1. Stabilization of bio-organic waste from farms by composting with rice straw
Soriano MD1, García-España L2, Lull C3, Boluda R2
1Department of Plant Production. Universitat Politècnica de València. Cami de Vera s/n València, Spain,
2Department of Plant Biology. Universitat de València. Andrés Estelles s/n Burjassot, València, Spain
3Department of Chemistry. Escuela Politècnica Superior de Gandía. Paranimf 1, Grau de Gandía, Spain
Abstract
Rice straw were used to recycle poultry manure (GA) and pork slurry (PU) in small-scale laboratory experiments. Pork slurry composts (PU) showed higher humus, nutrient and total metal contents, and greater electrical conductivity than poultry manure (GA).
The humus obtained showed lower content in organic matter, higher content in nutrients, lower quantity of metals, and less electrical conductivity (EC) than the initial products. With differences depending on the percentage of residue added.
The high concentration of metals and the high electrical conductivity of the initial mixtures of pig slurry explains the reduced reduction of metals in the pork slurry, with greater reduction of the final volume and its concentration. While low EC values and high phosphorus available are obtained in the manure's transformed waste. Composting is an efficient technology for recycling bio-waste, but the quantity and composition of the salts in the mixtures influence the quality of the final products.
Our study is based on the combination of pork manure and manure residues mixed with vegetable waste such as rice straw. Being the objectives of this study: (i) to test the viability of the mixture of rice straw with these farm wastes from pigs and hens to different ratios, and the evaluation of the final product, (ii) its valorization according to the load in heavy metals.
Results
The initial mixes also showed significant differences in nutrient content according to the type and dose of added bio-residue. The contents of C were high for the CoPUi and for the mixtures of bio-wastes in higher doses, their values oscillated between 408 g kg-1 (CoPUi) at 332 g kg-1 (GA2i). The intermediate organic carbon values ( g kg-1) corresponded to the resulting mixtures of GA1i and PU1i, and the organic carbon content corresponded to the final mixtures GA2f and CoGAf ( g kg-1).
The TKN were high for CoGAi and CoPUi controls and increased with dose with 23 g kg-1 in GA1f and 28 g kg-1 in PU2f. The lower TKN were for mixtures GA1f and PU1f (19-25 g kg-1). Finally, the amounts of avP2O5 were higher for controls and mixtures of bio-waste at the lowest dose (from 4.13 to 4.47 g kg-1). The avP2O5 for the remaining GAi and PUi mixtures oscillated between 5.23 and 6.03 g kg-1. According to the contents of OC, TKN and AvP2O5, the CoAGi and the final mixtures with low quantities of bio-wastes present reasons of C:N ratio around 14.
According to the total metallic content, it makes them between classes A and B. PU2f and PU1f and GA2f would be included in class B due to a total Cd (II) content slightly higher than 0.7 mg kg-1 (table 1 and 2). However, more than the total metallic content, the real concern of metals is their bioavailability, which facilitates their movement in agricultural land in the final products. Salinity can be one of the main parameters that favor it (Tittarelli et al. 2003). By observing the values of pure grubbing residues, pig manure has a high sodium content, which could eventually cause or aggravate salinity problems in some soils.
Table 1. Properties of the initial mixtures the rice straw with, poultry manure (GA) or pork slurry (PU); GA1 to GA2 poultry manure mixed with rice straw at 15, and 30%, respectively. PU1 to PU2: rice straw mixed with pork slurry (PU) at 15 and 30%.
