combined anaerobic and activated sludge anoxicoxic treatment for piggery wastewater

8/10/2019 Combined Anaerobic and Activated Sludge Anoxicoxic Treatment for Piggery Wastewater

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Combined anaerobic and activated sludge anoxic/oxic treatmentfor piggery wastewater

Rajinikanth Rajagopal a,b, Pierre Rousseau a,b, Nicolas Bernet c, Fabrice Bline a,b,

a Cemagref, UR GERE, 17, Avenue de Cucill, CS 64427, F-35044 Rennes, Franceb Universit Europenne de Bretagne, Francec INRA, UR50, Laboratoire de Biotechnologie de lEnvironnement, Avenue des Etangs, Narbonne F-11100, France

a r t i c l e i n f o

Article history:

Received 7 June 2010

Received in revised form25 September 2010

Accepted 27 September 2010

Available online 2 November 2010

Keywords:

Anaerobic digestion

Nitrification/denitrification

Raw slurry bypass

Partial nitrification (PN)

Piggery wastewater

a b s t r a c t

A process combining anaerobic digestion and anoxic/oxic treatment was developed to treat pig slurry

in-order-to partially convert organic matter (OM) into a valuable energy and simultaneously to comply

with the environmental constraints as regards to nitrogen removal. However, OM content of digested

pig slurry is insufficient to allow a further complete denitrification of the mineral nitrogen content.

Hence, four different configurations were designed and evaluated to manage the OM requirements and

achieve denitrification. Partial nitrification (PN) of ammonium to nitrite was also applied by regulating

oxygen inflow time. Thus, the combined process could remove 3852% of CODt, 7988% of CODs,

6675% of TN and 9899% of NH4+N concentrations depending on the slurry characteristics. Anaerobic

digestion was able to produce 5.9 Nm3 of CH4=m3slurry added. PN allowed a reduction in the oxygen and

OM requirements respectively for nitrification and denitrification. Thus, this process trims-down the

energy costs at the farm scale.

2010 Elsevier Ltd. All rights reserved.

1. Introduction

The disposal of piggery wastewater poses a considerable prob-

lem for farmers in Brittany (France). This is basically due to the

intensification of pig production in a very limited area (Rousseau

et al., 2008). The swine wastewater is widely used as fertilizer in

this region because of its high organic, nitrogen and phosphorus

content. However, if a large group of pigs are raised in a restricted

area for instance in Brittany, it is very difficult to land spread all the

swine wastewater produced. Consequently, the over-spreading of

swine waste on a restricted area, as regards to plant requirement,

leads to local soil pollution and eutrophicationof water body. It has

been reported that out of the 76 nitrate vulnerable zones defined in

France in terms of agricultural soils organic nitrogen inputs, 71 are

located in Brittany (Rapion et al., 2001). Henceforth, many coun-

tries including France are paying attention to the pollution prob-

lems originating from livestock farms, and have tightened

legislation and discharging standards (Circular DERF/SDAFMA/98-

3002, 1998; EU Environmental Regulations in Agriculture, 2009).

The degree of treatment required and the selection of suitable

treatment technique are usually dependent upon the wastewater

composition. Pig manure has considerable amounts of non-stabi-

lized organic matter (OM) and high concentrations of ammonia.

Anaerobic digestion could be applied before land application of

swine wastes in order to reduce the organic load, while recovering

methane as bioenergy and reducing the greenhouse gas emission

during storage (Bernet and Bline, 2009). However, the effluent

of the anaerobic digester contains high amounts of nitrogen,

mostly in the form of ammonia nitrogen. A post treatment may

be required mainly to remove ammonia before discharge and bio-

logical nitrificationdenitrification being the most extensively

used process (Obaja et al., 2003). As the C/N ratio after anaerobic

digestion is generally insufficient for denitrification, the main chal-

lenge in combining the anaerobic digestion process with an acti-

vated sludge nitrification/denitrification process lies in the

management of OM, while maximizing biogas production through

anaerobic digestion. There are two possible ways to optimize this

processviz.

