Optimizing water and resource recovery facilities (WRRF) for energy generation without compromising effluent quality

The primary separation unit (PSU) splits the organic load on the water and resource recovery facility (WRRF) between the primary sludge (PS) anaerobic digester (AD), where energy can be generated, and the biological nutrient removal (BNR) activated sludge (AS) reactor, where energy is consumed. With a CHONP element mass-balanced plant-wide stoichiometric and kinetic steady-state model, this paper explores quantitatively the impact of four cases of increasing organics removal efficiencies in the PSU on (i) settled wastewater characteristics, (ii) balanced solids retention time (SRT) of the Modified Ludzack-Ettinger (MLE) and University of Cape Town/Johannesburg (UCT/JHB) systems for lowest economical effluent N and P concentrations, (iii) reactor volume, (iv) energy consumption for aeration, pumping and mixing, (v) energy generation by AD of PS and waste activated sludge (WAS), (vi) N&P content of the PS and WAS AD dewatering liquor (DWL) and (vii) final effluent N and P concentrations with and without enhanced biological P removal (EBPR), and looks for an optimum WRRF layout for maximum energy recovery without compromising effluent quality. For the low biogas yield from the WAS AD, decreasing as the SRT of the BNRAS system gets longer and with the added complexity of N&P removal from the digested sludge DWL, makes AD of WAS undesirable unless P recovery is required. Because the wastewater biodegradable particulate organics (BPO) have a low N&P content, it is better to divert more biodegradable particulate organics to the PSAD with enhanced primary separation than digest WAS – the PSAD DWL can be returned to the influent with relatively small impact on final effluent N and P concentration.

A new method for rapeseed hulls purification – Proof of concept

The loss of fats in the hulls is one of the main obstacles limiting the industrial implementation of rapeseed dehulling. The main reason resides in the shape of rapeseed outer cotyledons which resemble to the hulls’ shape and make it difficult to separate. The purpose of this study is to propose a new method for the purification of rapeseed hulls. After primary separation by aspiration, the mixture of hulls and kernels is passed between a pair of flat rolls where kernels are flattened and stick to the metal while the hulls do not. We exploited this property to adapt a small laboratory flaker with two counter-rotating cylinders of 65 mm diameter with scrapers that make the kernels fall away from the hulls. Process optimization by tunning experimental conditions (hulls moisture content, roller spacing, roller speed and feed rate) allowed the determination of the optimal operating conditions. Experiments showed that wetting improves the purity of the hulls but reduces the one of the recovered kernels. A gap of 0.1 mm was necessary. In addition, it was shown that the sorting quality depends on the ratio flow-rate / rotation-speed. The best performances are reached around 1 g.s−1.rpm−1. In these conditions, the hulls and kernels purity were 96% and 94% respectively. This preliminary work has allowed us to prove the concept. The next step will be to develop a pilot plant to validate the process efficiency on a larger scale (100 kg/h).

Mechanism of recovery processes for rare earth and iron from Bayan Obo tailings

Rare earth (RE) and iron minerals in tailings exhibit fine embedded granularity and are closely associated with silicates, carbonates, and other lode minerals, which are difficult to be recycled. Studies of these tailings led to some new processes of ore dressing, involving grinding, RE flotation, strong magnetic separation, and positive iron flotation. In this closed circuit process, RE and iron minerals were separated after grinding, and the materials resulted from the flotation of small-sized RE and iron mineral particles were accurately controlled using a combination of inhibitors, dispersants, pH regulators, and collector agents. The ore dressing were ground to a fineness of 0.045 mm, which was a process accounting for 95.6% of the material. The amount of water glass, NXJ (a combination of sodium carbonate mixed with a fine mud dispersant), and BGH (hydroxamic acid collector, a combination of 3-carboxy-2-naphthylhydroxamic acid and C5-9 hydroxamic acid) used in the primary separation of RE were 2.4 kg/t, 2.5 kg/t, and 2.4 kg/t, respectively. The dosages of ammonium fluorosilicate and GXY (fatty acid collector, a combination of sodium oleate mixed with oxidized paraffin soap) used with iron coarse were 2.2 kg/t and 1.2 kg/t, respectively. The RE collectors achieved chemical separation of Ce, La, and other particles and formed stable five-membered cyclic chelates. Consequently, through the closed circuit experiment, the RE grade and recovery rate in the RE concentrate were improved to 50.3 and 61.6%, respectively. The total iron (TFe) grade and recovery rate in the TFe concentrate were improved to 64.0 and 30.0%, respectively, and other useful metals were also enriched; this process managed secondary recycling of RE and TFe possible, leading to improvements in resource utilization.

