The Biostability, Water Quality Changes And Biofilms Characteristics In A Simulated Reclaimed Water Distribution System

Municipal wastewater recycling is one of the effective ways to solve the problem ofurban water shortage. As a series of biological reactions always occur in the reclaimedwater networks, the water quality often degrades when it reaches to the endpoint user.So it is important to study the changes of water quality and the biostability for the use ofreclaimed water. Four CDC biofilm reactors were used as the simulated reclaimed waternetwork system. And the reclaimed water was taken from a wastewater treatment plantin Xi’an. The biostability, water quality changes and the biofilms characteristics werestudied through the simulated distribution system. The results were as the follows:(1) The averages of assimilable organic carbon (AOC) and microbial availablephosphorus (MAP) of the reclaimed water were454.61μg/L and13.81μg/L, bothexceeded200μg/L and3μg/L, indicating that its biostability was poor. Besides, theresults of biological regrowth potential (BRP) texts showed that, the number of HPCincreased250%after adding carbon source to the water, but increased only13.5%afteradding phosphorus source. It indicated that the organic carbon limited the bacterialregrowth in the reclaimed water under the conditions of carbon-phosphorus indicatorswere both high.(2) The chlorine was constantly decreasing, while the number of heterotrophicbacteria was increasing, which could reach250000cfu/mL at the end of the network.Meanwhile, the concentration of NH+4-N and NO-2-N in the effluent were dropped77.96%and90.37%, respectively, while the NO-3-N in the effluent were increased39.92%. The above results indicated that nitrification occurred obviously in thedistribution system took place. (3) There were some phosphate-accumulating bacteria in the biofilms, and thenumbers of heterotrophic bacteria declined along the distribution system. Both of totalphosphorus and nitrogen in the biofilm were reduced in the simulated network. Thebiofilms could accumulate Ferrum(Fe) and Manganese(Mn), which made the biofilmshave dark colour. For instance, the contents of Ferrum(Fe) and Manganese(Mn) in theR2were the highest, which reached29.35μg/mg and139.07μg/mg, respectively, whilein the R4were the lowest(only13.27μg/mg and61.37μg/mg, respectively). On the otherhand, R2had the minimum (0.7108mg/mg) of volatile solids, while R4had themaximum (0.75mg/mg).