Effect of mean cell residence time on the performance and microbial diversity of pre-denitrification submerged membrane bioreactors

The effect of mean cell residence time (MCRT) (5, 8.3, 16.7, and 33.3d) on domestic wastewater treatment performance had been investigated using four bench-scale pre-denitrification submerged membrane bioreactors (MBR) operated in parallel. The 33.3-d MCRT MBR had the lowest microbial activities in terms of specific oxygen uptake rate, specific denitrification rate and observed sludge yield. Excellent COD removal efficiency (more than 95%) and nitrification (more than 97%) were observed in all the four MBRs investigated. Even though high nitrification can be achieved in all the MBRs, total nitrogen (TN) removal efficiency was found to be affected by MCRT with a maximum of 77% at 33.3-d MCRT. Better TN removal efficiency achieved in the 33.3-d MCRT MBR was due to the combined effect of high mixed liquor concentration and lower dissolved oxygen concentration in the recycled mixed liquor. A comparison of terminal-restriction fragment length polymorphisms (T-RFLP) fingerprints based on 16S rRNA and nirS gene revealed that the microbial communities of 5- and 8.3-d MCRT are grouped under the same branch while 16.7- and 33.3-d MCRT are grouped in another branch. T-RFLP based on amoA gene shows that members from the Nitrosomonas genus were more dominant under shorter MCRT operating environment. Clustering analysis did not show any correlation with the organic and nitrogen removal performance obtained in this study.     

Photolysis of low concentration H2S under UV/VUV irradiation emitted from microwave discharge electrodeless lamps

The photolysis of simulating low concentration of hydrogen sulfide malodorous gas was studied under UV irradiation emitted by self-made microwave discharge electrodeless lamps (i.e. microwave UV electrodeless mercury lamp (185/253.7 nm) and iodine lamp (178.3/180.1/183/184.4/187.6/206.2 nm)). Experiments results showed that the removal efficiency (eta H2S) of hydrogen sulfide was decreased with increasing initial H2S concentration and increased slightly with gas residence time; H2S removal efficiency was decreased dramatically with enlarged pipe diameter. Under the experimental conditions with pipe diameter of 36 mm, gas flow rate of 0.42 standard l s(-1), eta H2S was 52% with initial H2S concentration of 19.5 mg m(-3) by microwave mercury lamp, the absolute removal amount (ARA) was 4.30 microg s(-1), and energy yield (EY) was 77.3 mg kW h(-1); eta H2S was 56% with initial H2S concentration of 18.9 mg m(-3) by microwave iodine lamp, the ARA was 4.48 microg s(-1), and the EY was 80.5mg kW h(-1). The main photolysis product was confirmed to be SO4(2-) with IC.     

Contamination levels of selected organochlorine and organophosphate pesticides in the Selangor River, Malaysia between 2002 and 2003

In Malaysia, rivers are the main source of public water supplies. This study was conducted from 2002 to 2003 to determine the levels of selected organochlorine and organophosphate pesticides in the Selangor River in Malaysia. Surface water samples have been collected seasonally from nine sites along the river. A liquid-liquid extraction followed by gas chromatography-mass spectrometry technique was used to determine the trace levels of these pesticide residues. The organochlorine pesticides detected were lindane, heptachlor, endosulfan, dieldrin, endosulfan sulfate, o,p'-DDT, p,p'-DDT, o,p'-DDE and p,p'-DDE whereas for organophosphate pesticides, they were chlorpyrifos and diazinon. At the river upstream where a dam is located for public water supply, incidents of pesticide levels exceeding the European Economic Community Directive of water quality standards have occurred. Furthermore, the wetland ecosystems located at the downstream of the river which houses the fireflies community is being threatened by occasional pesticide levels above EPA limits for freshwater aquatic organisms. The occurrence of these residual pesticides in the Selangor River can be attributed to the intense agriculture and urban activity.     

Synthesis, characterization and application of a novel chemical sand-fixing agent-poly(aspartic acid) and its composites

A novel sand-fixing agent-poly(aspartic acid) and its composites were synthesized to improve sand particles compressive strength and anti-wind erosion properties. The relationship between the concentration of sand-fixing agent and the sand-fixing properties was studied by three kinds of aging tests. Some composites were choose to improve the sand-fixing property and the composition of 40% xanthan gum and 60% ethyl cellulose were chosen to compare sand-fixing property with lignosulfonate. The results showed that the sand-fixing and water-retaining properties of xanthan gum and ethyl cellulose composites were better than that of lignosulfonate. The biodegradability experiment showed that the PASP and its composites were environment-friendly products and the field test showed that the PASP composites could improve wind erosion disturbance.     

混凝试验搅拌器的研制

影响混凝效果的因素众多,混凝沉淀烧杯试验是进行水的混合、絮凝、沉淀工艺研究、设计和生产指导的最有效方法之一,阐述了智能型混凝试验搅拌器的设计原理和技术性能.     

低浓度软锰矿浆烟气脱硫过程中的催化作用

通过对SO2-4浓度的分析,研究了低浓度软锰矿浆烟气脱硫过程中的液相和固相催化作用.研究表明:低浓度软锰矿浆中Fe(Ⅱ,Ⅲ)的浸出率很低(＜ 7%),致使Fe(Ⅱ,Ⅲ)离子的液相催化作用和Mn(Ⅱ)、Fe(Ⅱ,Ⅲ)离子间的液相协同作用不明显.该过程中实际生成的so2-4主要来自3个方面:MnO2的直接氧化还原作用,Mn(Ⅱ)的液相催化作用以及软锰矿固相组分的催化作用.其中,Mn(Ⅱ)的液相催化作用始终占据主导地位;MnO2的直接氧化还原作用与固相催化作用相比,在20 min前有明显的优势,而20 min后则几乎可以忽略不计.     

高分子絮凝剂CPF的合成和用于生活污水处理研究

通过改变水溶液聚合配比、温度和时间等得出合成高分子絮凝剂CPF的最佳工艺条件.并将合成的CPF絮凝剂与5种无机絮凝剂进行复配,对生活污水进行絮凝处理,优化出CPF与无机絮凝剂的最佳复配方案.采用最佳复配方案,进行了絮体回用效果实验,为CPF絮凝剂在水处理中的应用提供了重要的科学依据.     

Fuzzy input–output model for optimizing eco-industrial supply chains under water footprint constraints

Global water stress is expected to increase due to population growth, economic development and climate change. Because of this trend, there is an increased interest in the water intensity of industrial activities conducted via the product supply chain or within specified geographical boundaries or regions, both at the enterprise- or regulatory-level. The total water footprint of economic activities should be evaluated in consideration of local water resource consumption, virtual water trade and resource availability. As individual entities seek to protect their respective interests, the challenge is to optimize inter-regional trade of goods with the consideration of the interests of participants in the network. This work presents a fuzzy input–output model for optimizing supply chains under water footprint constraints. Two case studies, involving tile manufacturing and biofuel production, are considered to demonstrate the use of the model.     

GIS在广西香蕉低温冻害分析中的应用

根据香蕉生长状况、受害程度与低温冻害强度的关系,确定香蕉冻害的等级指标;利用广西90个气象台站30年的气候资料和台站地理信息,建立冻害指标的空间分析模型,采用GIS技术推算出1km×1km分辨率的冻害指标空间分布;并根据香蕉冻害分级指标,通过GIS的空间分析能力,分析了广西香蕉低温冻害的空间分布特征。