Waste Silica as a Valuable Component of Extensive Green-Roof Substrates

Abstract

Green roofs are becoming increasingly common practice of the urban sustainable environment. The growing substrate is the most important part of green-roof technology. The cost of engineering substrates can be reduced by using locally available components. Since green roofs are a relatively new concept in Poland, there is a need to examine substrate compositions and characteristics, including commonly used ingredients as well as alternative recycled/waste materials. The aim of our study was to assess the ability of locally sourced waste materials as roof-growing media amendments. In the greenhouse experiment we tested two grass and herb species mixtures and four waste substrate formulas. The locally disposed waste materials used as components of growing media included silica wastes (byproducts of metallic ferrosilicon alloys), cellulose, foundry sand, and organic waste material removed from the organic horizons of mucky peat. The engineered Si-waste substrates were compared with the commercially available media. The physico-chemical properties of components and substrates, their stability over time, and the influence on plant growth and mineral nutrient status were examined. Particle size distribution, bulk density, mass, water capacity, soil reaction, and total dissolved salt content of Si-waste-growing media were compatible with FLL standards. We found low amounts of available P and K, and high concentrations of Ca, Mg, S, and trace elements (with the exception of B) in Si-waste substrates in comparison with the control media. Silica waste materials have the potential to maintain pH with high buffering capacity. Engineered Si-waste substrates had a positive impact on plant growth and biomass. In general, these results indicate that contaminant elements contained in alkaline Si-waste substrates were not easily available to the root system, and consequently they did not restrict plant growth. We consider Si-wastes to be a valuable and environmentally responsible green roof media amendment.

Time-Dependent Changes in the Physico-Chemical Parameters and Growth Responses of Sedum acre (L.) to Waste-Based Growing Substrates in Simulation Extensive Green Roof Experiment

“…It was hypothesised that Si could alleviate heavy metal toxicity in plant; hence, 5% silica fume additive was included in each formula of the growing media. Silicon can reduce active heavy metal ions in substrate, plant metal uptake, and root to shoot translocation [33][34][35][36]. The Ca-aggregate was taken from the Czatkowice Limestone Mine in Krzeszowice, and Zn-aggregate (mining waste rock fragments as well as flotation residues)-from the Boleslaw Mine and Metallurgical Plant in Bukowno near Olkusz.…”

“…The high concentration of toxic metals might inhibit plant growth, reduce the content of chlorophyll, and damage root systems [43]. However, alkaline soil reaction limits the availability of trace elements for plants [34][35][36]. Symptoms of abnormal plant growth or excess of trace element in plants were not observed.…”

“…According to Datnoff et al [33], silicon may increase the drought tolerance of plants, which is extremely important in roof conditions. A preliminary study of substrates based on waste silica materials carried out by Krawczyk et al [35,36] showed that they can become a valuable component of the green roof media. In the second year of the experiment, the biomass of S. acre grown in the substrate based on silica waste was the highest in relation to the control and other prepared substrates (Figure 4b).…”

Do earthworms (D. veneta) influence plant-available water in technogenic soil-like substrate from bricks and compost?

“…These aggregates modify the micro-and mesoporosity of soils (Blouin et al 2013) and are more stable than other aggregates in soils (Jangorzo et al 2015). Furthermore, earthworms have an influence on the structure and the porosity of soils by their burrowing activities creating macropores whilst compressing the adjoining soil (Jangorzo et al 2015;Kooistra and Pulleman 2010). These influences on the physical structure consequently affect the hydraulic properties (Blouin et al 2013) and the water balance, i.e., infiltration, drainage, and evaporation, of the soil.…”

Feasibility of substitute building materials for circular use in urban green infrastructure

“…Furthermore, Asman et al 11 investigated the hydrological performance using rubber crumbs as drainage layer and proposed an optimum slope of 6% are suitable for lightweight green roofs. Krawczyk et al 12 identified waste silica as a valuable component of extensive green‐roof substrates, this material however is only available to a certain extent. Also Carson et al (2012) 13 put a focus on recycled and waste materials as GR substrates.…”