| The rural domestic sewage has become an important pollution source of China rural environment, not only endangering the health of rural residents, but also endangering the safety of groundwater and the water quality of the lake. The governance of rural domestic sewage is imperative. Pollution control of domestic sewage in villages and towns is obviously different from urban domestic sewage pollution control, mainly in the drainage system selection and application technology requirements. For rural domestic sewage pollution control, in the drainage system, combined system and separate system each has its advantages and disadvantages, and each has a wide range of applications, in the regional distribution, the control mode includes the decentralized processing and the relative centralized processing. The technology used should have the general characteristics of the less investment, low operation cost, good treatment effect, easy management and maintenance, also should have characteristics of the resistance to shock loading, the good removal effect for nitrogen of low C/N ratio sewage and other features. According to the general requirements of rural domestic sewage treatment technology, combined with the early experience in the development and application of humified media filter and research ideas of series technology for rural domestic wastewater treatment, based on the technical principle of biological aerated filter and sequencing batch biofilm process, the author developed a new process of alternate aeration biofilter, which can achieve the goals of the good removal effect for nitrogen of low C/N ratio sewage, easy operation and control, stable operation in a long time, small floor area, less excess sludge.In this experiment, using self designed alternate aeration biofilter test device,1-2mm ceramsite as filter media, the sewage of campus living area as treatment object, the author studied the influence of influent C/N ratio, reflux ratio and hydraulic loading on the pollutant removal efficiency of alternate aeration biofilter, initially identified the process controlling parameters on the best operating condition. And the removal efficiency of pollutants in each part of the experimental device, dissolved oxygen environment, head loss, and the apparent yield coefficient of the process were studied.The results showed that the nitrogen removal efficiency of the alternate aeration biofilter process increased with the increase of influent C/N ratio in a certain range. The device was operated in the hydraulic load of 0.81 m3/m2·d and reflux ratio of 130%, when the influent C/N ratio varied from about 2 to about 5, TN removal rate and volume load gradually increased. Among them, when the influent C/N was only about 4, the average TN removal rate of alternate aeration biofilter could reach 53.7%. When the influent C/N ratio was in the range of 5 to 9, TN removal rate and TN volume load fluctuated, but the removal rate remained within the range of 65%-75% in general.The optimum reflux ratio of the alternate aeration biofilter process is 200%. The device was operated in the hydraulic load of 0.81 m3/m2·d, the influent C/N ratio of 4, when the reflux ratio was 200%, the average TN removal rate was 68.3%, and the average TN volume load was 30.0 g/m3-d.When the influent C/N ratio was 4, the reflux ratio was 200%, the hydraulic loading increased from 0.81 m3/m2·d to 1.50 m3/m2·d, the device’s removal efficiency of COD, NH3-N and TP was still high, the average TN volume load increased from 30.0 g/m3·d to 40.8 g/m3·d, but the average TN removal rate decreased from 68.3% to 53.3%.When the device was operated in the hydraulic load of 0.81 m3/m2·d, the influent C/N ratio of 4, the reflux ratio of 200%, after alternating aeration side, the dissolved oxygen concentration in each part of the reactor experienced fluctuations first and then stabilized gradually. The upper part of anoxic zone’s dissolved oxygen concentration decreased to below 1 mg/L in 2h after the alternation, which informs that at this time the anoxic environment in anoxic zone’s filler layer has already formed. In stable operating conditions, the dissolved oxygen concentration in anoxic zone’s filler layer remained below 0.25mg/L, which created a good environment for anoxic microorganism, to ensure sufficient microbial carbon storage, which is beneficial to denitrification and phosphorus removal process, at the same time as the amount of assimilation carbon decreased, the sludge production reduced. The upper part of aerobic zone’s dissolved oxygen concentration stably remained at about 9mg/L, which was too high, leading to the reflux of nitrification liquid carrying excessive dissolved oxygen, and impact the anoxic zone. So in the further study, replace the ceramsite with lightweight filler in order to reduce the amount of aeration needed to make the filler slightly fluidized, thereby reducing the dissolved oxygen concentration in the aerobic zone.Operated in hydraulic load of 0.81 m3/m2·d, reflux ratio of 200%, hydraulic load of 0.81 m3/m2·d, reflux ratio of 300%, and hydraulic load of 0.81 m3/m2·d, reflux ratio of 200%, total head losses of the device after 48 hour’s operation were respectively 365 mm,564mm, and 986mm.Taking into account the application conditions of the intermittent use of the technology, the device was stopped running for 26 days, and then restarted. On the 1st day after restart, the device already had ideal removal efficiency to COD、NH3-N and TP, the removal rates were 88.1%、95.1% and 91.9% separately, at the same time, the TN removal rate was 47.3%. On the 2nd day after restart, the removal rate of TN was recovered to 66.4%, and the alternate aeration biofilter has the advantage of intermittent use.Under the condition of hydraulic load of 0.81 m3/m2·d, reflux ratio of 200%, the process’s sludge apparent yield coefficient is 0.06 kgMLSS/kgCODCr, which is much smaller than the A2/O process, is about 1/5 to 1/10 of the latter.The alternate aeration biofilter has high removal efficiency to the COD, NH3-N, TN in sewage, and especially has obvious advantages for dealing the low C/N ratio sewage, which will have broad application prospects in rural domestic sewage, initial rainwater, recycled water treatment and other sewage treatment fields. |
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