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Effect of intermittent-cycle extended-aeration treatment on the fate of carbonaceous material in pig slurry
“i,absratorio National de Engenharia Civil, Av. do Basil, LOI-1799 Lisboa Codexj Pomgal ‘IScotti& AgkAtural College, Dept. of Biochemical Sciences?Auchincniive, Ayr MA6 .YHB{ UK eceived 20 February
1995; revised version received 5 July 1995; accepted 25 July 4995)
A farnz-scale trea~~~~~tplant was studied during a year: Four d~~~re~t aeration cycles were tested in order to ,?bserve their efiects on the removal of carbon material atment plant per$ormance was a 60% reduction of aerah per day to 12 h per day. vaE mtes observed (over 95010ivr,teelms of ared to be related to the low aeration rates ugh isklei~te~~~tte~t operation of the aeratos The removai of solid material was more van’able. Percentage re vab of total s&ids from the liquid were between 10 a 70%. The separator low performances may have been TeEa& ~CIIthe highly diluted slug produced on the farm. However; consistent resuEts ‘were obtained in terms of the dry matter content of the separated maternal. A mean value of 2l”3% was obtained, with a standard deviation of3.5 The operatuzg costs zrelated to treatment were esfinzated on the basis of enera cmwh tion. Treatment of slurry consumed jYo,rykover 1 for 195 h of aeration per day to about 90 r 12 h aeration per day. US$2.50 per pig protrea Aerobic &ny duced. Key wora’s: Siuq
irezirplellt, carbon
removal,
Total solids @g/1) ‘Tora1 suspended solids \mg/l) otal volatile solids (mg/il) peciEac oxygen uplake rate
(mg
Volatile solids (mgil) Volatile s~s~~~de~ solids (mgj’i’l)
Elandling and excrexa a:e major lerns in the co ousing of farm anim i30rtugal. In the Past 15-20 years intensive farming methods have been widely adopted and the problems were aggravated by the increase in m-ban devei~~me~t and also by wider concerns to control pollution and protect the ~~v~r~~me~t. af ~ig-~r~d~~ct~~~ facilities have been d
It has been
estimate
inter-
mitte~t aeration.
S
ai oxygen demand (mgi’i) chemical oxygen demand (mg/l) iochemical oxygen demand (mgil) Soluble 5day biochemical oxygen demand Cmg@ Dissolved auger (q/l) ixed liquor (ni ixed Iipor SW ded solids [mgil) v&at&z suspended solids ixed liquor (mg/l-/E)
“Author BOwiaorn cclrrespondence
should be addressed.
m-es, such as suitable slurry treatment, acceptable spreading practices and restricted agricutture production in water catchment areas w Iready exceeds the 50 g so. The full-scale t iments took piace is about 40 km to the north of Lisbon. The sandy soil that prevail allows a relatively fast icai ekments throng thus co~tam~~at~ng the groun c~~ce~trat~~~ in this area is g and BOO rng NC&/l. The organic pol!ution arising both from slurry appkatisn on the s&k and direct
discharge into water-courses is also a problem that needs to be addressed. Most water-courses in the catchment area are heavily polluted and have a seasonal frow variation, i.e. there is essentially no QWduring 2-3 months during summer. The aerobic treat process described here was aimed at improvem f slurry characteristics, both in terms of carbon utrient removal rates, optimisation of aeration and overall plant performance, so that environmental pollution could be effectively minimised.
Fig. 1. This experiment was designed to monitor an optimise the activated-sludge treatment process wit intermittent feeding and aeration of separat gery slurry, and produce an efflue irrigation purposes or for direct r-course. The experimental peri 1993 and 2 February 1994 was d stages: ay to 7 July 1993, commencing
period, aera-
8 July to 25 August 1993, aeration time 165 h per day;
26 August to 3 November 4993, aeration time 14.5 h per day; 4 November 1993 to 2 FebruaPry 1994, aeration time 12 h per day. The timing of on/off aeration periods is illustrated in Fig. 2. 1200 pigs horssecP?jn five in two reception pits by oors twice a day. Most of lurry was collected during en 8:30 and 12:00, when the makn high-pressure ~asb~~g of piggery Boors was carried out, Slurry was then tran y gravity through a bar screen to a 35 m3 nk fitted with Bowswitches operating a 2.2 kW subch coukl deliver between 20 and 35 m3/h of slurry to a rotary screen separator with 065 mm mesh. T by gravity into a solids were collec the separated Iiquid the activated sludge was controkd by a mechanical valve. xtension of s:urry loading to the aera of time to minimise both the changes in the requirement in the antiquated-sludgy reactor an loading of the clarifier. The mixed liquor ( tank was aerated with ed on a concrete bridge over the reactor and was
)
solid phase
was powered
a 7.5 k
electrical motor which, ear box, rotated a turbine at 72 rpm. Tke rking intertnittentlyy, was autoby a timer. Since most of the separated iiquid &my was discharged into t 'ng hours, the aerator was tion lank during she r 8 h during and after this set to work continua phase. To decrease the ut, the aeration hours were progressively experimenta! stages t3y
the
was rhen disc first of three hoMing effluent
f~or irrigation
of fruit trees d
activated-sledge reactor overconical clarifier. The settled iggery slurry, separated
quid and solid frac-
The c~~ceut~at~o~s of TS indicate a relatively iarge dilution of slurry (dilution factor of about 4) (caused by a different manage with values indicated by tration of organic mat een 49 and 60% of and the separated liquid fraction. This is comparable with the results obtained by Sutton ct al. (1985) for diluted slurries (VS varied between 48 and 54% of >, but was lower than the values of up to 80% of TS in raw piggery slurry observed by Svoboda (1993). These low S concentrations were apparently rekated to the diet, different fron I and the large vohune of water use and is reflected in Solids remove
Fig. %. Aeration
ment ts prevent stored solids.
