Electrocoagulation coupled with electrooxidation for the simultaneous treatment of multiple pollutants in contaminated sediments

In situ and simultaneous remediation of a variety of pollutants in sediments remains a challenge. In this study, we report that the combination of electrocoagulation (EC) and electrooxidation (EO) is efficient in the immobilization of phosphorus and heavy metals and in the oxidation of ammonium and toxic organic matter. The integrated mixed metal oxide (MMO)/Fe anode system allowed the facile removal of ammonium and phosphorus in the overlying water (99% of 10 mg/L NH₄⁺-N and 95% of 10 mg/L P disappeared in 15 and 30 min, respectively). Compared with the controls of the single Fe anode and single MMO anode systems, the dual MMO/Fe anode system significantly improved the removal of phenanthrene and promoted the transition of Pb and Cu from the mobile species to the immobile species. The concentrations of Pb and Cu in the toxicity characteristic leaching procedure extracts were reduced by 99% and 97% after an 8 hr operation. Further tests with four real polluted samples indicated that substantial proportions of acid-soluble fraction Pb and Cu were reduced (30%–31% for Pb and 16%–23% for Cu), and the amounts of total organic carbon and NH₄⁺-N decreased by 56%–71% and 32%–63%, respectively. It was proposed that the in situ electrogenerated Fe(II) at the Fe anode and the active oxygen/chlorine species at the MMO anode are conducive to outstanding performance in the co-treatment of multiple pollutants. The results suggest that the EC/EO method is a powerful technology for the in situ remediation of sediments contaminated with different pollutants.     

稳定塘中枝角类的生物指示作用

经实验观察发现,在多级稳定塘的各个级别中,由于水质的差异、枝角类的数量、颜色、个体大小三特性发生规律性变化,所以,可利用枝角类这些特性变化确定稳定塘污水净化的程度。     

Stabilization of hexavalent chromium with pretreatment and high temperature sintering in highly contaminated soil

• Separate reduction and sintering cannot be effective for Cr stabilization. • Combined treatment of reduction and sintering is effective for Cr stabilization. • Almost all the Cr in the reduced soil is residual form after sintering at 1000°C. This study explored the effectiveness and mechanisms of high temperature sintering following pre-reduction with ferric sulfate (FeSO₄), sodium sulfide (Na₂S), or citric acid (C₆H₈O₇) in stabilizing hexavalent chromium (Cr(VI)) in highly contaminated soil. The soil samples had an initial total Cr leaching of 1768.83 mg/L, and Cr(VI) leaching of 1745.13 mg/L. When FeSO₄ or C₆H₈O₇ reduction was followed by sintering at 1000°C, the Cr leaching was reduced enough to meet the Safety Landfill Standards regarding general industrial solid waste. This combined treatment greatly improved the stabilization efficiency of chromium because the reduction of Cr(VI) into Cr(III) decreased the mobility of chromium and made it more easily encapsulated in minerals during sintering. SEM, XRD, TG-DSC, and speciation analysis indicated that when the sintering temperature reached 1000°C, almost all the chromium in soils that had the pre-reduction treatment was transformed into the residual form. At 1000°C, the soil melted and promoted the mineralization of Cr and the formation of new Cr-containing compounds, which significantly decreased subsequent leaching of chromium from the soil. However, without reduction treatment, chromium continued to leach from the soil even after being sintered at 1000°C, possibly because the soil did not fully fuse and because Cr(VI) does not bind with soil as easily as Cr(III).     

Controlled sintering for cadmium stabilization by beneficially using the dredged river sediment

