Analysis of flocculation/flotation as wastewater pretreatment

Bachelor thesis ANALYSIS OF FLOCCULATION/FLOTATION AS WASTEWATER PRETREATMENT September 2021 Julia Olmedo Gómez Julia Olmedo Gómez ANALYSIS OF FLOCCULATION/FLOTATION AS WASTEWATER PRETREATMENT Bachelor thesis Maribor, 2021 ANALYSIS OF FLOCCULATION/FLOTATION AS WASTEWATER PRETREATMENT Bachelor thesis Student: Julia Olmedo Gómez Student program: Engineering in industrial technologies, specialization in chemical engineering, Erasmus+ international exchange program. Supervisor: Doc. Dr. Dr. Andreja Nemet Co-supervisor: Alen Erjavec, Mag. Inž. Maribor, 2021 Analysis of flocculation/flotation as wastewater pretreatment I Analysis of flocculation/flotation as wastewater pretreatment II Analysis of flocculation/flotation as wastewater pretreatment III INDEX INDEX .................................................................................................................................... III DECLARATION .................................................................................................................... IV ACKNOWLEDGEMENTS ..................................................................................................... V ABSTRACT ........................................................................................................................... VI Povzetek ................................................................................................................................ VII LIST OF TABLES ............................................................................................................... VIII LIST OF FIGURES ................................................................................................................ IX APPLIED SYMBOLS AND ABBREVIATIONS .................................................................. X 1 Introduction and problem statement .................................................................................. 1 1.1 Water consumption overview .................................................................................... 1 1.2 Wastewater treatment ................................................................................................. 2 1.3 Aim of the thesis ........................................................................................................ 3 2 Theoretical background ..................................................................................................... 4 2.1 Flocculation/Flotation ................................................................................................ 4 2.2 Advanced Oxidation Process (AOP).......................................................................... 5 3 METHODS ........................................................................................................................ 7 3.1 Design of experiments ............................................................................................... 7 3.2 Wastewater treatment ................................................................................................. 7 3.2.1 First FF ............................................................................................................... 7 3.2.2 Advanced Oxidation Process (AOP) .................................................................. 8 3.2.3 Second FF ........................................................................................................... 9 3.3 HEM measurement .................................................................................................... 9 3.3.1 Extraction .......................................................................................................... 10 3.3.2 Solvent distillation ............................................................................................ 11 3.3.3 Calculations ...................................................................................................... 11 3.4 Mass of dried sludge ................................................................................................ 12 4 EXPERIMENTAL WORK ............................................................................................. 13 4.1 Design of experiment ............................................................................................... 13 4.2 Wastewater treatment process .................................................................................. 