Abstract
In this study, we propose the application of struvite precipitation for the sustainable recovery of nitrogen (N) and phosphorus (P) from anaerobic digestion (AD) effluents derived from swine manure. The optimal conditions for four major factors that affect the recovery of N and P were derived by conducting batch experiments on AD effluents obtained from four AD facilities. The optimal conditions were a pH of 10.0, NH4-N:Mg:PO4-P molar ratio of 1:1.4:1, mixing intensity of 240 s−1, and mixing duration of 2 min. Under these optimal conditions, the removal efficiencies of NH4-N and PO4-P were approximately 74% and 83%, respectively, whereas those of Cu and Zn were approximately 74% and 79%, respectively. Herein, a model for swine manure treatment that incorporates AD, struvite precipitation, and biological treatment processes is proposed. We applied this model to 85 public biological treatment facilities in South Korea and recovered 4722 and 51 tons/yr of NH4-N and PO4-P, respectively. The economic analysis of the proposed model’s performance predicts a lack of profitability due to the high cost of chemicals; however, this analysis does not consider the resulting protection of the hydrological environment. Field-scale studies should be conducted in future to prove the effectiveness of the model.
Highlights
According to the Annual Report of the Nationwide Water Pollution Source Survey published in 2017, domestic annual animal manure generation in South Korea is 50,220,000 tons/yr, of which 20,523,000 tons/yr is swine manure, representing the highest proportion of manure and accounting for approximately 41% of the total animal manure [1]
For post-treatment of Anaerobic digestion (AD) effluents, AD effluents obtained from the A1 facility were applied to agricultural farmland as liquid fertilizers, whereas those obtained from the A2, A3, and A4 facilities were treated in biological treatment facilities
Solid–liquid separated AD effluents discharged from the AD reactor of each facility were used because organic compounds affect the removal rate of NH4-N and PO4-P and the purity of struvite precipitates during struvite precipitation [39,40,41,42]
Summary
According to the Annual Report of the Nationwide Water Pollution Source Survey published in 2017, domestic annual animal manure generation in South Korea is 50,220,000 tons/yr, of which 20,523,000 tons/yr is swine manure, representing the highest proportion of manure and accounting for approximately 41% of the total animal manure [1]. Swine manure contains high concentrations of organic matter, nitrogen (N), and phosphorus (P). Anaerobic digestion (AD) has been widely studied worldwide as an effective treatment method for swine manure [4,5,6,7,8] because it can recover biogas in the form of methane (CH4) as an energy source, while effectively treating high concentrations of organic matter. AD effluents contain high concentrations of nutrients, such as ammonium nitrogen (NH4-N) and orthophosphate (PO4-P), and relatively high concentrations of toxic metals, such as copper (Cu) and zinc (Zn) [9,10,11] Toxic metals, such as Cu and Zn, are present in high concentrations in AD effluents because they are added in the feed as micro-supplements for pig growth [12], which has been reported previously [5,9,13]
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