● Dredged river sediment was proved as a ceramic precursor rather than a solid waste. ● Cd was stabilized in Cd-Al-Si-O phases at low temperatures via sediment addition. ● < 5% of Cd was leached out from sintered products even after a prolonged time. ● A strategy was proposed to simultaneously reuse wastes and stabilize heavy metals. Cd-bearing solid wastes are considered to be a serious threat to the environment, and effective strategies for their treatment are urgently needed. Ceramic sintering has been considered as a promising method for efficiently incorporating heavy metal-containing solid wastes into various ceramic products. Mineral-rich dredged river sediment, especially Al and Si-containing oxides, can be treated as alternative ceramic precursors rather than being disposed of as solid wastes. To examine the feasibility of using waste sediment for Cd stabilization and the phase transition mechanisms, this study conducted a sintering scheme for the mixtures of CdO and dredged river sediment with different (Al+Si):Cd mole ratios. Detailed investigations have been performed on phases transformation, Cd incorporation mechanisms, elemental distribution, and leaching behaviors of the sintered products. Results showed that Cd incorporation and transformation in the sintered products were influenced by the mole ratio of (Al+Si):Cd. Among the high-Cd series ((Al+Si):Cd = 6:1), CdSiO₃, Cd₂SiO₄, CdAl₂(SiO₄)₂ and Cd₂Al₂Si₂O₉ were predominant Cd-containing product phases, while Cd₂Al₂Si₂O₉ was replaced by CdAl₄O₇ when the mole ratio of (Al+Si):Cd was 12:1 (low-Cd series). Cd was efficiently stabilized in both reaction series after being sintered at ≥ 900 °C, with < 5% leached ratio even after a prolonged leaching time, indicating excellent long-term Cd stabilization. This study demonstrated that both Cd-containing phases and the amorphous Al-/Si-containing matrices all played critical roles in Cd stabilization. A promising strategy can be proposed to simultaneously reuse the solid waste as ceramic precursors and stabilize heavy metals in the ceramic products.     

镉砷复合污染土壤稳定化修复技术研究与应用

通过实施江西省某农田土壤中镉、砷污染修复项目,对各修复技术进行比选,并对优选出的稳定化修复技术涉及的钝化药归纳分析。通过小试筛选出合适的药剂种类,中试确定药剂的最佳添加量,再进行工程实施的系统性工艺研究和技术应用。结果表明：该技术在保证修复区增产的前提下实现了污染农田土壤的安全利用,形成了控源-降活-低吸-农产品安全达标生产的修复模式,构建了具有针对性的稳定化-农艺调控的联合修复技术体系,可实现重金属污染农田土壤修复、生态建设、经济效益的有机结合。     

华北稳定塘氧平衡的研究

溶解氧(DO)是氧化塘内有机物降解的主要动力,本文介绍了华北稳定塘中的妤氧塘和强化塘进行污水妤氧处理所需氧的来源主要是浮游藻类光合放氧。在春季和秋季藻类产的氧可占水体溶解氧总来源的80％左右,氧的消耗是以“水呼吸”耗氧为主,“泥呼吸”耗氧为次。从氧平衡的角度阐述了各塘有机物降解与藻类产氧、生物耗氧的关系。      

稳定塘中氧传递规律研究

在稳定塘污水处理过程中,氧是有机物好氧分解的重要组成部分,稳定塘中氧的来源有藻类光合放氧和大气复氧。本研究通过有光无光对比试验、大气复氧试验及对实际稳定塘中运行数据进行总结研究,定量分析藻类光合产氧和大气复氧量,计算在稳定塘中有机物的总去除量中各部分所占的比例,确定出大气复氧是稳定塘中氧传递的主要方式。      

温度试验中产品温度稳定的研究

阐述了温度试验中产品达到温度稳定的重要性,以及温度稳定的概念和确定方法。指出了直接测量法是最直观、最有效的方法,并对如何实施直接测量法提出了见解。另外还对影响产品温度稳定的外部因素进行了一些研究。     

沈阳市赵家沟垃圾填埋场稳定化与场地回用评价

对沈阳市一个关闭2年左右的垃圾卫生填埋场的稳定化状态进行了研究。对填埋场达到稳定化状态的时间进行预测以及不同时期的稳定化程度进行评价,并提出了填埋土地的再利用方案。     

Heavy metal and nutrient changes during vermicomposting animal manure spiked with mushroom residues

A pilot-scale trial of four months was conducted to investigate the responses of heavy metal and nutrient to composting animal manure spiked with mushroom residues with and without earthworms. Results showed that earthworm activities accelerated organic matter mineralization (e.g. reduction in C/N ratio, increase in total concentrations of N, P, K) and humification (e.g. increase in humic acid concentration, humification ratio and humification index). Despite composting increased total heavy metal (i.e. As, Pb, Cu, Zn) concentrations irrespective of earthworm, the availability of heavy metals extracted by DTPA significantly (P < 0.05) decreased particularly in treatments with earthworms introduced. The shift from available to unavailable fractions of heavy metals was either due to earthworm bioaccumulation, as indicated by total heavy metal concentrations being higher in earthworm tissues, or due to the formation of stable metal-humus complexes as indicated by the promotion of humification. Our results suggest that vermicomposting process could magnify the nutrient quality but relieve the heavy metals risk of agricultural organic wastes.