Shortcut Nitrification And Denitrification Controlled By Inhibitors And Its Application In Oil Shale Retorting Wastewater Treatment

Compared to the traditional biological nitrogen remomal process,short-cut nitrification can save oxygen consumption and organic carbon,shortens the hydraulic retention time,and achieves lower sludge production.Short-cut nitrification reduces the cost of wastewater treatment and at the same time makes it possible to efficiently remove nitrogen from wastewater with low carbon to nitrogen ratio.There are many factors affecting short-cut nitrification and denitrification.However,in practical application,it is difficult to control nitrite accumulation by single factor control,which increases the difficulty of short-cut nitrification and denitrification.Therefore,in this paper,we have studied the stabilization of short-cut nitrification and denitrification by adding inhibitors.The influence of various factors in short-cut nitrification process was reduced,and the short-cut nitrification of oil shale retorting wastewater was studied.Firstly,the effects of methanoic acid and hydrazine on the key enzymes of ammonia-oxidizing bacteria and nitrite-oxidizing bacteria were analyzed by MOE.The results showed that when methanoic acid was present,ammonia-oxidizing bacteria and denitrifying bacteria will gradually grow and become dominant bacteria;Hydrazine does not affect the functional metabolism of bacteria by binding to proteins,and the effect of hydrazine on short-cut nitrification may be a strong inhibitory effect on NOB.The feasibility of short-cut nitrification controlled by methanoic acid and hydrazine was explored.The influence of methanoic acid on short-cut nitrification was studied using simulated domestic wastewater as the treatment object in SBR system.In the pH range from 7.5 to 8.5,at room temperature,DO greater than 2 mg/L,every two days adding 0.25 mL/L in the reactor.When the system was stable,the average nitrite accumulation rate was 77.88%,the average removal rate of ammonia nitrogen was 99.65%,and the average removal rate of COD was 92.4%.Microscopic examination showed that the activated sludge had large zoogloea floc,compact structure,clear edge,and aspidisca and vorticlla were found in the activated sludge,which mean the system run stablely.Scanning electron microscopy showed that the amount of bacteria in activated sludge was mainly composed of Bacillus and coccus.High throughput sequencing analysis showed that after adding methanoic acid,the predominant strains of activated sludge increased,indicating that methanic acid contributed to the biological diversity.The inhibition mechanism of methanoic acid to short-cut nitrification showed that the accumulation of nitrite was mainly due to the promoting effect of methanoic acid on AOB activity which consists with the effect of methanoic acid on the activity of the key enzymes of AOB and NOB.The effect of hydrazine on short-cut nitrification in SBR system was studied.Once every other day dosing 7.5 mg/L hydrazine in the reactor can obtain better nitrite accumulation.The effluent annonium,effluent nitrite,average removal rate of COD of the reactor dosing 0 mg/L hydrazine and dosing 7.5 mg/L hydrazine were respectively 2.74 mg/L,1.44 mg/L;2.17 mg/L,12.23 mg/L and 93.2%,91.5%.The activated sludge dosing hydrazine was denser than the activated sludge without hydrazine,and the activated sludge dosing hydrazine contained a large amount of microbial bacteria.It can be seen from the SEM picture,when dosed 7.5mg/L hydrazine the activated sludge had more compact structure and the number of colony was obviously higher than that of the activated sludge without hudrazine.High-throughput sequencing analysis showed that,Thauera?Verrucomicrobiaceae_uncultured?env.OPS 17_norank?Rhodocyclaceae_unclassified were dominant bacteria only in the system dosed hydrazine.The analysis of the inhibition mechanisum showed that the accumulation of nitrite was mainly due to the inhibitory effect of hydrazine on NOB,which consists with the effect of hydrazine on the activity of the key enzymes of AOB and NOB.In view of the different inhibition mechanism of short-cut nitrification controlled by methanoic acid and hydrazine,short-cut nitrification joint controlled by methanoic acid