| Biogas plants are widely used in confined animal farms in China, for waste treatment andrenewable energy recovery, and it produces large amount of anaerobically digested liquid. Where thedigested liquid could not be applied to the farmland, it poses large threat to the environment due to thelack of appropriate treatment technologies. The object of this study is the deep treatment ofanaerobically digested swine wastewater. The characteristics of the wastewater were investigated. Basedon the sole treatment study of ammonia stripping and membrane bioreactor (MBR), the combinedprocesses were conducted to treat the digested liquid, and the coupling parameters were optimized.Additionally, the shifts of biological nitrogen removal bacteria communities were analysed. Finally,comparison study of influencing factors on shortcut nitrification of high-strength ammonia wastewaterwas investigated. The main conclusions drawn in this study are as follows.（1） Four swine farm biogas plants were surveyed, and the characteristics of digested wastewaterwere figured out, which had high ammonia nitrogen and low carbon to nitrogen ratio. The ammonianitrogen concentration was300-2000mgN/L and COD/TN ratio was1.0-3.5, which realved thatalkalinity deficiency for nitrification and lack of carbon source for denitrification.（2） Ammonia stripping was carried out to treat digested liquid. The effects of pH, air to liquidratio, and temperature on ammonia stripping was investigated and the parameters were optimized. Itsuggested that under the condition of pH of10.5, air to liquid ratio of2000-3000, and temperature of30oC, the ammonia removal rate was optimal of81.84%. After the treatment of ammonia stripping,ammonia was reduced and carbon to nitrogen ratio was increased, which was beneficial for subsequentbiological treatment.（3） MBR was implemented for the treatment of digested swine wastewater, and the effects of C/Nratio and ammonia concentration on biological nitrogen removal were investigated. The MBR showedsteady COD removal rate of about75%when COD/TN was at the range of1.78-8.76with a constantorganic load of0.5kgCOD/(m3·d). TN removal rate was highest of83%at COD/TN of8.76±0.30andBOD5/TN of3.02±0.09. MBR displayed high ammonia oxidizing efficiency with0.08kgN/(kgMLSS·d) and95%of ammonia was oxidized. The AOB abundance was stable at a high level of107-109copies/mL. The ammonia concentration had selective effect on AOB community. With decreaseof ammonia concentration, the diversity of the AOB community decreased. Nitrosomonas eutrophagradually disappeared, whereas Nitrosomonas sp. OZK11showed high affinity for the substrate and wasconstantly adapting to survive with the oxidization of digested swine wastewater.（4） The combined process of ammonia stripping and MBR were adopted for the treatment ofdigested swine wastewater, and the combined process of “Low-pH ammonia stripping and shortcutnitrogen removal in MBR” and parameters were optimized. Compared with the “High-pH ammoniastripping and traditional nitrogen removal”, the “Low-pH ammonia stripping and shortcut nitrogenremoval in MBR” could efficiently remove nitrogen with relatively low cost. Under the condition of NaOH addition amount of2.37±0.16g/L and pH increased to9.39±0.04,73%of ammonia and65%of TN were removed and COD/TN was increased to5.0-6.0by ammonia stripping process. In thesubsequent MBR, at DO of6.12±0.69mg/L, enlarging the ammonia loading rate of O zone to0.12-0.16kgN/(kgMLSS·d) and FA concentration increased to4-11mgNH3/L, nitrite accumulation wasenhanced to53%-71%.64%and30%of TN of the digested liquid were removed by Low-pH ammoniastripping and shortcut nitrogen removal in MBR, respectively. The concentration of the effluent fromthe combined process was lower than the national discharge standard (GB18926-2001). The combinedprocess did not input external carbon and did not have impact on biogas production, and it could recoverammonia. The total treatment period was2.0d, and the running cost was7.76RMB/m3.（5） Controlling prarameters of shortcut nitrification of high strength ammonia wastewater wasinvestigated, and the effect of FA on shortcut nitrification at high DO level was studied. With thetreatment of FA of10.61±2.89mgNH3/L and DO of4.48mg/L, ammonia oxidizing rate was91%andnitrite accumulation rate was83%at ammonia volumetric loading rate of2.05±0.16kgN/(m3·d) andsludge loading rate of1.41±0.06kgN/(kgMLSS·d), which was four times higher than that of the lowDO and low FA treatment (DO of1.75±0.09mg/L and FA of1.67±0.73mgNH3/L). Under the high DOcondition, the FA concentration of inhibition effect on NOB was7–16mg NH3/L. |
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