Parameter
GA1i
GA2i
PU1i
PU2i
CoGAi
CoPUi
Moisture %
51 (3)
43 (5)
82 (2)
83 (6)
91 (4)
OC g kg-1
322 (22)
362 (26)
302 (12)
358 (23)
401 (15)
408 (24)
pH 1:2.5
7.6 (0.3)
7.9 (0.1)
8.3 (0.2)
9.1 (0.3)
9.4 (0.2)
EC1:5 dS m-1
2.8 (0.2)
3.9 (0.1)
6.1 (0.2)
9.0 (0.1)
11.7 (0.2)
TKN g kg-1
21 (2)
22 (2)
30 (2)
33 (2)
20 (2)
26 (3)
avP2O5 g kg-1
6.47 (0.15)
5.23 (0.15)
4.27 (0.15)
5.67 (0.31)
6.03 (0.25)
4.13 (0.15)
C:N
17 (1)
16 (1)
10 (2)
11 (2)
20 (1)
Ca mg kg-1
3.8 (0.1)
0.9 (0.2)
2.6 (0.5)
5.9 (0.3)
Na mg kg-1
0.8 (0.1)
1.8 (0.2)
3.6 (0.3)
3.9 (2)
Cu mg kg-1
118 (14)
139 (22)
128 (2)
126 (5)
188 (26)
159 (2)
Zn mg kg-1
266 (35)
332 (34)
129 (14)
98 (13)
407 (53)
248 (30)
Ni mg kg-1
16.3 (2.0)
20.9 (3.3)
4.8 (0.1)
5.7 (0.3)
12.9 (5.9)
27.7 (8.9)
Cd mg kg-1
0.9 (0.1)
0.9 (0.0)
1.8 (0.1)
1.9 (0.1)
1.4 (0.2)
1.7 (0.3)
Table 2. Properties of the final mixtures the rice straw with, poultry manure (GA) or pork slurry (PU); GA1 to GA2 poultry manure mixed with rice straw at 15, and 30%, respectively. PU1 to PU2: rice straw mixed with pork slurry (PU) at 15 and 30%.
Conclusions All the analyzed materials presented values of their parameters of humification that allow to locate them like materials of good quality and with good degree of maturity, even if there are small variations between them. This would allow agricultural use without greater risk of impact to the environment and to the life of soil organisms. In the results it is concluded that manure is the most suitable material, from the point of view of use as fertilizer, since its parameters indicate that a more efficient mineralization process would occur.
Parameter
GA1f
GA2f
PU1f
PU2f
CoGAf
CoPUf
Moisture %
42 (1)
44 (3)
42 (3)
43 (1)
43 (3)
48 (6)
OC g kg-1
236 (7)
331 (7)
345 (20)
246 (9)
307 (11)
332 (20)
pH 1:2.5
7.1 (0.2)
7.5 (0.1)
7.6 (0.3)
7.8 (0.1)
8.1 (0.1)
8.2 (0.3)
EC1:5 dS m-1
1.6 (0.4)
1.8 (0.2)
2.9 (0.2)
2.9 (0.1)
4.1 (0.1)
4.2 (0.2)
TKN g kg-1
19 (1)
23 (2)
26 (2)
25 (2)
28 (1)
avP2O5 g kg-1
4.03 (0.46)
4.23 (0.74)
5.15 (0.15)
3.40 (0.50)
3.90 (0.26)
4.09 (0.30)
C:N
13 (0)
11 (1)
13 (1)
9 (1)
10 (1)
13 (2)
Ca mg kg-1
0.8 (0.2)
1.6 (0.3)
1.8 (0.1)
2.2 (0.2)
3.9 (0.5)
Na mg kg-1
0.4 (0.0)
0.6 (0.1)
0.8 (0.1)
1.2 (0.1)
2.1 (0.2)
4.8 (0.3)
Cu mg kg-1
112 (2.0)
115 (1.30)
187 (3.8)
196 (5.0)
226 (4.3)
187 (12.0)
Zn mg kg-1
1.5 (0.1)
2.9 (0.1)
2.3 (0.1)
2.3 (0.1)
Ni mg kg-1
1.0 (0.0)
1.5 (0.3)
1.03 (0.5)
2.2 (0.3)
2.2 (0.1)
1.78 (0.2)
Cd mg kg-1
0.2 (0.1)
0.9 (0.1)
1.1 (0.3)
1.2 (0.2)