(i) Optimize the management of the organic matter (OM) between

the anaerobic and anoxic/oxic reactors: For that, Kim et al. (2004)

andDeng et al. (2006) proposed a combined process based on an

anaerobic digester followed by an anoxic/oxic reactor ensuring

nitrogen removal by nitrification/denitrification. To provide

enough OM for denitrification in the anoxic/aerobic reactor, a frac-

tion of the raw wastewater was bypassed the digester and fed

directly to the anoxic/aerobic reactor. However, design and

management of the bypass ratio is difficult due to high fluctuating

characteristics of piggery wastewater and can lead to loss of OM in

0960-8524/$ - see front matter 2010 Elsevier Ltd. All rights reserved.doi:10.1016/j.biortech.2010.09.112

Corresponding author at: Cemagref, UR GERE, 17, Avenue de Cucill, CS 64427,

F-35044 Rennes, France. Tel.: +33 2 23 48 21 21; fax: +33 2 23 48 21 15.

E-mail address: [email protected](F. Bline).

Bioresource Technology 102 (2011) 21852192

Contents lists available at ScienceDirect

Bioresource Technology

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / b i o r t e c h
http://dx.doi.org/10.1016/j.biortech.2010.09.112mailto:[email protected]://dx.doi.org/10.1016/j.biortech.2010.09.112http://www.sciencedirect.com/science/journal/09608524http://www.elsevier.com/locate/biortechhttp://www.elsevier.com/locate/biortechhttp://www.sciencedirect.com/science/journal/09608524http://dx.doi.org/10.1016/j.biortech.2010.09.112mailto:[email protected]://dx.doi.org/10.1016/j.biortech.2010.09.112


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terms of biogas production. So, Bernet et al. (2000) proposed an

alternative process with recirculation of the nitrified effluent (i.e.

with recirculation rate of 23 times the feed flow rate) from the

aerobic to the anaerobic reactor primarily to achieve denitrification

inside the digester. This kind of process allowed a self-regulation of

the OM between denitrification and biogas production because, as

showed byBernet et al. (2000), denitrification is directly followed

by anaerobic digestion in the same reactor. As ammonia is one of

the inhibitors of methanogenesis, nitrified effluent recirculation

to the main feed dilutes the NH4 in the anaerobic digester and thus

this configuration is expected to improve the kinetics of anaerobic

degradation of pig manure. However, due to the important nitro-

gen concentration of the piggery wastewater and the low treated

effluent concentration required at the process output, the recycle

flow rate required is very high as compared to influent flow rate.

This led to a critical decrease of the hydraulic retention time

(HRT) or will need a dramatic increase of the reactor volume.

(ii) Reduce the consumption of OM during denitrification using par-

tial nitrification (PN) [also called nitrate short-cut treatment]:Nitro-

gen removal through nitrificationdenitrification can be achieved

via the nitrite pathway (NH4- > NO2- > N2) or the nitrate pathway

(NH4- > NO2- > NO3- > NO2- > N2). The nitrite pathway theoreti-

cally reduces about 25% of the oxygen requirements for nitrifica-

tion and 40% of the OM requirements for denitrification. In

addition, this process could reduce the production of biomass to

about 40% and increase the denitrification rate to 1.5 to 2 times

(Abeling and Seyfried, 1992;Rousseau, 2009). A number of studies

were performed to identify the optimal operating conditions to ob-

tain partial nitrification [PN] (Lu et al., 2006). This includes control

of one or more factors viz. temperature, dissolved oxygen (DO), pH,

free-hydroxylamine, operational and aeration pattern. The key

point is to favour the nitritation process and at the same time to

inhibit or suppress the nitratation process in order to have a bio-

mass enriched in ammonium oxidizing bacteria (AOB) and poor

in nitrite oxidizing bacteria (NOB).

Based on these results and aiming to optimize the OM use while

avoiding short HRT or wide reactor volume, the technical goal ofthis work was to develop a process combining anaerobic and an-

oxic/oxic treatment for pig slurry obtained from Brittany (France).

