de um compostado
Sousa1,*, J.R.; Fraga2, I.; Netto3, F.O.J.; Coutinho,1 J.
1Centro de Química, Dep. Biologia e Ambiente, Universidade de Trás-os-Montes e Alto Douro, Ap. 1013, 5001-911, Vila Real,
Portugal. e-mail: jricardo@utad.pt.
2CITAB, Universidade de Trás-os-Montes e Alto Douro, Ap. 1013, 5001-911, Vila Real, Portugal. 3EMA – Engenharia e Manutenção Ltda, São Paulo, Brasil
Abstract
Composting is considered as a biological technique stabilization of the organic wastes in order to make their soil application more environmental friendly.However, the quality of the material, evaluated by bioindicators, capable of reflecting the changes that occur during the process, is not taken into consideration by most of the producer agents. Thus, it is a necessary task to use indices capable to reflec the final quality of composted in order to make soil application more environmentally friendly. The work presented aims to evaluate the final quality of three com- posted produced in different regions of Brazil (Mato Grosso, MG; Florianópolis, FLO; and Campos Jordão, CJ), based on their degree of stability performed throught the activity of enzymes related to the cycles of C, N and P (β-glucosidase, β-glucosaminidase, arginine desaminase, urease, alkaline and acid phosphatase).Physico- chemical parameters were also determined in order to relate them to the enzymatic activities studied. The results revealed a similarity between the enzymes studied and chemical parameters as the N-NH4+/N-NO3- ratio, also
used as an indicator of quality, with the respectives values increase according to MG<CJ<FLO order. The en- zymes activities revealed high sensitivity to different processing conditions that occurred in the composting pro- cess and can be used as anbioindicator of compost stability.
Keywords: compost, stability, mineralization, bioindicators, enzymes. Resumo
A compostagem é tida como uma técnica biológica de estabilização de resíduos orgânicos de modo a tornar a sua aplicação ao solo mais eco-compatível. Todavia, a estabilidade do material final, avaliada por bioindicadores capazes de refletir as transformações que ocorrem durante o processo, não é tida em consideração pela maioria dos agentes produtores. Deste modo, torna-se obrigatória a utilização de índices capazes de refletir aquela qua- lidade final, de forma a tornar mais segura a sua aplicação ao solo ou a sua utilização como substratos. O traba- lho agora apresentado tem como objetivo a avaliação da qualidade final de 3 compostados produzidos em dife- rentes regiões do Brasil (Mato Grosso, MG; Florianópolis, FLO; e Campos Jordão,CJ), com base no respetivo grau de estabilidade, avaliado através da atividade de enzimas relacionadas com os ciclos do C, N e P (β-
glucosidade, β-glucosaminidase, argininadesaminase, urease, fosfatase ácida e alcalina). Parâmetros físico-
químicos foram igualmente determinados de modo a relacioná-los com a atividade enzimática. Os resultados revelaram uma similitude entre as enzimas estudadas e parâmetros químicos como a razão N-NH4+/N-NO3-
,também usada como indicador de qualidade, com os respetivos valores a aumentar segundo a ordem MG<CJ<FLO.A atividade enzimática revelouelevada sensibilidade às diferentes condições de transformaçãoem que ocorreram os processos de compostagem, podendo ser usada como indicador de estabilidade.
194 Introduction
The organic residues applied to the soil are considered a valuable resource, providing organic matter and nutrients, offering a low cost alternative to mineral fertilizers [1]. However, high waste production has result- ed in inadequate pratical soil application, promoting the appearing of environmental and nutritional cultures problems.
Composting has been used as a transfor- mation technique of organic residues, in order to minimize environmental problems associated with their management [2]. How- ever, assessed in terms of stability and ma- turity throught biological indicators, capable to reflecting the transformations accured during the process, the final quality of the compost is not taken into account by pro- ducing agents. Thus, it is required to use indexes able to reflect the final quality of the compost, in order to make more secure their application to soil or their use as substrates. There are several techniques to evaluate the final quality of compostes[3, 4]. Among these, the respirometric tests are the most widely used, since it reflects more accurately the transformation of organic matter during the composting process [5].Despiste the high accuracy, this technique lacks pratical application in routine laboratory work due to its time consuming and low exequibility. Alternatively, other techniques have been successfully tested in assessing the quality of compost involving the quantification of enzyme activity [6, 7]. These indicators may reflect the dynamics of the composting pro- cess in terms of the transformation of organ- ic matter and elements as N, P and S [8], providing information of stability of the com- post with more feasible form [7].
Thus, the present work aims to evaluate the final quality of three composts pro- duced in different regions of Brazil (Mato Grosso, Florianópolis and Campos Jordão), based in their degree of stability assessed by the activity of enzymes relat- ed to the cycles of C, N and P (β- glucosidade, β-glucosa-minidase, arginine desaminase, urease, alkaline and acid phosphatase). Physical and chemical pa- rameterswere determined in order to relate them to the enzyme activities.
Material and methods
Three composts were sampled in compost- ing systems developed in different regions of Brazil: (i) Mato Grosso (MG), (ii) Florianópo- lis (FLO) and (iii) Campos Jordão (CJ). The composts were obtained in open systems, conducted in windrows, with approximate dimensions of 2,0x1,0x0,7 m of length, width and height, respectively. Periodic controls of moisture and aeration were performed dur- ing the 180 days of composting. Aeration was performed manually in MG and CJ sys- tems, with periodic turning of the piles, while in FLO a static system was implemented, without turning. At the end of the process a composited sample, resulted of various sub- samples collected in different zones and depths of the pile, was taken to chemical characterization, with results being present- ed in Table 1.
