Effect Of Sodium Dodecyl Benzene Sulfonate On Anaerobic Treatment System Of Organic Wastewater With High Sulfur Content

Anaerobic biological treatment has been regarded as the preferred process for the treatment of high concentration organic wastewater by environmental protection workers at home and abroad due to its economic efficiency and energy recovery.However,the presence of high content of sulfates in wastewater will cause the sulfate reducing bacteria?SRB?and methane-producing archaebacteria?MPA?to compete for the substrate,thus affecting the methane production efficiency of the system.In particular,the high concentration of sulfide produced by sulfate reduction will inhibit the activity of MPA,leading to the instability or even collapse of the system.At present,there are many reports about the influence of sulfate on anaerobic system.However,some wastewater from chemical and pharmaceutical industries not only contains high concentration of sulfates,but also contains certain concentration of organic sulfur compounds.Although some studies have shown that the sulfur in these organic sulfides may be released into the system in the form of sulfates or sulfides in the anaerobic biological treatment system,the transformation rules of these sulfur substances and the effect on the processing performance of the anaerobic biological treatment system have not been paid much attention.Therefore,this study focuses on the typical organic sulfur compounds called dodecyl benzene sulfonate?SDBS?existing in some wastewater,using both short-term and long-term test to examine the performance of anaerobic treatment system,under the condition of sulfate and organic sulfide co-exist respectively.It's a systematic analysis about the competition between SRB and MPA,sludge properties and microbial population structure characteristics.The main research conclusions are as follows:?1?Batch test showed that under the condition of COD/SO₄^2-=10,low-concentration SDBS could be effectively degraded by anaerobic organisms,and the degradation products were mainly complex desulfurized benzene series compounds and mercaptoparblic acids.However,when SDBS concentration is higher than 30mg/L,it will be less easily degraded by anaerobic biodegradation as the concentration increases,and the degree of inhibition on activity of MPA will be greater.At the same time,when the concentration of SDBS is low,sulfate can be released,so the concentration of sulfate in the outlet water is greater than that in the inlet water.When the concentration is high,a large amount of sulfide can be released to inhibit the anaerobic reaction.Therefore,the SDBS concentration of 30mg/L was determined as the next stage of long-term impact test study.?2?The long-term test on the influence of the co-existence of inorganic sulfur and organic sulfur on the anaerobic system shows that the purification performance is affected by COD/SO₄^2-and SDBS.When the COD/SO₄^2-was 5-10,the anaerobic systems without and with SDBS?R1 and R2,respectively?were running stably,the COD removal rate remained at about 91%and 88%,and the sulfate reduction rate could be as high as 70%and 75%,respectively,the volume proportion of methane in biogas can be greatly increased,and the VFAs accumulation in the system can be reduced.Within the range of COD/SO₄^2-,carbon mass conservation accounting found that the COD equivalent ratio of methane in R2 was higher than that in R1,and MPA dominated the utilization of electron flow.However,in the stage of COD/SO₄^2-=2,the presence of SDBS in R2 significantly inhibited MPA,aggravated VFAs accumulation and reduced the COD ratio used for methane generation,and SRB occupied the electron flow more than MPA.System performance was much lower than R1 system.Therefore,COD/SO₄^2-should be controlled greater than 2 in the system with SDBS to ensure the stability of the reactor operation.In addition,it was found that the transformation law of SDBS and COD/SO₄^2-are closely related,with the decrease of COD/SO₄^2-,the SDBS removal rate decreased,which was converted to the decrease of sulfide content,leading to the accumulation of SDBS in the sludge in the later stage,and the combined effect of low COD/SO₄^2-on the system performance had caused serious inhibition.Due to the added SDBS containing less than 1%of the total sulfur in the water,the sulfate released from the batch test had no significant effect.In addition,the change of microbial concentration was observed,and it was found that when COD/SO₄^2-was less than 10,the decrease of COD/SO₄^2-would lead to the continuous decrease of microbial concentration and the increase of inorganic component concentration.The presence of SDBS helped to increase the concentration of MLVSS in the system and decreased the concentration of inorganic components.?3?The change of COD/SO₄^2-and the presence of SDBS have a significant impact on sludge morphology,extracellular polymer?EPS?and particle size distribution.The sem results showed that the microbial morphological types in the initial inoculation sludge with COD/SO₄^2-=10 were not as diverse as those at the end of COD/SO₄^2-=1.Moreover,the existence of SDBS enriched the species of microbial morphology in the system.During the R1 test,the total EPS content did not change significantly,and the polysaccharide and protein content were similar,and the protein was pretty much the same.The ratio of PN/PS generally showed a decreasing trend.The total EPS of R2was higher than that of R1,and the changes of total EPS and protein were quite obvious during the experiment,and the content of polysaccharide was always far less than that of protein.This indicates that in the presence of SDBS,microorganisms mainly secrete large amounts of proteins as a stress response.Sludge particle size is different under the influence of COD/SO₄^2-and SDBS.In the condition of high COD/SO₄^2-,there was no inhibitory effect on the formation of sludge particles,while the overall sludge particle size decreases obviously in the stage of low COD/SO₄^2-.In the stage of high COD/SO₄^2-,SDBS is conducive to the formation of sludge agglomeration structure,but with the decrease of COD/SO₄^2-,the sludge particle size decreases to some extent.On the whole,the sludge particle size of R2 was obviously larger than that of R1,and the proportion of large particles of sludge was larger too.Therefore,the sludge of R2 is easier to aggregate into a group,which is conducive to the formation and maintenance of the anaerobic environment inside the sludge,thus promoting the target reaction and accelerating the start of the anaerobic reaction process.?4?Analysis of high-throughput sequencing results showed that microbial flora abundance,species diversity and community structure were affected by COD/SO₄^2-and SDBS.In the system without SDBS,COD/SO₄^2-7 is most conducive to the growth and reproduction of microorganisms.When COD/SO₄^2-was 10,SDBS had almost no effect on microbial flora abundance.When COD/SO₄^2-was less than 10,SDBS significantly reduced the total microbial flora.In addition,microbial diversity decreased with the decrease of COD/SO₄^2-,and the existence of SDBS also reduced microbial diversity.The analysis of microbial community structure showed that methanogenic archaea using acetic acid as methane-producing substrate had the most important position,and SDBS was beneficial to increasing the proportion of methanogenic archaea using H₂/CO₂ and decreasing the proportion of methanogenic archaea using acetic acid.Especially when COD/SO₄^2-was 5 and 2,methanogenic archaea using H₂/CO₂ had a greater advantage.Desulfovibrio is relatively dominant in the sulfate reducing bacteria,which can generate acetic acid,thus reducing the matrix competition with methanogens and showing synergistic effects.