Full-scale experience for nitrogen removal from piggery waste.

The nitrogen-removal performances of three full-scale piggery wastewater treatment plants, with different organic and nitrogen loads, at the capacity ranges of 95 to 130 m3/d, were compared in this study. Plants 1 and 2 can be characterized as the modification of anoxic-aerobic operating systems, while an anaerobic and anoxic-aerobic system was used in plant 3. The influent piggery wastewater concentration for plant 1 was relatively lower, but with higher organic and nitrogen loads, resulting in higher chemical oxygen demand (COD) and ammonium-nitrogen in effluent. Plant 2 was operated with strong piggery wastewater, resulting in a higher operating temperature. The high temperature could inhibit the nitrifying activity in plant 2. Although plant 3 was operated with a higher influent total COD-to-total Kjeldahl nitrogen ratio (TCOD:TKN), an additional external carbon source was required to polish the final effluent to remove nitrogen. Influent COD in plant 3 was used in the anaerobic-anoxic reactor for both methane (CH4) production and denitrification. Based on various mass balances, including caloric, COD, and alkalinity, the key elements for the successful nitrogen removal from the piggery waste were reactor temperature (less than 35degrees C), influent TCOD:TKN (greater than 6), and alkalinity-to-TKN ratio (greater than 3).     

Variability of nitrous oxide and carbon dioxide emissions continuously measured in solid waste incinerators

Nitrous oxide and carbon dioxide were continuously measured and variability of emission factors (EFs) was evaluated in five municipal waste incinerators (MWIs) and four industrial waste incinerators (IWIs) from 24 to 86 days between 2008 and 2011. N₂O EFs were calculated by Monte Carlo simulation and mean N₂O EFs were 7.1, 107, 127, 219 g N₂O/ton waste combusted in MWIs with selective catalytic reduction (SCR) for NOx control, MWIs with selective non-catalytic reduction (SNCR), IWIs with SNCR, and a MWI using fluidized bed with SNCR, respectively. Climate-relevant CO₂ EFs ranged from 0.45 to 0.72 ton CO₂/ton waste combusted in MWIs. Maximum values of upper limit for 95% confidence intervals (CIs) of N₂O EFs estimated in each MWIs with SCR, MWIs with SNCR, IWIs with SNCR were 185, 94, 101% of mean N₂O EFs, respectively. Meanwhile, maximum values of upper limit for 95% CIs of CO₂ EFs were much lower as between 18 and 36% in those facilities. 84% CIs of mean N₂O EFs in MWIs with SNCR and IWIs with SNCR were overlapped indicating those values are not significantly different.