Efficacy of disposal wastewater sludge as "clean" fertilizer

Abstract

Extensive areas of irrigated soils are unproductive, due to the accumulation of salts in the soil profile occupied by root systems. It is estimated that about 15% of the total land area of the world has been degraded by salinization and soil erosion, which are among the major causes of desertification. The expected increase in the world’s population (~10 billion by 2050) needs food productivity to step up within a few decades. Organic fertilization is highly sustainable when compared to other options to date when taken into consideration as a solution to the highlighted issues. It is possible to use biological soil properties for evaluating the effects of organic matter application on soil characteristics. Different approaches have been suggested to solve these issues of soil destruction. This study focuses on selected organic materials (e.g., different agro-industrial by products, and composts) as effective tools to improve different soil properties of soils. However, further experimental investigations are needed to validate this approach in a wider range of soils, also combining waste recycling with other sustainable agronomic practices. The same amendments could likely be considered for soil remediation in the affected areas due to their high organic matter content. In fact, organic matter has several beneficial effects on agricultural fields, such as the slow release of nutrients, soil structure improvement, and the protection of soils against erosion. Selected studies were focusing on the effects of application of various organic matters (i.e., different organic waste materials, mixture of green waste compost) to two soils. In particular, such effects can be referred to chemical, biological, and physical soil properties. The observed results offer powerful evidence on the potential of organic fertilizers in improving soil properties. Such results showed the improving soil structure, increasing different enzyme activities and soil organic carbon, total nitrogen and extractable phosphorus and increasing soluble and Exchangeable-K + . Urease activity was increased by more than 150% in the mixed treatment, compared to the control. The incorporation of organic manure into the soil significantly increased soil phosphatase activity and soil respiration rate. 15 g·kg−1 of compost significantly improved soil physical-chemical properties, especially C and N contents. Enzyme activities were substantially promoted in presence of both amendments. However, there is no clarity whether organic matter, composts of organic wastes are as plant-friendly as the manure-based composts are believed to be. It is also not clear as to whether the action of green compost as a fertilizer depends on the species of plants being fertilized by it. This raises questions whether green organic composts are beneficial (or harmful) at all application rates or if there is a duality in their action which is a function of their level of application. The study reveals that, in general, organic matter composts of all are highly potent fertilizers.