Complete long-term monitoring of greenhouse gas emissions from a full-scale industrial wastewater treatment plant with different cover configurations

The greenhouse gas (GHG) emissions from wastewater treatment plants (WWTPs), consisting mainly of methane (CH4) 4 ) and nitrous oxide (N2O), 2 O), have been constantly increasing and become a non-negligible contributor towards carbon neutrality. The precise evaluation of plant-specific GHG emissions, however, remains challenging. The current assessment approach is based on the product of influent load and emission factor (EF), of which the latter is quite often a single value with huge uncertainty. In particular, the latest default Tier 1 value of N2O 2 O EF, 0.016 +/- 0.012 kg N2O - N kg TN-1 , is estimated based on the measurement of 30 municipal WWTPs only, without involving any industrial wastewater. Therefore, to resolve the pattern of GHG emissions from industrial WWTPs, this work conducted a 14-month monitoring campaign covering all the process units at a full-scale industrial WWTP in Shanghai, China. The total CH4 4 and N2O 2 O emissions from the whole plant were, on average, 447.7 +/- 224.5 kg CO2-eq d- 1 and 1605.3 +/- 2491.0 kg CO2-eq d-1,-1 , respectively, exhibiting a 5.2- or 3.9-times more significant deviation than the influent loads of chemical oxygen demand (COD) or total nitrogen (TN). The resulting EFs, 0.00072 kg CH4 kg COD- 1 and 0.00211 kg N2O - N kg TN-1 , were just 0.36% of the IPCC recommended value for CH4, 4 , and 13.2% for N2O. 2 O. Besides, the parallel anoxic-oxic (A/O) lines of this industrial WWTP were covered in two configurations, allowing the comparison of GHG emissions from different odor control setup. Unit-specific analysis showed that the replacement of enclosed A/open O with enclosed A/O reduced the CH4 4 EF by three times, from 0.00159 to 0.00051 kg CH4 kg COD- 1 , and dramatically decreased the N2O 2 O EF by an order of magnitude, from 0.00376 to 0.00032 kg N2O - N kg TN-1 , which was among the lowest of all full-scale WWTPs.