Electrocoagulation technique in enhancing COD and suspended solids removal to improve wastewater quality.

This paper presents a preliminary study for the removal of COD and suspended solids in wastewater treatment by combining magnetic field and electrocoagulation (EC) technology. The experiments were carried out using batch apparatus and setup in the static method. Batch experiments with two monopolar iron (Fe) plate anodes and cathodes were employed as electrodes. Wastewater samples were prepared from milk powder with an initial COD of 1,140 mgL(-1) and suspended solids of 1,400 mgL(-1) and acidic conditions were employed (pH approximately 3). DC current was varied from 0.5-0.8 A and operating times were between 30 and 50 min. The results show that the effluent wastewater was very clear (turbidity approximately 9 NTU) and its quality exceeded the direct discharge standard. The suspended solids and COD removal efficiencies were as high as 30.6 and 75.5%, respectively. In addition, the experimental results also show that the electrocoagulation could neutralise the pH of wastewater.     

Treatment of wine distillery wastewater by high rate anaerobic digestion.

Wine distillery wastewaters (WDW) are acidic and have a high content of potential organic pollutants. This causes high chemical oxygen demand (COD) values. Polyphenols constitute a significant portion of this COD, and limit the efficiency of biological treatment of WDWs. WDW starting parameters were as follows: pH 3.83, 4,185 mg/l soluble COD (COD(s)) and 674.6 mg/l of phenols. During operation, amendments of CaCO3 and K2HPO4, individually or in combination, were required for buffering the digester. Volatile fatty acid concentrations were < 300 mg/l throughout the study, indicating degradation of organic acids present. Mean COD(s) removal efficiency for the 130 day study was 87%, while the mean polyphenol, removal efficiency was 63%. Addition of 50 mg/l Fe(3+) between days 86 and 92 increased the removal efficiencies of COD(s) to 97% and of polyphenols to 65%. Addition of Co(3+) improved removal efficiencies to 97% for COD(s) and 92% for polyphenols. Optimization of anaerobic treatment was achieved at 30% WDW feed strength. Removal efficiencies of 92% and 84% were recorded at increased feed strength from days 108 to 130. High removal efficiencies of COD(s) and polyphenols after day 82 were attributed to the addition of macronutrients and micronutrients that caused pH stability and thus stimulated microbial activity.     

Optimization of Fenton process for decoloration and COD removal in tobacco wastewater and toxicological evaluation of the effluent

Decoloration and chemical oxygen demand (COD) removal in tobacco wastewater by Fenton process has been optimized under 25 +/- 2 degrees C. The results showed that the optimal range of conditions were pH 4.13-4.66, Fe(2+) 0.29-0.34 g/L and H2O2 > or = 2.73 g/L. Within this range, up to 95% of colour and 90% of COD was removed. In an enlarged system, setting the optimal conditions as pH 4.50, Fe(2+) 0.34 g/L and H2O2 4.00 g/L, the colour removal rate was 96.03 +/- 2.57%, with COD removal rate of 93.30 +/- 2.92%. The residual COD of 73.67 +/- 19.70 mg/L in effluent had hit the State's first-class standard for the industrial discharge in China (< 100 mg/L COD, GB8978-1996). The ecological safety of Fenton process has also been evaluated. When reaction completed, the content of hydroxyl free radical (OH) was 3.26 +/- 0.44 mg/L. There was no inhibition of Fenton effluent in growth of Escherichia coli, Pseudomonas putida, Pseudomonas sp. HF-1, Acinetobacter sp. TW and Sphingomonas sp. TY. No oxidative stress was induced on strain HF-1 by Fenton effluent. Thus, Fenton process was one of high-efficiency and ecologically safe strategy for tobacco wastewater advanced treatment.     

Application of chemical precipitation for piggery wastewater treatment.