15 4.2.1 Preparation of the wastewater for experiments ................................................ 15 4.2.2 First flocculation/flotation ................................................................................ 16 4.2.3 Advanced Oxidation Process (AOP) ................................................................ 17 4.2.4 Second flocculation/flotation ............................................................................ 17 4.3 HEM measurement .................................................................................................. 18 5 RESULTS AND DISCUSSION ..................................................................................... 19 6 CONCLUSIONS ............................................................................................................. 23 7 REFERENCES ................................................................................................................ 24 8 CURRICULUM VITAE ................................................................................................. 26 Analysis of flocculation/flotation as wastewater pretreatment IV DECLARATION I declare that I have written this thesis myself. Any contribution made by others are indicated separately. I have reviewed the literature in the field of my thesis under the following keywords: Source: Science Direct (https://www.sciencedirect.com/) Keywords: Number of references AOP 27,335 n-Hexane extractable material 31 Wastewater pretreatment 530 Flocculation/flotation 730 Source: COBISS+ (https://plus.si.cobiss.net/opac7/bib/search/advanced?db=cobib) Keywords: Number of references AOP 1,188 n-Hexane extractable material 4 Wastewater pretreatment 74 Flocculation/flotation 12 Total number of articles reviewed: 6 Total number of books reviewed: 1 Maribor, September 2021 Julia Olmedo Gómez Analysis of flocculation/flotation as wastewater pretreatment V ACKNOWLEDGEMENTS First of all, I would like to thank the person who made this thesis possible, Doc. Dr. Dr. Andreja Nemet who gave me the opportunity to write the thesis and work in the laboratory. She gave me all the facilities to understand and carry out the whole process. Thank you for the patience and trust shown to me. Also, I would like to thank Alen Erjavec, Mag. Inž. for teaching me how the method in the laboratory worked and for the trust shown. To my family, for having supported me from the distance and always have let me do what I really want in life. To my friends, not only to my college friends that made these four years of university the bests of my life but the friends that have been with me since high school. They been there for everything, and they have made me grown as a person. And of course, thank you Slovenia, specifically Maribor, which gave me five months of experiences in life. Maribor let me finish my degree and gave me friends that I know I will have by my side the rest of my life. I will never forget my Erasmus experience. Analysis of flocculation/flotation as wastewater pretreatment 2 hydroelectricity. Mining and manufacturing industry account for 18 %, followed by domestic consumption, which accounts for about 12 %. An average of 144 liters of water per person per day is supplied to European households. (Agencia Europea de Medio Ambiente, 2018) 1.2 Wastewater treatment We can consider wastewater (WW) as water that have been used at homes, industries or business and that must be treated before it is released back to the environment. It also includes water from the rain. (USGS, 2021). Conventional WW treatment plants often include the following steps (see Figure 1-2):  Pretreatment: it refers to the transport of wastewater to the treatment plant and includes processes such as roughing, screening, desanding and homogenizing. In this stage, the inflow is measured and controlled, and larger floating solids are removed.  Primary treatment: it includes the processes of decantation, flotation, clarification, filtration and neutralization. At this stage, flocculation/flotation (FF) is included to remove suspended solids. This process will be the one in which the thesis will go in depth and the one that will be optimized.  Secondary treatment: or biological treatment, is characterized by the use of microorganisms to remove pollutants from water either aerobically or anaerobically. These bacteria or algae carry out a process of oxidation of the pollutants.  