cycles.
rom raw shmy were stackable high proportion of may suggest low t for further treatoffensive odour emissions from
-Parameter
Raw siurry
Volume TS TSS
13.4 27 Not measured 15.8 5.9 8‘7 57.5 8.5 Not measured Not measured Not measured Not measured Not measured Not measured
vs
vss
PJH
Temperature Conductivity MkalinitJr C content
Separated liquid 13
21.5 17.5 lQ.5
Units
Separated solids
Units
m31day kg/m3 kg/m” kg/m3
0.4 211 Not measured
m3/day kg/m3 -
188
kg/m3
G
Not measured Not measured Not measured
-
RlSiCITl
Not
measui-ed
-
kg CaCC&im” kgim’ kgim3 kg/m3 kg/m3 kgim”
Not 305 Not Not Not Not
measured
-
measwed measured measured measured
g/kg .-
kgim3
;6 17.5 11.6 6.4 18.7 ;:: 2.8
prevented aeration for more than 36 h in the followays, as shown in Fig. 3. T 0 level decreased after energy was cut off. It tam the nsr_mal levels of aerator was put back into operation.
solid fraction, mixed liq treated
effluent
from
were analysed for various in Table 2. In addition: t edox potential and temperature during two each lasting a week. Chemical and biochemical analyses were performed according to the Standard J%YIhe ~~~~i~~tio~ of Hater and Wastewate si et al., 1989). COD was determined by molecular absorpspectrophotometry after 2 h digestion using a ange micromethod. e supernatant for the is of the soluble part of both BQD5 and centrifugation of samples at min (Evans et al., 1983).
ant characteristics
aeration
ox potential
level r between G and 1 to be related to high nitrate content of 1
restart of the aerator. es of Wedox potential were reiatively g/l. These variations are veIs 2re within a more pronounced when lower range (near 0 mg/l) As shown in Fig. 4, it higher loading periods t concentrations
are
the mean values of the data from al1 four mental periods. SS was controlled at concentration of the value of the whole 17 kg TSS/m3 (me ~~pertment) and varied between 85 and 32 kg/ be mean value sf weekly spot measurem concentration was 25 mgil during tbe experimental period. A minimum value of 0 was observed during periods when the aerator was switched off and a maximum of 6 mg/l was reac during aeration periods. This was confirmed by oneday continuous monitoring, when energy failure
Table 2. ~rogra~~~
of
tank at a
averaged
a mean value of 84 with a e ML temperature 214°C in summer.
eatment temperature was 47*1”Cfor the
g and
analyses
ofsa
Icesfor various ~~~~~~~~~~S -----
Parameter
PI-I Temperature Conductivity Alkalinity BOD,B8Qi,s COD GODS DO SOUR TS TSS vss TVS
Raw slurry
+ f %
After separation
+ % % c % t % +
Aeration tank
Sludge recirculation line
Effhent fr0.m clarifier h T 3 i % -%+ .A
% % +
f + t+ +
% + +
f +
Separated soiids
i % +
+ f
whole rn~~~to~i~g permd. value measured in ehe
The
mean
conductivity
The
percentage
rnj+/l but e biomass
removal
increased
of
Y30D5 increased
the last stage
of the
also to the effect of the
and
t, although
relatively
large into a water-course.
ffluent for irrigation. It would not satisfy the Portuuese ~e~~s~ati~~~which sets the limiting level to 3
15 mg/l, and so weI! below the actual limit, it ears that further treatment will be needed as tions and discharge consents.
during the whole experimental Pig. 6.
period
‘j and CO are shown in
Units
Parzmeter
Organic load (F/&Q Biomass yield (?f) Hydraulic retention
0.024 0.43 17.5
kg BOD,/kg X&day kg VSSJkg BQI&
kg/m3
Sludge production Sludge recircuulation
12.4 0.73 34 1.27
rate Waste-sludge
246
kg TSS/m”
tinx JMLVSS ~~~~~1~~~~
cancentra%ion Mean ceil residence time
?-i”uur!yvariations
days
was more
observed values seem to be in agreemenr- with values given in the literature for gery-waste treatment pla Koziarski, 1981), In order to knsw the bio the residual amount of organi it was necessary ts asse the total and soluble 330 rnatant in the
kg VS§/da;u -
of aeration time (Table 4)~ Tke soluble percentage removal did not va,ry ~~~~~~~a~~~~~~but indicated an almost complete removal of al! biodegradable material. The treatment s 55% of the solilble decrease
90
days
of DO, redox potential, temperature
and pH in the ?& for a week beginn:ng
2, .Februan;
8%.
