初沉池对污水中无机悬浮固体的影响

Influence of primary settling tank on influent inorganic suspended solids

随着生物除磷脱氮工艺的大量使用,初沉池的设置和取消一直在学术和工程界存在争议。以重庆市某污水厂为对象,从对无机悬浮固体(ISS)、COD和TN去除效果的角度探讨了初沉池在污水处理系统的重要性。研究结果表明,在合流制排水体制下,该污水厂进水污染物浓度非常高,COD、SS和ISS的平均浓度分别为560、1 100和780 mg/L;初沉池对COD、SS和ISS的去除率分别为61%、78%和85%,对ISS的去除率比COD高20%左右;污水经过初沉池沉淀之后,ISS/COD从1.7下降到0.7左右,COD/TN从8.0左右下降到4.3,粒径由40μm下降到30μm。初沉池对大粒径的ISS具有较好的去除效果,未能被去除的小粒径ISS容易悬浮在混合液中,降低MLVSS/MLSS。从ISS/COD的削减和保持混合液MLVSS/MLSS正常的角度来讲,初沉池不应取消。

With the extensive use of biological nitrogen removal process,the setting and cancellation of primary settling tank(PST) have been controversial in academic and engineering field. A wastewater treatment plant(WWTP) was selected as object,and the importance of the PST to WWTP was discussed from the perspective of inorganic suspended solids(ISS),chemical oxygen demand( COD) and total nitrogen( TN) removal by PST.The results showed that the influent pollutant concentrations were very high under combined sewage systems,with COD of 560 mg /L,suspended solids(SS) of 1 100 mg /L and ISS of 780 mg /L. The removal rates of PST for COD,SS and ISS were 61%,78% and 85%,respectively,and the removal rate of ISS was 20% higher than COD. After PST,the ISS /COD of wastewater decreased from 1. 7 to 0. 7,COD /TN decreased from 8. 0 to 4. 3,and the median particle size(D50) decreased from 40 μm to 30 μm. PST had better removal efficiency of ISS with larger D50,but the ISS with smaller D50 suspended in mixture easily,making MLVSS /MLSS reduction. From the perspective of ISS /COD reduction and keeping a normal MLVSS /MLSS,the PST should not be canceled.