Thus, this paper presents the experimental investigations to repre-

sent four possible combinations of configurations (with regard to

the literature results) on a pilot scale process for the optimization

of combined anaerobic digestion and biological nitrogen removal

procedures for the treatment of pig slurry.

2. Methods

2.1. Experimental design

Four phases of experiments were performed using the com-bined anaerobic and anoxic/oxic treatment process. As shown in

Fig. 1, different configurations were attempted in each phase of

the experiment and their operational parameters are shown in

Table 1. Based on the literature studies, three main configurations

were designed and evaluated such that anaerobic digestion took

place in a first reactor followed by nitrification/denitrification in

a second reactor, (i) with a partial raw slurry bypass of digester

to the anoxic/oxic reactor (50%) (Phase 1), (ii) with a partial bypass

of the digester (4030%) and additionally, 80% of nitrified effluent

from the anoxic/oxic reactor was recycled back to the digester

(Phases 2 and 3) and (iii) neither bypass nor recirculation (Phase

4). In addition to these configurations, a regulation was developed

to control oxygen supply in order to achieve PN in Phases 3 and 4.

The regulation developed to control oxygen supply was basedon the previous results (Boursier, 2003), which indicated that DO

concentration increased significantly from about 0.5 to more than

3 mgO2/L mainly to realise the end of nitritation process (Fig. 2).

From these results and in order to achieve PN, the aeration was

stopped in Phases 3 and 4, whenever the DO concentration reaches

the threshold value of 2 mgO2/L, it was assumed that nitritation

was completed. The DO level used to stop the oxygen supply (i.e.

2 mgO2/L, in this study) is mainly dependent on the influent char-

acteristics, oxygen transfer capacity etc. and, for field application,

the use of derivatives instead of the values should be more

accurate.

For each phase of the study, the reactor was operated for more

than 3 HRTs to obtain the steady state conditions. Thereafter, the

influent (feeding tank) and effluent samples (both from anaerobic

digester and activated sludge anoxic/oxic reactor) were analysed

for about 4 to 6 weeks.

2.2. Feed

Piggery wastewater was collected from an industrial pig farm in

Brittany (France). The wastewater was sieved through a 6 mm

diameter mesh to remove bigger particles. The sieved wastewater

was used as feed for the combined process. For each phase of the

study, about 1 m3 of slurry was collected at the same pig farm

but with different time period. This wastewater was then dis-

pensed into the screw-cap plastic containers and stored at 4o C be-

fore use. Hence, the characteristics of slurry were relatively stable

for each particular phase of experiment but found different when

compared between each phase. Table 2 presents the characteristics

of pig slurry used in each phase of the experiment. The CODt and

TN of the wastewaters used in this study varied from 42.8 to

61.8 gO2/kg and from 3.5 to 3.9 gN/kg, respectively, which is close

to the average characteristics of piggery wastewater reported in

France (Bernet and Bline, 2009).

2.3. Pilot plant description

2.3.1. Anaerobic reactorThe continuous stirred tank reactor (CSTR) had an active liquid

volume of 110 L (for Phases 1 and 2) and 120 L (Phases 3 and 4),

respectively. Initially, the digester was seeded with 50 L of waste-

water sludge taken from a municipal wastewater treatment plant

and the remaining volume was completed with tap water. The di-

gester was equipped with a hot water jacket to maintain a temper-

atureof 37 1oC and the mixing was performed using a centrifugal

pump (LSIO 15.9, Leroy Somer, France), which continuously recy-

cled the sludge from the bottom to the top of the reactor at a flow

rate of about 10 m3/h. Anaerobic reactor was fed sequentially every

12 h. Temperature, pH, and oxidationreduction potential (ORP)

were continuously monitored in the reactor using a data logger

(IQ Sensor Net 184XT, WTW, Germany) combined with adapted

probes (Senso Lyt 700IQ, WTW, Germany).

