Utilization of Sewage Sludge-Derived Pyrogenic Material as a Promising Soil Amendment

Vladimír Frišták,Martin Pipíška,Dominika Koperová,Gerhard Soja,Stephen M Bell,Reinhard Jagerhofer

doi:10.3390/agriculture12030360

Abstract

The use of advanced treatment technologies such as pyrolysis and carbonization of bio-waste materials has the promise to develop coupled solutions for organic C and P problems in the future of food processing. Sewage sludge-derived pyrogenic materials that are applied to the soil system contain notable levels of P (1–20%). However, only a small portion of total phosphorus is available for plants. Therefore, our study assessed the pretreatment of sewage sludge with Na2CO3 and subsequent pyrolysis at 400 °C and 500 °C for the production of MPCM400 and MPCM500 as potential alternatives for inorganic P fertilizers. Non-pretreated sewage sludge-derived pyrogenic carbonaceous materials (PCM400 and PCM500) were produced as controls. The derived materials obtained by slow pyrolysis at a residence time of 120 min and pyrolysis temperatures of 400 °C and 500 °C, were analyzed by determination of electrical conductivity (EC), pH, elemental analysis of total C, H, N, scanning electron microscopy (SEM) and total concentrations of P, Cd, Fe, Pb and Zn. PCM400, PCM500, MPCM400 and MPCM500 were characterized by analysis of total 16 US-EPA (U.S. Environmental Protection Agency) PAHs by a toluene extraction procedure. Additionally, PCM400, PCM500, MPCM400 and MPCM500 were tested by a germination test with cress seeds (Lepidium sativum L.) and a short-term rye seedling test. Total C concentrations were raised in the order: MPCM500 < MPCM400 < PCM500 < PCM500. Concentration of Σ16 US-EPA PAHs was almost five times higher at PCM500 (21.87 mg/kg) compared to PCM400 (4.38 mg/kg) and three times higher at MPCM500 (23.12 mg/kg) compared to MPCM400 (7.55 mg/kg) with a dominant role of two and three-ring aromatic structures. Total P-concentrations in rye biomass increased in the order for the controls: (2.43 ± 0.95 mg/g) < PCM400 (3.57 ± 0.27 mg/g) < PCM500 (4.04 ± 0.24 mg/g) < MPCM400 (5.23 ± 0.09 mg/g) < MPCM500 (5.57 ± 0.70 mg/g) < IF (7.53 ± 2.65 mg/g). Obtained results showed that pyrolysis materials produced from sewage sludge represent a potential alternative of conventional P inorganic fertilizers and organic C suppliers.

Highlights

Intensification of industrial activities and subsequent anthropogenic emissions of greenhouse gases will bring increases in global mean temperatures and climate changes
The relevance of soil organic C stems from its function as the primary component of soil organic matter, which has a stable moiety known as humus
It was found that higher extractable phosphorus contents can be achieved at a pyrolysis temperature of 500 ◦ C

Summary

Introduction

Intensification of industrial activities and subsequent anthropogenic emissions of greenhouse gases will bring increases in global mean temperatures and climate changes. A full understanding of how soil organic matter will respond to these changes in the climate system is crucial. This is because organic matter is a multi-functional component of soil that provides vital ecosystem services, including support of primary production [1]. The international initiative “4 per 1000” emphasised the importance in deceleration of climate changes but mainly carbon stabilization in soil by promoting of agro-environmental techniques that increase the amount of organic matter in soils and meet the 4% per year target [2]. 45% of all mineral soils in Europe have poor organic C content (0–2%) [3]. This enhances their vulnerability to biodiversity loss, soil erosion, compaction, reduced fertility and low water retention capacity.

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Conclusion