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Distribution of phosphorus, copper and zinc in activated sludge treatment process of swine wastewater
Bioresource Technology 101 (2010) 9399–9404
Contents lists available at ScienceDirect
Bioresource Technology journal homepage: www.elsevier.com/locate/biortech
Short Communication
Distribution of phosphorus, copper and zinc in activated sludge treatment process of swine wastewater Kazuyoshi Suzuki a, Miyoko Waki a,*, Tomoko Yasuda a, Yasuyuki Fukumoto a, Kazutaka Kuroda a, Takahiro Sakai b, Naoto Suzuki c, Ryoji Suzuki d, Kenji Matsuba e a
National Institute of Livestock and Grassland Science, National Agriculture and Food Research Organization, Ikenodai 2, Tsukuba, Ibaraki 305-0901, Japan Saga Prefectural Livestock Experiment Station, Yamauchi-machi, Miyano 23242-2, Takeo, Saga 849-2305, Japan Okinawa Prefecture Livestock and Grassland Research Center, Nakijin-mura-aza Syoshi 2009-5, Kunigami, Okinawa 905-0426, Japan d Aichi Agricultural Research Center, Nagakutecho, Oaza, Yazako-aza, Sagamine 1-1, Aichi 480-1193, Japan e Miyazaki Livestock Research Institute, Kawaminami-machi, Oaza, Kawaminami 21986, Koyugun, Miyazaki 889-1301, Japan b c
a r t i c l e
i n f o
Article history: Received 31 March 2010 Received in revised form 29 June 2010 Accepted 4 July 2010 Available online 27 July 2010 Keywords: Piggery wastewater Phosphorus Copper Zinc Activated sludge treatment
a b s t r a c t Changes in swine wastewater chemical features during an activated sludge treatment process were surveyed on 11 farms, and analyzed with non-biodegradable elements, i.e., phosphorus (P), copper (Cu), and zinc (Zn). In piggery wastewater, they were linearly correlated with suspended solid (SS) concentrations and the major portion was in solid fractions. After the pretreatment step, they were removed, with 80% for total P, 85% for total Cu, and 84% for total Zn. After the activated sludge process, total P, Cu, and Zn were then removed at 83%, 96%, and 95%, respectively. Removing SS thoroughly at each step was shown to be the most important factor in preventing outflow of these elements, since there are linear correlations or a positive relationship between the removal of SS concentrations and their removal in solid form. Most of the P, Cu, and Zn in activated sludge effluent was in soluble form, and the concentrations of Cu and Zn in the effluent were low enough, while further P removal might be required. Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction Phosphorus (P), copper (Cu), and zinc (Zn) are pollutants caused by swine waste in many regions (Steinfeld et al., 2006). Originally, they are contained in swine feed; Cu and Zn are especially added at a high concentration to improve feed efficiency and the health of swine (Nicholson et al., 1999; Takada, 2005; JLIA, 2005). Since swine can absorb only 10–20% of the Cu and Zn they ingest and 15–40% of the P in the case of popular feed ingredients, the rest is excreted (Takada, 2005); swine excrement contains high concentrations of these elements. For example, it has been shown that swine excrement contains P at 29,100 mg/kg dry-matter (dm), Cu at 135–374 mg/kg dm, and Zn at 431–471 mg/kg dm (Barnett, 1994; Nicholson et al., 1999; Isobe and Sekimoto, 1999). As a consequence, piggery wastewater and manure by-products such as slurry and compost contain P, Cu, and Zn in high concentrations. Manure by-products are applied to fields. Due to the necessity of effectively using P to fertilize fields, and the concern about excess loading of Cu and Zn, distributions of these elements in manure byproducts, their loading in soil, and their effects on plants and soil microbial activity have been well studied (Choudhary et al., * Corresponding author. Fax: +81 29 838 8606. E-mail address: [email protected] (M. Waki). 0960-8524/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2010.07.014
1996; Bolan et al., 2004a). To avoid environmental pollution, P, Cu, and Zn in piggery wastewater must be removed before discharging the purified wastewater into public water bodies. However, studies of these specific elements in piggery wastewater are relatively few. While carbon and nitrogen can be removed from swine wastewater in gaseous form by biodegradation in a wastewater treatment process, P, Cu, and Zn are non-biodegradable, and thus remain in liquid or solid fractions. Therefore, to prevent such harmful P, Cu, and Zn discharges into public water bodies, these elements must be separated from liquid fraction to solid fraction. Studies have shown that removals of solid and sludge are important for P, Cu, and Zn removal from pig slurry, because most of these elements are in solid or sludge form (Beline et al., 2004; Steinmetz et al., 2009). Activated sludge treatment is the most frequently used method for purification of swine wastewater. In a typical swine wastewater treatment process, solids are removed in two steps, i.e., a pretreatment step followed by an activated sludge separation step. There are several separation methods used on farms; primary sedimentation or separation using dewatering device with flocculants at the pretreatment stage and final sedimentation or membrane separation of activated sludge at the activated sludge separation step, which are the most prevalent in Japan. Even though solid separation methods vary on farms, details
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K. Suzuki et al. / Bioresource Technology 101 (2010) 9399–9404
about the distribution and changes of P, Cu, and Zn during the swine wastewater treatment process remain unclear. In the present study, we surveyed changes in these elements during the swine wastewater activated sludge treatment process on 11 farms, and analyzed the effect of each solid or sludge removal method on the elements removed. 2. Methods 2.1. Samples Wastewater samples were collected from 11 swine farms two or three times during samplings at 2–7 month intervals on each farm. The analytical measurement of the samples was started as soon as possible after sampling, and they were stored at 4 °C in the dark until the measurement ended. Raw swine wastewater was sampled as piggery wastewater. As a primary treatment, suspended solid (SS) removal by separation using a dewatering device with flocculants or by primary sedimentation has been adopted on many farms.
