Resposta da atividade bacteriana em reator de leito estruturado sob diferentes Cargas Orgânicas Volumétricas (COV)

Abstract

The objective of this study was to evaluate the response of bacterial activity in a structured bed reactor, of continuous and ascending flow in the removal of organic matter and nitrogen from wastewater from dairy products (crude concentration of 5.326 mg.L-1 of COD and 39 mg.L-1 of N-NH4 + ) under different volumetric organic loads (VOL). A reactor built in acrylic on a bench scale with a total volume of 2,27 L and a useful volume of 1,32 L was used. The structured bed was composed of four cylindrical polyurethane foam structures fixed inside the reactor. The reactor was operated with three experimental phases: Phase I with VOL of 1,2 kg COD.m3 .d-1; Phase II with VOL of 1.4 kg COD.m3 .d-1 and Phase III with VOL of 1.8 kg COD.m3 .d-1. The hydraulic detention time (HDT) was maintained at 16h during the whole experimental period. The reactor had an internal effluent recirculation system, with a ratio of 3. The temperature of the system was maintained at 28ºC, with 2/1 aeration and non-aeration cycles (intermittent aeration). Monitoring was carried out by analyzing pH, alkalinity, Chemical Oxygen Demand (COD), ammonia nitrogen (N-NH3), nitrite (N-NO2 - ), nitrate (N-NO3 - ), Total Kjeldahl Nitrogen (NKT), series of solids. Analyzes were performed to estimate the most probable number (MPN) of ammonia oxidizing bacteria (AOB), nitrite oxidizing bacteria (NOB) and denitrifying bacteria, as well as the colony forming units (CFU) count of heterotrophic bacteria. From the results, DQOT and DQOF removals greater than 90 and 91% were obtained, respectively, in all phases. In Phase I the largest removals of NKT and NT were obtained, 81 and 74% respectively, while in Phase II and III the smallest removals of NKT and NT were obtained, 74 and 70% for Phase II and 54% and 37% for Phase III, following the order. The increase in VOL influenced nitrogen removal by directly interfering with the ammonification process. The MPN concentrations of AOB and NOB decreased with the increase in VOL, in the same way, it was noted with scanning electron microscopy (SEM) that the abundance of microorganisms declined with a predominance of fungi. Regarding TS and VSS values, removals were also influenced by the increase in VOL. The speeds obtained in the kinetic tests were for nitrification via N-NH4 + from 0,11 to 0,21 mg NNH4 + .gSSV-1 .h-1, from nitrification via N-NO2 - was 0,08 to 0,09 mg N-NO2 - .gSSV-1.h-1 and denitrification via N-NO3 - from 0,78 to 0,85 mg N-NO3 - .gSSV-1 .h-1 for Phases II and III, respectively. Thus, it was concluded that the system composed of a structured bed reactor operated with intermittent recirculation and aeration in the treatment of dairy wastewater under different VOLs can be advantageous mainly for the simultaneous removal of organic matter and nitrogen, as well as promoting a stable and favorable environment for combined processes when combined with adequate operating conditions.