污水处理-英文文献3

ifi , Av lan how BOD com agi dras arat C h s prod adequately treated in order to avoid enviro ally de sembly Rev.1 d tures amon nd 200 me dat ropriat urbanwastewater may be investigated in ord In this sense, many types of water treatment are being used. Their human developing process, on the other, is rather known [13]. Researching on other procedures of water treatment has been the nia, an autoctonous tree from Turkey, and used them for coagulation– Desalination 249 (2009) 353–358 Contents lists available at ScienceDirect Desalin j ourna l homepage: www.e l differences lay on economical and technical features. Some interesting papers have been published about several natural and alternative ways of municipal wastewater treatment involving green filters [6] chemical primary separation and UV disinfection [7] or multi-stage procedures [8] in order to get rid of dangerous pollution. Several previous papers have pointed out the importance of urban wastewater management [9,10]. This type of waste has been a target flocculation process of wastewater. The authors demonstrated that tannin has a very good effect, combined with Al2(SO4)3 in order to enhance further stages of sludge removal. Zhan and Zhao [17] tried to remove lead from water by using an adsorbent, tannin-based gel. Process of metal removal is improved by tannin gelification. In the same sense, there are other references such as Nakano et al. [18] and Kim and Nakano [19]. for social studies, as it involves several aspe social structure and community organization dimension, it is very important to consider w ⁎ Corresponding author. E-mail addresses: jbelther@unex.es (J. Beltrán-Hered (J. Sánchez-Martín). 1 Tel.: +34 924289300x9033; fax: +34 924289385. 0011-9164/$ – see front matter © 2009 Elsevier B.V. Al doi:10.1016/j.desal.2009.01.039 er to broaden the variety capacity. Özacar and Sengil [16] characterized tannins obtained from valo- of technical possibilities of treatment. implications [3,4]. 2008 has been actu Year of Sanitation by the General As through its Resolution A/C.2/61/L.16/ 2006. Ineffective sanitation infrastruc millions of deaths by diarrhoea, mainly 6 million people blind from trachoma a with schistosomiases, just for giving so them in developing countries, so app nmental [2] and health clared the International of the United Nations ated on December, 4th, facilitate every year 2.2 g child under 3 years old, million people infected a [5]. Obviously, most of e technologies referring concerned towards cooperation among developing countries and they are working on an alternative process for water treatment, mostly bearing in mind concepts such as sustainability, affordability and social feasibility. In this sense, natural coagulants/flocculants are wide-spread, easy-handling resources that are not difficult to work with by non-qualified personnel. There are some examples of this agent, such asMoringa oleifera [14] or Opuntia ficus [15]. Tannins may be a new source for coagulant and flocculant agents. Few authors have investigated about tannin water treatment cts that have to do with [11,12]. According to this astewater management Özacar and S special data abo compounds, as w tannin–Al2(SO4) Palma et al. [ bark in order to removal. Bark its columns. ia), jsanmar@unex.es l rights reserved. d other papers. For several years, investigators are effluents may be a hazardous, noxiou uct [1] which should be scope of this an Human activity is a source of wastes. Particularly in urban settlements, wastewater that came from domestic and industrial Municipal wastewater treatment by mod J. Beltrán-Heredia ⁎, J. Sánchez-Martín 1 Universidad de Extremadura, Department of Chemical Engineering and Physical Chemistry a b s t r a c ta r t i c l e i n f o Article history: Accepted 30 January 2009 Available online 3 October 2009 Keywords: Tannin-based flocculant Municipal wastewater Flocculation Natural coagulants A new tannin-based coagu wastewater. TANFLOC has s dosage) and around 50% of with an efficiency that is temperature, and optimum content does not increase seems to be a flocculent sep been determined. TANFLO wastewater treatment. 1. Introduction ed tannin flocculant agent da. de Elvas, s/n. 06071, Badajoz, Spain t and flocculant agent (TANFLOC) has been tested in order to treat urban ed a high effectiveness in turbidity removal (almost 100%, depending on the 5 and COD removal, which makes TANFLOC an appropriate coagulant agent parable to alum's. Coagulant and flocculant process does not depend on tation speed and time have been found to be 40 rpm for 30 min. Polyphenol tically, and 30% of anionic surfactants are removed. Sedimentation process ion so Sludge Volumetric Index and its evolution with flocculant dosage have as been revealed as a quite effective coagulant and flocculant agent in © 2009 Elsevier B.V. All rights reserved. as a social change factor in developing countries, as the relationship between wastewater treatment and production, on one hand, and ation sev ie r.com/ locate /desa l engil [20] enhanced the previous article and gave ut trihalomethane formation and other undesirable ell as treated water safety. They worked always with 3 combination. 