The wastewater treated by these methods was sampled as pretreated wastewater, while wastewater treated by an activated sludge treatment process was sampled as activated sludge effluent. Membrane separation or final sedimentation methods are used for activated sludge separation on many farms. Using those two methods, four major types of sludge/solid separation units, type I–IV, were identified (Table 1). A type I unit involved pretreatment by separation using a dewatering device with flocculants, and a membrane-separation activated sludge process. A type II unit consisted of pretreatment by separation using a dewatering device with flocculants, and an activated sludge process that removed sludge by final sedimentation. A continuous activated sludge reactor with a sedimentation tank and a sequencing batch reactor were both included in this activated sludge unit. A type III unit included pretreatment by primary sedimentation, and a membrane-separation activated sludge process. A type IV unit involved pretreatment by primary sedimentation, and an activated sludge process that removed sludge by final sedimentation.
Table 1 Characteristics of surveyed farms and their wastewater treatment facilities. Type
Farm/sample name
Head of fattening pigs
Pretreatment method for solid–liquid separation
Treatment method
Aeration condition at activated sludge tank
I
A
1000
Membrane-separation activated sludge process
Intermittent
B
1000
Separation using dewatering device with flocculants Separation using dewatering device with flocculants
Membrane-separation activated sludge process
Continuous
C
6000 1000
dewatering device with
Activated sludge process (with 2 dilutions in aeration tank) Activated sludge process
Intermittent
D E
1100
dewatering device with
Activated sludge process
Continuous
F
4000
dewatering device with
Sequencing batch reactor
Intermittent
G
1200
Separation using flocculants Separation using flocculants Separation using flocculants Separation using flocculants Separation using flocculants
dewatering device with
Activated sludge process
Intermittent
III
H I
800 1500
Gravity sedimentation Gravity sedimentation
Membrane-separation activated sludge process Membrane-separation activated sludge process
Continuous Continuous
IV
J
850
Gravity sedimentation
Continuous
K
2800
Gravity sedimentation
Activated sludge process with attached growth material Activated sludge process
II
dewatering device with
Intermittent
Continuous
Table 2 Wastewater characteristics at each treatment step. (n = 30).
a
Piggery wastewater average ± SD
Pretreated wastewater average ± SD
pH SS (mg/L) BOD (mg/L)
7.9 ± 0.6 7200 ± 6400 (100)a 9400 ± 7100 (100)
8.1 ± 0.5 1200 ± 2500 (16) 3400 ± 2200 (39)
7.2 ± 1.3 58 ± 96 (1.8) 58 ± 75 (0.8)
Total N (mg/L) k-N (mg/L) NHþ 4 -N (mg/L) NO 2 -N (mg/L) NO3 -N (mg/L)
2500 ± 1300 (100) 2500 ± 1300 1700 ± 980 0.3 ± 0.4 1.1 ± 0.7
1200 ± 620 (52) 1200 ± 620 1000 ± 470 0.2 ± 0.4 0.5 ± 0.4
440 ± 540 (16) 300 ± 450 270 ± 430 74 ± 150 67 ± 99
Total P (mg/L) Soluble P (mg/L) Solid P (mg/L) Soluble/total (%)
330 ± 260 (100) 69 ± 70 (100) 270 ± 250 (100) 28 ± 21
67 ± 84 (20) 29 ± 15 (53) 38 ± 84 (14) 61 ± 27
35 ± 31 (17) 34 ± 31 (58) 2.7 ± 7.1 (1.4) 93 ± 15
Total Cu (mg/L) Soluble Cu (mg/L) Solid Cu (mg/L) Soluble/total (%)
4.7 ± 4.7 (100) 0.41 ± 0.64 (100) 4.3 ± 4.5 (100) 13 ± 11
0.62 ± 1.0 (15) 0.15 ± 0.12 (50) 0.5 ± 1.0 (11) 50 ± 43
0.23 ± 0.52 (4.2) 0.27 ± 0.49 (50) 0.021 ± 0.082 (1.0) 91 ± 25
Total Zn (mg/L) Soluble Zn (mg/L) Solid Zn (mg/L) Soluble/total (%)
12 ± 10 (100) 0.80 ± 1.8 (100) 11 ± 9.4 (100) 8.8 ± 9.3
1.5 ± 2.4 (16) 0.20 ± 0.19 (41) 1.3 ± 2.4 (14) 30 ± 30
0.31 ± 0.45 (5.3) 0.27 ± 0.41 (33) 0.055 ± 0.12 (0.7) 81 ± 23
Values in parentheses mean the average ratio to the concentration of piggery wastewater.
Activated sludge effluent average ± SD
K. Suzuki et al. / Bioresource Technology 101 (2010) 9399–9404
In many cases, the activated sludge process has been used for discharging the effluent wastewater into public water bodies; however, in the case of inadequate effluent water quality, the effluent was irrigated and not discharged into public water bodies. 2.2. Analytical method Standard analytical methods were used for SS, BOD, pH, Kjel dahl-N, NHþ 4 -N, NO2 -N, NO3 -N, P, Cu, and Zn (APHA, 1998). Supernatants of samples centrifuged at 3000 rpm (1300–2000g) for 10 min were measured as soluble element forms (soluble P, Cu, and Zn), while non-centrifuged samples were measured as total element forms (total P, Cu, and Zn). The remaining total and soluble elements were estimated as solid elements (solid P, Cu, and Zn). Phosphorus, Cu, and Zn were measured, respectively, by the stannous chloride method and the flame atomic absorption spectrometry method. Total elements were measured after perchloric acid digestion. When the measured values were less than the detection limit, the limit value was used as the sample concentration; 0.01 mg/L for total Cu, 0.01–0.1 mg/L for soluble Cu and 0.03 mg/ L for total Zn, and 0.03–0.2 mg/L for soluble Zn. When the proportion of soluble or solid forms to the total form was calculated, values less than the detection limit were eliminated, and any proportion above 100% due to measurement error was set at 100%. When the average ratio of wastewater concentrations to that of piggery wastewater was calculated, serious outliers of negative ratio were eliminated. Total nitrogen was calculated as the sum of Kjeldahl-N, NO 2 -N, and NO3 -N. The significance of the correlation coefficients between the SS concentration and total P, total Cu and total Zn concentrations in piggery wastewater and between the removed SS concentration and removed solid P, solid Cu and solid Zn by pretreatment was evaluated by regression analysis.
