Download PRUEBA DE COMUNICACIÓN ORAL

1
PROPERTIES OF BIOSOLIDS FROM SLUDGE TREATMENT WETLANDS FOR
2
LAND APPLICATION
3
4
Enrica Uggetti1, Ivet Ferrer1, Esther Llorens1, David Güell2, Joan García1,*
5
6
1
7
Environmental Engineering, Technical University of Catalonia (UPC)
8
c/ Jordi Girona 1-3, Building D1, E-08034 Barcelona, Spain.
9
E-mail
10
Environmental Engineering Division,
addresses:
[email protected],
Department of Hydraulic, Maritime and
[email protected],
[email protected],
[email protected]
11
Depuradores d’Osona, S.L. c/Historiador Ramon d’Abadal i de Vinyals 5, 3r, E-08500 Vic,
12
2
13
Spain
14
15
* Corresponding author:
16
Tel: +34 934016464
17
Fax: +34 934017357
18
E-mail address: [email protected]
19
1
20
Abstract
21
22
Sludge treatment wetlands consist of constructed wetlands which have been upgraded for
23
sludge treatment over the last decades. Sludge dewatering and stabilisation are the main
24
features of this technology, leading to a final product which may be recycled as an organic
25
fertiliser or soil conditioner. In this study, biosolids from full-scale treatment wetlands were
26
characterised in order to evaluate the quality of the final product for land application, even
27
without further post-treatment such as composting. Samples of influent and treated sludge
28
were analysed for pH, Electrical Conductivity, Total Solids (TS), Volatile Solids (VS),
29
Chemical Oxygen Demand (COD), Dynamic Respiration Index (DRI), nutrients (Total
30
Kjeldahl Nitrogen (TKN), Total Phosphorus (TP) and Potasium (K)), heavy metals and faecal
31
bacteria indicators (E. coli and Salmonella spp.). According to the results, sludge water
32
content and therefore sludge volume are reduced by 25 %. Organic matter biodegradation
33
leads to VS around 43-44 %TS and COD around 500 g·kgTS-1. The values of DRI24h (1000-
34
1500 mgO2∙kgTS-1∙h-1) indicate that treated sludge is almost stabilised final product. Besides,
35
the concentration of nutrients is quite low (TKN~4 %TS, TP~0.3 %TS and K~0.2-0.6 %TS).
36
Both heavy metals and faecal bacteria indicators meet current legal limits for land application
37
of the sludge. Our results suggest that biosolids from the studied treatment wetlands could be
38
valorised in agriculture, especially as soil conditioners.
39
40
Keywords: Compost, Reed Beds, Organic Waste, Wastewater.
41
2
42
1. Introduction
43
44
Sewage sludge is the organic waste generated by wastewater treatment processes, after solid
45
and liquid separation units. The amount of sludge produced and its composition depend on the
46
influent’s characteristics and wastewater treatment used. Sludge production in conventional
47
activated sludge processes ranges from 60 to 80 g of total solids per person per day . In
48
Europe, the Urban Wastewater Treatment Directive 91/271/EEC (Council of the European
49
Union, 1991) promoted the implementation of wastewater treatment plants (WWTP) with
50
secondary wastewater treatment in municipalities above 2000 Persons Equivalent (PE); and
51
the Water Framework Directive (Council of the European Union, 2000) encouraged
52
wastewater treatment even in municipalities below 500 PE. As a result sludge production has
53
increased in the European Union by 50 % since 2005 (Fytili and Zabaniotou, 2008). For
54
instance, in Catalonia (Spain) around 50 % of the WWTP (170) were constructed between
55
2000 and 2006 (Agencia Catalana del Agua, 2007).
56
57
In Spain, in order to manage the increasing amount of sludge produced the following
58
hierarchy was proposed (Consejo de Ministros, 2001): 1) valorisation in agriculture, 2)
59
energetic valorisation, and 3) landfilling. Agricultural valorisation is nowadays preferred to
60
landfilling, since sludge recycling ensures the return of organic constituents, nutrients and
61
microelements to crop fields which eases the substitution of chemical fertilizers
62
(Oleszkiewicz and Mavinic, 2002). Sludge disposal onto agricultural land is regulated by the
63
European Sludge Directive, which sets up land application of sewage sludge based on
64
maximum heavy metals concentrations (Council of the European Union, 1986). Recent
3
65
regulation proposals are more restrictive in terms of heavy metals, and also consider emerging
66
pollutants and microbial faecal indicators (Environment DG, EU, 2000).
