Provided for non-commercial research and educational use only. Not for reproduction or distribution or commercial use.
This article was originally published by IWA Publishing. IWA Publishing recognizes the retention of the right by the author(s) to photocopy or make single electronic
copies of the paper for their own personal use, including for their own classroom use, or the personal use of colleagues, provided the copies are not offered for sale and
are not distributed in a systematic way outside of their employing institution.
Please note that you are not permitted to post the IWA Publishing PDF version of your paper on your own website or your institution’s website or repository.
Please direct any queries regarding use or permissions to [email protected]
Integrated anaerobic treatment of dairy industrial
wastewater and sludge
Mauricio Passeggi, Ivan Lopez and Liliana Borzacconi
ABSTRACT
Mauricio Passeggi
Ivan Lopez
Liliana Borzacconi
Engineering Faculty,
University of the Republic,
J. Herrera y Reissig 565,
Montevideo,
Uruguay
E-mail: [email protected]
Performance parameters were studied in an alternative full-scale dairy effluent treatment system
comprising two anaerobic sludge-blanket reactors in parallel arrangement with upward flow,
internal fat-separation by flotation, external lamella settler and floated material digester. Reactors
were initially inoculated with flocculent sludge and granulated in a high-load stage. Using loading
rates up to a maximum 5.5 kgCOD/m3.d–hydraulic residence time of 17 hours- reactor efficiency
was found to remain stable around 90% of COD. Average sludge digester efficiency using a
loading rate of 3.5 kgVS/m3.d with a lipid content of 47% of COD amounted to 78% of VS (87% of
lipid removal). LCFA inhibition as assayed using palmitate was found to depend not only on the
palmitate concentration but also on the palmitate-to-biomass concentration ratio.
Key words | dairy wastewater, fat digester, full-scale, LCFA inhibition
INTRODUCTION
Depending on the type of product, equipment and unit
processes entailed in processing of dairy-based products,
effluent characteristics may vary widely according to indus-
trial plant. Thus, every individual situation must be con-
sidered separately with a view to ensuring appropriate
treatment design (Demirel et al. 2005). Nonetheless, on
account of process leakage of milk or milk-based products,
a number of constituents are systematically found in dairy
industrial wastewater: lactose, lipids, casein and other
proteins. Lipids, composed of triglycerides, are found mainly
in emulsions resulting from initial process stage of homo-
genization. In addition, effluents will be acidic or basic
according to chemical cleaning as used at any time of process.
The use of UASB reactors in dairy wastewater treatment
-as well as in the treatment of other complex effluents- has
found limited success in view of the fact that a considerable
amount of organic material hydrolyzes or degrades at an
excessively low rate, while normally building up within the
sludge blanket by entrainment or adsorption. The result is
the dilution of biomass, the affectation of mass transfer
properties and the impairment of sludge settling capacity.
Sludge activity is therefore reduced and sludge washed out
from the reactor in the outlet stream could occur (Sayed
1984; Sayed 1987; Rinzema 1993; Hwu et al. 1998).
Rapid adsorption and significantly slow degradation of
dairy fat emulsions were reported for batch studies using
biomass that was not adapted to degrading fats and a
substrate load as high as 12.6 grams of fat per gram of VSS
(Petruy & Lettinga 1997). Vidal et al. (2000) reported that
fat-rich dairy wastewater biodegradability rate is limited by
fats hydrolysis. They performed batch assays with non-
adapted biomass. However, using moderate loads and
substrate-adapted microorganisms, hydrolysis may not be
the rate limiting stage of total treatment process. Not limited
by hydrolysis, total process rate may be limited by a reduced
mass transfer rate due to LCFA adsorption onto sludge
(Pereira et al. 2003; Pereira et al. 2004), or by the inhibitory
effect of LCFA on acetotrophic methanogenic populations
(Perle et al. 1995; Hwu et al. 1996). According to research
reported by Hwu et al. (1998), sludge flotation in UASB
reactors due to LCFA adsorption may occur at lower LCFA
concentration than those that produce inhibitory effect.
doi: 10.2166/wst.2009.010
501 Q IWA Publishing 2009 Water Science & Technology—WST | 59.3 | 2009
With a view to studying the influence of the stage of
adsorption preceding lipid -and LCFA- degradation on the
performance of UASB reactors, several studies were made
using an intermittent effluent feed, leading to encouraging
results (Sayed 1984; Nadais et al. 2006). Cavaleiro et al.
