It is reported that residual aluminum from coagulation pretreatment can increase membrane fouling in nanofiltration (NF) or reverse osmosis (RO) desalination systems. However, the membrane fouling mechanism of residual aluminum and the effective control measures are not very clear. In this study, the nanofiltration membrane fouling caused by poly-aluminum chloride (PACl), the inhibitory effect of amino trimethylene phosphonic acid (ATMP) on aluminum foulants, and calcium carbonate scale in the presence of residual aluminum were investigated by permeate experiments and scanning electron microscopy (SEM) observation of the fouled membranes. Besides, the effect of adding ultrafiltration before nanofiltration on reducing membrane fouling caused by residual aluminum was also investigated. The results showed that most of the residual aluminum in feed eventually formed insoluble particles and fine flocs, and accumulated gradually on the membrane surface, which was a typical colloid particle fouling. ATMP can reduce the membrane fouling caused by residual aluminum to some extent, and the permeate flux ratio ( J/J c ) increased from 0.83 to 0.89 when ATMP increased to the optimal dose of 6 mg⋅L −1 . However, this means can still effectively eliminate carbonate scale, even in the presence of residual aluminum. Moreover, ultrafiltration pretreatment prior to nanofiltration was very effective to control membrane fouling, and the comprehensive cost was calculated to be only 0.006 $⋅m −3 . Therefore, the combined process of coagulation-ultrafiltration as a pretreatment of nanofiltration or reverse osmosis should be an ideal way to prevent membrane fouling caused by residual aluminum.
Jiangfeng Dai,Jiangwei Lou,Zhiyuan Jin,Tianhao Yu,Hui Xu,Dongsheng Wang
The secondary sedimentation tank in wastewater treatment facilities is critical for separating suspended solids and biomass from treated water, producing effluent suitable for discharge or further treatment. This study fabricated poly-aluminum silicate chloride (PASiC) through silicic acid modification of polyaluminum chloride (PACl) as the precursor matrix. The coagulation efficacy of PASiC in treating secondary sedimentation tank effluent was systematically investigated, with particular focus on the impact of ageing processes on floc structural stability.Experimental findings indicated that PASiC effectively reduced organic matter in effluent; however, the silicon component can form fine suspended particles that were challenging to settle, which slightly reduced turbidity removal efficiency. Specifically, the addition of silicon increased supernatant turbidity by 0.2 to 0.5 NTU compared to the control. During floc aging, PASiC proved effective in reducing and stabilizing residual aluminum in the supernatant, with silicon-modified PASiC achieving a residual aluminum reduction exceeding 0.1 mg/L. Notably, PASiC with a basicity of 1.0 and a Si/Al ratio of 1:10 (PACl 1.0 -1:10) yielded flocs with improved resistance to aging, as indicated by slower changes in the humification index and fluorescent active substances in the supernatant. It can be reasonably deduced that the incorporation of silicon facilitates the formation of a more resilient network configuration through its complexation with aluminum, and reinforces the hydrogen bonds. These findings provide a theoretical basis for mitigating floc aging challenges, such as sludge return in wastewater treatment processes.
危险品化学品经营许可证（带存储）