67
68
In practice, sludge treatment systems have to provide a final product suitable for land
69
application (fulfilling legislation requirements), with reasonable investment as well as
70
operational and maintenance costs. In this sense, sludge treatment wetlands might be regarded
71
as a recent technology for sludge management, which is particularly appropriate for small
72
communities from both an economical and environmental point of view.
73
74
Treatment wetlands (TW) reproduce self-cleaning processes occurring in natural wetlands
75
and are being used for wastewater treatment in many regions of the world (Caselles-Osorio et
76
al., 2007). Since the late 1980s, TW have been adapted for sludge treatment developing a
77
technology that is nowadays used in most European countries and in North America (Uggetti
78
et al., 2010).
79
80
Sludge treatment wetlands consist of shallow tanks filled with a gravel layer and planted with
81
emergent rooted wetland plants such as Phragmites australis (common reed) (Cole, 1998).
82
Thickened secondary sludge is pumped and spread on the wetland’s surface. Here, part of the
83
sludge water content is rapidly drained by gravity through the gravel layer; while another part
84
is evapotranspirated by the plants. In this way, a concentrated sludge residue remains on the
85
surface of the bed where, after the resting time, thickened sludge is anew spread, starting the
86
following feeding cycle.
87
4
88
The roots of the plants ease oxygen transfer to the gravel and sludge layers, creating aerobic
89
microsites that promote sludge mineralization and stabilization (Reed et al., 1988).
90
Furthermore, the complex root system maintains pores and small channels within sludge layer
91
that preserve the drainage efficiency through the bed (Nielsen, 2003b). When the sludge is
92
dry, the movement of plant stems by the wind prompts the cracking of the surface, improving
93
the aeration of the sludge layer.
94
95
During feeding periods, the sludge layer height increases at a certain rate (around 10 cm·year-
96
1
97
period (from 1–2 months to 1 year), aimed at improving sludge dryness and mineralisation.
98
The final product is subsequently withdrawn, starting the following operating cycle.
). When the layer approaches the top of the tank, feeding is stopped during a final resting
99
100
The quality of this product is the result of both dewatering processes (draining and
101
evapotranspiration) and organic matter biodegradation (Nielsen, 2003b). According to
102
Nielsen and Willoughby (2005) it is suitable for land application; although further post-
103
treatments might be required to improve sludge hygienisation (Zwara and Obarska-
104
Pempkowiak, 2000). Nevertheless, detailed studies on the properties of biosolids from
105
treatment wetlands are still lacking in the literature.
106
107
In this study, full-scale treatment wetlands were evaluated with the aim of studying the
108
efficiency of the process in terms of sludge dewatering, mineralization and hygienisation;
109
while assessing the quality of the final product for land application. To this end, physico-
110
chemical and microbiological parameters, together with stability indexes, were considered as
111
proposed in the European Sludge Directive (Council of the European Union (1986)), the 3rd
5
112
Draft EU Working Document on Sludge (Environment DG, EU, 2000) and the 2nd Draft EU
113
Working Document on Biological Treatment of Biowaste (Environment DG, EU, 2001).
114
115
2. Materials and methods
116
117
2.1. System’s description
118
119
The studied full-scale treatment wetlands are located at the WWTP of Seva (1500 PE), in the
120
province of Barcelona (Catalonia, Spain). The main characteristics of the facility are
121
summarised in Table 1. The sludge treatment wetlands were set-up in 2000 by transforming
122
existing conventional drying beds. They are planted with Phragmites australis. The total
123
surface area is 175 m2 and the sludge loading rate around 125 kg TS/m2·year, much higher
124
than the recommended value of 50-60 kgTS·m-2·year-1 (Burgoon et al., 1997; Edwards et al.,
125
2001; Nielsen, 2003a). Other details on the design and operation of the wetlands may be
126
found in Uggetti et al. (2009).
127
128
The first operating cycle lasted about 5 years; the sludge was then removed and the process
129
re-started between 2004 and 2005. The second operating cycle was finished by the end of
130
2008 in two of the wetlands (named 1 and 2). After a resting period of 4 months, the wetlands
131
were emptied with a power shovel and the final product was thereafter transported to a
132
composting plant.
133
134
2.2. Sludge sampling and characterization
135
6
136
When the wetlands were emptied (in 2008), the layer of dry sludge was about 60 cm high.
137
Two composite samples were prepared by mixing subsamples from each wetland; while an
138
integrated influent sample was obtained from subsamples collected during a whole week.
139
140
As recommended in the literature (Mujeriego and Carbó, 1994; Obarska-Pempkowiak et al.,
141
2003b; Soliva, 2001), the sludge quality was characterised in terms of: pH, Electrical
142
Conductivity (EC), Total and Volatile Solids (TS and VS), Chemical Oxygen Demand
143
(COD), Total Kjehldahl Nitrogen (TKN), Potassium (K), Total Phosphorous (TP), heavy
144
metals and faecal bacteria indicators (Salmonella spp. and Escherichia coli). Additionally, the
145
Dynamic Respiration Index (DRI) was determined according to Adani et al. (2000) and
146
Barrena et al. (2009).