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tures, due to various types of feed, livestock barns, service water use, etc. In the present study also, piggery wastewater showed a wide range in the values of chemical features: pH of 7.9 (6.2–9.1), SS of 7200 (520–27,000) mg/L, BOD of 9400 (2000– 36,000) mg/L, total nitrogen of 2500 (580–5500) mg/L, total P of 330 (48–1100) mg/L, total Cu of 4.7 (0.6–21) mg/L, and total Zn of 12 (1.4–40) mg/L (average, minimum–maximum). It is well known that the major portion of excreted SS (97%), P (90%), Cu (>95%), and Zn (>95%) are contained in feces (Haga, 1995; JLIA, 2005). As might be expected, these total P, Cu, and Zn concentrations in raw piggery wastewater correlated with the SS concentration, indicating feces contamination of the wastewater (Fig. 1) as shown by previous studies (Suzuki et al., 2007, 2008). In fact, the amount of Cu and Zn excretion by pig linearly increases with the increasing concentrations of Cu and Zn in feeds (JLIA, 2005). Moreover, the Cu and Zn concentration in feed varies among pig age and farm; especially feed for piglets has higher concentrations of them. The difference of feed composition would be the main reason for
3. Results and discussion 3.1. Piggery wastewater characteristics The chemical features in wastewater at each treatment step obtained from the survey on 11 farms were summarized in Table 2. Piggery wastewater is known to vary widely in its chemical fea-
Fig. 1. Relationship between SS concentration and total P, Cu, and Zn concentrations in piggery wastewater.
Fig. 2. Change in P (a), Cu (b), and Zn (c) concentrations by wastewater treatment at facilities using solid/sludge separation unit I–IV.
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–
Fig. 3. Relationship between removed SS concentration and removed solid P (a and d), solid Cu (b and e), and solid Zn (c and f) concentrations by pretreatment (a–c) and activated sludge treatment (d–f).
K. Suzuki et al. / Bioresource Technology 101 (2010) 9399–9404
the scattering of Cu to SS, or Zn to SS concentration ratio in piggery wastewater. 3.2. Piggery wastewater purification by pretreatment and activated sludge treatment In many cases of swine wastewater treatment, the process was comprised of pretreatment followed by activated sludge processing. The major portion of SS (average 84%) was removed at the pretreatment step, and was then removed with 98% of the piggery wastewater at the activated sludge step (Table 2). Major portions of BOD and total nitrogen occur in soluble form in piggery wastewater, with their removal at the pretreatment step reaching 61% and 48%, respectively, which is lower than that of SS. However, they are biologically degradable in gaseous form at the activated sludge step. At this step, 99% of BOD was removed, while total nitrogen removal was only 84%. The concentrations of SS and BOD in activated sludge effluent were 58 ± 96 and 58 ± 75 mg/L (average ± SD), respectively. Therefore, the SS and BOD removal alone would suffice in many swine wastewater treatment facilities. On the other hand, nitrogen removal would be inadequate in many cases, because the total nitrogen concentration in the effluent was 440 ± 540 mg/L (average ± SD). Nitrogen removal is caused mainly by biological nitrification and denitrification in the piggery wastewater activated sludge process. To improve the nitrogen removal, controlling the operation condition of the process would be required. However, the maximum removal potential depends on the influent features like the BOD to nitrogen ratio (Boursier et al., 2005; Waki et al., 2010). When the BOD to nitrogen ratio is low in the influent, an additional nitrogen removal process using external electron donors for post treatment of activated sludge might be required. Phosphorus, Cu, and Zn removal from wastewater was achieved by the separation of solid or sludge fractions using SS separation. In the present survey, the two-step removal by pretreatment and following activated sludge was observed at every four solid/sludge separation units of each compound; total P, Cu, and Zn (Fig. 2). Most were removed at the pretreatment step at rates of 80% for total P, 85% for total Cu, and 84% for total Zn removal (Table 2). Moreover, total element removal was carried out by removal of both solid and soluble forms; 86% of solid P, 47% of soluble P, 89% of solid Cu, 50% of soluble Cu, 86% of solid Zn, and 59% of soluble Zn included in the piggery wastewater were removed at the pretreatment step. Such removal of solid forms was linearly correlated at the pretreatment step with SS removal at both separation using the dewatering device with flocculants and primary sedimentation (P < 0.01, Fig. 3a–c). On the other hand, the correlation of soluble element removal and SS removal was obscure. It may be that soluble elements are adequately removed by the effects of flocculant chemicals, e.g., the chelating effect, etc., and by changes of physical and chemical features. At the activated sludge process also, removal of total P, Cu, and Zn was observed. The total form removal was caused by solid form removal of P, Cu, and Zn as about 99% removal (Table 2). However, soluble form elements were not removed or even a little increased at this step. The removal of SS has positive effects on solid P, Cu, and Zn removal in both membrane-separation activated sludge and final sedimentation, as shown in Fig. 3d–f. Normally, the SS concentrations of influents in an activated sludge tank are not very high; even if a high concentration of SS should accidentally occur, P, Cu, and Zn could be removed by the activated sludge processing. As a consequence, 83%, 96%, and 95% of total P, Cu, and Zn are removed, respectively, by the end of the activated sludge step. Concentrations of total Cu and total Zn in activated sludge effluent were 0.23 and 0.31 mg/L, respectively. These levels were considered to be sufficiently low, given that the typical standard concen-
