Determining how polymer-bubble interactions impact algal separation using the novel "Posi"-dissolved air flotation process

The novel dissolved air flotation (DAF) process that uses hydrophobically-modified polymers (HMPs) to generate positively charged bubbles (PosiDAF) has been shown to separate negatively charged algal cells without the need for coagulation-flocculation. Previous research has been limited to HMPs of poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) and, while they were effective at bench-scale, performance at pilot-scale was better using commercial poly(N,N-diallyl-N,N-dimethylammonium chloride) (PDADMAC). Hence, the aim of this research was to compare the effectiveness of PDADMAC modified with aliphatic and aromatic moieties in comparison to previously tested PDMAEMA HMPs in respect to algal cell separation and minimisation of effluent polymer concentration, as well as defining the underlying polymer-bubble interaction mechanisms. Polymer-bubble adhesion properties were measured using atomic force microscopy (AFM) while polymer concentration was monitored via zeta potential and, where possible, assays using fluorescence spectroscopy. Both PDADMAC functionalised with a fluorinated aromatic group (PDADMAC-BCF) and PDMAEMA modified with 1-bromodecane respectively, gave effective cell separation, while the treated effluent zeta potential values at maximum cell removal were lower than the other polymers trialled. The effluent polymer concentration when using PDADMAC-BCF was four times lower in comparison to another aromatically modified PDADMAC polymer. AFM studies indicated that, in contrast to the PDMAEMA-based polymers, the PDADMAC-based polymers did not adsorb closely to the bubble surface. The different polymer-bubble interactions indicate that separation mechanisms will also vary, potentially leading to differences in process effectiveness when explored at pilot scale

Rheological Characteristics of Municipal Thickened Excess Activated Sludge (TEAS): Impacts of pH, Temperature, Solid Concentration and Polymer Dose

Rheological characterization of sludge is known to be an essential tool to optimize flow, mixing and other process parameters in wastewater treatment plants. This study deals with the characterization of thickened excess activated sludge in comparison to raw primary sludge and excess activated sludge. The effects of key parameters (total solid concentration, temperature, and pH) on the rheology and flow behavior of thickened excess activated sludge were studied. The rheological investigations were carried out for total solid concentration range of 0.9–3.7 %w/w, temperature range of 23–55 °C, and pH range of 3.6–10.0. Different rheological model equations were fitted to the experimental data. The model equations with better fitting were used to calculate the yield stress, apparent, zero-rate, infinite-rate viscosities, flow consistency index, and flow index. The decrease in concentration from 3.7 to 3.1 %w/w resulted in a drastic reduction of yield stress from 27.6 to 11.0 Pa, while a further reduction of yield stress to 1.3 Pa was observed as solid concentration was reduced to 1.3 %w/w. The viscosity at higher shear rate (>600 s−1) decreased from 0.05 Pa·s down to 0.008 Pa·s when the total solid concentration was reduced from 3.7 to 0.9 %. Yield stress decreased from 20.1 Pa down to 8.3 Pa for the Bingham plastic model when the temperature was raised from 25 to 55 °C. Activation energy and viscosity also showed decreasing trends with increasing temperature. Yield stress of thickened excess activated sludge increased from a value of 6.0 Pa to 8.3 Pa when the pH was increased from 3.6 to 10.0. The effect of polymer dose on the rheological behavior of the thickening of excess activated sludge was also investigated, and the optimum polymer dosage for enhanced thickener performance was determined to be 1.3 kg/ton DS

Green Low-Carbon Technology for Metalliferous Minerals

Metalliferous minerals play a central role in the global economy. They will continue to provide the raw materials we need for industrial processes. Significant challenges will likely emerge if the climate-driven green and low-carbon development transition of metalliferous mineral exploitation is not managed responsibly and sustainably. Green low-carbon technology is vital to promote the development of metalliferous mineral resources shifting from extensive and destructive mining to clean and energy-saving mining in future decades. Global mining scientists and engineers have conducted a lot of research in related fields, such as green mining, ecological mining, energy-saving mining, and mining solid waste recycling, and have achieved a great deal of innovative progress and achievements. This Special Issue intends to collect the latest developments in the green low-carbon mining field, written by well-known researchers who have contributed to the innovation of new technologies, process optimization methods, or energy-saving techniques in metalliferous minerals development

Viscosity of aqueous and cyanate ester suspensions containing alumina nanoparticles

Concentrated aqueous alumina nanoparticle suspensions with additions of saccharides such as fructose, glucose, sucrose, and others were studied by rheometry and low temperature differential scanning calorimetry. The shear thinning behavior of the suspensions was used to develop a model based on fractal-type agglomeration which describes the viscosity decrease seen with the addition of these saccharides. The characteristics of particle flocculation were found to depend on the saccharide concentration and type. The developed model is in qualitative agreement with the observed melting behavior and earlier bound water hypothesis as illustrated by sub-zero DSC experiments. The effect of alumina nanoparticles on the viscosity and curing behavior of a bisphenol E cyanate ester monomer (BECy) suspension was investigated by rheometry as well. The viscosity was found to increase with solids content and was fit well by the Mooney equation. The viscosity reduction achieved at high particle loadings by the addition of benzoic acid was also investigated. NMR experiments indicate that benzoic acid interacts with the alumina particle surface

