The Influence Of Algae Bloom Accumulation On The Production Of Odorants

Taste and odor(T&O)compounds,induced by the accumulation of cyanobacteria,are frequently reported occurred in Zhushan,Meiliang,Gonghu and other bays of Taihu Lake.However,there are still no systematic studies on the occurrence conditions of T&O,characteristic of T&O,and influencing factors.Therefore,research on the formation process and driving mechanism of T&O compounds can provide more scientific and reasonable early warning of cyanobacteria-induced T&O accidents.In this study,the spatial distributions of T&O compounds in the sediments and overlying water in the typical area of Taihu Lake were investigated.The predictive equations between sediment nutrients and the production of T&O compounds with stepwise multiple linear regression analyses were established.Meanwhile,the changes of water quality and T&O compounds were analyzed during the decomposition of cyanobacteria through laboratory microcosm experiments.The effects of cyanobacteria biomass,temperature conditions and sediment conditions on the formation of T&O compounds were studied.And we further try to clarify the mechanism of occurrence of T&O compounds.Results are mainly as follows:(1)In the spatial distribution,the contents of DMDS?DMTS??-Cyclocitral and?-Ionone were significantly higher near the shoreline than that of the open area.Their concentrations were 36.78ng/L?22.17ng/L?4.33?g/L and 3.10 ?g/L in the overlying water,and 443.10?23.32?182.83 and 356.31 ng/(g·dw)in the surface sediments near the shoreline area,respectively.However,concentrations were 9.81 ng/L?3.83ng/L?0.97?g/L and 0.64 ?g/L in the overlying water,and 92.42?1.36?38.49 and 25.20 ng/(g·dw)in the surface sediments near the open area,respectively.It is suggesting that it is necessary to focus on the near shore zone area during the sediment dredging.The production of T&O compounds was closely associated with nutrients in the sediments.According to the predictive model,NH4+-N was an indicator for the production of DMDS?DMTS,TOC and NO3--N were excellent indicators for the production of ?-Cyclocitral and TOC was an indicator for the production of ?-Ionone.(2)The decay of cyanobacteria blooms caused increased nutrients and T&O compounds loading to water.And higher cyanobacteria biomass can enhance the concentration of T&O compounds.Under the same conditions,when the accumulation of cyanobacteria is above the certain threshold,it is probably generate odorous black water.Although cyanobacteria biomass significantly affected the duration of T&O compounds,there was no significant correlation between the release time of T&O compounds release and cyanobacteria biomass.During the decomposition of cyanobacteria,the production of odorous compounds were closely associated with TOC and so on.(3)Temperature has a significant effect on the decomposition of cyanobacteria to release nutrients and odor substances.Under the same accumulation of cyanobacteria,the higher the temperature,the faster the decomposition rate of cyanobacteria,the faster nutrients and odorant substances released.Under the low accumulation of cyanobacteria(accumulation thickness 3cm),the release of DMS,DMDS and DMTS at 33? is significantly higher than that at 25?;with the increase of cyanobacteria accumulation(accumulation thickness is more than 5 cm),the amount of DMS,DMDS and DMTS at 30??33? was further released than that at 25?.Therefore,when the amount of cyanobacteria accumulated exceeds a certain value,especially when the temperature exceeds 30?,the release amounts of DMS,DMDS and DMTS are significantly affected.When the accumulation of cyanobacteria is less than 3cm or the temperature below 25?,the algae's extinction and decomposition are slowed down to some extent,the occurrence probability of T&O accidents in water reduced.At the same time,temperature has a significant effect on the release of?-Cyclocitral and ?-Ionone.Regardless of the amount of cyanobacteria accumulated,the release of ?-Cyclocitral and ?-Ionone at 33? and 30? was significantly higher than that at 25?.Therefore,temperature will significantly accelerate the release rate of T&O compounds.So it is necessary to pay more attention to the accumulation of cyanobacteria especially in the summer.(4)In the presence/absence of sediments,there were difference in nitrogen,phosphorus nutrient and T&O compounds production(DMS,DMDS,DMTS).However,difference in ?-cyclocitral and ?-ionone is small under the presence/absence of sediments.Also,sediments would impel the T&O compounds occur ahead of time.Therefore,the decomposition of massive cyanobacteria was the main basis for the formation of T&O compounds,temperature and sediment will accelerate the release rate of T&O compounds.