Utilization of Dairy Wastewater for Sustainable Produciton

Abstract

Inefficient use of nitrogen and phosphorus leads to anthropogenic eutrophication of rivers, lakes, and oceanic basis worldwide, causing an environmental problem that can trigger a death cycle of an entire water body. Microalga, one of the organisms that benefits from the excessive nutrient runoff and uses the sunlight to catalyze reactions that cause eutrophication, can also be part of a solution. The study presented in this thesis represents a possible integrated solution for the nutrients accumulated, especially in dairy farms. This work shows how it is possible to treat dairy wastewater in large volumes, using plastic photobioreactors with an initial inoculum of microalgae, in this case Chlorella sp., in a mixotrophic solution (since the dairy wastewater used in this study was not sterilized). It was also shown that in pilot-scale, ratio 1:10 (dairy wastewater in water) was capable of removing high amounts of nutrients, up to 97.55% of ammonium, 39.27% of nitrate, and 27.05% of phosphate. The 1:10 was also capable of producing competitive biomass amounts when comparing to the controls, 1.575 ± 0.599 g.L^(-1) and 1.315 ± 0.240 g.L^(-1). Moreover, none of the treatments (control, controlN, 1:10, 1:10N, 1:30 and 1:30N) were significantly different from each other, considering the nutrients (〖NH〗_4^+, 〖PO〗_4^(3-), 〖NO〗_3^-) removal rates and biomass, when adding or not extra CO2. In addition, a study was carried to evaluate the taste preference of calves fed Chlorella sp. produced in the previous steps. Sterilized biomass was used for feeding trials with six Holstein and crossbred dairy heifer calves. No mycotoxins were found in the biomass and many heavy metals were tested, having the levels below the maximum content recommended for animal feeding. The microalgae biomass produced had a protein content of 49.2%, 2.32% of fat, 38.5% of carbohydrates, and around 10% of different minerals and nutrients. They were fed 0, 30, and 60 g of Chlorella sp. daily in a sequential elimination study. No difference were found for dry matter intake of calves fed 0, 30, or 60 g of Chlorella sp., indicating that microalgae may be added to the rations of calves without any adverse effects.