Realising full-scale control in wastewater treatment systems using in situ nutrient sensors

Abstract A major change in paradigm is taking place in the operation of wastewater treatment plants as automatic process control is becoming feasible. This change is due to a number of different reasons, not least the development of online nutrient sensors, which measure the key parameters in the biological nutrient removal processes, i.e. ammonium, nitrate and phosphate. The thesis is about realising full-scale control in wastewater treatment systems using in situ nutrient sensors. The main conclusion of the work is that it is possible to significantly improve the operational performance in full-scale plants by means of relatively simple control structures and controllers based on in situ nutrient sensors. The in situ location should be emphasised as this results in short dead time, hence making simple feedback loops based on proportional and integral actions effective means to control the processes. This conclusion has been reached based on full-scale experiments, where various controllers and control structures for the biological removal of nitrogen and the chemical removal of phosphorous have been tested. The full-scale experiments have shown that it is possible to provide significant savings in energy consumption and precipitation chemicals consumption, reduction in sludge production and improvement of the effluent water quality. The conclusions are supported by model simulations using the COST benchmark simulation platform. The simulations are used for investigating issues regarding the interactions between the main control handles working in the medium time frame (relative gain array analysis). The simulations have also been used for testing various control structures and controllers. Controllers for the following types of control are suggested and tested: „h Control of aeration to obtain a certain effluent ammonium concentration; „h Control of internal recirculation flow rate to obtain maximum inorganic nitrogen removal; „h Control of external carbon dosage together with internal recirculation flow rate to obtain a certain effluent total inorganic nitrogen concentration; „h Optimisation of the choice of sludge age. Additionally, a procedure for implementing new control structures based on nutrient sensor has been proposed. The procedure involves an initial analysis phase, a monitoring phase, an experimenting phase and an automatic process control phase. An international survey with the aim to investigate the correspondence between ICA (instrumentation, control and automation) utilisation and plant performance has been carried out. The survey also gives insight into the current state of ICA applications at wastewater treatment plants

Studies on Rheological Characteristic of Wastewater Treatment Plant (WWTP) Sludge and Process Optimization

Rheological behaviour of sludge is a function of various operational parameters. This research is aimed at investigating rheological characteristics of sludge from different sections of a wastewater treatment plant under the influence of varying operational parameters and determining experimentally the optimum operating conditions. It also involved the development of predictive rheological model based on historical data so that rheology can be used as a tool for the monitoring, control, and optimization of dewatering process

An ecological and experimental study of sediment-benthos interactions in a polluted estuary

Summary available: p.

Elucidation of the underlying mechanisms governing algae and cyanobacteria separation using the PosiDAF process

The novel PosiDAF process that uses cationic-polymer modified bubbles has been suggested as an alternative to conventional dissolved air flotation for the separation of algae. However, a cationic PosiDAF effluent compared to an anionic influent as detected by charge measurements indicated that effluent contained high polymer residuals and was undesirable. To prevent this, prior research investigated stronger polymer-bubble adhesion by developing hydrophobically modified polymers (HMPs) of poly(dimethylaminoethyl methacrylate) (PDMAEMA). However, while bench scale tests using the HMPs were successful, commercially available poly(diallyldimethylammonium chloride) (PDADMAC) outperformed the HMPs in pilot scale, suggesting that PDADMAC has a more suitable polymer backbone. Moreover, algal organic matter (AOM) released by cells, particularly biopolymers, was observed to influence cell separation. Further research is required to investigate alternate polymers and to determine more precisely the underlying mechanisms governing polymer-bubble-AOM interactions in PosiDAF. In this study, PDADMAC was modified with various aromatic and aliphatic pendant groups to generate several HMPs. Select HMPs of PDADMAC and previously investigated PDMAEMA were compared to evaluate polymer-bubble attachment and PosiDAF performance to separate algae and cyanobacteria. The composition of AOM, particularly biopolymers from each strain tested was characterised and their influence examined by conducting experiments with various AOM, protein and carbohydrate concentrations. The results showed that HMP coated bubbles had lower surface tensions and consequently, anionic effluents and strong polymer-bubble adhesion. Concurrently, cell separation was either comparable, or slightly better between HMPs. However, separation effectiveness varied for several algae, indicating that AOM impacted separation. Moreover, cell separation of the strains increased to > 95% when exudates from the best separated strain were added. On bulk and molecular characterisation of the cultures, the best separated strain was found to be biopolymer rich in comparison to the other strains. Hence, proteins and carbohydrates were dosed to study their influence and were observed to either depress or enhance the flotation depending on their character. It was concluded that the interplay of biopolymers with polymer-bubble-cell was responsible for the variations in cell removal observed across several strains. Overall, with a well-defined AOM character and low polymer residual in effluent, PosiDAF has been demonstrated as a robust and sustainable process