Resource Utilization of Biogas Waste as Fertilizer in China Needs More Inspections Due to the Risk of Heavy Metals

Yajun Chang,Jixiang Liu,Huijun Zhao,Fengfeng Du,Qiang Tang,Linhe Sun,Dongrui Yao,Jian Cui,Xiaojing Liu

doi:10.3390/agriculture12010072

Abstract

The utilization of livestock waste has attracted increasing attention in recent years. The presence of high levels of heavy metals is a major obstacle to the utilization of biogas as a fertilizer resource. In this study, the heavy metal contents in biogas residue, slurry, and discharged sewage from three representative farms of gooseries, henneries, and dairy farms in the Yangtze River Basin were investigated and assessed. The results demonstrated that heavy metals, including Cd, Mn, As, Cu, Pb, Cr, Zn, etc., could be detected in all biogas residues, with significantly different contents between farm types (p < 0.005). Specifically, biogas residues from the goosery and the dairy farms met “China’s Organic Fertilizer Standards” (COF Standards); however, Cd concentrations in biogas residues from hennery farms exceeded the limits by five times. The concentrations of Cd and Pb in biogas slurries from all of the farms exceeded the limits of the “China Farmland Irrigation Water Quality Standard” (CFIWQ Standard). In particular, the Pb concentrations in biogas slurry from the dairy farms exceeded the limits by 29 times, and the discharged sewage from all three farm types complied with the comprehensive sewage discharge standards in China; however, only that from the goosery farms was suitable for irrigation. Thus, it is recommended to increase the feed selection, biogas engineering, and biological-purification-supporting technology, and to carry out regular sampling inspections of the biogas residue, slurry, and discharged sewage for heavy metals, so that environmental and crop pollution risks can be reduced when they are used as sources of nutrients for eco-friendly agriculture.

Highlights

In the late 20th century, the global research on the utilization of biogas residue and biogas slurry increased rapidly, and countries around the world—including China, India, Pakistan, Germany, Australia, Bangladesh, Finland, Japan, Malaysia, and the United States—began to pay attention to environmental issues, and to pay more attention to the research of biogas slurry [1]
Biogas residue and slurry are rich in organic matter and nutrient elements, and returning to the field as fertilizer is the main method of their resource utilization around the world [40]
The results indicate that the biogas residues produced in different livestock and poultry breeding farms contain different kinds and contents of heavy metals

Summary

Introduction

In the late 20th century, the global research on the utilization of biogas residue (solid fraction) and biogas slurry (liquid fraction) increased rapidly, and countries around the world—including China, India, Pakistan, Germany, Australia, Bangladesh, Finland, Japan, Malaysia, and the United States—began to pay attention to environmental issues, and to pay more attention to the research of biogas slurry [1]. China is the world’s largest producer of livestock and poultry. The livestock and poultry breeding industry is a source of animal protein on which people depend, and an important part of China’s agricultural economy. Compared to 30 years ago, the current per capita consumption of meat in China has increased by 50%, and the demand for livestock, poultry, eggs, milk, cheese and other dairy products is increasing [2]. With the increase in intensive breeding, China’s livestock and poultry breeding has changed from traditional family sideline businesses to professional breeding households, breeding cooperatives, and breeding enterprises. The environmental pollution caused by the fast-developing livestock and poultry breeding industry has become increasingly prominent in China. The bioremediation and resource utilization of livestock/poultry waste needs to be addressed urgently [5,6,7,8,9]

Methods

Results

Conclusion