Biodegradação anaeróbia de efluente de laticínios hidrolisado por enzima Kluyveromyces lactis

Abstract

The dairy industry has a great impact due to the excessive consumption of water and the high production of residues, mainly liquids, per production unit. Dairy effluents need treatment before disposal in the environment. Due to the high organic load of the effluent, the treatment takes time, which implies larger treatment units. Thus, in order to reduce treatment time, the objective of the present study was to evaluate the degradation of dairy effluents in anaerobic reactors with and without the application of lactase produced by Kluyveromyces lactis. For evaluation, two sludge blanket and upward flow reactors (UASB) with 16 L of useful volume each were mounted on a bench scale, with the application of synthetic dairy effluent with and without the presence of lactase. The synthetic effluent (ARL) was prepared with the dilution of milk in order to apply organic loads of approximately 0.5, 1.0, 2.0 and 3.0 kg m-3 d-1 of COD to the reactors, comprising 4 phases lasting 45, 95, 95 and 45 days, respectively. The preparation of the synthetic effluent was carried out in the acidification and equalization tank (TAE), which had the concentration of nutrients corrected, with the addition of ammonium sulfate and potassium phosphate, in order to obtain a COD: N: P ratio of 500: 5: 1. The alkalinity was supplemented with sodium bicarbonate, maintaining an initial pH value of 7.0. The HRT was maintained at 1 day for all phases. The system was fed by means of metering pumps, from two TAEs. In one of the TAEs, lactase was added in batch. The first order degradation coefficient of organic matter (k) of the ARL with and without lactase was determined. In this assay, effluent samples were collected over 10 h submitted to constant mixing in a medium inoculated with sewage sludge to quantify the COD to assess the biodegradability of ARL and determine the k value in anaerobic medium. UASB1 that received ARL with lactase showed no difference in efficiency of COD removal compared to UASB2 that received ARL without lactase. The average efficiencies of each phase in terms of COD removal were 69, 77, 70 and 56% for UASB1 and 68, 72, 69 and 57% for UASB2. The reduction in efficiency in the last phase was due to an increase in the organic load applied to the system, and an increase in volatile organic acids in the reactors. From the Monod kinetics, the growth coefficient values (mg mg-1 d-1) were obtained; Kd - endogenous decay coefficient (d-1); μmax - maximum rate of microbial growth (d-1); KS - concentration of the limiting substrate (mg L-1), equal to 1.16 and 1.20; 0.05 and 0.04; 0.18 and 0.13; and 248 and 109, respectively for UASB1 and UASB2. After the batch biodegradability test, the values of k equal 2.50 d-1 for the ARL with the lactase, and 1.93 d-1 for the ARL were obtained. It can be concluded that the analysis of the anaerobic degradation of ARL in the UASB reactor proved to be adequate with the achievement of COD removal efficiencies considered satisfactory (70-76%). However, the increase in the organic volumetric load to values between 2 and 3 kg m-3 d-1 of COD, led to a reduction in alkalinity, accumulation of volatile acids in the reactor, and despite maintaining the pH (values around 7, 0), reduced COD removal efficiency (57%). The application of lactase as a pretreatment was not effective, it was evaluated, in increasing the biodegradability of synthetic wastewater from dairy products.