Foreword

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This document was prepared by Technical Committee ISO/TC 275, Sludge recovery, recycling, treatment and disposal.

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Introduction

Sludge is a kind of organic-based material originating from wastewater treatment, rich in humic substances, nitrogen, phosphorus and other trace nutrients, and its application to land is a significant pathway for nutrient cycling and improving soil fertility. However, sludge also contains various toxic pollutants, including heavy metals, organic pollutants, pathogenic bacteria and emerging pollutants. These contaminants are raising significant environmental and health concerns, with potential toxicity to humans and the ecosystem. Therefore, ecotoxicological evaluation is essential to ensure their safe and beneficial reuse.

This document provides requirements and recommendations on ecotoxicological evaluation, classification, and determination methods for sludge. It establishes a two-step evaluation procedure. The first step is to analyse the concentrations of heavy metals and harmful organic pollutants. If the concentration of any pollutant exceeds the limit of the standard, the sludge cannot be used for land application. If the concentrations of all contaminants are below their respective concentration limits, a second step of ecotoxicological evaluation is performed, including seed germination test of higher plants and reproduction toxicity test of earthworms.

Based on ecotoxicological evaluation results, this document classifies sludge into three distinct grades, Classes I, II, and III, to determine the appropriate land application pathway:

class I, the lowest toxicity level, with inhibition ratios for both seed germination and earthworm reproduction at or below 10 %, is suitable for land application in human-accessible areas;
class II, with inhibition ratios up to 20 %, is suitable for landscaping in human-accessible areas;
class III, a higher toxicity level with inhibition ratios up to 30 %, is restricted to landscaping in human-inaccessible areas, such as sandy land rehabilitation, and mine rehabilitation.

1 Scope

This document provides requirements and recommendations for the ecotoxicological evaluation and classification of sludge for land application, and suitable land application pathways. This document applies to sludge from wastewater treatment plants.

2 Normative references

3 Terms and definitions

4 Procedure for sludge toxicity evaluation

5 General requirements of sludge for land application

6 Ecotoxicological evaluation and classification

6.1 Ecotoxicological evaluation

6.2 Classification and land application pathway

7 Sampling and analysis methods

7.1 Sampling methods

7.2 Analysis methods for heavy metals and persistent organic pollutants

Bibliography