Tertiary treatment: its aim is to remove the organic load and nutrients by ion exchange, adsorption, disinfection (e.g. chlorination). It also removes some specific pollutants such as phosphates. (Marcela Fúquene & Viviana Yate, 2018) European Union has legislated in terms of water quality: on 23 October 2000, the "Directive 2000/60/EC of the European Parliament and of the Council establishing a framework for the Community action in the field of water policy" or, for short, the EU Water Framework Directive (WFD) was finally adopted. (European Comission, 2021). This thesis is dealing with wastewater treatment in a cosmetic industry. The current cleaning process in industry consist of two steps, namely i) AOP (Advanced Oxidation Process), and ii) FF. The sequence of treatment follows the logic of first oxidizing large organic molecules and after removing them in the FF process. However, it might not be the most optimal way as the HEM (n-Hexane Extractable Materials) decreases the efficiency the AOP process by heavily blocking the light to penetrate in the WW to be cleaned. The idea of this work was to perform additional FF process as pretreatment before AOP process. From previous experiment it was concluded that FF process in acid environment might be a successful way to decrease the HEM content. Analysis of flocculation/flotation as wastewater pretreatment 3 Figure 1-2: Scheme of a wastewater treatment plant (after TUHH, 2004) Few industrial applications are found dealing only with AOP WW treatment. In Plataforma Solar de Almería in Spain, this process is applied to the pretreatment of wash water of pesticide containers. It is said to be economical and to be applicable to industrial pharmaceutical process (Vogelpohl, 2007). The hypothesis is that if a first FF is carried out and optimize, the AOP could increase its efficiency because the UV light could penetrate deeper in the WW and decompose the remaining pollutants more successfully. That way, the stages that follow the treatment concerned to the thesis are: i. First FF in an acid environment. In this stage, iron sulphate (III) (Fe2(SO4)3) and a drop of polyelectrolyte are added to achieve the FF. ii. Advanced oxidation process (AOP). The pH is maintained between 2-2.7 by adding hydrochloric acid (HCl). In this stage, hydrogen peroxide (H2O2) is added. In addition, the sample is subjected to UV radiation by means of a lamp in the reactor. The hydroxide (OH-) ion oxidizes the organic compound present in the water into smaller molecules. Ideally, the end products are CO2 and water, however this is rarely the case. iii. Second FF in an alkaline environment. The pH has to be maintained above 8, so lime is added. Also, iron sulphate (III) (Fe2(SO4)3) and a drop of polyelectrolyte is added to achieve FF. 1.3 Aim of the thesis The aim of the thesis was to analyze the efficiency of flocculation/flotation as wastewater pretreatment before the AOP and second FF treatment. In this context the addition of Fe2(SO4)3 in first FF and H2O2 before AOP process was investigated in order the assess the efficiency of the entire treatment process. The amount of H2O2 added before AOP and the amount of Fe2(SO4)3 added before first FF were varied. The design of experiments was developed with the computer program Design-Expert. After the three-step: i) first FF, ii) AOP and iii) second FF WW treatment process was performed. The measure of HEM removal and sludge formation were the measures to assess the efficiency of the WW treatment. Analysis of flocculation/flotation as wastewater pretreatment 4 2 Theoretical background In this section, we will review the theoretical part of the problem that we will apply later for the experimental work. 2.1 Flocculation/Flotation As we have seen FF is the principal process of this work. This covers two distinct stages: i. Rapid mixing of dispersed coagulant into WW ii. Flocculation for agglomeration of small particles into large flocs by gentle agitation Then, flocs formed are allowed to settle down/float and removed as sludge while the treated water is transferred into the next treatment process or for discharge into a watercourse. (Teh et al., 2016). The aim is the elimination of suspended solids (SS) and as much of the organic materials possible. To remove SS and organics, a floc forming chemical is needed. This is what is called the coagulant. Then, it will be separated from water