. 4, Hourly variations of DO, redox potential, temperature and p
L for a week beginning 17 W~arch1894.
ig. 5. Variations of pH, temperature and coraductivity of the ML for the whole ~~e~~~e~~a~ period. verified that over 90% of the soluble CO to biological ~ctabo~~s~. It is tely susceptible generally found that such processes as extendedaeration systems, as in this study, and longer hydraulic retention times better effluent, with respect to solu
to zero.
on
~~od~~t~o~ of soluble ~~c~~b~a~ qroducts P) formed both drrring the grow
the
authors,
it is ve
all of the reported e axes whose amoun removed remained i odegradable fractio though no attempt was made to identify ihe conThe substances
invo
59
aeration - 16.5 h
Fig. 6.
aeration
aeration
T4.5 h
- !2 h
Percentage removal of both COD and BO&.
aeration
16.5h
-.------, aeraa(ion- 14.5 h
Fig. ‘9. COD and BOD5 of the treated effluent.
Stage
BOD5.S
(mgil) Ci> (ii> (iii)
990
(iv>
33
::
Residual fraction
Soluble % removal
COD (r@ld
CODS @sit)
Residua?
0.72 0.11 0.14 0.21
67 99 97 9%
13 &Xl 2160 810 1010
GO 545 560
0.77 0~68 057 -
it seems reasonable to assume to the recalcitrant matter 0s~ material, in~o~p~r~t~d celluse and bile dye) which is ult to remove with h&her treatment. Bortone a laboratory-scale sequencing
fraction
Soluble % removal 76
batch reactor >, observed values of the order of 300 mgil. Ge et al. (1993) conchded, from a series of experiments on an S treating pig slurs-y under nitsl~‘acation/denitrifiGatian ~~~~~t~~~§~that it was not possible to re e soleable e8D values furthcr than 250 mg/L MII higher Ie~eyels,of the order
of
1500 mg/l, were documented by Evans el ai (1983) for aerobic treatment of concentrate slurry in chemostat reactors. The ratio B0D5/G0D for separated untreated slurry varied between 0.3 and 0.35 and appears relacompared with values obtaine 55 by Oleszkiewicz, 1985, and O*4 by Overcash & Humenik, 1946). Solidsrunoval
The experimental ata concerning mechanical seParation efficiency f raw slurry varied widely. the Eiqerid Percentage removals of total solids were between 10 and 70%. Pain et al (1978) also observed considerable variations among the Performances of different types of mechanical s and concluded that their efficiency is i related to the level of dir&on of raw s er throughputs and more dilute lted in low performances. espite the variability of separator performance in terms of the Percentage of soli s removed from the liquid, consistent results were obtained in terms of the dry matter content of the separated material. A mean value of 21~3% was obtained, with a standard deviation of 35. The separated materia had; in general, a high level of volatile solids, over 85% of TS and a C/N ratio of 18. This maternal should be submitted for further treatment (e.g. composting with straw) before applying to the land. rated liquid fraction The TSS content of the 8. is plotted against total C re solids removal resulted in s reduction of bioc emical oxygen demand was less than could be implied as the coarse, separated, suspended solids should contain a high ~~oport~o~ of relatively indigestible material (Burton According to Baines et al. (1973), the liqui
of slurry separated through a 200 ,U mesh can con.to 90% of Ihe total D of the raw slurry. A s~g~i~cant removal of susgended solids had to be achieved, in order to comply with the disch consent prior to discharge into a water-course. actual max~m~rn allowa le load is 6 g TS/animaL oriugaI, is e¶~iva~e~t to about 500 TSS removal obtained t~~ro~~~o~t the experimental perio was over 90%. The TSS of the final effluent was maintained between 6 420 mg/l during the last two stages. The re rates obtained for each stage of the exxperiment are ted in Table 5~ Pr percentage of TSS related to the TS content the clarifier was very Iew (un 10%). The major Part of th id material contained in the final effluent mi to the dissolved and slowly which was difficult to remov was made to verify this suggestion.
eration times of al the equipment were monitored on a regular basis to umption. The mean energy mate the energy c in e~n~~rne~t and its assocsumptions for the iated monthly cost are presented in Table 6. It was estimated that about 115 k in the treatment pliant. A sumption of 155 kWh/day was of the experiments (195 h si’ aer a minimum of 90 kWhlday was when the aerator was set to work for onYPjr day. es required to carry out regular 8 mai~te~ar~ce tasks were also not weekly operation co sludge and visual the
TSS % removal
Aeration @I
Stage _I___---
85 87 99 98
19~5 16.5 14.5 12
0> (ii)
(iii) (iv)
tar). These tasks too min each week. Th the local sta costs of repair and repfacemeut of essential mechanscreen, aerator gear :cal equipment, su erentiate from those
meChanical
entire farm
ed and part of the stored in the pxrd system
~~~i~~~t~~a~ fields.
