The Potential Benefits and Limitations of Corn Cob and Sewage Sludge Biochars in an Infertile Oxisol

Jonathan Deenik,Michael Cooney

doi:10.3390/su8020131

Abstract

The thermal conversion of sewage sludge to biochar offers a promising alternative use for a hazardous waste material with potential benefits to agricultural productivity and soil quality. Three short-term greenhouse experiments were conducted to evaluate the effect of corn cob (CC) and sewage sludge (SS) biochars, with their anaerobically treated counterparts, on soil properties and plant growth in an infertile Oxisol. The anaerobically treated SS biochar showed the greatest concentration of bioavailable essential nutrients, but treatment only resulted in increased yields for the SS biochar in the first crop in the absence of added fertilizer. Both CC and SS biochars in combination with fertilizer doubled plant growth compared to the control in the first crop cycle, produced no significant effect in the second cycle, and more than tripled plant growth for the SS biochars in the third cycle. High ash content with high nutrient contributions (especially P) and a persistent liming effect explain the benefits of the SS biochars to plant growth. The SS biochar showed promise in mitigating the negative effects of soil Mn toxicity. Sewage sludge biochars reduced Cd bioavailability and had no significant effect on the bioavailability of other potentially toxic metals compared to the control.

Highlights

Managing sewage sludge is one of the most challenging and urgent problems facing an increasingly urban global population [1]
A growing urban global population has resulted in alarming increases in sludge production; China, for example, produced approximately 5 M T of dewatered sludge in 2009 up from 3.5 M T in 1998 [2] whereas recent estimates show that the European Union produces more than 10 M T annually [3], and in the United States according to the latest available data annual sludge production is approximately 6.5 MT [4]
With the exception of Cd where the sewage sludge (SS) biochars significantly reduced plant uptake in the first crop cycle, our results showed no significant effect of biochars on heavy metal accumulation

Summary

Introduction

Managing sewage sludge is one of the most challenging and urgent problems facing an increasingly urban global population [1]. Of particular interest, is the opportunity to convert hazardous materials such as sewage sludge into biochar, which when added to soils has the potential to improve soil quality and crop performance [10–12]. Sewage sludge derived biochars are typically high in mineral ash content, which could serve as a source of soluble essential plant nutrients and contribute liming potential in acidic soils [13]. There is a large and growing body of literature indicating that biochar applications to soil increase crop productivity and improve soil fertility and quality [23]. Along with the apparent benefits, there are reported negative effects from the application of some biochars to soil [7,23]; reduced soil N resulting in stunted plant growth [28,31] potential phytoxic effects from biochar derived polycyclic aromatic hyrocarbons (PAHs) [32,33], and some evidence for increased bioavailability of As [34]

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Conclusion