Ammonia Stripping of Biologically Treated Liquid Manure

Abstract

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.

Application of a Series of Continuously Fed Aerated Tank Reactors System for Recycling of Swine Slurry Nutrients

“…Part of the pH increase during aerobic biological treatment coincides with an increased CO 2 release from the system in relation to NH 3 as also described by Alitalo et al (2012) and is attributable to the solubility difference between these two components. In the present study slurry NH 4 + /DIC was larger for the treated compared to untreated manure (the respective NH 4 + /DIC -value for the treated (1.01, with HRT=4; 1.00 with HRT=3) compared to the untreated (0.85 with HRT=4; 0.90 with HRT=3) manure).…”

“…The chemical oxygen demand (COD) was analyzed according to standard SFS 5504 with HACH's closed tubes (dichromate oxidation). The volatile fatty acids (VFAs), total organic carbon (TOC), total phosphorus (Ptot), total nitrogen (Ntot), PO 4 3--P, NH 4 + -N, NO 3 --N, K + , Mg 2+ , Ca 2+ and Na + analyses were made as described by Alitalo et al (2012). Analyses were carried out on the total sample for TS, VS, COD, TOC, Ptot and Ntot and on the centrifuged supernatant for VFA, anions and cations.…”

“…Sommer & Husted, 1995). Previously described reasons for pH changes during aerobic biological treatment can be found in Alitalo et al (2012).…”

“…Aeration may cause nitrogen loss by (1) volatilization of ammonia (at pH 8.8, already 20% of total ammoniacal nitrogen will be in NH 3 molecules at 20°C (Alitalo et al, 2012) and (2) trough biological processes if the oxygen concentration is appropriately adjusted. The most common biological processes include nitrification, which oxidizes ammonium via nitrite to nitrate by autotrophs under aerobic conditions, and denitrification, which transforms nitrate into nitrite, then into nitrous oxide, nitric oxide, and finally to N 2 gas by denitrifying bacteria under anaerobic conditions (Wiesmann,1994).…”

“…Therefore, the manure treatment approach should be different from that of waste water and the ultimate goal should be complete nutrient recycling. This could be achieved through the following steps: (1) partial separation of phosphorus (in plant available form) and solid material prior to aerobic biological treatment; (2) conversion of manure through biological treatment into a form that enables further fractionation of manure effluent, (3) N separation with air stripping after the reduction of manure solid matter and biological pH raise (Alitalo et al, 2012) and (4) only after phosphorus and nitrogen removal and subsequent buffer capacity reduction; chemical treatment with reduced amounts of chemical coagulants, such as iron salts, aluminium salts or polymers. This paper presents the results of the study concerning aerobic biological treatment.…”