147
148
Sludge samples were analysed following the Standard Methods (APHA-AWWA-WPCF,
149
2001). Samples for COD, TKN, TP, K and heavy metals’ analyses were previously air dried
150
at room temperature (until constant weight); hence the results are expressed on a dry matter
151
basis (per kg or %TS). Air dried samples were subsequently diluted in distilled water (1:5) for
152
pH and EC measurements.
153
154
3. Results and discussion
155
156
The efficiency of the process in terms of sludge dewatering and mineralisation is usually
157
evaluated by the increase in dry matter (TS) and the decrease in organic matter (VS and COD)
158
contents, respectively. However, total organic matter content is not sufficient to assess the
159
stability of the product; indeed information on the amount of readily biodegradable organic
7
160
matter fraction is also needed. For instance, it can be deduced from the DRI. Besides, the
161
concentration of nutrients, heavy metals and faecal bacteria indicators are used to determine
162
the quality of biosolids for its application on land as organic fertilizers.
163
164
Tables 2 and 3 show the main characteristics of the influent and treated sludge from the full-
165
scale treatment wetlands. The results are here examined and discussed. A comparison with
166
average compost characteristics is proposed to assess the requirement of additional
167
composting post-treatment.
168
169
3.1 Sludge dryness
170
171
Secondary sludge produced by the contact-stabilization process is spread on the beds with
172
very high water content (typically around 99 %) (Table 2). Sludge moisture is significantly
173
reduced down to about 75 % during the treatment and after a resting period of 4 months. The
174
sludge volume is consequently reduced by 25 %. This is the main goal of dewatering
175
processes.
176
177
The dryness of the final product (TS~25 %) is lower than that observed in other facilities after
178
a resting period of approximately one year (TS around 30-40 %) (Nielsen, 2003b). In this
179
sense, a previous study indicated a poor dewatering efficiency in Seva’s system compared to
180
other Catalan facilities (Uggetti et al., 2009). One possible reason for this is that the sludge
181
loading rate (125 kgTS·m-2·year-1) is over twice the recommended value (50-60 kgTS·m-
182
2
·year-1) (Burgoon et al., 1997; Edwards et al., 2001; Nielsen, 2003a). This fact suggests that
8
183
the dryness of the final product could be further increased with a better system management
184
(i.e. reducing the sludge loading rate).
185
186
3.2 Organic matter content and stability
187
188
Table 2 shows organic matter contents expressed as VS and COD; as well as the DRI value.
189
The concentration of VS in the influent is quite low (~51 %TS) as a result of the high solids
190
retention time in the contact-stabilisation process.. Final values (43-45 %TS) are within the
191
range obtained after conventional sludge stabilisation techniques, such as anaerobic digestion
192
(Ferrer, 2008; Ferrer et al., 2008). Therefore, VS removal (7-8 %) is remarkably lower than
193
that usually observed in these type of processes with higher VS in the influents (Ferrer, 2008;
194
Ferrer et al., 2008). Again, the results are in accordance with a previous study on this system
195
(Uggetti el al., 2009). COD values indicate total organic matter reduction from 700 to some
196
500g·kgTS-1 (Table 2).
197
198
Comparisons with other systems are not straightforward, since the biodegradability of the
199
sludge depends on a number of parameters, including its nature and composition, amongst
200
others. For instance, VS were reduced to 20 %TS in pilot scale treatment wetlands in China
201
(Yubo et al., 2008). On the other hand, in compost samples organic contents are usually much
202
higher, around 60 % for compost of sewage sludge mixed with vegetable wastes (Bertan et
203
al., 2004), due to humic-like substances produced during composting process.
204
205
Organic matter in soil amendments can improve the properties and quality of soils, which is
206
essential to guarantee long-term soil fertility (Draeger et al.,1999). In particular, an increase in
9
207
organic matter content can improve physical properties (water retention, soil structure, water
208
infiltration, bulk density, porosity), chemical properties (cation exchange capacity, pH) and,
209
in some cases, biological properties (Moss et al., 2002, Andreoli et al., 2007). Such a
210
response depends on the sludge:soil ratio (Singh and Agrawal, 2008).
