aerobic biological treatment for intensive swine production

Bioresource Technology 100 (2009) 5424–5430

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Integrated anaerobic/aerobic biological treatment for intensive swine production Giuseppe Bortone * Regione Emilia-Romagna, Direzione Generale Ambiente, Difesa del Suolo e della Costa, via dei Mille 21, 40121 Bologna, Italy

a r t i c l e

i n f o

Article history: Received 15 June 2008 Received in revised form 1 December 2008 Accepted 3 December 2008 Available online 8 January 2009 Keywords: Piggery wastewater treatment Anaerobic digestion SBR Biological nutrient removal

a b s t r a c t Manure processing could help farmers to effectively manage nitrogen (N) surplus load. Many pig farms have to treat wastewater. Piggery wastewater treatment is a complex challenge, due to the high COD and N concentrations and low C/N ratio. Anaerobic digestion (AD) could be a convenient pre-treatment, particularly from the energetic view point and farm income, but this causes further reduction of C/N ratio and makes denitrification difficult. N removal can only be obtained integrating anaerobic/aerobic treatment by taking into account the best use of electron donors. Experiences gained in Italy during development of integrated biological treatment approaches for swine manure, from bench to full scale, are reported in this paper. Solid/liquid separation as pre-treatment of raw manure is an efficient strategy to facilitate liquid fraction treatment without significantly lowering C/N ratio. In Italy, two full scale SBRs showed excellent efficiency and reliability. Current renewable energy policy and incentives makes economically attractive the application of AD to the separated solid fraction using high solid anaerobic digester (HSAD) technology. Economic evaluation showed that energy production can reduce costs up to 60%, making sustainable the overall treatment. Ó 2008 Elsevier Ltd. All rights reserved.

1. Introduction Livestock manure represents one of the most significant contributions to the nitrogen (N) sources in Europe and, therefore, the recovery of N is strategic for economical and environmental reasons. Nevertheless, agronomic N recovery by manure land application has to be regulated according to good agricultural practices and vulnerability of the water bodies. In several EU regions, manure nutrients exceed the amount that can be utilized on land (170 kg N ha 1y 1 in Nitrate Vulnerable Zones -NVZ) according to the criteria of good agricultural practice set out by the Nitrates Directive. (Commission of the European Communities, 1991). A large area of Europe has been designated as NVZ (Commission of European Communities, 2007). In Emilia-Romagna region – Italy, NVZ are 56.9% (6020 km2) of the overall available arable land. This designation is due either to intrinsic hydro-geological characteristics of the territory and to the actual N load that could cause groundwater nitrate contamination and eutrophication of surface and coastal waters. This gives rise to significant N surplus in many European areas, like the Netherlands, Germany, Denmark and Italy, with surplus values higher than 100 kg ha 1y 1 (Commission of European Communities, 2007). Manure processing could help farmers to manage their surpluses and prevent further nitrate pollution of waters. In any case, manure treatment should be part of an integrated approach that

* Tel.: +39 0516396065; fax: +39 0516396991. E-mail address: [email protected] 0960-8524/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2008.12.005

considers not only the precautionary, integrated prevention pollution control (IPPC) and polluter pays principles but also the consumer’s protection in relation to the management of animal byproduct and health risks. Whatever the manure strategy is, the right equilibrium between natural resource/energy recovery, which is the first priority, and removal of nutrient surplus has to be taken into account. From an energetic view point, anaerobic digestion (AD) is also highly desirable through production of renewable energy such as methane. However, AD leaves an effluent with high N content and low C/N ratio that makes biological N removal difficult. The aim of this paper was to discuss the future integration of anaerobic and aerobic biological processes in livestock waste treatment. The discussion is based on practical experiences and optimization work in Italy integrating anaerobic and aerobic biological treatment of piggery wastewater that involved bench research, modelling and field improvements in two full scale projects. The role of solid–liquid separation in the successful integration of biological treatment is also analyzed. 2. Economic consideration on pork meat production Undoubtedly, NVZ designation has created uneven market conditions. As shown in Table 1, the cost of manure management is 2– 2.5 higher in NVZ than in ordinary zones (OZ). In addition, the high fluctuation of the pork meat prices in Italy often results in costs of meat production higher than the prices received by the producers. This makes the profitability of the meat production less attractive