by flotation, settling or adsorption. In this treatment, compounds such as ferric chloride or iron sulphate and/or polymer are added to the WW to destabilize the colloidal materials and this cause the small particles to join into larger settleable flocs (Amuda & Amoo, 2007). Coagulation is defined as the destabilization of suspension by making particles to aggregate. However, flocculation describes the process when the destabilized particles are made to contact each others, in order to form larger aggregates. Because of the size of colloidal particles (approximately 0.01 to 1 µm), attractive forces (Van der Waals) between particles are less strong than the repelling forces of the electrical forces. Due to this, particles tend to remain separated and dispersed in the suspension. To remove colloidal particles by settling or floating, the only practical way is if they settle/float rapidly. This means that particles must be larger. One destabilization method is the charge neutralization. It is achieved by adsorption of mononuclear and polynuclear metal hydrolysis species or polyelectrolytes on the surface of the particles. The most commonly used metal coagulants can be divided into aluminum and iron coagulants. The whole process can be seen in Figure 2-1. Figure 2-1: Scheme of coagulation. A) Colloidal particles, B) Addition of coagulant, and C) Destabilized colloidal particles (after Florencia Cevallos, 2015) In this work, in the laboratory, we would use polyelectrolyte and iron coagulants: ferrous sulphate. Analysis of flocculation/flotation as wastewater pretreatment 5 In addition to destabilization, flocculation is required as the next step to induce aggregation and settling/floating of large agglomerates. This is achieved by a gentle mixing of the suspension followed by letting aggregates to settle down/float. (Fig. 2-2) (Teh et al., 2016) (Marcela Fúquene & Viviana Yate, 2018) Figure 2-2: Diagram of how the addition of polyelectrolyte works (after Florencia Cevallos, 2015) 2.2 Advanced Oxidation Process (AOP) The goal of the process is the elimination of non-degradable, poorly soluble compounds in wastewater. It consists of an oxidation reaction at atmospheric pressure and temperature. The necessary oxidant agent is the hydroxyl radical (OH·) that owns a very high capacity as oxidant, with short time of reaction. For this, reaction’s speed is controlled by the diffusion (Florencia Cevallos, 2015). Due to high reactivity of hydroxyl radical, it is possible to remove organic and inorganic compounds achieving a reduction of BOD, COD, TOC and toxicity in wastewater. The process is particularly useful for solutions containing aromatics, pesticides, petroleum constituents, and volatile organic compounds. In addition, AOP could be used to treat effluents of secondary treated WW which then go to the tertiary treatment. The pollutants are converted into smaller inorganic compounds such as water, carbon dioxide and salts, and finally they undergo sedimentation (Liu et al., 2021). Hydroxyl radicals are produced with the help of one or more primary oxidants (ozone, hydrogen peroxide, oxygen) and/or energy sources (UV light) or ferric/ferrous salts. AOPs are characterized by its low selectivity and its high speed (Florencia Cevallos, 2015). The whole reaction of oxidation could be divided into three parts: i. Formation of OH⸱-. ii. Initial attacks on target molecules by OH- and their breakdowns to fragments. iii. Subsequent attacks by OH- until ultimate mineralization. The mechanisms of OH• formation depend on the technique of AOP that will be used. In this thesis the Fenton like process is assumed to happen. It presents high efficiency and low cost. The process consists of mixing hydrogen peroxide with iron salts (Fe2+ or Fe3+). The ferric/ferrous ion acts as a catalyst for the formation of hydroxyl radicals (OH•). The mechanism of the reaction is the following one: 1. Fe2+ + H2O2  Fe3+ + OH- + ·OH• (1) 2. Fe2+ + ·OH  Fe3+ + OH- (2) 3. R-H + HO•  oxidated products (3) Analysis of flocculation/flotation as wastewater pretreatment 6 Reaction number 1 corresponds to the formation of hydroxyl radicals. Then, they react by oxidating the ferrous cation (reaction 2) and, finally, they attack the organic compounds (reaction 3). The formation of radicals is catalyzed by the use of radiation UV (Photo-Fenton like Process). This increases the degradation speed of