An Experimental Study On In-situ Purification Of Black-odorous Water By An Integrated Artificially Strengthened Device

There is a strong interaction between human and water in urban rivers and lakes,which are not only a part of urban ecosystem,but also a"disaster area"of urban water pollution.Since 2015,the problem of urban black-odorous water has become increasingly serious in China,so that corresponding remediation has been vigorously developed.Researchers have carried out various attempts and studies on the treatment measures of urban black-odorous water.At present,the single remediation technology has the problems of narrow adaptability,insufficient treatment effect and unable to meet the practical engineering needs.Extracorporeal treatment measures have the problems of high cost,insufficient capacity and additional space.In-situ purification technology has the advantages of little land occupation,low investment and energy consumption,convenient operation,compatibility with natural system,and high treatment efficiency for main pollutants in water,so that it has become a hot spot of research and application at home and abroad.The combined in-situ purification technology/device can flexibly combine different remediation techniques according to specific water quality,which would exhibit positive synergic effect and greatly improve the performance of one single technique.The combined in-situ purification technology/device has gradually become an important branch of the improvement of urban black-odorous water quality.In this study,according to the artificially enhanced aeration and immobilized biofilm techniques,a set of in-situ purification equipments,i.e.,submerged immobilized biofilm and reoxygenation device,was originally designed to purify black-odorous water.First,the device was commissioned in trail run after its assemblage.During this process,the water quality of influent,effluent and each on-way reaction zone was monitored,to explore the purification effect and mechanism of the device and also support the subsequent improvement and optimization of it.Then a pilot test was conducted in the heavily polluted stagnant area of Democracy Lake in Chongqing University.The removal efficiency of main pollutants by the device was monitored and analyzed.The transparency of water was used as a key index to assess the water quality.The relationship between the transparency of water in Democracy Lake and other environmental factors was analyzed,which revealed the major influencing factor and following improvement of the transparency of water in Democracy Lake.The result provided technical support for the application of this device in improving the water quality of different waters.Here are the main conclusions:（1）The concentrations of COD_Cr,NH₃-N,NO₂-N,NO₃-N in water were reduced by 77.1%,90.8%,93.3%and 73.8%,respectively,during the commissioning of the device.The DO concentration in effluent was improved to five times than the original.The p H of water was stable in 8.0～8.4.The turbidity of effluent was lower than that of influent.（2）Both anoxic zone and aerobic zone of the device removed COD_Cr.The nitrification of nitrifying bacteria in aerobic zone was the dominant way to remove NH₃-N and NO₂-N,while NO₃-N was mainly removed by denitrifying bacteria in anoxic zone.DO gradient was formed in the biofilm in aerobic zone and at the same time simultaneous nitrification and denitrification（SND）occurred.The removal of NO₃-N was delayed due to the limited plug-flow aeration.（3）After 105 days of purification,the water quality of Democracy Lake was improved significantly.The concentration of NH₃-N was reduced from 34.1 mg/L to less than 8 mg/L,which met the requirements of black-odorous water treatment.The concentration of COD_Cr was reduced from 84.3 mg/L to 14 mg/L,which met the class III water quality standard of the environmental quality standard for surface water（GB3838-2002）.Within a radius of 25 m from the center of the device,the transparency of water and DO increased to 1.3 times（1.06 m）and 3.5 times（3.2 mg/L）,respectively,which met the requirements of black-odorous water treatment.The chlorophyll-a value（algae quantity index）was removed by 97%（5.5μg/L）,indicating the water was non-eutrophicated.（4）The water transparency of Democracy Lake was affected by many environmental factors.Pearson correlation and multiple stepwise regression analysis showed that chlorophyll-a,dissolved inorganic nitrogen and dissolved oxygen are the main factors affecting the transparency of Democracy Lake（P<0.01）.With the aid of aeration and artificially enhanced microbial metabolism,the device has achieved good nitrogen removal,increased the concentration of dissolved oxygen and efficiently controlled algal growth.Subsequent optimization of this device still focused on the oxygen filling efficiency of artificial aeration,the excellent performance of the film packing and the control of the manufacturing and operating cost.（5）The treatment capacity of a single device was about 1000 m³/d/set.For water with different qualities,multiple devices could be set at various points according to the water volume,and installed flexibly to remedy polluted water quickly and pertinently.The device strengthened the hydraulic circulation at corner and avoid the formation of local black odor.It was able to combine with other surface water treatments to achieve both short-term effect and long-term stability.