Spreading
di
nificant cost to the farmer, smail part of the residu were welcome to reuse and hquid effluent wit
mt
inwAve
any
sig-
since he 0
s
are
penditures during the experiments the farmer. The monthly means of alntenance (0 & M) costs for the arised in Table 7. su
duration of the e~~~rirn~~ts. The pigs were sent to a s~augbterb~us~ where they reached 100 kg in wei Each pig cost about US$160.00 to produce, but farmer could get only about US$P40. carcass, meaning a Ioss of US$20.00 V xi d~ctiQ~ cost was mainly due t resented about 65% of the total 0 ok & e cost related to slurry treatment was not significant when compared to the whole 0 ost s~g~~~ca~t would be the ene in Tabie 6, which was only 1.5% of the total
days aerobic treatment; per pig produced. relatively low treatment cost achieve s to be related to the ~~t~~rn~t~e~t a a!? strategy employed. In fact the energy cos rime than 3 aeration per per day) of t
Pig slurry frsm a commercial pggeiy can be processed by a relatively small, sern~-a~~~ma~~c plant, t a level of organic ~oll~t~~~ c~~~ce~~t~at~o~whit satisfies the standing Portuguese for the a water-body. Levels o’ 5 in the nt were maintained be 68 and his is s~bstant~a~~y lower than the ugh the TSS were between 50 an
any
‘FabEe6. z=P-eat
lower
concentration
_
Equipment
Mean energy consumption
monthlji cost
Associated
4.42 2.65 107.7 114.8
15 9 370 394
---
TotaI
Ttem -~ Feed Water sonnel c?icines Disinfectants Equipment Energy
Other Total
---__
onthly mean cost (US$) (Ref: 1994) 16 600 430 2200 60 350 3250 1145 1500 25 545
Similar treatment systems will surely contribute a general environmental imp national and EU promotion and would, therefcre, actively encsurage farmers t this technology.
63!92.
was partially fiuanced by the Iunder Contract No. S’1XEIA s The financial. support given by
to
to
the
.J. R. Wicudo, I. E Svobod~
62
JNICT/British appreciated.
Council
Protocol
S., Evans, M. (1973). Principles of t
was also greatly
Bakes,
t of animal
Agricultural Engineer, 2 Bicudo, J. R. & Madur
piggery wastes in Portugai
-
slurries.
F. (1991). Treatment a general overview.
of In
‘Xater Pollution: Modelling Measuring and Predictim (ed. &r C. A. Brebbia). Cornp~tat~o~a~ L. C. Wrobel
Mechanics, Southampton, and Elsevier Applied Scienc.e, London, pp. 579-93. ortone, G., Gemelli, S., Rambaidi, A. & Tilche A. (1992). Nitrification, denitrification and biological p&ate removal in SBR. treating piggery waste TkKater Sci. Teclznol., 26, 977-85. Burton, C. H. (1992). A review of strategies in the aerobic treatment of pig slurry: purpose, theory and method. .I Agric. Engng Rex, 53, 249-72. Charpentier, J. et al. (1987). Oxidation-reduction potential (ORP) regulation: a way to optimize pollution removal and energy savings in low load activated sludge process. Water Sci. Tixhnol., 19, 645-55. Clesceri, L. S., Greenberg, A. E. & Trussed, Stmdmd Methods fur the Ex WA, WPCF, WaShWastewater, 17th ede. APHA, ington, DC. EC Directive 91/676/EEC related to the protection of water against pollution caused by nitrates from agricultural sources. P. w., Evans, M. R., Deans; E. A., Hissett, R., Smith, Svoboda, I. F. & Thacker, F. E. (1983). The effect of
temperature and residence time oa aerobic rreatment of piggery slurry degradation of carbonaceous corn-pounds. Algnc. Wastes, s”?25-35. Gaudy, A. F. & Blachly, T. R. (1985). A study of the b~ode~radabi~~~ of residual COD. “9; MZEEI.,%I&” &uitrol Fed.) 54, 332-a. Germirli, F.: Bortone, G.: Orhon, D. & T&he, A. (1993). Fate of residuals in mitrification-denitr~~~at~o~ treatment of piggery wastewaters. Bores. Z%nd., 45, 205-11. Bleszkiewicz, J. A. (19&S). Cost-effective treatment of piggery wastewater. Agrk. Wastes, 12, 185-206. Oleszkiewicz, J. A. Br Koziarski. , S. 41981). Manaeement \ and treatment of wastes from large iiggeriesr &ic. Wastes, 3, 123-44. dr Humenik,
F. 9. (1976). State-of-the-
art: swine waste production and pretreatment processes. ect No. EPA 60012-76-290, Oklahoma, F., Hepherd, H. Q. 81 Pittman, R. J. (3978). s affecting the performance of four siurry separating machines. J. Agric. Engng Rex c 23, 231-42. Pitter, P. & Chudoba, J. (1990). ~~~~~g~~(~~~~l~~ of Organic SuDslances in lhe Aquatic
Envimnmerzi.
CZ
Press, Florida, USA. Portaria 810/90 de 10 de Setembro related to the disurry into wzter co’3rses. D. M., Jones, D. D,, Keil&D. T. & ). Use of nitrification inhibitors and nt with swine manure appiications. in Agricultural Wuste ~ti~izut~~~ and Mmagenzent. XGAE, 240-8.