G. Bortone / Bioresource Technology 100 (2009) 5424–5430 Table 1 Swine manure management cost comparison in ordinary (OZ) and nitrate vulnerable zones (NVZ)a. Zone characteristics

Cost (Euro/kg meat)

Cost (Euro/ton manure)

OZ (land spreading) NVZ (transport to OZ + Land spreading)

0.07 0.18

2.3 6.0

a

Data furnished courtesy of CRPA.

for new investment. Hence, to manage N surplus, low cost treatment are indeed necessary. Among the different N treatment technologies, biological processes present the lowest costs (Tchobanoglous and Burton, 1991). 3. The role of anaerobic digestion Nowadays, manure anaerobic digestion (AD) can contribute to sustain overall wastewater treatment costs. European Union policies for renewable energy and also the common agricultural policy (CAP) and sugar reforms are fostering energy crops, opening many possibilities for farms and agro-industries to integrate their incomes. Subsidies up to 30 cent-euro/kWh (Renewable Energy Incentive) are now ensured in Italy (Italian Parliament, 2007), and CAP is providing incentives up to 45 Euro/ha for energy crops, creating the ‘‘market” conditions for different soil uses and different productions. Anaerobic digestion of manure, either alone or in combination with other organic wastes or energy crops, represent an attractive option to increase farm income. As far as the N content of the digested piggery manure is concerned, AD gives rise only to an ammonification process as reported in Fig. 1, without significant N removal. Therefore, it causes further reduction of the C/N ratio and makes denitrification particularly difficult. Typically, the C/N ratio of the liquid after AD is lowered from an average of 10 down to about 4. For this reason, AD alone cannot overcome the problems related to the N surplus in NVZ and an integration approach is needed. 4. The role of integrated anaerobic/aerobic treatment Biological N removal can only be obtained combining anaerobic and aerobic treatments. This combination of two metabolic pro-

cesses has to take into account the use of electron donors. Therefore, effective integrated anaerobic/aerobic treatments can be achieved only by a better management of the electron fluxes. Several authors reported experimental and full scale applications of combined anaerobic–aerobic process configuration (Tilche et al., 1994; Bernet et al., 2000; Choi et al., 2005; Choi, 2007). For example, the Modified Ananox process (Tilche et al.,1994) represents a combination of anaerobic digestion and denitrification in hybrid upflow anaerobic filter (HUAF) integrated in an activated sludge nutrient removal treatment plant. (Fig. 2). Table 2 reports the main operational parameters of an experimental full scale plant implemented in northern Italy. Anaerobic process and sulphate reduction is carried out in the sludge bed at the bottom part of HUAF, while denitrification occurs in the upper part packed with filter media. The configuration maximizes the better use of the electron donors and also improves the process kinetics. For example, the volatile fatty acids (VFA) produced during the anaerobic process can be used as readily biodegradable COD for denitrification and phosphorus (P) release. It is noteworthy that the higher temperature due to the mesophilic condition of HUAF positively affects the kinetic rates of the activated sludge process, and that sulphides, generated during sulphate reduction processes under anaerobic conditions, can allow autotrophic denitrification. The experimental results confirmed the possibility to get simultaneous COD and N removal in the HUAF with a good removal efficiency of 55% for COD, 80% for N and a methane production of 0.9–0.7 Nm3CH4 m 3 reactor d 1 with a denitrification rate of 33 g N m 3 biofilter h 1 (Tilche et al. 1994). The limiting factor of HUAF denitrification capacity was related to HRT, and to the undesired increase of oxygen concentration at higher internal recycle rates, which resulted in a lower biogas production. The overall removal efficiency of the modified Ananox process was always higher than 90% for COD, N and P, nevertheless the effluent concentration of NO3–N and COD did not meet the required standards for surface water. 5. Solid–liquid separation for balancing COD/TKN ratio Another strategy for a better use of the carbon source in piggery wastewater treatment is represented by solid/liquid separation. Table 3 shows the average separation efficiency and the solid characteristics of two solid/liquid separation technologies based of flotation and centrifugation, that are often used as pre-treatment. It

70

65

55

4

N-NH (% of TKN)

60

50

45

5425

Digested Slurry Fresh Slurry

40 5-Dec 25-Dec 6-Jan 25-Jan 6-Feb 25-Feb 6-Mar 25-Mar 6-Apr 15-Apr 6-May 6-Jun Fig. 1. Nitrogen content of digested piggery manure.

