Paula Alvarenga1, Débora Rodrigues2, Clarisse Mourinha2, Patrícia Palma2,3*,

Amarílis de Varennes1, Nuno Cruz4, Luís A.C. Tarelho5, and Sónia Rodrigues4

1LEAF Research Unit, Instituto Superior de Agronomia, Universidade de Lisboa, Portugal2Depto. de Biociências, Escola Superior Agrária, Instituto Politécnico de Beja, Beja, Portugal, *E-mail contact: ppalma@ipbeja.pt

3ICT, Institute of Earth Sciences, University of Évora, Rua Romão Ramalho 59, Évora, Portugal4CESAM & Departamento de Química, Universidade de Aveiro, 3810-193 Aveiro, Portugal

5CESAM & Departamento de Ambiente e Ordenamento, Universidade de Aveiro, 3810-193 Aveiro, Portugal

Mining was an important activity for the socioeconomic development of Portugal, but it gave rise to the

appearance of large degraded areas, with: (i) Abnormally acid soils, (ii) high levels of potentially toxic trace

elements (e.g. Cu, Pb, Zn), and (ii) poor nutritional conditions.

On the other hand, the wastes produced in the pulp and paper industry, including biological sludge from

wastewater treatment and fly ashes from biomass combustion, present a composition with potential to be

used in the in situ remediation of these contaminated soils.

▪To evaluate the use of biomass ash and biological sludge, in different granular formulations, to improve

the quality of soils affected by mining activities (Aljustrel mine, Iberian Pyrite Belt, IPB).

▪To evaluate the need to apply an organic amendment (e.g. compost), to overcome the OM and N

deficiency.

▪To evaluate the possibility of establishing a plant cover in the amended soils with Agrostis tenuis Sibth.

1. Effects on soil chemical characteristics (Cont.)

▪ Contrary to non-amended control pots, it was possible to establish a plant cover with A. tenuis

in the amended soils, but some phytotoxic effects were observed over time, which could

possibly be attributed to the increase in the concentrations of soluble ions, like Na+ and Cl-,

whose extractable concentrations increased about 30x and 10x times, respectively, with the

higher amendments application rates.

▪ The simultaneous application of mineral fertilization and compost is necessary, to fully

overcome the deficiencies in OM, as well as in available N and P.

▪ It was possible to reduce the potentially toxic trace elements mobility in soil, and to correct its

acidity.

▪ It was possible to improve soils quality, as evaluated by soils enzymatic activities.

▪ It was possible to reduce the toxic response towards some aquatic organisms (the soils

retention function was improved).

▪ The investigation should proceed, using plants with higher resistance to salinity, or decreasing

the biomass ash application doses.

ACKNOWLEDGMENTS: This research was funded by Life No_Waste - LIFE14 ENV/PT/000369- “Management of biomass ash and organic waste in the recovery of degraded soils:

a pilot project set in Portugal”, and through the research units LEAF (UID/AGR/04129/2013) and CESAM (UID/AMB/50017/2013).

1. Effects on soil chemical characteristics (Fig. 1)

▪The amendments significantly increased soil pH, relatively to non-amended soil, to values between 6-

7.

▪The increase in soil salinity was small, but more marked with he simultaneous use of compost.

▪The mine soil had very low OM content (0.6%). That value only significantly increased with the

application of the higher dose of the granules (10% w/w 30S70A), or with the simultaneous application

of compost.

▪Mineral fertilization increased nitrogen (NKJ) content,

▪Compost application was very important to overcome OM and N deficiency.

▪Biomass ash and biological sludge granules were very effective to correct “available” P and K

deficiency, to high values for “available” P (101-200 mg kg-1 P2O5), and to “very high values” for

“available” K (> 200 mg kg-1 K2O).

▪Compost application was only important for the “available” P increase.

DWTR

allowed the selection of two different types of granules, and their

application rates:

▪10S90A: 10% cellulosic sludge + 90% biomass ash, and

▪30S70A: 30% cellulosic sludge + 70% biomass ash.

▪Indicated the need to apply mineral fertilization with N and P.

▪Suggested the evaluation of the simultaneous application of the equivalent to 50 t ha-1 of compost

(mixed municipal solid waste compost, MMSWC).

▪Pots with 1 kg of soil (4 replicates per treatment),

•Application rates 2.5, 5 and 10% (w/w), of both granules,

•Non-amended soil (S) and soil with mineral fertilization (SF) were used as controls.