(2008) reported that use of pulse-feeds results in increased
tolerance of acetotrophic methanogens to LCFA, and
suggest that satisfactory results for continuous operation
may be obtained following a stage of biomass acclimati-
zation by means of pulse-feed. Several studies demonstrated
that the use of flocculent sludge –rather than granular-
results in a higher efficiency in removing LCFA (Nadais
et al. 2003) and treating complex effluents (Sayed 1987). In
contrast, flocculent sludge appears to be less resistant to
LCFA inhibition (Hwu et al. 1996).
As a result of difficulties in treating complex effluents in
sludge-blanket reactors, pre-treatment methods are nor-
mally used, such as fat separation by means of flotation by
dissolved air. In order to obtain a compact system without
the need of previous fats separation, two UASB reactors
were modified to introduce a novel concept: Upflow
Anaerobic Sludge Blanket with internal fat separator and
external sludge recovery by settling. The system is com-
pleted by a floated material digester with the objective of
avoid sludge disposal. An analysis of this alternative
wastewater treatment system constructed at real scale in a
dairy industry in Melo City, Uruguay (Cooperativa de
Lecherıa de Melo) is presented in this paper. This dairy
industrial wastewater has lipid content higher than 40% of
total COD, and the mean flow is about 100 m3/d.
MATERIALS AND METHODS
System design and operation
In view of significant load and flow-rate fluctuations in
the plant’s effluent stream, a buffer tank (average hydraulic
residence time of 12 hours) was installed upstream of the
anaerobic reactors. Table 1 depicts the effluent characte-
ristics outlet the buffer tank, and Figure 1 shows the complete
treatment system lay-out, comprising the buffer tank, two
40 m3 anaerobic reactors (R1 and R2), a lamella settler and a
5 m3 digester of floated material.
Outlet effluents of both anaerobic reactors discharge to
a lamella settler with plates tilted 608 and spaced at 5 cm,
retaining part of the sludge carry-over from the reactors,
returning it to the feed box by means of pumping
equipment. The lamella settler operates at a residence
time of 15 minutes at full-load. The settling tank outlet is
discharged to municipal sewer.
A funnel-shaped sink for extraction of floating fat was
installed in both reactors, inside of the off-gas header and
two centimetres below liquid level. At each reactor, fat
extraction was performed by pumping from an external
chamber –acting as fat trap- receiving the discharge of the
sink, whereby float material is retained, returning the outlet
stream of this chamber to the reactor.
The reactors were inoculated with flocculent sludge
from an anaerobic treatment lagoon of an abattoir with
Specific Methanogenic Activity of 0.12 gCH4-COD/
gVSS.d. Intermittent and alternate feed rates were used at
start-up, with rate increasing gradually. Continuous feed
rate was used after 120 day operation, reaching the total rate
of wastewater generated by the plant 160 days after start-up.
Granulation process was analysed following the Jeison and
Chamy (1998) technique, immobilizing granules in agar and
then using the UTHSCA Image Tool software.
The float sludge digester was put in operation on day
290 in order to stabilize floating sludge extracted from the
reactors. Solid digester was inoculated with sludge from
the same lagoon as used for the reactors, and operated
under full mixing conditions with sludge recirculation by
means of pumping. The digester hold-up was recirculated
8 times per day. The digester outlet stream was discharged
Table 1 | Main characteristics of effluent outlet the buffer tank
Parameter Temp. (8C) pH BOD (mg/L) COD (mg/L) Fats (mg/L) TKN (mg/L) TSS (mg/L) VSS (mg/L)
Average 25.8 7.4 1710 2520 495 36 1020 710
Range 19–33 4.7–11 650–6240 430–15200 160–1760 14–90 250–2750 210–1890
502 M. Passeggi et al. | Integrated anaerobic treatment of dairy wastewater and sludge Water Science & Technology—WST | 59.3 | 2009
into R1 and R2 in order to retain the system’s biomass
hold-up.