Applications of Membrane Hydrocyclone Recovery of Silicon Carbide Powder

This work investigated the possibility of using membrane hydrocyclone as a separator to recover the silicon carbide powder. The weight percentage of silicon carbide powder is 62.9%. Classifying these powders by a 2.5 cm-diameter hydrocyclone that equips membrane tube in the center position, overflow and underflow are obtained. The results of the primary separation show that the overflow and underflow are about half of the proportion of solid, but silicon carbide powder content in the overflow is higher. Therefore, it is necessary to consider the recovery of silicon carbide powder contained in the overflow.

Wall-modelled large-eddy simulation of turbulent flow past airfoils

We present large-eddy simulation (LES) of flow past different airfoils with $Re_{c}$, based on the free-stream velocity and airfoil chord length, ranging from $10^{4}$ to $2.1\times 10^{6}$. To avoid the challenging resolution requirements of the near-wall region, we develop a virtual wall model in generalized curvilinear coordinates and incorporate the non-equilibrium effects via proper treatment of the momentum equations. It is demonstrated that the wall model dynamically captures the instantaneous skin-friction vector field on arbitrary curved surfaces at the resolved scale. By combining the present wall model with the stretched-vortex subgrid-scale model, we apply the wall-modelled LES approach to three different airfoil cases, spanning different geometrical parameters, different attack angles and low to high $Re_{c}$. The numerical results are verified with direct numerical simulation (DNS) at low $Re_{c}$, and validated with experiment data at higher $Re_{c}$, including typical aerodynamic properties such as pressure coefficient distributions, velocity components and also more challenging measurements such as skin-friction coefficient and Reynolds stresses. All comparisons show reasonable agreement, providing a measure of validity that enables us to further probe simulation results into aspects of flow physics that are not available from experiments. Two techniques to quantify hitherto unexplored physics of flows past airfoils are employed: one is the construction of the anisotropy invariant map, and the second is skin-friction portraits with emphasis on flow transition and unsteady separation along the airfoil surface. The anisotropy maps for all three $Re_{c}$ cases, show clearly that a portion of the flow field is aligned along the axisymmetric expansion line, corresponding to the turbulent boundary layer log-law behaviour and the appearance of turbulent transition. The instantaneous skin-friction portraits reveal a monotonic shrinking of the near wall structure scale. At $Re_{c}=10^{4}$, the interaction between the primary separation bubble and the secondary separation bubble contributes to turbulent transition, similar to the case of flow past a cylinder. At higher $Re_{c}=10^{5}$, the primary separation breaks into several small separation bubbles. At even higher $Re_{c}=2.1\times 10^{6}$, near the turbulent separation, the skin-friction lines show small-scale reversal flows that are similar to those observed in DNS of the flat plate turbulent separation. A notable feature of turbulent separation in flow past an airfoil is the appearance of turbulence structures and small-scale reversal flows in the spanwise direction due to the vortex shedding behaviour.

Lacking limit: Desire and the absurd

The article attempts to analyze the existential idea of the innate conflict between me, a human being, and the world, set in the psychoanalytical context of the primary separation between me — a tragic emptiness — and the other who is introduced to me in the form of the m(O)ther’s womb. (O) — from the French l’autre (the other) — literally marks the object-cause of my desire, l’objet a that escapes me radically (Latin radix meaning root), at the moment of me being born and separated from the mother. In this context, the radical separation made present in the primordial cut of the (O) is the very secret of both death and language.