The efficiency of biological aerobic treatment of ...

Q IWA Publishing 2008 Water Science & Technology—WST | 57.12 | 2008

1909

The efficiency of biological aerobic treatment of piggery wastewater to control nitrogen, phosphorus, pathogen and gas emissions F. Be´line, M. L. Daumer, L. Loyon, A. M. Pourcher, P. Dabert, F. Guiziou and P. Peu

ABSTRACT Due to the water pollution and in order to reduce the nitrogen load applied on soils, biological nitrogen removal treatment of piggery wastewaters was developed in Brittany (France), with 250–300 units running. Four types of treatment processes were built including a biological reactor allowing to remove about 60–70% of the nitrogen content as gas by nitrification/denitrification. The addition of different mechanical separators (screw-press, centrifuge decanter …) led to concentration of phosphorus in an exportable solid phase, allowing a reduction up to 80% of the phosphorus applied locally on soils. Moreover, a reduction of the gaseous emissions was observed using this management process as compared to conventional management (storage + land spreading) including ammonia (up to 68%) and greenhouse gases (55%). Finally, the level of enteric and pathogenic bacteria was also decreased with the treatment process as compared to conventional management

F. Be´line M. L. Daumer L. Loyon A. M. Pourcher P. Dabert F. Guiziou P. Peu Cemagref, Environmental management and biological treatment of wastes Research unit, 17 Avenue de Cucille´, CS 64427, F-35044, Rennes Cedex, France E-mail: [email protected]

systems. However, in spite of these results, the significant cost of the treatment must be underlined and alternative systems including anaerobic digestion will have to be studied. Key words

| biological nitrogen removal, gaseous emissions, nutrients, pathogens, piggery wastewater

INTRODUCTION In Europe, piggery wastewaters are traditionally used as

leaching. The average surface water NO2 3 concentration has

fertiliser for landspreading in agriculture, providing a

increased up to 38.1 mg/L and almost half of the monitored

significant source of nutrients. However, landspreading of

points have recorded a maximum concentration higher

any organic fertiliser in excess of the crop nitrogen

than 50 mg/L that is the maximum concentration allowed

requirements or in inappropriate soil and weather con-

for drinking water production (Rapion et al. 2001). The

ditions can lead to pollution of surface waters and aquifers.

guide value of 25 mg/L was exceeded by approximately 80%

In France, the region of Brittany, which accounts for only

of the measurements. The nitrate in surface water leads to

7% of the French agricultural land, is now responsible for

eutrophication of both inland and coastal water.

nearly 60% of the national pig production. In this intensive

This increase of nitrate concentration in surface and

livestock area, the organic nitrogen produced by the farms is

ground water in Europe led the European Commission to

frequently higher than the capacity of the land to recycle it

establish a directive called Nitrate Directive (European

as fertiliser. Consequently, the amount of organic nitrogen

Community 1991) which is intended to control nitrate

from animal wastewaters applied to the agricultural soils

leaching by establishing a common upper limit of permiss-

has been in excess for several years, leading to nitrate

ible nitrogen loads. For the application of this EU Nitrate

doi: 10.2166/wst.2008.316

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F. Be´line et al. | Aerobic treatment of piggery wastewater

Water Science & Technology—WST | 57.12 | 2008

Directive in the intensive livestock region in France, an

subsequently found in farm wastewater. The pathogenic

administrative upper limit on the amount of organic

micro-organisms most often isolated from animal manure

nitrogen produced annually by farms above which the

are Salmonella, Campylobacter, Yersinia enterocolitica and

treatment or export of animal waste is obligatory was

Cryptosporidium (Guan & Holley 2003).

defined (Be´line et al. 2004). In this context, the treatment

The aim of this paper is to summarize the data obtained

of livestock wastes, particularly piggery wastewaters,

for the past 8 years on the effectiveness of the biological

was developed during the last ten years. Among the

aerobic treatment of piggery wastewater as regard to the

technologies developed, the biological aerobic treatment

removal of nitrogen and phosphorus and also to the effect of

represents more than 80% of the farm treatment units. Such

this treatment on gaseous emissions and pathogenic

treatment removes up to 75% of total N from piggery

microorganisms elimination.

