Compost quality and its function as a soil conditioner of recultivation layers – a critical review

Abstract

During a period of 4 years, soil chemical and physical properties of the temporary capping system in Rastorf (Northern Germany) were estimated, whereby compost was partly used as soil improver in the upper recultivation layer. The air capacity and the available water capacity of soil samples were first determined in 2013 (without compost), and then in 2015 (with compost) under laboratory conditions. Herein, the addition of compost had a positive effect on: the air capacity up to 13.4 cm3cm−3; and the available water capacity up to 20.1 cm3cm−3in 2015, in the recultivation layer (0-20 cm). However, taking into account the in situ results of the tensiometer and frequency domain reflectometry measurements, the addition of compost had a negative effect. The soil-compost mixture led to restricted remoistening even after a normal summer drying period in autumn and induced more negative matric potentials in the recultivation layer. In summary, the soil-improving effect of the compost addition, in conjunction with an increased water storage capacity, is undeniable and was demonstrated in a combined field and laboratory study. Therefore, intensive hydrophobicity can inhibit the homogeneous remoistening of the soil, resulting in a decreased hydraulic effectiveness of the sealing system.

Effectiveness of Grassland Vegetation on a Temporary Capped Landfill Site

“…Longer phases during the vegetative period (July-September) nearly reached the wilting point of 65 mm, so, the evaporative zone (0.5 m) dried out more strongly and the transpiration capacity and thereby the ETa values of the grassland were restricted by (a) the inadequate water availability in the evaporative zone and (b) the limited water storage capacity, and (c) the limited capillary rise from deeper soil layers due to the compacted construction of the temporary capping system [5,6]. Thus, phases with water contents below the critical field capacity of 95 mm should be as short as possible to prevent desiccation in the deeper layer, thus, the modelled water content is a first indicator to describe the hydraulic stability of the capping system.…”

“…Temporary capping systems regularly consist of a recultivated layer, a drainage layer, and a sealing layer consisting of mineral substrates or in combination with polymers [6]. The major aim of the recultivated layer is to restrain landfill gas migration and to minimise leachate generation (precipitation contaminated with heavy metals or polycyclic hydrocarbons) by a high water storage capacity in combination with a distinct evapotranspiration rate from the vegetation and soil surface [3,7].…”

Effect of artificial soil compaction in landfill capping systems on anisotropy of air‐permeability

“…1.8 g cm -3 ) in the topsoil (0.05 m depth) are related to the compost, consisting of tree and shrub debris, that was applied and then incorporated in the topsoil by using a field cultivator after the installation of the mineral capping system in 2008. Compost application aimed at increasing the water holding capacity in the topsoil and improving the plant growth for water erosion protection (Beck-Broichsitter et al, 2018d). The structure formation (predominant crumbly structure) through swelling/shrinking processes was affected by wetting/drying cycles (Ajayi et al, 2019) along with biological processes that occurred over time (Horn et al, 2014), must also be considered when explaining the lower dry bulk density values of the topsoil.…”

Effect of Compaction on Soil Physical Properties of Differently Textured Landfill Liner Materials

“…The presented Ks values of both materials were comparatively higher than the legal-fixed value of 5 × 10 −9 m/s. Additional compaction may help to reduce the Ks values [26,32], but it is well known that quartz sand particles build-up stable structures with ongoing compaction [14], so the required Ks values, especially for bm, can hardly be reached [33]. In this case, the addition of three-layer clay minerals (i.e., smectite, vermiculite) could decrease the Ks values, but at the expense of an increasing shrinkage potential [34].…”

“…Consequently, high engineering demands are placed on the material. Considering the legally-fixed standards, (a) plant available water capacity In June 2013, as a result of erosion damage and less pronounced vegetative growth, approximately 100 m 3 of compost, produced in the local compost facility (Rastorf, Northern Germany) consisting of tree and shrub chippings and debris, was applicated by milling machine to the upper 0.2 m of the top liner (same boulder marl for Proctor compaction tests) of the Rastorf landfill on approximately 1000 m 2 [14,15]. The basic material was mechanically shredded and frayed and then stored in a composting plant for nearly 9 months to enhance the biochemical processes of composting between 70 • C and 100 • C. In 2013 (without compost: wco) and 2015 (compost: co), more than 80 undisturbed soil cores (diameter: 0.055 m, height: 0.04 m) were collected from a pit in the northeast part of the landfill (lat 54 • 28 N, long 10 • 32 E) in depths between 0.1 m and 0.2 m.…”