Svoboda, I. F. (3993). Piggery slurry aerobic treatment with heat recovery. Thesis submitted for the actor of Phiiosophy in the University of degree of Glasgow.
1995; revised version received 5 July 1995; accepted 25 July 4995)
A farnz-scale trea~~~~~tplant was studied during a year: Four d~~~re~t aeration cycles were tested in order to ,?bserve their efiects on the removal of carbon material atment plant per$ormance was a 60% reduction of aerah per day to 12 h per day. vaE mtes observed (over 95010ivr,teelms of ared to be related to the low aeration rates ugh isklei~te~~~tte~t operation of the aeratos The removai of solid material was more van’able. Percentage re vab of total s&ids from the liquid were between 10 a 70%. The separator low performances may have been TeEa& ~CIIthe highly diluted slug produced on the farm. However; consistent resuEts ‘were obtained in terms of the dry matter content of the separated maternal. A mean value of 2l”3% was obtained, with a standard deviation of3.5 The operatuzg costs zrelated to treatment were esfinzated on the basis of enera cmwh tion. Treatment of slurry consumed jYo,rykover 1 for 195 h of aeration per day to about 90 r 12 h aeration per day. US$2.50 per pig protrea Aerobic &ny duced. Key wora’s: Siuq
irezirplellt, carbon
removal,
Total solids @g/1) ‘Tora1 suspended solids \mg/l) otal volatile solids (mg/il) peciEac oxygen uplake rate
(mg
Volatile solids (mgil) Volatile s~s~~~de~ solids (mgj’i’l)
Elandling and excrexa a:e major lerns in the co ousing of farm anim i30rtugal. In the Past 15-20 years intensive farming methods have been widely adopted and the problems were aggravated by the increase in m-ban devei~~me~t and also by wider concerns to control pollution and protect the ~~v~r~~me~t. af ~ig-~r~d~~ct~~~ facilities have been d
It has been
estimate
inter-
mitte~t aeration.
S
ai oxygen demand (mgi’i) chemical oxygen demand (mg/l) iochemical oxygen demand (mgil) Soluble 5day biochemical oxygen demand Cmg@ Dissolved auger (q/l) ixed liquor (ni ixed Iipor SW ded solids [mgil) v&at&z suspended solids ixed liquor (mg/l-/E)
“Author BOwiaorn cclrrespondence
should be addressed.
m-es, such as suitable slurry treatment, acceptable spreading practices and restricted agricutture production in water catchment areas w Iready exceeds the 50 g so. The full-scale t iments took piace is about 40 km to the north of Lisbon. The sandy soil that prevail allows a relatively fast icai ekments throng thus co~tam~~at~ng the groun c~~ce~trat~~~ in this area is g and BOO rng NC&/l. The organic pol!ution arising both from slurry appkatisn on the s&k and direct
discharge into water-courses is also a problem that needs to be addressed. Most water-courses in the catchment area are heavily polluted and have a seasonal frow variation, i.e. there is essentially no QWduring 2-3 months during summer. The aerobic treat process described here was aimed at improvem f slurry characteristics, both in terms of carbon utrient removal rates, optimisation of aeration and overall plant performance, so that environmental pollution could be effectively minimised.
Fig. 1. This experiment was designed to monitor an optimise the activated-sludge treatment process wit intermittent feeding and aeration of separat gery slurry, and produce an efflue irrigation purposes or for direct r-course. The experimental peri 1993 and 2 February 1994 was d stages: ay to 7 July 1993, commencing
period, aera-
8 July to 25 August 1993, aeration time 165 h per day;
26 August to 3 November 4993, aeration time 14.5 h per day; 4 November 1993 to 2 FebruaPry 1994, aeration time 12 h per day. The timing of on/off aeration periods is illustrated in Fig. 2. 1200 pigs horssecP?jn five in two reception pits by oors twice a day. Most of lurry was collected during en 8:30 and 12:00, when the makn high-pressure ~asb~~g of piggery Boors was carried out, Slurry was then tran y gravity through a bar screen to a 35 m3 nk fitted with Bowswitches operating a 2.2 kW subch coukl deliver between 20 and 35 m3/h of slurry to a rotary screen separator with 065 mm mesh. T by gravity into a solids were collec the separated Iiquid the activated sludge was controkd by a mechanical valve. xtension of s:urry loading to the aera of time to minimise both the changes in the requirement in the antiquated-sludgy reactor an loading of the clarifier. The mixed liquor ( tank was aerated with ed on a concrete bridge over the reactor and was
)
solid phase
was powered
a 7.5 k
electrical motor which, ear box, rotated a turbine at 72 rpm. Tke rking intertnittentlyy, was autoby a timer. Since most of the separated iiquid &my was discharged into t 'ng hours, the aerator was tion lank during she r 8 h during and after this set to work continua phase. To decrease the ut, the aeration hours were progressively experimenta! stages t3y
the
was rhen disc first of three hoMing effluent
f~or irrigation
of fruit trees d
activated-sledge reactor overconical clarifier. The settled iggery slurry, separated
quid and solid frac-
The c~~ceut~at~o~s of TS indicate a relatively iarge dilution of slurry (dilution factor of about 4) (caused by a different manage with values indicated by tration of organic mat een 49 and 60% of and the separated liquid fraction. This is comparable with the results obtained by Sutton ct al. (1985) for diluted slurries (VS varied between 48 and 54% of >, but was lower than the values of up to 80% of TS in raw piggery slurry observed by Svoboda (1993). These low S concentrations were apparently rekated to the diet, different fron I and the large vohune of water use and is reflected in Solids remove
Fig. %. Aeration
ment ts prevent stored solids.
