Study On Water Quality Evaluation And Water Treatment Of Water Storage Pond In Guanzhong Area

The water storage pond is an important small-scale water and soil conservation project built to intercept rainwater in the northern China,with a long history.Water storage ponds can play a significant role in soil and water conservation in the Loess Plateau,and can also significantly improve the utilization efficiency of rainwater resources in areas with scarce precipitation.It can also provide local ecological landscapes of scarce land and wetlands,connecting rural water systems,flood prevention and drainage,and beautiful rural construction Significant.In the past 40 years,the water storage pond has been invaded and abandoned in large numbers,and its original functions have been lost.Since 2016,the Shaanxi Water Resources Department has regarded the construction and improvement of water storage ponds as an important part of the Guanzhong water system’s water and soil conservation,ecological restoration and rural revitalization.Thousands of waterlogging ponds have been built and repaired,and good results have been achieved.However,the water pollution of waterlogging pools had become a serious problem that hinders the construction of beautiful countryside and endangers the health of villagers.For the purpose of solving the water pollution problem of waterlogging pools in Guanzhong,a combination method of field investigation and indoor simulation was adopted.Firstly,starting with the analysis of the construction form and management and protection level of waterlogging pool,this study identified the source of water pollution,clarified the characteristics of water pollution,evaluated the water quality status,and put forward the treatment requirements of waterlogging pools.Then,based on the survey results,plant measures,chemical measures（Fe Cl₃）and plant-chemical combination mode were used to conduct an experimental study on water quality improvement of waterlogging pool,to explore the purification efficiency of different measures and to screen out the best treatment measures.Finally,the advantages and disadvantages of different measures were analyzed,combined with the rural social and economic conditions,and the best technical measures for water storage pond treatment are integrated.The main conclusions are as follows:（1）The construction form of waterlogging pool（anti-seepage form,slope protection form and greening condition）had no obvious impact on the sensory status of water quality.Waterlogging pool management and protection strategy was related to water pollution to a certain extent.Farmland non-point source pollution was not the main factor,while rural production and living sewage discharge is the main source of water pollution.There are many floating objects such as garbage in the water body,and the water body has high chroma,black odor or water bloom proportion was more than one fourth,and the sensory index of the water body was not good.（2）TN,TP,PO₄^3--P were the main pollution factors in the water body of the water storage pond,and the average pollution factor standard index of each point was 2.4,5.2 and3.8 respectively.In 42%of waterlogging pools,the p H value was greater than 9,and the average DO concentration reached susaturation state.The main characteristics of water pollution in the water storage pond were:（1）The high p H was not conducive to the growth of plants and microorganisms;（2）The Do concentration was over saturated and algae blooms;（3）P type pollution was the most serious,TN concentration exceeds the standard and is second only to TP,with an average concentration of 4.7mg/L.Therefore,The management requirement that reason put forward should be satisfied:（1）Green,ecological,and meet the need of the village landscape;（2）Rapid reduction of water P content,correction of p H,and continuous improvement of water self-purification capacity;（3）The price was low and the operation was simple.（3）The main ways of N and P removal by plants were plant absorption,nitrification and microbial assimilation and accumulation.Its purification features were that long-lasting purification effect,better purification performance for N-type pollutants,with an average removal rate of 78.2%;among the three plant-floating bed systems,canna had better adaptability to the water body of the water storage pond and has the best purification effect.The mechanism of P division by Fe Cl₃ was to combine with PO₄^3-to produce precipitation.The effect of removing P was affected by OH^-and other anions and organics in the water,and the precipitation adsorption reaction was reversible.The three dosages of Fe Cl₃measure were efficient and fast to purify P in the water body of the water storage pond,and the average removal rates of TP and PO₄^3--P are 61.2%and 73.3%,respectively.After adding 50 mg/L Fe Cl₃ treatments,the TP concentration of waterlogging pool was close to the standard ofⅤtype water on the surface;the Fe Cl₃ measure had a poor effect on the removal of N from the water body,and its effect on the removal of N were reflected in four aspect:inhibiting the growth of algae,affecting the enzyme activity of denitrification microorganisms,electron transfer in the process of REDOX of iron ions with different valence states,and affecting the proliferation and activity of denitrification microorganism.（4）The purification effect of the plant-Fe Cl₃ combination model was significant.The N and P purification mechanism of the combination model is not only related to the absorption characteristics of plants,the effect of iron on microbial activities and microbial enzyme activities,but also has an important effect on the purification effect of plants.Under the test conditions,the average removal rate of TN by the plant-Fe Cl₃ combination mode was 72.2%higher than that of Fe Cl₃ alone,and the average removal rate of TP was increased by 31.1%compared with the single plant method,and 29.5%higher than the single Fe Cl₃method;Canna+30 mg/L Fe Cl₃ dosage treatment had a good purification effect and relatively balanced purification capacity for various pollutants,which is the most suitable combination mode for the purification of waterlogging pool.