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Recycle for denitrification

Screen P-release In

Sludge pre-denit.

Nitrification and luxury P-uptake

Out

Sludge recycle

Coarse solids Anaer. reactor

Fig. 2. Flow-sheet of a modified ANANOX process for biological N and P removal from piggery wastewater.

Table 2 Main operation parameters of the modified ANANOX plant treating pre-screened piggery wastewater (fattening pig farm) (adapted from Tilche et al., 1994). Operational characteristics 55 m3 15 m3 (2.8 m3) 5 m3 d 1 From 2.2 to 4.4 (maximum) 25,000–30,000 mg COD/L 1450–1600 mg TKN/L 650–750 mg P/L

Operational plant volume Operational HUAF volume (packed Vol.) Influent flow rate Internal recycle rate (Qr/Qinf) Influent COD concentration Influent TKN concentration Influent P concentration

can be noticed that either flotation and centrifuge can allow a better balanced C/N ratio than AD. Therefore, it can be concluded that, compared to AD pre-treatment, a solid/liquid separation pre-treatment of raw manure produces a balanced liquid effluent that makes easier the biological N removal treatment. 6. Liquid fraction treatment in sequencing batch reactors Sequencing batch reactors (SBRs) are among the most effective activated sludge treatment plants for the treatment of the separated liquid fraction. SBRs use temporized cycles in a single reactor to perform the same reactions that continuous flow treatment trains do in different reactors, allowing integration of anaerobic– anoxic–oxic conditions. SBRs offer kinetic advantages compared to completely stirred tank reactors (CSTRs) due to concentration gradient and better regulation of the cycle duration related to wastewater characteristics and pollutant load. Moreover, they add flexibility due to the capability to modify the time duration of the different operational phases instead of having a fixed reac-

Table 3 Average separation efficiency and the solid characteristics of two solid–liquid separation unitsa. S/L separation unit

Separation efficiency

Solid fraction

COD (%)

N (%)

P (%)

COD (%)

N (kg/ t)

P (kg/ t)

kg/m3 ww

Flotation

50–70

3.0– 4.8 7.011.0

2.1– 3.5 6.0– 10.0

350–450

50–75

80– 90 60– 70

7–10

Centrifuge

30– 40 20– 35

a

20–28

Unpublished experimental data, courtesy of CRPA.

100–200

tion volume as in continuous flow configurations. This flexibility can allow to regulate N removal efficiency according to the specific nutrient needs of a farm or to increase removal efficiency to meet the discharge limits. SBR characteristics compared to CSTR can be summarised as follows: lower reaction volume; higher settling efficiency due to the static condition of the sedimentation phase; no recycling (less energy, investment and maintenance costs); improved sludge seattleability (due to phase alternation and unbalanced growth); gradient (batch) condition that allows kinetic analysis and process investigation by on-line monitoring; and suitability of SBRs for the design and application of robust control and automation systems. 6.1. Limiting factor using SBR with separated piggery wastewater Bortone et al (1992) studied two 5 L bench scale SBRs, each one treating 500 mL/d 1 of clarified (after centrifugation) piggery wastewater. A cycle with the following alternating phases of reaction was chosen: first denitrification and phosphorus release, first oxidation–nitrification, second denitrification and second oxidation–nitrification. The systems showed good flexibility and enhanced removal of COD, N and P was easily reached modifying the duration of each phase. Good removals of COD (93%), N (88– 93%) and P (95%) were obtained in both reactors. The best efficiency in N removal has been noticed in the reactor in which the feeding distribution was done in the two denitrification phases, allowing a better use of the organic substrate for the denitrifying bacteria. This confirmed that the limiting factor, in the removal of N from piggery wastewater, is represented by the too low C/N ratio. The study also showed that SBR cycle design is fundamental since it can improve efficiency to meeting the effluent standards for discharge or for fertilizing. 6.2. Modelling and control of SBRs Mathematical modelling is particular useful for design. Andreottola et al. (1997) modified the activated sludge model (ASM) N. 1 (IWA, 2000) originally developed for continuous flow systems so as to be used under sequential batch conditions. The nitrification process was splitted in two reactions: nitritation and nitratation, the same was done for the denitrification process. The calibrated and validated model was capable to predict N trends during the SBR operational cycles, which can be used to better control treatment efficiency. Simulations showed that the higher is the

