二次沉淀池是活性污(wu)泥(ni)系統的重(zhong)要組成部分，它用以澄清混合液(ye)并回(hui)(hui)收、濃(nong)縮活性污(wu)泥(ni)，其效(xiao)果的好(hao)壞，直接(jie)影(ying)響出水的水質和(he)回(hui)(hui)流污(wu)泥(ni)的濃(nong)度。因(yin)為沉淀和(he)濃(nong)縮效(xiao)果不好(hao)，出水中(zhong)就會(hui)增(zeng)加活性得泥(ni)懸(xuan)浮(fu)物，從(cong)而增(zeng)加出水的BOD 質量濃(nong)度；同時，回(hui)(hui)流污(wu)泥(ni)濃(nong)度也會(hui)降低(di)，從(cong)而降低(di)曝氣(qi)池中(zhong)混合液(ye)濃(nong)度，影(ying)響凈(jing)化效(xiao)果。

進水裝置

進(jin)入二(er)次(ci)沉(chen)淀(dian)(dian)(dian)(dian)池(chi)的(de)(de)活(huo)性(xing)污(wu)(wu)泥混合(he)(he)液(ye)在性(xing)質上也有其特點(dian)，即(ji)活(huo)性(xing)污(wu)(wu)泥混合(he)(he)液(ye)的(de)(de)濃(nong)度(du)高(2 000 -4 000 mg/L），有絮(xu)凝性(xing)能(neng)，因此，屬于成(cheng)(cheng)層(ceng)沉(chen)淀(dian)(dian)(dian)(dian)。它(ta)沉(chen)淀(dian)(dian)(dian)(dian)時，泥水(shui)之間有清(qing)晰的(de)(de)界面(mian)，絮(xu)凝體結成(cheng)(cheng)整(zheng)體共同(tong)下(xia)沉(chen)，初(chu)期泥水(shui)界面(mian)的(de)(de)沉(chen)速固定不變，僅與(yu)初(chu)始濃(nong)度(du)有關。進(jin)入二(er)次(ci)沉(chen)淀(dian)(dian)(dian)(dian)池(chi)的(de)(de)混合(he)(he)掖(ye)濃(nong)度(du)高于二(er)次(ci)沉(chen)淀(dian)(dian)(dian)(dian)池(chi)內澄(cheng)清(qing)液(ye)的(de)(de)濃(nong)度(du)，二(er)次(ci)沉(chen)淀(dian)(dian)(dian)(dian)池(chi)內容易(yi)產生二(er)次(ci)流現象(xiang)，進(jin)水(shui)混合(he)(he)液(ye)的(de)(de)相對密度(du)大(da)，在池(chi)下(xia)部流動。