Groundwater arsenic removal by coagulation using ferric(Ⅲ)sulfate and polyferric sulfate: A comparative and mechanistic study

Elevated arsenic(As) in groundwater poses a great threat to human health. Coagulation using mono- and poly-Fe salts is becoming one of the most cost-effective processes for groundwater As removal. However, a limitation comes from insufficient understanding of the As removal mechanism from groundwater matrices in the coagulation process, which is critical for groundwater treatment and residual solid disposal. Here, we overcame this hurdle by utilizing microscopic techniques to explore molecular As surface complexes on the freshly formed Fe flocs and compared ferric(III) sulfate(FS) and polyferric sulfate(PFS)performance, and finally provided a practical solution in As-geogenic areas. FS and PFS exhibited a similar As removal efficiency in coagulation and coagulation/filtration in a two-bucket system using 5 mg/L Ca(ClO)_2. By using the two-bucket system combining coagulation and sand filtration, 500 L of As-safe water( 10 μg/L) was achieved during five treatment cycles by washing the sand layer after each cycle. Fe k-edge X-ray absorption near-edge structure(XANES) and As k-edge extended X-ray absorption fine structure(EXAFS) analysis of the solid residue indicated that As formed a bidentate binuclear complex on ferrihydrite, with no observation of scorodite or poorly-crystalline ferric arsenate. Such a stable surface complex is beneficial for As immobilization in the solid residue, as confirmed by the achievement of much lower leachate As(0.9 μg/L–0.487 mg/L)than the US EPA regulatory limit(5 mg/L). Finally, PFS is superior to FS because of its lower dose, much lower solid residue, and lower cost for As-safe drinking water.     

絮凝沉淀-内电解-厌氧生物氧化预处理DDNP废水

二硝基重氮酚（DDNP）废水是一种严重污染环境和危害人体健康的难降解工业废水。采用絮凝沉淀-内电解-厌氧生物氧化组合工艺预处理DDNP废水,主要考察了内电解反应的进水pH值、反应时间、铁屑与焦炭的质量比和厌氧池停留时间对DDNP废水CODCr去除效果的影响。小试结果表明：以内电解的进水pH值为3,反应时间为120 min,铁屑与焦炭的质量比为12及厌氧池的停留时间为40 h为最佳工艺条件,在此条件下DDNP废水的CODCr去除率可达82.5%,并显著改善其可生化性。     

On-line batch production of ferrate with an chemical method and its potential application for greywater recycling with Al(III) salt

Ferrate(VI) salt is an oxidant and coagulant for water and wastewater treatment. It is considered as a possible alternative method in greywater treatment. However, challenges have existed in putting ferrate(VI) technology into full-scale practice in water and wastewater treatment due to the instability of ferrate solution and high production cost of solid ferrate products. This study demonstrated a new approach of greywater treatment with on-line batch production of Fe(VI) to which Fe(III) salt was oxidized at a weak acidity solution. A series of experiments were conducted to investigate the effect of Fe(VI) on light greywater (total organic carbon (TOC) = 19.5 mg/L) and dark greywater (TOC = 55 mg/L) treatment under different conditions with varying pH and Fe(VI) doses. In addition, the combination use of Fe(VI) and Al(III) salts was proved to be more efficient than using the Fe(VI) salts alone at greywater recycling. The optimum dosage of Fe(VI)/Al(III) salts was 25/25 mg/L for light greywater, 90/60 mg/L for dark greywater, respectively. The TOC values of both light greywater and dark greywater were reduced to less than 3 mg/L with the dosages. The cost for treating greywater was 0.06–0.2 $/ton at ferrate(VI) dosage of 25–90 mg/L and 0.008–0.024 $/ton at AlCl₃ dosage of 25–60 mg/L. The full operating cost needs further assessment before the Fe(VI)/Al(III) technology could be implemented in greywater treatment.     

氯化钙对聚合氯化铝混凝去除腐植酸的影响作用研究

研究了ＣａＣｌ２对ＰＡＣ混凝去除腐植酸的影响作用，发现ＣａＣｌ２可以改善混凝效果和沉淀性能。探讨了ｐＨ值、投加量、温度等因素的影响，对药剂费用进行了经济分析，为今后的实际应用提供了基本数据。     

Fe2+-H2O2催化氧化加混凝处理苯酚磺酸废水

采用H2O2－Fe^2 催化氧化－混凝联合工艺对苯酚磺酸（PSA）废水进行了试验研究，对H2O2和Fe^2 的投加量、pH值、温度（T）、时间（t）等工艺参数进行了优选。结果表明，在H2O2／COD0(g/g）＝1.5，H2O2／Fe^2 (moL/moL)=10:1、pH=3.0-4.0、T＝30℃、t=30min的条件下，COD为1198mg/L的PSA废水经该工艺处理，COD去除率达94％。试运行结果表明，其出水水质达到国家排放标准（GB8978－1996）。     