pollutants. The process is homogenous type as both chemical species are in aqueous phase. Usually, the increase in the concentration of reactants increase the efficiency and the kinetics of the reaction. However, an excess in iron concentration produces secondary reactions such as the formation of iron hydroxide; and an excess in hydrogen peroxide may result in a degradation of itself by the hydroxyl radicals (Florencia Cevallos, 2015). In our work, we will combine the Fenton like process with UV light: Photo-Fenton like process. Analysis of flocculation/flotation as wastewater pretreatment 7 3 METHODS In this section the laboratory equipment and methods are describe. The first part focuses on the WW treatment, while the second part is related to the analysis of the WW treatment, namely the HEM content and the mass of dried sludge formed within FF process during WW treatment. 3.1 Design of experiments An experiment is a systematic technique performed under controlled conditions to find an undiscovered effect, test or establish a hypothesis, or demonstrate a recognized effect. We know between which intervals the concentrations of the reactants move and the design of experiments will tell us the recipe we should follow according to a logic to validate our hypothesis. For experimental design it is normally used a program. The inputs in the program will be the factors that are controllable and the output that will be obtained are the responses analyzed. This design of experiments help to minimize the design costs, product material and labor complexity (MoreSteam, 2021). It represents a plan for carrying out the experiments in order to test the synergistic effects of various different parameters with acceptable statistical accuracy. 3.2 Wastewater treatment The laboratory inventory needed for this part was: 5 jars of 1L Pipettes of 5 and 10 mL 4-gang stirrer Separatory funnels Flasks of 250, 100, 50 mL pH-meter Reactor UV lamp Cooling system Jar of 2L Magnetic stirrer Syringes Oven Laboratory balance Desiccator 3.2.1 First FF When the wastewater for experiments (WWE) is ready, we add the designed volume of Fe2(SO4)3. This concentration of Fe2(SO4)3 (in mL/L) has been established by design of experiment and is multiplied by the volume of WWE to obtain the volume (in mL) that is needed to add of this reactant to every jar and 1 mL/L of polyelectrolyte is added to all jars. The jars are placed in the 4-gang stirrer and are left during 10 minutes to 100-140 rpm (Figure 3-1). Analysis of flocculation/flotation as wastewater pretreatment 8 Figure 3-1: Jars in the 4-gang stirrer. After this mixing, the water is poured in separatory funnels and left there for one day for the FF to take place. Sludge of this first FF is collected and dried in small jars in an oven at a temperature of 105 ⁰C for 4-5 days. 3.2.2 Advanced Oxidation Process (AOP) For the AOP, 1.8 L of water from first FF are collected. The water is poured into the reactor (Fig. 3-2) and stirred continuously with a stirring magnet. The corresponding volume of hydrogen peroxide (H2O2) is added then. The next step is to set the required pH of the mixture, which should be between 2 and 2.7. If it is higher, then, some drops of HCl (concentration: ≥37%) are added till the pH reaches that interval. The UV lamp is inside the reactor, while the WW sample is stirred around it. When the WW sample is prepared, the UV lamp is switched on. To maintain the AOP process within the required temperature range the UV lamp is cooled via cooling water cycle. The AOP process lasted for 30 mins and it is followed by second FF. Analysis of flocculation/flotation as wastewater pretreatment 9 Figure 3-2: Reactor of the AOP. 3.2.3 Second FF The second FF takes place in alkaline environment. Both the volume and pH of WW sample was measured. To perform FF process, the required volume of Fe2(SO4)3 is added. The concentration of Fe2(SO4)3 in this second FF to be added was always 1.5 mL/L. After addition of Fe2(SO4)3 a lime milk was added to reach the pH above 8, preferably around 8.5. Finally, 1 mL/L of polyelectrolyte was added to finish the FF process. During chemical additions, the mixture is stirred at about 400 rpm. When stirring for 10 minutes, the flocs are let to settle down. The sludge formed in this FF is also collected and dried in the oven. This sludge dries in approximately 2-3 days until constant weight. 