Driven by solving water shortage problems and meeting the increasing strict regulations of water quality, changes of supply water quality are commonly happening worldwide. These kinds of irregular changes can have impacts on drinking water distribution systems with accumulated material, leading to chemical, physical and microbiological deteriorations in water quality with (in)organics release and biofilm detachment. Household connection pipes (HCPs) are the last obstacle reaching customers’ taps. The long stagnation time, non- continuous flow, high surface to volume ratio and high water quality deterioration potential make the HCPs deserve more attention. In this study, the impacts of changing supply water quality from conventional treated groundwater to reverse osmosis treated water on aged HCPs were studied.
Aged HCPs were collected from customers and used for building test rigs in the lab. Three types of water quality were supplied to these HCPs, including Kamerik water by conventional treatment (KA), remineralized RO permeate (RE) and mixed water (MX, 70% RO permeate and 30% KA). Water samples were taken every week and the biofilm were compared before and after switching supply water from KA to MX and RE to reveal the potential changes on water quality and accumulated material in pipes. Whether and to what extent the deterioration would occur in the aged HCPs could therefore be determined.
Changes of water quality revealed that the release of ATP, Aeromonas, Fe and Al may happen in the first 8 weeks and then become stabilized again, no effects on As and Mn, and no release of Ca were observed. From the study related to changes of pipe harbored material, the results showed that less bacterial activity and elements’ accumulation (except for Ca) were observed, suggesting the impacts of changing supply water not only represented by the accumulation of bacterial, but also by inorganic material.

Rheological characterization of sludge is essential, since it is related to access sludge transportation and mixing performance, which is included in many processes in waste water treatment and sludge disposal. This study was carried out for characterizing the secondary sewage sludge after gravitational thickening from a Dutch wastewater treatment plant (WWTP), which was also concentrated by vacuum filtration. The measurements of flow curves and yield stress were carried out under conditions of different solid concentrations (TS) and temperatures. Both the Ostwald and Herschel-Bulkley (HB) models were used for fitting the measured data; and a hybrid model was recommended for describing the flow behavior in a wide range of shear rates. HB model was better for fitting the flow curve of the raw sludge within the whole range of shear rates and only at lower shear rates of the concentrated sludge. Moreover, Ostwald was better for the flow curves at higher shear rates of the concentrated sludge. Regarding the parameters in the model fitting, K and n values were in certain relationship with the temperature of each sample. A power law or exponential relationship was used for describing the correlation between the yield stress and the TS.