211
212
On the other hand, higher biological stability implies lower environmental impacts (like odour
213
generation, biogas production, leaching and pathogen’s re-growth) during land application of
214
the product (Mullet et al., 1998). Lasaridi et al. (1998) define biological stability as a
215
characteristic that determinates the extent to which readily biodegradable organic matter has
216
been decomposed. Referred to compost, the stability is a quality parameter related to the
217
microbial decomposition or microbial respiration activity of the composted matter (Komilis et
218
al., 2009).
219
220
The DRI is based on the rate of oxygen consumption and is a useful indicator of the biological
221
stability of a sample. In this study, the DRI24h from wetland samples ranged between 1100
222
and 1400 mgO2∙kgTS-1∙h-1. Such a stability degree is much higher than the values reported in
223
the literature for a mixture of primary and activated sludge (6680 mgO2∙kgTS-1∙h-1) and for
224
anaerobically digested sludge (3740 mgO2∙kgTS-1∙h-1) (Pagans et al., 2006).
225
226
In a recent study, Ponsá et al. (2008) analysed the DRI of the organic fraction of municipal
227
solid wastes at different stages of a mechanical biological treatment. These authors observed
228
DRI values above 7000 mgO2∙kgTS-1∙h-1 for the input material, a decrease to around 1500
229
mgO2∙kgTS-1∙h-1 for digested material and near 1000 mgO2∙kgTS-1∙h-1 for composted material,
230
with a value of 1000 mgO2∙kgTS-1∙h-1 for the output material. Similarly, Scaglia and Adani
10
231
(2008) found values around 2500 mgO2∙kgTS-1∙h-1 for input samples around 1100
232
mgO2∙kgTS-1∙h-1 for intermediate samples and between 300-600 mgO2∙kgTS-1∙h-1 for the final
233
product of the stabilisation process.
234
235
If DRI values are expressed with respect to the organic matter content (VS) of the sample, the
236
values from wetlands’ biosolids correspond to 490 and 610 mgO2∙kgVS-1∙h-1. According to
237
Scaglia et al. (2000) and Adani et al. (2004), stability values of 1000 mgO2∙VS-1∙h-1 are
238
representative of medium compost. This is in accordance with compost classes I and II
239
proposed by the American Society for Testing and Materials (1996), while compost classes III
240
and IV have higher biological stabilities (<500 mgO2∙VS-1∙h-1).
241
242
From the comparison of the obtained results whith those of other systems, it seems that
243
biosolids from the studied treatment wetlands may be considered a partially (and almost)
244
stabilised material. Therefore it can be speculated that, with sufficient resting time, the final
245
product may be valorised in agriculture even without further post-treatment in a composting
246
plant. Consequently, this would result in additional reduction of sludge treatment costs.
247
248
3.3 Nutrients
249
250
Sewage sludge may provide essential nutrients for plant growth. Biosolids are able to restore
251
nitrogen, phosphorus, sulphur and other nutrients in soils. The concentration of nutrients in
252
biosolids depends on sewage composition and treatment used, and on subsequent sludge
253
treatment processes.
254
11
255
Although they are essential for plant growth, nutrients (particularly nitrogen and phosphorus)
256
can be harmful when excessively applied. Different works have proved nitrogen accumulation
257
in soil (Walter et al., 2000, Hernandez et al., 1990); as well as phosphorus increase in sludge-
258
amended soils (Hernandez et al., 1990). It is well known that over application of nitrogen can
259
lead to nitrate contamination of groundwater; although such a risk is reduced if nutrients are
260
applied at agronomic rates (Moss et al., 2002). The great solubility of nitrate poses a high
261
contamination hazard to groundwater and is the main reason why biosolids application in
262
agricultural land is usually limited by the nitrogen uptake crop capability. In this sense, the
263
application rate must not lead to nitrogen inputs greater than the crop nitrogen requirements,
264
in order to avoid leaching to occur (Andreoli et al., 2007).
265
266
The concentration of the main nutrients (nitrogen, phosphate and potassium) in wetland
267
biosolids is shown Table 2. The results are consistent with a previous study carried out at the
268
same facility (Uggetti et al., 2009).
269
270
Sludge’s nitrogen comes from microbial biomass present in sludge and from wastewater
271
residues. In this study, TNK values (Table 2) decrease about a 50% from the influent to the
272
biosolids (~4 %TS). The values of the final sludge are therefore within the range of activated
273
sludge (Andreoli et al., 2007). For compost of sewage sludge, Bertran et al. (2004) give
274
slightly lower TNK values (2.53 %TS). Even lower TNK values (1.5 %TS) are given for
275
aerobically digested sewage sludge used on land (Gascó and Lobo, 2007).
