Spent Coffee Grounds in the Production of Lightweight Clay Ceramic Aggregates in View of Urban and Agricultural Sustainable Development

Abstract

This paper presents an innovative application for spent coffee grounds (SCGs) used as filler for the formulation of lightweight clay ceramic aggregates (LWA). LWA can be used for urban and agricultural purposes as a sustainable solution. Spent coffee grounds were tested as a pore forming agent partially acting as a replacement for red clay in material formulation before firing. Substitutions of 10, 15, and 20 wt.% of red clay were tested. The properties of lightweight aggregates with 15 wt.% of SCGs were improved using a specifically tailored fertilizer glass due to its low pH and conductivity within the soil tolerance range. Packaging glassy sand, cattle-bone flour ash, and potassium carbonate were mixed and melted in order to obtain this glass, which when added to the clayey batch functionalized the aggregates by phosphorus and potassium nutrients. The results (in particular, porosity and bulk density) show that the lightweight aggregates obtained have interesting properties for possible uses both in urban (e.g., green roofs as a drainage layer) and agricultural purposes. Moreover, pH and conductivity are in line with the Italian Standard regarding soil amendment (D.lgs. 75/2010). In addition, several leaching tests were performed in a solution containing 2 vol.% citric acid (C6H8O7) to evaluate the release capacity not only of nutrients (P and K) but also to check the presence and release of heavy metals, such as lead (Pb), that may come from the glassy precursor. The results obtained showed that nutrients are efficiently released in 21 days (P = 87.73% and K = 25.74% of released percentage) and Pb release is under the standard threshold of 30 ppm.

Preliminary Study on Sustainable NPK Slow-Release Fertilizers Based on Byproducts and Leftovers: A Design-of-Experiment Approach

“…), and this is consistent with firing treatment at around 1000 °C needed to obtain these aggregates. 23 As suggested from the elemental analysis of C-Glass and C-Ash, no significant concentrations of other elements are detected, confirming again the predominance of inorganic matter. No significant content of toxic compounds, such as heavy metals or chlorides, has been detected both in LWAs and BSF biomass, suggesting that the employment of these materials should not deliver toxic substances to the soil.…”

“…LWAs’ base was a local red clay (from a quarry in the province of Modena), in which 15 wt % spent coffee grounds were included as a poring agent, taking advantage of their combustion during sintering of the ceramic matrix following the results of a previous study. 23 Potassium and phosphorous were introduced into LWAs using vegetable biomass and bone flour ash as they were or through a well-tailored glass, named fertilizer glass. This glass is based on an industrial secondary raw material, named glassy sand, coming from the secondary treatment of packaging glass cullet (90 wt %) and an old cathode-ray tube screen glass recycling process (10 wt %) produced by an industry in the Piemonte region (still in northern Italy).…”

Comparison of Three Manufacturing Techniques for Sustainable Porous Clay Ceramics

“…Physical ( Table 2 ) and chemical ( Table 3 ) properties of pellets samples [ 3 ] were compared with those obtained by pressing and shell scaffold.…”

“…For the preparation of the specimens, a local ferruginous red clay (Zocca, Modena, Italy) and spent coffee grounds (SCGs) collected by the owner of a bar in Modena (Italy) were used. Due to the high humidity content (65% of water), the SCGs were dried by following a procedure optimized in a previous paper [ 3 ]. The use of a pore-forming agent (SCGs) was necessary only in the materials prepared by manual pelletization and pressing, while for those prepared by shell scaffold, due to the use of a sacrificial skeleton that burned during firing, it was not necessary.…”

“…A porous clay ceramic which belongs to clay ceramics materials, a class of materials with a solid market and a significant environmental impact from their manufacture to their distribution, was chosen as the final product. As a matter of fact, some works have been just published by the authors on lightweight ceramic aggregates [ 2 , 3 , 4 ] which belong to the aggregate materials and represent the second most consumed material after water [ 5 ], equal to 2282 million tons in Europe in 2016 [ 6 ]. The aggregate family is the main supplier of raw materials for the construction of infrastructures and buildings, as well as for industry and environmental protection, which confers to it a clearly strategic character [ 5 ].…”