干湿比对地下渗滤系统出水及N_2O释放的影响

Effect of the dry-wet ratio on the infiltrating quality and the N_2O emission in a subsurface sewage infiltration system

通过场地试验研究干湿比对地下渗滤系统(SWIS)除污能力及N_2O释放的影响,在原位平台的6个子单元上,设置干湿比分别为3∶1、2∶1、1∶1、1∶2、1∶3、0。结果表明,随干湿比减小,SWIS对COD和TN的去除率呈先增后减的趋势,而NH_4^+-N的去除率逐渐下降。N_2O产率随干湿比减小而逐渐升高,表明N_2O主要产生在氮的反硝化阶段。当干湿比为1∶1时,N_2O转化率达到最大值,即0.065%。因此建议在工程应用中将污水地下渗滤系统的稳定运行干湿比控制为1∶1,此时N_2O产率低于0.09 mg/(m^2·h),COD、NH_4^+-N及TN的去除率可分别达到92.8%、90.2%和82.4%,出水满足GB/T 18921—2002《城市污水再生利用景观环境用水水质》。

The present paper is aimed to trace and identify the effects of the different dry-wet ratios on the N_2O production,conversion and the pollutants removing efficiency under the subsurface sewage infiltration system（ SWIS）. For this purpose,we have conducted the field experiments in a sewage treatment plant on a university campus. We have set up the dry-wet ratio conditions in respective proportions of 3： 1,2： 1,1： 1,1： 2,1： 3 and 0 through controlling the drying and feeding time periods. The results of our experiments indicate that the dry-wet ratio tends to have significant effects on the pollutants removal,the production of N_2O and its transformation rate. For example,with the decrease of the dry-wet proportion from 3： 1 to 1： 1,it would be possible for the removal rates of COD and TN to increase from84. 9% ± 2. 6% and 77. 9% ± 0. 9% to 92. 8% ± 2. 9% and82. 4% ± 0. 6%,correspondingly. What is more,if the dry-wet ratio goes on decreasing to 0（ constant feeding）,the removal rates of COD and TN tend also fall to 81. 8% ± 1. 1% and70. 6% ± 0. 3%,respectively. Furthermore,with the decrease of the dry-wet ratio from 3： 1 to 0,it would also be possible for the removing rate of NH＋4-N to decrease from 94. 2% ± 0. 9% to80. 5% ± 0. 5%. Moreover,if the dry-wet ratio falls from 3： 1 to0,the average productive rate of N_2O may tend to increase from0. 08 mg/（ m2·h） to 0. 13 mg/（ m2·h）,whereas the conversion rate of N_2O may increase first and then would be followed by a decrease. Nevertheless,the dry-wet ratio of 1： 1 is likely to give out the highest conversion rate of N_2O,namely,0. 065%. Taking into account the factors of N_2O production,the conversion rate and pollutants removal efficiency,we prefer to recommend that the dry-wet ratio of SWIS should be set up as 1： 1 in the engineering applications,for,under such a condition,it is possible to keep the productive rate of N_2O below less than 0. 09 mg/（ m^2·h） with the conversion rate of N_2O well kept at a lower level. At the same time,it would be possible for the removal rates of COD,NH＋4-N and TN to reach 92. 8%,90. 2% and82. 4%,respectively,while the infiltrate quality can be made to meet the surface water quality standard of the urban landscape（ GB/T 18921—2002）.