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A prerequisite for efficient ammonia removal in air stripping is that the pH of the liquid to be stripped is sufficiently high. Swine manure pH is usually around 7. At pH 7 (at 20°C), only 0.4% of ammonium is in ammonia form, and it is necessary to raise the pH of swine slurry to achieve efficient ammonia removal. Because manure has a very high buffering capacity, large amounts of chemicals are needed to change the slurry pH. The present study showed that efficient air stripping of manure can be achieved with a small amount of chemicals and without strong bases like NaOH. Slurry was subjected to aerobic biological treatment to raise pH before stripping. This facilitated 8 to 32% ammonia removal without chemical treatment. The slurry was further subjected to repeated cycles of stripping with MgO and Ca(OH)2 additions after the first and second strippings, respectively, to raise slurry pH in between the stripping cycles. After three consecutive stripping cycles, 59 to 86% of the original ammonium had been removed. It was shown that the reduction in buffer capacity of the slurry was due to ammonia and carbonate removal during the stripping cycles.

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Single tank aeration systems operated in batch mode or sequential batch reactors based on intermittent aeration are generally applied for swine manure treatment in order to reduce nutrient content and odor. This study evaluated the feasibility of aerobic biological treatment conducted in a serial arrangement of continuously fed aerated tank reactors configuration with swine slurry on a pilot-scale. Compared to municipal wastewater treatment swine slurry rich in nutrients and solids requires different treatment standards for the applied methods to be economically and ecologically relevant. This study presents a sequential process scheme, in which biological treatment serves as a means of achieving a pH raise. This makes it possible to separate part of the nitrogen by stripping and enhances slurry precipitating/coagulation characteristics without substantial carbon or nitrogen loss in gaseous form (which is the opposite to that in a conventional active sludge process). The system was run with a hydraulic retention time (HRT) of three to four days (whole system), and a feedback of 0.8±0.2. During treatment, total organic carbon (TOC) reduction varied between 2.4% and 14.6% and the total nitrogen concentration change was less than 3%. Nearly 50% of the total phosphorus was reduced. The results indicated that the odor of liquid manure had decreased efficiently at best to a level at which there was no odor or only very faint odor. Concurrently, manure pH rose to 8.7.

No abstract