混凝沉淀工艺处理玻璃纤维生产废水试验研究

通过多种混凝剂对玻璃纤维生产废水进行混凝沉淀处理试验,结果表明,ＦｅＳＯ４．７Ｈ２Ｏ对玻纤废水具有较好的处理效果,并且探索了其处理的最佳工艺条件,在ＦｅＳＯ４．７Ｈ２Ｏ投加量为５００－８００ｍｇ／Ｌ,ＰＨ为６－１１时,出水各项指标均达到国家排标准。     

均匀设计法处理含硫废水的研究

对钠盐型和铵盐型含硫工业废水进行脱硫处理,采用均匀设计法设计试验,得到定量描述试验内在规律的多元非线性回归方程.用该回归方程计算的预测值与试验结果一致.对影响脱硫效果和脱硫效率的影响因素--絮凝剂投加量、pH以及废水含硫量进行了考察.利用回归方程,对反应体系进行了模拟优化处理.研究表明,在试验条件下,用聚合氯化铝作为絮凝剂、pH=7的条件下,采用两段工艺,可以使脱硫后废水含硫量降至40 mg/L以下,满足下游污水处理装置对含硫量的要求.     

Groundwater arsenic removal by coagulation using ferric(III) sulfate and polyferric sulfate: A comparative and mechanistic study

Elevated arsenic (As) in groundwater poses a great threat to human health. Coagulation using mono-and poly-Fe salts is becoming one of the most cost-effective processes for groundwater As removal. However, a limitation comes from insufficient understanding of the As removal mechanism from groundwater matrices in the coagulation process, which is critical for groundwater treatment and residual solid disposal. Here, we overcame this hurdle by utilizing microscopic techniques to explore molecular As surface complexes on the freshly formed Fe flocs and compared ferric(III) sulfate (FS) and polyferric sulfate (PFS) performance, and finally provided a practical solution in As-geogenic areas. FS and PFS exhibited a similar As removal efficiency in coagulation and coagulation/filtration in a two-bucket system using 5 mg/L Ca(ClO)₂. By using the two-bucket system combining coagulation and sand filtration, 500 L of As-safe water (<10 μg/L) was achieved during five treatment cycles by washing the sand layer after each cycle. Fe k-edge X-ray absorption near-edge structure (XANES) and As k-edge extended X-ray absorption fine structure (EXAFS) analysis of the solid residue indicated that As formed a bidentate binuclear complex on ferrihydrite, with no observation of scorodite or poorly-crystalline ferric arsenate. Such a stable surface complex is beneficial for As immobilization in the solid residue, as confirmed by the achievement of much lower leachate As (0.9 μg/L-0.487 mg/L) than the US EPA regulatory limit (5 mg/L). Finally, PFS is superior to FS because of its lower dose, much lower solid residue, and lower cost for As-safe drinking water.     

Investigating the coagulation of non-proteinaceous algal organic matter: Optimizing coagulation performance and identification of removal mechanisms

The removal of algal organic matter(AOM) is a growing concern for the water treatment industry worldwide. The current study investigates coagulation of non-proteinaceous AOM(AOM after protein separation), which has been minimally explored compared with proteinaceous fractions. Jar tests with either aluminum sulphate(alum) or polyaluminium chloride(PACl) were performed at doses of 0.2–3.0 mg Al per 1 mg of dissolved organic carbon in the p H range 3.0–10.5. Additionally, non-proteinaceous matter was characterized in terms of charge, molecular weight and carbohydrate content to assess the treatability of its different fractions. Results showed that only up to 25% of non-proteinaceous AOM can be removed by coagulation under optimized conditions. The optimal coagulation p H(6.6–8.0 for alum and 7.5–9.0 for PACl) and low surface charge of the removed fraction indicated that the prevailing coagulation mechanism was adsorption of non-proteinaceous matter onto aluminum hydroxide precipitates. The lowest residual Al concentrations were achieved in very narrow p H ranges, especially in the case of PACl. High-molecular weight saccharidelike organics were amenable to coagulation compared to low-molecular weight( 3 k Da)substances. Their high content in non-proteinaceous matter(about 67%) was the reason for its low removal. Comparison with our previous studies implies that proteinaceous and nonproteinaceous matter is coagulated under different conditions due to the employment of diverse coagulation mechanisms. The study suggests that further research should focus on the removal of low-molecular weight AOM, reluctant to coagulate, with other treatment processes to minimize its detrimental effect on water safety.     

纤维板厂废水处理实验

用明矾作混凝剂，生石灰为助凝剂剂对纤维板厂生产废水进行混凝处理，COD去除率达67％，其上清液用延时生化法，曝气12h后，出水COD，SS，PH，色度均达到行业排放标准，沉淀用低速离心脱水，效果显著，泥饼可作为燃料综合利用。