PACl和CTS对水华微囊藻混凝-过滤的影响

过滤去除水华蓝藻时易出现过滤材料堵塞，混凝预处理可以改变水华蓝藻在过滤过程中的藻饼过滤特性，从而提高过滤通量。混凝剂种类是影响混凝-过滤分离性能的重要因素。本研究利用聚合氯化铝(PACl)和壳聚糖(CTS)进行预混凝，研究了2种混凝剂对絮体特性及过滤通量、出水水质和生物质品质的影响，并进行了2种混凝剂优化剂量添加条件下的药剂成本分析。结果表明，采用PACl和CTS在优化剂量下，过滤通量从无预处理时的1 647 L·(m²·h)⁻¹分别提升到2 020 L·(m²·h)⁻¹和5 816 L·(m²·h)⁻¹，通量下降率由65.9%分别降低到23.2%和13.8%。两种不同混凝剂过滤性能的差异主要是由混凝形成的絮体大小和饼层阻力不同造成的。CTS、PACl混凝预处理减小了饼层的过滤比阻力系数。在优化剂量条件下，CTS、PACl混凝形成的饼层比阻力系数R_cs从无混凝剂时的4.49×10⁸ m·g⁻¹分别降低了95%和24%，达到了2.23×10⁷ m·g⁻¹和3.4×10⁸ m·g⁻¹。且CTS预处理形成饼层的比阻力系数是PACl预处理的1/15，因此，CTS更有利于提高混凝效率。虽然PACl的成本低于CTS，但使用PACl会造成藻类生物质中铝残留，因此考虑到生物质的资源化利用以及残余铝离子的回收成本，CTS比PACl略有优势，干生物质当量的药剂成本及残余铝离子的回收成本之和分别达到1 488元·t⁻¹和1 530元·t⁻¹。

Influence of PACl and CTS on the removal of Microcystis flos-aquae using coagulation-filtration

Filter block occurs easily when cyanobacteria bloom is removed by filtration. Coagulation pretreatment changes the characteristics of algae cake during filtration separation process, and thus improves the filtration flux. The type of coagulant is an important factor affecting the performance of coagulation filtration separation. In this study, polyaluminum chloride (PACl) and chitosan (CTS) were used for pre-coagulation. The effects of two coagulants on floc characteristics, filtration flux, effluent quality and biomass quality were studied. The cost analysis of reagents at the optimum dosages of these two coagulants was performed. The results showed that coagulation pretreatment could significantly reduce the flux declining in the process of filtration separation of Microcystis flos-aquae. At the optimal dosages of PACl and CTS, the filtration flux increased from 1 647 L·(m2·h)−1 to 2 020 L·(m2·h)−1 and 5 816 L ·(m2·h)−1, respectively, and the flux reduction rate decreased from 65.9% to 23.2% and 13.8%, respectively. The difference in filtration performance of these two coagulants were caused by the differences of flocs size and cake resistance after coagulation. CTS and PACl coagulation reduced the specific cake resistance dramatically. At the optimized dosages of CTS and PACl, the specific cake resistance(Rcs) reached 2.23×107 m·g−1and 3.4×108 m·g−1, respectively, which were 95% and 24% lower than that without coagulant. The Rcs of cake formed after CST pre-coagulation was 1/15 that after PACl pre-coagulation, thus CST was more favorable for the improvement of coagulation efficency. Although the cost of PACl was lower than that of CTS, PACl will cause the aluminum residues in the collected algal biomass. Therefore, considering the resource utilization of biomass and the recovery cost of residual aluminum, the total cost of CTS was still lower than PACl. The sum of chemical cost of dry biomass equivalent and recovery cost of residual aluminum ions reached 1 488 yuan ·t−1 and 1 530 yuan ·t−1, respectively.