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6 Ecological and Economic Aspects of the Integrated Sludge Treatment in STRBs

6 Ecological and Economic Aspects of the Integrated Sludge Treatment in STRBs

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Sludge Treatment Reed Beds (STRBs) as a Eco-solution of Sludge Utilization…


of heavy traffic and other dangerous machines. Such an equipment is needed only

during the emptying of beds/basins, which is every 10–15 years.

In addition, this is low-energy-consuming methods, because electricity is needed

only to pumps supplying sludge to the system. Operating costs are very low and

amount about 5–10 % of the cost of conventional methods (Kołecka and ObarskaPempkowiak 2013).



Based on own research and literature reports the following conclusions can be


1. Sludge Treatment Reed Beds are examples of eco-engineering solutions not only

due to natural processes, but also for economic and environmental reasons

2. The quality of sludge as well as climatic conditions should be taking into account

to proper design of reed system.

3. Proper operation of the systems requires at least 8 beds.

4. Sewage sludge stabilized in STRBs has high content of dry matter and low content of organic matter in comparison to sludge stabilized with conventional


5. The final residual sewage sludge can be used as potential fertilizer, thanks to the

relatively high concentrations of nitrogen and phosphorus in comparison to

organic fertilizers, eg. manure.


APHA-AWWA-WPCF. (2001). Standard methods for the examination of water and wastewater,

20th edition, Washington, APHA

Brix, H. (2014). Integrated sludge dewatering and mineralization in sludge treatment reed beds. In

14th IWA international conference on wetland system for pollution control (pp. 31–42).

Shanghai, P.R. China.

De Maeseneer, J.L. (1997). Constructed wetland for sludge dewatering. Water Science &

Technology, 35(5), 279–285.

Jørgensen, S.E., & Mitsch, W.J. (1989). Classification and examples of ecological engineering. In

W.J. Mitsch, & S.E. Jørgensen (Eds.), Ecological engineering: An introduction to ecological

engineering (pp. 13–19). New York: Wiley.

Kołecka, K., & Obarska-Pempkowiak, H. (2008). The quality of sewage sludge stabilized for a

long time in reed basins. Environment Protection Engineering, 34(3), 13–20.

Kołecka, K., & Obarska-Pempkowiak, H. (2009). Operation of reed systems used to stabilisation

of sewage sludge. Polish Journal of Environmental Studies, 6, 60–69.

Kołecka, K., & Obarska-Pempkowiak, H. (2013). Potential fertilizing properties of sewage sludge

treated in the Sludge Treatment Reed Beds (STRB). Water Science & Technology, 68(6),



K. Kołecka et al.

Matamoros, V., Nguyen, L.X., Arias, C.A., Nielsen, S., Laugen, M.M., Brix, H. (2012). Musk

fragrances, DEHP and heavy metals in a 20 years old sludge treatment reed bed system. Water

Research, 46, 3889–3896.

Nielsen, S. (1994). Biological sludge drying in reed bed systems - Six years of operation experience. In Proceedings of 4th international conference on wetlands systems for water pollution

control (pp. 447–457). Guangzhou P.R. China.

Nielsen, S. (2002). Sludge drying reed beds. In Proceedings of the 8th international conference on

the use of. Constructed wetlands in water pollution control (pp. 24–39). Arusha, Tanzania.

Nielsen, S. (2003). Sludge drying reed beds. Water Science & Technology, 48(5), 101–109.

Nielsen, S. (2005). Mineralization of hazardous organic compounds in a sludge reed bed and

sludge storage. Water Science & Technology 51(9), 109–117.

Nielsen, S. (2007). Helsinge sludge reed beds systems: Reduction of pathogenic microorganisms.

Water Science & Technology 56(3), 175–182.

Nielsen, S. (2011). Sludge treatment reed bed facilities – Organic load and operation problems.

Water Science & Technology 63(5), 941–947.

Nielsen, S., Peruzzi, E., Macci, C., Doni, S., Masciandaro, G. (2012). Stabilisation and mineralization of sludge in reed bed system after 10–20 years of operation. In 13th international IWA

specialist group conference on wetland systems for water pollution control 25–30 November

2012, Perth, Australia.

