| In this paper,the enhanced nitrogen removal technology of rural domestic sewage treatment facilities was studied.Firstly,with the household treatment equipmentpurification tank,which is the most mature technology and widely used in rural areas,as the object,the application effect and existing problems of purification tank in rural domestic sewage treatment were studied and analyzed.On this basis,the sequencing batch shake-flask experiment was carried out to study the effect and influencing factors of self-trophic denitrification of ferrous sulfide driven by ferrous sulfide to strengthen the denitrification of low C / N ratio wastewater.Finally,an integrated AO pilot plant with enhanced denitrification was designed,and continuous operation tests were carried out to study the removal effect of pollutants such as total nitrogen and explore the technical stability and influencing factors.The main conclusions are as follows:(1)The practical application effect of 64 purification tanks in the Yangtze River Delta plain river network area was investigated.It was found that COD and suspended solids removal effect was better,and the effluent compliance rate was higher.Total nitrogen and total phosphorus removal effect is poor,effluent compliance rate is low.The changes of pollutant concentration and operating conditions of each treatment unit in five purification tanks were investigated in detail.It was found that there were two main reasons for denitrification : one was the extremely low influent carbon nitrogen ratio(COD/TN ratio is 1.3 ± 0.96),and the carbon source was extremely insufficient;second,the redox potential of inclusion removal tank and anaerobic filter bed tank is too high to maintain anoxic conditions.It is not conducive to heterotrophic denitrification.(2)Through the sequential batch shaking flask experiment,a comparative experiment on the denitrification performance of sulfur iron autotrophy enhanced wastewater with low carbon nitrogen ratio(COD/TN is 1.0)was carried out.The results showed that when the initial nitrate nitrogen concentration was 50 mg / L,the denitrification rate of sulfur iron autotrophic + heterotrophic group was the fastest,and the nitrate nitrogen removal rate was as high as 82.5% at 216 hours of reaction.Compared with complete heterotrophic group and complete autotrophic group,it increased by 48.3% and 24.0% respectively.The first-order kinetic model has the best fitting effect on the nitrate nitrogen removal process in the experimental group with ferrous sulfide for autotrophic denitrification.(3)Through the sequencing batch shake flask experiment of water distribution with low COD/TN ratio,the influencing factors of iron sulfide autotrophic denitrification strengthening denitrification with ferrous sulfide as substrate were studied.The results showed that:?1 The particle size of ferrous sulfide had little effect on the denitrification efficiency,and the denitrification rate was the fastest when the particle size was 0.45 ?1 mm.?2 When the initial nitrate nitrogen concentration was high,a high concentration of nitrite nitrogen accumulation would be produced,which had a certain inhibitory effect on denitrification.Increasing COD/TN ratio is conducive to the improvement of denitrification efficiency.The initial p H of 4 ? 9 had little effect on denitrification.?3 When the reaction temperature dropped to 15 °C,the removal rate of nitrate nitrogen decreased from 100 % to 80 %,and further decreased to 46.4 % at 5 °C.The effect of low temperature on iron sulfide autotrophic denitrification was smaller than that on heterotrophic denitrification.?4 When the initial ammonia nitrogen concentration was 0 ? 50 mg / L,the denitrification efficiency was almost unaffected;high concentration of phosphate has a certain inhibitory effect on denitrification,and phosphorus is removed by iron ion precipitation in this process.(4)Based on the actual problems found in the investigation and the feasibility of the experimental results,an enhanced denitrification integrated AO small-scale test device was developed to carry out continuous operation test.The results showed that the increase of baffle flow in the anoxic zone was conducive to reducing DO concentration and maintaining the anoxic environment with DO < 0.5 mg / L.Changing hydraulic retention time and reflux ratio had little effect on nitrogen removal.After the aerobic zone was changed to intermittent aeration,the total nitrogen removal rate of the system increased from 33 % to 44 %.The removal rates of total nitrogen and total phosphorus increased from 44 % and 6 % to 61 % and 56 %,respectively,after adding polyurethane filler loaded with ferrous sulfide particles and ferric sulfide autotrophic denitrification sludge in anoxic zone.(5)The enhanced nitrogen removal mechanism of the integrated AO pilot plant was studied.It was found that DO concentration in the anoxic zone was stably controlled,and ammonia nitrogen was mainly converted to nitrate nitrogen in the aerobic zone,and then denitrification was removed with the reflux liquid to the anoxic zone.After iron sulfide autotrophic strengthening,activated sludge granulation was obvious in anoxic zone.The diversity and abundance of microbial communities were significantly lower than those before enhancement,but the abundance of microbial communities in iron-sulfur autotrophic denitrification was greatly improved.The abundance of typical iron-sulfur autotrophic denitrification bacteria(such as Arenimonas,Thiobacillus,Thermomonas,etc.)was higher,and the total abundance of iron-sulfur autotrophic denitrification bacteria was more than 45%. |
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