Effects Of Sewage Sludge Biochar On Crop Yield And Soil Physico-chemial Properties And The Risk Assessment Of Heavy Metals

Nowadays,China is undergoing a rapid development of urbanization,which has resulted in a dramatic increase of sewage sludge.How to dispose the sludge properly has been become one of hotspots in the environmental research.Pyrolysis has been regarded as a promising approach to transfer the sludge into valuable resources.In this study,the effects of pyrolytic sludge biochar on the soil chemico-physical properties,plant growth and heavy metal concentrations in soil were investigated in comparison to the untreated sludge.The objective of this study was to reveal the benefits and potential ecological risk of the application of sludge biochar on three crops(turnip,corn and pakchoi),in an attempt to testify the feasibility of using pyrolysis process to treat the sewage sludge and provide with a scientific guideline.The major results are as follows:1.The stimulating effects of the sludge biochar on crops growth were validated via a field trial,but only when a proper application rate was adopted.The highest yields of turnip,corn and pakchoi reached23.87 t/hm~2 in BC2 treatment,4.02 t/hm~2 in BC1 treatment,and 44.63 t/hm~2 in SS2 treatment,respectively.Comparing with the no addition control,the increase rates were up to 218.33%,27.22%and 56.58%,respectively.If the addition of sludge biochar was too high,it may pose an adverse effect on the crop production,taking the SS3 and BC3 treatments as examples.2.The application of sludge led to an increase of heavy metals concentrations including Cu,Zn,Pb and Pb in both root and above-ground tissues.A positive correlation was observed between the application rate and heavy metal content in plant.In accordance with the National Food Safety Standard(GB13106-91/GB2762-2012),the corn was safe for consumption while the Zn and Pb contents in turnip and pakchoi somehow exceeded the thresholds.In contrast,application of sludge biochar significantly reduced the heavy metals uptake by crops,resulting in a reduction of health risk by 23.73%,11.83%and25.47%in terms of turnip,corn and pakchoi,respectively.3.The contents of soil organic matter,alkali-hydrolyzable nitrogen and available phosphorus were increased due to the application of sludge or sludge-based biochar,to different extents.In addition,the application of the sludge or sludge-based biochar at proposed rates did not cause the soil contamination by the heavy metals,with an exception of Cd,which slightly exceeded the National Standard for Soil Environment Quality(GB15618-1995).4.In accordance with the relevant standards of EPA,the safe period of sludge treatments continuous application should be considered 27-110 years,of sludge-based biochar treatments continuous application should be considered 33-132 years.