Research On Water Supply Pipeline "Red Water" Control Technology Based On Production Data

In the safe transmission of drinking water through its distribution system it is essential to guarantee the quality of the tap water supplied.The characteristics of low pH,low alkalinity,and low hardness in the southern region of China have exacerbated the corrosion of water supply networks,and caused water quality problems such as“red water”.To solve this problem,the utility supplying Shenzhen started to implement a high-quality drinking water project in 2013.This project aimed to replace old pipelines with new stainless steel pipes,aiming to reduce the pollution of drinking water in the reticulated potable water system,thereby ensuring that tap water meets the“Standards for Drinking Water Quality”?GB5749-2006?.The water quality improvement status and the efficacy of“red water”control were studied both before,and during,the implementation of the high-quality drinking water project in Shenzhen.The water quality problems in the Shenzhen Water Supply Network were analysed by examining customer complaints,water quality monitoring,and other data.From the perspective of the customer complaints,water supply pipe network problems were mainly related to water pressure and quality:both of these problems occurred in areas of more severe pipeline aging and corrosion.Water quality complaints focus on two situations,firstly,there is more“red water”and odour in the early stage of the new pipeline construction,and secondly,water quality problems such as“red water”caused by changes in the hydraulic conditions in old pipelines.From the water quality monitoring data,the factory water was better overall,four microbiological indicators,13 toxicological indicators,two radioactivity indicators,and two conventional indicators of disinfection were used,but the detection values of individual indicators such as oxygen consumption were reaching the national standard limit,among the17 sensory traits and general chemical indicators,only the concentration of aluminium has exceeded an acceptable standard.Meanwhile,the different raw water sources and treatment processes in different water plants had a significant impact on various indicators.Comparing the water from the factory and the water in the pipe network,the indicators of water quality had been reduced during transmission,and the decay in residual chlorine concentration was the fastest.The quality of this drinking water was better than that of ordinary tap water.With regard to the issues relating to the new pipeline,three pipe materials?ductile iron,stainless steel,and HDPE?were selected as research objects,and the variable characteristics of water quality modelled.Within 25 days,the water quality in the ductile iron pipe changed most significantly.The colour of the water sampled from the ductile iron pipe reached 10degrees on the eighth day of operation,and it later decreased but remained at 4 degrees:the turbidity,pH,and TOC showed an increasing trend,the residual chlorine concentration decreased most significantly,and the conductivity was always greater than 0.15 mS/cm.Water quality changes in stainless steel pipes and HDPE pipes were the same:the initial changes were obvious and gradually stabilised in the later period of the study.During a 25-day monitored operating trial,the microstructure of the inner wall of the different pipe materials changed to significantly different extents.The inner wall of the ductile iron pipe changed from having loose porous grains to being relatively dense,with irregular,three-dimensional shaped particles;the stainless steel pipe was initially uniform,and formed uneven,spherical particles on its inner wall surface in the later period;the HDPE pipe was smooth and perforated initially,and the perforation thereof significantly increased in the middle stages of the monitoring period,and the surface roughness indicated a scaly texture in the later stages of testing.The elemental compositions of the inner wall of the pipes were different:the ductile iron pipe contained mainly O and Ca,the stainless steel pipe contained mainly Fe and Cr,and the HDPE pipe contained mainly C and O.The proportion of Proteobacteria in the microbial population in the internal water of different pipes?72.82%to 86.87%?was significantly higher than that in the raw water?48.45%?,and the relative contents of various microorganisms in different pipes differed significantly.Through simulation,the time to stable water quality indices,after pipeline replacement,can be determined from the sensory index.The ductile cast iron pipe,stainless steel pipe,and the HDPE pipe tended to be stable after the 20^th,eighth,and second days,respectively.It is also recommended that the utility flush the ductile cast iron pipe and stainless steel pipe on the eighth,and second,days,separately.With regard to the issues relating to the old pipelines,the variation in metal ion contents,colour,turbidity,and TOC during the soaking process of PP-R pipes,copper pipes,and galvanized steel pipes of similar ages were simulated in the laboratory under different pH conditions.The TOC in water from the PP-R pipe at different pH values was high,the pH,metal ion content,colour,and turbidity of water from the galvanized steel pipe were much higher than in samples from the PP-R pipe and the copper pipe due to the internal wall corrosion therein.In contrast,the stability,in descending order,was:copper,PP-R,then galvanized steel.Through correlation analysis,the old pipeline could control the pH of the water to around 7.65 thus ensuring stable water quality indices.The production re-mineralisation technology used in a water plant in Shenzhen increased the pH and effectively improved the water quality stability of the factory water.