Remoção de fósforo de efluente sanitário utilizando filtros com lodo de ETA

Abstract

The production of domestic sewage has increased considerably in recent decades and the deficiency of treatment systems in the removal of certain constituents contributes to the pollution of waterways by nutrients, mainly phosphorus. Phosphorus is considered the most important nutrient in eutrophication phenomena, making it the focus for improving the quality of water bodies, as it is the limiting element to triggering algal blooms. Phosphorus removal processes take place by physical, chemical and biological methods. An efficient and economically viable way to remove these substances from the sewage is through filtration, using material with the potential for adsorption of this constituent. Therefore, the objective of this work was to evaluate the removal of phosphorus in filters filled with sawdust and sludge from the Water Treatment Station (ETA). Two filtration columns were constructed using polyvinyl chloride (PVC) tubes with an internal diameter of 0.10 m and 1.00 m in height, which consisted of Filter 1 (F1) and Filter 2 (F2). The internal layers of the filters were filled in the following order: a 0.30 m layer of sawdust, followed by a 0.40 m layer of residue, ending with another 0.30 m layer of sawdust for F1; and mixture of sawdust and residue in the ratio of 1: 1 to F2. The sludge from the Federal University of Lavras (UFLA) ETA before being used was dried and sieved (0.425 mm). In addition, fine mesh screens were placed on both the lower and upper ends to prevent waste loss. The experiment was conducted for a period of 6 months, with analyzes of pH, total P, orthophosphate, electrical conductivity (CE), total nitrogen Kjeldahl (NTK), chemical oxygen demand (COD) and total, suspended and dissolved solids ( SST and SDT). For the sludge, the zero load point (PCZ) was evaluated and a sample was sent to the UFLA Soil Analysis Laboratory for its chemical characterization. Before the filter was made, the adsorptive capacity of the ETA sludge was determined in laboratory tests, evaluating the efficiency of removing phosphorus from sanitary effluent. Kinetic tests were performed, and the adsorption isotherms were determined using the Langmuir and Freundlich models. As a way of evaluating the viability of the residue generated in the filter after treatment as a fertilizer, it was also tested in plastic pots nº 05 with dimensions of 19 x 23 x 23 cm, the planting of tifton 85 grass with 4 treatments using the residue of the filters. T1 (Witness) - Solo + Tifton 85 grass; T2- Soil + biosolid (20%) + Tifton 85 grass; T3- Soil + biosolid (50%) + Tifton 85 grass; T4- Soil + biosolid (100%) + Tifton grass 85. The treatments had 3 replicates each, and the soil used was removed from the area belonging to UFLA, which is classified as Latossolo Vermelho Distrófico, clay texture. For the use of this soil, liming was performed to correct its pH, in which 2.64 t ha-1 of limestone were proportionally applied. The adsorption isotherms adjusted well to the experimental data and the best fit was obtained using the Freundlich model, with the maximum phosphorus adsorption capacity in the ETA sludge equal to 1.4 mg g-1. Tests have shown that this is an adsorbent with very fast reaction kinetics, and probably the kinetic mechanism is second order. The filters had total phosphorus removal efficiencies of 91%, phosphate 85 and 83%, respectively for F1 and F2. Regarding organic matter, the average COD values were 142.05 mg L-1 for the effluent at the end of the day for filter 1 and 142.17 mg L-1 for the effluent at the end of the day for the filter. 2, not differing statistically and with removal efficiency of approximately 58% for nitrogen (NTK), for both filters. Tifton grass 85 produced 51.7; 46.7; 21.2 and 24.9 g of dry matter for treatments T1, T2, T3 and T4, respectively, over a period of 30. However, for the conditions evaluated, the ETA sludge provided, on average, the same plant development compared to conventional fertilizer application.