Assessment of Biological and Chemical Contaminants of Urine-Derived Struvite Fertilizer
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Date
2024-12
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Addis Ababa University
Abstract
Nitrogen (N), phosphorus (P), and potassium (K) are nutrients that are essential for food production and are often referred to as NPK: NPK fertilizers are a crucial part of modern agriculture. Urine is one of the rich sources of nitrogen, phosphorus, and potassium and can be converted to struvite a kind of orthophosphate mineral that is precipitated by Mg, ammonium, and phosphate ions in equal molar ratios.(MgNH4PO4.6H2O) and its derivative struvite-K, potassium magnesium phosphate hexahydrate (MgKPO4·6H2O) to serve as fertilizer.However, it is commonly contaminated with bacterial pathogens, plasmids, phages, and residual antibiotic drugs which are hazardous to human and animal health. The goal of the current study was to assess the presence of these contaminants and their fate during the optimal process of producing struvite and its derivative K sample is a sample of potassium magnesium phosphate hexahydrate (MgKPO4·6H2O), from composite human urine. To this end, fresh pee, stored urine, and struvite samples throughout the struvite synthesis process were collected for DNA extraction and residual antibiotics analysis for Penicillin G, Cephalosporin, Cefotaxime, Ciprofloxacin, Tetracycline, Oxytetracycline and Doxycycline, Sulfamethoxazole. The community structure of the bacteria (pathogen) was studied with shotgun metagenomic and bioinformatic analysis, whereas the chemical contaminants were analyzed by ultra-high liquid chromatography mass spectrometery. The data showed that the Gram negative, Pseudomonadota (syn, Proteobacteria) was the most dominant bacterial phylum isolated from accounting for 60% and 43% followed by the Gram positive Bacilliota (Firmicutes) with 25% and 39% of the fresh and stored samples, respectively. The phylum Bacilliota (61%), Pseudomonadota (18%), and Bacterodota (12%) dominated the struvite-K sample. Amongest the Phylum Proteobacteria, members of the gamma-Proteobacteria displayed OTU counts of 12,116 on fresh urine samples which was twice (6,155) more than the OTU counts recorded from struvite (stored) samples. The Genome sequence analysis also showed that the genera Streptococcus, Bacillus, and Escherichia phages predominate; in fresh urine, where the Streptococcus phage is almost 50% of the OTU counts. Interestingly, the data showed he stored urine contained higher number of genes for antibiotic resistance than the fresh urine samples. Acinetobacter, Aeromonas, and Enterococcus are the key pathogens analyzed, whereas the top five resistance genes in all three samples were the aminoglycosides, carbapenem, chloramphenicol, erythromycin, and efflux pump. Despite a change in gene families, the carbapenem, aminoglycoside resistance, and efflux pump families were found to be persistent in struvite. Ciprofloxacin, cefotaxime, oxytetracycline, and tetracycline were among the antimicrobials. The calibration curves showed linearity coefficients (R2) ranged from 0.9778 to 0.9945. Tetracycline's mean recovery percentage was 92.86 ± 7.26, while sulfomethoxazole's ranged from 71.46 ± 12.62. However, the intra-day precision, which ranged from 5.05 percent for oxytetracycline to 17.66% for sulfomethoxazole, satisfied EPA and EU standards. The potential antibiotics had limits of quantification and detection that varied from (1.47-0.91) μg/kg and (3.03-9.77) μg/kg, respectively. Among the assessed antibiotics none was detected in the product struvite. Based on this study, the presence of pathogen genomes, antibiotic resistance genes and their carriers requires due attention during urine sanitization. The absence of residual antibiotic drugs in struvite indicates its potential safety for agricultural application while further study on the mechanism of disappearance is recommended.
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Keywords
Struvite, Human Urine, Fertilizer, Mobilomes Resistomes, Pathogens