Influence of zeta potential on the flocculation of cyanobacteria cells using chitosan modified soil

Using chitosan modified soil to flocculate and sediment algal cells has been considered as a promising strategy to combat cyanobacteria blooms in natural waters. However, the flocculation efficiency often varies with algal cells with different zeta potential (ZP) attributed to different growth phases or water conditions. This article investigated the relationship between ZP of Microcystis aeruginosa and its influence to the flocculation efficiency using chitosan modified soil. Results suggested that the optimal removal efficiency was obtained when the ZP was between -20.7 and -6.7 mV with a removal efficiency of more than 80% in 30 min and large floc size of >350 μm. When the algal cells were more negatively charged than -20.7 mV, the effect of chitosan modified soil was depressed (<60%) due to the insufficient charge density of chitosan to neutralize and destabilize the algal suspension. When the algal cells were less negative than -6.7 mV or even positively charged, a small floc size (<120 μm) was formed, which may be difficult to sink under natural water conditions. Therefore, manipulation of ZP provided a viable tool to improve the flocculation efficiency of chitosan modified soil and an important guidance for practical engineering of cyanobacteria bloom control.     

廊道式好氧活性污泥法工艺去除氨氮和CODCr的运行总结

研究分析廊道式活性污泥法工艺的诸多优点,同时发现适当的提高水力负荷有利于提高系统的生化处理效果和能力,最后还发现氨氮处理效果的增强,使SV30有所增大,他们之间有很好的正相关性;因为硝化菌群的絮凝效果较弱而引起的.     

Influences of influent carbon source on extracellular polymeric substances (EPS) and physicochemical properties of activated sludge

It is necessary to understand the bioflocculation, settling and dewatering characteristics in the activated sludge process in order to establish more efficient operational strategies. The influences of carbon source on the extracellular polymeric substances (EPS) and flocculation, settling and dewatering properties of the activated sludge were investigated. Laboratory-scale completely mixed activated sludge processes were used to grow the activated sludge with different carbon sources of starch, glucose and sodium acetate. The sludge fed with acetate had highest loosely bound EPS (LB-EPS) and that fed with starch lowest. The amount of tightly bound EPS (TB-EPS), protein content in LB-EPS, polysaccharide content and protein contents in TB-EPS, were independent of the influent carbon source. The polysaccharide content in LB-EPS of the activated sludge fed with sodium acetate was lower slightly than those of starch and glucose. The sludge also had a nearly consistent flocs size and the sludge volume index (SVI) value. ESS content of the sludge fed with sodium acetate was higher initially, although it was similar to those fed with glucose and starch finally. However, the specific resistance to filtration and normalized capillary suction time fluctuated first, but finally were stable at around 5.0 × 10⁸ m kg⁻¹ and 3.5 s L g⁻¹ SS, respectively. Only the protein content in LB-EPS weakly correlated with the flocs size and SVI of the activated sludge. But there was no correlation between any other EPS contents or components and the physicochemical properties of the activated sludge.     

The treatment of black-odorous water using tower bipolar electro-flocculation including the removal of phosphorus,turbidity, sulfion,and oxygen enrichment

• An innovative bubble column tower BPE was designed to treat the black-odorous water. • PO₄³⁻, S²⁻ and turbidity were removed, and dissolved oxygen was enriched in the BPE. • An aluminum bipolar electrode gave the best oxygen enrichment and pollutant removal. • Changes of microorganisms confirmed the improvement in water quality achieved. The large amount of municipal wastewater discharged into urban rivers sometimes exceeds the rivers’ self-purification capacity leading to black-odorous polluted water. Electro-flocculation has emerged as a powerful remediation technology. Electro-flocculation in a bubble column tower with a bipolar electrode (BPE) was tested in an attempt to overcome the high resistance and weak gas-floatation observed with a monopolar electrode (MPE) in treating such water. The BPE reactor tested had a Ti/Ta₂O₅-IrO₂ anode and a graphite cathode with an iron or aluminum bipolar electrode suspended between them. It was tested for its ability to reduce turbidity, phosphate and sulphion and to increase the concentration of dissolved oxygen. The inclusion of the bipolar electrode was found to distinctly improved the system’s conductivity. The system’s electro-flocculation and electrical floatation removed turbidity, phosphate and sulphion completely, and the dissolved oxygen level improved from 0.29 to 6.28 mg/L. An aluminum bipolar electrode performed better than an iron one. Changes in the structure of the microbial community confirmed a significant improvement in water quality.     

