Suitability of inorganic coagulants for algae-laden water treatment: Trade-off between algae removal and cell viability, aggregate properties and coagulant residue.

Inorganic coagulants could effectively precipitate algae cells but might increase the potential risks of cell damage and coagulant residue. This study was conducted to critically investigate the suitability of polyaluminum (PAC), FeCl3 and TiCl4 for algae-laden water treatment in terms of the trade-off between algal substance removal, cell viability, and coagulant residue. The results showed that an appropriate increase in coagulant dosage contributed to better coagulation performance but severe cell damage and a higher risk of intracellular organic matter (IOM) release. TiCl4 was the most destructive, resulting in 60.85% of the algal cells presenting membrane damage after coagulation. Intense hydrolysis reaction of Ti salts was favorable for the formation of larger and more elongated, dendritic structured flocs than Al and Fe coagulants. TiCl4 exhibited the lowest residue level and remained in the effluents mainly in colloidal form. The study also identified charge neutralization, chemisorption, enmeshment, and complexation as the dominant mechanisms for algae water coagulation by metal coagulants. Overall, this study provides the trade-off analyses between maximizing algae substance removal and minimizing potential damage to cell integrity and is practically valuable to develop the most suitable and feasible technique for algae-laden water treatment.

Assessment of toxicity and antimicrobial performance of polymeric inorganic coagulant and evaluation for eutrophication reduction.

In this study, the efficacy of the promising iron-based polymeric inorganic coagulant (POFC) was assessed for the reduction of eutrophication effect (freshwater toxicity) and the microbial loads from wastewater. Toxicity assessment for POFC was conducted on mice and skin cell lines. The results confirm the lower toxicity level of POFC. The POFC showed excellent antibacterial efficacy against Gram-positive and Gram-negative bacteria. Moreover, it demonstrated a remarkable effectiveness against black fungus such as Aspergillus niger and Rhizopus oryzae. Additionally, POFC showed antiviral effectiveness against the highly pathogenic H5N1 influenza virus as well as Middle East respiratory syndrome coronavirus (MERS-CoV) and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). POFC-based treatment gives excellent removal percentages for phosphate, and phosphorus at doses below 60 ppm with a low produced sludge volume that leads to 84% decrease in the rate of eutrophication and freshwater toxicity. At a POFC concentration of 60 ppm, remarkable reduction rates for total coliforms, fecal coliforms, and E. coli were achieved. After POFC-based coagulation, the produced sludge retains a lower bacterial density due to the antibacterial activity of POFC. Furthermore, it revealed that the observed removal efficiencies for fungi and yeasts in the produced sludge reached 85% at a POFC dose of 60 ppm. Overall, our research indicates that POFC has potential for application in pre-treatment of wastewater and serves as an antimicrobial agent.

Effects of polyaluminum chloride (PAX-18) on the relationship between predatory fungi and Lecane rotifers.

PAX-18 (polyaluminum chloride) is frequently used in WWTPs (wastewater treatment plants) to overcome sludge bulking. An alternative biological method is the usage of Lecane rotifers, which can be endangered by predacious fungi. We investigated the influence of different PAX-18 concentrations on the relationship between Lecane inermis and predacious fungi (Zoophagus and Lecophagus) differing in feeding mode. High PAX concentration (6 mg Al3+ L-1) strongly limited the number of the rotifers, which in low concentration (1.2 mg Al3+ L-1), after an initial decline, increased, but significantly slower than in control. Under the simultaneous influence of Lecophagus and PAX, rotifers were driven almost extinct at the high concentration, but survived at the lower concentration and increased in the control. When treated with Zoophagus, only one or two rotifers survived in treatments and control. High concentrations of PAX significantly restricted the growth of fungi, whereas in low concentrations and control conditions, their length increased, with Zoophagus growing much quicker than Lecophagus. Zoophagus was significantly more efficient in trapping rotifers regardless of PAX concentration. The trapping ability of mycelium following extended exposure to PAX was strongly limited at high concentrations, in comparison to control. Conidia of Zoophagus turned out to be considerably more resistant to PAX-18 and starvation than Lecophagus conidia.

[Sludge Conditioning Performance of Polyaluminum, Polyferric, and Titanium Xerogel Coagulants].

The sludge conditioning performance of inorganic Al, Fe, and Ti coagulants were systematically compared in terms of specific resistance to filtration (SRF), the content of protein and polysaccharide in extracellular polymeric substances (EPS), the change in three-dimensional excitation emission matrix fluorescence (3D-EEM), the molecular weight of organic matter in EPS, and the floc size and surface morphology. The sludge conditioning ability and the mechanism were systematically analyzed. The results showed that the sludge conditioning ability of the three inorganic coagulants was in the order of polyaluminum chloride (PAC) > titanium xerogel coagulant (TXC) > polymeric ferric sulfate (PFS). After conditioning, the contents of protein and polysaccharide in the EPS were greatly reduced, especially in the loosely bound EPS (LB-EPS). The combined capacity for coagulation between TXC/PFS and organic matter was stronger than that of PAC. The content of polysaccharide in LB-EPS was the key factor affecting the sludge dewatering performance but not the coagulated floc size. The surface charge and the chelating ability with organic matter co-determined the sludge dewatering ability. The organic cationic polymer, polyacrylamide (PAM), made the sludge aggregate via charge neutralization. However, the use of PAM alone was not a good choice owing to the low dewatering ability and the loose sludge structure. The results here are helpful for the selection of suitable coagulants for sludge conditioning.

Methods coagulation/flocculation and flocculation with ballast agent for effective harvesting of microalgae.

The effects of coagulant (FeCl3·6H2O), various flocculants based on polyacrylamide (PAA), polyethylenoxide (PEO) and flocculated biomass as ballast agent, dosage and sedimental time on flocculation efficiency of harvesting Chlorella vulgaris GKV1 cultivated in a laboratory were investigated. The results of this work indicated that the flocculation efficiency achieved about 90% after 5 min of sedimentation when adding of coagulant and flocculant mixture (FeCl3 50 mg/l+PEO based Sibfloc-718 7.5 mg/l) or flocculant with ballast agent (Sibfloc-718 7.5 mg/l+10% flocculated biomass). PAA and PEO showed good flocculation efficiency at dosage of 0.025 and 0.015 g/l, respectively without pH adjustment. Finally, the most suitable flocculation method was discussed in this paper.

Correlation of physicochemical properties and sludge dewaterability under chemical conditioning using inorganic coagulants.

This study investigated the effects of chemical conditioning with three representative inorganic coagulants (FeCl3, polyaluminum chloride (PACl) and high performance PACl (HPAC) on sludge dewaterability. We monitored the particle size, kinetic viscosity (KV), fractal dimension (D(F)) and extracellular polymeric substances (EPS) located in different layers of sludge floc (soluble, loosely-bound (LB), tightly-bound (TB)) to understand the correlation of dewaterability and physicochemical properties of sludge under chemical conditioning. The conditioning process included the rapid aggregation of sludge particles induced by charge neutralization and bridging followed by floc densification caused by double electric layer compression. The floc size and D(F) were increased after chemical conditioning, indicating that larger and more compact floc formed. The floc conditioned with FeCl3 was smaller but denser than that of PACl and HPAC. Furthermore, sludge dewaterability correlated well with the change in concentration of soluble EPS, LB-EPS and TB-EPS, but not with KV, D(F), floc size.