Abstract
Swine wastewater contains high concentrations of organic compounds, nutrients (nitrogen and phosphorus), heavy metals, and residual antibiotics, amongst others, that have negative impacts on the water environment. The main aim of this work was to remove nutrients from anaerobically digested swine wastewater using an intermittent cycle extended aeration system (ICEAS). The effects of operational parameters such as cycle time, organic loading rate, C/N ratio, and aeration/mixing ratio on the pollutant removal efficiencies of ICEAS were studied and compared with the performance of a conventional sequencing batch reactor (SBR). The following optimal conditions were obtained: cycle time, 6 h; organic loading rate, 0.86 kg COD m−3 day−1; C/N ratio, 2.49–2.82; and aeration/mixing ratio, 1.57. The pH was maintained in the range of 6.0–8.0. The total organic carbon (TOC), total nitrogen (TN), ammonium (NH4+), total phosphorus (TP), and color removal efficiencies of ICEAS were higher than those of the conventional SBR, with removal efficiencies of 95.22, 88.29, 97.69, 85.81, and 97.84%, respectively, compared to 94.34, 81.16, 94.15, 77.94, and 96.95%, respectively, observed in the SBR. TOC, TN, NH4+, TP, and the color removal efficiencies of ICEAS were higher by 0.88, 7.13, 3.54, 7.87, and 0.95%, respectively, than the conventional SBR. The good results from this study show that ICEAS is a promising technology for the removal of organic contaminants and nutrients from anaerobically digested swine wastewater and that the effluent water quality meets the Vietnamese discharge standard (QCVN 62-MT:2016/BTNMT) for swine wastewater effluents.
Highlights
The livestock sector, especially the swine industry, plays an important role in promoting agricultural development and the economy of a country (Shin et al, 2005)
The results show that, at a cycle time of 4.5 h, the total nitrogen (TN), total phosphorus (TP), and NH4+‒N removal efficiencies were not high and were only 51.67, 72.46, and 69.12%, respectively
The results show that the treatment efficiency after an aeration time of 195 min was nearly similar to those achieved at an aeration time of 165 min, with TN, total organic carbon (TOC), TP, ammonium, BOD5, and chemical oxygen demand (COD) removal efficiencies of 86.9, 94.9, 87.8, 97.8, 99.34, and 96.2%, respectively
Summary
The livestock sector, especially the swine industry, plays an important role in promoting agricultural development and the economy of a country (Shin et al, 2005). AD offers the following advantages: (i) treatment of high-strength wastewater, (ii) high conversion of chemical oxygen demand (COD) to biogas, (iii) ease of maintenance, (iv) good process control, (v) ability to tolerate fluctuating COD loads, i.e., feast and famine conditions, and (vi) good stability of the anaerobic biomass. This technique produces large amounts of anaerobically digested effluent that contains nutrients, inorganic salts, organic compounds (amino acid and B vitamins), and trace/heavy metals (Fe, Cu, and Zn). The development of a new technology to treat anaerobically digested swine wastewater is urgently required to satisfy the environmental discharge regulations (An et al, 2007; Daumer et al, 2007; Dosta et al, 2008)
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