wastewater. Today, about 250 – 300 treatment units are running in Brittany allowing to remove 6 – 7,000 tons of nitrogen per year (Levasseur & Lemaire 2006). However, this treatment does not affect the total amount of phos-

MATERIALS AND METHODS

phorus. Consequently, the management of products from

A survey of the technical characteristics of the piggery

biological aerobic treatment plants, based on nitrogen crop

wastewater treatment units built in Brittany was performed.

requirement, could result in over application of phosphorus

Following this survey, four farms representing the main

and other stable compounds to agricultural land. Sub-

types of treatment units were identified and their efficiency

sequent transfer of P from soils could occur in large

was evaluated.

quantities and contribute also to eutrophication (Greaves

Concerning nitrogen and phosphorus, the study was

et al. 1999). To alleviate this problem, an obligation of

performed by sampling the inlet and the outlet of each

phosphorus exportation was defined for farmer treating

treatment stage each week during 8 weeks for one farm of

large amount of nitrogen.

each type of treatment. For each farm, quantities of raw

Livestock wastes management is also a major source of

piggery wastewater and treated products released from the

gaseous pollutants, particularly ammonia (NH3) and green-

treatments units were monitored and recorded daily during

house gases [nitrous oxide (N2O) and methane (CH4)].

the 8-week period. For each farm, samples of the different

In fact, the contribution of the livestock wastes management,

products were taken on weekly basis. All samples were

including outdoor excretion, livestock housing, outdoor

kept at 48C until analysis (24 h maximum). Based on

storage and soil application, is 76.2%, 25.6% and 21.9%

these experimental results (concentration and flow rates),

of the total French NH3, N2O and CH4 emissions,

a nutrient distribution was established over the 8-week

respectively (CITEPA 2005a,b). France is committed to

period. For each component and each end product, the

the Convention on Long Range Transboundary Air Pollution

nutrient quantity was calculated as the percentage of

(LRTAP) for NH3, and the United Nations Framework

the component of the feed (raw piggery wastewater) that

Convention on Climate Change (UNFCCC) for greenhouse

was found in the end product under consideration.

gases. The Gothenburg and Kyoto Protocols included in

Standard analytical methods were used for total solids

the LRTAP and UNFCCC conventions contain objectives

(TS), chemical oxygen demand (COD), total ammoniacal

for the reduction of emissions.

nitrogen (TAN), total Kjeldahl nitrogen (TKN) and total

On the other hand, the constant increase in animal production

and

the

concentration

of

livestocks

in

small area of land raised the question of the possible

phosphorus (TP). Among the different techniques available, TAN was determined using steam distillation and TKN was determined using the macro-Kjeldahl method.

microbiological contamination of water. There is indeed a

Gaseous emissions (ammonia and greenhouse gases)

sanitary risk related to the use of livestock wastes in

from the different stages of treatment were measured for

agriculture. Even when healthy, animals may excrete

each type of unit and were compared to a traditional

micro-organisms pathogenic for humans which may be

management system (storage þ landspreading). Emissions


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from the various liquids were measured using a dynamic

reactor in which anoxic and aerobic phases alternate allowing

chamber technique (Peu et al. 1999). Emissions during the

nitrification and denitrification in the same tank (Figure 2).

storage of solid separated fractions were measured by

Neither decantation nor sludge recirculation is applied in the

enclosing the solid in a polytunnnel ventilated by a fan.

reactor leading to a hydraulic residence time (HRT) of 30–45

The concentrations of CH4 and N2O were analyzed either

days equal to the sludge residence time (SRT). Feeding is

by infrared detection or by gas chromatography. Ammonia

performed at the beginning of the anoxic phase providing the

concentration was determined by using trap bottles filled

organic matter required for denitrification.

with sulphuric acid followed by titration. The gas measure-

The units studied were built on farm producing between

ments were carried out over 4 –7 weeks at different seasons.

