A Population Balance Model for Shear-Induced Polymer-Bridging Flocculation of Total Tailings

Shear-induced polymer-bridging flocculation is widely used in the solid–liquid separation process in cemented paste backfill, beneficial to water recycling and tailings management in metal mines. A flocculation kinetics model based on Population Balance Model (PBM) is proposed to model the polymer-bridging flocculation process of total tailings. The PBM leads to a system of ordinary differential equations describing the evolution of the size distribution, and incorporates an aggregation kernel and a breakage kernel. In the aggregation kernel, a collision frequency model describes the particle collision under the combined effects of Brownian motions, shear flow, and differential sedimentation. A semi-empirical collision efficiency model with three fitting parameters is applied. In the breakage kernel, a new breakage rate coefficient model with another three fitting parameters is introduced. Values of the six fitting parameters are determined by minimizing the difference between experimental data obtained from FBRM and modeling result through particle swarm global optimization. All of the six fitting parameters vary with flocculation conditions. The six fitting parameters are regressed with the flocculation factors with six regression models obtained. The validation modeling demonstrates that the proposed PBM quantifies well the dynamic evolution of the floc size during flocculation under the given experimental setup. The investigation will provide significant new insights into the flocculation kinetics of total tailings and lay a foundation for studying the performance of the feedwell of a gravity thickener.

Multi-year diagnosis of unpredictable fouling occurrences in a full-scale membrane bioreactor

The membrane bioreactor (MBR) at the Traverse City Regional Wastewater Treatment Plant has experienced sudden and unpredictable periods of substantial permeability decline since 2011. Early observations detected irregularly-shaped gram-positive bacteria that correlated with plant upsets. Use of biomolecular techniques, such as DNA sequencing of laboratory isolates and the mixed liquor microbial community, and fluorescent in situ hybridization, identified the dispersed organisms as members of the genus Staphylococcus. However, Staphylococcus species were consistently present during normal operation and therefore were more likely to be an indicator of the upset, not the cause. The results suggest that these microorganisms are responding to specific influent wastewater constituents. We chemically analysed seven mixed liquor samples from periods of permeability decline in 2017 and 2018, and four samples from a period of normal operation. During upset conditions, the total carbohydrate content exceeded that of normal operation by 40%. Additionally, mixed liquor calcium concentrations were 65% above normal during the upset in 2017. It is hypothesized and supported through multivariate statistical analysis and estimation of specific resistance to filtration values that a calcium-intermediated polymer bridging mechanism with extracellular polymeric substance constituents is a major contributor to fouling and permeability disruptions in the Traverse City MBR.

High Flocculation of Coal Washing Wastewater Using a Novel Bioflocculant from Isaria cicadae GZU6722

Chanhua (Isaria cicadae) was known as a rare entomogenous fungus with various pharmacological activities since a long time ago in China, which has attracted considerable attention. However, less knowledge was maintained about its products as potential bioflocculants. In this work, a bioflocculant IC-1 produced by Isaria cicadae GZU6722, consisted mainly of protein (4%) and polysaccharides including neutral sugars (52.75%) and galacturonic acid (38.14%), was characterized. It presented high efficiency in flocculating coal washing wastewater, and the flocculating efficiency could reach 91.81% by addition of 24 mg l–1 IC-1 compared to the addition of 60 mg l–1 APAM (anionic polyacrylamide) under the same treatment conditions. The highest flocculating efficiency reached 95.8% in the presence of 2% CaCl2. Compared to APAM, the flocculating efficiency of coal washing wastewater by IC-1 varied little with the increasing dosage. Although the flocs in the APAM-assisted sediment were larger than that in the IC-1-assisted sediment after 1 min of sedimentation, few flocs were still found in the supernatant of both treated samples after 10 min of sedimentation. More interestingly, it was observed under the microscope that the flocs in the IC-1-assisted sediments were more compact than that in the APAM-assisted sediments, suggesting that polymer bridging might take place after IC-1 was added into the coal washing wastewater. The evaluation of costs indicated that the use of IC-1 to treat the coal-washing wastewater may be an economical and feasible way to avoid the extra cost for post-treatment of conventional flocculants.

Effectiveness of Natural Coagulant in Coagulation Process: A Review

Natural coagulants have been increasingly popular in the past few years due to its benefits and the fact that it resolves most of the associated problems when using chemical coagulants. Plant-based natural coagulants perform coagulation either by polymer bridging or charge neutralization, it can be extracted from various plant components. Concerted research and development efforts have been conducted in discovering new plant species and constituents that can be used as natural coagulants, which further boosting the effectiveness of existing plant-based natural coagulants. The objective of this paper is to provide a mini review on studies done over the span of ten years regarding plant-based natural coagulants. This paper also includes advantages and disadvantages of natural coagulants prior to identify several potential research gaps to provide platform towards the need of further study.

Pretreatment of Palm Oil Mill Effluent (POME) Using Magnetic Chitosan

Chitosan is a natural organic polyelectrolyte of high molecular weight and charge density; obtained from deacetylation of chitin. This study explored the potential and effectiveness of applying chitosan-magnetite nanocomposite particles as a primary coagulant and flocculent, in comparison with chitosan for pre-treatment of palm oil mill effluent (POME). A series of batch coagulation processes with chitosan-magnetite nanocomposite particles and chitosan under different conditions,i.e. dosage and pH were conducted, in order to determine their optimum conditions. The performance was assessed in terms of turbidity, total suspended solids (TSS) and chemical oxygen demand (COD) reductions. Chitosan-magnetite particles showed better parameter reductions with much lower dosage consumption, compared to chitosan, even at the original pH of POME,i.e. 4.5. At pH 6, the optimum chitosan-magnetite dosage of 250 mg/L was able to reduce turbidity, TSS and COD levels by 98.8%, 97.6% and 62.5% respectively. At this pH, the coagulation of POME by chitosan-magnetite was brought by the combination of charge neutralization and polymer bridging mechanism. On the other hand, chitosan seems to require much higher dosage,i.e. 370 mg/L to achieve the best turbidity, TSS and COD reductions, which were 97.7%, 91.7% and 42.70%, respectively. The synergistic effect of cationic character of both the chitosan amino group and the magnetite ion in the pre-treatment process for POME brings about enhanced performance for effective agglomeration, adsorption and coagulation.