Several series of experiments were conducted to investigate the treatment of piggery wastewater using chemical precipitation (CP) where various types of coagulants such as aluminium sulfate (Al2(SO4)3), poly aluminium chloride (PAC), ferric chloride (FeCl3), ferric sulfate (Fe2(SO4)3), ferrous sulfate (FeSO4) and ferrous chloride (FeCl2) were used. Throughout the experiments, CP was found to achieve high removal efficiencies for organic compounds and nutrients (nitrogen and phosphorus) from the piggery wastewater. Experimental results showed the optimal doses of FeCl3, Fe2(SO4)3, FeCl2 and FeSO4 was 2.0 g/L, while 0.31 g/L and 2.5 g/L were the optimum dose for PAC and Al2(SO4)3, respectively. The pH range 4-5 resulted in the best performance to all coagulants except FeCl2 and FeSO4, whose optimum pH were more than 6. Percentage removal efficiencies for COD were in the ranges of 70-80%, 90-95% for SS, 80-90% for organic-N and TP. Those removal efficiencies were achieved within 5 min of operation. Three times of repetition in CP resulted in higher removal efficiencies for COD, SS and colour up to 74%, 99% and 94% respectively, in which Al2(SO4)3 was used as the coagulant. Removal efficiencies of various water quality parameters in a continuously operated reactor were similar to those of the batch experiments. Biodegradable ratios (BOD5/COD) increased up to 65% after the application of CP.     

Effective degradation of para-chloronitrobenzene through a sequential treatment using zero-valent iron reduction and Fenton oxidation

In this study, zero-valent iron (ZVI) was used to pretreat para-chloronitrobenzene (p-CNB), and the major product was para-chloroaniline (p-CAN). By adding H(2)O(2) directly, further p-CAN degradation can be attributed to Fenton oxidation because ferrous ions (Fe(2+)) released during the ZVI corrosion could be used as an activator for H(2)O(2) decomposition. In the reduction process, the reduction efficiency of p-CNB as well as Fe(2+) concentration increased with increasing iron dosage and decreasing solution pH. Under the optimal conditions, 25 mg L(-1) of p-CNB could be transformed in 3 h when initial solution pH was 3.0 and ZVI dosage was 2.0 g L(-1). A sufficient amount of Fe(2+) (50.4 mg L(-1)) was obtained after the above reaction to activate H(2)O(2). In the Fenton process, the oxidization of p-CAN was also more effective in acidic conditions and it increased with increasing H(2)O(2) concentration. The control experiments showed that the sequential treatment was more effective than Fenton oxidation alone in treating p-CNB wastewater since the removal rate of total organic carbon (TOC) was improved by about 34%. It suggested that the amino function group is more susceptible to oxidative radical attack than the nitro function group. Therefore, sequential treatment using zero-valent iron reduction followed by Fenton oxidation is a promising method for p-CNB degradation.     

利用磁场处理水的研究

在对磁场处理循环水的DO ,pH ,ORP和温度等变化的测定 ,以及磁场处理水通过生锈铁管时 ,红锈逐渐变成黑锈的X线分析基础上 ,探讨了磁场水处理对生锈铁管的除锈、防锈机理。磁场水处理使得Fe2 O3在铁管表面形成致密的复合氧化物Fe3O4 ,对铁管起保护作用。     

污水处理厂回流液中回收磷酸铵镁的试验研究

用污水处理厂回流液进行磷酸铵镁(MAP)沉淀试验,研究化学沉淀法回收MAP的适宜条件.结果表明,pH为8～11时生成沉淀的主要成分为MAP;当pH为10,药剂配比n(NH+4)∶n(Mg2+)∶n(PO43-)控制在1∶1∶1和1∶1.4∶1时得到的晶体纯度高,前者形成的沉淀量为5.3 g/L,氨氮去除率为90.86%;后者形成的沉淀量为5.74 g/L,氨氮去除率为95.84%.分析表明从回流液中回收MAP可以大幅降低处理成本以及系统的氮磷负荷,还可解决MAP结垢问题,实现资源的再生.     

磁场对厌氧生物处理系统除铬(Ⅵ)效率的影响

研究磁场对2株已知高效除铬菌生长繁殖的促进作用,以及厌氧生物处理系统(ASBR)中添加磁粉对合成含铬废水和实际含铬电镀废水的净化效果的影响。通过试验,确定最佳磁场强度为6.0mT,磁场对微生物作用4h后,表现出对微生物生长繁殖的促进作用。尽管实际废水的处理效果比模拟废水处理效果差,Cr6+、总铬、CODCr达标时间延长了3~5h,但在磁场条件下,厌氧污泥系统处理模拟废水和实际废水至达标排放所需时间分别较不加磁场条件下提前约1h和2~3h。     

Experiences with a large-size WWTP based on activated sludge-biofiltration processes: 25 months of operation.

