Uptake of nutrients and heavy metals in struvite recovered from a mixed wastewater of human urine and municipal sewage by two vegetables in calcareous soil

Abstract

Struvite (MAP) recovered from a mixed wastewater of human urine and municipal sewage through a novel two-step precipitation method was well developed, but its nutrient availability and pollutant transmission to plants have not been investigated. The objective of this study is to explore the feasibility of using MAP as a phosphorus (P) fertilizer in cultivating vegetables by comparing with single superphosphate (SSP). A greenhouse pot experiment was conducted with two P rates (0 vs 0.4 g P2O5/pot) and two vegetables of cabbage and lettuce were planted in the calcareous soil. The vegetable biomass and chemical concentrations of nitrogen (N), P, and metal elements in the soil and vegetable tissues were determined. Results showed that MAP and SSP supply greatly increased the cabbage biomass compared with the unfertilized control because the supply of SSP/MAP enhanced the P, Mg, and K accumulation in the cabbage shoots. However, P fertilization decreased the lettuce biomass, especially MAP application, because the high soil pH and external P fertilization together hampered Zn uptake by the lettuce. The heavy metal concentrations in vegetables supplied by MAP were lower than the maximal contaminant levels for Chinese food safety national standard (GB2762-2017). Based on these findings, it was concluded that MAP is a promising P fertilizer for cultivating cabbage in the tested soil. However, the vegetable should be carefully considered in further studies when MAP is used as a P fertilizer in calcareous soils.