Evalution of the fate of greenhouse gas emissions from the sludge mineralisation process in Sludge Treatment Wetlands.

Mineralisation process of Greenhouse gas (GHG) emission data from a sludge treatment wetlands (STWs) has been lacked currently. A study was conducted to quantify the release rates of carbon dioxide (CO 2) and methane (CH 4) from three similar pilot-scale STW units in relation to seasonal change based on the release rates in order to estimate annual GHG release rates of mineralisation process. A static transparent chamber was adopted to measure gas emission without interference of absorption of sunlight by plants for photosynthesis. The three pilot configurations were unit STW1 with ventilation, unit STW2 with ventilation and reed plantings and unit STW3 with reed plantings; all located at Dakai wastewater treatment plant (WWTP), Dalian, China. The resting and loading periods were measured from April to November 2016 and then from April to November 2017, respectively. The results revealed that the release rates of CO 2 and CH 4 were significantly influenced by seasonal change: the highest release rates were recorded in summer and the lowest rates were recorded in winter. During both seasons, CH 4 releases during the resting period (negligible to 2.96 mg CH 4 m−2 d−1) were lower than that during the loading period (34 to 1492 CH 4 mg mm−2 d−1) while CO 2 releases were higher during the resting period (1368 to 81,911 mg CO 2 m−2 d−1) than that of the loading period (1351 to 30,872 mg CO 2 m−2 d−1). Additionally, the presence of plants showed significant impact on GHG emissions i.e. CH 4 emissions from STW2 and STW3 were higher than that of STW1. Comparison of data between STW2 and STW3 showed that CH 4 and CO 2 emissions were reduced in the presence of ventilation. Meanwhile, the measurement of residual sludge moisture content showed that STW2 had higher dewatering and mineralisation efficiencies compared to STW3 and STW1. The annual CO 2 -eq CH 4 emissions from the three STWs during loading and resting periods were in sequence as STW3 > STW2 > STW1, and the recorded annual CO 2 -eq CH 4 during the loading period was higher than that during the resting period. [ABSTRACT FROM AUTHOR]