21] used tannins extracted in situ from Pinus radiata polymerize a solid which is used in heavy metal elf was combined with a tannin solid into adsorption taken out and put into another separation funnel, in which 50 mL of cleaning solution was added. Funnel was shaken again, and the resultant organic fractionwas put into a 25-mL flask. It was filled up to the mark with trichloromethane and surfactant concentration was determined by visible spectrophotometry at 625 nm, with zero made with pure trichloromethane by using a HEλΙOS spectrophotometer. Reagents were prepared in the following way: • Cleaning solution: 43.5 g of NaH2PO4 (ALDRICH) was taken and it was diluted into 500 mL of distilled water. 6.6 mL of H2SO4 (PANREAC) 98% w/v was added and dilution was raised up to 1 L. • Methylene blue solution: 30 mg of methylene blue (ALDRICH) was added to 1 L of cleaning solution. Calibration equation was done with sodium lauryl sulphate (PANREAC). Polyphenol concentration was determined by Folin-Ciocalteau test [31]. 20 mL of sample was put into a 50-mL flask. 2.5 mL of Folin- Ciocalteau's phenol reagent (FLUKA) was added. Then, 5 mL of 20% sodium carbonate solution (SIGMA) was added, and the flask was filled up to the mark with distilled water. Absorbance was measured 354 J. Beltrán-Heredia, J. Sánchez-Martín / Desalination 249 (2009) 353–358 TANFLOC flocculant product is a trademark that belongs to TANAC (Brazil). It is a tannin-based product, which is modified by a physico- chemical process, and has a high flocculant power. It is obtained from an Acacia mearnsii bark. This tree is very common in Brazil and it has a high concentration of tannins. According to TANAC specification, TANFLOC is a vegetal water- extract tannin, mainly constituted of flavonoid structures with an average molecular weight of 1.7 kDa. More groups such as hydrocol- loid gums and other soluble salts are included in the TANFLOC structure. Chemical modification includes a quaternary nitrogen that gives TANFLOC cationic character. Several references have been found regarding this kind of chemical processes [22–24]. Most of them are patents, including the specific process for TANFLOC, which is reported [25]. The scientific literature refers a reaction mechanism that involves three reagents: a tannin mixture, mainly polyphenol tannins whose structure may be similar to flavonoid structures such as resorcinol A and pyrogallol B rings; an aldehyde such as formaldehyde and an amino compound, such as ammonia or a primary or secondary amine or amide compound [26]. The three reagents, under certain conditions of pH (under 7) and temperature (80 °C), may produce the mentioned flocculant agents. Under tannin denomination there are lots of chemical families. Tannins have been used traditionally for tanning animal skins, but it is possible to find several products that are distributed as flocculants. Tannins come from vegetal secondary metabolites [23]: bark, fruits, leaves… Acacia and Schinopsis are well-known tannin feedstock. However, it is not needed to search for tropical species: Castanea, Quercus ilex, suber or robur have also tannin-rich bark. The main aim of the present investigation is to characterize the coagulant and flocculant activity of this new tannin-based product as a municipal wastewater treatment. The chemical modification made on A. mearnsii tannin is not quite difficult and it is widely reported as Mannich base reaction [22], although specific industrial process for TANFLOC is under intellectual patent law. Therefore, this investigation should be considered as an initial approach to these kinds of coagulant and flocculant agents. 2. Materials and methods 2.1. Reagents TANFLOC has been kindly supplied by TANAC (Brazil). Al2(SO4)3.18H2O has been supplied by SIGMA. All reagents involved in analytical procedures have analytical purity. 2.2. Raw water Raw water was obtained from the Wastewater Treatment Plant of La Albuera, a little town near Badajoz (South West of Spain). This treatment plant was designed some years ago. It receives municipal wastewater from 4000 people. There are no significant influents of industrial wastewater, but some agricultural and livestock farms are present, so such diffuse pollution may occur. The effluent has a moderately low COD charge. Average incoming flow rate is 41.63 m3/h.Water involved in this study is collected after previous big solids separation and before oil and sand separation. The main physico-chemical characteristics of this water are referred in Table 1. If compared with other wastewater data found in literature [8,27] our working water has less pollutant charge, due surely to the nature of dumpings and above all the domestic origin of wastes. 