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trations in Japan are 3 and 2 mg/L, respectively. However, since total P in activated sludge effluent at an average 35 mg/L was not low enough, further study of the removal process may be required. The proportions of soluble or solid forms to total P, Cu, and Zn dramatically changed as the swine wastewater was purified. In piggery wastewater, a major portion of P, Cu, and Zn occurred in solid form, whereas the soluble form was only 8.8–28% (Table 2). The portions of soluble P, Cu, and Zn increased at the pretreatment to 30–61%, and then accounted for most of the activated sludge effluent at 81–93%. Soluble P removal from swine wastewater has been thoroughly studied, using various methods such as crystallization, adsorption, and biological methods (Osada et al., 1991; Bolan et al., 2004b; Suzuki et al., 2007). If further removal of Cu and Zn is attempted from activated sludge effluent, it should also be considered removal from the soluble form. In the present survey, wastewater purification performance could not be compared fairly among the four sludge/solid separation units, due to differences in wastewater characteristics and operating conditions. However, it should be noted that total Cu and Zn in activated sludge effluent tended to be low during separation using a dewatering device with flocculants, and during activated sludge processing that removes sludge by final sedimentation. As a consequence, the effluent at type II unit showed the lowest concentration of Cu and Zn (Fig. 2). There might be thorough removal of solid elements concomitant with SS removal and removal of soluble elements by the chemical effect at the separation using a dewatering device with flocculants. The final sedimentation after activated sludge processing might exert a positive effect by a moderate rise of pH due to denitrification. Since pH strongly affects the solubility of Cu and Zn bound to organics, hydroxides and sulfides, etc. (Hsu and Lo, 2000; Tchobanoglous et al., 2003), the extremely lower or higher pH condition was a concern for the Cu and Zn solubility increases among the pH range of the activated sludge effluent. Additionally, the present survey found that when the pH was accidentally low or high, highly soluble Cu and Zn concentrations in activated sludge effluent were observed (1.45 mg/L of Cu and 1.88 mg/L of Zn at pH 4.7, 2.30 mg/L of Cu at pH 8.6). It would be an important matrix to avoid an accidental decrease or increase in pH so as to prevent Cu and Zn discharges into public water. 4. Conclusions In the present study, P, Cu, and Zn profiles in swine wastewater during an activated sludge treatment process were surveyed on 11 farms. In piggery wastewater, concentrations of these elements were linearly correlated with the SS concentration, with most of them occurring in solid fraction. They were removed from the liquid fraction together with SS removal both by the pretreatment step and by sludge removal during the activated sludge step. Most of these elements in activated sludge effluent were in soluble fraction. Concentrations of Cu and Zn in the effluent were sufficiently low considering the discharge limit, while P removal may be insufficient. Acknowledgements We wish to thank Mrs. N. Akasaka for her skillful assistance. This research was partially supported by the Experimental Research Budget for Pollution Prevention and Natural Environment Conservation from the Japanese Ministry of the Environment. References APHA, 1998. Standard Methods for the Examination of Water and Wastewater, 20th ed. APHA.
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Barnett, G.M., 1994. Phosphorus forms in animal manure. Bioresour. Technol. 49 (2), 139–147. Beline, F., Daumer, M.L., Guiziou, F., 2004. Biological aerobic treatment of pig slurry in France: nutrients removal efficiency and separation performances. Trans. ASAE 47 (3), 857–864. Bolan, N.S., Adriano, D.C., Mahimairaja, S., 2004a. Distribution and bioavailability of trace elements in livestock and poultry manure by-products. Crit. Rev. Environ. Sci. Technol. 34 (3), 291–338. Bolan, N.S., Wong, L., Adriano, D.C., 2004b. Nutrient removal from farm effluents. Bioresour. Technol. 94 (3), 251–260. Boursier, H., Beline, F., Paul, E., 2005. Piggery wastewater characterisation for biological nitrogen removal process design. Bioresour. Technol. 96 (3), 351–358. Choudhary, M., Bailey, L.D., Grant, C.A., 1996. Review of the use of swine manure in crop production: effects on yield and composition and on soil and water quality. Waste Manag. Res. 14 (6), 581–595. Haga, K., 1995. Animal wastewater treatment for pollution control. Water Waste 37 (1), 44–49 (in Japanese). Hsu, J.H., Lo, S.L., 2000. Characterization and extractability of copper, manganese, and zinc in swine manure composts. J. Environ. Qual. 29 (2), 447–453. Isobe, H., Sekimoto, H., 1999. A survey of the contents of heavy metals in blended feed, feces and composts of swine. Jpn. J. Soil Sci. Plant Nutr. 70 (1), 39–44 (in Japanese). Japan Livestock Industry Association (JLIA), 2005. Japanese Feeding Standard for Swine, Tokyo (in Japanese). Nicholson, F.A., Chambers, B.J., Williams, J.R., Unwin, R.J., 1999. Heavy metal contents of livestock feeds and animal manures in England and Wales. Bioresour. Technol. 70 (1), 23–31.
Osada, T., Haga, K., Harada, Y., 1991. Removal of nitrogen and phosphorus from swine waste-water by the activated-sludge units with the intermittent aeration process. Water Res. 25 (11), 1377–1388. Steinfeld, H., Gerber, P., Wassenaar, T., Castel, V., Rosales, M., de Haan, C., 2006. Livestock’s Long Shadow. Food and Agriculture Organization of the United Nations Chapter 4, Rome. Steinmetz, R.L.R., Kunz, A., Drensler, V.L., Flores, E.M.D., Martins, A.F., 2009. Study of metal distribution in raw and screened swine manure. Clean-Soil Air Water 37 (3), 239–244. Suzuki, K., Tanaka, Y., Kuroda, K., Hanajima, D., Fukumoto, Y., Yasuda, T., Waki, M., 2007. Removal and recovery of P from swine wastewater by demonstration crystallization reactor and struvite accumulation device. Bioresour. Technol. 98 (8), 1573–1578. Suzuki, R., Masuda, T., Nakatani, H., Harada, H., 2008. A survey of zinc and copper contents of wastewater on pig farms in Aichi prefecture. Res. Bull. Aichi. Agric. Res. Ctr. 40, 163–169 (in Japanese). Takada, R., 2005. Reduction of copper and zinc contents in pig feces. Jpn. J. Swine Sci. 42 (4), 149–156 (in Japanese). Tchobanoglous, G., Burton, F.L., Stensel, H.D., 2003. Wastewater Engineering, 4th ed. NY. Waki, M., Yasuda, T., Fukumoto, Y., Kuroda, K., Sakai, T., Suzuki, N., Suzuki, R., Matsuba, K., Suzuki, K., 2010. Nitrogen concentrations of activated sludge process effluent of swine wastewater. J. Jpn. Soc. Water Environ. 33 (4), 33–39 (in Japanese).
