Estudo do processo semicontínuo de tratamento do soro do leite utilizando microalgas em sistema aberto

Abstract

The dairy industry is one of the most important sectors of the food industry, generating a large number of effluents, mainly whey, which has high concentrations of COD (chemical oxygen demand), TN (total nitrogen), and TP (total phosphate). Microalgae are photosynthetic microorganisms that have high efficiency in removing these contaminants and can be grown in open and semi-continuous systems, which have lower costs and greater flexibility. In this sense, this work aims to evaluate the use of the microalgae Tetradesmus obliquus LCE-01 in the treatment of whey diluted in concentrations of 1 and 4 % in a semi-continuous process in an open system without forced aeration and with constant illumination of (100 µmol m-2 s-1). For this, the remediation experiment was carried out with a total process time of 16 days (1 batch of 7 days and 3 semi-continuous cycles of 3 days) with TRV of 20, 40, 60, and 80 % in a feedback time of 3 days. (setting HRT at 15, 7.5, 5, and 3.75 days, respectively) and keeping the pH between 8 - 8.5. The experiments were monitored for pH, cell dry weight, COD, TN, and TP. Regarding COD, residual values of 200 - 250 and 240 - 600 mg L-1, for 1 and 4 % of the whey, are still high according to the European standard for the release of 125 mg L-1 . Regarding TN, residual values were 6 - 9.8 and 25 - 33 mg L-1 with a maximum removal rate of 80 and 60 % for 1 and 4 % respectively, with some experiments respecting the release limit of 10 - 15 mg L-1 and 70 – 80 % minimum removal rate. For TP, the residues were 1 - 6 and 9 - 16 mg L-1, also in some experiments fitting the European norm for release of 3.1 - 6.2 mg L1 , despite having had a maximum efficiency removal of 70 and 30 % for 1 and 4 % serum, respectively. It was noticed that the semi-continuous process showed stability of operation and that it needs improvements to remove a greater amount of contaminant. Between 250 - 600 mg L -1 of cell dry weight was produced, with the highest values obtained for whey at 4 %. It also verified the importance of daily maintenance of the pH of the system to values between 8 - 8.5 to effectively conserve the microalgae within the system. TRVs of up to 40 % for all contaminants had higher removal rates (except 60 and 80 % for whey 1 % but needs to be reevaluated). As suggestions for improving the system, we can mention the inclusion of forced aeration, longer refeeding times, and insertion of bacteria or fungi filaments. It was noticed that the organic load imposed with the 4 % diluted whey was in excess, mainly of TN and TP and sequential steps may be necessary to stabilize the residual parameters of the contaminants.