2.3.2. Anoxic/oxic reactor

The anoxic/oxic reactor used in this study was also a CSTR reac-

tor and had an active volume of 120 L (for Phases 1 and 3) and 125

L (Phases 2 and 4), respectively. Initially, about 50% of the reactor

liquid volume was added with sludge taken from another aerobic

reactor treating piggery wastewater and then tap water was used

to complete the remaining volume. Aeration was provided at a

flow rate of 0.8 m3/h by means of a compressor connected to a dif-

fuser at the bottom of the reactor. Reactor was kept at ambient

temperatures (2022oC) and mixing was carried out using a cen-

trifugal pump (LSIO 15.9, Leroy Somer, France), which continu-

ously recycled the sludge from the bottom to the top of the

reactor at a flow rate of about 10 m3

/h. The anoxic/oxic reactorwas operated in two 12-h operation cycles per day with sequential

2186 R. Rajagopal et al. / Bioresource Technology 102 (2011) 21852192


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feeding (at the beginning of the cycle) and intermittent aeration

ensuring anoxic conditions for denitrification (after feeding) fol-

lowed by oxic conditions for nitrification. Neither sludge decanta-

tion nor recirculation was applied, leading to HRT equal to sludge

retention time (SRT). In fact, as mentioned byBline et al. (2007),

no decantation was applied for the reactors in France because

the non-biodegradable suspended solids content of the piggery

wastewaters is high, leading to a difficult decantation.

During operation, this reactor was fed with digested effluent

from the anaerobic reactor and/or with raw wastewater from thefeeding tank. Similarly to anaerobic digester, temperature, pH,

and ORP were continuously monitored in this reactor. In addition,

DO was monitored using a specific probe (TriOxmatic 701IQ, WTW,

Germany).

2.4. Sampling and analysis

Liquid samples were regularly collected at various parts of the

plant (feeding tank, effluent of the anaerobic digester and activated

sludge anoxic/oxic reactor). Total (TS) and volatile (VS) solids, total

(CODt) and soluble (CODs) chemical oxygen demands, and totalKjeldahl nitrogen (TKN) were analysed according to Standard

Fig. 1. Different configurations of combined anaerobic and anoxic/oxic treatment process.

Table 1

Operating conditions for the combined anaerobic and anoxic/oxic reactor.

Parameter With bypass With bypass + recirculation Without bypass or recirculation

Phase 1 without PN Phase 2 without PN Phase 3 with PN Phase 4 with PN

R1a R2b R1a R2b R1a R2b R1a R2b

Aeration (h/cycle) 6 5 Regulationc Regulationc

HRT (d) 27.5 15.0 15.7 13.9 16.0 13.3 26.7 27.8

Overall Flow rate [Qin] (L/cycle) 4.0 2.5 2.5 2.25

Nitrogen Loading rate (kgN/m3 d) 0.25 0.19d 0.18d 0.14

Organic loading rate (kgCOD/m3 d) 1.87 2.31d 2.13d 2.32

a Reactor 1, anaerobic digester.b

Reactor 2, activated sludge anoxic/oxic reactor.c Regulation of aeration as described in the Section 2.d OLR and NLR were calculated considering the recirculated effluent.

R. Rajagopal et al. / Bioresource Technology 102 (2011) 21852192 2187


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Methods (APHA, 1992). Ammoniumnitrogen NH4 N was ana-

lysed on total wastewater by steam distillation using MgO fol-

lowed by back titration of the boric acid distillates using

sulphuric acid (0.1 M). Nitrite (NO2-

) and nitrate (NO3-

) were mea-sured by ionic chromatography (DIONEX, Sunnyvale, CA, USA).

Total Nitrogen (TN) was considered as sum of TKN, NO3- and

NO2-. Volatile fatty acids (VFA), namely acetate, propionate, buty-

rate, isobutyrate, valerate and isovalerate were determined by high

performance liquid chromatography (Waters Technology) accord-

ing toPeu et al. (2004). The biogas production was continuously

monitored by (i) combining pressure and temperature measure-

ments of the biogas and a solenoid valve allowing the release of

the biogas when the pressure in the reactor reaches 1.2 atmo-

sphere (for Phases 1, 2 and 3) or (ii) using an adapted gas flow me-

ter (Phase 4). Gas compositions, mainly methane, carbon dioxide

and nitrogen were measured using gas chromatograph (Varian

CP 4900, Chromatography Systems Middelburg, The Netherlands).