Contents lists available at ScienceDirect
Bioresource Technology journal homepage: www.elsevier.com/locate/biortech
Short Communication
Distribution of phosphorus, copper and zinc in activated sludge treatment process of swine wastewater Kazuyoshi Suzuki a, Miyoko Waki a,*, Tomoko Yasuda a, Yasuyuki Fukumoto a, Kazutaka Kuroda a, Takahiro Sakai b, Naoto Suzuki c, Ryoji Suzuki d, Kenji Matsuba e a
National Institute of Livestock and Grassland Science, National Agriculture and Food Research Organization, Ikenodai 2, Tsukuba, Ibaraki 305-0901, Japan Saga Prefectural Livestock Experiment Station, Yamauchi-machi, Miyano 23242-2, Takeo, Saga 849-2305, Japan Okinawa Prefecture Livestock and Grassland Research Center, Nakijin-mura-aza Syoshi 2009-5, Kunigami, Okinawa 905-0426, Japan d Aichi Agricultural Research Center, Nagakutecho, Oaza, Yazako-aza, Sagamine 1-1, Aichi 480-1193, Japan e Miyazaki Livestock Research Institute, Kawaminami-machi, Oaza, Kawaminami 21986, Koyugun, Miyazaki 889-1301, Japan b c
a r t i c l e
i n f o
Article history: Received 31 March 2010 Received in revised form 29 June 2010 Accepted 4 July 2010 Available online 27 July 2010 Keywords: Piggery wastewater Phosphorus Copper Zinc Activated sludge treatment
a b s t r a c t Changes in swine wastewater chemical features during an activated sludge treatment process were surveyed on 11 farms, and analyzed with non-biodegradable elements, i.e., phosphorus (P), copper (Cu), and zinc (Zn). In piggery wastewater, they were linearly correlated with suspended solid (SS) concentrations and the major portion was in solid fractions. After the pretreatment step, they were removed, with 80% for total P, 85% for total Cu, and 84% for total Zn. After the activated sludge process, total P, Cu, and Zn were then removed at 83%, 96%, and 95%, respectively. Removing SS thoroughly at each step was shown to be the most important factor in preventing outflow of these elements, since there are linear correlations or a positive relationship between the removal of SS concentrations and their removal in solid form. Most of the P, Cu, and Zn in activated sludge effluent was in soluble form, and the concentrations of Cu and Zn in the effluent were low enough, while further P removal might be required. Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction Phosphorus (P), copper (Cu), and zinc (Zn) are pollutants caused by swine waste in many regions (Steinfeld et al., 2006). Originally, they are contained in swine feed; Cu and Zn are especially added at a high concentration to improve feed efficiency and the health of swine (Nicholson et al., 1999; Takada, 2005; JLIA, 2005). Since swine can absorb only 10–20% of the Cu and Zn they ingest and 15–40% of the P in the case of popular feed ingredients, the rest is excreted (Takada, 2005); swine excrement contains high concentrations of these elements. For example, it has been shown that swine excrement contains P at 29,100 mg/kg dry-matter (dm), Cu at 135–374 mg/kg dm, and Zn at 431–471 mg/kg dm (Barnett, 1994; Nicholson et al., 1999; Isobe and Sekimoto, 1999). As a consequence, piggery wastewater and manure by-products such as slurry and compost contain P, Cu, and Zn in high concentrations. Manure by-products are applied to fields. Due to the necessity of effectively using P to fertilize fields, and the concern about excess loading of Cu and Zn, distributions of these elements in manure byproducts, their loading in soil, and their effects on plants and soil microbial activity have been well studied (Choudhary et al., * Corresponding author. Fax: +81 29 838 8606. E-mail address: [email protected] (M. Waki). 0960-8524/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2010.07.014
1996; Bolan et al., 2004a). To avoid environmental pollution, P, Cu, and Zn in piggery wastewater must be removed before discharging the purified wastewater into public water bodies. However, studies of these specific elements in piggery wastewater are relatively few. While carbon and nitrogen can be removed from swine wastewater in gaseous form by biodegradation in a wastewater treatment process, P, Cu, and Zn are non-biodegradable, and thus remain in liquid or solid fractions. Therefore, to prevent such harmful P, Cu, and Zn discharges into public water bodies, these elements must be separated from liquid fraction to solid fraction. Studies have shown that removals of solid and sludge are important for P, Cu, and Zn removal from pig slurry, because most of these elements are in solid or sludge form (Beline et al., 2004; Steinmetz et al., 2009). Activated sludge treatment is the most frequently used method for purification of swine wastewater. In a typical swine wastewater treatment process, solids are removed in two steps, i.e., a pretreatment step followed by an activated sludge separation step. There are several separation methods used on farms; primary sedimentation or separation using dewatering device with flocculants at the pretreatment stage and final sedimentation or membrane separation of activated sludge at the activated sludge separation step, which are the most prevalent in Japan. Even though solid separation methods vary on farms, details
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K. Suzuki et al. / Bioresource Technology 101 (2010) 9399–9404
about the distribution and changes of P, Cu, and Zn during the swine wastewater treatment process remain unclear. In the present study, we surveyed changes in these elements during the swine wastewater activated sludge treatment process on 11 farms, and analyzed the effect of each solid or sludge removal method on the elements removed. 2. Methods 2.1. Samples Wastewater samples were collected from 11 swine farms two or three times during samplings at 2–7 month intervals on each farm. The analytical measurement of the samples was started as soon as possible after sampling, and they were stored at 4 °C in the dark until the measurement ended. Raw swine wastewater was sampled as piggery wastewater. As a primary treatment, suspended solid (SS) removal by separation using a dewatering device with flocculants or by primary sedimentation has been adopted on many farms.
