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.

Sewage sludge as substrate in Schinus terebinthifolia raddi seedlings commercial production.

Schinus terebinthifolia Raddi is a species with several potential uses; selecting the proper substrate and fertilizer rate can be vital for seedling production in a nursery environment. This study aims to evaluate two substrates, namely: (i) sewage sludge (SS) from Ilha WWTP; (ii) a commercial substrate (CS) made of organic materials (mainly sphagnum peat). Increasing rates of controlled-release fertilizer - CRF (0, 3, 6, and 12 kg m-3) were applied. The experiment was completely randomized with a factorial 2 × 4 scheme (substrates × rates). The seedlings' growth, biomass, and quality were evaluated. The treatments were compared by Tukey test and regression analysis, where linear, quadratic, and cubic models were considered. Principal components analysis (PCA) and cluster analysis were performed. The CRF rates showed non-significant effects for most of the investigated variables in the SS substrate. In the CS, a 7.8 kg m-3 rate of CRF showed the best growth performance. The multivariate analysis of the morphological parameters proved suitable as a complementary approach to evaluate the seedlings' quality. Seedlings reached recommended values for height, diameter, and quality in the 100% SS substrate without chemical fertilizers; thus, Schinus terebinthifolia production in the SS from Ilha is recommended. Besides the growth advantage, the SS can promote nursery cost savings with commercial substrates and chemical fertilizers.

Caracterização de biossólido e potencial de uso na produção de mudas de Schinus terebinthifolia Raddi / Characterization of biosolids and potential use in the production of seedlings of Schinus terebinthifolia Raddi

RESUMO O presente trabalho teve como objetivo caracterizar técnica, química e biologicamente o biossólido proveniente da estação de tratamento de esgoto (ETE) de Alegria, Rio de Janeiro, e inferir sobre sua aptidão como componente do substrato para produção de mudas de Schinus terebinthifolia Raddi (aroeira pimenteira). Foram coletadas amostras significativas do biossólido, submetidas às análises química e biológica em um laboratório especializado, atendendo às especificações da legislação vigente (Resolução CONAMA nº 375/2006). No viveiro, foram testadas quatro diferentes formulações de substrato, compostas de diferentes proporções volumétricas de substrato comercial (SC) e biossólido (BIO), consistindo nos seguintes tratamentos: T1 (100% SC + 0% BIO); T2 (75% SC + 25% BIO); T3 (50% SC + 50% BIO); e T4 (0% SC + 100% BIO). O delineamento experimental foi o inteiramente casualizado, com 4 tratamentos, 4 repetições de 18 mudas. O biossólido atendeu às especificações da legislação quanto à sua composição. Aos 120 dias após a semeadura foram mensuradas a altura da parte aérea e o diâmetro do coleto, observando que o crescimento das mudas foi diretamente proporcional à concentração de biossólido no substrato. O biossólido da ETE Alegria atende à legislação de uso agrícola e mostrou ser viável tecnicamente para a produção de mudas de aroeira pimenteira.

ABSTRACT This study aimed to technically, chemically and biologically characterize the biosolids from the Sewage Treatment Plant (STP) of Alegria, Rio de Janeiro, Brazil, and infer about their aptitude as a substrate component for the seedlings production of Anadenanthera macrocarpa (Benth.) Brenan. Significant samples of biosolid were collected and submitted to chemical and biological analysis in a specialized laboratory, according to the specifications of the current Brazilian law (CONAMA Resolution nº 375/2006). In the forest nursery, four different formulations of substrate, composed by different volumetric proportions of commercial substrate (CS) and biosolids (BIO) were tested, consisting of the following treatments: T1 (100% SC + 0% BIO); T2: (75% SC + 25% BIO); T3: (50% SC + 50% BIO); e T4: (0% SC + 100% BIO). The experimental design was CRD, each of the four treatments having four replications of eighteen seedlings. The biosolid met the legal specifications concerning its composition. Fifty days after sowing, shoot height and stem diameter were measured. It was observed, for both characteristics, that seedling growth was directly proportional to the concentration of sewage sludge in the substrate. Finally, the Alegria ETE's biosolid attends the legislation and shows a technically viable alternative for the production of angico vermelho seedlings.