Study Of Water Quality Characteristics And Algal Bloom Prediction And Emergency Treatment For Haihe River Mainstream

Haihe River mainstream is located at the end of the Haihe River Watershed,with total length of 72 km.Because of lackage of natural runoff input all year round,it's water supply is basically depended on the tranfer of external water resource.Considering the existence of the watergate at the entrance to the sea,Haihe River mainstream has shown the characteristics of a stagnant river.In recent years,the removal and sealing of industrial sewage outfalls have been implemented along Haihe River mainstream,and certain results have been achieved.However,there are still urban sewage and agricultural runoff input along the river.Eutrophication is becoming more and more serious in Haihe River mainstream and algal bloom frequently in summer,which damages the ecological system balance and threats human health.It is helpful to improve the water environment of the Haihe River by fully understanding the change of water quality,pre-warning the algal bloom outbreak,and effectively removing the harmful algal.In this study,research has been conducted on water quality monitoring,algal prewarning and emergent algal treatment,with the aim to provide technical assistance in improving the water quality in the Haihe River watershed and controlling the algal bloom outbreak.First of all,water samples were collected monthly at about 10 sites?with slight changes during the study period?in Haihe River mainstream from 2015 to 2016.The analysis of water samples indicates that the water quality of the Haihe River mainstream is Class V to below Class V.The pollutant concentrations from upstream to downstream tend to increase.The monitoring of phytoplankton community structure indicated that the spatial characterization of phytoplankton is highly related with the concentration of bioavailable nutrients.In summer,cyanobacteria accounts for a larger proportion in the phytoplankton community.In the downstream where there is the largest nutrients concentration,the abundance value reaches the maximum and the biodiversity value is the lowest.Temperature and pH are the most important factors that affect the phytoplankton community changes.Realizing the prediction of algal blooms in advance is one of the important contents of constructing an effective monitoring system and emergency response.To prewarn the algal bloom,a model based on BP neural network was established to predict the daily change of chlorophyll concentration,with the water quality data and meteorological data used.Real-time chlorophyll concentration,air temperature,light intensity and air pressure are the four input variables.The model is used to predict the chlorophyll concentration in the Haihe River mainstream.When the forecast time is24 hours,12 hours and 6 hours,the Nash efficiency coefficients are 0.77,0.85 and0.93,and the forecast standard errors are 5.7,4.6 and 3.1?g/L.Thus,when the forecast time length is within 12 hours,the forecast accuracy could meet the demand of the algae bloom predict,and the data could assist short-period prewarning of algae bloom.Based on the spatial distribution of water quality in Haihe River mainstream,in this study a dynamic monitoring system was put forward,including routine monitoring,online buoy monitoring and pre-warning monitoring.The sampling sites of routine monitoring are state controlled sections and city control sections.Monitoring sites of online buoy monitoring are the same as that of routine monitoring and it is real time monitoring during the whole year.The indicators include pH,ammonium/ammonia ion,conductivity,salinity,dissolved oxygen?DO?,chlorophyll a,freshwater cyanobacteria and redox potential?ORP?.Prewarning monitoring is conducted mainly between early May and mid-October and three prewarning response classes are divided as yellow,orange and red.Most of the indicators of prewarning monitoring are chemical indicators(COD_Cr,nutrients)and real time meteorology data,hydrology data,phytoplankton data and observation elements are also included.In order to effectively implement the algal bloom emergency treatment,this study compared various algae bloom water treatment technologies to select a technical plan that is in line with the actual flow of the Haihe River,and designed a mobile algae water collection-separation-dehydration treatment equipment.A mobile algal bloom emergency spray equipment was also designed,and has shown a good practical application.