Keywords

10.1 Introduction

Municipal solid wastes microorganisms (fungi and bacteria) are responsible for degradation and biological transformation of organic matter. These microorganisms degradation is responsible for temperature increase in wastes (Mustin 1987) . Consequently composting is known of heat treatment (sanitization of compost) stabilization process of wastes with two principal steps: aerobic digestion and maturation (Hassen et al. 2001; Ben Ayed et al. 2007) . This process controlled and optimized different parameters especially temperature, water content, oxygenation to produce a stable and pathogens free-compost. Pathogens were destroyed within the thermophilic phase (Epstein 1997) . Heavy metals did not eliminate with heat treatment of the process (Richard 1992) . Consequently various countries from European Union and the USA have providing permissible limit of heavy metals content in MSW compost for land application. However Land application of MSW compost is an excellent way of recycling both the nutrients and the organic matter contained in waste and became the promising ways to correct the degraded soil (Sanchez-Mondero et al. 2004; Bouzaiane 2007a) . In agricultural systems, biotic (e.g., micro-organisms) and abiotic factors (e.g., soil acidity and water content) affect the fertility of the soil, its nutrient content and its organic matter. Soil amendment with mature MSW compost, affects both biotic and abiotic factors. In fact, the application of compost introduces new organic matter, nutrients and microbial organisms (Beffa et al. 1995) that considerably improve the texture of soils (Mays et al. 1973) , and increase the soil water content. Biotic factors such as the microbial biomass activities are stimulated (Pedra et al. 2007; Roca-Perez et al. 2009) . Measurement of soil microbial biomass and their extracellular enzymes after MSW compost application provide valuable information for soil quality and for a sustainable management of agricultural soils.

10.2 Soil Microbial Biomass Role and Assessment

Soil microbial biomass mainly bacteria and fungi and their extracellular enzymes activities (Tabatabai 1994) are responsible for the biological transformation that make nutrients available to plants and for sustaining soil functions. Since soil microbial communities play a critical and a key role in nutrient cycling and may be used as a sensitive and as an indicator of environmental changes or disturbance of soil management (Bouzaiane et al. 2007a) . In addition soil microbial biomass (SMB) is one of the major indices applied today to study soil fertility and soil health (Sparling 1997) and conducts biochemical transformations in soil (Breland and Eltun 1999) . Several studies showed that the SMB varies with soil management including the farming system (Hu et al. 1997) fertilisation (Salinas-Garcia et al. 1997) , municipal solid waste application (Jedidi et al. 2004; Bouzaiane et al. 2007a) and heavy metals (Garcia-Gil et al. 2000; Fagnano et al. 2011) .

Measurement of the soil microbial biomass provide valuable information for soil quality and for a sustainable management of agricultural soils. The potential influence of the SMB in a soil sample may be assessed by its amount (Anderson and Domsch 1989) . Assessment of SMB can be achieved by direct methods which asses the cultivable microbes, such as the plating counts (Paul and Johnson 1977) , or by several indirect methods which asses the non cultivable microbes, such as the chloroform fumigation-extraction method (CFE), the chloroform fumigation-incubation method (CFI) (Vance et al. 1987; Tate et al. 1988) , and the substrate-induced respiration (SIR).

The different methods (Vance et al. 1987; Brookes 1995) have been widely used to estimate microbial biomass under different field and laboratory conditions. The microbial biomass have been estimated, in both cultivated and uncultivated soils (Vong et al. 1990) , in forest soils (Gallardo and Schlesinger 1990) , edaphically conditions characterized by the alternation of desiccation–rehumidification cycles (Van Gestel et al. 1991) , as well as the effects of seasonally dried soils (Wu and Brookes 2005) . Molecular methods such as DNA quantification method has been used for SMB estimation in different soils (Marstorp et al. 2000; Bailey et al. 2002; Leckie et al. 2004) . The DNA quantification method (DNA) has been compared to the CFE method in different soils (Marstorp et al. 2000; Bailey et al. 2002; Leckie et al. 2004) and has been proposed as an alternative method of CFE to measure SMB (Marstorp et al. 2000; Anderson and Martens 2013) . Bouzaiane et al. (2007b) showed that the quantification of DNA yields could be used as an alternative and a reliable method to estimate microbial biomass in wheat cultivated soil after municipal solid waste compost application.

10.3 Municipal Solid Waste Composting Process

The municipal solid waste composting process has been defined as a controlled aerobic microbial process widely used to transform organic matter contained in wastes by their microbes into a stable product consisting of a humus-like substance (Michel and Reddy 1995) .

10.3.1 Composting Process

Composting is one of the most complex biotechnologies since many factors influence the optimization and the reproducibility of the process such as mechanical (wastes composition and mix), chemical (temperature of environmental conditions eg. season, pH, moisture water content, O2 concentration, porosity, C/N ratio), and biological parameters (microorganisms composition and content).

These different factors influence the quality and the degree of stability of the end product (Mondini et al. 2002; Jedidi et al. 2004) . In general the composting process occurs into three major and classic stages based on temperature parameter (Fig. 10.1) (Hassen et al. 2001; Ben Ayed et al. 2007) .