Investigation of colloidal biogenic sulfur flocculation: Optimization using response surface analysis

The colloidal properties of biogenic elemental sulfur(S~0)cause solid–liquid separation problems,such as poor settling and membrane fouling.In this study,the separation of S~0 from bulk liquids was performed using flocculation.Polyaluminum chloride(PAC),polyacrylamide(PAM)and microbial flocculant(MBF)were compared to investigate their abilities to flocculate S~0 produced during the treatment of sulfate-containing wastewater.A novel approach with response surface methodology(RSM)was employed to evaluate the effects and interactions of flocculant dose,pH and stirring intensity,on the treatment efficiency in terms of the S~0 flocculation and the supernatant turbidity removal.The dose optimization results indicated that the S~0 flocculation efficiency decreased in the following order PACMBFPAM.Optimum S~0 flocculation conditions were observed at pH 4.73,a stirring speed of 129 r/min and a flocculant dose of 2.42 mg PAC/mg S.During optimum flocculation conditions,the S~0f locculation rate reached 97.53%.Confirmation experiments demonstrated that employing PAC for S~0 flocculation is feasible and RSM is an efficient approach for optimizing the process of S~0 flocculation.The results provide basic parameters and conditions for recovering sulfur during the treatment of sulfate-laden wastewaters.     

南京建筑废弃泥浆絮凝减容效果与经济性分析

以南京市建筑废弃泥浆为研究对象,分别投加聚合氯化铝(PAC)、聚合硫酸铁(PFS)和阳离子聚丙烯酰胺(CPAM)开展絮凝减容试验,分析絮凝剂在不同投加量下泥浆沉降、水质指标及泥浆体积和含水率等的变化。结果表明：上述3种絮凝剂对泥浆均有较好的絮凝沉降效果,调理后泥浆的沉降速度由快变慢直至稳定,尾水水质可达到《污水排入城镇下水道水质标准》（GB 31962—2015）排放标准。CPAM调理的泥浆沉降效果最优,经过20 min的沉降,泥浆可实现减容80%以上,相对于直接将泥浆外运处置的费用,对泥浆絮凝减容后外运可以降低83%的成本。     

Effect of Mn2+ on the phosphorus removal and bioflocculation under anoxic condition

Manganese ion (Mn²⁺) generated from metallurgical, steel making and chemical industries enters sewage treatment plants and affects the sludge activity and flocculation. The effect of Mn²⁺ on the removal of chemical oxygen demand (COD) and total phosphorus (TP) and sludge activity were investigated in anoxic zone of an anaerobic/anoxic/oxic (A²O) process. The compositions and structures of extracellular polymeric substances (EPS) were characterized using three-dimensional excitation emission matrix fluorescence spectroscopy (3D-EEM), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) to reveal the relationship among Mn²⁺, EPS and sludge flocculation.The results showed that low concentration of Mn²⁺ (<5 mg/L) improved removal efficiencies of COD and TP and increased the activity of alkaline phosphatase, acid phosphatase and dehydrogenase. Meanwhile, the addition of Mn²⁺ increased total EPS, sludge contact angle, Zeta potential and sludge particle size, and thus enhanced sludge flocculation. However, high concentration of Mn²⁺ (>10 mg/L) hindered microbial flocculation and reduced removal efficiencies of the pollutants. When Mn²⁺was 5 mg/L, removal efficiencies of COD and TP reached 65% and 90%, respectively. Sludge flocculation was the best and SVI was 70.56 mL/g. The changes of Mn²⁺ concentration caused deviation of groups’ compositions in LB-EPS and TB-EPS, where the main components were always protein (PN) and polysaccharide (PS). The addition of Mn²⁺ resulted in the degradation of humic acids. However, it did not give rise to significant morphology changes of EPS.