dosage of the graft flocculant. For instance, this behaviour occurred for samples D(St-g-AMD), 2D(St-g-2AMD) and D(St-g- 3AMD) in the case of TSS and COD and for samples D(St-g-AMD) and D(St-g-2AMD) in the case of FM. The flocculation reaches its maximum at an optimal copolymer concentration. Beyond this dosage, the flocculation decreases due to destabilization of the flocs formed and their re-suspension by the excess of polymeric flocculant [16,39]. Moreover, certain dosages of some flocculants resulted in very poor efficiency compared to that of the mixture of inorganic coagulants when applied alone. As an example, a dosage of 0.5 mg/l of 6D(St-g-2AMD) for TSS and dosages of 1 mg/l and 1.5 mg/l of D(St-g-2AMD) and 0.5 mg/l of 6D(St-g-3AMD) for COD. On the other hand, although the highest levels of efficiency were determined for FM indicator, only the sample 2D(St-g-2AMD) of 1.5 mg/l showed a level that follows the national requirements for such an indicator. This behaviour could be due to the internal architecture that determines the macromolecule conformation in water solution, giving some peculiarities of flocculation behaviour [40]. Starch is a complex mixture of rigid linear (amylose) and highly branched (amylopectin) polymers with broad distribution of molecular weights. The effect of structural features on flocculation properties can be even stronger for starch, meaning the increasing rigidity of macromolecules leads to a reduced flocculation efficiency [41,42]. According to the results of flocculation study, it can be concluded that although the efficiency for removal of TSS and COD from tested wastewater was good, the concentration of fatty matters does not meet the level required by national regulation regarding the quality of wastewaters discharged to urban sewerage systems. In this case, the wastewater should be preceded by another treatment process (i.e., electrocoagulation [43]) or a subsequent biological treatment [44] or even a mixture of graft flocculants could be used in order to achieve the FM level allowed by current standards of quality. Taking into consideration that an essential feature of wastewater flocculation is the elimination of suspended solids and as much organic material as possible [45], our grafted flocculants displayed promising flocculating ability by reduction of environmental concerned parameters (TSS, COD and FM) from wastewater 275

collected from a meat processing plant. Among the series of graft copolymers, the sample D(St-g-3AMD) had superior performance by considerably reducing the overall organic load (TSS, COD and FM) of tested wastewater. The high monomer-to-starch ratio and the low irradiation dose specific to this sample led to the highest viscosity as a probable result of longer grafted pamd chains. As Lee et al. [2] reviewed in their work, molecular weight and viscosity are the key factors that affect the flocculation performance. Accordingly, high viscosity correlated with high molecular weight showed very good performance in the tested wastewater at a dosage of 0.5 mg/l for all analysed water quality indicators. Moreover, all results proved that the addition of a natural polymeric flocculant to inorganic coagulants is effective in the reduction of TSS, COD and FM, reducing thus the amount of coagulant used and cost of the coagulation-flocculation process. These findings are in agreement with other previous works [39,44,46]. 4. Conclusions New starch-based flocculants were synthesized via simultaneous graft copolymerization in aqueous solutions of acrylamide onto starch substrate induced by an electron beam irradiation. The monomer conversion, grafting percentage and copolymer features may be controlled by chemical composition of initial mixture exposed to electron beam and by applied irradiation dose. The grafting parameters and viscosity were correlated with both monomer concentration and irradiation dose. However, a lower viscosity for samples with higher AMD concentration and higher irradiation dose could be more likely assigned to either the polysaccharide degradation or formation of shorter average chains of pamd that can give lower molecular weight. FTIR study of graft copolymer showed that the increase of AMD concentration caused the absorbance decrease of the starch characteristic triplet band at around 1151, 1078 and 1024 cm -1 concomitantly with an obvious increase of absorption band found at 1604-1612 cm -1 (N-H band). In the coagulation-flocculation experiments at the laboratory level, the synthesized copolymers showed a great potential to reduce the quality indicators (total suspended solids, chemical oxygen demand and fatty matter in suspension) of the wastewater from the meat industry. The flocculation efficiency of copolymers depends on their features and dosage used. Besides, these flocculating materials have the advantage of a good flocculating efficiency with low dosage as well as easy handling. In conclusion, starch-graft copolymers having good flocculating ability can be rapidly produced with good yields by simultaneous electron beam irradiation with low doses and no additional chemicals. 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