The South-Budapest Wastewater Treatment Plant (SBWWTP) had been operated as a high-load activated sludge (AS) plant since the middle of the 60s. According to the requirements proposed by the water authorities the treatment process had to be upgraded into nutrient (phosphorus and nitrogen) removal. The upgrade of the plant comprised implementation of BIOFOR type nitrifying (NP) and post-denitrifying (DN) biofilters downstream of the AS stage. Phosphorus removal was obtained by chemical precipitation that can be done at five different points for feeding ferric-sulfate (Fe2(SO4)3). Partial flow recirculation was administered from the nitrifying BIOFOR unit ahead of the AS basin for pre-denitrification utilizing raw wastewater as carbon source. The plant performance was monitored since the test operation period for 25 months. Experience revealed that significant nitrification occurs in the high-load activated sludge basin originally designed for carbon removal. During the summer period (characterized by temperature of 20-25 degrees C) about 37-42% ammonium conversion rate was observed in the reactor. The decreasing temperature in the wintertime resulted in lower nitrification rates, of about 6-10%. The combined activated sludge-biofiltration process proved its viability in the removal of organic matter, nitrogen and phosphorus. In this special configuration the AS system plays a key role in the nitrogen and organic matter removal.     

The dissolution characteristics of calcium sulfide and utilization as a precipitation agent in acidic wastewater effluent treatment

The dissolution characteristics of CaS in the presence of CO2 has been investigated by monitoring sulfide speciation, solution conductivity and pH during dissolution. The sulfide speciation associated with CaS dissolution was utilized for metal precipitation from acidic wastewater effluents. The mechanism involved in the dissolution process was observed to be pH-dependent, characterized by increased solution conductivity as the HS(-) species becomes dominant in solution in the form of the Ca(HS)2 complex. The replacement of HS(-) by CO3(2-) in the Ca(HS)2 complex triggered CaCO3 precipitation and H2S stripping and this was characterized by decreased solution pH and conductivity. The sulfide to total metal molar ratio was observed to have an effect on the pH and therefore sulfide speciation as well as extent of metal removal. The utilization of CaS in the treatment of acidic wastewater effluents demonstrated complete metal removal, with the potential of a pH-controlled selective metal removal and recovery.     

Modification of granular activated carbon using low molecular weight polymer for enhanced removal of Cu(2+) from aqueous solution.

Palm shell activated carbon was modified via surface impregnation with polyethyleneimine (PEI) to enhance removal of Cu(2+) from aqueous solution in this study. The effect of PEI modification on batch adsorption of Cu(2+) as well as the equilibrium behavior of adsorption of metal ions on activated carbon were investigated. PEI modification clearly increased the Cu(2+) adsorption capacities by 68% and 75.86% for initial solution pH of 3 and 5 respectively. The adsorption data of Cu(2+) on both virgin and PEI-modified AC for both initial solution pH of 3 and 5 fitted the Langmuir and Redlich-Peterson isotherms considerably better than the Freundlich isotherm.     

北京城市河湖水质净化组合工艺中MIEX投加方式的影响研究

采用磁性离子交换树脂(MIEX)—混凝(PAC)—膜(MF)的联合工艺进行再生水回补型城市河湖地表水净化研究,考察了磁性离子交换树脂投加条件对主要污染物的去除效果。结果表明:MIEX的混合速度为500 r/min,反应时间为30 min,沉淀时间为20 min时,MIEX—PAC—膜的联合工艺对水中TP、TN、叶绿素a和浊度的去除率分别为66.67%、69.62%、76.51%和96.70%。此外,组合系统对COD、DOC和UV254等表征有机物含量的指标的去除率达到了68.00%、40.53%和58.77%,实现了对不同分子量区间内有机物的完整去除。     

Simultaneous copper ion removal and hydrogen production from water over a TiO? nanotube photocatalyst

