Abstract
Previous studies on the water quality of surface runoff often focused on the chemical oxygen demand (COD), nitrogen, phosphorus, and total suspended solid (TSS), but little is known in terms of the inorganic suspended solids (ISS). This research investigated the effects of ISS carried by surface runoff on the treatment efficiency of the pretreatment facilities and the ratio of mixed liquor volatile suspended solid to mixed liquor suspended solid (MLVSS/MLSS) of the activated sludge in a wastewater treatment plant (WWTP) with the anaerobic-anoxic-oxic (AAO) process in Chongqing city, China. The results showed that the surface runoff had a long-lasting impact on the grit removal capacity of the grit chamber, affecting the normal operation after the rainfall. In contrast, the primary sedimentation tank showed strong impact resistance with higher removal rates of COD, TSS, and ISS. Nonetheless, the primary settling tank aggravates the removal of organic carbon in sewage during rainfall, having a negative impact on subsequent biological treatment. The ISS in the surface runoff could increase the sludge concentration and decrease the MLVSS/MLSS ratio. After repeated surface runoff impact, the MLVSS/MLSS ratio in the activated sludge would drop below even 0.3, interrupting the normal operation of WWTP.
Highlights
Urban surface runoff contains toxic and harmful pollutants, which might be significantly greater than those of urban sewage
Researchers paid the most attention to the nutrient contaminants (such as chemical oxygen demand (COD), total nitrogen (TN), total phosphorus (TP)) [15,16], total suspended solids (TSS) [17], and heavy metals [18] in surface runoff
The liquid level
Summary
Urban surface runoff contains toxic and harmful pollutants (such as suspended solids, vehicle emissions, air sedimentation, etc.), which might be significantly greater than those of urban sewage. A number of studies have focused on investigating the impacts of urbanization degree [8,9], seasonal variation [10,11], and land use [12,13] on surface runoff pollutants and the contribution of surface runoff to pollutants in the combined drainage system [7,14] In these studies, researchers paid the most attention to the nutrient contaminants (such as chemical oxygen demand (COD), total nitrogen (TN), total phosphorus (TP)) [15,16], total suspended solids (TSS) [17], and heavy metals [18] in surface runoff.
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