The Research On Construction Of Compound Bio-vermiculite Bed And Bio-regeneration Of Vermiculite In The Constructed Wetland

With the development of society, the total amount of sewage discharge in our country is increasing constantly and the problem of water pollution is becoming worse gradually. At present in the field of sewage disposal, constructed wetland sewage treatment technology is more and more concerned because of its low construction expenses, low operating cost, low maintenance technology, and high ecological benefits. However, it exist some problems, such as large engineering area, the quality of surface water changes with the season replacement and the substance layer is easy to be jammed, etc.How to improve the systematic ability of deamination and dephosphorization has been a focus of research on constructed wetland sewage treatment technology. The application of absorptive filling in the constructed wetland system offered a new idea and method for solving this problem (such as zeolite and vermiculite, etc.), but most of the researches just aim at the previous stage when the adsorption capacity is strong. while how to regenerate the adsorption capacity of the filling by economic means and restore the capability of deamination and dephosphorization effectively in the wetland system is the key of the filler used in the constructed wetland sewage treatment technology.To these problems described above, natural vermiculite was used as the main filling in the research. First, the buffer system of the vermiculite bed was introduced in the constructed wetland and its buffer performance was investigated; Secondly, studied the bio-regeneration process of ammonium-saturated vermiculite in four types of constructed wetland cells; Last, constructed a compound biological vermiculite bed, and investigated the systematic performance, function of the plant and the result of reoxygenation, and proposed the improvement for the system.The main results of this subject were as following:(1) As an alternative solution to the poor performance of constructed wetlands in municipal sewage treatment in winter, a buffer system using natural vermiculite as filling was introduced into the system. Experimental data obtained from the present study indicated that the buffer unit, with a filling height of 60 cm, kept the effluent quality of sewage with all indexes below the first class of national discharge standards (GB 18918-2002) for more than 45 days when the rate of hydraulic load of the influent was 1.4 m3/m2.d.(2) The main factor that influenced the effect of the buffer units was the thickness of vermiculite layer and the content of oxygen; The buffering capacity of the introduced unit can be further improved by increasing the dosage of natural vermiculite and the DO of the influent, lengthening the hydrology residence time and regulating the pH.(3) Further experiments were conducted to test the effect of buffering capacity bio-regeneration for ammonium-saturated vermiculite under relatively high temperatures (25-30℃) in Summer and Autumn seasons. The results showed that the removal of the adsorbed NH4+ on vermiculite through nitrification, denitrification, bio-uptake and plant root oxygen supply effectively increased the adsorption capacity of vermiculite. The dynamics of the bio-generation process followed an exponential relation. The simulation equation of the four systems were as following:(1) W=1.8948exp(-0.0093t),R2=0.8443; (2)W=1.9078exp(-0.0196t),R2=0.9604;(3) W=1.9524exp(-0.0249t),R2=0.9783; (4) W=1.9137exp(-0.022t), R2=0.9595(4) Plant species, drainage time and carbon source were found to be important factors affecting the regeneration capacity, oxygen amount and carbon source were the essential factors. The results of regeneration showed that the regeneration rate in plant-treatment cells reached 88.2%-91.3% in 90d; Lengthening the drainage time could intensity the function of nitrification and adding extra carbon source could intensity the function of denitrification, while 1‰is the optimal adding amount of carbon source (count according to ethanol).(5) Compound biological vermiculite bed was Constructed as a new kind of subsurface flow constructed wetland in this research, and the results showed that the bed system kept the effluent quality with all indexes below the second class of national discharge standards (GB 18918-2002) and the removal rate of pollutants more than 65% when the rate of hydraulic load of the influent was 1.0 m3/m2.d. The systematic treatment efficiency of wetlands can be improved greatly if we use the bed system as a unit of the constructed wetland.(6) After comparing the four kinds of wetland plants we found that:the order of the management difficulty of the plants was:water spinach>Water hyacinth>Canna generalis>Walter Candle (from the difficult to the easy); The order of the value ofΔm is: Water hyacinth>Canna generalis>Water spinach> Walter Candle (from great to the small); The order of the decontamination capacity of the plants is:Water hyacinth>Canna generalis>Water spinach> Walter Candle. So, in practical application, in order to realize the greatest benefit of the wetland sewage disposal system, we should synthetically consider the ecological value, landscape value, economic value of the wetland plants to meet different wetland systems and different treatment requirements.(7) The DO of the sewage was improved in the wetland by the design of three stage overfall, when the falling height was higher than 45cm, the amount of oxygenation during each stage was more than 0.57 mg/L. Especially, the reoxygenation rate up to 75% during the first stage overfall. All of these proved that the design of three stage overfall in the wetland sewage disposal system was a feasible method to increase the DO of the sewage.