Experimental Study On Treatment Of Restaurant Wastewater With Constructed Wetland System

As a simple, effective, ecological treatment technology, the vertical flow constructed wetlands has been widely used in treatment of sewage and industrial wastewaters. The combined process (anaerobic tank + constructed wetland + artificial floating rafts) is set up to treat the restaurant wastewater.In the experiment, the best combined substrate subsurface of constructed wetland is chosen, the growth and adaptation of wetland plants are researched and the influencing factors of constructed wetland is analysed. The results show that:Combinations of soil and silver sand, soil and quartz sand are studied for treatment of restaurant wastewater. Soil with sand is helpful to elimination of pollutants and the soil is prior to sand in the adsorption of N, P.According to their leaf number and biomass, the plants grow well in wetland. The most growing speed of Oenanthe javanica is between February and March, as well as Ipomoea aquatica in July. The water tolerance ability of Oenanthe javanica is better than that of Ipomoea aquatica. The survival percentage is higher when the roots are in half submergence in water than fully submergence in water. The serious-pollution durability of Oenanthe javanica is better than Ipomoea aquatica, but not stable. Oenanthe javanica is greater than Ipomoea aquatica in the absorption capacity of the P, while it is less than Ipomoea aquatica in the absorption capacity of the N.In anaerobic tank, the recalcitrant pollutants in restaurant wastewater can be changed into small organic molecules, which is beneficial to the subsequent treatment. The average removal rate of COD and TP in anaerobic tank are 25% and 33% in winter respectively, as well as they are 39%and 32.5% in spring and summer respectively.In constructed wetland system, the best HRT of wetland is between 1d~1.5d, the best HLR is 0.15 m/d. When the pH is about 7.0~7.7, the average removal rate of NH4+-N, TP and COD are 90%, 80% and 85%, respectively. When the temperature is about 25℃~35℃, the average removal rate of NH4+-N, TP and COD is the highest, reaching 90%, 80% and 85%~90%, respectively. Ability of wetland process'treatment of pollutants varies with different seasons, it is higher in spring and summer than in winter, but it is'not stabler than in winter. The average removal rate of COD in the two-class wetlands(first-class and secondary-class) are 69.3% and 49.6% in spring and summer, they are 54.1% and 58.9% in winter. The average removal rate of NH4+-N in two-class wetlands are 84.8% and 59.7% in spring and summer, they are 73.2% and 71.4% in winter. The average removal rate of TP fluctuates seasonally, 50%~95% in summer and 35%~70% in winter. Artificial floating rafts is beneficial to improve the water quality of the system, and the average removal rate of NH4+-N, TP and COD are 62.4%,56.2% and 39.5%, respectively.After Combined process's treatment, effluent quality of the restaurant wastewater can reach the requirement of Standards of discharge of municipal wastewater Quality(GB18918-2002).