Evaluation of influence of the Catanduva (SP) Wastewater Treatment Plant (WWTP) in São Domingos river water quality

ABSTRACT Non-treated wastewater is responsible for the pollution of urban rivers, and it is mandatory to evaluate the behavior of these rivers before and after the construction of a Wastewater Treatment Plant (WWTP). The aim of this study was to evaluate the water quality of São Domingos River (SDR) after the start of the Catanduva/SP WWTP operation, whose average removal efficiencies were: biochemical oxygen demand (BOD; 93.71%), ammonia nitrogen (73.12%), total phosphorus (25.70%), turbidity (85.16%), and total solids (31.75%). We used 768 data collected upstream and downstream of the city of Catanduva/SP, previously analyzed by CETESB (state environmental agency). Dredging works carried out during the evaluated period were responsible for a significant temporary worsening in the water quality of the SDR in Catanduva. Two years after the beginning of the Catanduva WWTP, there was a significant improvement in SDR water quality, with a reduction in the average concentrations of BOD (20.97 to 5.73 mg.L−1), ammonia nitrogen (3.84 for 0.99 mg.L−1), and Escherichia coli (105 to 104 CFU.100 mL−1) were reduced; and DO concentration (0.90 to 3.12 mg.L−1) increased. The Principal Component Analysis (PCA) indicated that the water quality of the river downstream of Catanduva is approaching the same quality verified upstream of the city. These data suggest that SDR may be considered a Class 3 river (Resolution CONAMA 357/05) in the future and may even be used for human supply, reducing the high demand for groundwater in the region.摘要：未经处理的废水是城市河流污染的主要诱因，因此必须对污水处理厂（Wastewater Treatment Plant, WWTP）建成前后的河流水环境状况开展评估。本研究旨在评估卡坦杜瓦/圣保罗市污水处理厂投运后，圣多明戈斯河（São Domingos River, SDR）的水质情况。该污水处理厂的平均污染物去除效率分别为：生化需氧量（biochemical oxygen demand, BOD）93.71%、氨氮73.12%、总磷25.70%、浊度85.16%以及总固体31.75%。 本研究采用了由州级环境机构CETESB此前完成分析的768组监测数据，采样点位覆盖卡坦杜瓦/圣保罗市河段的上下游区域。评估期间实施的疏浚工程，曾导致卡坦杜瓦市境内的圣多明戈斯河水质出现显著的暂时性恶化。 卡坦杜瓦市污水处理厂投运两年后，圣多明戈斯河水质得到显著改善：生化需氧量（BOD）平均浓度从20.97 mg·L⁻¹降至5.73 mg·L⁻¹，氨氮平均浓度从3.84 mg·L⁻¹降至0.99 mg·L⁻¹，大肠埃希氏菌（Escherichia coli）浓度从10⁵ CFU·100 mL⁻¹降至10⁴ CFU·100 mL⁻¹；溶解氧（dissolved oxygen, DO）浓度则从0.90 mg·L⁻¹升至3.12 mg·L⁻¹。 主成分分析（Principal Component Analysis, PCA）结果显示，卡坦杜瓦市下游河段的河流水质正逐步趋近于该市上游河段的水质水平。本研究数据表明，圣多明戈斯河未来有望被划定为符合巴西国家环境委员会（Conselho Nacional do Meio Ambiente, CONAMA）第357/05号决议规定的Ⅲ类河流，甚至可用于人类供水，从而缓解该地区对地下水的高需求。