Thermochemical Treatment of Sewage Sludge Ash (SSA)—Potential and Perspective in Poland

Marzena Smol,Stefan Anton Kugler,Christian Adam

doi:10.3390/en13205461

Abstract

Phosphorus (P) recovery from sewage sludge ash (SSA) is one of the most promising approaches of phosphate rock substitution in mineral fertilizers and might be a sustainable way to secure supply of this raw material in the future. In the current investigation, the process of thermochemical treatment of SSA was applied to SSA coming from selected mono-incineration plants of municipal sewage sludge in Poland (Cracow, Gdansk, Gdynia, Lodz, Kielce and Szczecin). The Polish SSA was thermochemically converted in the presence of sodium (Na) additives and a reducing agent (dried sewage sludge) to obtain secondary raw materials for the production of marketable P fertilizers. The process had a positive impact on the bioavailability of phosphorus and reduced the content of heavy metals in the obtained products. The P solubility in neutral ammonium citrate, an indicator of its bioavailability, was significantly raised from 19.7–45.7% in the raw ashes and 76.5–100% in the thermochemically treated SSA. The content of nutrients in the recyclates was in the range of 15.7–19.2% P2O5, 10.8–14.2% CaO, 3.5–5.4% Na2O, 2.6–3.6% MgO and 0.9–1.3% K2O. The produced fertilizer raw materials meet the Polish norms for trace elements covered by the legislation: the content of lead was in the range 10.2–73.1 mg/kg, arsenic 4.8–22.7 mg/kg, cadmium 0.9–2.8 mg/kg and mercury <0.05 mg/kg. Thus, these products could be potentially directly used for fertilizer production. This work also includes an analysis of the possibilities of using ashes for fertilizer purposes in Poland, based on the assumptions indicated in the adopted strategic and planning documents regarding waste management and fertilizer production.

Highlights

Phosphorus (P) is one of the primary nutrients for plant growth.It is a non-renewable [1], but a fundamental element for all living organisms as P is an important component of nucleic acids and lipids and plays a strategic role in energy transfer at the cell level [2].P is involved in many of the life processes of plants; it participates in the process of photosynthesis, as well as the synthesis of carbohydrates, proteins and fats
The sewage sludge ash (SSA) from six Polish plants of municipal sewage sludge combustion are characterized by a high content of selected nutrients
Based on the available analyses, the SSA as the input for P recovery is the preferable solution in terms of the independence of sludge incineration plants, their recovery efficiency [18] and the location of the Wastes generated in municipal wastewater treatment plants (WWTPs) are valuable sources of P that can be successfully used as substitutes for the production of mineral fertilizers

Summary

Introduction

Phosphorus (P) is one of the primary nutrients for plant growth (next to nitrogen and potassium).It is a non-renewable [1], but a fundamental element for all living organisms as P is an important component of nucleic acids and lipids and plays a strategic role in energy transfer at the cell level [2].P is involved in many of the life processes of plants; it participates in the process of photosynthesis, as well as the synthesis of carbohydrates, proteins and fats. Phosphorus (P) is one of the primary nutrients for plant growth (next to nitrogen and potassium). It is a non-renewable [1], but a fundamental element for all living organisms as P is an important component of nucleic acids and lipids and plays a strategic role in energy transfer at the cell level [2]. P is involved in many of the life processes of plants; it participates in the process of photosynthesis, as well as the synthesis of carbohydrates, proteins and fats. It affects the rapid growth of roots and stimulates tillering. As P is an essential nutrient for photosynthetic carbon assimilation, and the most common nutrient, its sustainable and circular management is of particular interest to researchers and practitioners operating in the fertilizer sector [4]

Methods

Results

Conclusion