cycles.
rom raw shmy were stackable high proportion of may suggest low t for further treatoffensive odour emissions from
-Parameter
Raw siurry
Volume TS TSS
13.4 27 Not measured 15.8 5.9 8‘7 57.5 8.5 Not measured Not measured Not measured Not measured Not measured Not measured
vs
vss
PJH
Temperature Conductivity MkalinitJr C content
Separated liquid 13
21.5 17.5 lQ.5
Units
Separated solids
Units
m31day kg/m3 kg/m” kg/m3
0.4 211 Not measured
m3/day kg/m3 -
188
kg/m3
G
Not measured Not measured Not measured
-
RlSiCITl
Not
measui-ed
-
kg CaCC&im” kgim’ kgim3 kg/m3 kg/m3 kgim”
Not 305 Not Not Not Not
measured
-
measwed measured measured measured
g/kg .-
kgim3
;6 17.5 11.6 6.4 18.7 ;:: 2.8
prevented aeration for more than 36 h in the followays, as shown in Fig. 3. T 0 level decreased after energy was cut off. It tam the nsr_mal levels of aerator was put back into operation.
solid fraction, mixed liq treated
effluent
from
were analysed for various in Table 2. In addition: t edox potential and temperature during two each lasting a week. Chemical and biochemical analyses were performed according to the Standard J%YIhe ~~~~i~~tio~ of Hater and Wastewate si et al., 1989). COD was determined by molecular absorpspectrophotometry after 2 h digestion using a ange micromethod. e supernatant for the is of the soluble part of both BQD5 and centrifugation of samples at min (Evans et al., 1983).
ant characteristics
aeration
ox potential
level r between G and 1 to be related to high nitrate content of 1
restart of the aerator. es of Wedox potential were reiatively g/l. These variations are veIs 2re within a more pronounced when lower range (near 0 mg/l) As shown in Fig. 4, it higher loading periods t concentrations
are
the mean values of the data from al1 four mental periods. SS was controlled at concentration of the value of the whole 17 kg TSS/m3 (me ~~pertment) and varied between 85 and 32 kg/ be mean value sf weekly spot measurem concentration was 25 mgil during tbe experimental period. A minimum value of 0 was observed during periods when the aerator was switched off and a maximum of 6 mg/l was reac during aeration periods. This was confirmed by oneday continuous monitoring, when energy failure
Table 2. ~rogra~~~
of
tank at a
averaged
a mean value of 84 with a e ML temperature 214°C in summer.
eatment temperature was 47*1”Cfor the
g and
analyses
ofsa
Icesfor various ~~~~~~~~~~S -----
Parameter
PI-I Temperature Conductivity Alkalinity BOD,B8Qi,s COD GODS DO SOUR TS TSS vss TVS
Raw slurry
+ f %
After separation
+ % % c % t % +
Aeration tank
Sludge recirculation line
Effhent fr0.m clarifier h T 3 i % -%+ .A
% % +
f + t+ +
% + +
f +
Separated soiids
i % +
+ f
whole rn~~~to~i~g permd. value measured in ehe
The
mean
conductivity
The
percentage
rnj+/l but e biomass
removal
increased
of
Y30D5 increased
the last stage
of the
also to the effect of the
and
t, although
relatively
large into a water-course.
ffluent for irrigation. It would not satisfy the Portuuese ~e~~s~ati~~~which sets the limiting level to 3
15 mg/l, and so weI! below the actual limit, it ears that further treatment will be needed as tions and discharge consents.
during the whole experimental Pig. 6.
period
‘j and CO are shown in
Units
Parzmeter
Organic load (F/&Q Biomass yield (?f) Hydraulic retention
0.024 0.43 17.5
kg BOD,/kg X&day kg VSSJkg BQI&
kg/m3
Sludge production Sludge recircuulation
12.4 0.73 34 1.27
rate Waste-sludge
246
kg TSS/m”
tinx JMLVSS ~~~~~1~~~~
cancentra%ion Mean ceil residence time
?-i”uur!yvariations
days
was more
observed values seem to be in agreemenr- with values given in the literature for gery-waste treatment pla Koziarski, 1981), In order to knsw the bio the residual amount of organi it was necessary ts asse the total and soluble 330 rnatant in the
kg VS§/da;u -
of aeration time (Table 4)~ Tke soluble percentage removal did not va,ry ~~~~~~~a~~~~~~but indicated an almost complete removal of al! biodegradable material. The treatment s 55% of the solilble decrease
90
days
of DO, redox potential, temperature
and pH in the ?& for a week beginn:ng
2, .Februan;
8%.