Generated biogas was used to increase reactor influent
stream temperature by 3–48C, in addition to keeping the
digester contents at a temperature between 328C and 388C.
A concentric tubes exchanger constructed in stainless steel
was used to increase the temperature of the influent and of
the digester content.
Data recording and system operation analysis
Reactor performance was evaluated by monitoring the
organic matter removal on a COD and a fat-and-oil basis.
In view of wastewater fluctuations, R1 and R2 influent and
effluent streams were analyzed weekly using refrigerated 24-
hour samples collected daily. COD was determined for all
combined samples. A settling stage was used prior to
analysis, so that COD determinations include soluble
COD and colloidal COD, avoiding distorted measurement
resulting from variable sludge carry-over. Fats and oils were
analyzed monthly using combined samples of influent and
effluent streams (Standard Methods, APHA, AWWA, WEF
1995). Temperature and pH measurements were recorded
daily for point samples of the influent and effluent streams;
and total alkalinity, bicarbonate alkalinity and volatile fatty
acids were determined by titration for point samples on a
three-times-per-week basis. Generated biogas was moni-
tored daily by meters connected to either reactor.
Lamella settler performance was evaluated by daily
measurement of settleable solids in after 30 minutes, for
both influent and effluent stream samples.
Digester performance was evaluated by monitoring the
rate of volatile solid removal and the rate of fat-and-oil
removal. Daily volume measurements were made of floated
sludge extracted from the reactors and fed to the digester;
and digester inlet and outlet samples were analysed on a
weekly basis for Total Solids, Volatile Solids and Fats and
Oils. Digester temperature was measured twice a day, at the
beginning and end of the heating period.
Assaying LCFA inhibition
To evaluate the effect of LCFA inhibition, batch tests were
carried out with different relationships of LCFA/VSS.
LCFA inhibition was assayed in batch runs using sodium
palmitate — the largest abundant of milk triglycerides and
primer of smaller LCFA present in the milk. Granular
adapted sludge from the UASB reactors was used to
perform the tests. Triplicate measurements were made in
150 mL vials with varying concentration of biomass
(expressed as VSS) and palmitate, while the acetate
concentration was kept constant as shown in Table 2.
Figure 1 | Treatement plant lay-out. (—) continuous flow; (– – –) intermittent flow.
503 M. Passeggi et al. | Integrated anaerobic treatment of dairy wastewater and sludge Water Science & Technology—WST | 59.3 | 2009
RESULTS AND DISCUSSION
Sludge blanket reactors
Figure 2 shows reactor feed loads and removal efficiency
in COD (weekly average). Removal efficiency remained at a
value around 90% of COD for load values increasing up to
5.5 kg/m3.d; the hydraulic residence time remaining at a
value around 17 hours during the maximum load stage.
Reactor temperature fluctuated within the range of 208C to
308C throughout the experiment and did not appear to have
a significant effect on the COD removal efficiency.
Operation of the reactors R1 and R2 was started with
440 and 400 kgVSS, respectively (mean concentration
values of 11 and 10 kgVSS/m3). Figure 3 shows the VSS
evolution. A reduction in VSS concentration to 5 g/L during
the initial stage was due to carry-over. About 290 kgVSS of
sludge were added to both reactors between days 162 and
250 to recover the initial concentration of sludge. Granula-
tion started around days 350 and 400 for R2 and R1
respectively; on day 400 small granules of an average size of
0.57 mm and 0.45 mm were measured in R2 and R1
respectively. Granulation resulted in a reduction in sludge
carry-over and led to an increase in VSS concentration to
above 20 g/L. The sludge volume index decreased from
37 mL/g in the inoculum to12 mL/g upon completion of
granulation. In despite flocculent sludge has been reported
to be more efficient in the treatment of effluents with a high
LCFA concentration (Pereira et al. 2002; Nadais, et al. 2003)
as well as complex effluents (Sayed 1987), the sludge has
granulated spontaneously in the higher-organic load stage,
resulting in improved sludge retention capacity.
