Chemical characteristics and valuation of sewage sludge from four different wastewater treatment plants.

Sewage sludge contains plant nutrients and organic matter in its composition, making it a potential partial substitute for mineral fertilizers if it meets environmental, agronomic, and sanitary standards. The objective was to evaluate the content of nutrients and heavy metals in the sludge generated in four wastewater treatment stations (WWTPs) in Rio de Janeiro state and assess its potential value and usefulness. The samples of 19 batches from the WTTPs Alegria, Barra da Tijuca, Ilha do Governador, and Sarapuí were analyzed. The WWTPs differ in methods and processes used for treating sewage and sludge. The total contents of C, N, P, K, Ca, Mg, Fe, Al, Na, Co, Mn, As, Ba, Cd, Cr, Cu, Ni, Se, Pb, and Zn were evaluated, as well as the ratio C/N, pH, organic matter content, and electrical conductivity. The grouping of sludge samples was assessed using principal components (PCA) and cluster analysis. The economic valuation of sludge was conducted utilizing the substitute goods method, which compared the sludge's N-P-K contents with the prices of consolidated nutrient sources. All the evaluated sludge batches exhibited concentrations of heavy metals below the limits allowed by Brazilian law, along with high levels of nutrients and organic matter. Considering the chemical characteristics, all evaluated materials showed potential for agricultural use, but it is crucial to evaluate the microbiological characteristics of sludge batches before agriculture application. PCA and cluster analysis demonstrated that sludge samples from the same WWTP clustered close to each other, demonstrating higher similarity among themselves than with samples from other WWTPs. The sludge had an average added value of U$ 88.46 per megagram, considering the total contents of N, P, and K in its composition. Land application of sewage sludge can reduce the need to purchase mineral fertilizers, thereby supporting the feasibility of reusing this material in the agricultural sector.

Fertilizers with coated urea in upland rice production and nitrogen apparent recovery / Doses de fertilizantes com ureia revestida na produção de arroz de terras altas e recuperação aparente de nitrogênio

Urea is the most used N fertilizer for upland rice, however, a great percentage of N loss can occur with the use of this fertilizer. The use of products that provide reduction of N loss for urea fertilizers can contribute to increase N use efficiency. The objective of this study was to determine the effect of N rates applied in the form of coated urea in the content and accumulation of N in dry biomass, apparent recovery of nitrogen and grain yield of upland rice. The experimental design was a randomized complete blocks arranged in a 4 x 3 + 1 factorial scheme. The treatments consisted of four sources of N fertilizer [1. Common urea; 2. Polymer-coated urea for slow release of N (PCU); 3. urea with the urease inhibitor N-(n-Butyl) thiophosphoric triamide (NBPT); and 4. urea coated with copper sulfate and boric acid as urease inhibitors (UCCB)], with three fertilization rates (30, 60 and 90 kg ha-1 of N). In addition, we included a control treatment without N application. Coated urea did not provide increases in rice grain yield in relation to common urea. The increasing amount of N resulted in significant increases in rice grain yield (from 3217 to 5548 kg ha-1, 2010/11, and from 3392 to 4560 kg ha-1, 2011/12). The apparent nitrogen recovery rate decreased with the increase in N applied doses.

A ureia é o fertilizante nitrogenado mais utilizado para o arroz de terras altas, no entanto, esse fertilizante tem grande percentual de perda de N. O uso de produtos que proporcionam redução da perda de N em fertilizantes com ureia pode contribuir para aumentar a eficiência de uso do nitrogênio. O objetivo deste estudo foi determinar o efeito de doses de N aplicadas na forma de ureia encapsulada no teor e acúmulo de N na biomassa seca, recuperação aparente de nitrogênio e produtividade de grãos de arroz de terras altas. O delineamento experimental foi em blocos ao acaso no esquema fatorial 4 x 3 + 1. Os tratamentos consistiram de quatro fontes de N fertilizante [1. ureia tradicional; 2. Polímero de ureia revestida para liberação lenta de N (PCU); 3. ureia com o inibidor de urease N- (n-butil) triamida tiofosfórico (NBPT); e 4. ureia revestida com sulfato de cobre e ácido bórico como inibidores de urease (UCCB)], com três doses de fertilizante (30, 60 e 90 kg ha-1 de N). Além disso, incluímos uma testemunha sem aplicação de N. Ureia revestida não forneceu aumentos no rendimento de grãos de arroz em relação à ureia comum. O aumento da quantidade de N resultou em aumentos significativos no rendimento de grãos de arroz (de 3217 para 5548 kg ha-1, 2010/11, e de 3392 para 4560 kg ha-1, 2011/12). A taxa de recuperação aparente de nitrogênio diminuiu com o aumento das doses aplicadas de N.