| Biofilm processes of the important biological wastewater treatment method, easy operation, powerful resistance to impact load, less surplus sludge, were widely used. Biofilm had passed through four successive periods, incubation period, growth period, stable period and aging period. However, if biofilm could not be self-renewal, the aging biofilm would accumulate and leading to decline the water quality. At present, the physical and chemistry methods, high energy cost, polluting water, long recovery phase, were used to wipe off the aging biofilm.The Lindeman’s law indicates that energy flows among the trophic levels that only10%of the total energy could be used by the next trophic level and90%is lost because of respiration and decomposition. Biofilm exist as a ecosystem, consist of algae, bacteria, fungus, protozoa, metazoan and surroundings. Thus, we could lengthen the food chain and strengthen the predation by adding the microfauna. According to the Lindeman’s law, if we lengthened the food chain, the energy would be lost and the biomass be reduced accordingly. Therefore, the aging biofilm could be renewal by adding micofauna.Accumulation aging of biofilm plays a vital important role on biofilm activity and purification efficiency. It is economically, environmentally and simply biological method to lengthen the food chain and strengthen the predation by adding microfauna. Previous studies have demonstrated that rotifers, widely distributed in waters, are considered to be ideal microfauna. In the current study, according to the biological theories, we compared the variation of biofilm index, after and before adding rotifers, to discuss the effect of rotifers to improve the biofilm activity. During the first stage, study the biofilm developing of group B and group C, compared with group A. And during the second stage, study the changes of the property of biofilm of group C after adding rotifers, compared with group B. The results indicated that:(1) After being cultivated for about a month, there had formed a layer of biofilm gradually. Several species, such as algae, protozoa, monostyla, philodina, nematode, aeolosoma hemprichi and so on, observed by microscopic. It was a sign of the mature of biofilm.(2) During the period of biofilm developing, the removal rate of NH3-N ranged from1.12%to9.12%in group A, with an average of4.26%. The removal rate of NH3-N ranged from11.03%to91.16%in group B, with an average of52.78%. The removal rate of NH3-N ranged from11.89%to91.67%in group C, with an average of54.94%. The paired test analysis indicated that the difference of NH3-N removal rate between group A and group B was very significant (P<0.01). The difference of NH3-N removal rate between group A and group C was very significant (P<0.01). The difference of NH3-N removal rate between group B and group C was not significant (p>0.05).(3) During the period of biofilm developing, the removal rate of TP ranged from5.98%to15.18%in group A, with an average of12.62%. The removal rate of TP ranged from9.98%to26.07%in group B, with an average of18.07%. The removal rate of TP ranged from9.71%to26.78%in group C, with an average of19.69%. The paired test analysis indicated that the difference of TP removal rate between group A and group B was very significant (P<0.01). The difference of TP removal rate between group A and group C was very significant (P<0.01). The difference of TP removal rate between group B and group C was not significant (P>0.05).(4) During the period of biofilm developing, the removal rate of CODcr ranged from4.79%to21.97%in group A, with an average of11.61%. The removal rate of CODcr ranged from10.08%to38.43%in group B, with an average of20.71%. The removal rate of CODcr ranged from7.18%to37.91%in group C, with an average of20.14%. The paired test analysis indicated that the difference of CODcr removal rate between group A and group B was very significant (P<0.01). The difference of CODcr removal rate between group A and group C was very significant (P<0.01). The difference of CODcr removal rate between group B and group C was not significant (P>0.05).(5) The independent samples t-test analysis indicated that the difference of biofilm dry weight between group B and group C during period Ⅰ (without rotifers) and period Ⅱ (with rotifers) was not significant (P>0.05). The difference of biofilm dry weight change rate between group B and group C was not significant (P>0.05). The difference of biofilm activity between group B and group C during period Ⅰ (without rotifers) was not significant (P>0.05), but very significant (P<0.01) during period Ⅱ (with rotifers). The difference of biofilm activity change rate between group B and group C was very significant (P<0.01). The difference of total bacteria count between group B and group C during period Ⅰ (without rotifers) was not significant (P>0.05), but very significant (P<0.01) during period Ⅱ (with rotifers). The difference of total bacteria count change rate between group B and group C was very significant (P<0.01).(6) After adding rotifers, the paired test analysis indicated that the difference of NH3-N, TP and CODcr removal rate between group B and group C was not significant (P>0.05).The bacterial and biofilm activity could be improved by adding rotifers. Meanwhile, the feeding cost of rotifers was low. And rotifers would not pollute the environment. Therefore, adding rotifers may offer a new way to solve the problem of biofilm’s.accumulation aging. |
PDF Full Text Request