The resulting combined effect of microbial growth,
sludge supply from the digester and carry-over in the
effluent allowed operation of the reactors without sludge
blowdown.
Lamella settler
Until the sludge granulated, the external settling tank
operated at efficiency around 60% as measured in settleable
solids, thus preventing reactor wash-out. Following granu-
lation, sludge carry-over was notably reduced, thus reducing
the relevance of settling in overall process. Settleable solids
at the settling tank outlet averaged 2.7 mL/L.
Floated sludge extraction and digestion
The volume of extracted float material did not vary
considerably with load. Mean values of daily extractions
from R1 and R2 (containing fats, sludge and insoluble
protein) amounted to 79 L and 73 L, standard deviation
being 54 L and 52 L respectively (using 458 input data for
either reactor). The fat digester, discharging digested sludge
into the reactors, started operating on day 290 with a HRT
of 34 days and temperature ranging between 328C and 408C.
Table 2 | Experimental conditions used in inhibition assays
Assay 1 2 3 4 5 6 7
Biomass (gVSS/L) 2 2 1 2 4 2 2
Palmitate (g/L) 0 0.25 0.5 0.5 0.5 0.75 1
Ratio (gPa/gVSS) 0 0.125 0.5 0.25 0.125 0.375 0.5
Acetate (g/L) 3 3 3 3 3 3 3
Figure 2 | Organic load applied to reactors and COD removal efficiency of the system.
Figure 3 | Volatile suspended solids content in the reactors. concentration is referred
to total reactor volume.
504 M. Passeggi et al. | Integrated anaerobic treatment of dairy wastewater and sludge Water Science & Technology—WST | 59.3 | 2009
The applied load averaged 3.5 kgVS/m3.d, with a fat and oil
content amounting to 47% of VS in the feed. Over the study
period, average efficiency amounted to 78% on a VS basis
and 87% on a fat content basis. Outlet concentrations
measured monthly (n ¼ 10) were 18 ^ 9 g/L and
4.8 ^ 3.9 g/L for VS and fat content respectively. Fat
removal efficiency was considerably high for a sludge
digester. While not emulsified, the fat load is within the
floated sludge in intimate contact with a large amount of
biomass adapted to lipids as substrate. Besides, the flow
model, nearly equivalent to a stirred continuous reactor,
enables operation at a relatively low concentration of fat
and LCFA, which may inhibit degradation.
Assaying LCFA inhibition
Specific methanogenic activity was found to decrease with
increasing palmitate concentration and with increasing
palmitate-to-VSS ratio (Figure 4). According to results, a
reliable measurement of the inhibitory effect of palmitate on
said activity would require, in addition to the determination
of IC50, an indication of the inhibitor-to-biomass ratio used
for such determination. Further, not only it is recommended
to ensure proper contact and mixing in order to prevent
LCFA build-up, but it is also important to ensure the system
operates at a high biomass concentration.
CONCLUSIONS
A compact system consisting in two modified UASB
reactors and a floated sludge digester was assayed at
industrial conditions to treat dairy wastewater. Results
here reported demonstrate the feasibility of treating dairy
industrial effluent without prior fat separation in anaerobic
reactors, even when the content of lipidic material may be
higher than 40% of COD. COD removal efficiencies around
90% are achieved in stable operating conditions.
Inhibitory effects of palmitate (representing the LCFA)
depend not only of palmitate concentration but palmitate
to biomass ratio.
Even using moderate loading rates, in flocculent sludge
fed by dairy wastewater granulation can occur. Hence,
retention of sludge into the reactor is favoured, and this
enables the use of higher feed loads.
The floated sludge digester achieves high efficiency,
allowing operates the system without sludge discharge for
final disposal.
ACKNOWLEDGEMENTS
To managers and workers of COLEME, for the good
attitude to include changes and to operate the reactors.