and hydrazine was studied.When dosing method was methanoic acid-hydrazine2 the best short-cut nitrification effect could obtained.After the system run stable,the average effluent ammonium was 0.79 mg/L,the average ammonium removal rate was 98.5%,the average nitrite accumulation rate was 92.4%and the average effluent nitrate was 1.81 mg/L.A total of 11 phyla were identified in the 16 sRNA gene sequence,Proteobacteria accounted for 64.23%in the methanoic acid-hydrazine2 system,followed by Bacteroidetes,accounting for 21.94%.Flavobacterium?Nitrosomonas?Chlorobium?Comamonas were dominant bacteria only in the methanoic acid-hydrazine2 system,Flavobacterium has the effect of denitrification,Nitrosomonas reflects the stable operation of short-cut nitrificationi,Comamonas has the ability to remove nitrogen and degrade organic compound,so it can be seen that the system has strong short-cut nitrification ability.The factors such as HRT,pH,influent ammonia concentration and influent COD concentration which influenced the short-cut nitrification and denitrification in MBBR were studied by single factor.Multi-factor influence on short-cut nitrification in MBBR when dosing methanoic acid-hydrazine 2 or not was also studied.The results showed that,the realization of short-cut nitrification was the result of multi-factor interaction;the change of each factor affected the realization of short-cut nitrification.However,by adding methanoic acid-hydrazine combined inhibitor in the device could weaken the influence of the parameters in the system on the accumulation of nitrite and maintain therelatively stable short-cut nitrification.The short-cut nitrification and denitrification of oil shale retorting wastewater were studied in MBBR.Experiments showed that gradually increase the proportion of oil shale retorting wastewater to biofilm domesticated was the optimum start mode.After domestication by adding methanoic acid-hydrazine can quickly start short-cut nitrification,when the system running stable the average nitrite accumulation rate can up to 97%or more.when the influent of MBBR system was 2-fold dilution of the oil shale retorting wastewater,the average COD removal rate,average ammonium removal rate and average TN removal rate were respectively 79.0%,78.9%and 47.5%.With the HRT prolonged,the removal rate of COD changed little,and the average removal rale of ammonia and TN were increased to 85.2%and 59.8%,respectively.The average effluent ammonium and TN were respectively 27.39 mg/L and 126.34 mg/L.Throughout the experiment,the nitrite accumulation rate remained above 90%and was almost unaffected by changes in influent water quality,so it can be seen that the addition of methanoic acid-hydrazine2 plays a very important role in the stable operation of short-cut nitrification.In addition,according to the price of methanoic acid and hydrazine and the amount of dosing,the daily cost of treating 1 ton of water is about 0.67 yuan,which is economically feasible compared to the carbon source and energy consumption realized by short-cut nitrification and denitrification.When the short-cut nitrification and denitrification of oil shale retorting wastewater were studied by layered MBBR,the average nitrite accumulation rate was 96.5%,which was 2.6 percentage points higher than not layered MBBR.It is suggested that the layered MBBR has a positive effect on nitrite accumulation.High-throughput analysis showed that,with the stable operation of each stage of the experiment,although the species abundance and microbial diversity of biofilm decreased,but the number of dominant bacteria did not decrease.Nitrosomonas?Thiobacillus?Parcubacteria_norank?Comamonas?Ferruginibacter?Diaphorobacter were dominant bacteria only at the end of the experiment when the influent of MBBR system was 2-fold dilution of the oil shale retorting wastewater.Nitrosomonas became the dominant bacteria in the system to permit the stable operation of short-cut nitrification.Thauera?Hydrogenophilaceae_uncultured were dominant bacteria of biofilm during the entire experimental process,Both of these bacteria have ability to remove nitrogen and Thauera has the ability to degrade a variety of aromatic pollutants,which shows that the system has strong ability of nitrogen removal and organic degradation.