Research On The Effect Of Fe²⁺ To The Anaerobic Breakdown Of Residual Sludge From City Wastewater Treatment Plant

The city sewage treatment plant can achieve good effect by making the use of activated sludge to treat the high concentration wastewater, But the problem is how to use efficient method to solve the large amount of excess sludge. City sewage treatment plant sludge not only contain volatile organic compounds such as fatty acids and protein, but also rich in phosphorus, nitrogen and other nutrients, it has the potential to recycle and utilize the value. Making full use of energy and nutrients on sewage sludge can treat the residual sludge without endangering the environment of land resources, and also save the additional operating costs of sludge treatment, fully tapping the huge potential resources and recycling use of it. Cell lysis technique exploits the use of the resources and attracts more people to pay attention to it, this technique can promote the decomposition of microbial cell wall in sludge, make the cell structure smaller and easy to be dissolved, so as to achieve the purpose of reduction of solid waste's concentration.At present, most of the domestic and foreign scholars have studied the mechanism of sludge breaking in the case of an external carbon source, but it may be significantly different from the natural reaction machanism which have no additional nutrients.This paper experiment add Fe SO4·7H2O to the reflux sludge which is from the municipal wastewater treatment plant's secondary setting tanksewage sludge, to study the effect of Fe²⁺ on the release of ammonia nitrogen, phosphate, COD and VFAs in the anaerobic sludge under the condition of no external carbon sources by using the serum bottle and batch experiments, characterizing Three-Dimensional Fluorescence Spectrum of sludge's liquid phase by the methods of parallel factor analysis.The conclusions are follows:?1?With the anaerobic conditions of absence of external carbon source?Constant temperature water?33?? bath shaker?120r/min?,Fe²⁺ plays a significant role for promoting the release of nutrients from the cells of microorganisms in sludge.When the concentration of Fe²⁺ is gradually increased from 0mg/L to 1450mg/L,Microorganisms' abilities of dissolved nitrogen,phosphorus and COD released from opend bursts cell is increased when the concentration of Fe²⁺ is gradually enhanced.The highest concentrations of ammonia nitrogen, phosphate and COD were as high as 350mg/L, 135mg/L and 2200mg/L and were 5 times,11 times of the control group.After eight days,the concentration of each indicator is no longer significantly fluctuate.Sludge system is in a dynamic equilibrium.For the production of VFAs,the highest concentration of acetic acid reached 280mg/L,the highest concentration of propionate reached 500mg/L.There are three components:proteins coenzyme NADH and fulvic acid in the three-dimensional fluorescence map.A small amount of coenzyme F420 appeared in the process of methane production.And there are two major volatile fatty acids were detected, which are acetic acid and propionate.The amount of propionate reached 500mg/L in the fifth day when the concentration of Fe²⁺ is 20mg/L.The yield of acetic acid was up to 225mg/L when the concentration of Fe²⁺ is 800¹450mg/L.There is no toxic effect on excess sludge when the concentration of Fe²⁺ is high?800¹450mg/L?.The indicator changes and economy consideration from the point of view:as the amount of Fe²⁺ was added to the 200³50mg/L, the residual sludge could release nutrients to achieve good results.?2?According to the preliminary experimental results,selectin 200mg/LFe²⁺ as the adding amount,adding different concentrations of NaHCO₃ as buffer material,studying the effect of low Fe²⁺/NaHCO₃ combined treatment on activated sludge.The results showed that when the concentration of NaHCO₃ was 5g/L, the sludge had a significant effect on the cells.And high concentration of Fe²⁺ hydrolysis of excess sludge caused excess VFAs,NaHCO₃ can neutralize the excess VFAs.In order to avoid the toxicity of accumulated VFAs to anaerobic sludge.maintain the stability of the pH in the reaction system,the conversion of acetic acid to acetic acid was improved. Methanogenic stage has been advanced on the fourth day,and the fluorescence intensity of F420 was enhanced.?3?The initial pH of the sludge had a very important influence on a series of anaerobic fermentation.Regulating the initial pH of excess sludge?4,7,10respectively?Studying the effect of pH on anaerobic sludge digestion.The results show that in the short fermentation time?about 20 days? within the initial pH adjusted to acidic?pH=4?,excess sludge can achieve good effect of cell lysis effect.can obtaine more soluble nitrogen, phosphorus and COD than alkaline and neutral conditions.The highest concentration of ammonia nitrogen is 263.62mg/L.Short chain fatty acids?acetic acid,propionic acid and butyrate? with higher concentration can be produced.the biochemical degradation ability of sludge was improved.The low pH anaerobic fermentation environment is beneficial to the iron element in the form of free state ferrous iron.The fluorescence score in the pH=4 value of the highest from the parallel factor analysis, pH=10 second, pH=7 score minimum. From the concentration of ferrous ions, the concentration of Fe²⁺ is 200mg/L than the concentration of 350mg/L score high. From the parallel factor analysis, we found that the highest value of the fluorescence score is in pH=4, the second is in pH=7, the lowest score is in pH=10. The Fe²⁺ concentration is higher than the concentration of 350mg/L, which is higher than the concentration of 200mg/L in the concentration of ferrous ions.