Drinking water safety is of great concern all around the world. Two strategies can be pursued to maintain biological stable drinking water during distribution in the network: (i) without a residual disinfectant, in which bacterial growth is controlled by very low biodegradable nutrients in the water by extensive pre-treatment and a well-maintained network and (ii) with a residual disinfectant in the water during distribution. Independent of the strategy, maintaining water quality during the transportation processes has always been a challenge, and there is a need for a better understanding of the impact of biological stability strategies using systematic studies. In this study, the impact of no residual disinfectant, residual chlorine and residual monochloramine on chemical and microbial water quality were investigated. It is anticipated that studies with pilot distribution networks will lead to better control of drinking water safety, in terms of biological stability and DBPs formation. Meanwhile, computer models applied in this study fitted disinfectant decay kinetics, and appeared to correspond with the experimental data for THMs and biofilm formation, and hence provided more insights in terms of predicting the behaviour of the system in the future, while their accuracy can also be calibrated and verified by the future experimental data.

Zinc smelters in the European Union are now facing a lot of problems, especially under the attack of the Covid-19. This study reviewed the situation of the zinc smelting industry in the EU, including production methods, application of raw materials, pollution control, and waste treatment. The vast majority of smelters use hydro-metallurgical process to obtain high-purity zinc products. Roasting – leaching – electro-winning method is well developed, accepting a large range of raw materials and also has economic advantages. However, the problem with this method is the generation of large amounts of leaching residues. Many researchers have been worked on this and proposed many solutions. It can be improved by increasing leaching efficiency and can better recover valuable metals from the leaching residues. As for environmental pollution in the zinc smelting industry, sulphur emissions have been under well control, and both waste water and solids can be partly recycled in the process. But the storage and disposal of leaching residues are the main problems that still exist and need to be resolved.