A one-dimensional (1-D) mesoporous TiO? nanotube (TiNT) was successfully synthesized via a hydrothermal-calcination process, and employed in simultaneous photocatalytic Cu(2+) removal and H? production. Under irradiation, Cu(2+) in the wide concentration range of 8-800 ppm, could be reduced rapidly, and the reduction was not severely impacted by co-existing inorganic ions in solution. Simultaneous with Cu(2+) reduction, noticeable H? was produced over the in-situ fabricated Cu incorporated TiNT (Cu-TiNT) photocatalyst, while H? evolution rate was controlled by the Cu(2+) reduction process, due to competition of electron capture between protons and Cu(2+). In addition, H? generation activity of Cu-TiNT depended on the initial Cu(2+)/Ti ratio, and could be depressed by co-existing ions in solution. Fast Cu(2+) reduction and remarkable H? evolution confirmed the feasibility of simultaneous Cu(2+) removal and H? production over a TiNT photocatalyst.     

Biological treatment of heavy metals in acid mine drainage using sulfate reducing bioreactors.

The uncontrolled release of acid mine drainage (AMD) from abandoned mines and tailing piles threatens water resources in many sites worldwide. AMD introduces elevated concentrations of sulfate ions and dissolved heavy metals as well as high acidity levels to groundwater and receiving surface water. Anaerobic biological processes relying on the activity of sulfate reducing bacteria are being considered for the treatment of AMD and other heavy metal containing effluents. Biogenic sulfides form insoluble complexes with heavy metals resulting in their precipitation. The objective of this study was to investigate the remediation of AMD in sulfate reducing bioreactors inoculated with anaerobic granular sludge and fed with an influent containing ethanol. Biological treatment of an acidic (pH 4.0) synthetic AMD containing high concentrations of heavy metals (100 mg Cu(2+)l(-1); 10 mg Ni(2+)l(-1), 10 mg Zn(2+)l(-1)) increased the effluent pH level to 7.0-7.2 and resulted in metal removal efficiencies exceeding 99.2%. The highest metal precipitation rates attained for Cu, Ni and Zn averaged 92.5, 14.6 and 15.8 mg metal l(-1) of reactor d(-1). The results of this work demonstrate that an ethanol-fed sulfidogenic reactor was highly effective to remove heavy metal contamination and neutralized the acidity of the synthetic wastewater.     

Fe-O/CeO_2催化剂的制备、表征及其对垃圾渗滤液微波催化氧化活性的研究

以浸渍法制备用于常温常压微波催化氧化工艺的负载型Fe-O/CeO_2催化剂并通过XRD和SEM手段进行表征;利用优化制备后的催化剂进行微波催化氧化垃圾渗滤液的研究.结果表明:Fe-O/CeO_2催化剂中活性组分Fe以α-Fe_2O_3和CeFe_2的形式存在.在渗滤液初始COD_(Cr)5 736 mg/L、氨氮1 840 mg/L、色度500倍和pH 8.69的条件下,在Fe-O/CeO_2投加量10 g/L、H_2O_2(30%)投加量22.5 mL/L、微波功率800 W、微波辐射时间10 min和水样初始浓度C_(水样)/C_(原水)为100%的最佳运行条件下,微波催化氧化工艺对COD_(Cr)、氨氮和色度的去除率分别为73%、78%和85%;在反应的第4～8 min和第2～8 min,COD_(Cr)和氨氮去除率分别与反应时间呈近似直线的关系.     

Comparison between ozone and ferrate in oxidising geosmin and 2-MIB in water.

Among the chemicals causing taste and odour (T&O) in drinking water, the most commonly identified and problematic ones are geosmin and 2-MIB (2-methylisoborneol). Since the reported odour thresholds of geosmin and 2-MIB are as low as 4 and 8.5 ng/L, respectively, they are not readily removed by conventional water treatment processes. In this study, ozone (O3) and ferrate (Fe(VI)) were applied to oxidise geosmin and 2-MIB. Their performances were compared in terms of removal efficiency of geosmin and 2-MIB. In the case of O3, removal efficiency of geosmin and 2-MIB ozonation at different initial O3 doses, H2O2/O3 ratios and water temperatures were evaluated. The oxidation rates of geosmin and 2-MIB by Fe(VI) were measured within pH 6-8. The effect of H2O2 addition was also evaluated. In summary, O3, especially with H2O2, could almost completely oxidise geosmin and 2-MIB, while Fe(VI) could not oxidise them more than 25% at any pH that was considered in this study. This was attributed to the structure of the organics and high reaction selectivity of Fe(VI). Further study should be conducted to find the reason of inhibition of oxidation by Fe(VI).     

