As for more sophisticated approaches, rotary drum composting devices are
probably the oldest mechanical processing systems developed to treat organic wastes
(Fitzpatrick et al. 2005), although they have come into fashion again recently
(Gajalakshmi and Abbasi 2008). Here, the starting material is shredded and moistened prior to being fed into the chamber, i.e., a downward-slanted cylindrical drum
(3–4 m in diameter and up to 30 m long), which is slowly rotating (1 rpm). Moisture,
air, and out-gases are controlled throughout the process and a fair grade of decomposition is achieved within a few days (Manderson 2009). Therefore, further stabilization of the outgoing material is accomplished by piling or windrowing the
material outdoor. Rotating drums and tunnel composters with moving beds are the
best examples of continuous, plug-flow processes (Gajalakshmi and Abbasi 2008).
The maximum control over the process parameters is secured using the in-vessel
systems. Due to the level of engineering reached in these composting approaches,
in-vessel composters bear striking resemblance with solid-state “reactors” used in
other industrial application. These systems differ in their size, their shape and the
devices used to force aeration and mechanical mixing; however, they share a
common feature, i.e., they are batch composters where decomposition processes
occur in a confined space under optimal conditions. This makes in-vessel systems
the most efficient and advanced composting methods, but at the same time the least
cost-effective treatment option.
23.3 Composting Practices for the Bioremediation of Solid
Wastes Contaminated with Recalcitrant Organic
Pollutants
The first scientific reports describing composting approaches for soil bioremediation
purposes date back to the 80s (Antizar-Ladislao et al. 2004; Loick et al. 2009). Since
then a consistent (Antizar-Ladislao et al. 2005) number of studies have been
published on this subject, and several literature reviews have critically discussed
the feasibility of composting for bioremediation practices (Ro et al. 1998; Semple
et al. 2001; Antizar-Ladislao et al. 2004; Chen et al. 2015; Kästner and Miltner
2016). Many of such studies have reported on laboratory-scale approaches mainly
aimed at optimizing the process parameters and the operating conditions to maximize the contaminant removal but composting methodologies have proven effective
towards a wide range of contaminants even at higher operational scales (i.e., pilotand field-scale) (Antizar-Ladislao et al. 2004; US EPA 1997).
The principle of co-composting consists of mixing the contaminated matrix (e.g.,
soil) with non-hazardous organic amendments, which are typically biowastes used as
the input material for conventional composting (e.g., garden and agricultural wastes,
manure, sludge biosolids). The ratio in which the two wastes are mixed can vary, but
generally the proportion of the non-contaminated substrate is higher than 20–30% of
the total (Loick et al. 2009). Different composition of the organic substrate has been
used to optimize the C/N balance and the matrix porosity, thus sustaining the
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O. Lhotský et al.
probably the oldest mechanical processing systems developed to treat organic wastes
(Fitzpatrick et al. 2005), although they have come into fashion again recently
(Gajalakshmi and Abbasi 2008). Here, the starting material is shredded and moistened prior to being fed into the chamber, i.e., a downward-slanted cylindrical drum
(3–4 m in diameter and up to 30 m long), which is slowly rotating (1 rpm). Moisture,
air, and out-gases are controlled throughout the process and a fair grade of decomposition is achieved within a few days (Manderson 2009). Therefore, further stabilization of the outgoing material is accomplished by piling or windrowing the
material outdoor. Rotating drums and tunnel composters with moving beds are the
best examples of continuous, plug-flow processes (Gajalakshmi and Abbasi 2008).
The maximum control over the process parameters is secured using the in-vessel
systems. Due to the level of engineering reached in these composting approaches,
in-vessel composters bear striking resemblance with solid-state “reactors” used in
other industrial application. These systems differ in their size, their shape and the
devices used to force aeration and mechanical mixing; however, they share a
common feature, i.e., they are batch composters where decomposition processes
occur in a confined space under optimal conditions. This makes in-vessel systems
the most efficient and advanced composting methods, but at the same time the least
cost-effective treatment option.
23.3 Composting Practices for the Bioremediation of Solid
Wastes Contaminated with Recalcitrant Organic
Pollutants
The first scientific reports describing composting approaches for soil bioremediation
purposes date back to the 80s (Antizar-Ladislao et al. 2004; Loick et al. 2009). Since
then a consistent (Antizar-Ladislao et al. 2005) number of studies have been
published on this subject, and several literature reviews have critically discussed
the feasibility of composting for bioremediation practices (Ro et al. 1998; Semple
et al. 2001; Antizar-Ladislao et al. 2004; Chen et al. 2015; Kästner and Miltner
2016). Many of such studies have reported on laboratory-scale approaches mainly
aimed at optimizing the process parameters and the operating conditions to maximize the contaminant removal but composting methodologies have proven effective
towards a wide range of contaminants even at higher operational scales (i.e., pilotand field-scale) (Antizar-Ladislao et al. 2004; US EPA 1997).
The principle of co-composting consists of mixing the contaminated matrix (e.g.,
soil) with non-hazardous organic amendments, which are typically biowastes used as
the input material for conventional composting (e.g., garden and agricultural wastes,
manure, sludge biosolids). The ratio in which the two wastes are mixed can vary, but
generally the proportion of the non-contaminated substrate is higher than 20–30% of
the total (Loick et al. 2009). Different composition of the organic substrate has been
used to optimize the C/N balance and the matrix porosity, thus sustaining the
476
O. Lhotský et al.