Pré-tratamento enzimático de efluentes com elevado teor de gordura empregando células íntegras lipolíticas

Abstract

Dairy industry wastewater contain high levels of lipids, being often dumped into watercourses without previous treatment. Due to the low solubility in water and solidification at room temperature, the lipids cause many problems to the anaerobic digestion, reducing the effluent biodegradability. As an alternative the enzymatic technology has been used to the development of products and processes less aggressive in environmental terms. However, factors associated with the high cost of obtaining the enzymes, related to the extraction and purification steps, make it impossible to apply them on an industrial scale. In this context, whole cells from the filamentous fungus Penicillium citrinum URM 4216 was prepared and used to perform the enzymatic hydrolysis of lipid-rich wastewater, facilitating the subsequent application of the anaerobic effluent treatment. The whole cells were cultivated in a basal medium containing per litre: carbon source (30 g), nitrogen source (70 g), NaNO3 (1 g), KH2PO4 (1 g) and MgSO4.7H2O (0.5 g) in flasks under orbital agitation for 96 h. Lipase activity was measured both dry biomass (mycelium-bound lipase) and filtrate (extracellular lipase). The mycelium-bound lipase production was maximized and physicochemical parameters, such as carbon (olive, soybean, colza and sunflower oils) and nitrogen (soy peptone, bacterial peptone and yeast extract) sources, initial pH of the medium (5.0; 5.5; 6.0; 6.5; 7.0; 7.5 and 8.0), temperature of fermentation (30 and 40°C) and inoculum size (105; 106; 107; 108 spores) were studied to determine the best conditions for mycelium-bound lipase production. Olive oil and soy peptone were found to be the best carbon and nitrogen sources, respectively, and the adjustment of the culture broth to pH 7.0 and 30°C of incubation temperature with inoculum size of 107 spores improved the mycelium-bound lipase activity. Under the optimized conditions, the whole cells were prepared and showed the lipase activity of 240 ± 18 U g-1 against only 15.2 ± 1.4 U g-1 to the filtrated, indicating the retention of lipase into the mycelium. The performance of whole cells was evaluated in the hydrolysis of crude milk wastewater, showing promising results. The rate of fatty acid production increased by 12 times the values presented for the same type of effluent without enzymatic treatment, to 6 hours of reaction. Tests were also carried out on the enzymatic hydrolysis of industrial wastewater, using free and immobilized enzymes. The use of free cells in reactive medium pH 8.0 showed a high percentage of enzymatic hydrolysis around 92.50.4 % to 48 hours of reaction. In order to perform the specific methanogenic activity test (SMA), was checked the simultaneous use of lipolytic whole cells, inoculum and crude wastewater (condition 1), prehydrolysed wastewater and inoculum (condition 2), and anaerobic biodigestion of the crude wastewater and inoculum (condition 3 / control), for a maximum period of 72h. The assays were evaluated by the Gompertz model, indicating a lower lag phase for the process involving the enzymatic treatment (condition 2). No significant COD removals were obtained from the industrial wastewater when compared to the results obtained for the anaerobic biodigestion process of crude wastewater plus the inoculum. The maximum rate of methane production was achieved in less time for trials involving the hybrid treatment of lipid-rich wastewater. The results demonstrated the potential for the application of enzymatic pretreatment as an integral part of the biological treatment of lipid-rich wastewater.