276
277
Phosphorus in sludge comes from biomass formed during wastewater treatment, residues and
278
phosphate-containing detergents and soaps. Biosolids can be seen as phosphorus source
12
279
assuring a slow and continued release to plants (Andreoli et al., 2007). In this study, TP
280
values show a clear decrease from the influent to treated sludge (0.08-0.28 %TS). The values
281
of the final product are within the range of digested sludge (Gascó and Lobo, 2007) and quite
282
lower than in composted sewage sludge (Bertran et al., 2004).
283
284
The concentration of potasium does not seem to vary along the treatment, with values ranging
285
between 0.18 and 0.62 %TS. These values are in accordance with sludge compost (Bertran et
286
al., 2004); but lower than in digested sludge (Gascó and Lobo, 2007).
287
288
In general, sludge is characterized by a considerable variability in nutrient’s content,
289
depending on the wastewater source and treatment process (Moss et al., 2002). The
290
concentration of nutrients is needed to ensure appropriate dosages of the sludge prior to land
291
application. The required agricultural doses are frequently dependent on the fertilizer and soil
292
characteristics (Pomares and Canet, 2001; Andreoli et al., 2007). Since nitrogen concentration
293
in biosolids usually meets the crop needs, application rates are generally calculated based on
294
the nitrogen requirements of each crop, whereas phosphorus and potasium can be
295
supplemented with chemical fertilisers (Andreoli et al., 2007).
296
297
3.4 Heavy metals and faecal bacteria indicators
298
299
The main hazard associated to sludge application on agricultural soils is the potential long
300
term accumulation of toxic elements (Singh and Agrawal, 2008), which may then be uptaken
301
by crops. Such elements include both inorganic pollutants, like heavy metals, and organic
302
micropollutants. Currently, however, only heavy metals concentrations are regulated for land
13
303
application of sewage sludge (Council of the European Union, 1986). Since treated sludge
304
may have considerable amounts of pathogens, depending on the treatment processes used,
305
limit values for faecal bacteria indicators have also been proposed (Environment DG, EU,
306
2000). According to this proposal, conventionally treated sludge has to contain ≤3 log10
307
E.coli·gTS-1, and Salmonella spp. has to be absent in 2 gTS.
308
309
Table 3 summarises the concentration of heavy metals and faecal bacteria indicators in the
310
treatment wetlands samples, together with the limits proposed in the3rd Draft EU Working
311
Document on Sludge (Environment DG, EU, 2000). There are only little differences between
312
influent sludge and the final product with regards to heavy metals, suggesting that heavy
313
metals accumulation is negligible. Furthermore, in all cases the concentrations are clearly
314
below the limits proposed, which are more restrictive than current legislation (Council of the
315
European Union, 1986).
316
317
Heavy metals bioavailability in soil and plants depends on the following parameters: soil pH,
318
plant species and their cultivars, growth stage, biosolids source, soil condition and the
319
chemistry of the element (Warman and Termeer, 2005). According to these authors, it is
320
important to monitor Cu and Zn contents of plant tissues after a few years of sludge
321
applications to verify the tolerance levels for animals and feed, or human food.
322
323
With regards to pathogens, it can be seen that Salmonella spp. was not detected (Table 3). On
324
the other hand, E. coli was present but in all cases in small quantities. Both faecal bacteria
325
indicators are well below the limits proposed.
326
14
327
4. Conclusions
328
329
This study looked at the properties of biosolids from sludge treatment wetlands
and
330
compared them with other stabilised products, such as anaerobic digested sludge and
331
compost. Focus was put on the quality of biosolids for its use on land as organic fertilisers and
332
soil conditioners. From this work, the following conclusions can be drawn.
333
334
In the full-scale wetlands studied, sludge water content (and volume) is reduced by 25 %,
335
from 99 to 75 %. Apparently, these results would be further improved by adjusting the sludge
336
loading rate to recommended values, which may reduce the moisture content to 60-70 %.
337
338
Organic matter biodegradation leads to VS around 45 %TS and COD around 500 g·kgTS-1 in
339
the final product, within the range of digested sludge but lower than in sludge compost.
340
Besides, DRI values (1000-1400 mgO2∙kgTS-1∙h-1) indicate a partly stabilised product, close
341
to a high stabilisation degree corresponding to the final product of a composting process. This
342
suggests that composting post-treatments would not be needed, if sufficient resting time
343
would be left at the end of the wetland’s cycle. Monitoring the stabilisation degree during the
344
final resting period would be advisable to minimise the duration of such a period.
345
346
The concentration of nutrients, heavy metals and faecal bacteria indicators suggest that the
347
final product would be suitable as organic fertiliser and soil conditioner.