REFERENCES
APHA, AWWA, WEF 1995 Standard Methods for the Examination
of Water and Wastewater, 19th edition.
Demirel, B., Yenigun, O. & Onay, T. T. 2005 Anaerobic treatment
of dairy wastewater: a review. Process Biochem. 40,
2583–2595.
Cavaleiro, A. J., Pereira, M. A. & Alvez, M. 2008 Enhancement of
methane production from long chain fatty acid based effluents.
Bioresour. Technol. 99(10), 4086–4095.
Hwu, C.-S., Donlon, B. & Lettinga, G. 1996 Comparative toxicity of
long-chain fatty acids to anaerobic sludge from various origins.
Wat. Sci. Technol. 34(5-6), 351–358.
Hwu, C.-S., Tseng, S.-K., Yuan, C.-Y., Kulik, Z. & Lettinga, G. 1998
Biosorption of long-chain fatty acids in UASB treatment
process. Water Res. 32(5), 1571–1579.
Figure 4 | Palmitate inhibition effect on specific methanogenic activity.
505 M. Passeggi et al. | Integrated anaerobic treatment of dairy wastewater and sludge Water Science & Technology—WST | 59.3 | 2009
Jeison, D. & Chamy, R. 1998 Novel technique for measuring the
size distribution of anaerobic granular sludge, V Taller y
Seminario latinoamericano de tratamiento anaerobio de agues
residuales, Vina del Mar, Chile.
Nadais, M. H., Capela, M. I., Aroja, L. M. & Duarte, A. C. 2003
Biosorption of milk substrates onto anaerobic flocculent and
granular sludge. Biotechnol. Prog. 19, 1053–1055.
Nadais, M. H., Capela, M. I. & Aroja, L. M. 2006 Intermittent vs
continuous operation of upflow anaerobic sludge bed reactors
for dairy wastewater and related microbial changes. Wat. Sci.
Technol. 54(2), 103–109.
Pereira, M. A., Pires, O. C., Mota, M. & Alves, M. M. 2002
Anaerobic degradation of oleic acid by suspended and
granular sludge: identification of palmitic acid as a key
intermediate. Water Sci. Technol. 45(10), 139–144.
Pereira, M., Cavaleiro, A., Mota, M. & Alves, M. 2003 Accumulation
of long chain fatty acids onto anaerobic sludge under steady
state and shock loading conditions: effect on acetogenic and
metanogenic activity. Water Sci. Technol. 48(6), 33–40.
Pereira, M., Mota, M., Alvez, M. 2004. The important role of mass
transfer limitations caused by Long Chain Fatty Acids
accumulation onto the anaerobic sludge. Proceedings of the
10th IWA Congress on Anaerobic Digestion. Montreal,
Canada.
Perle, M., Kimchie, S. & Shelef, G. 1995 Some Biochemical Aspects
of the Anaerobic Degradation of Dairy Wastewater. Water
Res. 29(6), 1549–1554.
Petruy, R. & Lettinga, G. 1997 Digestion of a milk-fat emulsion.
Bioresour. Technol. 61, 141–149.
Rinzema, A. 1993 Anaerobic Digestion of Long-Chain Fatty Acids in
UASB and Expanded Granular Sludge Bed Reactors. Process
Biochem. 28, 527–537.
Sayed, S. 1984 Anaerobic treatment of slaughterhouse wastewater
using a flocculent sludge UASB reactor. Agric. Wastes 11,
197–226.
Sayed, S. 1987 Anaerobic treatment of slaughterhouse
wastewater using a granular sludge UASB reactor. Biol.
Wastes 21, 11–28.
Vidal, G., Carvalho, A., Mendez, R. & Lema, J. M. 2000 Influence of
the content in fats and proteins on the anaerobic
biodegradability of dairy wastewaters. Bioresour. Technol. 74,
231–239.
506 M. Passeggi et al. | Integrated anaerobic treatment of dairy wastewater and sludge Water Science & Technology—WST | 59.3 | 2009
Top Related