. 4, Hourly variations of DO, redox potential, temperature and p
L for a week beginning 17 W~arch1894.
ig. 5. Variations of pH, temperature and coraductivity of the ML for the whole ~~e~~~e~~a~ period. verified that over 90% of the soluble CO to biological ~ctabo~~s~. It is tely susceptible generally found that such processes as extendedaeration systems, as in this study, and longer hydraulic retention times better effluent, with respect to solu
to zero.
on
~~od~~t~o~ of soluble ~~c~~b~a~ qroducts P) formed both drrring the grow
the
authors,
it is ve
all of the reported e axes whose amoun removed remained i odegradable fractio though no attempt was made to identify ihe conThe substances
invo
59
aeration - 16.5 h
Fig. 6.
aeration
aeration
T4.5 h
- !2 h
Percentage removal of both COD and BO&.
aeration
16.5h
-.------, aeraa(ion- 14.5 h
Fig. ‘9. COD and BOD5 of the treated effluent.
Stage
BOD5.S
(mgil) Ci> (ii> (iii)
990
(iv>
33
::
Residual fraction
Soluble % removal
COD (r@ld
CODS @sit)
Residua?
0.72 0.11 0.14 0.21
67 99 97 9%
13 &Xl 2160 810 1010
GO 545 560
0.77 0~68 057 -
it seems reasonable to assume to the recalcitrant matter 0s~ material, in~o~p~r~t~d celluse and bile dye) which is ult to remove with h&her treatment. Bortone a laboratory-scale sequencing
fraction
Soluble % removal 76
batch reactor >, observed values of the order of 300 mgil. Ge et al. (1993) conchded, from a series of experiments on an S treating pig slurs-y under nitsl~‘acation/denitrifiGatian ~~~~~t~~~§~that it was not possible to re e soleable e8D values furthcr than 250 mg/L MII higher Ie~eyels,of the order
of
1500 mg/l, were documented by Evans el ai (1983) for aerobic treatment of concentrate slurry in chemostat reactors. The ratio B0D5/G0D for separated untreated slurry varied between 0.3 and 0.35 and appears relacompared with values obtaine 55 by Oleszkiewicz, 1985, and O*4 by Overcash & Humenik, 1946). Solidsrunoval
The experimental ata concerning mechanical seParation efficiency f raw slurry varied widely. the Eiqerid Percentage removals of total solids were between 10 and 70%. Pain et al (1978) also observed considerable variations among the Performances of different types of mechanical s and concluded that their efficiency is i related to the level of dir&on of raw s er throughputs and more dilute lted in low performances. espite the variability of separator performance in terms of the Percentage of soli s removed from the liquid, consistent results were obtained in terms of the dry matter content of the separated material. A mean value of 21~3% was obtained, with a standard deviation of 35. The separated materia had; in general, a high level of volatile solids, over 85% of TS and a C/N ratio of 18. This maternal should be submitted for further treatment (e.g. composting with straw) before applying to the land. rated liquid fraction The TSS content of the 8. is plotted against total C re solids removal resulted in s reduction of bioc emical oxygen demand was less than could be implied as the coarse, separated, suspended solids should contain a high ~~oport~o~ of relatively indigestible material (Burton According to Baines et al. (1973), the liqui
of slurry separated through a 200 ,U mesh can con.to 90% of Ihe total D of the raw slurry. A s~g~i~cant removal of susgended solids had to be achieved, in order to comply with the disch consent prior to discharge into a water-course. actual max~m~rn allowa le load is 6 g TS/animaL oriugaI, is e¶~iva~e~t to about 500 TSS removal obtained t~~ro~~~o~t the experimental perio was over 90%. The TSS of the final effluent was maintained between 6 420 mg/l during the last two stages. The re rates obtained for each stage of the exxperiment are ted in Table 5~ Pr percentage of TSS related to the TS content the clarifier was very Iew (un 10%). The major Part of th id material contained in the final effluent mi to the dissolved and slowly which was difficult to remov was made to verify this suggestion.
eration times of al the equipment were monitored on a regular basis to umption. The mean energy mate the energy c in e~n~~rne~t and its assocsumptions for the iated monthly cost are presented in Table 6. It was estimated that about 115 k in the treatment pliant. A sumption of 155 kWh/day was of the experiments (195 h si’ aer a minimum of 90 kWhlday was when the aerator was set to work for onYPjr day. es required to carry out regular 8 mai~te~ar~ce tasks were also not weekly operation co sludge and visual the
TSS % removal
Aeration @I
Stage _I___---
85 87 99 98
19~5 16.5 14.5 12
0> (ii)
(iii) (iv)
tar). These tasks too min each week. Th the local sta costs of repair and repfacemeut of essential mechanscreen, aerator gear :cal equipment, su erentiate from those
meChanical
entire farm
ed and part of the stored in the pxrd system
~~~i~~~t~~a~ fields.