•Soil + amendments were watered to 60% WHC in one day, and roughly mixed in the next day.

•After an incubation period of 20 d, pots were sown with Agrostis tenuis,

•All pots, except the control, received a basal dressing of N and P.

•Two months after growing, outdoors, occasionally watered, soils and plants were analyzed.

•Soil characteristics: pH(H2O), EC, OM, NKjeldahl, extractable P and K.

•Total and leachable trace elements in soils: aqua-regia digestion and the soil water-extract (1:10

w/v), obtained with the DIN 38414-S4 (1984) method.

•Soil enzymatic activities: dehydrogenase, β-glucosidase, acid-phosphatase, cellulase, protease and

urease.

•The capacity to establish a plant cover with Agrostis tenuis.

•Soil ecotoxicological bioassays with the soil-water extracts: (i) luminescence inhibition of Vibrio

fischeri; (ii) 24-h mortality test with Thamnocephalus platyurus; and (iii) 72-hours population growth of

the green microalgae Pseudokirchneriella subcapitata.

acid soil (pH 5.0), with high electrical conductivity (EC 2.7 mS

cm-1), low OM content (0.6% DM), and high trace element content (1420 mg Cu kg-1, 1195 mg Pb kg -1 and

681.0 mg Zn kg-1, DM).

Biomass ash (from the combustion of

forest residues) can correct some nutrient

deficiencies (K, P, Mg and Ca), and are

alkaline (pH 9-13), which can improve the

buffering capacity of acid soils…

… but, they are insufficient to provide

OM and N to mine soils.

Their combination with biological sludges

(cellulosic sludges), from the paper mill

wastewater treatment plant, can

overcome that deficiency.

The co-granulation of

biomass ash with biological

sludges, can produce a

material easier to transport

and to apply (especially for

fly ashes).

1-1,5 cm

pH EC

a

a a a

ab

a

a

bcd

abc

cde

def

def

efg

def

fg

g

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

OM

(%

, g/1

00

g D

M)

Without compost With compost

OM (%)

a

b b b

bc

b b

c

c

d d

d

d d

d d

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

NK

j (%

, g/1

00

g D

M)

Without compost With compost

NKJ (%)

a

ab

abc b

cd

def

bcd

de

hij

cde

efg

fgh

gh

i

j

fgh

ij

k

0

50

100

150

200

250

Pex

trac

(mg P

2O

5kg

-1D

M)

Without compost With compost

Pextractable Kextractable

Figure 1 – Effects of the treatments on soil physicochemical characteristics (mean ± standard deviation, n=4). Columns marked with the

same letter are not significantly different (Tukey test, p>0.05).

Soil-water extract pH CuextractableZnextractable

Extractable Pb, Cr, Cd and Ni were very low, below the limits of detection of the technique: LD(Pb) =

0.17 mg/L; LD(Cr) = 0.17 mg/L; LD(Cd) = 0.01 mg/L; LD(Ni) = 0.03 mg/L.

3. Effects on soil-water extract chemical properties and

trace elements leachability

2. Effects on soil enzymatic activities

Dehydrogenase -glucosidase

Acid-phosphatase Cellulases

The improvement in soil quality

was evidenced by the increase

in the enzymatic activity of

dehydrogenase, an overall

indicator of microbial activity,

and by the activity of both

enzymes from the C-cycle, -

glucosidase and cellulases

(very active because of C-

content of the cellulosic

sludges.

Acid-phosphatase was not so

affected by the amendments

application, and protease and

urease activities remained very

low, below the detection limits.Figure 2 – Effects of the treatments on soil soil enzymatic activities (mean ± standard deviation,

n=4). Columns marked with the same letter are not significantly different (Tukey test, p>0.05).

4. Effects on soil-water extract ecotoxicity

P. Subcapitata growth inhibition

Figure 3 – Effects of the treatments on soil-water

extract toxicity towards P. subcapitata (% growth

inhibition) (mean ± standard deviation, n=3).

Table 1 – Effects of the treatments on soil-water

extract toxicity (mean ± standard deviation, n=3). ▪ In general, the

amendments decreased

the toxicity of the soil-

water extracts towards

the organisms used.

▪ The beneficial effects of

the compost application,

when simultaneously used

with the granules, was not

evident.