Fig. 10.1
figure 1

Major classic phases of municipal solid waste composting process based on temperature parameter

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Mesophilic Phase: During this phase, the temperature and the water content increased as a consequence of increase of psychrophilic and mesophilic microorganisms which improved the biodegradation of organic compounds like lipids glucose and amino acid (Mustin 1987) . This phase is short in time between 20 and 30 days (Hassen et al. 2001; Ben Ayed et al. 2007) , the temperature increased to reach 45 °C to improve the maximum of biodegradation.

Thermopilic Phase: this phase is important in time which could be occurred between 30 and 100 days of composting process (Hassen et al. 2001; Ben Ayed et al. 2007) . This phase improve the development of thermophilic microorganisms according to the authors. The temperature must be maintained below 65 °C inside the windrow of wastes by ventilation and watering. Marrug et al. (1993) mentioned that temperature above 60 °C affect the decomposition rate of the waste organic matter as a result of microbes activities decrease. This phase is known as a phase of compost sanitation which heat sensitive pathogens like viruses, bacteria, protozoa or helminthes (Strauch 1991) could be eliminated.

Cooling or Stabilization Phase: in this phase the temperature began to decrease after 12th week according to Hassen et al. 2001 and after 111 days according to Ben Ayed et al. (2007). By the end of the process, the average temperature inside the windrow showed a reduction of values to reach approximately 30 °C. This decrease was the result of depletion of organic compounds in compost and C/N ratio tend to stabilize. The end product or compost is available for agricultural use. This practice is becoming one of the most promising ways for the remediation of degraded soils (Bouzaiane et al. 2007a) . However, the main requirement for the safe use or application of compost to agricultural lands is its degree of stability, which implies stable organic matter content (Castaldi et al. 2004, 2008; Mondini et al. 2004) .

Bouzaiane et al. (2011) evaluated that the microbial biomass C and N and DNA content during the municipal solid waste composting process can be used to understand the compost stability state. According to the authors biological properties could be combined to chemical properties, to indicate the compost stability.

10.3.2 MSW Compost Application Improves Agricultural Soil Properties

Application of MSW compost in agricultural soils can directly improves soil physico-chemical properties such as soil organic matter contents, soil aggregates, buffering capacity (Reeves 1997) and soil biological properties such as soil microbial biomass and activity (Pedra et al. 2007; Roca-Perez et al. 2009) .

10.3.2.1 MSW Compost Application Improves Soil Physico-Chemical Properties

Compost from MSW represents an important resource of organic matter to maintain and restore soil fertility. Since it is important source of the plants nutrient and is of great value nowadays, particularly in those countries where the organic matter content of the soil is low (Castaldi et al. 2004) . Bouzaiane et al. (2007a) showed that the application of MSW compost improves the organic matter of degraded soils in semiarid zone of Mediterranean countries like Tunisia. Roca-Perez et al. (2009) reported that the application of MSWC into the soil increased soil quality in two soils from Spain and increased soil organic matter, N, P and stable aggregates from both amended soils.

The soil addition with mature or stable MSW compost represents a valuable and effective tool to increase the long term of soil aggregates. Recently Spaccini and Piccolo (2013) showed that field application on three different agricultural soils of mature compost improve the distribution of water stable aggregates with the significant improvement of soil aggregate stability.

In the other hand MSW compost could reduce the adverse effects of salinity showed by Lakdhar et al. (2008) in Hordeum maritimum under greenhouse conditions. Plants were cultivated in pots filled with soil added with 0 and 40 t ha−1 of MSW compost, and irrigated twice a week with tap water at two salinities (0 and 4 g l−1 NaCl). According to the authors the MSW compost may be safely applied to salt-affected soils without adverse effects on plant physiology.

10.3.2.2 MSW Compost Application Improves Soil Microbial Biomass and Activity

Addition of good quality of compost may increase global microbial biomass and enhance soil enzyme activity (Albiach et al. 2000; Debosz et al. 2002; Garcia-Gill et al. 2000) . The improve of this soil biological properties was study with many authors to evaluate the MSW compost effect. Perruci (1990) showed that microbial biomass, carbon, nitrogen, sulphur and phosphorus were significantly increased over a period of 12 months in a soil treated with compost of municipal solid waste.

According to Garcia-Gill et al. (2000) , a long-term field experiment utilizing barley received MSW compost at 20 t ha−1 (C20) or at 80 t ha−1 (C80) were studied. The effects of these applications on soil enzyme activities and microbial biomass at crop harvest were measured after nine years in upper horizon of 0–20 cm. In comparison with the control (no amendment soil) MSW compost addition increased biomass C by 10 and 46 % at application rates of 20 and 80 t ha−1, respectively. The authors evaluated enzyme activities and they showed that the dehydrogenase and catalase enzymes, were higher in the MSW compost treatments by 730 (C20) and 200 % (C80), respectively, indicating an increase in the microbial metabolism in the soil as a result of the mineralization of biodegradable C fractions contained in the amendments. The addition of MSW caused different responses in hydrolase enzymes. Phosphatase activity decreased with MSW (± 62 % at both rates) to less than that in the control treatments. Urease activity decreased by 21 % (C20) and 28 % (C80), possibly being affected by the heavy metals contained in the MSW. However, β-glucosidase and protease increased with MSW compost.