Spreading
di
nificant cost to the farmer, smail part of the residu were welcome to reuse and hquid effluent wit
mt
inwAve
any
sig-
since he 0
s
are
penditures during the experiments the farmer. The monthly means of alntenance (0 & M) costs for the arised in Table 7. su
duration of the e~~~rirn~~ts. The pigs were sent to a s~augbterb~us~ where they reached 100 kg in wei Each pig cost about US$160.00 to produce, but farmer could get only about US$P40. carcass, meaning a Ioss of US$20.00 V xi d~ctiQ~ cost was mainly due t resented about 65% of the total 0 ok & e cost related to slurry treatment was not significant when compared to the whole 0 ost s~g~~~ca~t would be the ene in Tabie 6, which was only 1.5% of the total
days aerobic treatment; per pig produced. relatively low treatment cost achieve s to be related to the ~~t~~rn~t~e~t a a!? strategy employed. In fact the energy cos rime than 3 aeration per per day) of t
Pig slurry frsm a commercial pggeiy can be processed by a relatively small, sern~-a~~~ma~~c plant, t a level of organic ~oll~t~~~ c~~~ce~~t~at~o~whit satisfies the standing Portuguese for the a water-body. Levels o’ 5 in the nt were maintained be 68 and his is s~bstant~a~~y lower than the ugh the TSS were between 50 an
any
‘FabEe6. z=P-eat
lower
concentration
_
Equipment
Mean energy consumption
monthlji cost
Associated
4.42 2.65 107.7 114.8
15 9 370 394
---
TotaI
Ttem -~ Feed Water sonnel c?icines Disinfectants Equipment Energy
Other Total
---__
onthly mean cost (US$) (Ref: 1994) 16 600 430 2200 60 350 3250 1145 1500 25 545
Similar treatment systems will surely contribute a general environmental imp national and EU promotion and would, therefcre, actively encsurage farmers t this technology.
63!92.
was partially fiuanced by the Iunder Contract No. S’1XEIA s The financial. support given by
to
to
the
.J. R. Wicudo, I. E Svobod~
62
JNICT/British appreciated.
Council
Protocol
S., Evans, M. (1973). Principles of t
was also greatly
Bakes,
t of animal
Agricultural Engineer, 2 Bicudo, J. R. & Madur
piggery wastes in Portugai
-
slurries.
F. (1991). Treatment a general overview.
of In
‘Xater Pollution: Modelling Measuring and Predictim (ed. &r C. A. Brebbia). Cornp~tat~o~a~ L. C. Wrobel
Mechanics, Southampton, and Elsevier Applied Scienc.e, London, pp. 579-93. ortone, G., Gemelli, S., Rambaidi, A. & Tilche A. (1992). Nitrification, denitrification and biological p&ate removal in SBR. treating piggery waste TkKater Sci. Teclznol., 26, 977-85. Burton, C. H. (1992). A review of strategies in the aerobic treatment of pig slurry: purpose, theory and method. .I Agric. Engng Rex, 53, 249-72. Charpentier, J. et al. (1987). Oxidation-reduction potential (ORP) regulation: a way to optimize pollution removal and energy savings in low load activated sludge process. Water Sci. Tixhnol., 19, 645-55. Clesceri, L. S., Greenberg, A. E. & Trussed, Stmdmd Methods fur the Ex WA, WPCF, WaShWastewater, 17th ede. APHA, ington, DC. EC Directive 91/676/EEC related to the protection of water against pollution caused by nitrates from agricultural sources. P. w., Evans, M. R., Deans; E. A., Hissett, R., Smith, Svoboda, I. F. & Thacker, F. E. (1983). The effect of
temperature and residence time oa aerobic rreatment of piggery slurry degradation of carbonaceous corn-pounds. Algnc. Wastes, s”?25-35. Gaudy, A. F. & Blachly, T. R. (1985). A study of the b~ode~radabi~~~ of residual COD. “9; MZEEI.,%I&” &uitrol Fed.) 54, 332-a. Germirli, F.: Bortone, G.: Orhon, D. & T&he, A. (1993). Fate of residuals in mitrification-denitr~~~at~o~ treatment of piggery wastewaters. Bores. Z%nd., 45, 205-11. Bleszkiewicz, J. A. (19&S). Cost-effective treatment of piggery wastewater. Agrk. Wastes, 12, 185-206. Oleszkiewicz, J. A. Br Koziarski. , S. 41981). Manaeement \ and treatment of wastes from large iiggeriesr &ic. Wastes, 3, 123-44. dr Humenik,
F. 9. (1976). State-of-the-
art: swine waste production and pretreatment processes. ect No. EPA 60012-76-290, Oklahoma, F., Hepherd, H. Q. 81 Pittman, R. J. (3978). s affecting the performance of four siurry separating machines. J. Agric. Engng Rex c 23, 231-42. Pitter, P. & Chudoba, J. (1990). ~~~~~g~~(~~~~l~~ of Organic SuDslances in lhe Aquatic
Envimnmerzi.
CZ
Press, Florida, USA. Portaria 810/90 de 10 de Setembro related to the disurry into wzter co’3rses. D. M., Jones, D. D,, Keil&D. T. & ). Use of nitrification inhibitors and nt with swine manure appiications. in Agricultural Wuste ~ti~izut~~~ and Mmagenzent. XGAE, 240-8.
Svoboda, I. F. (3993). Piggery slurry aerobic treatment with heat recovery. Thesis submitted for the actor of Phiiosophy in the University of degree of Glasgow.