Nitrogen-Free Cationic Starch Flocculants: Flocculation Performance, Antibacterial Ability, and UF Membrane Fouling Control

Abstract

In light of growing concerns about the formation of nitrogen-based disinfection byproducts (N-DBP) and the possible contribution from the use of quaternary-ammonium-containing flocculants, there is growing interest in the alternative use of quaternary phosphonium salts, which have been reported to have a lower DBP formation potential, stronger cationic properties, lower cytotoxicity, and greater stability. In this study, the performance of N-free quaternary-phosphonium-modified starch flocculants (S-BTP), synthesized through a facile one-step method using commercially available raw materials, in the treatment of bacteria-laden waters (E. coli as the model bacteria) was assessed in both jar tests and a bench-scale continuous-flow flocculation–sedimentation–ultrafiltration process. In jar tests, the effects of the cationic degree of substitution (DS) and dosage of the flocculant, solution pH, and presence of model contaminants on treatment performance were studied. One particular flocculant (S-BTP3), with a DS of 19.3%, displayed high removal efficiencies of E. coli, turbidity, and UV254 from water, comparable with those of ammonium-based analogues and conventional alum, via a combination of charge attraction, polymer bridging, and antibacterial effects. S-BTP3 also possessed better bactericidal properties (99.4% of E. coli killed) than alum (41.4% killed) and did not cause the release of intracellular substances into the treated water. In the continuous-flow flocculation–sedimentation–UF tests, S-BTP3 was superior to alum in the flocculation and antibacterial performance, and in mitigating UF membrane fouling. The results have clearly demonstrated the multiple benefits of the use of N-free cationic starch flocculants in water treatment as an alternative to conventional chemicals.

Hydrophobic-modified metal-hydroxide nanoflocculants enable one-step removal of multi-contaminants for drinking water production

“…For each HOC-M series, the ZPs of HOC-M increased with the accumulation of metal atoms in the shells. The increasingly positive ZPs of the nanoflocculants were beneficial for improving not only the stability of nanoparticles in the stock solution but also the capacity for removing negatively charged water contaminants in flocculation ( Wang et al., 2020a ). TEM-EDX images visualized the micro-structures of HOC-M in stock solutions ( Figures 1 K–1M), where C filled the core and metal elements were only distributed in the exterior.…”

Reduction of Ultrafiltration Membrane Fouling by the Pretreatment Removal of Emerging Pollutants: A Review

“…However, the release of IOM and the production of nitrogen-containing disinfection by-products (N-DBP) mean that quaternary ammonium groups are considered unsafe. Compared with the quaternary ammonium group, when starch is used as the precursor surface to graft quaternary phosphine salt, it can achieve a higher bactericidal effect (99.4%), without the risk of N-DBP, and can prevent the diffusion of aromatic proteins and other IOMs after the death of bacteria [ 135 , 136 , 137 , 138 ]; in addition, compared with alum, it significantly improves membrane pollution mitigation [ 138 , 139 ].…”

Single-cell protein production from purple non-sulphur bacteria-based wastewater treatment

“…The use of algae could be advantageous due to their ability to utilize carbon dioxide as the sole carbon substrate, the ability of a subgroup to utilize atmospheric nitrogen, their low nucleotide levels (around 4-6%), moderate protein content (40-60%), and their relative ease of harvesting especially when considering macroalgae (Janssen et al, 2022;Wang et al 2020). However, algae also lack sufficient levels of sulphur-based AA.…”

“…A study that incorporated both a biosurfactant (saponin) and bioflocculant (chitosan) into a microalgae culture reported a flocculation efficiency of over 93% (Kurniawati et al 2014). Other flocculants like cationic starch, Moringa oleifera, clearing nut, and tannin have also been utilized (Abdul Hamid et al 2014;Abdul Razack et al 2015;Bracharz et al 2018;Wang et al 2020). The dosage and flocculation efficiency of these compounds depend on a wide range of factors like the pH of the culture, the net negative charge of the cells, settling time, stirring speed, temperature, and biomass concentration.…”