Towards a better hydraulic cleaning strategy for ultrafiltration membrane fouling by humic acid: Effect of backwash water composition

As a routine measurement to alleviate membrane fouling, hydraulic cleaning is of great significance for the steady operation of ultrafiltration (UF) systems in water treatment processes. In this work, a comparative study was performed to investigate the effects of the composition of backwash water on the hydraulic cleaning performance of UF membranes fouled by humic acid (HA). Various types of backwash water, including UF permeate, Milli-Q water, NaCl solution, CaCl₂ solution and HA solution, were compared in terms of hydraulically irreversible fouling index, total surface tension and residual HA. The results indicated that Milli-Q water backwash was superior to UF permeate backwash in cleaning HA-fouled membranes, and the backwash water containing Na⁺ or HA outperformed Milli-Q water in alleviating HA fouling. On the contrary, the presence of Ca^2 + in backwash water significantly decreased the backwash efficiency. Moreover, Ca^2 + played an important role in foulant removal, and the residual HA content closely related to the residual Ca^2 + content. Mechanism analysis suggested that the backwash process may involve fouling layer swelling, ion exchange, electric double layer release and competitive complexation. Ion exchange and competitive complexation played significant roles in the efficient hydraulic cleaning associated with Na⁺ and HA, respectively.     

Hydraulic performance of Compacted Clay Liners (CCLs) under combined temperature and leachate exposures

Experimental investigations were carried out to investigate the effect of thermo-chemical exposures on the hydraulic performance of Compacted Clay Liners (CCLs) in landfills. Hydraulic conductivity of most CCL specimens was increased by two to three times their initial values when exposed to 55 °C for 75 days. CCL specimens also experienced increases in their hydraulic conductivities when exposed to leachate at room temperature. This behaviour could be due to the decrease in viscosity when the permeant was changed from tap water to leachate. However, as the leachate exposure time exceeded the first 15 days, hydraulic conductivity readings decreased to as much as one order of magnitude after 75 days of leachate permeation at room temperature. The gradual decrease in the CCLs hydraulic conductivities was most likely due to chemical precipitation and clogging of pore voids within the soils which seemed to reduce the effective pore volume. The rate of hydraulic conductivity reduction due to leachate permeation was slower at higher temperatures, which was attributed to the lower permeant viscosity and lower clogging occurrence. The observed hydraulic behaviours were correlated to the physical, mineral, and chemical properties of the CCLs and described below.     

SIMPLE DESIGN FOR SIMULTANEOUS STEADY-STATE INFILTRATION EXPERIMENTS WITH RING INFILTROMETERS1

ABSTRACT: A successful procedure for measuring steady-state infiltration rates at remote locations is described. The equipment for the simultaneous experiments is of simple design, inexpensive, and rugged. A total of 247 steady-state infiltration measurements were made across a small rangeland catchment using the procedure as described. The reason for the measurements was to characterize the spatial variability of infiltration across the catchment. The limiting factor for the multiple-ring system as employed in this study was a sufficient water supply to conduct the experiments to completion.     

革新的UNITANK法处理城市污水的特性

对UNITANK法的传统运行模式做了改进。在此基础上，考察了水力停留时问、溶解氧浓度和泥龄等重要因素对处理效果的影响。结果表明，将系统控制在适宜的条件下，出水COD和NH3-N均可达到污水综合排放一级标准。提出了后续研究中改善除磷效果的措施。     

Sources and Distribution of Polychlorinated Terphenyls at a Major US Aeronautics Research Facility

O -deethylase (EROD) activity to a similar degree as PCB Aroclor 1254 and to a greater extent than PCT Aroclor 5460. The presence of high concentrations of PCTs contributed to the facility being included on the National Priorities List. It subsequently became the first US federal facility to sign a Federal Facility Agreement, identifying cleanup responsibilities, prior to formal listing.     

水工隧洞岩溶涌水的水文法计算

在总结数个不同类型水工隧洞岩溶涌水实例的基础上,提出了采用水文参数计算水工隧洞岩溶涌水的新方法,即利用同地区岩溶管道水及中小河流实测得到的最大径流模数,或据常年日暴雨计算得到的径流模数,乘以不同的折减系数来计算隧洞岩溶涌水量。折减系数考虑了岩溶管道与水工隧洞的接触关系、岩溶管道水的补给及出流特征,并提出了相应的经验值。     

(艹屈)和5-甲基(艹屈)的ab initio计算

湾区非角环上的甲基取代能大大增加多环芳烃的致癌性,量子化学的从头计算(ab initio)指出,5-甲基(艹屈)C1-C2键的电子性质有利于在此健发生亲电反应,电子密度分布图说明5-甲基(艹屈)在C1—C2键周围的电子密度明显大于(艹屈)相应部分的电子密度,这也有利于亲电试剂的进攻,因而在代谢过程中,5-甲基(艹屈)容易在此位置发生亲电氧化形成环氧化物,进而形成终致癌剂,这就使5-甲基(艹屈)的致癌性比(艹屈)大大增强。     

4m压力管离心铸造机液压传动

此文在介绍4m压力管离心铸造工艺对液压传动工作要求的基础上,重点介绍了液压传动的工作原理、组成及其主要特点.     

A fetus with a chromosome 13 ring and placenta with chromosome 13 rod/ring mosaicism

A fetus was identified by prenatal cytogenetic diagnosis as having a karyotype 46,XY,r(13) (p11q13). Termination of the pregnancy yielded a severely malformed fetus. Fetal abnormalities included anencephaly, imperforate anus and urethral meatus, severe talipes, syndactyly, cardiac defects and other anomalies. Confirmatory studies on cultured placental villi cells indicated a second cell line, 46,XY, −13,+ 13qter→cen::13ql3→qter. This cell line was not detectable in cells derived from the fetus despite extensive studies. It seems likely that the two cell lines arose simultaneously with selection favouring the 46,XY,r(13) line. How the chromosome rearrangements may have arisen is discussed. We are unaware of other cases where a cell line identifiable by a chromosome abnormality appeared to be confined to placental tissue. However, studies on placental tissue may be helpful in understanding the origin of other unbalanced de novo rearrangements.     

Genetic and Environmental Effects Assessment in Scots Pine Provenances Planted in Central Siberia

Scots pine provenance trials were established in 1964 in forest-steppe and in 1974 in southern taiga zones of Central Siberia from seeds collected over whole Russia. Tree-ring characteristics (radial growth and density chronologies) from 12 and 16 provenances planted in those plantations were measured densitometrically. Tree-ring analysis revealed a retention of a genetically fixed response to climatic factors proper to pines' origin. Trees from higher latitudes keep the orientation towards accelerated growth at the beginning of a growing season, which is followed by a rapid transition to formation of latewood cells and deceleration of growth earlier, than in medium-latitude trees. Main climatic factors controlling tree-rings formation differed slightly between different provenances within plantations. Genetically fixed ability of the provenances are not great (less than 15%), that proves high adaptability of pines to abrupt climatic change. Tree-ring formation of Scots pine provenances is mainly determined by the environmental factors.