348
349
On the whole, the studied system demonstrates the efficiency of sludge treatment wetlands for
350
sludge dewatering and stabilisation, with low treatment costs; and leading to a final product
15
351
which could be used on land without further post-treatment, reducing sludge management
352
costs. Characterization of similar systems would be advisable to corroborate these results.
353
354
Acknowledgements
355
356
This work was financed by the Catalan Water Agency (ACA) and the Spanish Ministry of
357
Environment (MMARM, Projects A335/2007 and 087/PC08). Technicians of Depuradores
358
d’Osona S.L. are greatly acknowledged for their support to this study. Enrica Uggetti kindly
359
acknowledges the Technical University of Catalonia and Esther Llorens the Juan de la Cierva
360
Programme of the Spanish Ministry of Education and Science (MEC). Joan García is grateful
361
to the School of Civil Engineering of Barcelona (ETSECCPB).
362
363
References
364
365
366
Adani, F., Lozzi, P., Genevini, P.L. (2000). Determination of biological stability by oxygen
uptake on municipal solid waste and derived products. Compost Sci.Util. 9, 163-178.
367
Adani, F., Confalonieri, R., Tambone, F. (2004). Dynamic Respiration Index as descriptor of
368
the biological stability of organic wastes, Journal of Environmental Quality 33, pp.
369
1866–1876.
370
Agència Catalana de l’Aigua (2007) La gestió de fangs de depuració d’aigües residuals
371
municipals a Catalunya. Evolució històrica i estratègia de futur (nou programa de
372
fangs). In: III Jornades Tècniques de Gestió de Sistemes de Sanejament d’Aigües
373
Residuals,
Barcelona,
Spain.
URL:
16
374
http://www.mediambient.gencat.net/aca/ca//agencia/agenda/jornades_tecniques003/po
375
nencies/inici.jsp
376
Andreoli, C.V, Pegorini, E.S., Fernandes, F., Santos H.F. (2007). Land application of sewage
377
sludge. In: Sludge treatment and disposal. Cleverson, Von Sperling & Fernandes Eds.
378
IWA Publishing, London, UK, 2007.
379
American Society for Testing and Materials. (1996). Standard test method for determining the
380
stability of compost by measuring oxygen consumption. D 5975-96. ASTM Int, West
381
Conshohocken, PA.
382
383
384
385
386
387
APHA-AWWA-WPCF (2001). Standard Methods for the Examination of Water and
Wastewater (20th ed.), American Public Health Association, Washington DC.
Barrena, R., D’Imporzano, G., Ponsá, S., Gea, T., Artola, A., Vázquez, F., Sánchez, A., Adani,
F. (2009). Journal of Hazardous Materials 162 (2-3), pp 1065-1072.
Bertrán, E., Sort, X., Soliva, M., Trillas, I. (2004). Composting winery waste: sludges and
grape stalks. Bioresource Technology 95, 203-208.
388
Consejo de Ministros (2001). Resolución de 14 de junio de 2001, de la Secretaría General de
389
Medio Ambiente, por la que se Dispone la Publicación del Acuerdo de Consejo de
390
Ministros, de 1 de junio de 2001, por el que se Aprueba el Plan Nacional de Lodos de
391
Depuradoras de Aguas Residuales 2001-2006. Boletín Oficial del Estado 166, de 12
392
de julio de 2001.
393
Burgoon, P.S., Kirkbride, K.F., Henderson, M. and Landon, E. (1997). Reed beds for biosolids
394
drying in the arid Northwestern Unitated States. Water Science and Technology 35 (5),
395
287-292.
17
396
Caselles-Osorio, A., Puigagut, J., Segú, E., Vaello, N., Granés, F., García, D. and García, J.
397
(2007). Solids accumulation in five full-scale subsurface flow constructed wetlands.
398
Water Research 41 (6), 1388-1398.
399
400
Cole, S. (1998). The Emergence of Treatment Wetlands. Environmental Science and
Technology A-Pages 32 (9), 218A-223A.
401
Council of the European Union (1986). Council Directive 86/278/EEC of 12 June 1986 on the
402
Protection of the Environment, and in Particular of the Soil, when Sewage Sludge is
403
Used in Agriculture. Official Journal of the European Union L 181, 04/07/1986, 6-12.
404
Council of the European Union (1991). Council Directive 91/271/EEC of 21 May 1991
405
Concerning Urban Wastewater Treatment. Official Journal of the European Union L
406
135, 30/05/1991, 40-52.
407
Council of the European Union (1991). Directive 2000/60/EC of the European Parliament and
408
of the Council of 23 October 2000 Establishing a Framework for the Community
409
action in the Field of Water Policy. Official Journal of the European Union L 327,
410
30/05/1991, 1-73.
