Avaliação de um protótipo de Sistema Alagado Construído para o tratamento de água residuária de queijaria com soro de leite vegetado com Cymbopogon citratus

Abstract

The dairy industry has significant socioeconomic importance, particularly in Minas Gerais, but faces substantial environmental challenges related to the treatment of dairy wastewater (DWW). These effluents present high organic loads and elevated nutrient concentrations, such as phosphorus and nitrogen, requiring costly treatment processes that are often financially unfeasible for producers of different scales. Furthermore, conventional treatment methods do not completely remove pollutants, especially nutrients, reinforcing the need for sustainable solutions capable of efficiently removing these compounds. In this context, the present study aimed to evaluate the performance of a prototype Horizontal Subsurface Flow Constructed Wetland system (HSSF-CW) as an alternative for treating dairy wastewater subjected to different organic loading rates generated by the controlled addition of whey. The research was conducted at the facilities of the Agricultural Research Company of Minas Gerais / Cândido Tostes Dairy Institute (EPAMIG ILCT). The experimental infrastructure consisted of three beds constructed from adapted 200-L plastic drums, with the following dimensions: 0.91 m in length, 0.35 m of useful height, and 0.50 m in width. Each unit was filled with gravel (no. 0) and vegetated with lemongrass (Cymbopogon citratus (DC.) Stapf). The CWs were operated in four-day cycles, during which they were fed with wastewater and subsequently maintained at rest. Three experimental conditions corresponding to different organic loading rates were evaluated. Monitoring occurred between March 24, 2025, and July 4, 2025, totaling seven sampling events of treated wastewater collected from the beds. The experiment was conducted in a Randomized Complete Block Design (RCBD), with three treatments (CW1, CW2, and CW3) and seven operational cycles considered as blocks. The following variables were analyzed: pH, electrical conductivity, turbidity, BOD₅,20, COD, phosphorus, nitrogen, oils and grease, total solids, total suspended solids, total fixed solids, total volatile solids, fixed suspended solids, and volatile suspended solids. The results were subjected to analysis of variance (ANOVA) and, when significant, means were compared using the Student-NewmanKeuls (SNK) test, both at a 5% significance level. For electrical conductivity, the t-test was applied at the 5% significance level. The CW systems showed significant reductions in BOD₅,20, COD, phosphorus, oils and grease, total solids, and suspended solids. Mean BOD₅,20 removal efficiencies were 80% (CW1), 81% (CW2), and 67% (CW3). COD removal ranged from 60% to 78%, while total phosphorus removal was 63% (CW1), 42% (CW2), and 70% (CW3). Total nitrogen removal ranged from 51% to 66% (p > 0.05), and oils and grease removal reached 83%, 75%, and 54% for CW1, CW2, and CW3, respectively. Solid fractions varied between 50% and 65%, with no significant differences among systems. It is concluded that the HSSF-CW vegetated with lemongrass demonstrated satisfactory performance at the prototype scale, particularly under moderate organic loads, representing a low-cost, efficient, and environmentally sustainable alternative for dairy wastewater treatment, with potential application in artisanal cheese production units.