Evidence on the causes of the rising levels of COD_(Mn) along the middle route of the South-to-North Diversion Project in China:The role of algal dissolved organic matter

As the biggest inter-basin water transfer scheme in the world,the South-to-North Water Diversion Project(SNWD) was designed to alleviate the water crisis in North China.The main channel of the middle route of the SNWD is of great concern in terms of the drinking water quality.In this study,we tested the hypothesis that the dissolved organic matter(DOM) derived from the planktonic algae causes the rising levels of COD_(Mn) along the middle route by monitoring data on water quality(2015-2019,monthly resolution).The results showed that algal density in the main channel increased along the channel and was significantly correlated with COD_(Mn)(p <0.01).Five fluorescent components of DOM,including tyrosine-like(14.85%),tryptophan-like(22.48%),microbial byproduct-like(26.34%),fulvic acid-like(11.41%),and humic acid-like(24.92%) components,were detected.The level of tyrosine-like components increased along the channel and was significantly correlated with algal density(p<0.01),indicating that algae significantly changed the level of DOM in the channel.Algal decomposition and metabolism were found to be the main mechanisms that drive the changes in COD_(Mn).Therefore,controlling algal density would be an important measure to prevent further increase in CODMn and for the guarantee of excellent water quality.

Interactions between metal ions and the biopolymer in activated sludge： quantification and effects of system pH value

The quantification and effects of system pH value on the interactions between Pb（II） and the biopolymer in activated sludge were investigated. The biopolymer had two protein-like fluorescence peaks （Ex/Em = 280 nm1326-338 nm for peak A; Ex/Em = 220-230 nm/324-338 nm for peak B）. The fluorescence intensities of peak B were higher than those of peak A. The fluorophores of both peaks could be largely quenched by Pb（ll）, and the quencher dose for peak B was about half of that for peak A. The modified Stern-Volmer equation well depicted the fluorescence quenching titration. The quenching constant （Ka） values for both peaks decreased with rising system pH value, and then sharply decreased under alkaline conditions. It could be attributed to that the alkaline conditions caused the reduction of available Pb（II） due to the occurrence of Pb（OH）2 sediments. The Ka values of peak B were bigger than those for peak A at the same system pH values. Accordingly, the aromatic proteins （peak B） played a key role in the interactions between metal ions and the biopolymer.