NWMP. (2014). National Waste Management Plan 2014, Annex to Resolution No. 217 of the

Council of Ministers from 24 December 2010 (item 1183) [in Polish].

Obarska-Pempkowiak, H., Tuszynska, A., Sobocinski, Z. (2003). Polish experience with sewage

sludge dewatering in reed systems. Water Science & Technology, 48(5), 111–117.

Odum, H.T., & Odum, E.C. (2003). Concepts and methods of ecological engineering. Ecological

Engineering, 20, 339–361

Peruzzi, E., Macci, C., Doni, S., Mascinadaro, G., Peruzzi, P., Aiello, M., Ceccanti, B. (2009).

Phragmites australis for sewage sludge stabilization. Desalination 246, 110–119.

Stefanakis, A.I., & Tsihrintzis, V.A. (2011). Dewatering mechanisms in pilot-scale sludge drying

reed beds: Effect of design and operational parameters. Chemical Engineering Journal, 172(1),


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sludge (year 2015, item 257) [in Polish]

Troesch, S., Liénard, A., Molle, P., Merlin, G., Esser, G.(2009). Sludge drying reed beds: A full and

pilot-scales study for activated sludge treatment. Water Science & Technology 60(5),


Uggetti, E., Ferrer, I., Llorens, F., García, J. (2010). Sludge treatment wetlands: A review on the

state of the art. Bioresource Technology, 101, 2905–2912

Vincent J., Molle P., Wisniewski C., Lienard A. (2011). Sludge drying reed beds for septage treatment: Towards design and operation recommendations. Bioresource Technology, 102,


Vincent, J., Forquet, N., Molle, P., Wisniewski, C. (2012). Mechanical and hydraulic properties of

sludge deposit on sludge drying reed beds (SDRBs): Influence of sludge characteristics and

loading rates. Bioresource Technology, 116, 161–169.

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in reed beds, Water Science & Technology, 41, 65–68

Chapter 10

Dairy Wastewater Treatment by a Horizontal

Subsurface Flow Constructed Wetland

in Southern Italy

Fabio Masi, Anacleto Rizzo, Riccardo Bresciani, and Carmelo Basile

Abstract Evidence on the efficiency of horizontal flow constructed wetlands (HF

CWs) in treating dairy wastewater in the Mediterranean region is reported, showing

results from the 3 year long monitoring of a HF CW treatment plant situated in

southern Italy. The HF CW treats a mixture of different wastewaters produced by a

dairy farm (dairy, milking, milk cooling, restaurant, and house). Samples of wastewater quality (pH, COD, and N-NH4+) were collected at the inlet and outlet of HF

CWs from February 2012 to May 2015. The effluent COD concentrations from

dairy activities alone were also collected during the same period, showing the most

relevant contribution of dairy wastewater in terms of organic loads. The start-up

phase was influenced by the influent pH being too low, which was fixed by adopting

a serum separation. The system showed some stress during a management phase

lasting 2 months, requiring then 1 month of recovery period. The overall treatment

performance is now very satisfactory, with 94.3 % COD removal efficiency based

on average influent and effluent values, while a slight increase in effluent N-NH4+

was registered, probably due to organic matter ammonification.

Keywords Dairy wastewater treatment • Horizontal subsurface flow constructed

wetland • Mediterranean climate



Dairy wastewater is usually produced by the cleaning and sterilization of the milking equipment and by the wash-down of the manure-spattered walls and floors of

the milking parlor (Kadlec and Wallace 2009). These activities lead to a dairy

F. Masi (*) • A. Rizzo • R. Bresciani

IRIDRA S.r.l., Via Alfonso la Marmora 51, 50121, Florence, Italy

e-mail: fmasi@iridra.com

C. Basile

Fattoria della Piana, Candidoni, Reggio Calabria, Italy

© Springer International Publishing Switzerland 2016

J. Vymazal (ed.), Natural and Constructed Wetlands,

DOI 10.1007/978-3-319-38927-1_10



F. Masi et al.

wastewater characterized by high organic matter concentrations and a wide range of

pH as reviewed by Vymazal (2014). The organics present in the wastewater are

mainly carbohydrates, proteins and fats originating from the milk. A wide range of

pH (between 3.5 and 11) is encountered in the literature, due to use of both alkaline

and acidic cleaners and sanitizers. The seasonality of typical dairy activities and the

different products produced (milk, butter, yoghurt, ice cream, and cheese) lead to a

wide range of dairy wastewater quality in the literature (BOD5 1400–50,000 mg L−1;

COD 2000–90,000 mg L−1; N-NH4+ 20–150 mg L−1).

