Abstract
In order to explore a safe, effective way to use sludge as agricultural fertilizer it is necessary to effectively separate and remove the heavy metals embedded in sludge. In the study, the ozone-electric two-stage treatment was used to transform heavy metal copper in the sludge, and then the treated sludge was used for maize production and the transferring of Cu in cultivation medium and plants, and the enrichment effect of Cu in plant were investigated. According to composition of culture substance, five treatments were set in maize planting experiments: CK, Agricultural soil without addition; T1, Agricultural soil supplemented with raw sludge; T2, Agricultural soil treated with ozone sludge; T3, Agricultural soil with ozone treated and electric treated sludge; T4, Agricultural soil added with common organic fertilizer. The results showed that in different treatments, the Cu content of organs showed the order of root> stem> leaf> cob> grain. Comparing root Cu content, the lowest was in T1 treatment, which was 11.60 mg/kg, while the lowest of grain Cu content was found in CK treatment, which was 1.36 mg/kg. In the upper, middle and lower soil layers, the highest and lowest Cu content was in T4 and CK, respectively. In both middle and lower soil layers, the Cu content of T1, T2 and T3 sludge treatments had a trend of T1>T2>T3; the difference of the Cu enrichment ability between different organs is not significant in the same soil layer. From each treatment, the Cu enrichment ability of plant of CK was higher than that of other treatments. According to the ability of Cu transferring to the above-ground part of plant, treatments are ranked as CK>T3>T4>T1>T2. The transferring of Cu from soil to plant was mainly affected by fertilizer level and the transferring rate of Cu from soil to stem, leaf and root was relatively high, but it was hardly affected by sludge. In summary, after ozone-electro treatment, the application of sludge does not significantly affect the Cu content in maize, and the Cu content in each treatment does not exceed the limit value of agricultural production.
Highlights
More and more domestic sludge is produced with the advancement of China’s urbanization, and technologies on how to dispose the sludge safely and economically have been widely concerned across our country
According to composition of culture substance, five treatments were set in maize planting experiments: CK, Agricultural soil without addition; T1, Agricultural soil supplemented with raw sludge; T2, Agricultural soil treated with ozone sludge; T3, Agricultural soil with ozone treated and electric treated sludge; T4, Agricultural soil added with common organic fertilizer
The amount of Cu in mud phase increased at first and decreased, while the Cu amount in water phase had been increasing gradually, with the fast increase rate occurred at 20 min after ozone aeration, but no Cu peak happened at 40 min after ozone aeration (Figure 1), indicating more Cu would be released from sludge later
Summary
More and more domestic sludge is produced with the advancement of China’s urbanization, and technologies on how to dispose the sludge safely and economically have been widely concerned across our country. Sludge contains various organic and inorganic plant nutrients (Su, et al 2012), which is capable of improving soil fertilities (Yang, et al 2009; Sharma, et al 2017), so the use of sludge as fertilizer is the most potential disposing way. In China, the use of sludge as fertilizer accounts for 44.83% of total sludge volume (Zhang, et al 2015). For the pollutants from sludge, heavy metals have a significant impact on the quality of crops, for they are highly toxic (Zhang, et al 2015), hardly decomposed by microorganisms, and enriched in crops if applied in farmland, doing harm to human (Liang, et al 2009), and copper (Cu) is a typical heavy metal elements from sludge. Cu is common in biological tissues, existing ls.ideasspread.org
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