The use of composts in agricultural soils is a widespread practice and the positive effects on soil and plants are known from numerous studies. Ros et al. (2006) investigate a long term of crop-rotation (maize, summer-wheat and winter barley) in field experiment in Austria. The application of compost produced from urban organic wastes at rate of 175 kg N ha−1 yr−1 for 12 years. The microbial biomass C (B C ), was analyzed at different depths (0–10, 10–20 and 20–30 cm). The results showed that the continued addition of compost to soil enhances B C compared to control soil and which this effect declined with depth.

The application of organic wastes as amendments to improve soil properties has become a very common practice, especially under Mediterranean semiarid conditions. Bouzaiane et al. (2007b) evaluated the microbial biomass C and N (BC and BN) by the chloroform fumigation-extraction (CFE) method and microbial biomass DNA concentration in a loam-clayey wheat cultivated soil. They obtained the highest values of microorganisms counts with MSW compost at 40 t ha−1. The microbial biomasses C and N and DNA concentration increased in wheat cultivated soil amended with MSW compost at 40 t ha−1 in comparison with 80 t ha−1 and in the superficial profile (0–20 cm) than in the deep one (20–40 cm). Recently Mardomingo et al. (2013) have investigated the changes in soil microbial activity under field conditions over a one-year period after the application of a single high dose (160 Mg ha− 1 dry mass) of municipal solid waste compost (MSWC). Measurements were made for microbial biomass carbon (MBC), basal respiration (BR) and enzymatic activities evaluated by assays of catalase (CA), dehydrogenase (DA), urease (UA), protease (PA), phosphatase (PhA) and β-glucosidase (βGA). This organic amendment produced different effects on soil microbial activity. The application of MSWC significantly increased (p ≤ 0.05) the BC, with the highest content observed in summer season (1369.1 ± 13.2 mg C kg−1). According to the authors soil microbial activity (BR, CA, DA and hydrolase activity) remained stable throughout the one-year period in MSW compost.

Other authors were interested on the biopesticide view of organic materials that could be used to control many soil-borne plant pathogens (Boulter et al. 2000; Hoitink et al. 1993) . Since the microbial biodiversity may be increased (Peacock et al. 2001) and soil borne pathogens may be reduced by stimulation of antagonistic organisms (Tilston et al. 2002) allowing less use of potentially fumigants or pesticides (Pascual et al. 2000; Ros et al. 2005) . Moreover MSW compost could contained many antagonistic microorganisms such as Bacillus sublilis, Trichoderma and Pseudomonas (Serra-Wittling et al. 1996; Hoitink et al. 1993) that controlled wheat plants phytopathogenic like Fusarium oxysporum.

10.3.2.3 Effect of MSWC Heavy Metals on Agricultural Soil

Heavy metals do not degrade throughout the composting process, and frequently become more concentrated due to microbial degradation and loss of carbon and water from the compost (Richard 1992) . A significant decrease of soil microbial biomass was noted after three years of MSW compost application (Bouzaiane et al. 2007b) . The decrease of microbial biomass was due to heavy metals content elevation in compost at 80 t ha−1 treated soil. Thus according to the authors the highest rate of MSW compost induced the lowest ratio of biomass C to soil organic carbon and the lowest ratio of biomass N to soil organic nitrogen.

Carbonell et al. 2011 conducted to assess the inputs of metals to agricultural land from soil amendments. Maize seeds were exposed to a municipal solid waste (MSW) compost (50 Mg ha−1) and NPK fertilizer (33 g plant−1) amendments considering N plant requirement until the harvesting stage with the following objectives: (1) determine the accumulation of total and available metals in soil and (2) know the uptake and ability of translocation of metals from roots to different plant parts, and their effect on biomass production. According to the authors the results showed that MSW compost increased Cu, Pb and Zn in soil, while NPK fertilizer increased Cd and Ni, but decreased Hg concentration in soil. The root system acted as a barrier for Cr, Ni, Pb and Hg, so metal uptake and translocation were lower in aerial plant parts. Biomass production was significantly enhanced in both MSW and NPK fertilizer-amended soils (17 %), but also provoked slight increases of metals and their bioavailability in soil. The highest metal concentrations were observed in roots, but there were no significant differences between plants growing in amended soil and the control soil. Important differences were found for aerial plant parts as regards metal accumulation, whereas metal levels in grains were negligible in all the treatments.

10.4 Conclusion

The MSW compost application to an agricultural soil can improve and maintain soil quality by decreasing the need of chemical fertilizers and pesticides, improving soil tillage, increasing soil microbial biomass and enzyme activities, increasing the organic matter of degraded soils and increasing the plants productivities. However the MSW compost could be contaminated by heavy metals, toxics compounds and pathogens that limits the use of the compost. The utilization of MSW compost in low rate should be used for sustainable agricultural soil to mitigate the cumulative effects of environmental pollution and gain public acceptance.