2.4.1. Respirometric assay

For determination of specific nitrification capacity of activated

sludge samples, autotrophic oxygen uptake rates (OUR) were

determined according toNowak et al. (1994). A fresh and well aer-

ated sample of activated sludge collected from the aeration tank

was poured into an aerated glass reactor (V = 10 L with a working

volume of 67 L) equipped with an additional 0.4 L respiration cell

as described by Boursier et al. (2005). The respiration cell was

equipped with an oxygen electrode (Cellox 325, WTW, Germany)

connected to a recorder allowing to monitor over time the DO

depletion in the vessel due to substrate utilization and then, to

determine the specific oxygen uptake rate. The pH of the reactor

was measured by a probe (Sentix 41, WTW, Germany) and was reg-

ulated by sulphuric acid or sodium hydroxide. Temperature and pHin the respirometer were maintained at 20 C and 7.5. After an aer-

ation period of 24 h in order to reach the endogenous respiration

level, a first substrate addition using NaNO2- (10 mgN/L) was per-

formed in the sludge followed by a second substrate addition using

NH4Cl (20 mgN/L) after 30 min. From the difference between OUR

before and after the first addition, the nitratation capacity of the

sludge was determined, considering the oxygen to nitrogen con-sumption ratio of 1.1 gO2/gN. While the difference observed before

and after the second addition gives the nitritation capacity consid-

ering a ratio of 3.28 gO2/gN.

2.4.2. Biochemical methane potential

Biochemical methane potential (BMP) was determined using

batch incubations lasting 3035 days at 35 C. The measurements

were performed in triplicates using 330 ml Schott-Duran glass bot-

tles, in which the slurry to headspace ratio was maintained at 0.5.

About 30 g of inoculum taken from a laboratory digester treating

piggery wastewater, 30 g of substrate and 40 g of tap water were

added in each bottle. After the addition of inoculum, substrate

and water, the bottles were capped with a thick rubber septum

(Schott-Duran) and the headspace was flushed with pure N2 gas.During incubation, biogas production was monitored every day

(from day 1 to 10, depending on the production) by pressure mea-

surement of the headspace using a manometer (2085 P, Digitron,

UK). When the headspace absolute pressure exceeded 1200 mbar,

a gas sample was collected for analysis using a manual gas-tight

syringe Agilent (25 ml 0.5 ml). After sampling, the remaining

overpressure of the bottle was removed to restore atmospheric

pressure. Pressure monitoring allowed the measurement of the

accumulated amount of biogas. Trials without substrate addition

(replaced by tap water) were performed to calculate the endoge-

nous methane production of the sludge.

3. Results and discussion

The COD and nitrogen behaviours at the inlet and outlet of the

whole process (i.e. combined anaerobic digestion and biological

nitrogen removal process) at steady state conditions in each phase

of the study are shown inFigs. 3 and 4, respectively.

0

50

100

150

200

250

300

350

0 5 10 15 20

Time (hours)

Nitrogen(mgN/L)

0

1

23

4

5

6

7

8

DO

(mgO2/L)

NO2-

NO3-

NH4+

DO

Anoxic phase Oxic phase

End of nitritation

Fig. 2. Nitrogen and DO evolution during anoxic/oxic treatment of piggery

wastewater (adapted fromBoursier, 2003).

Table 2

Characteristics of pig slurry.

