Metal Sulfide Precipitation: Recent Breakthroughs and Future Outlooks

The interest in metal sulfide precipitation has recently increased given its capacity to efficiently recover several metals and metalloids from different aqueous sources, including wastewaters and hydrometallurgical solutions. This article reviews recent studies about metal sulfide precipitation, considering that the most relevant review article on the topic was published in 2010. Thus, our review emphasizes and focuses on the overall process and its main unit operations. This study follows the flow diagram definition, discussing the recent progress in the application of this process on different aqueous matrices to recover/remove diverse metals/metalloids from them, in addition to kinetic reaction and reactor types, different sulfide sources, precipitate behavior, improvements in solid–liquid separation, and future perspectives. The features included in this review are: operational conditions in terms of pH and Eh to perform a selective recovery of different metals contained in an aqueous source, the aggregation/colloidal behavior of precipitates, new materials for controlling sulfide release, and novel solid–liquid separation processes based on membrane filtration. It is therefore relevant that the direct production of nanoparticles (Nps) from this method could potentially become a future research approach with important implications on unit operations, which could possibly expand to several applications.

The Study of Optimization of Flocculation and Destabilization Technology of Waste PEM Drilling Fluid in Bohai Oilfield

In light of the difficulty of solid-liquid separation of waste PEM drilling fluid in the Bohai oilfield, constructing an inorganic-organic flocculation system is proposed and the processing method of destabilization technology is optimized. The biggest influence factor on the flocculation process of PEM drilling fluid was determined by designing an orthogonal test. The flocculation mechanism was researched through single factor optimization, combined with zeta potential and particle size distribution test. The results showed that the most significant factors affecting the flocculation of waste PEM drilling fluid were the dosage of inorganic flocculant CaCl2 and flocculation pH value. When the dosage of inorganic flocculant CaCl2 was 1.2% (w/v), the dosage of organic flocculant SDYJ-2 was 0.05%, the flocculation pH value was 3, and the flocculation time was 5 min, the flocculation technology reached the optimization and then the liquid yield can reach 70.96%. The mechanism of flocculation and destabilization was as follows: the inorganic flocculant of CaCl2 mainly reduced the zeta potential of clay particles through electric neutralization. 1% CaCl2 could reduce the potential mean value of drilling fluid system from -38.1 mV to -32.5 mV, and then decrease the repulsion among suspensions. Through bridging curling and electric neutralization, the organic flocculant of SDYJ-2 can absorb and wrap the clay particles after flocculation destabilization to form a network spatial structure, which made clay particles aggregate into large flocs and particles. D50 can increase by 21.5 times, when the concentration of SDYJ-2 was 0.15%.

Green Process: Improved Semi-Continuous Fermentation of Pichia pastoris Based on the Principle of Vitality Cell Separation

The large-scale fermentation of Pichia pastoris for recombinant protein production would be time consuming and produce a large amount of waste yeast. Here we introduce a novel semi-continuous fermentation process for P. pastoris GS115 that can separate vitality cells from broth and recycle the cells to produce high-secretory recombinant pectate lyase. It is based on differences in cell sedimentation coefficients with the formation of salt bridges between metal ions and various cell states. Compared to batch-fed cultivation and general semi-continuous culture, the novel process has significant advantages, such as consuming fewer resources, taking less time, and producing less waste yeast. Sedimentation with the addition of Fe3+ metal ions consumed 14.8 ± 0.0% glycerol, 97.8 ± 1.3% methanol, 55.0 ± 0.9 inorganic salts, 81.5 ± 0.0% time cost, and 77.0 ± 0.1% waste yeast versus batch-fed cultivation to produce an equal amount of protein; in addition, the cost of solid–liquid separation was lower for cells in the collected fermentation broth. The process is economically and environmentally efficient for producing recombinant proteins.

A Study on the Possibility of Measuring Sludge Sedimentation Using Contrast Detection Characteristics of CdS Photoresistors

Although operators periodically measure the sludge volume index (SVI) to stabilize the bioreactor and solid–liquid separation during the wastewater treatment process, there is a problem of inconsistency attributed to the subjective judgment of the operator. This study aims to investigate the possibility of securing objective data by employing CdS (cadmium–sulfur) photoresistors for SVI measurements. The sedimentation velocity of settling sludge was measured using LED (Light Emitting Diode) lights at the same level as the installed CdS photoresistors. As a result of the experiment, the settling velocity of sludge in the CdS photoresistors’ installation position H1 to H8 (non-flocculent settling), H9 to H12 (discrete flocculent settling) and H13 to H18 (zone settling and compressive settling), was 0.594 mm/s, 0.180 mm/s and 0.056 mm/s, respectively. Through this study, it was confirmed that measuring sludge sedimentation using the CdS photoresistors is possible. If the measurement of solid matter in sludge using several sludge sedimentation measurements is enabled in the future, it will be possible to develop calculation algorithms to measure the SVI.