411
Draeger, K., Pundsack, J., Jorgenson, M., Mulloy, W.E. (1999). Watershed Effects and
412
Biosolids Land Application: Literature Review. Water Environmental Research
413
Foundation. Project 96-REM-2.
414
Edwards, J.K., Gray, K.R., Cooper, D.J., Biddlestone, A.J. and Willoughby, N. (2001). Reed
415
bed dewatering of agricultural sludges and slurries. Water Science and Technology 44
416
(11-12), 551-558.
417
418
Environment DG, EU. (2000). Working Document on Sludge 3rd Draft. URL:
http://ec.europa.eu/environment/waste/sludge/pdf/sludge_en.pdf.
18
419
420
Environment DG, EU. (2001). Working Document on Biological Treatment of Biowaste 2nd
Draft. URL: http://ec.europa.eu/environment/waste/sludge/pdf/sludge_en.pdf.
421
Ferrer, I. (2008) Study of the Effect of Process Parameters on the Thermophilic Anaerobic
422
Digestion of Sewage Sludge, Evaluation of a Thermal Sludge Pretreatment and
423
Overall Energetic Assessment. PhD Thesis, Universitat Autònoma de Barcelona
424
(Spain), 160 pp.
425
Ferrer I., Ponsá S., Vázquez F., Font, X. (2008). Increasing biogas production by thermal (70
426
ºC) sludge pre-treatment prior to thermophilic anaerobic digestion. Biochemical
427
Engineering Journal 42 (2), 186-192.
428
429
430
431
Fytili, D. and Zabaniotou A. (2008). Utilization of sludge in EU application of old and new
methods – A review. Renewable & Sustainable Energy Reviews 12, 116-140.
Gascó, G., Lobo, M.C. (2007). Composition of a Spanish sewage sludge and effects on
treated soil and olive trees. Waste Management 27, 1494-1500.
432
Hernández, T., Moreno, J.I., Costa, F. (1999). Influence of sewage sludge application on
433
croop yields and heavy metals avaylability. Soil Science & Plant Nutrition 37 (2), 201-
434
210.
435
436
437
438
Komilis, D. P., Tziouvaras I. S. (2209). A statistical analysis to assess the madurity and
stability of six composts. Waste Management 29, 1504-1513.
Lasaridi, K.E., Stentiford, E. I. (1998). A simple respirometric technique for assessing
compost stability. Water Research 32, 3717-3723.
439
Moss, L.H., Epstein, E., Logan, T. (2002). Evaluating Risks and Benefits of Soil Amendments
440
Used in Agriculture. International Water Association and Water Environmental
441
Research Foundation (co-ed.). Alexandria VA.
19
442
443
444
445
Mujeriego, R. and Carbó, M. (1994). Sludge Reuse in Agriculture (In Catalan). Technical
Report. Consorci de la Costa Brava. Girona (Spain).
Muller, W., Fricke, K., Vogtmann, H. (1998). Biodegradation of organic matter during
mechanical biological treatment of MSW. Compost Science and Utilization 6, 42-52.
446
Nielsen, S. (2003a). Sludge drying reed beds. Water Science and Technology 48 (5), 101-109.
447
Nielsen, S. (2003b). Sludge treatment in wetland systems. In: The Use of Aquatic
448
Macrophytes for Wastewater Treatment in Constructed Wetlands. . 8-10 May. Dias V
449
and Vymazal J. (ed). Lisbon (Portugal).
450
451
Nielsen, S. and Willoughby, N. (2005). Sludge treatment and treatment wetlands systems in
Denmark. Water and Environmental Journal 19 (4), 296-305.
452
Obarska-Pempkowiak, H., Tuszynska, A., Sobocinski, Z. (2003). Polish experience with
453
sewage sludge dewatering in reed systems. Water Science & Technology 48 (5), 111-
454
117. Oleszkiewicz, J. A. and Mavinic, D. S. (2002). Wastewater biosolids: an overview
455
of processing, treatment and management. Journal of Environmental Engineering
456
Science 1, 75-88.
457
Pagans, E., Barrena, R., Font, X., Sánchez, A. (2006). Ammonia emissions from the
458
composting of different organic wastes. Dependency on process temperature.
459
Chemosphere 62 (9), 1534-1542.
460
Pomares, F., and Canet, R. (2001). Organic Waste Utilization in Agriculture: Origin,
461
Composition and Characterization (In Spanish). Boixadera J. and Teira M.R. (ed.).
462
Lleida (Spain).
463
Ponsá, S., Gea, T, Alerm, L., Cerezo, J., Sánchez, A. (2008). Comparision of aerobic and
464
anaerobic stability indices throught a MSW biological treatment process. Waste
465
Management 28 (12), 2735-2742.