2.3. Jar-test procedure Jar-test was selected as the standard treatment in order to study flocculant process [28]. The procedure was: 0.5 L of turbidity-known wastewater was put into a beaker. Certain dose of flocculant was added, and beaker was put into a Jar-test apparatus (VELP-Scientifica JLT4). Two stirring periods were applied: one at 100 rpm for 2 min and another one at a lower speed for a longer period. In order to study the influence of this last period, its duration and agitation intensity were varied. Turbidity was measured by a HI93703 turbidimeter (Hanna Instruments) 1 h after Jart-test was finished. Turbidity sample was obtained from the center of the beaker, 3 cm from the surface. 2.4. Analytical methods All analytical measures were made according to the American Public Health Association standard methods [29]. Measures referring sludge production and Sludge Volumetric Index (SVI) were done with a 25-mL calibrated test tube and 1-L Imhoff cone. In the first case, a 25-mL sample was collected just after coagulation and flocculation process (without sedimentation) and suspended solids were deter- mined by millipore fine filtration (45 μm glass fiber filter). In the second case, Imhoff cone received a 0.5-L sample of treated water and it was allowed to settle for 1 h. Then, sludge volume was measured as Imhoff cone was calibrated. Anionic surfactants were determined by a method based on methylene blue-anionic surfactant association [30]. 10 mL of clarified sample was put into a separation funnel. 25 mL of trichloromethane (PANREAC) and 25 mL of methylene blue solution (PANREAC) were added and the funnel was shaken vigorously. Organic fraction was Table 1 Raw water characterization data. Parameter Value Units Turbidity 82.5 NTU Suspended solids 100 ppm Total solids 650 ppm Anionic surfactants 3.9 ppm Polyphenols 6.4 Tannic acid equivalent ppm KMnO4 oxidability 65.6 O2 ppm Biological oxygen demand 130 O2 ppm Chemical oxygen demand 210 O2 ppm Chloride 21.3 Cl− ppm Calcium 94.6 Ca2+ ppm Hardness 444 CaCO3 ppm Conductivity 1006 μS cm−1 Nitrate 22.5 NO3− ppm Nitrite 0.04 N ppm Ammonium 2.1 N ppm Phosphate 7.3 P ppm Total phosphorus 11.9 P ppm pH 8.2 at 725 nm after 1 h. Zero was made with reagents without sample in a 50-mL flask, filled up with distilled water. Results are expressed in tannic acid equivalent ppm. For the COD determination, a Selecta Tembloc oven modwas used. A PF-10 Macherey-Nagel photometer, and test cuvettes were pre- prepared for the desired measurement range (the range of concen- trations selected was 50–1000 mg O2/L). In addition, BOD5 was determined by electronic pressure sensor in an OxiTop-C system of WTW. 3. Results and discussion 3.1. Comparison between TANFLOC and alum effectiveness As a first approach to the importance of this new flocculant agent, a general test comparing alum effectiveness has been carried out. Raw water has been treated with 100 ppm of each product in a standard Jar-test procedure, which consisted of 100 rpm for 2 min and 30 rpm for 20 min, 1-hour settling and samples collected from the superna- can be appreciated, no high differences are found affecting this parameter. Turbidity removal varies between 80 and 90%. It keeps rather constant, but a slight improvement is observed when increasing agitation speed from 30 to 40 rpm. Stirring speed is important from the point of view of helping flocs to be formed [33] so 40 rpm value was selected as optimum one. 3.2.2. Agitation time A 40 rpm speed was applied then in a time-variable assay. Agitation time was varied from 5 to 30 min. Fig. 2 shows an almost linear variation of effectiveness in turbidity removal. This parameter seems to be not so important, as turbidity removal varies between 80 Fig. 2. Influence of temperature, agitation time and agitation speed. 355J. Beltrán-Heredia, J. Sánchez-Martín / Desalination 249 (2009) 353–358 tant clear surface. Both products have demonstrated a high level in clarifying, almost the same in turbidity removal, COD and BOD5. In the case of KMnO4 oxidability (another measure of organic matter) TANFLOC has revealed a very slight enhancement compared with alum. These results may be seen in Fig. 1. Using this new tannin-based flocculant may encourage attending to three main aspects: a) Natural origin of TANFLOC makes it more affordable and more available than alum, as it can be synthesized directly in situ. b) pH adjustment is not needed in TANFLOC water treatment, so reagent saving is guaranteed. c) Several health considerations may be done referring to Alzhei- mer's disease and alum [32] 3.2. Jar-test parameters Two main parameters have been varied in order to optimize Jar- test procedure. This assay consists of two stages: a rapid mixing stage (100 rpm, 2 min) which was kept as there are evidence that it would enhance the final result [28] and then another slow mixing stage, which was the target of the study. Exhausting TANFLOC effectiveness is not favorable in order to evaluate