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number of denitrification/oxidation–nitrification phases per day, the lower is the concentration of nitrate in the effluent. Another possibility for SBR control and automation could be based on pH and oxidation–reduction potential (ORP) monitoring (Spagni et al., 2007). Control of a swine manure treatment process using a specific feature of ORP and pH has been demonstrated to be very promising for N removal in swine SBRs by several authors (Ra et al., 1999; Kishida et al., 2003). As an example, in Fig. 3, a track of pH and ORP, recorded during an operational cycle alternating 2 h anoxic/anaerobic and 4 h oxic/nitrification phases, at S. Anna farm SBR, that will be fully described later in this paper, is reported. During the anoxic phase ORP decreases almost continuously; a bending point, indicated as nitrate knee in Fig. 3, corresponds to the end of the denitrification process. A useful breakpoint was also identified in the pH curve, where the nitrate apex indicates the end of the denitrification process. Denitrification process results in an increased pH, whereas once nitrate and nitrite are depleted, pH tends to decrease due to fermentative reactions under anaerobic conditions. Oxic phases also displayed typical features of the signal curves. At the beginning of the aerobic phase a sharp ORP increase was shown due to aeration. ORP breakpoint is acknowledged as indicating the end of the nitrification process. During aeration, pH decreased almost continuously up to an ammonia valley indicating that ammonia had reached complete oxidation (nitritation). It was demonstrated that monitoring and control systems can allow to achieve nitrogen removal optimization via nitrite with nitritation and denitritation processes. Nitrogen removal via nitrite using SBRs can allow savings up to 25% of aeration required for nitrification and up to 40% of COD required for denitrification (Yamamoto et al., 2006). 6.3. Full scale SBRs in Emilia-Romagna, Italy On the basis of these experiences, since late nineties, full scale SBRs were constructed in Emilia-Romagna Region, Italy to upgrade existing continuous flow activated sludge systems. 6.3.1. Magreta plant Fig. 4 shows a schematic diagram of the Magreta SBR plant flow scheme with the main volumes reported. In this plant, the raw pig-

gery wastewater from a full cycle farm with 950 ton of live weight is first dewatered by mechanical (centrifuge) separation of solid and liquid fractions; the liquid fraction is subsequently treated by nitrification–denitrification in a SBR; and the solid fraction is used for composting. The discharge of effluent in sewer system for final treatment in municipal plants or for land spreading are both taken as possible options according to the fertilization plan and current nutrient needs by the farm. The main effluent characteristics of Magreta SBR plant is reported in Fig. 5; it can be noticed that, in spite of the high removal efficiency (>90%), discharging limits required by Italian Law (COD = 125 mg/L, NO3–N = 20 mg/ L; P-Tot = 10 mg/L) cannot be met. 6.3.2. S. Anna plant Higher removal efficiency has been obtained in another full scale SBR plant by applying a more effective operational cycle strategy. The S. Anna plant treats piggery wastewater from a full cycle piggery farm (partially slotted floor) with an animal population of about 800 ton of live weight, with an estimated wastewater production of about 120–150 m3/d (150–190 L/d per ton of live weight). Previous papers on the subject (Tilche et al., 2001), described in detail the rationale of the process design. Briefly, each 24 h period was divided into six 4-h modules, five reaction modules and one settling phase. Each reaction module was composed of 2 h of anoxic–anaerobic conditions and 2 h of oxic conditions. The anoxic– anaerobic phase started with a 5 min mixing period without feed followed by about l h (variable due to level control) anoxic feed. The oxic phase was characterized by the transfer to the settlers of a portion of the mixed liquor towards the end of the phase; this strategy was chosen to better manage the sludge age (fixed to about 20 d) with respect to the option of extracting the settled sludge. In the final 4 h settling phase, supernatant extraction started after 2.5 h of settling and was level controlled. Data in Table 4 show the average characteristics of the raw manure influent, the centrifuge supernatant in the equalization tank, and treated SBR effluent. It was demonstrated that the higher the number of cycles per day (within a limit given by kinetic considerations), the higher could be the nutrient removal potential. Splitting of the daily feed