4,500 and 8,000 pigs per year, leading to piggery wastewaters

For the evaluation of the pathogenic micro-organisms

volumes ranged from 5,000 to 7,500 m3 per year. Con-

behaviour, microbial analyses were carried out on samples

sequently, the influent flow rates of the units studied during

from different treatment units. The effectiveness of treatment

this work varied between 14 and 20 m3·days21 and the

was evaluated by comparing the extent of E. coli, enterococci,

volumes of the biological reactors were ranged from 600 to

Salmonella and Cryptosporidium survival. All microbial

900 m3. The average characteristics of the influent, summar-

analyses were done within 48 h after sampling. E. coli and

ized on Table 1, led to organic load and nitrogen load

enterococci were counted using ColilertY and EnterolertY, respectively. Salmonella was enumerated using enrichment

21 21 and 0.1 kgN.m23 about 1 –2 kgCOD.m23 reactor ·day reactor ·day ,

respectively.

broth followed by inoculation onto XLT4 agar and identifi-

For the type 1, the treatment consists to remove

cation of typical colonies with API 20E strips. Crypto-

nitrogen from raw piggery wastewater in the biological

sporidium were detected by filtration, immunomagnetic separation of the oocysts, and immunofluorescence assay. The sampling was carried out over periods of 6 to 12 months.

reactor. Then, sedimentation of the treated wastewater is applied. The sludge is spread on land around the farm while the wastewater is used for irrigation on cultivated soils. The type 2 is similar to type 1 except that the liquid and solid parts of raw piggery wastewater are separated using a screw-

RESULTS AND DISCUSSIONS

press before the biological reactor. Only the liquid effluent

Description of the biological aerobic treatment units

from the mechanical separation is treated in the biological

developed in France

reactor. The solid phase from the mechanical separation is exported out of the farm. Type 3 is similar to type 2 except

Four major types of biological treatment were identified

that the mechanical separation is a decanter centrifuge

(Figure 1). All types are based on the use of a single biological

instead of a screw-press. Type 4 is similar to the type 2

Figure 1

|

Schematic representations of the four types of farm-scale treatment units: RS ¼ raw piggery wastewater, Rp ¼ reception pit, R ¼ biological reactor, ScP ¼ Screw-press separator, DeC ¼ Decanter centrifuge separator, Ls ¼ land spreading of the product, D ¼ sedimentation, StS ¼ storage tank of sludges, StL ¼ storage tank of effluent, Ir ¼ product used for irrigation, Ms ¼ mechanical separator, and Ex ¼ product exported out of the farm.

Figure 2

|

Reactor of a biological aerobic treatment plant running at farm.


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Table 1

|


Average characteristics of the piggery wastewaters treated by biological nitrogen removal

Characteristics

TS (mg·l

Average concentrations

21

)

40,500

TAN (mgN·l

21

)

2,500

TKN (mgN·l21)

3,700

21

TP (mgP·l

)

COD (mg O2·l21)

1,100 44,000

except that the sedimentation of treated piggery wastewater is replaced by a mechanical separation. In this later case, both solid phases issued from mechanical separation are

Figure 4

exported out of the farm.

Fate of nitrogen and phosphorus

|

Gaseous emissions from traditional management and treatment units calculated as a percentage of the amount of wastewater fed to the treatment units.

wastewater compared to the traditional management (Loyon et al. 2007). In the contrary, the nitrous oxide

For total nitrogen, the difference between input and output

emissions were increased. Globally, the results show a large

of the treatment units was between 62 and 72% (Figure 3),

decrease of the greenhouse gases (methane and nitrous

which is attributed mainly to the nitrogen removed in the

oxide) and ammonia (NH3) when a biological treatment is

biological reactor. Mechanical separation of the raw piggery

compared to conventional management. The reduction was

wastewater before biological treatment allows concentrat-

30 – 52% for NH3 when the biological plant included

ing 22 – 26% of the phosphorus in the solid phase using a

mechanical separation and was 68% when there was no

screw-press and 80% using a decanter centrifuge. Consider-

separation. Greenhouse gases (CH4 and N2O) were reduced

ing the whole removal of nutrients as the sum of nitrogen

by about 55% whatever the composition of the biological

removed by nitrification and denitrification and the nitro-

treatment plant.

