Research On The Water Purification Function Of Different Submerged Plants Under The Conditions Of Effluent Of Sewage Treatment Plants

At present, treated effluent of sewage treatment plants is the main source of urban rivers of Kunming. Therefore, it is a new task for comprehensive control of water quality of urban rivers to retreat treated effluent of sewage treatment plants and improve river landscape. Based on treated effluent of sewage treatment plants, this article discusses possibilities of building an artificial self-stable aquatic plant community and effect of water purification by modeling, and provide technical supports for river landscape improvement. The research results show that:(1) When treated effluent of sewage treatment plants meets the requirements of Standard1A of Chinese Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant, the survival rate of all the experiment submerged plants (Potamogeton natans, Potamogeton malaianus, Potamogeton crispus and Ceratophyllum) is up to100%. After four months of growth, the plant height of all the experiment plants are close to water depth, which indicates that the experiment plants in treated effluent that is up to Standard1A grows well. In the period when plants grow well (2010.9-12), all the treatment groups have the capacity to purify water, among which the group of mixed cultivation (simultaneously cultivating Potamogeton natans, Potamogeton crispus and Ceratophyllum) can remove more ammonia nitrogen than the group of Potamogeton malaianus (individually cultivating Potamogeton malaianus) and the group of Potamogeton crispus (individually cultivating Potamogeton crispus) do every month in the first period of the experiment. With growth of plants, total nitrogen removal rate and COD removal rate of the group of mixed cultivation are obviously higher than the group of Potamogeton malaianus and the group of Potamogeton crispus. Compared with other treatments, the group of mixed cultivation removes total phosphorus more unsteadily.Generally speaking, the purification effect of mixed cultivation is superior to that of individually cultivating submerged plants. The research shows that All the chosen plants have the effect of purifying water In the period when plants grow well, but the purification capacity is limited and the purification effect can not meet the requirements of the surface water Class V water standard.Growth of each plant community is influenced profoundly by heavy rain of single point. December12,2010, Kunming was plunged into a heavy rain of single point. The water quality of treated effluent of sewage treatment plants declined (NH4-N:6.22mg/L, TP: 1mg/L, TN:19.8mg/L and COD:65.3mg/L). The water contained a large amount of suspended matter, resulting in severe light attenuation of underwater. Suspended matter adhered onto surface of plants’leaves, which gave rise to hindrance of photosynthesis and respiration. All the treated submerged plants appeared suppressive growth. When the water quality of treated effluent was up to Standard1A, growth of each submerged plant could not recover, and plants gradually did out. In the period when plants decline and die (2011.1-7), the purification capacity of all the treatment submerged plants is obviously lower than that of the period when plants grow well. The purification capacity goes down with plants declining. And the dead plants can also pollute the water.Research has shown thatthe water purification capacityreduced significantly when the growing conditions of submerged plants changed. To maintainthe water purification capacity of all the treatment submerged plants, the growing environment of submerged plants must satisfy their growing conditions.(3) In the period of the experiment, Ceratophyllum grows best among all the experiment submerged plants and is the last one to die, which indicates that it has pollution resistance.