9.0 100

8.9 0

ORP (mV)

8.7

-200

-300

pH

8.8

-100

8.6

-400

-500

ORP pH

8.5

10.00.04 10.13.04 10.26.04 10.39.03 10.52.03 11.05.02 11.18.02 11.31.01 11.44.01 11.57.00 12.00.00 12.10.00 12.22.59 12.35.59 12.48.59 13.01.58 13.14.58 13.27.57 13.40.57 13.53.56 14.06.56 14.19.55 14.32.55 14.45.55 14.58.54 15.11.54 15.24.53 15.37.53 15.50.52 16.03.52 16.16.51 16.29.51

8.4

Fig. 3. Oxidation reduction potential (ORP) and pH, recorded during an operational cycle alternating 2 hours anoxic/anaerobic and 4 hours oxic/nitrification phases, at S. Anna farm SBR treatment plant.

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Fig. 4. Schematic of the Magreta SBR treatment plant.

50000

4000

10000

2000

COD in COD out

6000

20000

4000

1000

2000

0 01/09/1999

3000

1500

2000

1000

1000

500

0 01/10/1999

0 01/01/2000

01/05/2000

01/09/2000

01/01/2001

01/05/2001

TKN out (mg/kg)

30000

TKN in (mg/kg)

8000

COD out (mg/kg)

COD out (mg/kg)

40000

TKN in TKN out

0 01/02/2000

01/06/2000

1200

01/10/2000

01/02/2001

01/06/2001

1200

1000

1000

800

800

600

600

400

400

200

200

0 01/09/1999

P out (mg/kg)

P in (mg/kg)

Pin Pout

0 01/01/2000

01/05/2000

01/09/2000

01/01/2001

01/05/2001

Fig. 5. Chemical oxygen demand COD, nitrogen (NTK) and phosphorus (P) concentrations in influent and effluent of the Magreta SBR treatment plant.

in equal parts at the beginning of each anoxic–anaerobic phase resulted in driving most of the available electrons towards the removal of nitrogen and phosphorus, thus using efficiently most of the oxygen for nitrification. The S. Anna SBR has proved to be an efficient biological treatment system that is capable of removing COD (99%), N (98%) and P (96%). 7. Solid fraction treatment As reported above, current policy incentives for bioenergy production makes economically attractive the application of AD to the separated solid fraction. The recommended AD process is

influenced by the choice of the separation system applied to raw swine manure. Two separation options are common in Italy: either Table 4 Average characteristics of raw feed, centrifuge supernatant in the equalization tank and treated effluent of S. Anna farm SBR (adapted from Tilche et al., 2001).

TS (g/kg) VS (g/kg) BOD5 (mg/L) COD (mg/L) TKN (mg/L) T–P

Raw influent

Equalization tank

SBR effluent

18.6 13.1 – 24,800 1960 547

6.0 2.6 – 6020 681 91

– – 93 356 29.1 22

G. Bortone / Bioresource Technology 100 (2009) 5424–5430 Table 5 Costs of S. Anna farm SBRa.

Depreciation Maintenance Polyelectrolyte Energy Manpower Total a

Costs (Euro)

Percentage (%)

60,994 14,502 4185 62,766 5475 147,922

41.2 9.8 2.8 42.4 3.7 100

Unpublished data courtesy of Envis Srl.

Table 6 Comparison between overall treatment costs with and without AD at S. Anna farm SBR.