Phase CODt (gO2/kg) CODs (gO2/kg) VFA (gO2/L) BMP (Nm3 CH4/m

3) NH4 N (gN/kg) TN* (gN/kg) TS (g/kg) VS (g/kg) pH

1 51.4 4 19.4 2 10.8 10.5 0.9 2.5 0.4 3.8 0.2 52.3 6 34.1 4 7.1 0.5

2 46.4 6 19.6 2 10.4 9.9 0.2 2.4 0.3 3.9 0.1 54.5 3 34.2 1 7.8 0.4

3 42.8 4 14.6 1 7.6 8.7 1.3 2.2 0.1 3.5 0.1 43.4 2 27.1 1 7.8 0.4

4 61.8 5 11.9 1 3.5 10.1 0.8 2.3 0.1 3.9 0.1 50.1 2 36.3 1 8.3 0.3

* For the influent, N oxidized forms (NO3 and NO2 ) are equal to 0.

0

10

20

30

40

50

60

70

Experimental phase

COD

(gO2/kg)

CODs

CODp

INF

EFF

INF

EFF

INF

EFF

INF

EFF

1 2 3 4

Fig. 3. Influent (INF) and effluent (EFF) COD behaviours in the overall process.

2188 R. Rajagopal et al. / Bioresource Technology 102 (2011) 21852192


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while maintaining similar COD and nitrogen removal efficiency i.e.

38 and 73% for CODt and TN, respectively. The COD removal and

associated CH4production in the digester were slightly lower than

that of Phase 2 but not significantly different. In this case, if we

considered that most of the nitrogen was removed through NO2-

pathway (with a required COD/N ratio between 2.5 and 4.2 in this

case), the calculated CODbiodegraded/Nremoved ratio of 4.5 suggests

that the bypass ratio could be slightly decreased without decreas-

ing the denitrification efficiency.

3.4. Operation with neither bypass nor recirculation (Phase 4)

For Phase 4 of the study i.e. without bypass or recirculation,

similar results were observed with 52%, 81%, 75% and 99% of re-

moval efficiencies for CODt, CODs, TN and NH4 N, respectively.

For this phase, a lower value of CH4 production was observed

(0.17 Nm3/kg COD removed) compared to the theoretical values,

which was explained by the technical problems while measuring

the volume of biogas. Also, a corrected CH4 value was calculatedaccording to the COD removed during this experiment and the

average CH4 production (0.28 Nm3/kg COD removed) obtained dur-

ing the other three experiments. Thus, the COD removal and the

CH4 production in the digester were higher than those observed

in the other configurations with 21.1 kg COD removed/m3 of slurry

and 5.9 Nm3/m3 of slurry, respectively. The calculated CODbiodegrad-

ed/Nremoved ratio of 3.7 in the anoxic/oxic reactor suggests that most

of the COD removed was used for denitrification in this configura-

tion even with the PN.

3.5. Comparison of the four configurations

From Tables 2 and 3, it is clear that the characteristics of the pig-

gery wastewater in each experiment were relatively different(mainly in terms of COD and therefore COD/N ratios) and thus the

comparisons are intrinsically difficult to do with respect to the re-

sults obtained from different configurations. The characteristics of

thepig slurry were probably dependenton thehistory of thepiggery

wastewater, especially as a consequence of any substantial degra-

dation occurred (or not) before sampling at the farm. However,

the results obtained from these four phases leads to the discussion

of the main advantages/disadvantages of each configuration.

The configuration proposed byKim et al. (2004)andDeng et al.

(2006) was tested in Phase 1. In this process, the raw slurry was di-

vided into two parts, i.e. one part was fed into anaerobic digester,

while the other part was bypassed into anoxic/oxic reactor in order

to provide enough OM for denitrification. It was successfully eval-

uated during this study using a bypass ratio of 0.5. Due to this highbypass ratio, the CH4 production was quite low as regards to the

quantity of slurry treated and equal to 2.5 Nm3/m3. HRT applied

in the digester during this phase (27.5 days) produced only 48.6%

of the methanogenic potential indicating that the anaerobic bio-

degradation of the piggery wastewater was slow.

