Application of waste lemon extract to rehabilitate the copper-contaminated farmland through gravitational soil flushing and stabilization

The present study aimed to investigate the effect of the waste lemon extract on the flushing treatment of the copper-contaminated soil collected from contaminated farmland, in which the copper concentration was measured as high as 2487 mg/kg. The soil flushing solution was prepared using the extract from collected waste lemons. The soil flushing treatment using the solution containing commercial citric acids was also conducted for comparison. Additionally, the waste lemon was used for soil rehabilitation after composting treatment.

The soil copper concentration treated with the solution containing waste lemon extract decreased more than that treated by the commercial citric acid solution at the comparable citric acid concentration. This is because the waste lemon extract solution contains additional co-dissolved organic substances other than citric acid and the flushing treatment had a higher retention time. For the treatment with lemon extract, the soil pH values were 4.56, 5.70 and 6.29 before, after lemon extract flushing and after compost treatment. The copper plant availability dropped from 677 mg/kg for the soil before flushing to 156 mg/kg after stabilization with composted waste lemon. Therefore, the citric acid flushing combined with stabilization was found effective for heavy metal removal in the soil environment.