gen and phosphorus exported out of the farm (contained in

The abatement of NH3 and CH4 emissions observed for

the solid phase), the different units of biological treatment

the systems including biological aerobic treatment as

allow to remove between 70 and 90% of the nitrogen and

compared to conventional management is mainly due to

between 0 and 80% of the phosphorus.

the decrease of the time of storage of the raw piggery wastewater. Indeed, with conventional management, the

Gaseous emissions

wastewater is stored during 4 –6 months without any treatment and, consequently, ammonia and methane emis-

As shown on Figure 4, emissions of ammonia and methane

sions are important and varied from 4.1– 6.7 g[N]m22·d21

were reduced using biological aerobic treatment of piggery

and 44.5– 56.9 g[C]m23·d21, respectively. In contrast, with the treatment process, the piggery wastewater is stored only 2 – 3 weeks in similar conditions while

the

longer

storage

period

occurs

after

the

treatment. In this case, emissions are very low (0.16 – 0.26 g[N]m22·d21, 0.6– 7.6 g[C]m23·d21) due to the previous nitrogen removal and organic matter degradation. Concerning N2O, the emissions observed represented Figure 3

|

Distribution of nitrogen and phosphorus in the various effluents of the processes calculated as a percentage of the amount of wastewater fed to the treatment units.

less than 1% of the total nitrogen entering the treatment plants.


1913

Figure 5

|


The fate of enteric bacteria during treatment of piggery wastewater.

Enteric micro-organisms behaviour

reduce the nitrogen load applied to the soils. The results

The behaviour of enteric bacteria was studied in the effluents of biological aerobic treatment units of piggery wastewaters. Microbial analyses were performed on raw piggery wastewaters, treated piggery wastewaters (corresponding to sludge in settling tank after biological treatment) and in effluents after storage in lagoons which received liquid from settling or from mechanic filtration of sludge. Indicator counts in raw piggery

obtained during this study show clearly the efficiency of the system as regards this nutrient. Moreover, the used of mechanical separation (screw-press or centrifuge decanter) of the piggery wastewater concentrates phosphorus in a solid and exportable product, allowing also the reduction of phosphorus load applied locally to the soils. In addition to the efficiency of the biological aerobic treatment of piggery

wastewaters varied from 6 £ 103 to 5 £ 106 g21 of dry matter

wastewaters as regards with nutrients management, others

for E. coli, from 6 £ 104 to 4 £ 106 g21 for enterococci

positive impacts were observed. Indeed, this kind of treatment

(Figure 5). The variations observed (about 2 logarithmic

led to a reduction of gaseous emissions (ammonia and

units) are in the same order of magnitude than those reported

greenhouse gases) as compared to conventional management

by Hill & Sobsey (2003), Vanotti et al. (2005). Salmonella were

(storage and land spreading). In the same way, the level of

detected in 62% of the samples. The succession of aerobic

enteric and pathogenic bacteria is lower in the products issued

digestion and anaerobic sludge storage clearly affected

from this kind of treatment as compared to piggery waste-

the survival of enteric bacteria as shown in Figure 5. The

waters from conventional management. Even if the products

pathogenic bacteria Salmonella was isolated in 20% of

from the treatment are not completely free of pathogens, the

the treated piggery wastewater and were not detected in the

sanitary risk involved during land spreading is probably lower

effluent

treatments

than with the piggery wastewaters issued from conventional

studied, initially designed for nitrogen and phosphorus

management. However, the cost of the biological aerobic

removal, make it possible to decrease the level of enteric

treatment of piggery wastewater is important and varied from 8

bacteria, but they do not achieve complete sanitisation of

to 20 Euros/m3 of wastewater treated. The running costs are

the by-products which are intended for spreading on

mainly due to the energy requirement for mechanical

agricultural land.

separation of piggery wastewater (particularly for centrifuge

stored

in

lagoons.

The

manure

decanter) and for oxygen transfer into the biological reactor. Face to the increase of the energy cost, anaerobic digestion

CONCLUSIONS

could play an important rule in the management of organic wastes, but in the regions with nitrogen surplus, this process

Initially, the biological aerobic treatment of piggery waste-

allowing to produce methane, and then energy, will have to be

water was developed, in France, to remove nitrogen and to

associated with nitrogen removal process.

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