Biochar for removal of pollutants from cotton pulp black liquor and its impact on agricultural ecosystem

The rapid growth of the textile industry has made cotton pulp black liquor (CPBL) a major source of wastewater, which contains high levels of organic pollutants and heavy metals that pose significant threats to aquatic and soil ecosystems. Traditional treatment methods are often expensive and inefficient. In this study, we prepared modified “Hui” jujube leaves biochar (M-YBC), and applied it to the treatment of CPBL. By analyzing the composition changes of CPBL, it is found that M-YBC has high efficiency in removing organic pollutants and heavy metals. To assess the impact of the treated CPBL on the agricultural ecosystem, a soil-cultivated mung bean sprout irrigation experiment was conducted. The results showed that M-YBC has an outstanding adsorption capacity of 890.15 mg/g for CPBL. After treatment, the COD of CPBL decreased from 285.51 g/L to 0.02 g/L, and the pH decreased from 13 to 7. Heavy metals like copper, iron, manganese, and chromium were undetectable. Irrigation experiments showed that untreated CPBL inhibited the growth of mung bean sprouts, with low germination rate and no survival. However, the germination rate and survival rate of M-YBC treated CPBL and distilled water irrigated mung bean sprouts are both above 85 %. High-throughput sequencing analysis showed that M-YBC treatment significantly increased the α-diversity index of the rhizosphere soil microbial community and alleviated the negative impact of CPBL on microbial community . This study shows that M-YBC can effectively remove pollutants from CPBL, promote the healthy growth of mung bean sprouts, and stabilize the soil microbial community . • M-YBC achieves a high adsorption capacity of 890.15 mg/g for CPBL, indicating its excellent adsorption performance. • The untreated CPBL inhibits the growth of mung bean sprouts, while sprouts watered with M-YBC-treated CPBL grow normally. • Untreated CPBL destroyed soil microorganism diversity, but M-YBC-treated CPBL promoted it.