The configuration suggested by Bernet et al. (2000), in which

denitrification takes place in the digester by recirculating a part

of the nitrified effluent from the outlet of the oxic reactor to the di-

gester was experimented in the Phases 2 and 3. However, this pro-

cess is not practically feasible if a low mineral nitrogen

(NH4 NO2 NO

3


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duration was regulated. The efficiency of the PN was proved by (i)

the nitratation rate observed during Phase 3 (Table 5), which was

equal to 0 as compared to the rate observed during Phase 2

(5.6 mgN/L h) and (ii) more NO2 accumulation in the effluent of

Phases 3 and 4 as compared to Phases 1 and 2 (Fig. 4B).

As previously described, the PN implementation led to similar

nitrogen removal but required OM for denitrification and oxygen

for nitrification were lower. For example, the aeration duration

was fixed to 5 h/cycle for the Phase 2 without PN, while the aver-

age aeration duration for Phase 3 with PN was approximately

23 h/cycle. Considering that the influent characteristics were

almost similar between Phases 2 and 3, the results indicate that

PN significantly decreases the aeration requirement for nitrogen

removal.

According to the presented and discussed results, though a pre-

cise comparison between each configuration was difficult due to

the differences in influent characteristics, the main advantages/dis-

advantages are resumed inTable 6. It is clear that the addition of a

recirculation is not an interesting option because of the increase in

the energy for pumping and the decrease in CH4 production. The

implementation of aeration control to obtain PN reduces the en-

ergy consumption for oxygen supply and also increases the OM

consumption in the digester, theoretically leading to a higher

CH4 production. Indeed, the most advantageous configuration

was the one operated with neither raw slurry bypass nor recircula-

tion associated with PN (Phase 4) with higher CH4production and

lower energy consumption for oxygen supply. The energy required

for heating the digester is slightly higher for this configuration than

for Phase 1 because the digested slurry volume is more significant

(only 50% was digested in Phase 1). But this increase in energy con-

sumption for heating is largely compensated by the surplus of CH4produced. However, it is important to note that the biodegradable

COD of the wastewater used in this phase was estimated to be

31.8 kg COD/m3, which is relatively higher than that estimated

by Boursier et al. (2005) for piggery wastewater. In fact, biodegrad-

able COD was estimated between 4 and 26.4 kg COD/m3 and an

average biodegradable COD of 1520 kg COD/m3 is widely consid-ered for piggery wastewater in France. Moreover, the HRT gener-

ally applied for the digesters is often longer than 2530 days

(Clemens et al., 2006), resulting in higher degradation in the diges-

ter and less biodegradable COD available for nitrogen removal.

Hence, such a configuration (neither recirculation nor bypass)

could not run efficiently on farm because the biodegradable COD

available for nitrogen removal would be lower than that observed

in Phase 4 and therefore should lead to an incomplete denitrifica-

tion. Thus, the use of a raw influent bypass is suggested by the

authors in this design. Considering an average biodegradable

COD of 1520 kg COD/m3, a bypass of 2030% combined with PN

would be efficient for nitrogen removal.

Economically, this combined process is attractive as it produces

CH4 as a renewable energy and, at the same time, it reduces the

aeration requirement for nitrogen removal by having PN and less

oxygen requirement for COD removal due to its primary removal

in the digester. Accordingly, this process could reduce the energy

costs at the farm scale.

4. Conclusions

Different configurations combining anaerobic and anoxic/oxic

treatment were experimentally evaluated during this study.

The best configuration (i.e. Phase 4) could remove up to 52% of the

COD and 75% of the nitrogen with a CH4 production of

5:9 Nm3=m3slurry added. Theapplication of partial nitrification (PN) im-

proved the energy balance of the systembecause (1) oxygen supply

for nitrification was quite low due to PN and (2) simultaneously, it

reduced organic matter (OM) requirements because nitrite denitri-

fication requires a lower COD/N ratio than nitrate denitrification,

which can be used to produce CH4in the digester.

Acknowledgments

This study has been supported by the French National Research

Agency (ANR) through the PRECODD program (Ecotechnology and

Sustainable Development).

