| Aquaculture solid wastes is mainly derived from the residual bait,feces in aquaculture system and the metabolites of breeding object which contain a large number of biodegradable substances.Using anaerobic digestion technology,these substances can be hydrolyzed acidification to produce organics that can be used by denitrifying bacterial.As the carbon source needed for the denitrification process of the aquaculture wastewater,it can realize the resource recycling of the cultured solid waste.However,in the process of organic hydrolysis of solid wastes is accompanied by a large number of ammonia production.Thus,how to achieve the rational use of solid waste and the effect of the simultaneous removal of nitrate nitrogen and ammonia nitrogen has become a hot issue in recent yearsBased on simultaneous nitrification and denitrification(SND)system,in this study,the factors affect the nitrogen removal efficiency and the effect of the treatment of recirculating aquaculture wastewater by using solid waste fermentation liquor as carbon source were studied in order to provide a theoretical reference for the rational and effective utilization of solid waste and the healthy breeding mode of zero-emissions of recirculating aquaculture system.1.Effect of fermentation of solid waste as carbon source for treatment of inorganic nitrogen in aquaculture waterThe effect of simultaneous denitrification on the fermentation of solid waste from different solid-liquid ratio was studied.The results showed that when the solid waste and the culture wastewater of group A 1:4,Total solid suspension(TSS)3756.5±958.1 mg/L,C/N=12.33;group B 1:3,TSS=5109.0±1127.12 mg/L,C/N=10.49;and group C 1:2.5,TSS=5828.5±2008.8 mg/L,C/N=6.63,temperature 35℃ and 180 r/min constant temperature shaker for anaerobic fermentation 24 h,group A is more fully hydrolyzed,and the highest content of soluble chemical oxygen demand(SCOD)in fermentation was 639.93±128.52 mg/L,which was higher than that of 1:3,1:2.5 SCOD content in solid-liquid ratio increased by 11.6 % and 42.5 % on average.At the same time,the average removal rate of nitrides in group A,B and C was 58.8±28.1 %,44.8±28.6 % and 29.4±19.3 %,respectively.The maximum removal rates were 98.1±3.4 %、97.3±2.1 % and 76.2±2.6 %,respectively.The average removal rate of ammonia nitrogen in group A,B and C was 76.6±23.8 %,76.0±22.8 % and 77.6±20.7 %.Besides,nitrite nitrogen did not accumulate.The total nitrogen removal rate in group A was 71.2±20.3 %,70.5±16.7 % in group B and 60.3±15.3 % in group C,and the better denitrification effect was obtained.Among them,1:4,TSS=3756.5± 958.1 mg/L,C/N=12.33 had the best effect.2.Changes of VFA at different fermentation times and simultaneous denitrification under different C/N ratiosBased on the fist experiment,the effects of different fermentation time on the concentration of VFA produced by fermentation of solid waste were studied,and the effect of simultaneous denitrification under different carbon and nitrogen ratios was studied.The results showed that the content of volatile fatty acids produced in the fermentation system was higher at the fermentation temperature of 35 ℃ and the initial pH was consistent.At the 4th day of fermentation,the mass concentration of volatile fatty acids reaching a maximum of 3129.38±885.19 mg/L.At the 3rd day,the content of VFA reached 3032.77±197.93 mg/L,and the advantage of the fourth day was not obvious.However,after 5 d,the concentration of VFA did not increase with the increase of fermentation time,but decreased.At the end of the experiment,the content of volatile fatty acids decreased from 3129.38±885.19 mg/L to 1825.07±152.9 mg/L.Considering all aspects of the factors,that 1:4 ratio of solid waste fermentation,the best time for 4 d.When the reactor DO is controlled at 0.25~0.5 mg/L,temperature 25 ℃,pH 6.5~7.5,the effect of nitrogen removal under six different C/N ratio was obvious.The removal rate of nitrate nitrogen is about 70 %.Besides,with the increase of C/N,the removal rate of total phosphorus increased,and when C/N = 22.32,the total phosphorus removal rate was the highest,89.2±2.7 %.3.The effect of denitrification and dephosphorization under different HRT with solid waste fermentation as carbon sourceIn this experiment,the effects of different hydraulic retention time(HRT)on denitrification were studied in this part.The results show that in the SBR reactor,When DO 0.25~ 0.5 mg/L,pH 6.5~7.5,temperature 25 ℃,C/N=3.09,HRT 4 h,water exchange rate of 0.5 L/h,total nitrogen and phosphorus removal effect is obvious,nitrate nitrogen and ammonia nitrogen average removal rate reached 85.4±6.0 % and 52.7±12.1 %.The removal rate of ammonia nitrogen increased with the increase of hydraulic retention time,but the removal benefit was not obvious,and the accumulation of nitrite was not accumulated in the whole experiment.Besides,the removal rate of total phosphorus did not increase with the increase of HRT,but the removal efficiency was similar under 4 different HRT,and the average removal rate was more than 60 %.4.Effects of three different carbon sources on simultaneous nitrification and denitrificationThis experiment explores the effect of simultaneous denitrification and phosphorus removal in the SBR with solid waste fermentation,glucose and methanol as carbon sources.The results show that the denitrification effect of the three different carbon sources is methanol best under DO 0.25~0.5 mg/L,temperature 23 ℃ and pH 6.5~7.5.Besides,The denitrification effect is Methanol>Solid waste fermentation>glucose,(the mean values of C/N ratios are 7.40、6.57 and 7.3),and the removal rate of total nitrogen in methanol group was only 10.9 % higher than that of solid waste fermentation broth.The removal rates of total nitrogen were 67.9 ± 17.4 %,60.5 ± 16.6 % and 31.8 ± 13.8 % respectively.The solid waste fermentation broth group also had better removal effect on total phosphorus and was significantly higher than that of methanol and glucose groups.So the solid waste fermentation as a carbon source of aquaculture wastewater treatment,can achieve a good effect of nitrogen and phosphorus removal. |
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