3.3 HEM measurement The list of the laboratory inventory needed is the following: Flat-bottomed spherical flasks Oven Desiccator Volumetric flask of 500 mL Laboratory balance Flask of 50 and 100 mL Separatory funnel Filter funnel Filter papers Glass rod Rotavapor After each WW treatment stage, 500 mL of water are collected for HEM measurement. Also, 500 mL of the initial WWE are collected to enable the HEM removal calculation. As the The UV lamp is introduced through this opening at the top. Analysis of flocculation/flotation as wastewater pretreatment 10 samples were not measured immediately after treatment their pH was lowered below 2 by addition of H2SO4 (4M). The HEM measurement consisted of extraction, solvent distillation and calculations phases. 3.3.1 Extraction The flat-bottomed flask is first dried in an oven at 105-115 ⁰C during at least 2 hours and after cooled down to room temperature in desiccator. The weight of the flask is measured at room temperature. A 500 mL water sample in volumetric flask is used for measured. This is half of the amount of sample required in the method (500 mL instead of 1 L) due to the shortage of it. Because of that, we also use only half of the required amount of n-hexane. First, half of the sample is poured in separatory funnel. To the other half of sample left in flask, 15 mL an n-hexane are added with at least 85 % purity. The volumetric flask is then shaken to allow the extraction liquid-liquid for 1-2 minutes. The sample from flask then poured into the separatory funnel. The volumetric flask is rinsed with small portions (5 mL) of n-hexane and poured into the funnel. For the extraction to take place, the separatory funnel is shaken for 3 minutes. The sample in separatory funnel is left for 10 minutes to allow the organic phase and the aqueous phase to separate. The aqueous phase is the lower one. After 10 mins the organic phase is collected in a small flask (100 mL). The separatory funnel is rinsed with small portions of n-hexane (5-10 mL) until there are no rests of lipids in the walls of the funnel. In the Figure 3-3, we can observe the two phases: the aqueous is more amount and has a purple color in our case, while the organic one is only a thin whitish layer. Figure 3-3: HEM measurement extraction phase. A filter paper (MN 615 cellulose filter, ff) is placed in a filter funnel and filled to about half full of Na2SO4 anhydrous. The organic phase is then drained through the Na2SO4 into the preweighed flask. If needed additional filter papers with Na2SO4 anhydrous was used. When the Na2SO4 anhydrous cannot absorb more water, it hardens and that indicates that another filter Organic phase Aqueous phase Analysis of flocculation/flotation as wastewater pretreatment 11 with Na2SO4 anhydrous should be used. The small flask is rinsed with n-hexane and pour it into the pre-weighed spherical flask. 3.3.2 Solvent distillation This part of the measure starts by connecting the spherical flask to the rotavapor (Fig. 3-4). The lower half of the flask is immersed in the water bath with a temperature of 50 ⁰C. The speed of the rotavapor is 40 rpm. Figure 3-4: Rotavapor. The pressure in rotavapor is first set to 900 mbar, after to 700 mbar, nest to 500 mbar and finally to 350 mbar. At each pressure level the sample was left for 10 minutes. After distillation on rotavapor the sample in flask is dried in oven at 70 ⁰C for 30 minutes. After, it is placed in a desiccator with silica gel until it cools to room temperature. Finally, the flask with the dried residue is weighed. 3.3.3 Calculations The mass of the dried HEM mHEM is calculated as the mass of the flask with the dried HEM mHEM+FLASK minus the tare mass of the flask mFLASK (Eq. 1): HEM HEM+FLASK FLASK m m m  (1) The mass concentration of γHEM HEM in the sample is calculated as the mass of dried HEM divided by the volume of wastewater sample (Eq. 2). HEM HEM WW_sample m V   (2) (U.S. Environmental Protection Agency, 2010) Analysis of flocculation/flotation as wastewater pretreatment 18 Table 4-4: Value of each variable for second FF. STD Volume of water (L) mL of Fe2(SO4)3 pH 1 1.30 2.0 8.82 2 1.30 2.0 11.53 3 1.30 2.0 10.02 4 1.20 1.8 8.64 5 1.10 1.7 10.15 6 1.10 1.7 9.31 7 1.30 2.0 8.66 8 1.40 2.1 9.91 9 1.25 1.9 9.61 After the second FF, as we have seen, the flocs are let to settle down. With S1, this does not occur till one day after. However, with S2, flocs settle down in half an hour (Figure 4-7). Figure 4-6: Sludge of second FF. 4.3 HEM measurement This work only covers the final degree of lipid removal and therefore only the HEM of the three WWE samples and the HEM of the samples obtained after the second FF (W2FF) will be measured. The influence of surfactants as well as their removal is not our concern in this work. Also, the level of removal after each stage is out of the scope of this work. For the measurement of the samples after second FF, the method described in section 3.3 was followed. However, for HEM measurement of WWE, the WWE is diluted 1:10. We mix 50 mL of WWE with 450 mL of distilled water. Due to this, a recalculation of HEM will be necessary to be done. That means that equation 2 shall be multiplied by 10 due to the dilution to obtain the real concentration. To achieve higher accuracy, the flask was weighted two times and then, the average was done. In addition, Vs of equation 2 corresponds to the volume of the volumetric flask which is equal to 0.5 L. Analysis of flocculation/flotation as wastewater pretreatment 19 5 RESULTS AND DISCUSSION About the sludge formed in the first FF, we can analyze the following Table 5-1. It shows the total mass of sludge formed in the separatory funnels before putting it in the oven and the final dry mass after the complete drying in the oven. Table 5-1: Sludge removed in the first FF (wet and dry). STD V init (L) m sludge (g) V sludge (L) m d ry _ mass (g) 1 4.00 1928.27 1.92 29.61 2 4.00 769.10 0.70 17.96 3 4.00 1154.93 1.10 8.90 4 4.00 1348.19 1.38 26.09 5 4.00 1472.07 1.40 9.54 6 4.00 1188.35 1.10 8.44 7 3.75 1226.99 1.10 8.69 8 4.00 1214.96 1.15 9.00 9 3.75 1524.98 1.35 10.35 If we compare results, STD 1, 2 and 4 used S1 and we can observe that the dry mass formed is much higher (it goes from almost 18 g till almost 30 g) than the other STD that used S2 or no surfactant. With the ones that used S2 or no surfactant the dry mass is around 9 g. This confirms the hypothesis that the type of surfactant significantly affects not only the FF but the whole process. In table 5-2 we have the results of the dry mass after the oven of the sludge of the second FF. Table 5-2: Dry mass removed in the second FF. STD Dry mass (g) 1 0.39 2 1.55 3 1.52 4 0.62 5 0.92 6 2.61 7 5.55 8 2.94 9 3.27 As we expect, the dry mass in the second FF is much lower than the dry mass of the first FF. However, we cannot see differences related on the type of surfactant used. Only we can comment that without surfactants the dry mass values obtained are a little bit higher than the others (5.55 g and 3.27 g). From the HEM measurement the following results of Tables 5-3 and 5-4 are obtained: Analysis of flocculation/flotation as wastewater pretreatment 20 Table 5-3: HEM calculations for WWE. WWE Tare weight (g) Final weight (g) 𝛾  (mg) HEM (mg/L) 1 134.7645 135.2087 444.25 8885.0 2 134.7612 134.9053 144.10 2882.0 3 170.9804 171.0709 90.55 1811.0 Table 5-4: HEM calculations for W2FF. STD Tare weight (g) Final weight (g) 𝛾  (mg) HEM (mg/L) 1 170.9786 171.1435 164.85 329.7 2 134.7598 134.8461 86.30 172.6 3 99.4280 99.4315 3.50 7.0 4 100.8799 100.9793 99.35 198.7 5 99.4303 99.4311 0.75 1.5 6 100.8717 100.9051 33.35 66.7 7 100.8739 100.8745 0.65 1.3 8 100.8673 100.8733 6.00 12.0 9 178.1160 178.1294 13.35 26.7 The cosmetics industry has set the limit of emissions of HEM in 100 mg/L after the whole process. If we analyze the table 5-4, we observe that 3 out of 9 experiments does not fit this limit. But we can realize that these three experiments use WWE 1 with S1. Obviously, the sample with S1 had much higher content of HEM compared to other samples. Despite having very high HEM content the HEM concentrations were nearby the limits. Also, literature (Method 1664, Revision B: n-Hexane Extractable Material (HEM; Oil and Grease) and Silica Gel Treated n-Hexane Extractable Material (SGT-HEM; Non-polar Material) by Extraction and Gravimetry) set the method detection limit of HEM in 1.4 mg/L. As we can see, the value of HEM at the end of experiment STD 7 is lower than this value. We can conclude that the experiment 7 has almost eliminated all the HEM but to calculate the final removal we will change this value to 1.4 instead of 1.3. After determining of HEM concentration before and after treatment, the percentage of removal was calculated using the Equation 3. 