Recovery of NH -N and PO -P from urine using sludge-derived biochar as a fertilizer: performance and mechanism.

Sludge-derived biochar (BS) was prepared by pyrolyzing municipal sludge at different temperatures and was used to recover NH -N and PO -P from urine. The effects of dosage, adsorption time, and urine concentration on the adsorption of NH -N and PO -P were investigated, and the adsorbed BS was used as a fertilizer to study its effect on the growth of pakchoi cabbage. The Elovich model was more consistent with the adsorption processes of NH -N and PO -P. Both the NH -N and PO -P adsorption isotherm model agreed with the Redlich-Peterson model. The Langmuir model showed that the largest adsorption capacity of BS600 for NH -N and PO -P could reach 114.64 mg g and 31.05 mg g, respectively. The NH -N adsorption mechanism of BS may have complexation with O-containing functional groups and precipitation reactions, while the removal mechanism of PO -P was co-precipitation. The pot experiment demonstrated that adsorbed BS600 can better promote the growth of pakchoi cabbage with the same amount of addition. With the addition of 5% adsorbed BS600, the weight of cabbage was 64.49 g heavier than without the addition of BS600. This research provided theoretical support for the recovery of NH -N and PO -P from urine as a fertilizer.