垂直潜流锰砂人工湿地处理钢铁废水

研究了以锰砂为填料的垂直流人工湿地处理钢铁废水的效果,试验结果表明:湿地系统对CODCr、Fe、Mn、TP、NH3-N的平均去除率分别为52%、97%、94%、95%和83%.夏季湿地对各种污染物的去除效果最好.HRT在2～5 d时,其改变对污染物的去除影响很小,低温条件对NH3-N的去除效果有一定的影响.对以Fe、Mn、浊度的去除为目的的人工湿地而言,在南方的冬季仍可达到良好效果.     

脉冲磁场处理含菌废水的实验研究

利用脉冲磁场杀菌设备对含菌废水进行处理,以生活污水脉冲磁场杀菌为例,研究磁场强度、脉冲数、pH值和污水温度对杀菌效果的影响。结果表明:①随着磁场强度,脉冲数或pH值的增加,细菌去除率会出现一峰值,杀菌效果最好;之后随着磁场强度、脉冲数或pH值的进一步增加,杀菌效果反而变差。在磁场强度分别为7.6T和6.6T左右时,细菌总数杀菌率和大肠菌群杀菌率分别出现了峰值;在脉冲数分别为10和12时细菌总数和大肠菌群杀菌率出现峰值。②细菌总数去除率和大肠菌群去除率都随污水温度的上升而升高,污水温度越高,微生物对磁场的敏感性越强,杀菌效果越好。③脉冲磁场对生活污水杀菌的主次因素为:磁场强度>脉冲数>污水温度>pH值。     

Influence of CO2 scrubbing from biogas on the treatment performance of a high rate algal pond.

Biogas produced by anaerobic treatment of wastewater can be collected and used for power generation. However, the biogas may require scrubbing to prevent corrosion by H2S and to improve engine efficiency by reducing the CO2 content. HRAP can be used to scrub biogas during the daytime when they are carbon-limited and have high pH. This study investigates the influence of the carbon dioxide addition from biogas scrubbing on high rate algal pond wastewater treatment performance (in terms of BOD, NH4-N, DRP and E. coli removal) and algal production (growth and species composition). Batch culture experiments were conducted in laboratory microcosms (2 L) and outside mesocosms (20 L). Results indicate that CO2 addition and reduced culture pH increased algal production and nutrient assimilation, decreased high pH mediated nutrient removal processes (phosphate precipitation and ammonia volatilisation), but had little influence on the ability of the culture to remove filtered BODs. Disinfection, as indicated by E.coli removal; was reduced, however, further research on virus removal, which is not affected by culture pH, is required. These preliminary findings indicate the potential to scrub C02 from biogas using high rate pond water without decreasing the effectiveness of wastewater treatment and enabling increased recovery of wastewater nutrients as algal biomass.     

Treatment of spent brine from a nitrate exchange process using combined biological denitrification and sulfate precipitation.

A combined biological denitrification and sulfate precipitation process was developed to treat and reuse the spent brine produced by a nitrate exchange system. Although the spent brine contained a relatively high salt concentration, more than 80% of NO3(-)-N fed into the denitrification reactors was removed at a nitrate-N loading rate of 2.2 g NO3(-)-N/l x day, regardless of the presence or absence of sulfate up to 8,000 mg/l. Sulfate present in the spent brine was successfully removed by the addition of BaCl2 and the settling velocity of BaSO4 suspension was remarkably enhanced by FeCl3 coagulation. Since most of the chloride consumed in regenerating the exhausted resins was replaced during chemical treatment with BaCl2 and FeCl3, it was possible to reuse the treated spent brine as a regenerant after compensating for the small amount of unreplaced NaCl.