References

Abeling, U., Seyfried, C.F., 1992. Anaerobicerobic treatment of high-strength

ammonium wastewaternitrogen removal via nitrite. Water Sci. Technol. 26

(56), 10071015.

HA, A.P., 1992. Standard Methods for the Examination of Water and Wastewater,

18th ed. American Public Health Association, Washington DC, USA.

Bline, F., Boursier, H., Daumer, M.L., Guiziou, F., Paul, E., 2007. Modelling of

biological processes during aerobic treatment of piggery wastewater aiming at

process optimisation. Bioresour. Technol. 98, 32983308.

Bernet, N., Delgenes, N., Akunna, C., Delgenes, J.P., Moletta, R., 2000. Combined

anaerobicaerobic SBR for the treatment of swine wastewater. Water Res. 34

(2), 611619.

Bernet, N., Bline, F., 2009. Challenges and innovations on biological treatment of

livestock effluents. Bioresour. Technol. 100, 54315436.

Boursier, H., 2003. Etude et modlisation des processus biologiques au cours du

traitement arobie du lisier de porcs en vue dune optimisation du procd

(Study and modelling of biological processes during aerobic treatment of

piggery wasrewaters aiming at process optimization). Ph.D. Thesis, Institut

National des Sciences Appliques de Toulouse, France.

Boursier, H., Bline, F., Paul, E., 2005. Piggery wastewater characterisation for

biological nitrogen removal process design. Bioresour. Technol. 96, 351358.

Circular DERF/SDAFMA/98-3002, 1998. Ministry of Agriculture and Fisheries and

Ministry of Environment. 21st January.

Clemens, J., Trimborn, M., Weiland, P., Amon, B., 2006. Mitigation of greenhouse gas

emissions by anaerobic digestion of cattle slurry. Agric. Ecosyst. Environ. 112(23), 171177.

Deng, L.W., Zheng, P., Chen, Z.I., 2006. Anaerobic digestion and post-treatment of

swine waste water using IC-SBR process with bypass of raw wastewater.

Process Biochem. 41, 965969.

EU Environmental Regulations in Agriculture, 2009. Final Report Prepared for

Environment Agency. In: Mills, J., Dwyer. J. (Eds.), Countryside and Community

Research Institute, April.

Kim, D.H., Choi, E., Yun, Z., Kim, S.W., 2004. Nitrogen removal from piggery waste

with anaerobic pre-treatment. Water Sci. Technol. 49 (56), 165171.

Lu, G., Zheng, P., Jin, R., Qaisar, M., 2006. Control strategy of shortcut nitrification. J.

Environ. Sci. China 18 (1), 5861.

Nowak, O., Schweignofer, P., Svardal, K., 1994. Nitrification inhibition a method for

the estimation of actual maximum autrotrophic growth rates in activated

sludge systems. Water Sci. Technol. 30 (6), 919.

Obaja, D., Mac, S., Costa, J., Sans, C., Mata-Alvarez, J., 2003. Nitrification,

denitrification and biological phosphorus removal in piggery wastewater

using a sequencing batch reactor. Bioresour. Technol. 87, 103111.

Peu, P., Bline, F., Martinez, J., 2004. Volatile fatty acids analysis from pig slurry

using high-performance liquid chromatography. Int. J. Environ. Anal. Chem. 84(13), 10171022.

Table 5

Nitrification rate measured by respirometry (at 20 C and pH 7.5).

Activated sludgewithout PN (Phase 2)

Activated sludgewith PN (Phase 3)

Nitritation rate

(mg N L1 h1)

19.2 2.7 10.9 1.2

Nitratation rate

(mg N L1 h1)

5.6 2.9 0

Table 6

Comparison between the four configurations.

Parameters Phase 1 Phase 2 Phase 3 Phase 4

CH4 produced / +

Energy for digester heating / = =

Energy for oxygen supply / = + +

Energy for pumping / =

/, reference value; +, advantage; , disadvantage; =, equal to the reference.

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combined anaerobic and activated sludge anoxicoxic treatment for piggery wastewater

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