Treatment of dairy wastewater through conventional biological treatment technologies (e.g., activated sludge) is problematic for a number of reasons: (i) the high

variability in both hydraulic and organic loads of dairy wastewater can be difficult

to manage, since more temporally constant influent loads are needed to ensure

appropriate performance; (ii) the high organic loads lead to high sludge production,

increasing the management costs; and (iii) the need for specialized operation and

management staff is a burdensome extra cost, especially for small- and mediumsized dairies. Hence, more flexible constructed wetland (CW) treatment technologies have been widely adopted to treat dairy wastewater (Kadlec and Wallace 2009;

Vymazal 2014). Among the different CW configurations, horizontal subsurface

flow (HF CW) has been one of the most widely used solutions for treatment of dairy

wastewater, showing satisfactory removal efficiencies of 50–98 % for BOD5 and

40–96 % for TSS (Vymazal 2009, 2014). However, a recent literature review

(Vymazal 2014) found a lack of evidence of HF CW capability to treat dairy wastewater in the Mediterranean region. For this reason, a 3-year case study of HF CWs

used to treat wastewater from a dairy farm in southern Italy is reported here as a

representative case study of HF CW performance in the Mediterranean climate.


Material and Methods

The experimental case study is located at Fattoria della Piana, Candidoni (Italy –

38°N, 15°E), a farm situated in the South of Italy. The farm promotes an ecosustainable approach, recovering the end-products from the dairy (serum) and stable

(manure) to produce biogas, and treating wastewaters with CWs.

Fattoria della Piana wastewater comes from a number of sources: houses and a

restaurant (maximum 12 residents and 100 restaurant users); the milk cooling plant

(average 20 m3d−1); the dairy (20 tons per day of processed milk, which produces

20 m3d−1 of wastewater); and milking (200 livestock, which produce 20 m3d−1 of

wastewater). On average, the daily wastewater quantity is 85 m3d−1.

A CW treatment plant has been built to treat this wastewater. According to Italian

law, the Fattoria della Piana wastewater can be classified as domestic, and therefore

quality limits are only imposed for COD, TSS, and pathogens concentrations. The

scheme of the wastewater treatment plant is reported in Fig. 10.1: an equalization

10 Dairy Wastewater Treatment by a Horizontal Subsurface...


Fig. 10.1 Scheme of CW wastewater treatment plant

tank is installed for the dairy wastewater; primary treatment for wastewater from all

the different sources is performed by a three-chamber septic tank; four horizontal

flow constructed wetlands (HF CWs) are installed in parallel as secondary treatment, with a total surface area of 2280 m2 (theoretical hydraulic retention time –

HRT – 5.3 days; gravel Ø 8 mm, depth 0.8 m, 15 m W / 38 m L for each of the four

HF beds). Each HF CW is also subdivided in 2 hydraulically separated sectors to

facilitate management operations, therefore the CW treatment plant is composed of

8 separated sectors. The treated effluent is discharged into a small stream. The treatment plant started operation in February 2012. Since the pH of influent wastewater

was too low in the first operational period, the serum from dairy activities (highly

acidic) has been separated and sent to an anaerobic digester for biogas production

since the middle of May 2012. Management activities were performed between

December 2014 and January 2015, during which only 7 of 8 sectors were operational and the water table within the beds was reduced.