20
466
467
468
469
Reed, S.C., Crites, R.W. and Middlebrooks, E.J. (1988). Natural Systems for Waste
Management and Treatment. McGraw Hill Book Co., 261.
Scaglia B., Tambone, F., Genevini, P.L., Adani F. (2000). Respiration index determination: a
dynamic and static approach. Compost Science and Utilization 8 (2), 90–98.
470
Scaglia, B., Adani, F. (2008). An index for quantifying the aerobic reactivity of municipal
471
solid wastes and derived waste products. Science of the Total Environment 394, 183-
472
191.
473
474
475
476
Singh, R.P., Agrawal, M. (2008). Potencial enefits and risks of land application of sewage
sludge. Waste Management 28, 347-358.
Soliva, M. (2001). Composting and Management of Organic Residues (In Catalan). Estudis i
Monografies 21. Diputació de Barcelona. Barcelona (Spain).
477
Uggetti, E., Llorens, E., Pedescoll, A., Ferrer, I., Castellnou, R., García, J. (2009). Sludge
478
dewatering and stabilization in drying reed beds: characterization of three full-scale
479
systems in Catalonia, Spain. Bioresource Technology 100, 3882-3890.
480
481
Uggetti, E., Ferrer, I., Llorens, E., García, J. (2010). Sludge treatment wetlands: a review on
the state of the art. Bioresource Technology, submitted.
482
Walter, I., Cuevas, G., García, S., Martínez, F. (2000). Biosolid effects on soil and native plant
483
production in a degraded semiarid ecosystem in central Spain. Waste Management &
484
Research 18 (3), 259-263.
485
Warmar, P.R., Termeer, W.C. (2005), Evaluation of sewage sludge, septic waste and sludge
486
compost applications to corn and forage: Ca, Mg, S, Fe, Mn, Cu, Zn and B content of
487
crops and soils. Bioresouce Technology 96, 1029-1038.
488
Yubo, C., Tieheng, S., Lihui, Z., Tingliang, J., Liping, Z. (2008). Performance of wastewater
489
sludge ecological stabilization. Journal of Environmental Sciences 20, 385-389.
21
490
491
Zwara, W. and Obarska-Pempkowiak, H. (2000). Polish experience with sewage sludge
utilization in reed beds. Water Science and Technology 41 (1), 65-68.
492
22
493
Table 1. Characteristics of the WWTP in Seva (Catalonia, Spain).
Treated population equivalent
Type of treatment
1500
Contact-stabilisation
Wastewater flow rate (m3/d)
180 (summer) / 400 (winter)
Sludge production (kg TS/d)
60
Number of treatment wetlands (beds)
7
Total surface area (m2)
175
Nominal height for sludge accumulation (m)
~0.8
Sludge loading rate (kg TS/m2·year)
125
494
495
23
496
Table 2. Physico-chemical properties of influent sludge and biosolids from treatment
wetlands.
Parameter
Influent
Wetland 1
Wetland 2
pH
6.75
6.21
6.27
EC 1:5 (dS/m)
0.3
1.51
1.88
1.1 ± 0.0
24.2 ± 0.6
25.8 ± 2.1
VS (TS%)
51.5 ± 0.8
42.9 ± 1.8
44.6 ± 3.0
COD (g·kgTS-1)
709 ± 11
554 ± 32
494 ± 55
-
1400 ± 300
1100 ± 200
TKN (%TS)
9.76
4.02
4.87
TP (%TS)
2.68
0.13
0.39
K (%TS)
0.27
0.18
0.62
Physical properties
TS (%)
Organic matter
DRI24h (mgO2∙kgTS-1∙h-1)
Nutrients
497
Note: TS, VS and COD were analysed in triplicate; DRI was analysed in duplicate.
498
24
499
Table 3. Concentration of heavy metals and faecal bacteria indicators in influent sludge and
biosolids from treatment wetlands.
Parameter
Influent
Wetland 1
Wetland 2
Limit values
Heavy metals
Cr (ppm)
51
55
59
800
Ni (ppm)
39
30
32
200
Cu (ppm)
252
318
213
800
Zn (ppm)
719
588
641
2000
Cd (ppm)
1.7
0.8
0.8
5
Hg (ppm)
<1.5
<1.5
<1.5
5
Pb (ppm)
53
73
76
500
Absence
Absence
Absence
Absence in 50g
<3
<3
<3
<500 MPN·g-1
Faecal bacteria indicators
Salmonella spp.
(presence/absence in 25g)
E. coli (MPN·g-1)
500
Note: Limit values proposed in the 3rd Draft EU Working Document on Sludge (Environment
501
DG, EU, 2000).
502
25