The wastewater treated by these methods was sampled as pretreated wastewater, while wastewater treated by an activated sludge treatment process was sampled as activated sludge effluent. Membrane separation or final sedimentation methods are used for activated sludge separation on many farms. Using those two methods, four major types of sludge/solid separation units, type I–IV, were identified (Table 1). A type I unit involved pretreatment by separation using a dewatering device with flocculants, and a membrane-separation activated sludge process. A type II unit consisted of pretreatment by separation using a dewatering device with flocculants, and an activated sludge process that removed sludge by final sedimentation. A continuous activated sludge reactor with a sedimentation tank and a sequencing batch reactor were both included in this activated sludge unit. A type III unit included pretreatment by primary sedimentation, and a membrane-separation activated sludge process. A type IV unit involved pretreatment by primary sedimentation, and an activated sludge process that removed sludge by final sedimentation.
Table 1 Characteristics of surveyed farms and their wastewater treatment facilities. Type
Farm/sample name
Head of fattening pigs
Pretreatment method for solid–liquid separation
Treatment method
Aeration condition at activated sludge tank
I
A
1000
Membrane-separation activated sludge process
Intermittent
B
1000
Separation using dewatering device with flocculants Separation using dewatering device with flocculants
Membrane-separation activated sludge process
Continuous
C
6000 1000
dewatering device with
Activated sludge process (with 2 dilutions in aeration tank) Activated sludge process
Intermittent
D E
1100
dewatering device with
Activated sludge process
Continuous
F
4000
dewatering device with
Sequencing batch reactor
Intermittent
G
1200
Separation using flocculants Separation using flocculants Separation using flocculants Separation using flocculants Separation using flocculants
dewatering device with
Activated sludge process
Intermittent
III
H I
800 1500
Gravity sedimentation Gravity sedimentation
Membrane-separation activated sludge process Membrane-separation activated sludge process
Continuous Continuous
IV
J
850
Gravity sedimentation
Continuous
K
2800
Gravity sedimentation
Activated sludge process with attached growth material Activated sludge process
II
dewatering device with
Intermittent
Continuous
Table 2 Wastewater characteristics at each treatment step. (n = 30).
a
Piggery wastewater average ± SD
Pretreated wastewater average ± SD
pH SS (mg/L) BOD (mg/L)
7.9 ± 0.6 7200 ± 6400 (100)a 9400 ± 7100 (100)
8.1 ± 0.5 1200 ± 2500 (16) 3400 ± 2200 (39)
7.2 ± 1.3 58 ± 96 (1.8) 58 ± 75 (0.8)
Total N (mg/L) k-N (mg/L) NHþ 4 -N (mg/L) NO 2 -N (mg/L) NO3 -N (mg/L)
2500 ± 1300 (100) 2500 ± 1300 1700 ± 980 0.3 ± 0.4 1.1 ± 0.7
1200 ± 620 (52) 1200 ± 620 1000 ± 470 0.2 ± 0.4 0.5 ± 0.4
440 ± 540 (16) 300 ± 450 270 ± 430 74 ± 150 67 ± 99
Total P (mg/L) Soluble P (mg/L) Solid P (mg/L) Soluble/total (%)
330 ± 260 (100) 69 ± 70 (100) 270 ± 250 (100) 28 ± 21
67 ± 84 (20) 29 ± 15 (53) 38 ± 84 (14) 61 ± 27
35 ± 31 (17) 34 ± 31 (58) 2.7 ± 7.1 (1.4) 93 ± 15
Total Cu (mg/L) Soluble Cu (mg/L) Solid Cu (mg/L) Soluble/total (%)
4.7 ± 4.7 (100) 0.41 ± 0.64 (100) 4.3 ± 4.5 (100) 13 ± 11
0.62 ± 1.0 (15) 0.15 ± 0.12 (50) 0.5 ± 1.0 (11) 50 ± 43
0.23 ± 0.52 (4.2) 0.27 ± 0.49 (50) 0.021 ± 0.082 (1.0) 91 ± 25
Total Zn (mg/L) Soluble Zn (mg/L) Solid Zn (mg/L) Soluble/total (%)
12 ± 10 (100) 0.80 ± 1.8 (100) 11 ± 9.4 (100) 8.8 ± 9.3
1.5 ± 2.4 (16) 0.20 ± 0.19 (41) 1.3 ± 2.4 (14) 30 ± 30
0.31 ± 0.45 (5.3) 0.27 ± 0.41 (33) 0.055 ± 0.12 (0.7) 81 ± 23
Values in parentheses mean the average ratio to the concentration of piggery wastewater.
Activated sludge effluent average ± SD
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In many cases, the activated sludge process has been used for discharging the effluent wastewater into public water bodies; however, in the case of inadequate effluent water quality, the effluent was irrigated and not discharged into public water bodies. 2.2. Analytical method Standard analytical methods were used for SS, BOD, pH, Kjel dahl-N, NHþ 4 -N, NO2 -N, NO3 -N, P, Cu, and Zn (APHA, 1998). Supernatants of samples centrifuged at 3000 rpm (1300–2000g) for 10 min were measured as soluble element forms (soluble P, Cu, and Zn), while non-centrifuged samples were measured as total element forms (total P, Cu, and Zn). The remaining total and soluble elements were estimated as solid elements (solid P, Cu, and Zn). Phosphorus, Cu, and Zn were measured, respectively, by the stannous chloride method and the flame atomic absorption spectrometry method. Total elements were measured after perchloric acid digestion. When the measured values were less than the detection limit, the limit value was used as the sample concentration; 0.01 mg/L for total Cu, 0.01–0.1 mg/L for soluble Cu and 0.03 mg/ L for total Zn, and 0.03–0.2 mg/L for soluble Zn. When the proportion of soluble or solid forms to the total form was calculated, values less than the detection limit were eliminated, and any proportion above 100% due to measurement error was set at 100%. When the average ratio of wastewater concentrations to that of piggery wastewater was calculated, serious outliers of negative ratio were eliminated. Total nitrogen was calculated as the sum of Kjeldahl-N, NO 2 -N, and NO3 -N. The significance of the correlation coefficients between the SS concentration and total P, total Cu and total Zn concentrations in piggery wastewater and between the removed SS concentration and removed solid P, solid Cu and solid Zn by pretreatment was evaluated by regression analysis.