𝜂 = 𝐻𝐸𝑀 𝑖𝑛 𝑊𝑊𝐸 − 𝐻𝐸𝑀 𝑖𝑛 𝑊 2 𝐹𝐹 𝐻𝐸𝑀 𝑖𝑛 𝑊𝑊𝐸 · 100 (3) That way, the removal is obtained (Table 5-5): Analysis of flocculation/flotation as wastewater pretreatment 21 Table 5-5: Percentage of removal after the whole process. STD η 1 96.29 2 98.06 3 99.76 4 97.76 5 99.95 6 97.69 7 99.92 8 99.58 9 98.53 When Table 5-5 is analyzed, we can conclude that the percentage of removal is very high, it goes from 96.3% till more that 99.9%. In average, with this new first FF, the percentage of removal is 98.61%. By comparison of the dried sludge formation, it can be concluded that the vast majority of HEM is removed in first FF. That way, we can state that introducing this new FF the cleaning of WW is efficient. However, four experiments were still to be carried out so the results of optimization of concentrations of reactants could not be done and we cannot predict which exact concentration of Fe2(SO4)3 and H2O2 are the optimal. To sum up, main results are reflected in the following Table 5-6. Additionally, the sludge formation per initial sample volume before FF1 γsludge-init was calculated. The initial volume, when surfactants were added was 4 L, while the volume of sample with no surfactant addition was 3.75 L. It is clearly visible, that samples with higher initial HEM content had higher mass of sludge formed between 4.07 g/L up to 6.25 g/L. Interestingly enough, the lower addition of Fe2(SO4)3 resulted in higher sludge formation, however, the HEM removal rate was lower. The samples with lower HEM content, where S2 was used, resulted in lower sludge formation, which is expected as there is less pollutant to remove. Table 5-6: Summary of results. STD Surfactant type V Fe2(SO4)3 (mL) V H2O2 (35%)/mL m 1. FF (g) m 2 . FF (g) m total (g) γ sludge - init (g/L) HEM initial (mg/L) HEM final (mg/L) η (%) 1 1 0.8 9.9 29.61 0.39 30 7.50 8885.0 329.7 96.29 2 1 1.6 9.9 17.96 1.55 19.51 4.88 8885.0 172.6 98.06 3 2 0.8 18.0 8.90 1.52 10.42 2.61 2882.0 7.0 99.76 4 1 1.6 18.0 26.09 0.62 26.71 6.68 8885.0 198.7 97.76 5 2 0.6 13.9 9.54 0.92 10.46 2.61 2882.0 1.5 99.95 6 2 1.8 13.9 8.44 2.61 11.05 2.76 2882.0 66.7 97.69 7 0 1.1 8.2 8.69 5.55 14.24 3.80 1811.0 1.3 99.92 8 2 1.2 19.7 9.00 2.94 11.94 2.98 2882.0 12.0 99.58 9 0 1.1 13.9 10.35 3.27 13.62 3,63 1811.0 26.7 98.53 Analysis of flocculation/flotation as wastewater pretreatment 22 The HEM removal rate was in all cases high. It could be seen that in this case lower addition of Fe2(SO4)3 resulted in higher HEM removal and lower sludge formation. What it is interesting to note is that samples with no additional surfactants (7 and 9) had lower HEM content compared to samples with S2 content (3,5,6,8) but the sludge formation was higher. This clearly indicates that surfactant type and content have impact on HEM removal in the entire process. Analysis of flocculation/flotation as wastewater pretreatment 23 6 CONCLUSIONS The goal of this work was to analyze the efficiency of the HEM removal throughout the entire process of wastewater treatment consisting of flocculation/flotation process in acid environment; followed by advanced oxidization process carried out with H2O2 with UV lamp and flocculation/flotation process in alkaline environment. Each experiment was prepared with different concentrations of Fe2(SO4)3 and H2O2 with addition of different samples with high surfactant content or samples with only high HEM content. As can be concluded, all experiments that were carried out had the HEM removal higher than 96.29 % representing a very successful HEM removal. The limit of 100 mg/L HEM after treatment was achieved in 6 cases, only in samples with enormously high initial HEM content was not below, however even in the worst case the HEM content decreased from 8885 mg/L to 329.7 mg/L. In cases where the HEM content was in line with the usual content of HEM in WW all the samples were well below the set limit. Another important conclusion of this work is the impact of the type and content of surfactants being present in the samples. As the removal rate and sludge formation was lower in case with added surfactant it can be interpreted that surfactants or at least this one type of surfactant can have a negative impact on the HEN removal. This is in accordance with the theory of flocculation/flotation and the surfactant composition. In these cases, one should be aware of additional charges in the surface of surfactants when designing the FF process. 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