Samples of wastewater quality (pH, COD, and N-NH4+) were collected at the

inlet and outlet of the HF CWs from February 29, 2012 to May 11, 2015. Effluent

COD concentrations from the dairy equalization tank were also collected during the

same period. The wastewater quality dataset is analyzed here to investigate the functioning and efficiency of the HF CW treatment plant for dairy wastewater mixed

with other pollutant sources (e.g., milking, domestic). Moreover, we describe in

detail the atypical functioning phases of start-up and management, to understand

the HF CW response during these critical phases.




F. Masi et al.

Results and Discussion

Role of Dairy Wastewater on the Mixed Wastewater


The samples collected at the effluent of the equalization tank can be considered

representative of the dairy wastewater composition, while those collected at the

influent of the HF CW are representative of the mixed wastewater. The dairy almost

always has higher COD concentrations than the mixed wastewater (Fig. 10.2). The

average COD concentration in dairy wastewater during the study period was

4079 mg L−1 (Table 10.1), which is within the range reported by Vymazal (2014;

2000–90,000 mg L−1) and twice the average influent concentration of the mixed

wastewater. No relevant changes in pH were observed (Table 10.1). Since only three

values of N-NH4+ concentration from the equalization tank effluent have been measured, the same analysis has not been done for N-NH4+.

The mixing of dairy wastewater with other, less concentrated pollution sources

(wastewater from milking, milk cooling, the restaurant, and houses in this specific

case) has beneficial effects and should be always performed when possible in farm

wastewater treatment. Mixing dairy wastewater with less concentrated wastewater

reduces the organic matter concentration in the HF CW influent, limiting the risk of

clogging and thus increasing the lifespan of the treatment plant. Furthermore, the

domestic blackwater provides nutrients that are often lacking in agricultural


Fig. 10.2 COD concentrations in effluent from the equalization tank (representative of the dairy

wastewater – diamonds) and inflow of the HF CW (representative of the mixed wastewater – stars)

at Fattoria della Piana (Candidoni, Italy) from February 2012 to May 2015

10 Dairy Wastewater Treatment by a Horizontal Subsurface...


Table 10.1 Descriptive statistics of pH values and COD concentrations in the effluent from the

equalization tank (representative of the dairy wastewater) and in the inflow of the HF CW

(representative of the mixed wastewater)


St. dev.



# of samples














COD (mg L−1)













Data collected after the starting period, from July 2012 to May 2015

Fig. 10.3 Correlation between influent (triangles) and effluent (crosses) COD concentrations

from the HF CW and influent pH (diamonds) in the starting period (from February to September,



Start-Up Phase

The first operational period failed in COD removal due to low influent pH (average

value of 4.9 from March 2012 to the middle of May 2012). In order to deal with this

issue the serum (highly acidic) has been separated at the source and sent to an

anaerobic digester for biogas production since the middle of May 2012. This

approach promoted an increase in influent pH (around 6), which produced a more

suitable environment for the bacterial communities and, consequently, a higher HF

CW removal efficiency. This is confirmed by Fig. 10.3, where the improvement in

COD treatment performance is clearly correlated with the increased influent pH

prompted by serum separation.

Data reported in the literature show a wide range of pH values for dairy wastewater (Vymazal 2014), which can be highly acidic or highly basic (reported pH


F. Masi et al.

values ranging from as low as 3.5 to as high as 11). For this reason, a preliminary

design to optimize pH is not possible without first analyzing the wastewater to be

treated. Hence, it is important to consider some possible ways of managing pH during the design phase (in this case, the possibility of separating the serum) and carefully analyze treatment performance during the start-up phase.


Management Phase

After two and a half years of proper functioning, some management activities were

performed at the end of 2014, for an early appearance of clogging signals in 1 of the

8 sectors of the CW system, mainly due to some overloads events that took place in

the former period. The management, which was done between December 2014 and

January 2015, required a limitation on the number of hydraulically separated sectors

to treat the wastewater (7 instead of 8, which increased the hydraulic loading rate for

each of the remaining 7) and lowering the water table within the beds (reducing the

hydraulic retention time). As visible in Fig. 10.4, during the management phase the

system showed some stress, maintaining good removal efficiencies but exceeding

the limit of 160 mg L−1 (Fig. 10.4). After all 8 hydraulically separated sectors and

the correct water level were re-established (in February 2015), the HF CW needed

a recovery period of almost 1 month to re-establish the removal efficiencies obtained

before the management phase.