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tures, due to various types of feed, livestock barns, service water use, etc. In the present study also, piggery wastewater showed a wide range in the values of chemical features: pH of 7.9 (6.2–9.1), SS of 7200 (520–27,000) mg/L, BOD of 9400 (2000– 36,000) mg/L, total nitrogen of 2500 (580–5500) mg/L, total P of 330 (48–1100) mg/L, total Cu of 4.7 (0.6–21) mg/L, and total Zn of 12 (1.4–40) mg/L (average, minimum–maximum). It is well known that the major portion of excreted SS (97%), P (90%), Cu (>95%), and Zn (>95%) are contained in feces (Haga, 1995; JLIA, 2005). As might be expected, these total P, Cu, and Zn concentrations in raw piggery wastewater correlated with the SS concentration, indicating feces contamination of the wastewater (Fig. 1) as shown by previous studies (Suzuki et al., 2007, 2008). In fact, the amount of Cu and Zn excretion by pig linearly increases with the increasing concentrations of Cu and Zn in feeds (JLIA, 2005). Moreover, the Cu and Zn concentration in feed varies among pig age and farm; especially feed for piglets has higher concentrations of them. The difference of feed composition would be the main reason for
3. Results and discussion 3.1. Piggery wastewater characteristics The chemical features in wastewater at each treatment step obtained from the survey on 11 farms were summarized in Table 2. Piggery wastewater is known to vary widely in its chemical fea-
Fig. 1. Relationship between SS concentration and total P, Cu, and Zn concentrations in piggery wastewater.
Fig. 2. Change in P (a), Cu (b), and Zn (c) concentrations by wastewater treatment at facilities using solid/sludge separation unit I–IV.
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–
Fig. 3. Relationship between removed SS concentration and removed solid P (a and d), solid Cu (b and e), and solid Zn (c and f) concentrations by pretreatment (a–c) and activated sludge treatment (d–f).
K. Suzuki et al. / Bioresource Technology 101 (2010) 9399–9404
the scattering of Cu to SS, or Zn to SS concentration ratio in piggery wastewater. 3.2. Piggery wastewater purification by pretreatment and activated sludge treatment In many cases of swine wastewater treatment, the process was comprised of pretreatment followed by activated sludge processing. The major portion of SS (average 84%) was removed at the pretreatment step, and was then removed with 98% of the piggery wastewater at the activated sludge step (Table 2). Major portions of BOD and total nitrogen occur in soluble form in piggery wastewater, with their removal at the pretreatment step reaching 61% and 48%, respectively, which is lower than that of SS. However, they are biologically degradable in gaseous form at the activated sludge step. At this step, 99% of BOD was removed, while total nitrogen removal was only 84%. The concentrations of SS and BOD in activated sludge effluent were 58 ± 96 and 58 ± 75 mg/L (average ± SD), respectively. Therefore, the SS and BOD removal alone would suffice in many swine wastewater treatment facilities. On the other hand, nitrogen removal would be inadequate in many cases, because the total nitrogen concentration in the effluent was 440 ± 540 mg/L (average ± SD). Nitrogen removal is caused mainly by biological nitrification and denitrification in the piggery wastewater activated sludge process. To improve the nitrogen removal, controlling the operation condition of the process would be required. However, the maximum removal potential depends on the influent features like the BOD to nitrogen ratio (Boursier et al., 2005; Waki et al., 2010). When the BOD to nitrogen ratio is low in the influent, an additional nitrogen removal process using external electron donors for post treatment of activated sludge might be required. Phosphorus, Cu, and Zn removal from wastewater was achieved by the separation of solid or sludge fractions using SS separation. In the present survey, the two-step removal by pretreatment and following activated sludge was observed at every four solid/sludge separation units of each compound; total P, Cu, and Zn (Fig. 2). Most were removed at the pretreatment step at rates of 80% for total P, 85% for total Cu, and 84% for total Zn removal (Table 2). Moreover, total element removal was carried out by removal of both solid and soluble forms; 86% of solid P, 47% of soluble P, 89% of solid Cu, 50% of soluble Cu, 86% of solid Zn, and 59% of soluble Zn included in the piggery wastewater were removed at the pretreatment step. Such removal of solid forms was linearly correlated at the pretreatment step with SS removal at both separation using the dewatering device with flocculants and primary sedimentation (P < 0.01, Fig. 3a–c). On the other hand, the correlation of soluble element removal and SS removal was obscure. It may be that soluble elements are adequately removed by the effects of flocculant chemicals, e.g., the chelating effect, etc., and by changes of physical and chemical features. At the activated sludge process also, removal of total P, Cu, and Zn was observed. The total form removal was caused by solid form removal of P, Cu, and Zn as about 99% removal (Table 2). However, soluble form elements were not removed or even a little increased at this step. The removal of SS has positive effects on solid P, Cu, and Zn removal in both membrane-separation activated sludge and final sedimentation, as shown in Fig. 3d–f. Normally, the SS concentrations of influents in an activated sludge tank are not very high; even if a high concentration of SS should accidentally occur, P, Cu, and Zn could be removed by the activated sludge processing. As a consequence, 83%, 96%, and 95% of total P, Cu, and Zn are removed, respectively, by the end of the activated sludge step. Concentrations of total Cu and total Zn in activated sludge effluent were 0.23 and 0.31 mg/L, respectively. These levels were considered to be sufficiently low, given that the typical standard concen-
