Aging of unfilled polyethylene (PE) films in concentrated (80–100 ppm) chlorine dioxide (DOC) solutions at 20°C and 40 has been studied by IR spectrophotometry, melt rheometry, chlorine titration, and tensile testing to establish the mechanisms of PE degradation induced by DOC, to determine some important kinetic parameters, to identify the embrittlement mechanism, and to examine the possibility to predict nonempirically embrittlement from a kinetic model. Experimental results reveal that DOC initiates PE oxidation. This latter is responsible for hydroperoxide build‐up, and chain scissions occur when hydroperoxides reach a critical concentration above which they decompose bimolecularly. The weight average molar mass Mw decreases and embrittlement occurs when Mw approaches a value of 70 kg mol−1 as previously found in thermooxidation studies. A mechanistic scheme involving all the elementary steps of PE autooxidation plus one initiation and one termination step involving DOC has been elaborated. The kinetic scheme derived from this mechanistic scheme has been solved numerically and the results of simulations have been compared with experimental results. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers

This article deals with the failure of polyethylene pipes transporting chlorine dioxide (DOC) disinfected water under pressures of few bars. Accelerated aging tries made at 20 or 408C show that the antioxidant is rapidly consumed in a superficial layer until a depth of about 1.2 mm. Carbonyl groups appear in a sharper layer of few hundreds micrometers. Natural aging results at various places, for various times up to about 30 years, reveal also a superficial attack with a depth of the order of 1.2 mm. An antioxidant loss by migration, in the whole sample thickness, is also observable. The shape of antioxidant concentration profiles indicates that the crossing of interfaces controls partially the whole migration kinetics. Failures, with brittle cracking, were observed in natural aging, after exposure times of the order of 5-15 years, i.e., far before the expected lifetime (50 years). A kinetic model has been elaborated to predict the time to failure. It is based on a chemical unit, which models the radical processes induced by DOC, and a mechanical unit based on an empirical creep law and a failure criterion depending of the molar mass calculated by the chemical unit.

The new treatment plant at Saint's Hill has been operating since May 1992 and biologically treats ground‐water to remove iron, ammonium/ammonia and manganese. The paper describes the project, the processes involved, the significance of pilot‐plant studies, the different stages of commissioning and plant efficiency. This method of treatment, although new to the UK, is well‐established in France, and reference to existing plants using the processes is made for purposes of indicating the range of applicability of biological treatment processes. Specific conditions are required for biological processes. Not all raw waters can be economically treated to produce an environment which is appropriate for bacterial activity. Conditions for biological iron and manganese removal are different. The paper illustrates the importance of pilot studies to establish the feasibility of biological processes and to determine the design parameters for industrial‐scale works.

Groundwaters from chalk aquifers which are used as a supply for drinking water are often contaminated with pesticides ‐ in particular, atrazine. This paper discusses the use of an industrial‐scale ultraviolet chamber to reduce the concentration of atrazine in a chalk‐derived water which is used for drinking water supply. The concentration of atrazine varied between 0.1 μg/l and 0.5 μg/l, and the raw water was spiked when necessary. Results for other pesticides contaminants are also presented.The efficiency of atrazine removal is dependent only on the energy input and is constant, regardless of the initial concentration. Hydrogen peroxide improves the efficiency of ultraviolet irradiation but requires high doses.

This paper describes an investigation using biological‐iron removal for the elimination of arsenic (III). Groundwater was spiked with sodium arsenite and filtered through a pilot unit. As the water filtered through the sand, arsenic was retained on the iron oxides which were continuously produced by the bacteriological activity. Under specific aeration and pH conditions, both arsenic and iron were eliminated. This process can be used for the design of a full‐scale biological treatment plant.