Fig. 10.4 Influent (triangles) and effluent (crosses) COD concentration from the HF CW treatment plant at Fattoria della Piana (Candidoni, Italy) before, during, and after the management

phase, which lasted from December 2014 to January 2015. Black continuous line indicates the

Italian limit for discharge into surface water. Vertical axis is in logarithmic scale

10 Dairy Wastewater Treatment by a Horizontal Subsurface...


These results suggest that HF CWs are able to recover the treatment performance

after a management phase in a relevantly short time period and the frequency of

such maintenance operations is very low.


Overall Treatment Performance

Influent and effluent COD concentrations from the HF CWs for the analyzed period

(from February 2012 to May 2015) are shown in Fig. 10.5, highlighting very good

performances in COD treatment. Aside from the start-up and management phases,

the effluent COD concentration was almost always below the Italian limit of

160 mg L−1 for discharge of wastewater in fresh water bodies, except in a few cases.

Table 10.2 summarizes the influent and effluent pH, N-NH4+, and COD from the

HF CWs, using only data after the start-up phase, but including the management

phase (i.e., from July 2012 to May 2015). pH was quite stable (low standard deviation) both at the influent and the outlet, with values within the range for optimal

bacterial activity (approximately 6–9 – Kadlec and Wallace 2009). COD removal

efficiency was very high, with a relatively stable, low effluent concentration

(Fig. 10.6). Average COD removal efficiency was 94.3 % based on all 156 samples

(Table 10.2), and 93.1 ± 4.9 % (69–97.8 %) when considering only the samples corresponding to a HRT of 4–6 days (52 samples). A slight increase in average N-NH4+

effluent concentration was observed (Fig. 10.6); this is probably due to ammonifica-

Fig. 10.5 Influent (triangles) and effluent (crosses) COD concentration from the HF CW treatment plant at Fattoria della Piana (Candidoni, Italy) from February 2012 to May 2015. Black

continuous line indicates the Italian limit for discharge into surface water. Vertical axis is in logarithmic scale

F. Masi et al.


Table 10.2 Descriptive statistics of pH, N-NH4+, and COD concentrations at the inflow and

outflow of the HF CW. Data collected after the starting period, from July 2012 to November 2014


St. dev.



# of samples














N-NH4+ (mg L−1)













COD (mg L−1)













Fig. 10.6 Average and standard deviation of COD and N-NH4+ concentrations at HF CW inflow

and outflow

10 Dairy Wastewater Treatment by a Horizontal Subsurface...


tion of the high organic nitrogen content within influent loads (Kadlec and Wallace

2009), determined by high concentrations of proteins in the dairy wastewater

(Vymazal 2014). These results suggest that a second, aerobic stage to promote nitrification (e.g., vertical flow constructed wetland – VF CW – Kadlec and Wallace

2009) should be included in cases where there are limits on effluent nitrogen concentrations. A future analysis of influent and effluent total Kjeldhal nitrogen (TKN)

is planned to confirm this hypothesis.



The organic load of dairy wastewater from Fattoria della Piana, Candidoni (Italy –

38°N, 15°E), has been successfully reduced by the HF CW treatment plant from

2012 to 2015. The wastewater effluent from the HF CW met the current Italian

water quality limits except during the start-up phase and a particular management

phase. This study demonstrates the validity of CW technology in treating wastewaters produced by dairies in Mediterranean regions and provides useful insights on

how to deal with start-up and management phases for this particular application of

the HF CW treatment plant.

Acknowledgements Authors would like to thank Sarah Widney for language improvement of the



Kadlec, R., & Wallace, S. (2009). Treatment wetlands, (2nd ed.) Boca Raton: CRC Press.

Vymazal, J. (2009).The use constructed wetlands with horizontal sub-surface flow for various

types of wastewater. Ecological Engineering, 35, 1–17.

Vymazal, J. (2014). Constructed wetlands for treatment of industrial wastewaters: A review.

Ecological Engineering, 73, 724–751.

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