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trations in Japan are 3 and 2 mg/L, respectively. However, since total P in activated sludge effluent at an average 35 mg/L was not low enough, further study of the removal process may be required. The proportions of soluble or solid forms to total P, Cu, and Zn dramatically changed as the swine wastewater was purified. In piggery wastewater, a major portion of P, Cu, and Zn occurred in solid form, whereas the soluble form was only 8.8–28% (Table 2). The portions of soluble P, Cu, and Zn increased at the pretreatment to 30–61%, and then accounted for most of the activated sludge effluent at 81–93%. Soluble P removal from swine wastewater has been thoroughly studied, using various methods such as crystallization, adsorption, and biological methods (Osada et al., 1991; Bolan et al., 2004b; Suzuki et al., 2007). If further removal of Cu and Zn is attempted from activated sludge effluent, it should also be considered removal from the soluble form. In the present survey, wastewater purification performance could not be compared fairly among the four sludge/solid separation units, due to differences in wastewater characteristics and operating conditions. However, it should be noted that total Cu and Zn in activated sludge effluent tended to be low during separation using a dewatering device with flocculants, and during activated sludge processing that removes sludge by final sedimentation. As a consequence, the effluent at type II unit showed the lowest concentration of Cu and Zn (Fig. 2). There might be thorough removal of solid elements concomitant with SS removal and removal of soluble elements by the chemical effect at the separation using a dewatering device with flocculants. The final sedimentation after activated sludge processing might exert a positive effect by a moderate rise of pH due to denitrification. Since pH strongly affects the solubility of Cu and Zn bound to organics, hydroxides and sulfides, etc. (Hsu and Lo, 2000; Tchobanoglous et al., 2003), the extremely lower or higher pH condition was a concern for the Cu and Zn solubility increases among the pH range of the activated sludge effluent. Additionally, the present survey found that when the pH was accidentally low or high, highly soluble Cu and Zn concentrations in activated sludge effluent were observed (1.45 mg/L of Cu and 1.88 mg/L of Zn at pH 4.7, 2.30 mg/L of Cu at pH 8.6). It would be an important matrix to avoid an accidental decrease or increase in pH so as to prevent Cu and Zn discharges into public water. 4. Conclusions In the present study, P, Cu, and Zn profiles in swine wastewater during an activated sludge treatment process were surveyed on 11 farms. In piggery wastewater, concentrations of these elements were linearly correlated with the SS concentration, with most of them occurring in solid fraction. They were removed from the liquid fraction together with SS removal both by the pretreatment step and by sludge removal during the activated sludge step. Most of these elements in activated sludge effluent were in soluble fraction. Concentrations of Cu and Zn in the effluent were sufficiently low considering the discharge limit, while P removal may be insufficient. Acknowledgements We wish to thank Mrs. N. Akasaka for her skillful assistance. This research was partially supported by the Experimental Research Budget for Pollution Prevention and Natural Environment Conservation from the Japanese Ministry of the Environment. References APHA, 1998. Standard Methods for the Examination of Water and Wastewater, 20th ed. APHA.
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Barnett, G.M., 1994. Phosphorus forms in animal manure. Bioresour. Technol. 49 (2), 139–147. Beline, F., Daumer, M.L., Guiziou, F., 2004. Biological aerobic treatment of pig slurry in France: nutrients removal efficiency and separation performances. Trans. ASAE 47 (3), 857–864. Bolan, N.S., Adriano, D.C., Mahimairaja, S., 2004a. Distribution and bioavailability of trace elements in livestock and poultry manure by-products. Crit. Rev. Environ. Sci. Technol. 34 (3), 291–338. Bolan, N.S., Wong, L., Adriano, D.C., 2004b. Nutrient removal from farm effluents. Bioresour. Technol. 94 (3), 251–260. Boursier, H., Beline, F., Paul, E., 2005. Piggery wastewater characterisation for biological nitrogen removal process design. Bioresour. Technol. 96 (3), 351–358. Choudhary, M., Bailey, L.D., Grant, C.A., 1996. Review of the use of swine manure in crop production: effects on yield and composition and on soil and water quality. Waste Manag. Res. 14 (6), 581–595. Haga, K., 1995. Animal wastewater treatment for pollution control. Water Waste 37 (1), 44–49 (in Japanese). Hsu, J.H., Lo, S.L., 2000. Characterization and extractability of copper, manganese, and zinc in swine manure composts. J. Environ. Qual. 29 (2), 447–453. Isobe, H., Sekimoto, H., 1999. A survey of the contents of heavy metals in blended feed, feces and composts of swine. Jpn. J. Soil Sci. Plant Nutr. 70 (1), 39–44 (in Japanese). Japan Livestock Industry Association (JLIA), 2005. Japanese Feeding Standard for Swine, Tokyo (in Japanese). Nicholson, F.A., Chambers, B.J., Williams, J.R., Unwin, R.J., 1999. Heavy metal contents of livestock feeds and animal manures in England and Wales. Bioresour. Technol. 70 (1), 23–31.
Osada, T., Haga, K., Harada, Y., 1991. Removal of nitrogen and phosphorus from swine waste-water by the activated-sludge units with the intermittent aeration process. Water Res. 25 (11), 1377–1388. Steinfeld, H., Gerber, P., Wassenaar, T., Castel, V., Rosales, M., de Haan, C., 2006. Livestock’s Long Shadow. Food and Agriculture Organization of the United Nations Chapter 4, Rome. Steinmetz, R.L.R., Kunz, A., Drensler, V.L., Flores, E.M.D., Martins, A.F., 2009. Study of metal distribution in raw and screened swine manure. Clean-Soil Air Water 37 (3), 239–244. Suzuki, K., Tanaka, Y., Kuroda, K., Hanajima, D., Fukumoto, Y., Yasuda, T., Waki, M., 2007. Removal and recovery of P from swine wastewater by demonstration crystallization reactor and struvite accumulation device. Bioresour. Technol. 98 (8), 1573–1578. Suzuki, R., Masuda, T., Nakatani, H., Harada, H., 2008. A survey of zinc and copper contents of wastewater on pig farms in Aichi prefecture. Res. Bull. Aichi. Agric. Res. Ctr. 40, 163–169 (in Japanese). Takada, R., 2005. Reduction of copper and zinc contents in pig feces. Jpn. J. Swine Sci. 42 (4), 149–156 (in Japanese). Tchobanoglous, G., Burton, F.L., Stensel, H.D., 2003. Wastewater Engineering, 4th ed. NY. Waki, M., Yasuda, T., Fukumoto, Y., Kuroda, K., Sakai, T., Suzuki, N., Suzuki, R., Matsuba, K., Suzuki, K., 2010. Nitrogen concentrations of activated sludge process effluent of swine wastewater. J. Jpn. Soc. Water Environ. 33 (4), 33–39 (in Japanese).