SBR SBR + AD

Treatment costs (Euro/m3)

Treatment costs (Euro/kg meat)

5.0–6.0 2.4

0.18 0.07

mechanical dewatering by centrifuge, as in the two full scale SBR plants described above, or flotation. The advantages of flotation are related to a better pumping and mixing of the solid fraction due to lower dry matter content (more wet), an easier application of AD CSTR, with lower investment costs than with high solids anaerobic digesters (HSAD). Disadvantages of flotation are represented by the higher volume for AD. On the other hand, advantages of mechanical centrifuge dewatering are represented by the lower volume, while disadvantages are the high energy consumption and the need for innovative and effective HSAD. Even though a growing number of HSAD is nowadays recorded (Gorecki et al., 1993; Bull and Cook, 2004), further technologies development is still needed. Promising results have been reached in this field on bench scale as well as on full scale. As an example, Gorecki et al. (1993) carried out AD of the centrifuge solid fraction with a high volumetric organic load (10 kg COD/m3 d 1) and HRT of 10 days, at solid concentration up to 15–20%, with a VS removal efficiency up to 60%. The process conditions allowed a methane yield equal to 39 Nm3 CH4/solid tons. Applying this experimental results to the S. Anna farm solid fraction it is calculated that 500 m3CH4 d 1 (14 ton/d; 160 gVS/kg; 2240 kg CODrem/d; 0.22 Nm3CH4/kgCOD rem) can be obtained corresponding to 1700 kWhd 1 (765 kWh (ton live weight) 1y 1).

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farms to less concentrated areas, for full fertilizing nutrient recovering by land spreading, is very difficult for several reasons: the presence in the same areas of traditional crops and typical productions, like in Italy the parmesan cheese, and also for other reasons related to food quality and safety market strategies. One possible solution is to export manure nutrients to less concentrated areas. Therefore, technologies for manure valorisation and volume reduction are needed. Solid/liquid separation of raw manure is a key technology, since it can concentrate a high quantity of nutrients in a small volume, making transportation off-farm easier and cheaper. The remaining liquid fraction could be used on-farm as fertilizer. Rather often, especially for large, intensive swine farms, N surplus still remains after soli/liquid separation, therefore many farmers will benefit with further treatment to reduce nitrogen load. C/N ratio represents the main treatment bottle neck. Better electron donors use is needed, therefore solid–liquid separation as pre-treatment allows a more balanced C/N ratio in liquid fraction. Among the available biological technologies, SBRs showed the most promising performances. According to lab-scale as well as full scale results, SBR allows up to 98% removal of COD, N and P, and moreover it’s easy to be managed and controlled. Thus, the proposed process can represent a new chance for solving environmental problems generated by large industrial piggeries. Economic evaluations indicated that the operative costs are affordable by most pig farmers, with minor impact on meat price. Electric energy costs, that represent the biggest cost item, can be greatly reduced if the separated solids are anaerobically digested for cogeneration. Co-digestion with energy crops and/or organic wastes can even increase the profitability of the process. For these reasons, in Italy, several integrated anaerobic/aerobic biological treatment for intensive swine production are going to be constructed and revamped in the near future. Acknowledgements I wish to acknowledge Alessandro Spagni (ENEA) for the precious contribution to all this work with particular regards to the monitoring and control issues, Luigi Petta (Envis, SRL) for the economical assessment of the treatment costs, Sergio Piccinini and CRPA for all experimental data on full scale treatment plants. Finally I wish to thank Matias Vanotti, Ariel Szogi and OECD, who gave me the chance to recall old ideas and past experiences on piggery wastewater treatment, that I hope will be also useful for my new regulatory work at Emilia-Romagna region. References

8. Economic evaluation Table 5 shows the yearly costs of S. Anna farm SBR treatment plant. As it can be noticed, energy and initial investment represent most (>80%) of the costs. The overall cost for the treatment is equal to 5–6 Euro/m3 of treated swine manure, representing a significant part of the overall cost production reported in Table 1. This allows concluding that treatment could not be easily sustained by farmers. Costs can be reduced greatly if the separated solid (primary and secondary sludge) is anaerobically digested to produce biogas for cogeneration. In Table 6, a comparison between overall cost with and without AD is reported. It is put in evidence that under this strategy the costs can be reduced up to 60% (to 2.4 Euro/m3), making sustainable the overall treatment. 9. Conclusion Nowadays, manure treatment demand is increasing due to N surplus in most of the European areas. De-localization of piggery