the importance of these parameters, so an intermediate dosage (20 ppm) was selected to work on. 3.2.1. Agitation speed Agitation speed was varied between 10 and 50 rpm for a fixed period of 10 min. Turbidity removal results are shown in Fig. 2. As it Fig. 1. Effectiveness comparison between TANFLOC and alum. and 90% too. 30 min was selected as an average value in order to complete the Jar-test procedure that would be used in the whole investigation: 100 rpm, 2 min plus 40 rpm, 30 min. 3.3. Temperature influence Temperature has been evaluated as a factor in the coagulation/ flocculation process. The reason why it has been introduced in this study has to do with seasonal variation; temperature of effluents may be rather different in summer than in winter; or affecting to lakes or ponds where temperature may be raised up. But temperature is also important in order to extrapolate the present results to other similar effluents, such as industrial ones, which may come into the treatment plant with very different conditions. As it can be seen in Fig. 2 as well, temperature does not affect the effectiveness of the process. By varying temperature from 10 to 40 ºC no enhancement or worsening in turbidity removal is observed. Hence, TANFLOC may be an effective coagulant/flocculant agent even in the case of thermal-contaminated waters. to alum or iron salts are avoided [39]. Fig. 4. Solid and sludge production variables. 356 J. Beltrán-Heredia, J. Sánchez-Martín / Desalination 249 (2009) 353–358 3.4. Operating parameters and treated water quality In order to characterize treated water, several parameters that have to do with flocculation and sedimentation process have been evaluated. 3.4.1. Dosage influence Assays with dosage variation have been carried out. Flocculant dosage has been varied between 0 and 150 ppm. As it can be appreciated in Fig. 3, turbidity removal increases quite quickly with flocculant dosage. 80%-effectiveness is achieved rather fast, with no more than 40 ppm of TANFLOC. Almost a total turbidity removal appears with dosages around 100 ppm. These results are quite competitive to those reported by other researchers. For example, Sansalone and Kim [34] has recently used up to 150 ppm of alum (Al2 (SO4)3.18H2O) and up to 100 ppm of iron chloride (FeCl3) to achieve a turbidity reduction of 75% in a similar municipal wastewater. 3.4.2. Sludge production and suspended solids removal Sludge production is an important task in order to evaluate efficiency in coagulation/flocculation process [35]. It may be as low as possible, and sludge volume may be reduced as well. Due to this fact, aluminium-induced coagulation usually is said to be a high-sludge production process, so it became a disadvantage [36]. In the case of TANFLOC, sludge production, sludge volume and the relationship Fig. 3. General turbidity removal evolution with flocculant dosage. between these two parameters, which is called Sludge Volumetric Index (SVI), have been determined. SVI is defined by Eq. (1): SVI = Vs Ws ð1Þ where Vs is the volume that is occupied by the sludge (mL) and; Ws is the sludge mass (g). As it can be appreciated in Fig. 4, the three magnitudes increase as flocculant dosage becomes higher. Suspended solids and sludge volume increasing have a less steep slope than SVI. From 80 ppm and ahead, flocculation capacity of TANFLOC seems to be less efficient, and a sludge compression seems to appear as SVI decreases. This fact is rather normal in sedimentation process [37]. These SVI values are quite interesting because they are rather lower than others, as reported by Fernández-Leborans and Moro [38] where almost every SVI valuewas over 150 mL/g. In addition, several disadvantages linked Fig. 5. Surfactant removal assay. 3.4.3. Anionic surfactant and polyphenol removal 3.4.3.1. Anionic surfactants. Surfactant dumping into environment represents a harmful and noxious practice. They may be useful and needed compounds, but they are also considered dangerous and non- desirable substances because of their impact on water animal and vegetal life. The main aspects in which surfactants modify on environmental equilibrium involve groundwater and lakes pollution, pharmaceutical product binding (so pollution activity of these kinds of chemical compounds is considerably increased), animal and human toxicity and biopersistance [40]. These are the main reasons it has been evaluated anionic surfactant removal by this tannin-based flocculant. As it can be seen in Fig. 5, TANFLOC reaches to remove almost 30% of anionic surfactants, surely due to surfactant-turbidity adsorption and further turbidity removal. This removal tends to be constant since 60–80 TANFLOC ppm dosage and ahead, as no improvement is observed with the highest dosages. 5 treatment. As it can be seen in Table 1, not so high levels of organic modality, BANCO SANTANDER subprogram. Authors thank also the Oficina Universitaria de Cooperación al Desarrollo de la Universidad d