Evolution of Biochemical Parameters During Composting of Various Wastes Compost

Abstract

In Tunisia the most treatment waste is landfill (50% of wastes were land filled) and only 5% are composted. And since our soil become more and more poor in organic matter, green waste can be a significant source of organic matter; in parallel we cited the domestic waste and dead posodonia collected from beaches. All these wastes coming from various origins can be exploited to produce stable compost able to correct the deficiency of soil. Exploiting waste could lead at different quality of mature compost. We are not interested in only the quality of the mature compost but we are interested in the time of the composting cycle. The goals of this study were to characterize the maturity and the sanitary quality of compost in relation with the feed stock source (green waste (C1), green waste mixed with Posidonia (C2) and municipal solid waste (C3). The results obtained showed that the duration of the cycle of composting depends on the nature of the substrate. The longest cycle (200 days) was observed with the feed stock source C3. The C/N ratios ranged between 22 and 27 at the beginning of the cycle of composting and decreased notably during time of composting. NH₄-N decreased over the progress cycle and at the end of composting progress, all wastes presented a content of NH₄-N not exceeding the maximal value recommended for mature compost (400 mg kg^-1). The CO2 released by C1 was of approximately 6000 mg C-CO2 DM kg^-1 at the start of the cycle and it reached at the end of the cycle of composting 2300 mg C-CO2 DM kg^-1. Nevertheless, the deshydrogenase activity (DHA) recorded was important during the thermophilous phase at the level of the three piles C1, C2 and C3, where it reached the respective values of 5.9; 6.2 and 4 TPFS/TPF/g of DM. Maturity stage showed the values of 0.3; 0.8 and 0.4 TPFS/TPF/g of DM, respectively. Salmonella appeared only at the level of the piles C2 et C3 at the beginning of composting. After 40^th days composting these bacteria are not detected. Staphylocoques were not detected at the level of the two piles C1 and C2. The number of these bacteria was important in the compost C3, where it fluctuated between 10³ and 10⁵ bacteria g^-1 of dry matter. Statistical analyses showed that the compost of municipal solid waste C3 presented a value of salinity (6.8 g Kg^-1 of DM) higher than those obtained at the level of the other studied piles 2.6 g kg^-1 of DM for C1; 4 g Kg^-1 of DM for C2). We also noted that the compost C2 was relatively rich in P (2.17%/ of DM) and MgO (2.62% of DM) as compared with the two other studied piles which contain a percentage of MgO of 0. 73 in C1 pile and 0. 8 in C3 pile. Although important heavy metals contents determined in the three studied composts were lower than the levels indicated by the standards of the European Union.