Nutrient released characteristics of struvite-biochar fertilizer produced from concentrated sludge supernatant by fluidized bed reactor. (1st January 2023) - Li, Yingxue
Abstract: With the exacerbating water eutrophication globally, it is important to recover nitrogen (N) and phosphorus (P) from sewage for recycle. In this study, coconut shell biochar and ethylene diamine tetraacetic acid (EDTA) were added into the designed fluidized bed reactor (FBR) to create struvite-biochar. N and P released from struvite-biochar and the recovery efficiency of N and P from concentrated sludge supernatant were analyzed. Results showed that the optimal operation condition for hydraulic retention time (HRT), pH, Mg/P molar ration, and addition amount EDTA were 90 min, 9.5, 1.2, and 0.2 g/L, respectively. The recovery efficiency of NH4 + -N and PO4 3- -P, and purity struvite for FBR were 34.41%–38.05%, 64.95–68.40%, and 84.15%, respectively. The recovery efficiency of NH4 + -N and PO4 3- -P were respectively increased by 7.23% and 5.36% when FBR with addition of 0.33 g/L coconut shell biochar, but purity struvite from struvite-biochar decreased by 45.70%. Contents of As, Cd, Pb, and Cr in struvite and struvite-biochar were all lower than Chinese Standard Limits of Fertilizer. Compared to commercial chemical fertilizer, such as superphosphate and urea, struvite-biochar and struvite have slowly released N and P. The amounts of released P, NO3 − -N and NH4 + -N from struvite-biochar were higher than struvite during the five leaching times. Compared with struvite, the total amounts of released P, NO3 − -N and NH4 + -N from struvite-biochar increased by 4.9%, 3.5% and 8.3%, respectively. Therefore, it is valuable to add biochar into FBR to recovery N and P from concentrated sludge supernatant and make struvite-biochar as a slow-release fertilizer. Highlights: The fluidized bed reactor (FBR) designed to create struvite-biochar. The recovery efficiency of nutrient was increased when FBR with addition biochar. Total amounts of released nutrient of struvite-biochar was higher than struvite. The struvite-biochar is a slow-release fertilizer.