Andreottola, G., Bortone, G., Tilche, A., 1997. Experimental calibration and validation of a simulation model for nitrification/denitrification in SBRs. Water Sci. Technol. 35, 113–120. Bernet, N., Delgenes, N., Akuna, J.C., Delgenes, J.P., Moletta, R., 2000. Combined anaerobic–aerobic SBR for the treatment of piggery wastewater. Water Res. 34, 611–619. Bortone, G., Gemelli, S., Rambaldi, A., Tilche, A., 1992. Nitrification, denitrification and biological phosphate removal in sequencing batch reactors treating piggery wastewaters. Water Sci. Technol. 26, 977–985. Bull, L., Cook, M., 2004. Environmentally Superior Technology ORBIT/HSAD report. Available from: . Choi, E., 2007. Piggery Wastewater management. Towards a Sustainable Future. IWA Publishing, London SW1H0QS, UK. Choi, E., Kim, D., Eum, Y., Yun, Z., Min, K., 2005. Full-scale experience for nitrogen removal from piggery waste. Water Environ. Res. 77, 381–389. Commission of the European Communities, 1991. Council Directive of 12 December 1991 concerning the protection of waters against pollution caused by nitrates from agriculture sources (91/676/EEC). Commission of European Communities, 2007. On implementation of Council Directive 91/676/EEC concerning the protection of waters against pollution caused by nitrates from agricultural sources for the period 2000–2003. Report from the Commission to the Council and European Parliament, 19.3.2007, COM(2007) 120 final, SEC(2007)339.

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Gorecki, J., Bortone, G., Tilche, A., 1993. Anaerobic treatment of the centrifuged solid fraction of piggery wastewater in an inclined plug flow reactor. Water Sci. Technol. 28, 107–114. Italian Parliament, 2007. Italian Law 1 ottobre 2007, no. 159 ‘‘Interventi urgenti in materia economico-finanziaria, per lo sviluppo e l’equità fiscale”, published on ‘‘Gazzetta Ufficiale” n. 229, October 2, 2007. IWA, 2000. Task group on mathematical modelling for design and operation of biological wastewater treatment. Activated sludge models ASM1, ASM2, ASM2d and ASM3. International Water Association Publishing, London, UK. Kishida, N., Kim, J., Chen, M., Sasaki, H., Sudo, R., 2003. Effectiveness of oxidation– reduction potential as monitoring and control parameters for nitrogen removal in swine wastewater treatment by sequencing batch reactors. J. Biosci. Bioeng. 96, 285–290. Ra, C.S., Lo, K.V., Mavinic, D.S., 1999. Control of a swine manure treatment process using a specific feature of oxidation reduction potential. Bioresour. Technol. 70, 117–127.

Spagni, A., Lavagnolo, M.C., Scarpa, C., Vendrame, P., Rizzo, A., Luccarini, L., 2007. Nitrogen removal optimization in a sequencing batch reactor treating sanitary landifill leachate. J. Environ. Sci. Health A 42, 757–765. Tchobanoglous, G., Burton, F.L., 1991. Wastewater Engineering: Treatment, Disposal and Reuse. Irwin/McGraw-Hill, Boston, Mass,USA. Tilche, A., Bortone, G., Forner, G., Indulti, M., Stante, L., Tesini, O., 1994. Combination of anaerobic digestion and denitrification in a hybrid upflow anaerobic filter integrated in a nutrient removal treatment plant. Water Sci. Technol. 30, 405– 414. Tilche, A., Bortone, G., Malaspina, F., Piccinini, S., Stante, L., 2001. Biological nutrient removal in a full scale SBR treating piggery wastewater: results and modelling. Water Sci. Technol. 43, 363–371. Yamamoto, T., Takaki, K., Koyama, T., Furukawa, K., 2006. Novel partial nitritation treatment for anaerobic digestion liquor of swine wastewater using swim-bed technology. J. Biosci. Bioeng. 12, 497–503.