Table 1 – Physical-chemical characteristics of the
composts under studied.
To evaluate the biological stability of the composts was determined the activity of several enzymes related to the cycles of C, N and P, namely the β-glucosidade, β- glucosaminidase, arginine desaminase, urease and alkaline and acid phosphomo- noesterases, applying the procedures de- scribed by [9, 10, 11].
A variance analysis was performed to as- sess the effect of compost nature in the ac- tivity of each studied enzyme, for a probabil- ity level of 95%. The mean values were separated by Tukey test, based on the de- termination of honest significant difference (HSD) for the same level of probability (α=0.05).
Results and discussion
The results showed a significant effect (p<0.05) of composts nature in the enzymat-
Parameter MG FLO CJ H2O (g kg-1) 119,2 550,8 337,7 pH (H2O) 7,4 8,0 7,6 pH (KCl 1M) 6,6 7,3 7,1 Cond. Elet. (dS m-1) 0,18 1,33 2,09 C (g kg-1) 394,5 446,7 377,3 N (g kg-1) 10,1 25,3 14,3 P (g kg-1) 0,8 4,9 4,4 NH4+-N (mg kg-1) 41,3 661,8 33,3 NO3--N (mg kg-1) 268,8 52,8 150,8 NH4+-N:NO3--N < 1,0 > 1,0 < 1,0 C:N 39,1 17,7 26,4
ic activity. All studied enzymes showed the same trend, with their values increase in the order MG<CJ<FLO.
In the β-glucosidase, specific enzyme of the C cycle [12], the registered activity values in CJ and FLO was, respectively, 1.3 and 5.1 times higher than in MG. In turn, the en- zymes relating with N cycle as arginine desaminase and urease, showed same order values increase between studied composts. Both enzymes registered lower activity val- ues in MG. For the others composted a sig- nificant increase activity was observed, with average values of 4.6 in FLO and 2.3 in CJ. In the β-glucosaminidase, the differences between the MG compost and FLO and CJ proved to be even higher. This enzyme, involve in the degradation of carbohy- drates, such as hemicelluloses and cellu- lose, or glycoproteins [12], registered in the FLO and CJ composts an activity value, respectively, 13.2 and 3.6 times higher than in MG compost.
For enzymes related to the P cycle, acid and alkaline phosphatases, the highest activity values were observed in FLO composted. In the CJ compost, the alka- line and acid phosphatase activities repre- sent 37.3% and 47.4% while in MG 12.6% and 15.6% of observed activity in FLO, respectively.
The results showed significant differences in enzyme activities between the studied composts, explained by the conditions that influence the transformations of organic matter during the respective processes. Static systems as the FLO, due to lower availability of O2, severely limit microbial
activity compared with systems with revolv- ing applied as CJ and MG, promoting a higher preservation of organic matter [13], as suggest the respective C and N content (Table 1). In FLO compost, the value of NH4+-N:NO3--N ratio superior to 1, indicator
of low biological stability [14], may reflect the presence of labile compounds such pro- teins, carbohydrates and fatty acids that inducing a higher enzyme activity than in CJ and MG composts.
This is corroborated by [15] and [13] that, respectively, observed an increment of en- zyme activity such as β-glucosidase, β-
glucosaminidase and urease and arginine desaminase in the initial phase of compost- ing process, in wich predominates labile compounds that decreasing with the respec- tive deplection until the maturity phase. Also associated with composting conditions, the moisture content can also influence the enzymatic activity. Authors as [16] observed that activity of enzymes like urease and argi- nine desaminase are more affected by lower moisture conditions, which help to explain the minor activities of these enzymes in MG compared to CJ and FLO composts.
The presence of microorganisms, such fun- gi, it is also strongly dependent of moisture levels [13]. The lowest moisture level of the MG compost (Table 1) can also explain the minor activity of β-glucosidase, since the respective production is dependent of the presence of these microorganisms [15]. For the enzymes relating with P cycle, the results revealed a similar trend among them and in relation to others studied enzymes. Despite the alkaline conditions registered in all composts (Table 1), acid and alkaline phosphatase activities are similar, with both enzymes to regist a higher activity in FLO compost. The high acid phosphatase ob- served under these conditions may be as- sociated with the formation of enzyme- humus complex, improving the resistence of enzyme to desnaturation phenomena [7]. This fact can reveal a more sensitivity of these enzymes to the bioavailability of the compounds than the pH values in the com- posts.
Conclusions
The results revealed that the enzymes are inducible indicators, with their activity related to the chemical quality of composts resulting of organic matter transformations influenced by evolution of the respective physical, chem- ical and biological conditions. All enzymes studied showed high sensitivity in assessing the stability of composts with the respective variation followed other indices used in quali- ty compost evaluation, as NH4+-N:NO3--N
ratio. Thus, due to sensibility to different composted conditions, enzymes can be used as bioindicators of the stability of composts, allowing time savings in terms of analysis,
196
due to speed, exequibility and cost applica- tion compared to respirometric techniques used in the quality compost evaluation.
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